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Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico
Palac¢~,eography, PalaeoclimaloloKv, PalaeoecoloKv, 83 ( 1~)91): Z217 263
217
Elsevier Science Publishers B.V., Amsterdam
Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico Silvia Spezzaferri and Isabella Premoli Silva Dipar~qmenlo di Scienze della Terra, UniversitL'l di Milano, via Man~iaqalli, 34, Milano 2#133, Italy (Received F e b r u a r y 1, 1990: revised a n d accepted M a y 30, 1990)
ABSTRACT Spezzaferri, S. and Premoli Silva, 1., 1991. Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico. Palaeogeogr. Palaeoclimalol., Palaeoecol., 83:217 263. A relatively extended Oligocenc pelagic sequence with good to medium recovery, drilled during DSDP Leg 77 in the Gulf of Mexico, yielded rich and ~vell diversified planktonic foraminiferal faunas. Planktonic foraminifera recorded m Hole 53gA span the interval from Zone P I9 through P22. Evolutionary lineages were observed among the globoquadrinids, the globigerinitids, and the "'Glohit,,erina" c~peroen.~isand Glohi,~ermoi&'sprimordius groups. Quantitative analysis of planktonic foraminiferal assemblages shows that faunas fluctuate in abundance and species diversity throughout the sequence. A few of these fluctuations that could be related to selective dissolution are mainly confined to the early-mid Oligocene. A climatic curve was constructed using as warmer indicators, Turhorolalia pseudoampliaperlura, Glohoquadrina lripartila, Denm,~lohij,,erina ,elohularis, Denloqlohi~er#m haroemoenensis, "Glohi~,,erina" ciperoensi.~ and Glohi~,ermoide.~ groups, and ('a.~si,eerinella chipolen.~is: and as cooler indicators, ('atapsydrax spp., Glohoromloides spp., Suhhotina an~iporoi~h,s group, Glohieerma s. str., and the tenuitellids. Three major intervals are identifiable in the climatic curve: Interval 1 (lower) up to Zone P20 predominantly cooler: Interval 2 (intermediate) up to the upper part of Zone P21a with warm and cool fluctuations: and lnter~ al 3 (upper), warmer, with a large positive peak, duc to abundant "G. "ang, ulisuturalis, at the beginning of Zone P2 lb with recooling midway in Zonc P22. In Intervals I and 2 planktonic foraminiferal faunas are dominated by temperate forms. Interpretation of planktonic foraminiferal data suggests that coolcr water conditions characterize the early-mid Oligocene: during the mid Oligocene (most of Zone P2 l a) water masses exhibit peculiar characteristics transitional to the warmer ~aters prevailing during the late Oligocene. Warmer conditions were not definitely settled in Zone P22, however, as indicated by the cooler cpisode following the warmest peak. These climatic trends are inconsistent with those inferred from oxygen isotopes except at small scale. In fact, oxygen isotope values for Oligocene Atlantic Ocean are too heavy (thus too cool) in comparison ~ith the high abundance and diversity of warm taxa, expecially in Zone P22. When values are lighter (warmer), as m Zone PI9. abundance and diversity of warm indices are too low. 1o explain such a cool isotope values m presence of highly diversified and abundant warm planktonic foraminifera, we suggest (1) that the oxygen isotope ratio used for estimating Oligocene paleotcmperal ures might be 1%,, heavier than Eocene values and further increased for the late Oligocene. This hypothesis mrplies the presence of a relatively extended ice cap in Antarctica in the early and mid Oligocene, and probably an increase in ice volume during the late Oligocenc: (2) heavier isotope values might be related to an increase in salinity, or (~) by a combination of both ice cap and increase in salinity.
Introduction
During the biostratigraphic study of Oligocene planktonic foraminiferal assemblages recovered in Hole 538A (Gulf of Mexico), it was apparent that the composition of planktonic foraminiferal fau0031-01~2,9I S03.50
(
1991
nas changes through the stratigraphic interval investigated. More specifically, the relative abundance of some taxa fluctuated from layer to layer. Because preservation could not account for these changes, which also occurred in the best preserved samples, it became apparent that the changes
Elsevier Science Pnblishers B.V.
218
S. S P E Z Z A F E R R I A N D I. P R E M O L I SILVA
could be related to climatic fluctuations and/or to changes in the properties of water masses. In order to investigate the significance of such faunal fluctuations, quantitative analyses of the planktonic foraminiferal content were performed. Hole 538A material appeared to be particularly suitable for investigating a possible climatic signal for much of the Oligocene. Previous studies reported only data from selected Oligocene time-slices (Haq et al., 1977), but a continuous sequence has never been investigated in detail, especially in the Atlantic.
nannofossil ooze of late and middle Miocene age which rests unconformably on late Oligocene foraminiferal nannofossil ooze. The Oligocene sediments consist of foraminiferal nannofossil ooze from 6 mbsf to 69 mbsf (Core 77-538A-2-CC to Core 77-538A-8-CC), followed downhole by about 10 m of foraminiferal nannofossil chalk (Core 77538A-9) and about 40 m of nannofossil chalk (Core 77-538A-10 to Core 77-538A-14-1, 100 cm). A hiatus at 177.5 mbsf separates Oligocene sediments from late Eocene radiolarian nannofossil limestone. Several volcanic ash layers, 1-2 cm thick, are interbedded in the light-colored Oligocene pelagic sediments (see Fig.2). Sixty-four samples (Cores 77-538A-2-CC to 141, 51 54 cm) have been analysed for their foraminiferal content and a biostratigraphic study was performed without picking. Samples were washed on >40 btm and > 150 btm sieves under running water. To construct the climatic curve, quantitative analysis of planktonic foraminifera was performed on the same samples previously used for biostratigraphy. For both sieve fractions (see above) an aliquot of residue was evenly spread over a picking tray with a grid, so that approximately 300 specimens of planktonic foraminifera from each
Materials and methods Hole 538A was drilled on the top of the Catoche Knoll (23°50.98'N and 85°10.26'W, water depth 2740m), a large topographic feature located approximately 25 km northeast of the Campeche Escarpment, and rising 750 m above the abyssal floor of the Gulf of Mexico (Burlier, Schlager et al., 1984) (Fig.l). Hole 538A penetrated 268.5m of sediments resting on metamorphic basement. Eleven and a half out of the 36 cores taken belong to the Oligocene, with a recovery rate of 52.6%. The uppermost 6 m belong to a condensed sequence of nannofossil ooze and foraminiferal
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Fig.l. Location map of Hole 538A, Leg 77, Gulf of Mexico. Present water depth 2740 meters.
OI 1(7()( f NI P L A N K I O N I (
FORAMINIFERAI
BIOSTRATIGRAPH~ AND PALEO(IJMA]I(
I N T E R P R [ FA I I O N
210
sieve fraction could be counted on randomly choosen grid squares. In cases when the number of specimens in the >150 ~tm fraction was less than 300, the total number was counted. Raw numbers were transformed to percentages of the total planktonic foraminiferal fauna. Abundances of single species or groups of species were separately calculated for each fraction and as the total abundance in a sample. Percentage curves were then constructed for either single species or groups of species displaying phylogenetic affinities. To show the degree of preservation/dissolution the number of fragmented specimens were counted and plotted in separate curves.
Planktonic foraminiferal biostratigraphy The Oligocene sequence at Site 538 appears almost complete from Zone PI9 through Zone P22. Planktonic foraminiferal faunas are generally rich. Their abundance and preservation, however, vary from poor, especially in the lower part, to increasingly better towards the top of the studied interval. The index species are well represented throughout and the zonal boundaries were easily identified. The zonal scheme by Blow (1969) modified by Hardenbol and Berggren (1978) applies to Hole 538A sediments. The distributions of planktonic foraminiferal species are plotted in Fig.3, where preservation of planktonic foraminifera, amount of washed residue, presence and abundance of volcanic glass and radiolarian are also included. Several generic names among planktonic foraminifera will appear in the text and figures in brackets: for the explanation see the taxonomic appendix. The identified zones are listed below (from bottom to top). Zone P19 (Core 14-1.51 54 cm to (%re 13-1, 40 42 cm J Definition. Interval from the first occurrence (FO) of Globoquadrina sellii to the last occurrence (LO) of the pseudohastigerinids.
~,
t~+::t2
~3
-fl i ,~]4
Fig,2. Lithologic log, recover~, and sample position through dcpth of Oligocene sediments in Hole538A.
220
S. S P E Z Z A F E R R I
[-.!
[.
AND
I. P R E M O L I
SILVA
~
ii
DEPTH C
i n
O
R
E
m S
SECTIONS CENTIMETRES
Pseudohast igerlna barbadoensls Pseudciha St I g e r l na m, ra PSeudohastlflerlna nagu~wlChlensls " S l o O I q e r ina ampl apertura Turboro~a! a pseudoampllapertur~
Subboti na utilisindex "Globigerina" euapertura "Gl oboquadnina" tapuriensis TenuiteHa munda - T,c)emenciae
. . I
P a r a g l o b O r o t a l i a )pima nana S u b b o t i n a praeturr~t illna OlobOquadr ina s e l l l i
'Globlgerina" prasaep,s .
.
.
. .
. .
. .
.
.
.
I
,
-
-
. . . .
--,W-
~
-
. . . . . . . . .
i
Dentoglobigerina gentoglobigerina
I,
Globoguadrina r o h r l
,
.
Catapsydrax unlcavus Globorotaloldes suterl
i
. . . . . .
"
~ "
I.
I °l
-' .......
-
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I
i
i
)iil)iilli!iiiT4:: .
.
.
....
.
.
.
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.
.
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.
_-T"
.
.
.
.
.
.
.
.
.
.
.
.
." "-.-- .....
.
.
.
.
,ii
.
.
.
Catapsydra~ m a r t l n l Dentoglobigerina larmeui Dentoglobiger~na p s e u d o v e n e z u e l a n a
Catapsydra~ dlSSlmllis c~peroensls S u b b o t i n a gortanll
.
.
.
.
.
.
.
.
.
P a r a g l o b o r o t a h a oplma op~ma Subbotlna lab:acrassata P a r a g / o b o r o t a l l a ? sp.
. I
.
pe~icrus
Paraglob0rotalia slakensis group
Catapsydrax Spp,
. . . . . . . . . . . . . . . . . . . . . . .
......
I
oraebullolde~
"G1obigerina" brazieri Turborotalia cf.increbescens Subbotlna a n g i p o r o i d e s m l n l m a Catapsydra~ g l o b ~ f O ~ l S
Glaboquadrlqa ~raedehiscens Globoquadrlna tripartita G:oblgerlna' venezuelaqa
i
~i_:l:
Globlgerlna
.
Oloborotaloides
?1!-~!!!-.
P a r a g l o b o r o t ~ l i a pseud0continuosa Dentoglobigerina globularis Catapsydra~ disslmilis disslmilis "Globigerina" ciQeroensis
,
I
:::::1::-::
.
---:jLI-,,-~,
_; .....
......... ..........
Ea~sigerlnella Chlpolensis elongated Heterohelicldae Subbotina anglporoides anglporoides
. . . .
i
. . . .
.
"Globigerina" anguliofficinalis Glob~gerlna obacnltaensis Globlgemna officinalis Tenultella g ~ a Tenuitellinata angustiumbi]icata
I
. . . . . . . .
I
galavlsi baroemoenensls
Globorotaloides varlabllis G1oblgerineila obesa 'G1Oblger~noides' praeprlmordluS
Catapsydra× afrlcanus "Globigerlna" angulioff./angulisut Dentoglobigerina globularis/al:ispira Dentoglobigerina galavisi/baroemoenen "Globigerlna" angulisuturalis
I . .
.
Parag/obor~talla
siakensls
Dentoglobigerina altisp~ra globosa
-
-::i--::T
.-
'
...... ;:- ......
G/oblgerina
oua~nitaensis
gnaucki
G1obigerinita juvenilis "Globigerlna" sp. •- - i O l o b l g e r , n a
praenulloides o c t ? u s a
"Gl0blgerina" ciperoensis fariasi O O b l g e , lnOl~eS p r l l n o r d , u s
"Globigerina" woodi woodi Paragloborotalia pseudokuglem P r o t e n t e l l a group $/oboqua~rlna ~nalLns,,,
• o0~
. . . . . .
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ooo
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very scarce
,
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G= good preservation
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,oo,
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scarce
•
• . 0 0 , . . o . o o . . . a
• ....
. . . . . . . . . . . . . . . .
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poop., oo • Oo • • ,oo oo,,°o • o o
medium scarce
M :~dium preservation
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P
.poop • Ooo,oo° oo oo
medium abundant poor preservatlon
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~.... .... i --z_: liiii... ~:" ::. •. . . , .°"': o . .o o . . .°°°'"1°°'°'°°" o . o . . . . o o o ~ . . o : o .o. . . F']
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>40~ >IS0 >40~
>Ifi0 p >40p
>150 p
>a0~
>150 p
PRESERVATION WASHED
VOLCANIC
RESIDUES GLASS
RADIOLARIANS
very abundant VP very poor preservation
Fig.3. Stratigraphic ranges o f O l i g o c e n e p l a n k t o n i c foraminifera and identified b i o z o n e s in H o l e 538A. B i o z o n e s after Blow (1969) m o d i f i e d by H a r d e n b o l and Berggren (1978).
OI I ( J O ( [ N[ P L A N K I O N I C F ( ) R A M I N I F t - R A [ .
BIOSI RA I IGRAPH'r
A N D P , % L I ¢ O C L I M A I 1 ( IN I I R P R t
Remarks. Preservation and abundance of planktonic foraminifera in this interval vary from very poor to scarce, to fairly good and high. In general the > 40/am fractions yield a better preserved and more abundant planktonic fauna than the > 150/am fractions. Radiolarians, mainly confined to the finest fractions, increase in abundance from the bottom to the top of this interval. Planktonic foraminiferal faunas are dominated by dentoglobigerinids, along with less common globoquadrinids and turborotaliids. The most common species are Dentoglobigerina galavM and transitional froms to Dentoglob~erina haroemoenensis, whereas typical D. baroemoenensis is rare and possesses a poorly developed tooth. Dentoglobigerina globularis is rare. Among the globoquadrinids G/oboquadrina rohri and "Globoquadrina" tapuriensis are rather common, whereas Globoquadrina sellii is rare and scattered. Turborotalia pseudoampliapertura is common only at some levels. Other components of the faunas are the catapsydracids, globorotaloids, the Subbotina angiporoides group, large Globigerinids, rarer high-spired subbotinids, and "Glob~erina" ampliapertura. Fine fractions are dominated by the pseudohastigerinids and chiloguembelinids. Minor components include the tenuitellids, Cassigerinella chipolensis, juvenile Paragloboratalia siakensis, P. opima nana. and Globigerina s. str. A few "Glohigerina" ciperoensis and "G. "angulio~cinalis occur in all size-fractions from the base of this interval, whereas rare specimens of Globiquadrina praedehiscens are recorded in only one sample. It is noteworthy that Paragloborotalia opima opima appears in the topmost sample attributed to this zone. Zone P20 (Core 12-CC to Core IO-CC)
Definition. Interval from the LO of pseudohastigerinids to the LO of "Globigerina" ampliapertura. Remarks. Planktonic foraminiferal faunas vary from moderately rich to rich and from very p o o r to fairly well preserved, except in Sample 12-3, 40-42 cm where the fauna is rich and well preserved. Radiolarians are abundant in the finest fractions. Planktonic foraminiferal assemblages of this zone
I A 1 ION
221
are similar to those from the underlying interval except for the scarcity of the pseudohastigerinids, very rare specimens of which still occur randomly throughout. Among the dentoglobigerinids D. haroemoenensis is more consistently present than D. galavisi, "Gloh(eerina ampliapertura, along with more c o m m o n Turhorotalia pseudoampliapertura and very rare T. increhescens, all fluctuate in abundance from layer to layer. These latter species are poorly preserved and decorticated (peeled). Paragloborotalia opirna opima is consistently present throughout the zone, although never common. In the middle portion of this zone wc observed a few specimens of a globigerinid displaying the same morphology and cancellate wall structure as GlohigerinoMes primordius, but without supplementary apertures. This taxon is here informally called "Globigermoides" praeprimordius, Globoquadrina praedehiscens is absent. Fine fractions are dominated by the chiloguembelinids and tenuitellids along with rarer cassigerinellids. The "Globigerina" ciperoensis group, Glohigerina s. str., and Paraglohorotalia siakensis are rare. Glohigerinella ohesa first occurs in the middle of this interval. Zone P21 (Core 10-5, 95 97 cm to Core 6-1.
40 42 cm) Definition. Interval from the LO of "Globigerina" ampliapertura to the LO of Paraglohorotalia opima opima. Remarks. More than half of the samples studied belong to this zone. Planktonic foraminifera are poorly preserved in the lower part of this interval, but starting in Core 9 progressively improve in preservation and increase in abundance towards its top. Radiolarians are highly variable in abundance from absent to common. In agreement with Hardenbol and Berggren (1978) the boundary between Subzones P21a and P21b is placed at the disappearance of the chiloguembelinids. The interval attributable to Subzone P21b is very thin (about 5 m thick) in comparison with Subzone P21a (more than 40 m thick). This difference in thickness between the two subzones suggests that a hiatus has eliminated a portion of Subzone P21 b.
222
Paragloborotalia opima opima the zonal marker, is present throughout this interval. It fluctuates in abundance from layer to layer, with a marked increase in abundance from Core 9 upwards. Highest abundance is always in the >1501am fraction. The chiloguembelinids vary in abundance from 25% to > 50% of the total fauna. Just before their disappearance they decrease to < 10% in Core 6-CC and increase again to 15% in Sample 63, 4 0 - 4 2 c m , but are absent in Sample 6-2, 40-42 cm. The subzonal boundary was placed between the last two samples. Assemblages of this zone include most species and species groups recorded throughout the sequence. The number of species, however, is never constant, but fluctuates from layer to layer. Within this zone the "Globigerina" ciperoensis group increases in abundance and in overall size, and "G." angulisturalis displays a peak in abundance of > 4 0 % just above the LO of the chilogumbelinids. Dentoglobigerina globularis increases in abundance in the upper half of the zone, where it is associated with transitional forms to D. altispira globosa and with D. altispira globosa just before the extinction level of the chiloguembelinids. Dentoglobigerina baroemoenensis shows the opposite trend; it is more abundant in the lower half of this interval and decreases upwards. The Globoquadrina tripartita group and large globigerinids are never abundant, but fluctuate throughout. Common in the lower portion, the Subbotina angiporoides group disappears before the top of Subzone P21a, whereas the high-spired subbotinids are a minor component of the faunas and their record is scattered. Paragloborotalia siakensis increases in abundance and overall size within this zone. It is especially frequent in the lower portion, and after a marked decrease in abundance in Sample 9-3, 100-102 cm, it gradually increases again in the upper portion of the zone. Globigerina s. str. increases slightly and gradually in abundance and overall size. "Globigerinoides" praeprimordius is rare. Globigerinitajuvenilis and "Globigerina'" sp. 2, a form related to "Globigerina" woodi (Premoli Silva and Spezzaferri, 1990) first appear at the top of Subzone P21a. Fine fractions are dominated by the chiloguembelinids in Subzone P21 a associated with common cassigerinellids, whereas the tenuitellids decrease in
S. S P E Z Z A F E R R I A N D 1. PREMOLI SILVA
abundance upwards. In Subzone P21b the smallsized assemblages consist of abundant "G." ciperoensis group, common Globigerina s. str., P. siakensis, P. opima opima, P. opima nana, and the cassigerinellids increase in abundance. Zone P22 (Core 5-CC to Core 2-CC)
Definition. Interval from the LO of Paragloborotalia opima opima to the FO of Paragloborotalia kugleri. Remarks. The upper boundary of the zone is missing because an unconformity truncates the sequence in the uppermost part of this zone. The presence of evolutionary advanced P. pseudokugleri in the last Oligocene sample, however, indicates that Zone P22 is nearly complete (Premoli Silva and Spezzaferri, 1990). The planktonic forminiferal assemblages of this interval are rich, well diversified and better preserved from Core 3 upwards. Radiolarians increase in abundance up to core 3-2, 70-72 cm, but they are absent in the uppermost samples studied. Planktonic foraminiferal faunas are dominated by dentoglobigerinids, globoquadrinids, the "Globigerina" ciperoensis group, and Globigerina s. str., the last two in both fractions, associated with less abundant paragloborotaliids, catapsydracids, globorotaloids, large globigerinids, and tenuitellids. Several species, which first appear at the base of this zone include Globigerinoides primordius, Protentella spp., Paragloborotalia pseudokugleri, "Globigerina" woodi, and Globoquadrina binaiensis. Paragloborotalia pseudokugleri is consistently present, whereas the others may be absent in some samples. "Globigerinoides" praeprimordius is always present either alone or associated with G. primordius. Globoquadrina praedehiscens is discontinuously present and the transition to Globoquadrina dehiscens was never observed. A few specimens of Cassigerinella chipolensis occur in the > 150 I.tm fraction. Fine fractions are dominated by representatives of the "Globigerina" ciperoensis group, Globigerina s. str., and cassigerinellids, whereas the tenuitellids gradually decrease in abundance upwards. Very rare specimens attributable to Streptochilus pristinum occur in a few samples.
,[ I ( i O ( ' [
N[
PI_ANK
I ONl(
FORAMINIFERAL
BIOSq RA I 1(3R~tPHY
AND
PALEOCI.IMA'I
The stratigraphic ranges o f some species in Hole 3 8 A depart from the ranges given in the literature Bolli, 1957; Blow, 1969: Jenkins, 1971; Molina, 979; Bolli and Saunders, 1985). They are, in tratigraphic order (Fig.4): 1. Dentoglobigerina baroemoenensis is recorded rom the beginning o f the studied sequence, ttributed to Zone PI9. 2. "Globigerina" ciperoensis first occurs close to he base o f Zone P19, whereas "G." angulisuturalis ppears at the top o f Zone P20. 3. Primitive Paragloborotalia siakensis appears /ithin the lower part o f Zone P19, whereas largeized P. siakensis is recorded from the middle ortion o f Subzone P21 a. 4. Suhhotina hrazieri occurs as rare specimens eginning in Zone P19. 5. Paragloborotalia opima opima first occurs at ae top o f Zone P19 associated with abundant seudohastigerinids.
STANDARD EVENTS
IC IN I IRPR[
[A I ION
._.
6. Pseudohast~eerina barhadoensis disappears at the top o f Zone P19 at the time o f the dramatic decrease in abundance o f all pseudohastigerinids, whereas very rare, small-sized specimens o f P. micra and P. naguewichiensis are recorded also in Zone P20, apparently in situ. 7. Globigerinella obesa appears in the middle portion o f Zone P20. 8. Forms transitional between Dentoglohigerina globularis and D. altispira glohosa first occur at the top o f Zone P20. 9. Subbotina utilisindex disappears at the top o f Zone P20. 10. Subhotina angiporoides minima disappears in the middle portion of Subzone P21a, whereas Subbotina angiporoides angiporoides last occurs close to the top o f that same subzone. 11. Glob~eerinita juvenilis and forms related to "Globigerina" woodi (= "Globigerina" sp. 2) first appear in the upper portion o f Subzone P21a.
MAIN EVENTS IN T H E INDIAN OCEAN
MAIN EVENTS IN T H E G U L F O F MEXI(
incre~.sing abundance of
Globigetinoid~ i m m a t ~ , G, bollii, G trilobus - J GIob~germoid~ss p p
N4
Globigennita uvula, Globg,erinita glatinata
paraglo~rocalia kuglen
Globoquad,qna dehisced. Pa~toboe~calia pseudo~leri/p, kuglen transition GIoboretaloides sp. 2 large C~igerinella spp. ( > 150~)
large C~,sigerin¢ Uids ( > 150~)
Globoquadnna binaie~is. GIoblgerinoidespnmordius, Po.~obocotadia pseudokugleri. D. altispim globosa. I~ slakemis ( • ZS0~.)
Globigednoid~prlmoedim, Pa,'~lobo,~abapseude.'kugle
Paeagloborotalia opima opima
Proterttella s p p
b P21~-'~
Chiloguembelinaspp
a
~ large Cass~ednella spp. ( > 150~,)
~ "Globigerina" ~pliapetrura
~]t
~Jlarge
t~
t v~Pseudohattigerina micra, P+nagu~ichiensis , Turfio~tali "-~"GIobi~rina" an~lioff~cinalia/ "G,"angulisutuzalis transi ~ entoglobigednaglobularis/D, alt~piraglobosa tramitic GIobigeeineUa obesa
P20
P~aelobomtalia onima onima ~
Cassigecinellamaninezpicoi, Cassigennellaglobulosa. D. baroemoenensls, Patagloborotalia siake~i~ ( < 150a) Globoquadnna selliJ
Ii
C,~sigerinellids ( • 150-)
Subboti~ ~gipo~ides gr. ~-J~lobigcrinitajuvenilis, "Globigerina" sp. probably related to "G. wood~~ group -----~- Sub~cina angtlmroldes anglpomldea D. globulo~i~/D, alti~pi~globosalransition, GIob~gerimtajuvenil~. "Globigerina" ongulisuturalis. P~tentella s p p Turborotaliids ~ "GIobigedna'ciperoemis /"G."anguliofficinaltslransitiov
'
I i
Hantkeninids a n d Psh. danwlle~is
I
i.
Pmudohastig~rina barbadoemis Paragloborotalia opima opima
Paragloborocalla suak~nsis (40-15Qu ), Globoquadetna pr~deh~ce~ .....J " Globigerina "cipe~nsis, "Glob,gerina "b~ien ~ Dentoglobigerma baroem~ne~is
Turborotalia pseuabampliapertura, Z i n c ~ b e ~ . "Globoquad.4na" tapune~, CaraigerineUachil~le~is , high-spired Subbotinids, S. atlgipoemdes group. Dentoglobige~na galamsi
Tenuitellids,
g.4. Calibration of second order events to the major biostratigraphic events among Oligocene planktonic foraminifera plotted vs. the w latitude standard zonal scheme of Oligocene age (Blow, 1969) in Hole 538A and Indian Ocean Leg II 5 sites (Premoli Silw~ and ~ezzaferri, 1990).
224
12. Globigerinoides primordius, Paragloborotalia pseudokugleri, "Globigerina" woodi, Protentella spp., and Globoquadrina binaiensis are already present from the base of Zone P22. Their true first occurrence cannot be detected because of the hiatus inferred at the top of Subzone P21b. Some of these first occurrences are in agreement with those observed in coeval sequences from Indian Ocean sites drilled during Leg 115 (Premoli Silva and Spezzaferri, 1990), (Fig.4). Specifically, these include the FO of Dentoglobigerina baroemoenensis, primitive Paragloborotalia siakensis and
P. opima opima, "Globigerinella" obesa, Globoquadrina praedehiscens, "Globigerina" sp. 2, Paragloborotalia pseudokugleri, and Globoquadrina binaiensis. The FO of "'Globigerina" angulisuturalis, Dentoglobigerina globularis/D, altispira globosa transition, and D. altispira globosa are also close in stratigraphical terms between the two areas. Moreoever, two abundance peaks of largesized ( > 150 jam) cassigerinellids occur at the top of Subzone P21a and within Zone P22 in both the Gulf of Mexico and the Indian Ocean.
Quantitative analyses In order to quantify species abundances and diversities 300 specimens were counted, when possible, in both the coarse ( > 150 gm) and fine ( < 1 5 0 to >40 gm) fractions. Figures 5 7 show percentage distribution of 32 species or groups of species present in each sample (see Fig.3 and species list). Percentages in >1501am and 150-40 p.m fractions were plotted separately along with a cumulative total %. Species plotted separately from their groups are those already known to have a climatic significance or whose significance has never been investigated or clarified (Haq et al., 1977; Douglas and Savin, 1978; Premoli Silva and Boersma, 1989). Analysis of the percentage curves allows us to distinguish three groups of taxa which display different patterns (Figs.5-7). (1) The first group include "Globigerina" ampliapertura high-spired subbotinids, Paragloborotalia opima nana, Paragloborotalia sp., Globigerinella obesa (all in Fig.5), and Subbotina utilisindex (Fig.6). They are all a minor components of the
S S P E Z Z A F E R R I A N D I. P R E M O L I SILVA
faunas and show no patterns. The paragloborotaliids become slightly more important when combined with the Paragloborotalia siakensis group. (2) The second group includes a number of taxa which are relatively abundant, almost consistently present, and display discrete, but moderate fluctuations in abundance. They are the large globigerinids (Fig.5), the Subbotina angiporoides group (Fig.8), the tenuitellids (Fig.6), the Catapsydrax and Globorotaloides groups (Fig.6), and the Dentoglobigerina baroemoenensis and Globoquadrina tripartita groups (Fig.7). (3) The third group includes the remaining species, either as single species or as discrete groups, which display large fluctuations in abundance and have restricted stratigraphic ranges. Some of them such as the pseudohastigerinids (Fig.5), the elongate heterohelicids ( = Chiloguembelina spp.) (Fig.5), and the Turborotalia pseudoampliapertura group (Fig.7) are common to abundant in the lower portion of the sequence; the Paragloborotalia siakensis group (Fig.5), Tenuitellinata angustiumbilicata (Fig.6), the Globigerina s. str. group (Fig.6), the "Globigerina" ciperoensis group (Fig.7), the Dentoglohigerina globularis group (Fig.7), Globigerinoides group (Fig.6), and Paragloborotalia pseudokugleri (Fig.5) tend to increase in abundance in the middle to upper portion; and finally, Paragloborotalia opima opima (Fig.6) fluctuates in the central portion (Zone P21), whereas Cassigerinella chipolensis (Fig.5) displays five abundance peaks scattered throughout. The percentage curves of Figs.5 7 also show that (1) the pseudohastigerinids seems to be covariant with the chiloguembelinids, which increase in abundance at the pseudohastigerinid extinction, (2) the T. pseudoampliapertura group fluctuates in phase with the previous groups (in 1) and opposite to the S. angiporoides group, globorotaloids, and tenuitellids. Similar patterns are exhibited by C. chipolensis, (3) the D. globularis, the "G." ciperoensis, and Globigerinoides groups exhibit trends opposite to Globigerina s. str., and (4) T. angustiumbil'oata "eems to replace the tenuitellids beginning in the upper part of Subzone P21a. On the basis of all the observations derived from the percentage curve patterns, three intervals can
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be distinguished in the studied sequence, which can be roughly identified (in stratigraphic order) as the lower, pseudohastigerinid-chiloguembelinid dominated interval (Interval 1); the middle, chiloguembelinid paragloborotaliid-dentoglobigerinid interval (Interval 2); and finally, the upper, "G. " ciperoensis-D, globularis-Globigerina- T. angustiumbilicata interval (Interval 3). This partitioning is also reflected in the climatic curve (Fig.8). Climatic curve The three intervals, as mentioned above, are characterized by higher or lower abundances of different taxa, some of which are known to have climatic significance. In this chapter we analize the abundance patterns of planktonic foraminifera from a climatic point of view in order to construct a climatic curve.
Previous biogeographic studies of Oligocene planktonic foraminifera identified index species for the different Atlantic bioprovinces and showed how bioprovincial faunas evolved through time (Haq et al., 1977; Boersma and Premoli Silva, 1986; Premoli Silva and Boersma, 1989). The Oligocene biogeographic index groups are reported in Table 1. Out of these index groups some may be considered as warmer province indicators ( T. pseudoampliapertura, G. tripartita, D. globularis, D. baroemoenensis, "G. " ciperoensis, and Globigerinoides groups, and Cassigerinella). They proliferated at low latitudes and migrated out of the tropical belt by the end of the Oligocene. Other groups ( Catapsydrax, Globorotaloides, S. angiporoides, and Globigerina s. str. groups, and the tenuitellids) can be interpreted as cooler province indicators because of their abundance and constant occurrence at high latitudes (see Haq et al.,
()[ I ( J ( ) ( t Nil PI.ANK I O N I C I O R A M I N I F E R & I B I O S I R A I I ( J R A P H ' t A N D P,'kLEO(I I M A I I (
IN[I RPR| I , \ I I O N
TABLE I Oligocenc biogcographic index groups (Prcmoli Silva and Boersma, 1989) AGE
LOWER LATITUDES
MIDDLE LATITUDES
HIGHER LATITUDES
Northeast
EARLY OLIGOCEN E
T pseudoamphapertura r mcrebescens flood ol biserlal heterohel~lds typical G~ tnpamt~ denlOgloblgerinids
3 chambered denlogloblgennlds Glot)lgertna C un~cavus Ca~apsyorax P nana tenultelhds ~enuitelhds GloOorotalo~des pseudohastigenmds G ouach#aensts tew Iurborolahlds esp "G" arrlphapertura T pseudoamplKapertufa "G" tapurlens~s rare austral spectes esp S ut~hs~nde~ S braz,en
MIDDLEOLIGOCENE
a~lgloboquadrmlds flood of blserial heterohelK;Els • pseudoan~phapertura rare P slakens;s Globorotaloide5
Gq praedehtscens P ssakens~s ~enuitelhdS 3 clTambered denloglo~lgerlnK3s S gortan# Catapsydrax rare austral speoes in lhe SOulh
LATE OLIGOCENE
"G" ctperoens;s all globoquadrimds "G" anguhsutura#s P optma oplrna Casslgennella GOes ontt)ordlus Neogenestreplochihds ten~lrlelhds (P22)
OK pseudol(ug~en CataPsydeax Catapsydrax tnJe glob~jenmds 3 chambered denlog~ob~genmds Globorotalo~les C~ btrlalensts in southeast "G" ctperoensls P s~akensls GI kugJen group S COrl)alenta P $takensts tenullelhds "G" wooOr G;ta luvenlhs GJfa g~tmata
1977). According to stable isotope analysis, the former group includes species registering negative (depleted) (3laO values and are mainly warmer dwellers, while the second group includes species giving more positive (enriched) a180 values and are cooler-dwelling taxa (Boersma and Shackleton, 1977: Douglas and Savin, 1978: Poore and Matthews, 1984). In Hole 538A planktonic foraminiferal assemblages warm indicators are mainly belonging to the third group of taxa previously mentioned, which exhibit discrete distributional abundance patterns, whereas the cold indices, mainly confined to the second group, display moderate fluctuation in abundance and appear to be a common component of planktonic foraminiferal assemblages throughout. The only exception is the Subbotina angiporoi~#s group which appears to be replaced by Gloh(¢erina s. str. in the upper part of the sequence (from Subzone P21a to Zone P22). Among the remaining species or group of species, which are here considered as "temperate" indices, there are also some groups such as the pseudohastigerinids and chiloguembelinids which largely fluctuate in abundance. They also belong to the third group.
high diversify abundant S uhhsmdex S angtporoJdes S mtr~rna Catapsydrax true glOblgenmds rate turborotalilds rare pa ragloborot ah=ds raFe globOquadnmds
Northwest
Southwest
blsenal heterohehctds GloborotaPJides rare globoquadrln~ds S ang,poro~des S ut#ts~ndex pseudohashgerm~ds
S ut,hsmdex S ~-azren lenulleHids S rnmsrna {rue glob~genn~s Catapsydrax
largeglob~genmds true gbobwgenmds Globorotalo~des Catapsydrax rare P optma oplma rare 3 chambered dentoglobqgenmds
T munda (P21 moves to SoutP Atlanhc in P22~ P s,a~(ens,s GloborotaJotdes Irue globqgedmds large globlgerinids GI aft penDheroronda
The plot of total abundance of warmer taxa is called the warm species curve (Fig.8). This shows rather regular fluctuations with lows of slightly less than 5% to one high >20°/; in Interval 1. In Interval 2 the total abundance (from > 5 % to > 20%) of warm indicators slightly, but gradua[ly increases upwards. In Interval 3 the abundance of warm forms markedly increases, with minimum values never below 25%, and maximum values as high as 60%. The cooler species curve, based on the total abundance of cooler taxa, shows Four discrete intervals in which highest values (positive peaks) range from about 25% to about 40%, separated by lows whose minimum values are close to 10%. The first two peaks, with values of 30% and around 35%, occur at the beginning (Zone P19) and in the upper half (Zone P20) in Interval 1, respectively. The third positive peak, stratigraphically more extensive, lies in the upper part of Interval 2 (mid Subzone P21a), with maximum values which never reach 30%: the fourth one is in Interval 3 (mid Zone P22), with a m a x i m u m value > 4 0 % . Temperate species make up the bulk of planktonic foraminiferal faunas from the base ot" the
230
S. SPEZZAFERRIAND I. PREMOLI SILVA
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sequence to upper Subzone P21a, corresponding to the entire Intervals 1 and 2 (Fig.9). In both intervals, their combined abundances range from 55 60% to 75-80% of the faunas. Conversely, temperate forms decrease in absolute abundance throughout the entire Interval 3 (upper part of Subzone P21a to Zone P22), with values ranging from 25 to > 60% of the faunas. Temperate faunal composition changed through the three intervals. In the lower half of Interval 1
(Zone P19), the pseudohastigerinids and chiloguembelinids each comprise 20% or more of the total fauna, whereas in the remainder of Interval 1 and in the lower half of Interval 2 (Zones P20 and P21 a lower part) the chiloguembelinids account for at least 30% of the total fauna. In Interval 2 the P. siakensis group is more common; the large globigerinids, P. opima opima, other paragloborotaliids, and T. angustiumbilicata each comprise about 5% of temperate species abundance. In
OI IGO('} NE PLANK F()NI(" FORAMINIFERAL BIOSTRAflGRAPHY AND PALEO('LIMA'H( IN IERPRt'I A II()N
Interval 3, within the range of P. opima opima (Subzone P21b), P. opima opima and P. siakensis together account for about 20% of the total fauna, whereas in the upper part (Zone P22) the temperate forms, T. angustiumhilicata, P. siakensis, and large globigerinids, contribute respectively 15 20%, 15%. and about 10% of the total fauna. Paraglohorotalia pseudokugleri in some samples reaches values as high as about 15%. The climatic curve (Fig.8), derived from the algebraical sum of percent abundances of warm (positive) and cool (negative) indices, shows that Interval 1 is characterized by negative values, except for one single, very low positive peak in the lowermost part (lower Zone P19). Interval 1 also contains the most negative peak of the entire curve which occurs in its upper part (most of Zone P20). In Interval 2, the curve is mainly negative with five positive peaks, three of which barely cross the zero line and the other two are more positive around + 7 (lower) and + 10 (upper), respectively. The curve, although negative is less negative than in Interval 1. In Interval 3 the climatic curve is predominantly' positive with values as high as almost + 50. It is, however, interrupted by a short negative, inversion of about 15 in the upper half (mid Zone P27).
Diversil v patterns In order to identify better the climatic signal, species diversity (number of species) as well as diversity among the warm, temperate, and cool groups were calculated for each sample. As shown in Fig. 10, total diversity fluctuates in the lower part of the sequence (through the lower level of Interval
23 I
2, or lower Subzone P21a). Overall diversity then increases and fluctuations are less pronounced. Some discrete intervals characterized by different mean diversity' values have been detected (Table 2, Fig. 10). Diversity patterns, however, do not show the same partitioning as the climatic curve does. In Interval 1 diversity values range from less than 20 species (lower Zone PIg) to almost 35 in the upper part (upper Zone P20), with mean diversity values around 25, except at the top where mean values are around 30. Interval 2 starts with mean diversity values as high as > 30, but the remaining lower half has a mean diversity value of less than 23 (up to mid Subzone P21al. From the upper half of Interval 2 (upper Subzone P21a) diversity gradually increases with mean values ranging from about 28 to 35 at the end of lnterwtl 3. No major change in diversity can be detected at the middle (1) to upper (2) interval transition. Diversity among the three groups of species displays, in general, less pronounced fluctuations with the curve of the warm species best parallelling that of the total diversity. The lowest fluctuations are observed in the temperate diversily curve. As shown in Table 2 and in Fig. 10, the lowest mean diversity value of the entire sequence in the lower half of Interval 2 (lower Subzone P21a) is due to the combined low values in all three groups. The second low value characterizes most of Interval I (upper Zone PI9 lower Zone P20) and is mainly related to low values in the warm group, which. conversely, contributes to the higher diversity values of Interval 3. Because the degree of evolutionary overturn (originations plus extinctions) in the faunas is minor, it was not plotted. Oligocene faunas
TABLE 2 M e a n diversity values ( n u m b e r o f species) o f total p l a n k t o n i c f o r a m i n i f e r a l f a u n a s , a n d o f w a r m , t e m p e r a t e , a n d c o o l indices t h r o u g h O l i g o c e n e s e d i m e n t s in H o l e 5 3 8 A INTERVALS
TOTAL~ DIVERSITY
WARM SPECIES MEAN DIVERSITY
2-CC/6-1, 40-42cm 6-2, 40-42/9-CC 9-1,6-7cm/10-5,62-63cm 10-5,95-97cm/12-1,40-42cm 12-2,40-42crn/13-3,40-42cm " 13-CC/14-1,51-54cm
35 27.88 22.5 30.1 24.3 26
14 8.88 6.86 9.66 6.4 8.25
TEMPERATESPECIES COOL:::~..~ES MEAN DIVERSITY MEAN DIVERSITY 10.7 9.2 8.2 9.5 10.3 10.5
10.3 9.5 7.35 11 7.6 7.25
232
s. S P E Z Z A F E R R I A N D I. P R E M O L I SILVA
PLANKTONIC FORAMINIFERALFRAGMENTS
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TEMPERATESPECIES COLDSPECIES DIVERSIFY DIVERSIFY
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Fig. 10. Total species diversity (number of species) curve plotted against warm, cool, and temperate planktonic foraminiferaldiversity curves, and against the abundance of fragmented tests in Hole 538A. Data from Fig.3. Patterns mark the three intervals identified in the climatic curve of Fig.8.
predominantly consist o f long ranging taxa originated in the Eocene or in the Oligocene, prior to the beginning o f the sequence studied, and extending into the Miocene. Comparison between diversity and percent abundance curves reveals that the warm taxa increase in abundance when their diversity increases and vice versa (Figs.8 and 10). A m o n g the cool group, diversity and abundance curves are
mainly parallel except in the lower and uppermost parts o f Interval 2 (lower middle and uppermost Subzone P21a) where increases in diversity correspond to decreasing abundances. The two curves relative to the temperate group show very few correlative points (Figs.9 and 10). They, in fact, depart one from the other markedly, as in Interval 3 (Zone P22) where a slight increase in diversity corresponds to a marked drop in abundance, or in
O1 I G O ( | N I P L A N K I ONIC F O R A M I N I F E R A L B I O S T R A T I G R A P H Y AN[) P A L E O ( ' L I M A I IC IN I [ RPRE~ekTION
Interwfl 2 (midway into Subzone P21a) where the highs and lows on the curves are offset. Discussion and results
Dissolution q~l~,c/s In order to separate the signature of dissolution from the primary signals, abundance and diversity curves are compared with the curve of abundance of test fragments. Dissolution, in fact, can result in an artificial increase in abundance of solutionresistant or thick-walled taxa (Boersma and Premoll Silva, 1983). Comparison between total diversity curve and percentage curve of fragmented specimens shows that the two curves are mainly opposite (Fig. 10). These opposite patterns are more evident when comparing the diversity curve with >1501am fraction fragmentation curve. This implies that dissolution affected the faunal composition and may be responsible for some of the low species diversity recorded in the curve (Fig. 10). Abundance and diversity curves of warm species, like the total diversity curve, show opposite fluctuations with respect to fragmentation, so dissolution certainly affected the warm group. In particular, dissolution effects appear more pronounced in the lower portion of the sequence (Fig.8). In Interval 2 (Subzone P21a) dissolution seems to affect particularly the large-sized forms. When dissolution strongly decreases or is absent in Interval 3 (uppermost Subzone P21a through Zone P22), the warm group increases in both diversi D and abundance. To a lesser degree dissolution seems to have also affected the cool species. Cool species diversity and abundance curves fluctuate inversely with fragmentation (Figs.9 and 10). In some cases, however decreases in abundance of cool species do not correspond to increasing fragmentation. What is surprising is that the temperate group was very little affected by these dissolution epi-. sodes. The already high percentages recorded for the temperate group are thus emphasized by partial removal of either the warm taxa or both the warm and cool groups (Fig.9). It appears that the climatic curve of the lower
233
part of the sequence is negative because of dissolution which preferentially removed the warm group, as testified by a decrease in both abundance and species richness among this group. These warm taxa are known to be more susceptible to dissolution (Boersma and Premoli Silva, 1983). In this case, the climatic signal suggesting a cooling may be artificial. In the mid to upper part of Interval I (Zone P20), however, the cool taxa increase in abundance (up to about 40%) but fragmentation decreases to rather low values. This occurs also midway into Interval 2 (mid Subzone P21a). We interpret these two events as real cooling events, as corroborated by a slight decrease in abundance of the temperate group. The Interval 1 curve (Zones P19 and P20) is thus characterized by a temperate signal at the beginning evolving into a definitely cooler signal, which reversed close to the transition between Interval 1 and Interval 2 (top of Zone P20). In the middle to upper part of Interval 2 (Subzone P21a, Core 9 and most of Core 8) decreased dissolution corresponds to a moderate increase in abundance of warm forms and a more marked increase in the coot group, whereas temperate forms slightly decrease. Within the cool group some old taxa, such as those belonging to the Subbotina angiporoMes group, disappear whereas Glohi,gerina s. str. increases in abundance associated with a slight increase of the tenuitellids. These events are not an artifact of dissolution and indicate a change in watermass properties. Lower in Interval 3 (upper Subzone P21a through Subzone P21b) when dissolution decreased, warm taxa became much more abundant and the temperate fauna sharply decreased in abundance. The middle part of Interval 3 (Subzone P21b and lowermost Zone P22) is characterized by the lowest percentages of the temperate group, which are replaced by the warm and cool groups: the warm groups is more abundant in the lower part of the interval, and the cool group displays the highest percentages in the uppermost part of this interval (most of Zone P22). The percentages of the temperate group partially recovered at the close of the sequence. This trend is well represented in the climatic curve, which from highly positive values returns
234
to negative values in the mid to upper part of Interval 3 (middle of Zone P22) (Fig.8). In summary, because of absence of dissolution Interval 3 registered the real climatic signal. Moreover, the fact that temperate taxa are less abundant in this interval suggests water mass properties have changed and became more similar to the Neogene-type, in which warm and cool niches were well differentiated and higher abundance of either warm or cool groups correlates with warming or cooling events respectively. Interval 3 is predominantly warm with a recooling midway.
S. SPEZZAFERRI A N D 1. PREMOLI SILVA
TABLE 3 Stable isotopic values of two speciesof planktonic foraminifera from five selected samples corresponding to highs and lows of the climatic curve in Fig.8. "GIobigerina"angulisuturalis= warmer dweller; Globorotaloidessuteri-cooler dweller SAMPLES
PLANKTONIC SPECIES
3-1,100-102
cm
4-1,134-136
cm
5-CC 6-2,40-42
cm
7-3,40-42
cm
"G." angulisuturalis G. suteri "G." angulisuturalis G. suteri "G." angulisuturalis G. suteri "G." angulisuturalis G. suteri "G." angulisuturalis G. suteri
al 8 PDB
al 3C PDB
-0.10 0.73 -0.40 1.33 -0.36 1.09 -0.33 1.38 -0.08 1.53
1.25 0.87 1.14 0.47 1.23 0.31 1.53 0.45 0.63 0.51
Isotope data Atlantic oxygen isotope curves indicate mild warming events through the course of the Oligocene (Boersma, 1977; Boersma and Shackleton, 1977, 1978; Biolzi, 1983, 1985; Belanger and Matthews, 1984; Shackleton et al., 1984). Warm peaks (most depleted oxygen isotope ratios) were registered in Zones P21b and upper Zone P22 in equatorial and South Atlantic Sites 366 and 357. Two additional warm peaks, in Zones P19 and P21a, were registered at Site 540 in the Gulf of Mexico. The relatively depleted near-surface values, ranging from -0.77%0 to -1.92%o, are suggestive of only mild surface water warming. Oxygen isotope values of plantktonic foraminifera living at cooler levels in the water column also became more depleted through this time. At western equatorial Site 354 where Biolzi (1985) measured "Globigerina" venezuelana, warmings were registered in Zone P20 up to lower Zone P21 and midway into Zone P22. Reinterpreting Biolzi's biostratigraphic zonal attributions (1985) through Boersma's data (1977), the major isotopic events recorded at Site 354, including the cooling event midway in Zone P22, appear to correspond to those from Site 366 (Boersma and Shackleton, in prep.), although the absolute values are somewhat more depleted at Site 354. Oxygen isotope values of warm and cool water species from our material in Hole 538A were relatively enriched and showed little intersample variation (Table 3). There was only an approximately 1.00%o interplanktonic oxygen isotope
gradient. Hole 538A values were substantially more positive (1.4 0.6%0) than those from other sites, including nearby Site 540. Samples containing the highest numbers of warm water planktonic foraminiferal indices did not produce more depleted (warmer) oxygen isotope values than samples in which warm water planktonic indices were less numerous.
Summary and conclusions (1) Planktonic foraminiferal distribution patterns indicate (a) an increase in abundance of warm indices towards the top of the sequence, (b) the cold indices remain relatively constant in abundance throughout, whereas the temperate indices drastically decrease in importance in late Oligocene Subzone P21b and Zone P22. This fact is in relationship with the disappearance of the chiloguembelinids in mid Zone P21. (2) There is a general correspondence between higher diversity, greater numbers of warm water index species, and higher paleotemperature in near surface waters, although the Oligocene isotopic record from the Atlantic Ocean is still incomplete. Isotope values do show patterns roughly consistent with the well-characterized three intervals on the climatic curve. In the lower to mid Oligocene there is little correspondence between the climatic curve and faunal properties. (3) Zone P22 can be separated into two warm and one cool interval. The partition of the generally warmer Zone P22 (about - 1 . 1 to
OI 1(;O( EN[{ P L A N K r O N l ( ; F O R A M I N I F E R A L B I O S T R A T I G R A P H Y A N D P A L E O ( L I M A T I ( I N I E R P R E I A I I O N
-1.15%o) by a moderate cooling event (about -().5%,) in the isotope curve seems to correlate to the trend in the climatic curve, which becomes negative in the middle of the zone because of the increased abundance of cool indices. (4) A cool interval indicated by oxygen isotopes in mid Subzone P21a is coeval with increased abundances of cool water indices. A corresponding decrease in dissolution allows us to state that the cooling event is real. (5) A cooling in upper Zone P21a corresponds to an increase in dissolution. This is shown by decreased abundances of the warm indices, whereas species diversity of the warm group remains high and abundance of cool species increases only slightly. (6) A cooling indicated by the oxygen isotope record of the Oligocene in Zone P21b is not reflected in the fossil data at Site 538. Neither the diversity nor the cool index curves registered this event. Its absence corroborates the occurrence of a short hiatus as inferred at the top of Subzone P21b by the exceptionally thin section attributable to this subzone. (7) The relatively good correspondence between isotope curves and fossil data typical at other times is not demonstrated in Zone P19. Isotope data indicates generally the warmest paleotemperatures through the Oligocene after Zone P18. The fauna is, however, dominated by temperate indices, while abundance of warm or cool species is lower. In this interval, the only fact consistent with a warming is the first appearance of warm indices, such as the "G'lohi,~erina" ciperoensis group, which will proliferate later in the Oligocene. (8) In Zone P20 warm episodes indicated by the oxygen isotope curve do not correspond with warm index high abundance, whereas diversity in the warm group and in the total fauna is relatively high. Dissolution may account for this discrepancy. (9) Dominance of temperate taxa in low to mid Oligocene faunas suggests unusual hydrographic conditions in oceanic upper waters during Zones P19 P21a. The abundance of chiloguembelinids, the major component of the temperate group, would suggest conditions of relativelty high fertility through this interval (Boersma and Premoli
235
Silva, 1988, 1989). This hypothesis is in agreement with the occurrence of radiolarians throughout (Fig.3). (10) During warming in Zone P22 the numbers of both warmer and cooler taxa increase, whereas temperate taxa strongly decrease in abundance (Fig.9). Apparently a larger number of niches were available in the warmest near surface and coolest, subsurface layers. Both warm and cool groups in Zone P22 include more modern (at least Miocene in age) analogues such as Glohi~erinoides and Globi,gerina, the latter in high abundance. Surface water masses probably became more similar to those of the Neogene during late Oligocene Zone P22. ( 1 l) In general the paleotemperatures suggested by oxygen isotope values appear too low to support the abundance of warmer water indices early in Zone P22, whereas in Zone PI9 the highest temperature values of the Oligocene correspond to low abundance and diversity of the warm species. It is not clear why such discrepancies occur and why the inferred Oligocene temperatures are so low. Estimated temperatures lower than 1 5 C would prevent the survival of larger benthic foraminifera such as the lepidocyclinids (Adams et al., 1986), which, on the contrary, colonized even the mid latitude by mid to late Oligocene time. (12) There are several possible explanations for the low paleotemperature estimates ot" the Oligocene: (1) poor preservation prevented our obtaining real values from the various planktonic foraminifera. It is unlikely that this would apply to all Oligocene sites analyzed: (2) the mean oxygen isotope ratio for the Oligocene ocean might be about 1%o heavier than that of the Eocene. In order to accommodate the disagreement between the enrichment of warm taxa in Zone P22 and the isotope values, another oxygen isotope ratio might characterize the late Oligocene ocean. This hypothesis implies rather extended ice cap(s) covering Antarctica since the beginning ot" the Oligocene, further increasing in size by the late Oligocene, and large enough to be registered in the oxygen isotope ratio. The suggestion of an ice cap in Antarctica by Oligocene time is supported by recent discoveries on land in Eastern Antarctica and deep-sea drilling in Prinz Bay (Harwood et al., 1989: Barton, Larsen
236
et al., 1989; Barron, Larsen et al., 1989); (3) heavier isotope values are related to an increase in salinity, due to stronger evaporation during the Oligocene; and (4) the latter two effects might have combined to alter the isotopic ratios. (13) Dissolution was important in the early-mid Oligocene interval at Hole 538A, although the site was located at lower bathyal depths at this time. It appears that cooler waters were flowing at bathyal depths through the Gulf of Mexico and may be responsible for the dissolution lower in the sequence as well as for the short hiatus inferred in Zone P21b. Another possible explanation could be that higher fertility in surface waters at this time resulted in an enrichment of organic carbon at depth causing a calcium carbonate deficiency at the sediment/water interface. A combined effect of both, however, cannot be ruled out. In summary, evolution of planktonic foraminiferal faunas in Hole 538A points towards a gradual overall warming from early to late Oligocene time. Despite cooling events and dissolution effects, this trend is marked by an overall increase in the number of warm species. This climatic trend is consistent with that inferred from oxygen isotopes, in the sense that warmer paleotemperatures correspond with appearance of warm species. Oxygen isotope values, however, appear too cool in comparison with the high abundance and diversification of warmer taxa, especially in late Oligocene early Zone P22. Acknowledgements The authors are indebted to DSDP-IPOD for having invited one of us (IPS) to participate on Leg 77. The authors would like to thank A. Boersma for fruitfull discussions about biostratigraphic and environmental interpretations of the Paleogene succession, C. McNulty, the other foraminiferal expert on board Leg 77, for his help during and after the cruise, and N. J. Shackleton for performing stable isotopic analyses. The authors are deeply indebted to G. Pezzi for sample preparation, to M. Minoli for providing graphic support, and to G. Chiodi for printing photographs, all of whom are from the Department of Earth Sciences, University of Milan. We also wish to thank A. Rizzi, C N R of
S. S P E Z Z A F E R R I A N D I, P R E M O L I SILVA
Milan, for SEM operation. The paper was reviewed by H. M. Bolli, R. L. Fleischer, and A. Boersma. Financial support for this research was provided by MPI 40% grant to IPS, and PhD program to SS. Species list and taxonomic notes That planktonic foraminiferal faunas encountered in the Oligocene sediments recovered in Hole 538A are abundant and highly diversified, much more than what is known from the literature (e.g. Bolli, 1957; Bolli and Saunders, 1985), is testified by the long list of species. Species are listed in alphabetical order by genus. The generic and specific concepts and the species groups used by Boersma and Premoli Silva (1983), Boersma et al. (1987), and by Premoli Silva and Boersma (1988, 1989) are retained herein, whenever possible. Several groups are still informal due to their uncertain taxonomic position based on different wall structure with respect to those in the original generic description. The most controversial forms are those previously attributed to the genus Globigerina. Although most Oligocene globigerinids belong to the spinose group, they possess a cancellate wall which does not exist in true Globigerina (Cifelli, 1982; Hemleben et al., 1988). A taxonomic revision of Paleogene planktonic foraminifera is in progress by the "Paleogene Planktonic Foraminifera Working Group". Reference is made to the most reliable illustrations reported in the literature. Most of the species identified are illustrated in Plates I XVIII.
Cassigerinella chipolensis (Cushman and Ponton, 1932) (=Cassidulina chipolensis Cushman and Ponton). (Plate VIII, 6a-b.). See Bolli and Saunders (1985), fig.16 (1-2). Genus Catapsydrax
Catapsydrax africanus (Blow and Banner, 1962) (= Globigerinita africana Blow and Banner). (Plate I, 3a). See Blow and Banner (1962), pl.XV, figs.A C; fig.ll (i-iv). Catapsydrax dissimilis (Cushman and Bermudez, 1937) (=Globigerina dissimilis Cushman and Ber-
O L l ( i O ( t NI P L A N K F O N I C F O R A M I N I F E R A L B I O S T R A T I G R A P H Y A N D P A L E O C L I M A T I ( I N T E R P R [ £ I A I ION
237
mudez). See Blow and Banner (1962), pl.XIV, fig.d. Also included here are specimens that exhibit a lobulate periphery like typical C. dissimilis and possess, when present, a clear bulla with only two infralaminal accessory apertures (Plate l, la d). Catapsydrax dissimilis ciperoensis (Blow and Banner, 1962) (=Globigerinita dissimilis ciperoensis Blow and Banner). (Plate I, 4a b). See Blow and Banner (1962), pI.XIV, figs.A C. Catapsydrax globij~rmis (Blow and Banner, 1962) (=Globi~erinita gloh(formis Blow and Banner). (Plate I, 2a~b). See Blow and Banner (1962), pI.XIV, figs.S U. Catapsydrax martini (Blow and Banner 1962) ( = Glob~Terinita martini Blow and Banner). Plate I, figs.5a c). See Blow and Banner (1962), pI.XIV, fig.0). Catapsydrax unicavus Bolli, Loeblich and Tappan, 1957. See Bolli et al. (1957), pl.7, figs.9a c. Only specimens very close to the holotype have been included in C. unicavus.
Dentoglobigerina larmeui (Akers 1955) (= Glohoquadrina larmeui Akers). (Plate II, 6a c). See
Chiloguembelina cubensis (Palmer, 1934) ( = Guemhelina cubensis Palmer). (Plate X, 5a 9b). See
"Globigerina" ciperoensis group All the species of this group possess a spinose, cancellate wall. "Globigerina" anguliofficinalis Blow, 1969. (Plate IV 5a d). See Blow (1969), pl.ll, figs. l 5. This species, associated with transitional forms to "G." angulisuturalis increases in size ( > 150 lam) in Zone P21b (Plate IV, 3a c). "Globigerina" angulisuturalis Bolli, 1957. (Plate IV, la, 2a d, 4a b). See Bolli (1957), pl.22, figs. l l a c. This species increase conspicuously in abundance at P21a/P21b zonal boundary. "Globigerina" ciperoensis Bolli, 1957. (Plate IV, 7a-b; Plate V, 3a-c, 4a d). See Bolli (1957), pl.22, figs. 10a b. "Globigerina"J~triasi Bermudez, 1961. (Plate IV, 6a d). See Bolli and Saunders (1985), fig. 13 (9).
Palmer (1934), figs. l 6. Genus
Dentoglobigerina
Dentoglohigerina baroemoenensis group Dentoglohigerina haroemoenensis (Le Roy, 1939) (= Glohigerina baroemoenensis Le Roy). (Plate II, 4a c). See Molina (1979), pl.22, figs.2a c. Dentoglobigerina galavisi (Bermudez, 1961 ) ( = Glohigerina galavisi Bermudez). (Plate II, la d). See Bermudez (1961), pl.4, fig.3. Transitional forms to D. haroernoenensis occur in Zone P19 (Plate II, 2a c, 3a d).
Dentoglobigerina globularis group Dentoglobigerina altispira globosa (Bolli, 1957) (=Glohoquadrina altispira globosa Bolli). (Plate III, 4a b). See Bolli and Saunders (1985), fig. 15 (1). Dentoglohigerina globularis (Bermudez, 1961) (= Globoquadrina glohularis Bermudez). (Plate II, 5a c, 7a c; Plate III, la c). See Molina (1979), pl.19, fig. la c. Transitional forms to D. altispira globosa occur in Zones P20. (Plate III, 3a c, 6a, 7a).
Jenkins (1971), pl.17, figs.522 524. Some specimens of comparable size and overall shape as D. larmeui but possessing a triangular tooth are figured in Plate VII, 3a b and Plate XVII under the name of Dentoglobigerina sp. aft. D. larmeui. They occur throughout the sequence, but never in abundance.
Dentoglobigerina pseudovenezuelana (Blow and Banner, 1962) (= Globigerina venezuelana Hedberg and Bolli, 1957). (Plate III, 5a b). See Blow and Banner (1962), pl.XI, figs.J L, N, O. Very rare.
"Globigerina" ampliapertura Bolti, 1957. (Plate XIII, 6a~d). See Bolli (1957), pl.22, figs.5 6. Typical specimens are very rare. Wall surface of this taxon is cancellate, possibly spinose (see Blow and Banner, 1962), then its generic attribution is still uncertain.
Genus
Globigerina
Globigerina officinalis Subbotina, 1953. (Plate VI, la b, 2a-c). See Subbotina (1953), pl.l l, figs. 1 - 7.
Globigerina ouachitaensis Howe and Wallace, 1932. (Plate VI, 5a c). See Blow and Banner (1962), pl.IX, figs.D, H K. Transitional form to Globi~erina ouachitaensis gnauki occur from the upper part of Zone P21a (Plate V, l a d ) .
238
PLATE
s. SPEZZAFERRI AND I. PREMOLI SILVA
I
(for e x p l a n a t i o n see p.243)
OLIGOCFNE PLANK1ONIC FORAMINIFERAL
PLATE
II
(for explanation see p.243)
B I O S T R A 1 I G R A P H Y A N D P A L E O C L I M A 1 IC I N F E R P R E T A I ION
239
240
P L A T E III
(for explanation see p.243)
S. S P E Z Z A F E R R I A N D 1. P R E M O L I S I L V A
O L I ( i O ( ' E N I PLANKIONI(" FORAMINIFERAL BIOSTRATIGRAPHY ~ND PALEOCLIMAIlC INTERPRETATION
P L A T E IV
(for explanation see p.243)
24[
242
PLATE V
S. S P E Z Z A F E R R I A N D I. P R E M O L ! S I L V A
OLIGO('ENE PLANKTONIC FORAMINIFERALBIOSTRATIGRAPHYAND PALEOCLIMATICINTERPRETATION
243
PLATE 1 (see p.238)
la d. Catapsydrax dissimilis dissimilis (Cusman and Bermudez), Sample 538A-5-CC. Catapsydrax globiformis (Blow and Banner), Sample 538A-8-CC. Catapsydrax africanus (Blow and Banner), Sample 538A-3-2, 70 72 cm, (a) side view. Catapsydrax dissimilis ciperoensis (Blow and Banner), Sample 538A-5-CC. Catapsydrax martini (Blow and Banner), Sample 538A-6-2, 40-42 cm. GIoborotaloides suteri Bolli, Sample 538A-10-CC. (a) Spiral view, (b) side view, (c) umbilical view. and (d) wall structure, except
2a b. 3a. 4a b. 5a c. 6a-c.
when differently specified.
PLATE 11 (see p.239) la c. Dentoglobigerina galavisi (Bermudez), Sample 538A-3-CC. 2a c. Dentoglob~erina galavisi (Bermudez)/D. baroemoenensis (Le Roy) transition, Sample 538A-3-CC. 3a d. l)entoglobi,~erina galavisi (Bermudez)/D. baroemoenensis (Le Roy) transition, Sample 538A-10-3, 95- 97 cm. 4a c. Dentoglobigerina baroemoenensis (Le Roy), Sample 538A-10-4, 95 97 cm. 5a-c. l)entoglobigerina globularis (Bermudez), Sample 538A-6-CC. 6a c. Dentogh>bigerina larmeui (Akers), Sample 538A-3-CC. 7a c. Dentoglobi,eerina globularis (Bermudez), Sample 538A-6-CC. (a) Spiral view, (b) side view, (c) umbilical view and (d) wall structure, except when differently specified. Figs.3, 4, 5, same magnification.
PLATE III (see p.240)
la c. Dentoglobigerina globularis (Bermudez), Sample 538A-5-CC. c. Globoquadrina tripartita (Koch), Sample 538A-8-CC. c. Dentoglobigerina globularis (Bermudez)/D. altispira globosa (Bolli) transition, Sample 538A-5-CC. b. Dentoglobigerina altispira globosa (Bolli), Sample 538A-4-CC, (a) spiral view, (b) umbilical view. b. Dentoglobigerina pseudovenezuelana (Blow and Banner), Sample 522-32-1, 49 cm, (a) spiral view, (b) umbilical view. Dentoglobigerina globularis (Bermudez)/D. altispira globosa (Bolli) transition, Sample 538A-5-CC. Dentoglobigerina globularis (Bermudez)/D. altispira globosa (Bolli) transition, Sample 538A-5-CC. (a) Spiral view, (b) side view,
2a 3a 4a 5a 6a. 7a.
(c) umbilical view, and (d) wall structure, except when differently specified. Figs.4 and 5, same magnification.
PLATE IV (see p.241) l a. 2a d. 3a c. 4a-b. 5a d. 6a-d. 7a b.
"Globigerina" "Globigerina" 'Globigerina" "Globigerina" "Globigerina" "Globigerina" "Globigerina"
angulisuturalis Bolli, Sample 538A-6-1, 40 42 cm. angulisuturalis Bolli, Sample 538A-7-2, 40-42 cm. anguliofficinalis Blow/"G." angulisuturalis Bolli transition, Sample 538A-11-1, 4(I-42 cm. angulisuturalis Bolli, Sample 538A-6-1, 40-42 cm, (a) umbilical view. anguliofficinalis Blow, Sample 538A-4-CC. ciperoensisfariasi Bermudez, Sample 538A-4-CC. ciperoensis Bolli, Sample 538A-2-CC. (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure,
except when differently specified. Figs.5 and 6, same magnification.
PLATE V la d. 2a c. 3a--d. 4a- d.
GIobigerma ouachitaensis Globigerma ouachitaensis "Globigerina" ciperoensis "Globigerina" ciperoensis
Howe and Wallace/G. ouachitaensis gnauki Blow and Banner transition, Sample 538A-4-CC. gnauki Blow and Banner, Sample 538A-3-CC.
Bolli, Sample 538A-4-CC. Bolli, Sample 538A-4-CC. (a) Spiral view, (b) side view, and (c) umbilical view, and Id) wall structure except when differently specified. Figs. l 4, same magnification. Figs. ld, 3d, 4d, same magnification.
244
PLATE
S. SPEZZAFERRI AND 1. PREMOLI SILVA
VI
(for explanation see p.246)
()LIGO( FNE PLANK1ONIC FORAMINIFERAL BIOSTRATIGRAPH'( AND PAI~EO('LIMA11( INTERPRF IA IION
PLATE VII
(for e x p l a n a t i o n see p . 2 4 6 )
245
246
s. S P E Z Z A F E R R I A N D 1. P R E M O L I SILVA
Globigerina ouachitaensis gnauki Blow and Banner, 1962. (Plate V, 2a-c). See Blow and Banner (1962), pl.IX, figs.L-N. Globigerina praebulloides Blow, 1959. (Plate VI, 3 a - c , 4 a - d ) . See Blow and Banner (1962), pl.IX, figs.O Q. Globigerina praebulloides occlusa Blow and Banner, 1962. (Plate VIII, l a - d ) . See Blow and Banner (1962), pl.IX, figs.U-W. Large globigerinids All the species o f this g r o u p possess a spinose, cancellate wall. "Globigerina" euapertura Jenkins, 1960. (Plate VII, 4a-c). See Jenkins (1985), fig.6 (18a-c). "Globigerina" prasaepis Blow, 1969. (Plate VII, 6a-c). See Blow (1969), pl.10, fig.13; pl.18, figs.3 7. "Globigerina" venezuelana Hedberg, 1937. (Plate VII, 2 a - c , 5 a - b . See Bolli and Saunders (1985), fig. 13 (20).
Other globigerinids All the species o f this g r o u p possess a spinose, cancellate wall. "'Globigerina'" brazieri (Jenkins, 1966) ( = Globigerina brazieri Jenkins). See Jenkins (1985), fig.6 (20a-c). "Globigerina" labiacrassata (Jenkins, 1966) ( = Globigerina labiacrassata Jenkins). See Jenkins (1985), fig.6 (19a-c). Very rare. "Globigerina'" woodi s. str. Jenkins, 1960. See Chaproniere (1988), pl.1 and 2. In our material in addition to typical "G."woodi, which has four chambers in the last whorl and a wide-arched aperture occasionally with a thin lip, there are rare forms plotted as "Globigerina" sp. characterized by three to three and a half chambers in the last whorl, a subrectangular profile, and a mediumsized, low-arched aperture. They appear to be related to "G." woodi s. str.
Globigerinita juvenilis (Bolli, 1957) ( = Globigerma
PLATE Vl (see p.244) la-b. 2a c. 3a-c. 4a-d. 5a-c. 6a-c.
Globigerinaofficinalis Subbotina, Sample 538A-2-CC. Globigerinaofficinalis Subbotina, Sample 538A-4-CC. Globigerinapraebulloides Blow, Sample 538A-4-CC. Globigerinapraebulloides Blow, Sample 538A-4-CC. Globigerinaouachitaensis How and Wallace, Sample 538A-2-CC. Globigerinapraebulloides Blow, Sample 538A-4-CC. This specimen shows recrystallized wall. (a) Spiral view. (b) side view, (c) umbilical view, and (d) wall structure. Figs.1 and 3, same magnification.
PLATE VII (see p.245) la-d. 2a c. 3a b. 4a-c. 5a-b. 6a-c.
"Globigerina"prasaepisBlow, Sample 538A-5-CC. "Globigerina"venezuelana Hedberg, Sample 538A-3-CC. Dentoglobigerinaaft. D. larmeui (Akers), Sample 538A-6-CC, (a) side view, (b) wall structure. "Globigerina"euapertura Jenkins, Sample 538A-12-CC. "'Globigerina"venezuelana Hedberg, Sample 522-21-2, 22 cm, (a) umbilical view. "Globigerina'"prasaepis Blow, Sample 538A-12-CC. (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure, except when differently specified.
PLATE VIII la-d. 2a-c. 3a. 4a d. 5a-c. 6a-c.
Globigerinapraebulloides occlusa Blow and Banner, Sample 538A-4-2, 40-42 cm. This specimen shows recrystallized wall. "Globigerinoides'"praeprimordius, Sample 538A-10-4, 95-97 cm. Globigerinoidesprimordius Blow and Banner, Sample 538A-5-CC. Globigerinoidesprimoridus Blow and Banner, Sample 538A-4-CC. "Globigerina'"normal "Globigerinoides"praeprimordiusSample 538A-I0-5, 2-3 cm. Cassigerinellachipolensis(Cushman and Ponton), Sample 538A-6-2, 40-42 cm, (a) side view, (b) umbilical view. (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure, except when differently specified. Figs.4 and 5, same magnification.
O L I ( i O ( ' I NI P L A N K T O N I (
P L A T E VIII
FORAMINIFERAL
BIOSTRA I IGRAPH~
A N D P'S, L E O ( L I M A T I ( " I N I E R P R E
I A IION
247
248
S. S P E Z Z A F E R R | A N D 1. P R E M O L I SILVA
juvenilis Bolli). See Bolli (1957), pl.24, figs.5 and 6. Its first occurrence is within Zone P21a. Rare. Genus
Globigevinoides
Globigerinoides primordius Blow and Banner, 1962. (Plate VIII, 3a, 4a-d). See Bolli and Saunders (1985), fig.20 (16). Typical forms are preceded in Zone P21 by specimens displaying the same shape and wall structure as G. primordius without supplementary apertures. The latter are plotted under the informal name of "Globigerinoides"praeprimordius (Plate VIII, 2a-c). Genus
Globoquadrina
Globoquadrina binaiensis (Koch, 1935) ( = Globigerina binaiensis Koch). (Plate IX, 6a c). See Bolli and Saunders (1985), fig.14 (6-10). Globoquadrina dehiscens praedehiscens Blow and Banner, 1962 (Plate IX, la-c). See Blow and Banner (1962), pl.15, figs.O-S. Globoquadrina sellii Borsetti, 1959 (Plate IX, 7a-c). See Bolli and Saunders (1985), fig.14 (11). "Globoquadrina" tapuriensis (Blow and Banner, 1962) (=Globigerina tripartita tapuriensis Blow and Banner). (Plate IX, 3a-c, 4a-b). See Blow and Banner (1962), pl.10, figs.H-K. The genus Globoquadrina is kept in brackets because this species does not possess the typical tooth of the genus Globoquadrina. Globoquadrina tripartita (Koch, 1926) ( = Globigerina bulloides var. tripartita Koch). (Plate III, 2a c; Plate IX, 2a c). See Bolli and Saunders (1985), fig.14 (13). Globoquadrina rohri (Bolli 1957) (=Globigerina rohri Bolli). (Plate IX, 5a-c). See Bolli (1957), pl.36, figs.4a-b.
Genus
Globiger&ella
Globigerinella obesa Bolli, 1957. (Plate XI, figs.3a c). See Bolli (1957), P1.29, figs.2a-3. This species possesses a pole-like spines in a fiat wall like true Globigerina, then it cannot belong to the genus Globorotalia. Its taxonomic position, however, is still uncertain, because it evolves into Globigerinella praesiphonifera (Premoli Silva and Spezzaferri, 1990). Genus
Globorotaloides
Globorotaloides permicrus (Blow and Banner, 1962) (=Globorotalia (Turborotalia) permicra Blow and Banner). (Plate X, l a-c). See Blow and Banner (1962), pl.XII, figs.N-P. Globorotaloides suteri Bolli, 1957 (Plate I, 6a-c; Plate X, 3a-b, 4a-d). See Bolli (1957), pl.27, figs.9 13. Globorotaloides variabilis Bolli, 1957 (Plate X 2a-b). See Bolli and Saunders (1985), fig.18 (9a-c). Genus
Paragloborotalia
Paragloborotalia opima nana (Bolli, 1957) (=GIoborotalia opima nana, Bolli) (Plate XI, 4a-c). See Bolli (1957), pl.28, figs.3a-c. Paragloborotalia opima opima (Bolli, 1957) ( = Globorotalia opima opima Bolli). (Plate XI, 5a-c, 6a-b). See Bolli (1957), pl.28, figs.la 2. Paragloborotalia pseudocontinuosa (Jenkins, 1967) (=Globorotalia pseudocontinuosa Jenkins (Plate XI, la c; Plate XII la-c, 2a; Plate XVI, figs.2a d). See Jenkins and Srinivasan (1986), pl.5, figs.2 4. From Subzone P21a some specimens show a tendency to have four and a half to five chambers in the last whorl. Paragloborotalia pseudokugleri Blow, 1969 (Plate XI, 7a c). See Blow (1969), pl.10, figs.4-6. Rare
PLATE IX la c. 2a c. 3a c. 4a b. 5a-c. 6a-c. 7a-c.
Globoquadrinadehiscenspraedehiscens Blowand Banner, Sample 538A-2-CC. Globoquadrinatripartita (Koch), Sample 538A-8-CC. "GIoboquadrina"tapuriensis (Blow and Banner), Sample 538A-10-4, 95-97 cm. Globoquadrinatapuriensis(Blow and Banner), Sample 558-25-5, 73 cm. Globoquadrinarohri (Bolli), Sample 538A-7-CC. Globoquadrinabinaiensis Koch, Sample 538A-3-CC. GIoboquadrinasellii Borsetti, Sample538A-4-CC.(a) Spiral view,(b) side view,(c) umbilicalview,and (d) wall structure,except when differentlyspecified. Figs.l, 2 and 3, same magnification.
Ol I(~O( [N[: P L A N K T O N I C F O R N M I N I F E R A L B I O S T R A f l G R A P H Y A N D P A L E O C L I M ~ I I ( IN I E R P R E T A IION
P L A T E IX
249
250
PLATE X
(for explanation see p.253)
S. S P E Z Z A F E R R I A N D 1. P R E M O L I SILVA
OI I(;O(1 N FI PLANK I O N I ( FORAMINIFERAL BIOSTRATIGRAPH'Y AND PALEOCLIMATI( INTERPRETATION
PLATE XI
( f o r e x p l a n a t i o n see p . 2 5 3 )
25]
)-52
P L A T E XII
S. S P E Z Z A F E R R I A N D I PREMOLI SILVA
OI I ( i O ( ' [ N! P L A N K I O N I C F O R A M I N I F E R A L
BIOSI RA I IGRAPH'Y A N D P A L E O ( ' L I M A [1( I N - I E R P R E T A I I O N
specimens displaying transitional characters to P. kugh,ri occur at the top of the sequence. Recent investigations by Spezzaferri (in press) suggest that on the basis of the wall structure (cancellate with spines) the former "Globorotalia" kugleri group should be attributed to the genus Paragloborotalia. Paraglohorotalia siakensis (Le Roy, 1938) ( = Glohi~erina siakensis le Roy) (Plate XI, 2a c). See Molina (1979), pl.28, figs. la c; Kennett and Srinivasan (1983), pl.42, figs.l, and 6--8. Paraglohorotalia sp. Some specimens as that illustrated in Plate XII, 3a-d may be related to Paragloborotalia semivera (Hornibrook). They occur in Zone P20 up to mid Subzone P21a. Genus Protentella
Protentella sp. (Plate XIII, la-c, 4a c). Under this informal species are grouped a number of proten-
25~
tellids, slightly trochoidal, that possess four to five chambers in the last whorl, with an extraumbilical aperture bordered by a rim. They first occur in Zone P22 and are rare. Genus Pseudohastigerina
Pseudohastigerina barbadoensis Blow, 1969 (Plate XIV, 3a b). See Blow (1969), pl.53, figs.7 9. Pseudohastigerina naguewichiensis (Myatliuk, 1950) ( = Globigerinella naguewichiensis Myatliuk) (Plate XIV, la-c, 2a-b, 5a c). See Toumarkine and Luterbacher(1985), fig.21 (10 16). Pseudohastigerina micra (Cole, 1927) ( = Nonion micrus Cole) (Plate XIV 4a b). See Blow (1979), pl.253, figs. l 9. The specimen illustrated is from Late Eocene Core 14-CC. The Oligocene forms display the same small size as the other pseudohastigerinids.
PLATE X (see p.250) 1 a c . Globoromloides permicrus (Blow and Banner), Sample 538A-7-CC. 2a b. Globorotahmles variahilis Bolli, Sample 538A-6-CC, (b) umbilical view. 3a b. GloborotaloMes suteri Bolli, Sample 366-9-2, 12 cm, (b) umbilical view. 4a d. Globorotah#des suteri Bolli, Sample 538A- I I-2, 40 42 crn. 5a. Chiloguembelina cubensis Palmer, Sample 538A-7-4, 40 42 cm, oblique axial view. 6a. Chiloguembelina cubensis Palmer, Sample 538A-6-CC, axial view. 7a. Chiloguembelina cubensis Palmer, Sample 538A-12-1, 40 42 cm, apertural side view. Chiloguembelina cuhensis Palmer, Sample 538A-12-l, 40 42 cm, apertural side view. 9a b. Chiloguemhelina cubensis Palmer, Sample 538A-12-1, 40 42 cm, (a) apertural side view, Ib) detail o f g a . (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure, except when differently specified. Figs. l and 3, same magnification.
PLATE XI (see p.25l) la 2a 3a 4a 5a 6a 7a
c. c. c. c. c. b. c.
Paragloborotalia pseudocontinuosa (Jenkins), Sample 538A-7-CC. Paraglohorotalia siakensis (Le Roy), Sample 538A-3-CC. Glob~gerinclla obesa (Bolli), Sample 538A-6-1, 40 42 cm. Paragloborotalia opima nana (Bolli), Sample 538A-7-2, 40 42 cm. Paragloborotalia opima opima (Bolli), Sample 538A-7-2, 40 42 cm. Paragloborotalia opima opima (Bolli), Sample 538A-9-CC. Paragloborotalia pseudokugleri Blow, Sample 538-A-3-1, 100-102 cm. (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure, except when differently specified. Figs. l and 2, same magnification.
PLATE XII la c. 2a. 3a d. 4a c. 5a.
Paragloborotalia pseudocontinuosa (Jenkins), Sample 538A-1 I-CC. Paragloborotalia pseudocontinuosa (Jenkins), Sample 538A-11-I, 40-42 cm. Paragqoborotalia sp., Sample 538A-10-2, 95 97 cm. Paraglohorotalia sp., Sample 538A-10-2, 95 97 cm. Paraglohorotalia sp., Sample 538A-10-3, 95-97 cm, (a) umbilical view. (a) Spiral view, (b) side view, (cj umbilical view, and (d) wall structure, except when differently specified. Figs. l, 2 and 4, 5, same magnification.
254
PLATE XIII
(for explanation see p.257)
s. S P E Z Z A F E R R I A N D I. P R E M O L I SILVA
( ) L I G O ( I NE P L A N K 1 0 N I C I-ORAM I N I F E R A L BIOS I RA I IGRAPHY A N D PAI.EO( I IMA l 1( INT[ RPR[ 1A 1 ION
PLATE
XIV
(for explanation
see p.257)
2q5
256
P L A T E XV
S. S P E Z Z A F E R R I A N D 1. P R E M O L I SILVA
Ol I G O ( [ N[ P L A N K I O N I ( F O R A M I N I F E R A L BIOSI R A T I G R A P H ~ A N D P A L E O ( L I M A r I(" IN IERPR[!TA FION
Suhhotina angiporoides group Suhhotina angiporoides angiporoides ( H o r n i b r o o k , 1965) ( = G l o b i g e r i n a angiporoides H o r n i b r o o k ) . (Plate XV, figs.3a d, 4a b). See H o r n i b r o o k (1965), pl. la i and pl.2. This taxon displays a large morphological variability. Subhotina angiporoides minima (Jenkins, 1966) (=Globigerina anjziporoides H o r n i b r o o k subsp. minima Jenkins). (Plate XV, la d, 2a). See Jenkins (1966), fig.7 (52 57). Subbotina utilisindex (Jenkins and Orr, 1973) ( = Glohigerina utilisindex Jenkins and Orr). (Plate XVI, 4a d). See Jenkins and Orr (1973), pl.1, figs. 1 6; pl.2, figs. 1 9: pl.3, figs. l - 3 . The main characteristics of this species are the much more round final c h a m b e r and f n e r wall structure than S. linaperta s. str. (see Premoli Silva and Spezzaferri, 1990). Subbotina utilisindex disappears in the middle Oligocene just prior to S. angiporoides and S. an~ziporoides minima.
High-spired subbotinids Subhotma praeturritilina (Blow and Banner, 1962)
_~7
( = Glohigerina turritilina praeturritilina Blow and Banner). (Plate XVI, la c). See Blow and Banner (1962), pl.XIII, figs.A C. Subbotina gortanii (Borsetti, 1959) ( = Catapswtra.v gortanii Borsetti). (Plate XVI, 3a d). See Borsetti (1959),pl.l, figs.la lc. Very rare.
Genus Tenuitella Tenuitella clemenciae (Bermudez, 1961) ( : Turhorotalia clemenciae Bermudez). (Plate XVIII, la c, 4a c). See Bermudez (1961), pl.17, fig. 10. Intermediate forms between T. clemenciae and T. mumh~ are often present (Plate X V I I I . 3a d). Tenuitella g e m m a (Jenkins, 1971 ) ( = GIohorotalia (Turborotalia; g e m m a Jenkins). (Plate XVIII, 6a c). See Jenkins (1971), pl.10, figs.263 269. Tenuitella munda (Jenkins, 1966) (=Glohorotalia munda Jenkins). See Jenkins ( 1966), figs. 14 and 15.
Genus Tenuitellinata Tenuitellinata angustiumhilicata (Bolli, 1957) ( = Globigerina ciperoensis an~ustiumbilicata Bolli).
PLATE XIII (see p.254) la c. 2a c. 3a. 4a d. 5a c. 6a d.
Protentella sp. Sample 538A-2-CC. furhorola/ia pseudoampliapertura (Blow and Banner), Sample 538A-14-1, 0 2 cm. furhorotaiia pseudoampliapertura (Blow and Banner), Sample 538A-14-1, 0 2 cm, (a) side view: Protentella sp., Sample 538A-2-CC. "GIobi~,,erina"sp. Sample 538A-10-CC. This specimen is probably related to the "Globi~,erina" woodi group. "Glohi~erina"arnpliapertura Bolli, Sample 538A-10-CC. (a) Spiral view, (b) side view, (c) umbilical view. and (d) wall structure. except when differently specified. Figs.l, 2, and 5, 6, same magnification.
PLATE XIV (see p.255) la 2a 3a 4a 5a
c. b. b. b. c.
Pseudohasli~erina naguewichiensis (Myatliuk), Sample 538A-13-CC. Pseudohasti¢erina naguewichiensis (Myatliuk), Sample 538A-13-CC. P.;eudohastifzerinaharhadoensis Blow, Sample 538A-13-CC. P;eudohastigerina micra (Cole), Sample 538A-14-CC. Pseudohastigerinanaguewichiensis (Myatliuk), Sample 538A-13-CC. (a) Spiral view, (b) side view, and (c) wall structure, except when differently specified. All specimens, same magnification. Figs. lc and 5c, same magnification.
PLATE XV l a-c. 2a. 3a d. 4a b.
Suhhotina an~,iporoides minima (Jenkins), Sample 538A-13-1, 86 99 cm. Suhbotinaang'iporoides minima (Jenkins), Sample 538A-12-3.40 42 cm. Suhhotina angiporoides ang,iporoides (Hornibrook), Sample 538A-10-4, 95 97 cm. Subhotina an~ziporoides anf;iporoides (Hornibrook), Sample 538A-I I-CC, (a) Spiral view, (b) side view. (c) umbilical view, and (d) wall structure, except when differently specified.
258
PLATE
s. SPEZZAFERRI AND 1. PREMOLI SILVA
XVI
(for e x p l a n a t i o n see p.261)
()I_IGOCI NE P L A N K T O N I (
FORAMINIFERAL
PLATE XVII
(for explanation see p.261)
BIOSTRATIGRAPHY AND PALEOCLIMATIC INTERPRETATION
_39
260
P L A T E XVIII
S. S P E Z Z A F E R R I
A N D 1. P R E M O L I
SILVA
()1 I(iO( [ N I P L A N K I O N I C F ( ) R A M I N I F I RAL B I O S I R A I I G R A P H ' ~ , \ N I ) PAl I{()( I A M A I I ( [ N I I ( R P R I I A I ION
2t, l
PLA'FE XVI (see p.25S) I a c. Suht~otim~ praeturritilim~ (Blow and Banner), Sample 538A- 12-4, 40 42 cm, 2a d. f'arag, lohorolalia pseudocontinuosa (Jenkins), Sample 53,~A-10-2, 95 97 cm, 3a d. Suhholina jmrlanii (BorscHt), Sample 538A- 13-1, ~6 99.cm. 4a d. Suhhozina ulili.vindex (Jenkins and err), Sample 538A-13-I, 86 99 cm. {a) Spiral "view. (b) side viev., (c) umbilical xiew, and !d) wall structure, except when differently specitied. Figs.2d and 3d. same magnification.
PLATE XVI1 (see p.25% [ a d . l)ento~lohi~,,erma aft. D. larmeui tAkers), Sample 538A-4-CC 2a d. I)ento~dohi~,eriml aft. D. larmeui tAkers), Sample 538A-6-CC. 3a d. l)ento~,/(~k,~,,erina aft'. D. /armeui tAkers), Sample 538A-6-CC 4a b. l)enlo~,/rd,~,,erina aft. O. larnu, ui tAkers). Sample 538A-6-C('. (a) spiral side slightly oblique. (b) umbilical side wilh a broken chamber. 5 a b. l)enlo,el¢,hi~erma aft. D. larmeui takers), Sample 538A-6-CC.(b) umbilical view. 6a. I)enlo,e/ol,i~,,eriml aff. D. larmeui (Akers), Sample 538A-6-CC. la) Spiral view, (b) side vie'-*, (c) umbilical xicv,, and (d) v, all structure with particulars of teeth, except when differently specified. All specimens, same magnification: Eigs.2d and 3d. same magnilicalion.
PLATE XVIII [ U C.
2a 3a 4a 5a 6a
d. d. c. d. c
71,m~itel/a ~lemem'iae (Bermudez), Sample 538A-12-4, 40 42 cm. Tem~itel/inam an~u~tiumhilicala (Bolli), Sample 53SA- I I -CC. 7~'#mitella ch,tm,nciae (Bermudez), T, mumta (Jenkins) intermediate l\)rm, Samplc 538A 7-4, 40 42 cm. 7~,mdtella clemem'iae (Bermudez), Sample 538A-12-4, 40 42 cm, (a) umbilical view, (b) side xiew. and Ic) wall structure, Tem~ile//inala an~,,u.sliumhilicala (Bolli), Sample 53SA- 10-CC. Te,uilella ,£,cmma (Jenkins), Sample 538A-10-5, 2 3 cm. (a) Spiral view, (b) side view, (c) umbilical viex~, and (d) wall structure, except when difl'crenlly specified Figs.2d and 3d. same magnification.
(Plate XVIII, 2a d, 5a d). See Li Qianyu (1987), pl.2. figs. 15, 17 19. Genus Turborotalia Turhorotalia increbescens (Bandy, 1949) ( = Glohi,~erina increhe.wens Bandy). See Bolli and Saunders (1985). fig. 14 (5). Very, rare. Turhorotalia pseudoampliaperlura (Blow' and Bannor, 1962) ( = Gloh~,,erina pseudoampliapertura Blow' and Banner). (Plate XIII, 2a c, 3a). See Bolli and Saunders 1985), tig. 1 (4). References Adams, (7. G., Bunerlin, J. and Samanta, B. K., 1986. Larger foraminifera and events at the Eocene/Oligocene boundary in the Indo-West Pacitic region. In: C. Pomerol and 1. Premoli Siha (Editors), Terminal Eocene Events (Dev. Paleontol. Stratigr. 9). Elsevier, Amsterdam, pp. 237 252. Barren..1. A.. l_arsen. B., Baldauf, J. G. el al., 1989. Proximal and distal evidence of the history of the East Antarctic ice sheet: Result,',, from O D P Leg 119. In: 3rd Int. Conf. Palcoceanogr... Cambridge. T E R R A abstr., I: 3.
Belanger, P. E. and Manhews, R. K., 1984. The forammilLqal isotope record across the EoceneOligocene boundary at Deep Sea Drilling Project Site 540. In: R T. Buffier, W. Schlager et al., lnit. Rep. DSDP, 77:589 593. Bermudez, P. J.. 1961. ('ontribuci6n al cstudio de las Globigerinidae de la region Caribe-Anfillana tPaleoceneRecientc). Memorias de la Ill Congreso Geologico Venezolane, tome I11. Soc. (}eel. Venez., Bol. Geol., Publ. Espec., 3: [119 139~. Bcrmudcz. P. J. and Seiglie, B. S., 1967. A new gellUS and species of foraininifcr from the early Miocene of Puerto Rico. Tulane Stud. Geol.. 5(3): 177 [79. Biolzi, M . . 1983. Stable isotopic stud,, of Oligocenc Miocene sediments from DSDP Site 354, Equatorial Atlantic. Mar. Micropaleontol., 8:121 I39 Biolzi, M., 1985. The Oligocene Miocene boundar', m sclectcd Atlantic, Mediterranean and Paratethyan sections based on stratJgraphic and stable isotope evidence. Mere. Sci. Geol. Padova, 37:303 378. Blow, W. H.. I969. Late middle Eocene to Recent planktonic l\mmfiniferal biostratigraphy In: Prec. l:irst Int. ('onf. Planktonic MicrotBssils. Geneva. Bri!l. I.ciden, I, pp. 199 422. Blow. W. It., 1979. The Cainozoic (}lobigerinida. BM1, Leiden. 1410 pp. Blow. W. H. and Banner. F. T_ 1962. The Mid-Tertiary (Upper
262 Eocene to Aquitanian) Globigerinacea. In: F. E. Eames, F. T. Banner, W. H. Blow and W. J. Clarke (Editors), Fundamentals of Mid-Tertiary Stratigraphical Correlation. Cambridge Univ. Press, pp. 61 151. Boersma, A., 1977. Cenozoic planktonic foraminifera, DSDP Leg 39, South Atlantic. In: P. R. Supko, K. Perch-Nielsen et al., Init. Rep. DSDP, 39: 643-656. Boersma, A. and Premoli Silva, 1., 1983. Paleocene planktonic foraminiferal biogeography and the paleoceanography of the Atlantic Ocean. Micropaleontology, 29(4): 355-381. Boersma, A. and Premoli Silva, I., 1986. Terminal Eocene events: planktonic foraminifera and isotopic evidence. In: C. Pomerol and I. Premoli Silva (Editors), Terminal Eocene Events (Dev. Paleontol. Stratigr., 9). Elsevier, Amsterdam, pp. 213-224. Boersma, A. and Premoli Silva, I., 1988. Boundary conditions of Atlantic oxygen minimum zones. Riv. Ital. Paleontol. Stratigr., 93(4): 479-506. Boersma, A. and Premoli Silva, I., 1989. Atlantic Paleogene biserial heterohelicids and oxygen minima. Paleoceanography, 4(3): 271 286. Boersma, A., Premoli Silva, I. and Shackleton, N. J., 1987. Atlantic Eocene planktonic foraminiferal paleohydrographic indicators and stable isotope paleoceanography. Paleoceanography, 2(3): 287-331. Boersma, A. and Shackleton, N. J., 1977. Tertiary oxygen and carbon isotope stratigraphy, Site 357 (mid latitude South Atlantic). In: P. R. Supko, K. Perch-Nielsen et al., lnit. Rep. DSDP, 39:911 924. Boersma, A. and Shackleton, N. J., 1978. Oxygen and carbon isotope record through the Oligocene Site 366, Equatorial Atlantic. In: Y. Lancelot, E. Seibold et al., lnit. Rep. DSDP, 41:957 962. Bollk H. M., 1957. Planktonic Foraminifera from the Oligocene-Miocene Cipero and Lengua formations of Trinidad, B.W.1. Bull. U.S. Natl. Mus., 215:97 124. Bolli, H. M. and Saunders, J. B., 1985. Oligocene to Holocene low latitude planktic foraminifera. In: H. M. Bolli, J. B. Saunders and K. Perch-Nielsen (Editors), Planktic Stratigraphy. Cambridge Univ. Press, pp. 155 262. Borsetti, A. M., 1959. Tre nuovi Foraminiferi plantonici dell'Oligocene piacentino. G. Geol., 27:205 212. Buffier, R. T., Schlager, W. et al., 1984. Init. Rep. DSDP, 77, 747 pp. Chaproniere, G. C. H., 1988. Globigerina woodi from the late Oligocene and early Miocene of southeastern Australia. J. Foraminiferal Res., 18(2): 124 129. Cita, M. B., Vergnaud-Grazzini, C., Robert, C., Chamley, H., Ciaranfi, N. and D'Onofrio, S., 1977. Paleoclimatic record of a long deep sea core from the Eastern Mediterranean. Quat. Res., 8:205 235. Cifelli, R., 1982. Early occurrences and some phylogenetic implications of spiny, honeycomb textured planktonic Foraminifera. J. Foraminiferal Res., 12:105 115. Douglas, R. G. and Savin, S. M., 1978. Oxygen isotope evidence for the depth stratification of Tertiary and Cretaceous planktonic foraminifera. Mar. Micropaleontol., 3: 175 196. Fleisher, R. L., 1974. Cenozoic planktonic foraminifera and biostratigraphy, Arabian Sea Deep Sea Drilling Project, Leg
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23A. In: R. B. Whitmarsh, O. E. Weser, D. A. Ross et al., Init. Rep. DSDP, 23: 1001-1072. Haq, B. U., Premoli Silva, I. and Lohmann, G. P., 1977. Calcareous plankton paleobiogeographic evidence for major climatic fluctuations in the Early Cenozoic Atlantic Ocean. J. Geophys. Res., 82: 3861-3876. Hardenbol, J. and Berggren, W. A., 1978. A new Paleogene numerical time scale. In: G. Cohee, M. Glaessner and H. Hedberg (Editors), Contributions to the Geologic Time scale. AAPG, Tulsa, OK, pp. 213 234. Harwood, D. N., Webb, P. N. and Barrett, P. J., 1989. Multiple Cenozoic glaciations of Antarctica from terrestrial and continental shelf data. In: 3rd Int. Conf. Paleoceanogr., Cambridge, TERRA Abstr., 1: 2. Hemleben, C. H., Spindler, M. and Anderson, O. R., 1988. Modern Planktonic Foraminifera, Springer, New York, NY, 363 pp. Hornibrook, N. de B., 1965. Globigerina angiporoides n. sp. from the Upper Eocene and Lower Oligocene of New Zealand and the status of Globigerina angipora Stache, 1865. N. Z. J. Geol. Geophys., 8(6): 834-838. Jenkins, D. G., I966. Planktonic foraminiferal zones and new taxa from the Danian to Lower Miocene of New Zealand. N. Z. J. Geol. Geophys., 8: I088-1126. Jenkins, D. G., 1971. Cenozoic planktonic foraminifera of New Zealand. N. Z. Geol. Surv. Paleontol. Bull., 42:1 278. Jenkins, D. G., 1985. Southern mid-latitude Paleocene to Holocene planktic foraminifera. In: H. M. Bolli, J. B. Saunders and K. Perch-Nielsen (Editors), Plankton Stratigraphy. Cambridge Univ. Press, pp. 263-282. Jenkins, D. G. and Orr, W. N., 1973. Globigerina utilisindex n. sp. from the Upper Eocene-Oligocene of the eastern equatorial Pacific. J. Foraminiferal Res., 3(3): 133-135. Kennett, J. P. and Srinivasan, M. S., 1983. Neogene Planktonic Foraminifera. A Phylogenetic Atlas. Hutchinson and Ross, Stroudsburg, PA, 265 pp. Li, Qianyu, 1987. Origin, phylogenetic development and systematic taxonomy of the Tenuitella plexus (Globigerinitidae, Globigerinina). J. Foraminiferal Res., 17(4): 298-320. Molina, E., 1979. Oligocene-Mioceno inferior por medio de foraminiferos planctonicos en el sector central de las Cordilleras Beticas (Espana). Thesis, Univ. Granada and Zaragoza. Palmer, D. K., 1934. The foraminiferal genus Guembelina in the Tertiary of Cuba. Mem. Soc. Cubana Hist. Nat., 8: 73-76. Poore, R. Z. and Matthews, R. K., 1984. Late Eocene-Oligocene oxygen- and carbon-isotope record from South Atlantic Ocean, Deep Sea Drilling Project Site 522. In: K. J. Hsu, J. L. LaBreque et al., Init. Rep. DSDP, 73: 725-736. Premoli Silva, I. and Boersma, A., 1988. Atlantic Eocene planktonic foraminiferal historical biogeography and paleohydrographic indices. Palaeogeogr., Palaeoclimatol., Palaeoecol., 67(3/4): 315-356. Premoli Silva, I. and Boersma, A., 1989. Atlantic Paleogene planktonic foraminiferal bioprovincial indices. Mar. Micropaleontol., 14: 357-371. Premoli Silva, I. and Spezzaferri, S., 1990. Paleogene planktonic foraminifer biostratigraphy and paleoenvironmental remarks of Paleogene sediments from Indian Ocean Sites, Leg 115. In: J. Backman, R. A. Duncan et al., Proc. ODP Sci. Reports, 115:277 314.
()[ IG()( I NI ['LANKIONIC FORAMINIF[RAL BIOSTRATIGRAPHYAN[) PALEO('IIMAII( IN II RPRI IAI ION Shackleton. N. J., ttall. M. A. and Boersma, A., 1984. Oxygen and carbon isotope data from Leg 74 foraminifers. In: T. C. Moore Jr., P. D. Rabinowitz et al., lnit. Rep. DSDP. 74: 509 612. Spezzaferri. S., m press. Evolution and taxonomy of the Paragloborotalia kugleri (Bolli) lineage. J. Foraminiferal Res.
26~
Thunell, R. C. and Reynolds, 1,. A.. 19S4. Se(limentation oF plantktonic foraminifera: Seasonal changes in species flux in the Panama Basin. Micropaleontology, 30(3): 243 262. Toumarkine, M. and Luterbacher, H. P.. 19S5. Paleocenc and Eocene planktic Foraminifera. l n : H . M . Bolli, J B. Saunders and K. Perch-Nielsen (Edilors). Planktonic Stratigraphy Cambridge Univ. Press, pp. 87 154.
217
Elsevier Science Publishers B.V., Amsterdam
Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico Silvia Spezzaferri and Isabella Premoli Silva Dipar~qmenlo di Scienze della Terra, UniversitL'l di Milano, via Man~iaqalli, 34, Milano 2#133, Italy (Received F e b r u a r y 1, 1990: revised a n d accepted M a y 30, 1990)
ABSTRACT Spezzaferri, S. and Premoli Silva, 1., 1991. Oligocene planktonic foraminiferal biostratigraphy and paleoclimatic interpretation from Hole 538A, DSDP Leg 77, Gulf of Mexico. Palaeogeogr. Palaeoclimalol., Palaeoecol., 83:217 263. A relatively extended Oligocenc pelagic sequence with good to medium recovery, drilled during DSDP Leg 77 in the Gulf of Mexico, yielded rich and ~vell diversified planktonic foraminiferal faunas. Planktonic foraminifera recorded m Hole 53gA span the interval from Zone P I9 through P22. Evolutionary lineages were observed among the globoquadrinids, the globigerinitids, and the "'Glohit,,erina" c~peroen.~isand Glohi,~ermoi&'sprimordius groups. Quantitative analysis of planktonic foraminiferal assemblages shows that faunas fluctuate in abundance and species diversity throughout the sequence. A few of these fluctuations that could be related to selective dissolution are mainly confined to the early-mid Oligocene. A climatic curve was constructed using as warmer indicators, Turhorolalia pseudoampliaperlura, Glohoquadrina lripartila, Denm,~lohij,,erina ,elohularis, Denloqlohi~er#m haroemoenensis, "Glohi~,,erina" ciperoensi.~ and Glohi~,ermoide.~ groups, and ('a.~si,eerinella chipolen.~is: and as cooler indicators, ('atapsydrax spp., Glohoromloides spp., Suhhotina an~iporoi~h,s group, Glohieerma s. str., and the tenuitellids. Three major intervals are identifiable in the climatic curve: Interval 1 (lower) up to Zone P20 predominantly cooler: Interval 2 (intermediate) up to the upper part of Zone P21a with warm and cool fluctuations: and lnter~ al 3 (upper), warmer, with a large positive peak, duc to abundant "G. "ang, ulisuturalis, at the beginning of Zone P2 lb with recooling midway in Zonc P22. In Intervals I and 2 planktonic foraminiferal faunas are dominated by temperate forms. Interpretation of planktonic foraminiferal data suggests that coolcr water conditions characterize the early-mid Oligocene: during the mid Oligocene (most of Zone P2 l a) water masses exhibit peculiar characteristics transitional to the warmer ~aters prevailing during the late Oligocene. Warmer conditions were not definitely settled in Zone P22, however, as indicated by the cooler cpisode following the warmest peak. These climatic trends are inconsistent with those inferred from oxygen isotopes except at small scale. In fact, oxygen isotope values for Oligocene Atlantic Ocean are too heavy (thus too cool) in comparison ~ith the high abundance and diversity of warm taxa, expecially in Zone P22. When values are lighter (warmer), as m Zone PI9. abundance and diversity of warm indices are too low. 1o explain such a cool isotope values m presence of highly diversified and abundant warm planktonic foraminifera, we suggest (1) that the oxygen isotope ratio used for estimating Oligocene paleotcmperal ures might be 1%,, heavier than Eocene values and further increased for the late Oligocene. This hypothesis mrplies the presence of a relatively extended ice cap in Antarctica in the early and mid Oligocene, and probably an increase in ice volume during the late Oligocenc: (2) heavier isotope values might be related to an increase in salinity, or (~) by a combination of both ice cap and increase in salinity.
Introduction
During the biostratigraphic study of Oligocene planktonic foraminiferal assemblages recovered in Hole 538A (Gulf of Mexico), it was apparent that the composition of planktonic foraminiferal fau0031-01~2,9I S03.50
(
1991
nas changes through the stratigraphic interval investigated. More specifically, the relative abundance of some taxa fluctuated from layer to layer. Because preservation could not account for these changes, which also occurred in the best preserved samples, it became apparent that the changes
Elsevier Science Pnblishers B.V.
218
S. S P E Z Z A F E R R I A N D I. P R E M O L I SILVA
could be related to climatic fluctuations and/or to changes in the properties of water masses. In order to investigate the significance of such faunal fluctuations, quantitative analyses of the planktonic foraminiferal content were performed. Hole 538A material appeared to be particularly suitable for investigating a possible climatic signal for much of the Oligocene. Previous studies reported only data from selected Oligocene time-slices (Haq et al., 1977), but a continuous sequence has never been investigated in detail, especially in the Atlantic.
nannofossil ooze of late and middle Miocene age which rests unconformably on late Oligocene foraminiferal nannofossil ooze. The Oligocene sediments consist of foraminiferal nannofossil ooze from 6 mbsf to 69 mbsf (Core 77-538A-2-CC to Core 77-538A-8-CC), followed downhole by about 10 m of foraminiferal nannofossil chalk (Core 77538A-9) and about 40 m of nannofossil chalk (Core 77-538A-10 to Core 77-538A-14-1, 100 cm). A hiatus at 177.5 mbsf separates Oligocene sediments from late Eocene radiolarian nannofossil limestone. Several volcanic ash layers, 1-2 cm thick, are interbedded in the light-colored Oligocene pelagic sediments (see Fig.2). Sixty-four samples (Cores 77-538A-2-CC to 141, 51 54 cm) have been analysed for their foraminiferal content and a biostratigraphic study was performed without picking. Samples were washed on >40 btm and > 150 btm sieves under running water. To construct the climatic curve, quantitative analysis of planktonic foraminifera was performed on the same samples previously used for biostratigraphy. For both sieve fractions (see above) an aliquot of residue was evenly spread over a picking tray with a grid, so that approximately 300 specimens of planktonic foraminifera from each
Materials and methods Hole 538A was drilled on the top of the Catoche Knoll (23°50.98'N and 85°10.26'W, water depth 2740m), a large topographic feature located approximately 25 km northeast of the Campeche Escarpment, and rising 750 m above the abyssal floor of the Gulf of Mexico (Burlier, Schlager et al., 1984) (Fig.l). Hole 538A penetrated 268.5m of sediments resting on metamorphic basement. Eleven and a half out of the 36 cores taken belong to the Oligocene, with a recovery rate of 52.6%. The uppermost 6 m belong to a condensed sequence of nannofossil ooze and foraminiferal
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Fig.l. Location map of Hole 538A, Leg 77, Gulf of Mexico. Present water depth 2740 meters.
OI 1(7()( f NI P L A N K I O N I (
FORAMINIFERAI
BIOSTRATIGRAPH~ AND PALEO(IJMA]I(
I N T E R P R [ FA I I O N
210
sieve fraction could be counted on randomly choosen grid squares. In cases when the number of specimens in the >150 ~tm fraction was less than 300, the total number was counted. Raw numbers were transformed to percentages of the total planktonic foraminiferal fauna. Abundances of single species or groups of species were separately calculated for each fraction and as the total abundance in a sample. Percentage curves were then constructed for either single species or groups of species displaying phylogenetic affinities. To show the degree of preservation/dissolution the number of fragmented specimens were counted and plotted in separate curves.
Planktonic foraminiferal biostratigraphy The Oligocene sequence at Site 538 appears almost complete from Zone PI9 through Zone P22. Planktonic foraminiferal faunas are generally rich. Their abundance and preservation, however, vary from poor, especially in the lower part, to increasingly better towards the top of the studied interval. The index species are well represented throughout and the zonal boundaries were easily identified. The zonal scheme by Blow (1969) modified by Hardenbol and Berggren (1978) applies to Hole 538A sediments. The distributions of planktonic foraminiferal species are plotted in Fig.3, where preservation of planktonic foraminifera, amount of washed residue, presence and abundance of volcanic glass and radiolarian are also included. Several generic names among planktonic foraminifera will appear in the text and figures in brackets: for the explanation see the taxonomic appendix. The identified zones are listed below (from bottom to top). Zone P19 (Core 14-1.51 54 cm to (%re 13-1, 40 42 cm J Definition. Interval from the first occurrence (FO) of Globoquadrina sellii to the last occurrence (LO) of the pseudohastigerinids.
~,
t~+::t2
~3
-fl i ,~]4
Fig,2. Lithologic log, recover~, and sample position through dcpth of Oligocene sediments in Hole538A.
220
S. S P E Z Z A F E R R I
[-.!
[.
AND
I. P R E M O L I
SILVA
~
ii
DEPTH C
i n
O
R
E
m S
SECTIONS CENTIMETRES
Pseudohast igerlna barbadoensls Pseudciha St I g e r l na m, ra PSeudohastlflerlna nagu~wlChlensls " S l o O I q e r ina ampl apertura Turboro~a! a pseudoampllapertur~
Subboti na utilisindex "Globigerina" euapertura "Gl oboquadnina" tapuriensis TenuiteHa munda - T,c)emenciae
. . I
P a r a g l o b O r o t a l i a )pima nana S u b b o t i n a praeturr~t illna OlobOquadr ina s e l l l i
'Globlgerina" prasaep,s .
.
.
. .
. .
. .
.
.
.
I
,
-
-
. . . .
--,W-
~
-
. . . . . . . . .
i
Dentoglobigerina gentoglobigerina
I,
Globoguadrina r o h r l
,
.
Catapsydrax unlcavus Globorotaloldes suterl
i
. . . . . .
"
~ "
I.
I °l
-' .......
-
I
I
i
i
)iil)iilli!iiiT4:: .
.
.
....
.
.
.
i.
.
.
"
.
_-T"
.
.
.
.
.
.
.
.
.
.
.
.
." "-.-- .....
.
.
.
.
,ii
.
.
.
Catapsydra~ m a r t l n l Dentoglobigerina larmeui Dentoglobiger~na p s e u d o v e n e z u e l a n a
Catapsydra~ dlSSlmllis c~peroensls S u b b o t i n a gortanll
.
.
.
.
.
.
.
.
.
P a r a g l o b o r o t a h a oplma op~ma Subbotlna lab:acrassata P a r a g / o b o r o t a l l a ? sp.
. I
.
pe~icrus
Paraglob0rotalia slakensis group
Catapsydrax Spp,
. . . . . . . . . . . . . . . . . . . . . . .
......
I
oraebullolde~
"G1obigerina" brazieri Turborotalia cf.increbescens Subbotlna a n g i p o r o i d e s m l n l m a Catapsydra~ g l o b ~ f O ~ l S
Glaboquadrlqa ~raedehiscens Globoquadrlna tripartita G:oblgerlna' venezuelaqa
i
~i_:l:
Globlgerlna
.
Oloborotaloides
?1!-~!!!-.
P a r a g l o b o r o t ~ l i a pseud0continuosa Dentoglobigerina globularis Catapsydra~ disslmilis disslmilis "Globigerina" ciQeroensis
,
I
:::::1::-::
.
---:jLI-,,-~,
_; .....
......... ..........
Ea~sigerlnella Chlpolensis elongated Heterohelicldae Subbotina anglporoides anglporoides
. . . .
i
. . . .
.
"Globigerina" anguliofficinalis Glob~gerlna obacnltaensis Globlgemna officinalis Tenultella g ~ a Tenuitellinata angustiumbi]icata
I
. . . . . . . .
I
galavlsi baroemoenensls
Globorotaloides varlabllis G1oblgerineila obesa 'G1Oblger~noides' praeprlmordluS
Catapsydra× afrlcanus "Globigerlna" angulioff./angulisut Dentoglobigerina globularis/al:ispira Dentoglobigerina galavisi/baroemoenen "Globigerlna" angulisuturalis
I . .
.
Parag/obor~talla
siakensls
Dentoglobigerina altisp~ra globosa
-
-::i--::T
.-
'
...... ;:- ......
G/oblgerina
oua~nitaensis
gnaucki
G1obigerinita juvenilis "Globigerlna" sp. •- - i O l o b l g e r , n a
praenulloides o c t ? u s a
"Gl0blgerina" ciperoensis fariasi O O b l g e , lnOl~eS p r l l n o r d , u s
"Globigerina" woodi woodi Paragloborotalia pseudokuglem P r o t e n t e l l a group $/oboqua~rlna ~nalLns,,,
• o0~
. . . . . .
o.0~
. . . . . . . . . . .
o
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ooo
• ooo,oooooo•Oooo~ o
•
very scarce
,
o
G= good preservation
o
,oo,
oo~ oo /
OOlOO
scarce
•
• . 0 0 , . . o . o o . . . a
• ....
. . . . . . . . . . . . . . . .
o ....
Ioo Io olO, i,o
poop., oo • Oo • • ,oo oo,,°o • o o
medium scarce
M :~dium preservation
0
P
.poop • Ooo,oo° oo oo
medium abundant poor preservatlon
•
o.o.L o..o
~.... .... i --z_: liiii... ~:" ::. •. . . , .°"': o . .o o . . .°°°'"1°°'°'°°" o . o . . . . o o o ~ . . o : o .o. . . F']
' ~ ; ~ = i ~ o . . . e o "
>40~ >IS0 >40~
>Ifi0 p >40p
>150 p
>a0~
>150 p
PRESERVATION WASHED
VOLCANIC
RESIDUES GLASS
RADIOLARIANS
very abundant VP very poor preservation
Fig.3. Stratigraphic ranges o f O l i g o c e n e p l a n k t o n i c foraminifera and identified b i o z o n e s in H o l e 538A. B i o z o n e s after Blow (1969) m o d i f i e d by H a r d e n b o l and Berggren (1978).
OI I ( J O ( [ N[ P L A N K I O N I C F ( ) R A M I N I F t - R A [ .
BIOSI RA I IGRAPH'r
A N D P , % L I ¢ O C L I M A I 1 ( IN I I R P R t
Remarks. Preservation and abundance of planktonic foraminifera in this interval vary from very poor to scarce, to fairly good and high. In general the > 40/am fractions yield a better preserved and more abundant planktonic fauna than the > 150/am fractions. Radiolarians, mainly confined to the finest fractions, increase in abundance from the bottom to the top of this interval. Planktonic foraminiferal faunas are dominated by dentoglobigerinids, along with less common globoquadrinids and turborotaliids. The most common species are Dentoglobigerina galavM and transitional froms to Dentoglob~erina haroemoenensis, whereas typical D. baroemoenensis is rare and possesses a poorly developed tooth. Dentoglobigerina globularis is rare. Among the globoquadrinids G/oboquadrina rohri and "Globoquadrina" tapuriensis are rather common, whereas Globoquadrina sellii is rare and scattered. Turborotalia pseudoampliapertura is common only at some levels. Other components of the faunas are the catapsydracids, globorotaloids, the Subbotina angiporoides group, large Globigerinids, rarer high-spired subbotinids, and "Glob~erina" ampliapertura. Fine fractions are dominated by the pseudohastigerinids and chiloguembelinids. Minor components include the tenuitellids, Cassigerinella chipolensis, juvenile Paragloboratalia siakensis, P. opima nana. and Globigerina s. str. A few "Glohigerina" ciperoensis and "G. "angulio~cinalis occur in all size-fractions from the base of this interval, whereas rare specimens of Globiquadrina praedehiscens are recorded in only one sample. It is noteworthy that Paragloborotalia opima opima appears in the topmost sample attributed to this zone. Zone P20 (Core 12-CC to Core IO-CC)
Definition. Interval from the LO of pseudohastigerinids to the LO of "Globigerina" ampliapertura. Remarks. Planktonic foraminiferal faunas vary from moderately rich to rich and from very p o o r to fairly well preserved, except in Sample 12-3, 40-42 cm where the fauna is rich and well preserved. Radiolarians are abundant in the finest fractions. Planktonic foraminiferal assemblages of this zone
I A 1 ION
221
are similar to those from the underlying interval except for the scarcity of the pseudohastigerinids, very rare specimens of which still occur randomly throughout. Among the dentoglobigerinids D. haroemoenensis is more consistently present than D. galavisi, "Gloh(eerina ampliapertura, along with more c o m m o n Turhorotalia pseudoampliapertura and very rare T. increhescens, all fluctuate in abundance from layer to layer. These latter species are poorly preserved and decorticated (peeled). Paragloborotalia opirna opima is consistently present throughout the zone, although never common. In the middle portion of this zone wc observed a few specimens of a globigerinid displaying the same morphology and cancellate wall structure as GlohigerinoMes primordius, but without supplementary apertures. This taxon is here informally called "Globigermoides" praeprimordius, Globoquadrina praedehiscens is absent. Fine fractions are dominated by the chiloguembelinids and tenuitellids along with rarer cassigerinellids. The "Globigerina" ciperoensis group, Glohigerina s. str., and Paraglohorotalia siakensis are rare. Glohigerinella ohesa first occurs in the middle of this interval. Zone P21 (Core 10-5, 95 97 cm to Core 6-1.
40 42 cm) Definition. Interval from the LO of "Globigerina" ampliapertura to the LO of Paraglohorotalia opima opima. Remarks. More than half of the samples studied belong to this zone. Planktonic foraminifera are poorly preserved in the lower part of this interval, but starting in Core 9 progressively improve in preservation and increase in abundance towards its top. Radiolarians are highly variable in abundance from absent to common. In agreement with Hardenbol and Berggren (1978) the boundary between Subzones P21a and P21b is placed at the disappearance of the chiloguembelinids. The interval attributable to Subzone P21b is very thin (about 5 m thick) in comparison with Subzone P21a (more than 40 m thick). This difference in thickness between the two subzones suggests that a hiatus has eliminated a portion of Subzone P21 b.
222
Paragloborotalia opima opima the zonal marker, is present throughout this interval. It fluctuates in abundance from layer to layer, with a marked increase in abundance from Core 9 upwards. Highest abundance is always in the >1501am fraction. The chiloguembelinids vary in abundance from 25% to > 50% of the total fauna. Just before their disappearance they decrease to < 10% in Core 6-CC and increase again to 15% in Sample 63, 4 0 - 4 2 c m , but are absent in Sample 6-2, 40-42 cm. The subzonal boundary was placed between the last two samples. Assemblages of this zone include most species and species groups recorded throughout the sequence. The number of species, however, is never constant, but fluctuates from layer to layer. Within this zone the "Globigerina" ciperoensis group increases in abundance and in overall size, and "G." angulisturalis displays a peak in abundance of > 4 0 % just above the LO of the chilogumbelinids. Dentoglobigerina globularis increases in abundance in the upper half of the zone, where it is associated with transitional forms to D. altispira globosa and with D. altispira globosa just before the extinction level of the chiloguembelinids. Dentoglobigerina baroemoenensis shows the opposite trend; it is more abundant in the lower half of this interval and decreases upwards. The Globoquadrina tripartita group and large globigerinids are never abundant, but fluctuate throughout. Common in the lower portion, the Subbotina angiporoides group disappears before the top of Subzone P21a, whereas the high-spired subbotinids are a minor component of the faunas and their record is scattered. Paragloborotalia siakensis increases in abundance and overall size within this zone. It is especially frequent in the lower portion, and after a marked decrease in abundance in Sample 9-3, 100-102 cm, it gradually increases again in the upper portion of the zone. Globigerina s. str. increases slightly and gradually in abundance and overall size. "Globigerinoides" praeprimordius is rare. Globigerinitajuvenilis and "Globigerina'" sp. 2, a form related to "Globigerina" woodi (Premoli Silva and Spezzaferri, 1990) first appear at the top of Subzone P21a. Fine fractions are dominated by the chiloguembelinids in Subzone P21 a associated with common cassigerinellids, whereas the tenuitellids decrease in
S. S P E Z Z A F E R R I A N D 1. PREMOLI SILVA
abundance upwards. In Subzone P21b the smallsized assemblages consist of abundant "G." ciperoensis group, common Globigerina s. str., P. siakensis, P. opima opima, P. opima nana, and the cassigerinellids increase in abundance. Zone P22 (Core 5-CC to Core 2-CC)
Definition. Interval from the LO of Paragloborotalia opima opima to the FO of Paragloborotalia kugleri. Remarks. The upper boundary of the zone is missing because an unconformity truncates the sequence in the uppermost part of this zone. The presence of evolutionary advanced P. pseudokugleri in the last Oligocene sample, however, indicates that Zone P22 is nearly complete (Premoli Silva and Spezzaferri, 1990). The planktonic forminiferal assemblages of this interval are rich, well diversified and better preserved from Core 3 upwards. Radiolarians increase in abundance up to core 3-2, 70-72 cm, but they are absent in the uppermost samples studied. Planktonic foraminiferal faunas are dominated by dentoglobigerinids, globoquadrinids, the "Globigerina" ciperoensis group, and Globigerina s. str., the last two in both fractions, associated with less abundant paragloborotaliids, catapsydracids, globorotaloids, large globigerinids, and tenuitellids. Several species, which first appear at the base of this zone include Globigerinoides primordius, Protentella spp., Paragloborotalia pseudokugleri, "Globigerina" woodi, and Globoquadrina binaiensis. Paragloborotalia pseudokugleri is consistently present, whereas the others may be absent in some samples. "Globigerinoides" praeprimordius is always present either alone or associated with G. primordius. Globoquadrina praedehiscens is discontinuously present and the transition to Globoquadrina dehiscens was never observed. A few specimens of Cassigerinella chipolensis occur in the > 150 I.tm fraction. Fine fractions are dominated by representatives of the "Globigerina" ciperoensis group, Globigerina s. str., and cassigerinellids, whereas the tenuitellids gradually decrease in abundance upwards. Very rare specimens attributable to Streptochilus pristinum occur in a few samples.
,[ I ( i O ( ' [
N[
PI_ANK
I ONl(
FORAMINIFERAL
BIOSq RA I 1(3R~tPHY
AND
PALEOCI.IMA'I
The stratigraphic ranges o f some species in Hole 3 8 A depart from the ranges given in the literature Bolli, 1957; Blow, 1969: Jenkins, 1971; Molina, 979; Bolli and Saunders, 1985). They are, in tratigraphic order (Fig.4): 1. Dentoglobigerina baroemoenensis is recorded rom the beginning o f the studied sequence, ttributed to Zone PI9. 2. "Globigerina" ciperoensis first occurs close to he base o f Zone P19, whereas "G." angulisuturalis ppears at the top o f Zone P20. 3. Primitive Paragloborotalia siakensis appears /ithin the lower part o f Zone P19, whereas largeized P. siakensis is recorded from the middle ortion o f Subzone P21 a. 4. Suhhotina hrazieri occurs as rare specimens eginning in Zone P19. 5. Paragloborotalia opima opima first occurs at ae top o f Zone P19 associated with abundant seudohastigerinids.
STANDARD EVENTS
IC IN I IRPR[
[A I ION
._.
6. Pseudohast~eerina barhadoensis disappears at the top o f Zone P19 at the time o f the dramatic decrease in abundance o f all pseudohastigerinids, whereas very rare, small-sized specimens o f P. micra and P. naguewichiensis are recorded also in Zone P20, apparently in situ. 7. Globigerinella obesa appears in the middle portion o f Zone P20. 8. Forms transitional between Dentoglohigerina globularis and D. altispira glohosa first occur at the top o f Zone P20. 9. Subbotina utilisindex disappears at the top o f Zone P20. 10. Subhotina angiporoides minima disappears in the middle portion of Subzone P21a, whereas Subbotina angiporoides angiporoides last occurs close to the top o f that same subzone. 11. Glob~eerinita juvenilis and forms related to "Globigerina" woodi (= "Globigerina" sp. 2) first appear in the upper portion o f Subzone P21a.
MAIN EVENTS IN T H E INDIAN OCEAN
MAIN EVENTS IN T H E G U L F O F MEXI(
incre~.sing abundance of
Globigetinoid~ i m m a t ~ , G, bollii, G trilobus - J GIob~germoid~ss p p
N4
Globigennita uvula, Globg,erinita glatinata
paraglo~rocalia kuglen
Globoquad,qna dehisced. Pa~toboe~calia pseudo~leri/p, kuglen transition GIoboretaloides sp. 2 large C~igerinella spp. ( > 150~)
large C~,sigerin¢ Uids ( > 150~)
Globoquadnna binaie~is. GIoblgerinoidespnmordius, Po.~obocotadia pseudokugleri. D. altispim globosa. I~ slakemis ( • ZS0~.)
Globigednoid~prlmoedim, Pa,'~lobo,~abapseude.'kugle
Paeagloborotalia opima opima
Proterttella s p p
b P21~-'~
Chiloguembelinaspp
a
~ large Cass~ednella spp. ( > 150~,)
~ "Globigerina" ~pliapetrura
~]t
~Jlarge
t~
t v~Pseudohattigerina micra, P+nagu~ichiensis , Turfio~tali "-~"GIobi~rina" an~lioff~cinalia/ "G,"angulisutuzalis transi ~ entoglobigednaglobularis/D, alt~piraglobosa tramitic GIobigeeineUa obesa
P20
P~aelobomtalia onima onima ~
Cassigecinellamaninezpicoi, Cassigennellaglobulosa. D. baroemoenensls, Patagloborotalia siake~i~ ( < 150a) Globoquadnna selliJ
Ii
C,~sigerinellids ( • 150-)
Subboti~ ~gipo~ides gr. ~-J~lobigcrinitajuvenilis, "Globigerina" sp. probably related to "G. wood~~ group -----~- Sub~cina angtlmroldes anglpomldea D. globulo~i~/D, alti~pi~globosalransition, GIob~gerimtajuvenil~. "Globigerina" ongulisuturalis. P~tentella s p p Turborotaliids ~ "GIobigedna'ciperoemis /"G."anguliofficinaltslransitiov
'
I i
Hantkeninids a n d Psh. danwlle~is
I
i.
Pmudohastig~rina barbadoemis Paragloborotalia opima opima
Paragloborocalla suak~nsis (40-15Qu ), Globoquadetna pr~deh~ce~ .....J " Globigerina "cipe~nsis, "Glob,gerina "b~ien ~ Dentoglobigerma baroem~ne~is
Turborotalia pseuabampliapertura, Z i n c ~ b e ~ . "Globoquad.4na" tapune~, CaraigerineUachil~le~is , high-spired Subbotinids, S. atlgipoemdes group. Dentoglobige~na galamsi
Tenuitellids,
g.4. Calibration of second order events to the major biostratigraphic events among Oligocene planktonic foraminifera plotted vs. the w latitude standard zonal scheme of Oligocene age (Blow, 1969) in Hole 538A and Indian Ocean Leg II 5 sites (Premoli Silw~ and ~ezzaferri, 1990).
224
12. Globigerinoides primordius, Paragloborotalia pseudokugleri, "Globigerina" woodi, Protentella spp., and Globoquadrina binaiensis are already present from the base of Zone P22. Their true first occurrence cannot be detected because of the hiatus inferred at the top of Subzone P21b. Some of these first occurrences are in agreement with those observed in coeval sequences from Indian Ocean sites drilled during Leg 115 (Premoli Silva and Spezzaferri, 1990), (Fig.4). Specifically, these include the FO of Dentoglobigerina baroemoenensis, primitive Paragloborotalia siakensis and
P. opima opima, "Globigerinella" obesa, Globoquadrina praedehiscens, "Globigerina" sp. 2, Paragloborotalia pseudokugleri, and Globoquadrina binaiensis. The FO of "'Globigerina" angulisuturalis, Dentoglobigerina globularis/D, altispira globosa transition, and D. altispira globosa are also close in stratigraphical terms between the two areas. Moreoever, two abundance peaks of largesized ( > 150 jam) cassigerinellids occur at the top of Subzone P21a and within Zone P22 in both the Gulf of Mexico and the Indian Ocean.
Quantitative analyses In order to quantify species abundances and diversities 300 specimens were counted, when possible, in both the coarse ( > 150 gm) and fine ( < 1 5 0 to >40 gm) fractions. Figures 5 7 show percentage distribution of 32 species or groups of species present in each sample (see Fig.3 and species list). Percentages in >1501am and 150-40 p.m fractions were plotted separately along with a cumulative total %. Species plotted separately from their groups are those already known to have a climatic significance or whose significance has never been investigated or clarified (Haq et al., 1977; Douglas and Savin, 1978; Premoli Silva and Boersma, 1989). Analysis of the percentage curves allows us to distinguish three groups of taxa which display different patterns (Figs.5-7). (1) The first group include "Globigerina" ampliapertura high-spired subbotinids, Paragloborotalia opima nana, Paragloborotalia sp., Globigerinella obesa (all in Fig.5), and Subbotina utilisindex (Fig.6). They are all a minor components of the
S S P E Z Z A F E R R I A N D I. P R E M O L I SILVA
faunas and show no patterns. The paragloborotaliids become slightly more important when combined with the Paragloborotalia siakensis group. (2) The second group includes a number of taxa which are relatively abundant, almost consistently present, and display discrete, but moderate fluctuations in abundance. They are the large globigerinids (Fig.5), the Subbotina angiporoides group (Fig.8), the tenuitellids (Fig.6), the Catapsydrax and Globorotaloides groups (Fig.6), and the Dentoglobigerina baroemoenensis and Globoquadrina tripartita groups (Fig.7). (3) The third group includes the remaining species, either as single species or as discrete groups, which display large fluctuations in abundance and have restricted stratigraphic ranges. Some of them such as the pseudohastigerinids (Fig.5), the elongate heterohelicids ( = Chiloguembelina spp.) (Fig.5), and the Turborotalia pseudoampliapertura group (Fig.7) are common to abundant in the lower portion of the sequence; the Paragloborotalia siakensis group (Fig.5), Tenuitellinata angustiumbilicata (Fig.6), the Globigerina s. str. group (Fig.6), the "Globigerina" ciperoensis group (Fig.7), the Dentoglohigerina globularis group (Fig.7), Globigerinoides group (Fig.6), and Paragloborotalia pseudokugleri (Fig.5) tend to increase in abundance in the middle to upper portion; and finally, Paragloborotalia opima opima (Fig.6) fluctuates in the central portion (Zone P21), whereas Cassigerinella chipolensis (Fig.5) displays five abundance peaks scattered throughout. The percentage curves of Figs.5 7 also show that (1) the pseudohastigerinids seems to be covariant with the chiloguembelinids, which increase in abundance at the pseudohastigerinid extinction, (2) the T. pseudoampliapertura group fluctuates in phase with the previous groups (in 1) and opposite to the S. angiporoides group, globorotaloids, and tenuitellids. Similar patterns are exhibited by C. chipolensis, (3) the D. globularis, the "G." ciperoensis, and Globigerinoides groups exhibit trends opposite to Globigerina s. str., and (4) T. angustiumbil'oata "eems to replace the tenuitellids beginning in the upper part of Subzone P21a. On the basis of all the observations derived from the percentage curve patterns, three intervals can
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be distinguished in the studied sequence, which can be roughly identified (in stratigraphic order) as the lower, pseudohastigerinid-chiloguembelinid dominated interval (Interval 1); the middle, chiloguembelinid paragloborotaliid-dentoglobigerinid interval (Interval 2); and finally, the upper, "G. " ciperoensis-D, globularis-Globigerina- T. angustiumbilicata interval (Interval 3). This partitioning is also reflected in the climatic curve (Fig.8). Climatic curve The three intervals, as mentioned above, are characterized by higher or lower abundances of different taxa, some of which are known to have climatic significance. In this chapter we analize the abundance patterns of planktonic foraminifera from a climatic point of view in order to construct a climatic curve.
Previous biogeographic studies of Oligocene planktonic foraminifera identified index species for the different Atlantic bioprovinces and showed how bioprovincial faunas evolved through time (Haq et al., 1977; Boersma and Premoli Silva, 1986; Premoli Silva and Boersma, 1989). The Oligocene biogeographic index groups are reported in Table 1. Out of these index groups some may be considered as warmer province indicators ( T. pseudoampliapertura, G. tripartita, D. globularis, D. baroemoenensis, "G. " ciperoensis, and Globigerinoides groups, and Cassigerinella). They proliferated at low latitudes and migrated out of the tropical belt by the end of the Oligocene. Other groups ( Catapsydrax, Globorotaloides, S. angiporoides, and Globigerina s. str. groups, and the tenuitellids) can be interpreted as cooler province indicators because of their abundance and constant occurrence at high latitudes (see Haq et al.,
()[ I ( J ( ) ( t Nil PI.ANK I O N I C I O R A M I N I F E R & I B I O S I R A I I ( J R A P H ' t A N D P,'kLEO(I I M A I I (
IN[I RPR| I , \ I I O N
TABLE I Oligocenc biogcographic index groups (Prcmoli Silva and Boersma, 1989) AGE
LOWER LATITUDES
MIDDLE LATITUDES
HIGHER LATITUDES
Northeast
EARLY OLIGOCEN E
T pseudoamphapertura r mcrebescens flood ol biserlal heterohel~lds typical G~ tnpamt~ denlOgloblgerinids
3 chambered denlogloblgennlds Glot)lgertna C un~cavus Ca~apsyorax P nana tenultelhds ~enuitelhds GloOorotalo~des pseudohastigenmds G ouach#aensts tew Iurborolahlds esp "G" arrlphapertura T pseudoamplKapertufa "G" tapurlens~s rare austral spectes esp S ut~hs~nde~ S braz,en
MIDDLEOLIGOCENE
a~lgloboquadrmlds flood of blserial heterohelK;Els • pseudoan~phapertura rare P slakens;s Globorotaloide5
Gq praedehtscens P ssakens~s ~enuitelhdS 3 clTambered denloglo~lgerlnK3s S gortan# Catapsydrax rare austral speoes in lhe SOulh
LATE OLIGOCENE
"G" ctperoens;s all globoquadrimds "G" anguhsutura#s P optma oplrna Casslgennella GOes ontt)ordlus Neogenestreplochihds ten~lrlelhds (P22)
OK pseudol(ug~en CataPsydeax Catapsydrax tnJe glob~jenmds 3 chambered denlog~ob~genmds Globorotalo~les C~ btrlalensts in southeast "G" ctperoensls P s~akensls GI kugJen group S COrl)alenta P $takensts tenullelhds "G" wooOr G;ta luvenlhs GJfa g~tmata
1977). According to stable isotope analysis, the former group includes species registering negative (depleted) (3laO values and are mainly warmer dwellers, while the second group includes species giving more positive (enriched) a180 values and are cooler-dwelling taxa (Boersma and Shackleton, 1977: Douglas and Savin, 1978: Poore and Matthews, 1984). In Hole 538A planktonic foraminiferal assemblages warm indicators are mainly belonging to the third group of taxa previously mentioned, which exhibit discrete distributional abundance patterns, whereas the cold indices, mainly confined to the second group, display moderate fluctuation in abundance and appear to be a common component of planktonic foraminiferal assemblages throughout. The only exception is the Subbotina angiporoi~#s group which appears to be replaced by Gloh(¢erina s. str. in the upper part of the sequence (from Subzone P21a to Zone P22). Among the remaining species or group of species, which are here considered as "temperate" indices, there are also some groups such as the pseudohastigerinids and chiloguembelinids which largely fluctuate in abundance. They also belong to the third group.
high diversify abundant S uhhsmdex S angtporoJdes S mtr~rna Catapsydrax true glOblgenmds rate turborotalilds rare pa ragloborot ah=ds raFe globOquadnmds
Northwest
Southwest
blsenal heterohehctds GloborotaPJides rare globoquadrln~ds S ang,poro~des S ut#ts~ndex pseudohashgerm~ds
S ut,hsmdex S ~-azren lenulleHids S rnmsrna {rue glob~genn~s Catapsydrax
largeglob~genmds true gbobwgenmds Globorotalo~des Catapsydrax rare P optma oplma rare 3 chambered dentoglobqgenmds
T munda (P21 moves to SoutP Atlanhc in P22~ P s,a~(ens,s GloborotaJotdes Irue globqgedmds large globlgerinids GI aft penDheroronda
The plot of total abundance of warmer taxa is called the warm species curve (Fig.8). This shows rather regular fluctuations with lows of slightly less than 5% to one high >20°/; in Interval 1. In Interval 2 the total abundance (from > 5 % to > 20%) of warm indicators slightly, but gradua[ly increases upwards. In Interval 3 the abundance of warm forms markedly increases, with minimum values never below 25%, and maximum values as high as 60%. The cooler species curve, based on the total abundance of cooler taxa, shows Four discrete intervals in which highest values (positive peaks) range from about 25% to about 40%, separated by lows whose minimum values are close to 10%. The first two peaks, with values of 30% and around 35%, occur at the beginning (Zone P19) and in the upper half (Zone P20) in Interval 1, respectively. The third positive peak, stratigraphically more extensive, lies in the upper part of Interval 2 (mid Subzone P21a), with maximum values which never reach 30%: the fourth one is in Interval 3 (mid Zone P22), with a m a x i m u m value > 4 0 % . Temperate species make up the bulk of planktonic foraminiferal faunas from the base ot" the
230
S. SPEZZAFERRIAND I. PREMOLI SILVA
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sequence to upper Subzone P21a, corresponding to the entire Intervals 1 and 2 (Fig.9). In both intervals, their combined abundances range from 55 60% to 75-80% of the faunas. Conversely, temperate forms decrease in absolute abundance throughout the entire Interval 3 (upper part of Subzone P21a to Zone P22), with values ranging from 25 to > 60% of the faunas. Temperate faunal composition changed through the three intervals. In the lower half of Interval 1
(Zone P19), the pseudohastigerinids and chiloguembelinids each comprise 20% or more of the total fauna, whereas in the remainder of Interval 1 and in the lower half of Interval 2 (Zones P20 and P21 a lower part) the chiloguembelinids account for at least 30% of the total fauna. In Interval 2 the P. siakensis group is more common; the large globigerinids, P. opima opima, other paragloborotaliids, and T. angustiumbilicata each comprise about 5% of temperate species abundance. In
OI IGO('} NE PLANK F()NI(" FORAMINIFERAL BIOSTRAflGRAPHY AND PALEO('LIMA'H( IN IERPRt'I A II()N
Interval 3, within the range of P. opima opima (Subzone P21b), P. opima opima and P. siakensis together account for about 20% of the total fauna, whereas in the upper part (Zone P22) the temperate forms, T. angustiumhilicata, P. siakensis, and large globigerinids, contribute respectively 15 20%, 15%. and about 10% of the total fauna. Paraglohorotalia pseudokugleri in some samples reaches values as high as about 15%. The climatic curve (Fig.8), derived from the algebraical sum of percent abundances of warm (positive) and cool (negative) indices, shows that Interval 1 is characterized by negative values, except for one single, very low positive peak in the lowermost part (lower Zone P19). Interval 1 also contains the most negative peak of the entire curve which occurs in its upper part (most of Zone P20). In Interval 2, the curve is mainly negative with five positive peaks, three of which barely cross the zero line and the other two are more positive around + 7 (lower) and + 10 (upper), respectively. The curve, although negative is less negative than in Interval 1. In Interval 3 the climatic curve is predominantly' positive with values as high as almost + 50. It is, however, interrupted by a short negative, inversion of about 15 in the upper half (mid Zone P27).
Diversil v patterns In order to identify better the climatic signal, species diversity (number of species) as well as diversity among the warm, temperate, and cool groups were calculated for each sample. As shown in Fig. 10, total diversity fluctuates in the lower part of the sequence (through the lower level of Interval
23 I
2, or lower Subzone P21a). Overall diversity then increases and fluctuations are less pronounced. Some discrete intervals characterized by different mean diversity' values have been detected (Table 2, Fig. 10). Diversity patterns, however, do not show the same partitioning as the climatic curve does. In Interval 1 diversity values range from less than 20 species (lower Zone PIg) to almost 35 in the upper part (upper Zone P20), with mean diversity values around 25, except at the top where mean values are around 30. Interval 2 starts with mean diversity values as high as > 30, but the remaining lower half has a mean diversity value of less than 23 (up to mid Subzone P21al. From the upper half of Interval 2 (upper Subzone P21a) diversity gradually increases with mean values ranging from about 28 to 35 at the end of lnterwtl 3. No major change in diversity can be detected at the middle (1) to upper (2) interval transition. Diversity among the three groups of species displays, in general, less pronounced fluctuations with the curve of the warm species best parallelling that of the total diversity. The lowest fluctuations are observed in the temperate diversily curve. As shown in Table 2 and in Fig. 10, the lowest mean diversity value of the entire sequence in the lower half of Interval 2 (lower Subzone P21a) is due to the combined low values in all three groups. The second low value characterizes most of Interval I (upper Zone PI9 lower Zone P20) and is mainly related to low values in the warm group, which. conversely, contributes to the higher diversity values of Interval 3. Because the degree of evolutionary overturn (originations plus extinctions) in the faunas is minor, it was not plotted. Oligocene faunas
TABLE 2 M e a n diversity values ( n u m b e r o f species) o f total p l a n k t o n i c f o r a m i n i f e r a l f a u n a s , a n d o f w a r m , t e m p e r a t e , a n d c o o l indices t h r o u g h O l i g o c e n e s e d i m e n t s in H o l e 5 3 8 A INTERVALS
TOTAL~ DIVERSITY
WARM SPECIES MEAN DIVERSITY
2-CC/6-1, 40-42cm 6-2, 40-42/9-CC 9-1,6-7cm/10-5,62-63cm 10-5,95-97cm/12-1,40-42cm 12-2,40-42crn/13-3,40-42cm " 13-CC/14-1,51-54cm
35 27.88 22.5 30.1 24.3 26
14 8.88 6.86 9.66 6.4 8.25
TEMPERATESPECIES COOL:::~..~ES MEAN DIVERSITY MEAN DIVERSITY 10.7 9.2 8.2 9.5 10.3 10.5
10.3 9.5 7.35 11 7.6 7.25
232
s. S P E Z Z A F E R R I A N D I. P R E M O L I SILVA
PLANKTONIC FORAMINIFERALFRAGMENTS
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TEMPERATESPECIES COLDSPECIES DIVERSIFY DIVERSIFY
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Fig. 10. Total species diversity (number of species) curve plotted against warm, cool, and temperate planktonic foraminiferaldiversity curves, and against the abundance of fragmented tests in Hole 538A. Data from Fig.3. Patterns mark the three intervals identified in the climatic curve of Fig.8.
predominantly consist o f long ranging taxa originated in the Eocene or in the Oligocene, prior to the beginning o f the sequence studied, and extending into the Miocene. Comparison between diversity and percent abundance curves reveals that the warm taxa increase in abundance when their diversity increases and vice versa (Figs.8 and 10). A m o n g the cool group, diversity and abundance curves are
mainly parallel except in the lower and uppermost parts o f Interval 2 (lower middle and uppermost Subzone P21a) where increases in diversity correspond to decreasing abundances. The two curves relative to the temperate group show very few correlative points (Figs.9 and 10). They, in fact, depart one from the other markedly, as in Interval 3 (Zone P22) where a slight increase in diversity corresponds to a marked drop in abundance, or in
O1 I G O ( | N I P L A N K I ONIC F O R A M I N I F E R A L B I O S T R A T I G R A P H Y AN[) P A L E O ( ' L I M A I IC IN I [ RPRE~ekTION
Interwfl 2 (midway into Subzone P21a) where the highs and lows on the curves are offset. Discussion and results
Dissolution q~l~,c/s In order to separate the signature of dissolution from the primary signals, abundance and diversity curves are compared with the curve of abundance of test fragments. Dissolution, in fact, can result in an artificial increase in abundance of solutionresistant or thick-walled taxa (Boersma and Premoll Silva, 1983). Comparison between total diversity curve and percentage curve of fragmented specimens shows that the two curves are mainly opposite (Fig. 10). These opposite patterns are more evident when comparing the diversity curve with >1501am fraction fragmentation curve. This implies that dissolution affected the faunal composition and may be responsible for some of the low species diversity recorded in the curve (Fig. 10). Abundance and diversity curves of warm species, like the total diversity curve, show opposite fluctuations with respect to fragmentation, so dissolution certainly affected the warm group. In particular, dissolution effects appear more pronounced in the lower portion of the sequence (Fig.8). In Interval 2 (Subzone P21a) dissolution seems to affect particularly the large-sized forms. When dissolution strongly decreases or is absent in Interval 3 (uppermost Subzone P21a through Zone P22), the warm group increases in both diversi D and abundance. To a lesser degree dissolution seems to have also affected the cool species. Cool species diversity and abundance curves fluctuate inversely with fragmentation (Figs.9 and 10). In some cases, however decreases in abundance of cool species do not correspond to increasing fragmentation. What is surprising is that the temperate group was very little affected by these dissolution epi-. sodes. The already high percentages recorded for the temperate group are thus emphasized by partial removal of either the warm taxa or both the warm and cool groups (Fig.9). It appears that the climatic curve of the lower
233
part of the sequence is negative because of dissolution which preferentially removed the warm group, as testified by a decrease in both abundance and species richness among this group. These warm taxa are known to be more susceptible to dissolution (Boersma and Premoli Silva, 1983). In this case, the climatic signal suggesting a cooling may be artificial. In the mid to upper part of Interval I (Zone P20), however, the cool taxa increase in abundance (up to about 40%) but fragmentation decreases to rather low values. This occurs also midway into Interval 2 (mid Subzone P21a). We interpret these two events as real cooling events, as corroborated by a slight decrease in abundance of the temperate group. The Interval 1 curve (Zones P19 and P20) is thus characterized by a temperate signal at the beginning evolving into a definitely cooler signal, which reversed close to the transition between Interval 1 and Interval 2 (top of Zone P20). In the middle to upper part of Interval 2 (Subzone P21a, Core 9 and most of Core 8) decreased dissolution corresponds to a moderate increase in abundance of warm forms and a more marked increase in the coot group, whereas temperate forms slightly decrease. Within the cool group some old taxa, such as those belonging to the Subbotina angiporoMes group, disappear whereas Glohi,gerina s. str. increases in abundance associated with a slight increase of the tenuitellids. These events are not an artifact of dissolution and indicate a change in watermass properties. Lower in Interval 3 (upper Subzone P21a through Subzone P21b) when dissolution decreased, warm taxa became much more abundant and the temperate fauna sharply decreased in abundance. The middle part of Interval 3 (Subzone P21b and lowermost Zone P22) is characterized by the lowest percentages of the temperate group, which are replaced by the warm and cool groups: the warm groups is more abundant in the lower part of the interval, and the cool group displays the highest percentages in the uppermost part of this interval (most of Zone P22). The percentages of the temperate group partially recovered at the close of the sequence. This trend is well represented in the climatic curve, which from highly positive values returns
234
to negative values in the mid to upper part of Interval 3 (middle of Zone P22) (Fig.8). In summary, because of absence of dissolution Interval 3 registered the real climatic signal. Moreover, the fact that temperate taxa are less abundant in this interval suggests water mass properties have changed and became more similar to the Neogene-type, in which warm and cool niches were well differentiated and higher abundance of either warm or cool groups correlates with warming or cooling events respectively. Interval 3 is predominantly warm with a recooling midway.
S. SPEZZAFERRI A N D 1. PREMOLI SILVA
TABLE 3 Stable isotopic values of two speciesof planktonic foraminifera from five selected samples corresponding to highs and lows of the climatic curve in Fig.8. "GIobigerina"angulisuturalis= warmer dweller; Globorotaloidessuteri-cooler dweller SAMPLES
PLANKTONIC SPECIES
3-1,100-102
cm
4-1,134-136
cm
5-CC 6-2,40-42
cm
7-3,40-42
cm
"G." angulisuturalis G. suteri "G." angulisuturalis G. suteri "G." angulisuturalis G. suteri "G." angulisuturalis G. suteri "G." angulisuturalis G. suteri
al 8 PDB
al 3C PDB
-0.10 0.73 -0.40 1.33 -0.36 1.09 -0.33 1.38 -0.08 1.53
1.25 0.87 1.14 0.47 1.23 0.31 1.53 0.45 0.63 0.51
Isotope data Atlantic oxygen isotope curves indicate mild warming events through the course of the Oligocene (Boersma, 1977; Boersma and Shackleton, 1977, 1978; Biolzi, 1983, 1985; Belanger and Matthews, 1984; Shackleton et al., 1984). Warm peaks (most depleted oxygen isotope ratios) were registered in Zones P21b and upper Zone P22 in equatorial and South Atlantic Sites 366 and 357. Two additional warm peaks, in Zones P19 and P21a, were registered at Site 540 in the Gulf of Mexico. The relatively depleted near-surface values, ranging from -0.77%0 to -1.92%o, are suggestive of only mild surface water warming. Oxygen isotope values of plantktonic foraminifera living at cooler levels in the water column also became more depleted through this time. At western equatorial Site 354 where Biolzi (1985) measured "Globigerina" venezuelana, warmings were registered in Zone P20 up to lower Zone P21 and midway into Zone P22. Reinterpreting Biolzi's biostratigraphic zonal attributions (1985) through Boersma's data (1977), the major isotopic events recorded at Site 354, including the cooling event midway in Zone P22, appear to correspond to those from Site 366 (Boersma and Shackleton, in prep.), although the absolute values are somewhat more depleted at Site 354. Oxygen isotope values of warm and cool water species from our material in Hole 538A were relatively enriched and showed little intersample variation (Table 3). There was only an approximately 1.00%o interplanktonic oxygen isotope
gradient. Hole 538A values were substantially more positive (1.4 0.6%0) than those from other sites, including nearby Site 540. Samples containing the highest numbers of warm water planktonic foraminiferal indices did not produce more depleted (warmer) oxygen isotope values than samples in which warm water planktonic indices were less numerous.
Summary and conclusions (1) Planktonic foraminiferal distribution patterns indicate (a) an increase in abundance of warm indices towards the top of the sequence, (b) the cold indices remain relatively constant in abundance throughout, whereas the temperate indices drastically decrease in importance in late Oligocene Subzone P21b and Zone P22. This fact is in relationship with the disappearance of the chiloguembelinids in mid Zone P21. (2) There is a general correspondence between higher diversity, greater numbers of warm water index species, and higher paleotemperature in near surface waters, although the Oligocene isotopic record from the Atlantic Ocean is still incomplete. Isotope values do show patterns roughly consistent with the well-characterized three intervals on the climatic curve. In the lower to mid Oligocene there is little correspondence between the climatic curve and faunal properties. (3) Zone P22 can be separated into two warm and one cool interval. The partition of the generally warmer Zone P22 (about - 1 . 1 to
OI 1(;O( EN[{ P L A N K r O N l ( ; F O R A M I N I F E R A L B I O S T R A T I G R A P H Y A N D P A L E O ( L I M A T I ( I N I E R P R E I A I I O N
-1.15%o) by a moderate cooling event (about -().5%,) in the isotope curve seems to correlate to the trend in the climatic curve, which becomes negative in the middle of the zone because of the increased abundance of cool indices. (4) A cool interval indicated by oxygen isotopes in mid Subzone P21a is coeval with increased abundances of cool water indices. A corresponding decrease in dissolution allows us to state that the cooling event is real. (5) A cooling in upper Zone P21a corresponds to an increase in dissolution. This is shown by decreased abundances of the warm indices, whereas species diversity of the warm group remains high and abundance of cool species increases only slightly. (6) A cooling indicated by the oxygen isotope record of the Oligocene in Zone P21b is not reflected in the fossil data at Site 538. Neither the diversity nor the cool index curves registered this event. Its absence corroborates the occurrence of a short hiatus as inferred at the top of Subzone P21b by the exceptionally thin section attributable to this subzone. (7) The relatively good correspondence between isotope curves and fossil data typical at other times is not demonstrated in Zone P19. Isotope data indicates generally the warmest paleotemperatures through the Oligocene after Zone P18. The fauna is, however, dominated by temperate indices, while abundance of warm or cool species is lower. In this interval, the only fact consistent with a warming is the first appearance of warm indices, such as the "G'lohi,~erina" ciperoensis group, which will proliferate later in the Oligocene. (8) In Zone P20 warm episodes indicated by the oxygen isotope curve do not correspond with warm index high abundance, whereas diversity in the warm group and in the total fauna is relatively high. Dissolution may account for this discrepancy. (9) Dominance of temperate taxa in low to mid Oligocene faunas suggests unusual hydrographic conditions in oceanic upper waters during Zones P19 P21a. The abundance of chiloguembelinids, the major component of the temperate group, would suggest conditions of relativelty high fertility through this interval (Boersma and Premoli
235
Silva, 1988, 1989). This hypothesis is in agreement with the occurrence of radiolarians throughout (Fig.3). (10) During warming in Zone P22 the numbers of both warmer and cooler taxa increase, whereas temperate taxa strongly decrease in abundance (Fig.9). Apparently a larger number of niches were available in the warmest near surface and coolest, subsurface layers. Both warm and cool groups in Zone P22 include more modern (at least Miocene in age) analogues such as Glohi~erinoides and Globi,gerina, the latter in high abundance. Surface water masses probably became more similar to those of the Neogene during late Oligocene Zone P22. ( 1 l) In general the paleotemperatures suggested by oxygen isotope values appear too low to support the abundance of warmer water indices early in Zone P22, whereas in Zone PI9 the highest temperature values of the Oligocene correspond to low abundance and diversity of the warm species. It is not clear why such discrepancies occur and why the inferred Oligocene temperatures are so low. Estimated temperatures lower than 1 5 C would prevent the survival of larger benthic foraminifera such as the lepidocyclinids (Adams et al., 1986), which, on the contrary, colonized even the mid latitude by mid to late Oligocene time. (12) There are several possible explanations for the low paleotemperature estimates ot" the Oligocene: (1) poor preservation prevented our obtaining real values from the various planktonic foraminifera. It is unlikely that this would apply to all Oligocene sites analyzed: (2) the mean oxygen isotope ratio for the Oligocene ocean might be about 1%o heavier than that of the Eocene. In order to accommodate the disagreement between the enrichment of warm taxa in Zone P22 and the isotope values, another oxygen isotope ratio might characterize the late Oligocene ocean. This hypothesis implies rather extended ice cap(s) covering Antarctica since the beginning ot" the Oligocene, further increasing in size by the late Oligocene, and large enough to be registered in the oxygen isotope ratio. The suggestion of an ice cap in Antarctica by Oligocene time is supported by recent discoveries on land in Eastern Antarctica and deep-sea drilling in Prinz Bay (Harwood et al., 1989: Barton, Larsen
236
et al., 1989; Barron, Larsen et al., 1989); (3) heavier isotope values are related to an increase in salinity, due to stronger evaporation during the Oligocene; and (4) the latter two effects might have combined to alter the isotopic ratios. (13) Dissolution was important in the early-mid Oligocene interval at Hole 538A, although the site was located at lower bathyal depths at this time. It appears that cooler waters were flowing at bathyal depths through the Gulf of Mexico and may be responsible for the dissolution lower in the sequence as well as for the short hiatus inferred in Zone P21b. Another possible explanation could be that higher fertility in surface waters at this time resulted in an enrichment of organic carbon at depth causing a calcium carbonate deficiency at the sediment/water interface. A combined effect of both, however, cannot be ruled out. In summary, evolution of planktonic foraminiferal faunas in Hole 538A points towards a gradual overall warming from early to late Oligocene time. Despite cooling events and dissolution effects, this trend is marked by an overall increase in the number of warm species. This climatic trend is consistent with that inferred from oxygen isotopes, in the sense that warmer paleotemperatures correspond with appearance of warm species. Oxygen isotope values, however, appear too cool in comparison with the high abundance and diversification of warmer taxa, especially in late Oligocene early Zone P22. Acknowledgements The authors are indebted to DSDP-IPOD for having invited one of us (IPS) to participate on Leg 77. The authors would like to thank A. Boersma for fruitfull discussions about biostratigraphic and environmental interpretations of the Paleogene succession, C. McNulty, the other foraminiferal expert on board Leg 77, for his help during and after the cruise, and N. J. Shackleton for performing stable isotopic analyses. The authors are deeply indebted to G. Pezzi for sample preparation, to M. Minoli for providing graphic support, and to G. Chiodi for printing photographs, all of whom are from the Department of Earth Sciences, University of Milan. We also wish to thank A. Rizzi, C N R of
S. S P E Z Z A F E R R I A N D I, P R E M O L I SILVA
Milan, for SEM operation. The paper was reviewed by H. M. Bolli, R. L. Fleischer, and A. Boersma. Financial support for this research was provided by MPI 40% grant to IPS, and PhD program to SS. Species list and taxonomic notes That planktonic foraminiferal faunas encountered in the Oligocene sediments recovered in Hole 538A are abundant and highly diversified, much more than what is known from the literature (e.g. Bolli, 1957; Bolli and Saunders, 1985), is testified by the long list of species. Species are listed in alphabetical order by genus. The generic and specific concepts and the species groups used by Boersma and Premoli Silva (1983), Boersma et al. (1987), and by Premoli Silva and Boersma (1988, 1989) are retained herein, whenever possible. Several groups are still informal due to their uncertain taxonomic position based on different wall structure with respect to those in the original generic description. The most controversial forms are those previously attributed to the genus Globigerina. Although most Oligocene globigerinids belong to the spinose group, they possess a cancellate wall which does not exist in true Globigerina (Cifelli, 1982; Hemleben et al., 1988). A taxonomic revision of Paleogene planktonic foraminifera is in progress by the "Paleogene Planktonic Foraminifera Working Group". Reference is made to the most reliable illustrations reported in the literature. Most of the species identified are illustrated in Plates I XVIII.
Cassigerinella chipolensis (Cushman and Ponton, 1932) (=Cassidulina chipolensis Cushman and Ponton). (Plate VIII, 6a-b.). See Bolli and Saunders (1985), fig.16 (1-2). Genus Catapsydrax
Catapsydrax africanus (Blow and Banner, 1962) (= Globigerinita africana Blow and Banner). (Plate I, 3a). See Blow and Banner (1962), pl.XV, figs.A C; fig.ll (i-iv). Catapsydrax dissimilis (Cushman and Bermudez, 1937) (=Globigerina dissimilis Cushman and Ber-
O L l ( i O ( t NI P L A N K F O N I C F O R A M I N I F E R A L B I O S T R A T I G R A P H Y A N D P A L E O C L I M A T I ( I N T E R P R [ £ I A I ION
237
mudez). See Blow and Banner (1962), pl.XIV, fig.d. Also included here are specimens that exhibit a lobulate periphery like typical C. dissimilis and possess, when present, a clear bulla with only two infralaminal accessory apertures (Plate l, la d). Catapsydrax dissimilis ciperoensis (Blow and Banner, 1962) (=Globigerinita dissimilis ciperoensis Blow and Banner). (Plate I, 4a b). See Blow and Banner (1962), pI.XIV, figs.A C. Catapsydrax globij~rmis (Blow and Banner, 1962) (=Globi~erinita gloh(formis Blow and Banner). (Plate I, 2a~b). See Blow and Banner (1962), pI.XIV, figs.S U. Catapsydrax martini (Blow and Banner 1962) ( = Glob~Terinita martini Blow and Banner). Plate I, figs.5a c). See Blow and Banner (1962), pI.XIV, fig.0). Catapsydrax unicavus Bolli, Loeblich and Tappan, 1957. See Bolli et al. (1957), pl.7, figs.9a c. Only specimens very close to the holotype have been included in C. unicavus.
Dentoglobigerina larmeui (Akers 1955) (= Glohoquadrina larmeui Akers). (Plate II, 6a c). See
Chiloguembelina cubensis (Palmer, 1934) ( = Guemhelina cubensis Palmer). (Plate X, 5a 9b). See
"Globigerina" ciperoensis group All the species of this group possess a spinose, cancellate wall. "Globigerina" anguliofficinalis Blow, 1969. (Plate IV 5a d). See Blow (1969), pl.ll, figs. l 5. This species, associated with transitional forms to "G." angulisuturalis increases in size ( > 150 lam) in Zone P21b (Plate IV, 3a c). "Globigerina" angulisuturalis Bolli, 1957. (Plate IV, la, 2a d, 4a b). See Bolli (1957), pl.22, figs. l l a c. This species increase conspicuously in abundance at P21a/P21b zonal boundary. "Globigerina" ciperoensis Bolli, 1957. (Plate IV, 7a-b; Plate V, 3a-c, 4a d). See Bolli (1957), pl.22, figs. 10a b. "Globigerina"J~triasi Bermudez, 1961. (Plate IV, 6a d). See Bolli and Saunders (1985), fig. 13 (9).
Palmer (1934), figs. l 6. Genus
Dentoglobigerina
Dentoglohigerina baroemoenensis group Dentoglohigerina haroemoenensis (Le Roy, 1939) (= Glohigerina baroemoenensis Le Roy). (Plate II, 4a c). See Molina (1979), pl.22, figs.2a c. Dentoglobigerina galavisi (Bermudez, 1961 ) ( = Glohigerina galavisi Bermudez). (Plate II, la d). See Bermudez (1961), pl.4, fig.3. Transitional forms to D. haroernoenensis occur in Zone P19 (Plate II, 2a c, 3a d).
Dentoglobigerina globularis group Dentoglobigerina altispira globosa (Bolli, 1957) (=Glohoquadrina altispira globosa Bolli). (Plate III, 4a b). See Bolli and Saunders (1985), fig. 15 (1). Dentoglohigerina globularis (Bermudez, 1961) (= Globoquadrina glohularis Bermudez). (Plate II, 5a c, 7a c; Plate III, la c). See Molina (1979), pl.19, fig. la c. Transitional forms to D. altispira globosa occur in Zones P20. (Plate III, 3a c, 6a, 7a).
Jenkins (1971), pl.17, figs.522 524. Some specimens of comparable size and overall shape as D. larmeui but possessing a triangular tooth are figured in Plate VII, 3a b and Plate XVII under the name of Dentoglobigerina sp. aft. D. larmeui. They occur throughout the sequence, but never in abundance.
Dentoglobigerina pseudovenezuelana (Blow and Banner, 1962) (= Globigerina venezuelana Hedberg and Bolli, 1957). (Plate III, 5a b). See Blow and Banner (1962), pl.XI, figs.J L, N, O. Very rare.
"Globigerina" ampliapertura Bolti, 1957. (Plate XIII, 6a~d). See Bolli (1957), pl.22, figs.5 6. Typical specimens are very rare. Wall surface of this taxon is cancellate, possibly spinose (see Blow and Banner, 1962), then its generic attribution is still uncertain.
Genus
Globigerina
Globigerina officinalis Subbotina, 1953. (Plate VI, la b, 2a-c). See Subbotina (1953), pl.l l, figs. 1 - 7.
Globigerina ouachitaensis Howe and Wallace, 1932. (Plate VI, 5a c). See Blow and Banner (1962), pl.IX, figs.D, H K. Transitional form to Globi~erina ouachitaensis gnauki occur from the upper part of Zone P21a (Plate V, l a d ) .
238
PLATE
s. SPEZZAFERRI AND I. PREMOLI SILVA
I
(for e x p l a n a t i o n see p.243)
OLIGOCFNE PLANK1ONIC FORAMINIFERAL
PLATE
II
(for explanation see p.243)
B I O S T R A 1 I G R A P H Y A N D P A L E O C L I M A 1 IC I N F E R P R E T A I ION
239
240
P L A T E III
(for explanation see p.243)
S. S P E Z Z A F E R R I A N D 1. P R E M O L I S I L V A
O L I ( i O ( ' E N I PLANKIONI(" FORAMINIFERAL BIOSTRATIGRAPHY ~ND PALEOCLIMAIlC INTERPRETATION
P L A T E IV
(for explanation see p.243)
24[
242
PLATE V
S. S P E Z Z A F E R R I A N D I. P R E M O L ! S I L V A
OLIGO('ENE PLANKTONIC FORAMINIFERALBIOSTRATIGRAPHYAND PALEOCLIMATICINTERPRETATION
243
PLATE 1 (see p.238)
la d. Catapsydrax dissimilis dissimilis (Cusman and Bermudez), Sample 538A-5-CC. Catapsydrax globiformis (Blow and Banner), Sample 538A-8-CC. Catapsydrax africanus (Blow and Banner), Sample 538A-3-2, 70 72 cm, (a) side view. Catapsydrax dissimilis ciperoensis (Blow and Banner), Sample 538A-5-CC. Catapsydrax martini (Blow and Banner), Sample 538A-6-2, 40-42 cm. GIoborotaloides suteri Bolli, Sample 538A-10-CC. (a) Spiral view, (b) side view, (c) umbilical view. and (d) wall structure, except
2a b. 3a. 4a b. 5a c. 6a-c.
when differently specified.
PLATE 11 (see p.239) la c. Dentoglobigerina galavisi (Bermudez), Sample 538A-3-CC. 2a c. Dentoglob~erina galavisi (Bermudez)/D. baroemoenensis (Le Roy) transition, Sample 538A-3-CC. 3a d. l)entoglobi,~erina galavisi (Bermudez)/D. baroemoenensis (Le Roy) transition, Sample 538A-10-3, 95- 97 cm. 4a c. Dentoglobigerina baroemoenensis (Le Roy), Sample 538A-10-4, 95 97 cm. 5a-c. l)entoglobigerina globularis (Bermudez), Sample 538A-6-CC. 6a c. Dentogh>bigerina larmeui (Akers), Sample 538A-3-CC. 7a c. Dentoglobi,eerina globularis (Bermudez), Sample 538A-6-CC. (a) Spiral view, (b) side view, (c) umbilical view and (d) wall structure, except when differently specified. Figs.3, 4, 5, same magnification.
PLATE III (see p.240)
la c. Dentoglobigerina globularis (Bermudez), Sample 538A-5-CC. c. Globoquadrina tripartita (Koch), Sample 538A-8-CC. c. Dentoglobigerina globularis (Bermudez)/D. altispira globosa (Bolli) transition, Sample 538A-5-CC. b. Dentoglobigerina altispira globosa (Bolli), Sample 538A-4-CC, (a) spiral view, (b) umbilical view. b. Dentoglobigerina pseudovenezuelana (Blow and Banner), Sample 522-32-1, 49 cm, (a) spiral view, (b) umbilical view. Dentoglobigerina globularis (Bermudez)/D. altispira globosa (Bolli) transition, Sample 538A-5-CC. Dentoglobigerina globularis (Bermudez)/D. altispira globosa (Bolli) transition, Sample 538A-5-CC. (a) Spiral view, (b) side view,
2a 3a 4a 5a 6a. 7a.
(c) umbilical view, and (d) wall structure, except when differently specified. Figs.4 and 5, same magnification.
PLATE IV (see p.241) l a. 2a d. 3a c. 4a-b. 5a d. 6a-d. 7a b.
"Globigerina" "Globigerina" 'Globigerina" "Globigerina" "Globigerina" "Globigerina" "Globigerina"
angulisuturalis Bolli, Sample 538A-6-1, 40 42 cm. angulisuturalis Bolli, Sample 538A-7-2, 40-42 cm. anguliofficinalis Blow/"G." angulisuturalis Bolli transition, Sample 538A-11-1, 4(I-42 cm. angulisuturalis Bolli, Sample 538A-6-1, 40-42 cm, (a) umbilical view. anguliofficinalis Blow, Sample 538A-4-CC. ciperoensisfariasi Bermudez, Sample 538A-4-CC. ciperoensis Bolli, Sample 538A-2-CC. (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure,
except when differently specified. Figs.5 and 6, same magnification.
PLATE V la d. 2a c. 3a--d. 4a- d.
GIobigerma ouachitaensis Globigerma ouachitaensis "Globigerina" ciperoensis "Globigerina" ciperoensis
Howe and Wallace/G. ouachitaensis gnauki Blow and Banner transition, Sample 538A-4-CC. gnauki Blow and Banner, Sample 538A-3-CC.
Bolli, Sample 538A-4-CC. Bolli, Sample 538A-4-CC. (a) Spiral view, (b) side view, and (c) umbilical view, and Id) wall structure except when differently specified. Figs. l 4, same magnification. Figs. ld, 3d, 4d, same magnification.
244
PLATE
S. SPEZZAFERRI AND 1. PREMOLI SILVA
VI
(for explanation see p.246)
()LIGO( FNE PLANK1ONIC FORAMINIFERAL BIOSTRATIGRAPH'( AND PAI~EO('LIMA11( INTERPRF IA IION
PLATE VII
(for e x p l a n a t i o n see p . 2 4 6 )
245
246
s. S P E Z Z A F E R R I A N D 1. P R E M O L I SILVA
Globigerina ouachitaensis gnauki Blow and Banner, 1962. (Plate V, 2a-c). See Blow and Banner (1962), pl.IX, figs.L-N. Globigerina praebulloides Blow, 1959. (Plate VI, 3 a - c , 4 a - d ) . See Blow and Banner (1962), pl.IX, figs.O Q. Globigerina praebulloides occlusa Blow and Banner, 1962. (Plate VIII, l a - d ) . See Blow and Banner (1962), pl.IX, figs.U-W. Large globigerinids All the species o f this g r o u p possess a spinose, cancellate wall. "Globigerina" euapertura Jenkins, 1960. (Plate VII, 4a-c). See Jenkins (1985), fig.6 (18a-c). "Globigerina" prasaepis Blow, 1969. (Plate VII, 6a-c). See Blow (1969), pl.10, fig.13; pl.18, figs.3 7. "Globigerina" venezuelana Hedberg, 1937. (Plate VII, 2 a - c , 5 a - b . See Bolli and Saunders (1985), fig. 13 (20).
Other globigerinids All the species o f this g r o u p possess a spinose, cancellate wall. "'Globigerina'" brazieri (Jenkins, 1966) ( = Globigerina brazieri Jenkins). See Jenkins (1985), fig.6 (20a-c). "Globigerina" labiacrassata (Jenkins, 1966) ( = Globigerina labiacrassata Jenkins). See Jenkins (1985), fig.6 (19a-c). Very rare. "Globigerina'" woodi s. str. Jenkins, 1960. See Chaproniere (1988), pl.1 and 2. In our material in addition to typical "G."woodi, which has four chambers in the last whorl and a wide-arched aperture occasionally with a thin lip, there are rare forms plotted as "Globigerina" sp. characterized by three to three and a half chambers in the last whorl, a subrectangular profile, and a mediumsized, low-arched aperture. They appear to be related to "G." woodi s. str.
Globigerinita juvenilis (Bolli, 1957) ( = Globigerma
PLATE Vl (see p.244) la-b. 2a c. 3a-c. 4a-d. 5a-c. 6a-c.
Globigerinaofficinalis Subbotina, Sample 538A-2-CC. Globigerinaofficinalis Subbotina, Sample 538A-4-CC. Globigerinapraebulloides Blow, Sample 538A-4-CC. Globigerinapraebulloides Blow, Sample 538A-4-CC. Globigerinaouachitaensis How and Wallace, Sample 538A-2-CC. Globigerinapraebulloides Blow, Sample 538A-4-CC. This specimen shows recrystallized wall. (a) Spiral view. (b) side view, (c) umbilical view, and (d) wall structure. Figs.1 and 3, same magnification.
PLATE VII (see p.245) la-d. 2a c. 3a b. 4a-c. 5a-b. 6a-c.
"Globigerina"prasaepisBlow, Sample 538A-5-CC. "Globigerina"venezuelana Hedberg, Sample 538A-3-CC. Dentoglobigerinaaft. D. larmeui (Akers), Sample 538A-6-CC, (a) side view, (b) wall structure. "Globigerina"euapertura Jenkins, Sample 538A-12-CC. "'Globigerina"venezuelana Hedberg, Sample 522-21-2, 22 cm, (a) umbilical view. "Globigerina'"prasaepis Blow, Sample 538A-12-CC. (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure, except when differently specified.
PLATE VIII la-d. 2a-c. 3a. 4a d. 5a-c. 6a-c.
Globigerinapraebulloides occlusa Blow and Banner, Sample 538A-4-2, 40-42 cm. This specimen shows recrystallized wall. "Globigerinoides'"praeprimordius, Sample 538A-10-4, 95-97 cm. Globigerinoidesprimordius Blow and Banner, Sample 538A-5-CC. Globigerinoidesprimoridus Blow and Banner, Sample 538A-4-CC. "Globigerina'"normal "Globigerinoides"praeprimordiusSample 538A-I0-5, 2-3 cm. Cassigerinellachipolensis(Cushman and Ponton), Sample 538A-6-2, 40-42 cm, (a) side view, (b) umbilical view. (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure, except when differently specified. Figs.4 and 5, same magnification.
O L I ( i O ( ' I NI P L A N K T O N I (
P L A T E VIII
FORAMINIFERAL
BIOSTRA I IGRAPH~
A N D P'S, L E O ( L I M A T I ( " I N I E R P R E
I A IION
247
248
S. S P E Z Z A F E R R | A N D 1. P R E M O L I SILVA
juvenilis Bolli). See Bolli (1957), pl.24, figs.5 and 6. Its first occurrence is within Zone P21a. Rare. Genus
Globigevinoides
Globigerinoides primordius Blow and Banner, 1962. (Plate VIII, 3a, 4a-d). See Bolli and Saunders (1985), fig.20 (16). Typical forms are preceded in Zone P21 by specimens displaying the same shape and wall structure as G. primordius without supplementary apertures. The latter are plotted under the informal name of "Globigerinoides"praeprimordius (Plate VIII, 2a-c). Genus
Globoquadrina
Globoquadrina binaiensis (Koch, 1935) ( = Globigerina binaiensis Koch). (Plate IX, 6a c). See Bolli and Saunders (1985), fig.14 (6-10). Globoquadrina dehiscens praedehiscens Blow and Banner, 1962 (Plate IX, la-c). See Blow and Banner (1962), pl.15, figs.O-S. Globoquadrina sellii Borsetti, 1959 (Plate IX, 7a-c). See Bolli and Saunders (1985), fig.14 (11). "Globoquadrina" tapuriensis (Blow and Banner, 1962) (=Globigerina tripartita tapuriensis Blow and Banner). (Plate IX, 3a-c, 4a-b). See Blow and Banner (1962), pl.10, figs.H-K. The genus Globoquadrina is kept in brackets because this species does not possess the typical tooth of the genus Globoquadrina. Globoquadrina tripartita (Koch, 1926) ( = Globigerina bulloides var. tripartita Koch). (Plate III, 2a c; Plate IX, 2a c). See Bolli and Saunders (1985), fig.14 (13). Globoquadrina rohri (Bolli 1957) (=Globigerina rohri Bolli). (Plate IX, 5a-c). See Bolli (1957), pl.36, figs.4a-b.
Genus
Globiger&ella
Globigerinella obesa Bolli, 1957. (Plate XI, figs.3a c). See Bolli (1957), P1.29, figs.2a-3. This species possesses a pole-like spines in a fiat wall like true Globigerina, then it cannot belong to the genus Globorotalia. Its taxonomic position, however, is still uncertain, because it evolves into Globigerinella praesiphonifera (Premoli Silva and Spezzaferri, 1990). Genus
Globorotaloides
Globorotaloides permicrus (Blow and Banner, 1962) (=Globorotalia (Turborotalia) permicra Blow and Banner). (Plate X, l a-c). See Blow and Banner (1962), pl.XII, figs.N-P. Globorotaloides suteri Bolli, 1957 (Plate I, 6a-c; Plate X, 3a-b, 4a-d). See Bolli (1957), pl.27, figs.9 13. Globorotaloides variabilis Bolli, 1957 (Plate X 2a-b). See Bolli and Saunders (1985), fig.18 (9a-c). Genus
Paragloborotalia
Paragloborotalia opima nana (Bolli, 1957) (=GIoborotalia opima nana, Bolli) (Plate XI, 4a-c). See Bolli (1957), pl.28, figs.3a-c. Paragloborotalia opima opima (Bolli, 1957) ( = Globorotalia opima opima Bolli). (Plate XI, 5a-c, 6a-b). See Bolli (1957), pl.28, figs.la 2. Paragloborotalia pseudocontinuosa (Jenkins, 1967) (=Globorotalia pseudocontinuosa Jenkins (Plate XI, la c; Plate XII la-c, 2a; Plate XVI, figs.2a d). See Jenkins and Srinivasan (1986), pl.5, figs.2 4. From Subzone P21a some specimens show a tendency to have four and a half to five chambers in the last whorl. Paragloborotalia pseudokugleri Blow, 1969 (Plate XI, 7a c). See Blow (1969), pl.10, figs.4-6. Rare
PLATE IX la c. 2a c. 3a c. 4a b. 5a-c. 6a-c. 7a-c.
Globoquadrinadehiscenspraedehiscens Blowand Banner, Sample 538A-2-CC. Globoquadrinatripartita (Koch), Sample 538A-8-CC. "GIoboquadrina"tapuriensis (Blow and Banner), Sample 538A-10-4, 95-97 cm. Globoquadrinatapuriensis(Blow and Banner), Sample 558-25-5, 73 cm. Globoquadrinarohri (Bolli), Sample 538A-7-CC. Globoquadrinabinaiensis Koch, Sample 538A-3-CC. GIoboquadrinasellii Borsetti, Sample538A-4-CC.(a) Spiral view,(b) side view,(c) umbilicalview,and (d) wall structure,except when differentlyspecified. Figs.l, 2 and 3, same magnification.
Ol I(~O( [N[: P L A N K T O N I C F O R N M I N I F E R A L B I O S T R A f l G R A P H Y A N D P A L E O C L I M ~ I I ( IN I E R P R E T A IION
P L A T E IX
249
250
PLATE X
(for explanation see p.253)
S. S P E Z Z A F E R R I A N D 1. P R E M O L I SILVA
OI I(;O(1 N FI PLANK I O N I ( FORAMINIFERAL BIOSTRATIGRAPH'Y AND PALEOCLIMATI( INTERPRETATION
PLATE XI
( f o r e x p l a n a t i o n see p . 2 5 3 )
25]
)-52
P L A T E XII
S. S P E Z Z A F E R R I A N D I PREMOLI SILVA
OI I ( i O ( ' [ N! P L A N K I O N I C F O R A M I N I F E R A L
BIOSI RA I IGRAPH'Y A N D P A L E O ( ' L I M A [1( I N - I E R P R E T A I I O N
specimens displaying transitional characters to P. kugh,ri occur at the top of the sequence. Recent investigations by Spezzaferri (in press) suggest that on the basis of the wall structure (cancellate with spines) the former "Globorotalia" kugleri group should be attributed to the genus Paragloborotalia. Paraglohorotalia siakensis (Le Roy, 1938) ( = Glohi~erina siakensis le Roy) (Plate XI, 2a c). See Molina (1979), pl.28, figs. la c; Kennett and Srinivasan (1983), pl.42, figs.l, and 6--8. Paraglohorotalia sp. Some specimens as that illustrated in Plate XII, 3a-d may be related to Paragloborotalia semivera (Hornibrook). They occur in Zone P20 up to mid Subzone P21a. Genus Protentella
Protentella sp. (Plate XIII, la-c, 4a c). Under this informal species are grouped a number of proten-
25~
tellids, slightly trochoidal, that possess four to five chambers in the last whorl, with an extraumbilical aperture bordered by a rim. They first occur in Zone P22 and are rare. Genus Pseudohastigerina
Pseudohastigerina barbadoensis Blow, 1969 (Plate XIV, 3a b). See Blow (1969), pl.53, figs.7 9. Pseudohastigerina naguewichiensis (Myatliuk, 1950) ( = Globigerinella naguewichiensis Myatliuk) (Plate XIV, la-c, 2a-b, 5a c). See Toumarkine and Luterbacher(1985), fig.21 (10 16). Pseudohastigerina micra (Cole, 1927) ( = Nonion micrus Cole) (Plate XIV 4a b). See Blow (1979), pl.253, figs. l 9. The specimen illustrated is from Late Eocene Core 14-CC. The Oligocene forms display the same small size as the other pseudohastigerinids.
PLATE X (see p.250) 1 a c . Globoromloides permicrus (Blow and Banner), Sample 538A-7-CC. 2a b. Globorotahmles variahilis Bolli, Sample 538A-6-CC, (b) umbilical view. 3a b. GloborotaloMes suteri Bolli, Sample 366-9-2, 12 cm, (b) umbilical view. 4a d. Globorotah#des suteri Bolli, Sample 538A- I I-2, 40 42 crn. 5a. Chiloguembelina cubensis Palmer, Sample 538A-7-4, 40 42 cm, oblique axial view. 6a. Chiloguembelina cubensis Palmer, Sample 538A-6-CC, axial view. 7a. Chiloguembelina cubensis Palmer, Sample 538A-12-1, 40 42 cm, apertural side view. Chiloguembelina cuhensis Palmer, Sample 538A-12-l, 40 42 cm, apertural side view. 9a b. Chiloguemhelina cubensis Palmer, Sample 538A-12-1, 40 42 cm, (a) apertural side view, Ib) detail o f g a . (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure, except when differently specified. Figs. l and 3, same magnification.
PLATE XI (see p.25l) la 2a 3a 4a 5a 6a 7a
c. c. c. c. c. b. c.
Paragloborotalia pseudocontinuosa (Jenkins), Sample 538A-7-CC. Paraglohorotalia siakensis (Le Roy), Sample 538A-3-CC. Glob~gerinclla obesa (Bolli), Sample 538A-6-1, 40 42 cm. Paragloborotalia opima nana (Bolli), Sample 538A-7-2, 40 42 cm. Paragloborotalia opima opima (Bolli), Sample 538A-7-2, 40 42 cm. Paragloborotalia opima opima (Bolli), Sample 538A-9-CC. Paragloborotalia pseudokugleri Blow, Sample 538-A-3-1, 100-102 cm. (a) Spiral view, (b) side view, (c) umbilical view, and (d) wall structure, except when differently specified. Figs. l and 2, same magnification.
PLATE XII la c. 2a. 3a d. 4a c. 5a.
Paragloborotalia pseudocontinuosa (Jenkins), Sample 538A-1 I-CC. Paragloborotalia pseudocontinuosa (Jenkins), Sample 538A-11-I, 40-42 cm. Paragqoborotalia sp., Sample 538A-10-2, 95 97 cm. Paraglohorotalia sp., Sample 538A-10-2, 95 97 cm. Paraglohorotalia sp., Sample 538A-10-3, 95-97 cm, (a) umbilical view. (a) Spiral view, (b) side view, (cj umbilical view, and (d) wall structure, except when differently specified. Figs. l, 2 and 4, 5, same magnification.
254
PLATE XIII
(for explanation see p.257)
s. S P E Z Z A F E R R I A N D I. P R E M O L I SILVA
( ) L I G O ( I NE P L A N K 1 0 N I C I-ORAM I N I F E R A L BIOS I RA I IGRAPHY A N D PAI.EO( I IMA l 1( INT[ RPR[ 1A 1 ION
PLATE
XIV
(for explanation
see p.257)
2q5
256
P L A T E XV
S. S P E Z Z A F E R R I A N D 1. P R E M O L I SILVA
Ol I G O ( [ N[ P L A N K I O N I ( F O R A M I N I F E R A L BIOSI R A T I G R A P H ~ A N D P A L E O ( L I M A r I(" IN IERPR[!TA FION
Suhhotina angiporoides group Suhhotina angiporoides angiporoides ( H o r n i b r o o k , 1965) ( = G l o b i g e r i n a angiporoides H o r n i b r o o k ) . (Plate XV, figs.3a d, 4a b). See H o r n i b r o o k (1965), pl. la i and pl.2. This taxon displays a large morphological variability. Subhotina angiporoides minima (Jenkins, 1966) (=Globigerina anjziporoides H o r n i b r o o k subsp. minima Jenkins). (Plate XV, la d, 2a). See Jenkins (1966), fig.7 (52 57). Subbotina utilisindex (Jenkins and Orr, 1973) ( = Glohigerina utilisindex Jenkins and Orr). (Plate XVI, 4a d). See Jenkins and Orr (1973), pl.1, figs. 1 6; pl.2, figs. 1 9: pl.3, figs. l - 3 . The main characteristics of this species are the much more round final c h a m b e r and f n e r wall structure than S. linaperta s. str. (see Premoli Silva and Spezzaferri, 1990). Subbotina utilisindex disappears in the middle Oligocene just prior to S. angiporoides and S. an~ziporoides minima.
High-spired subbotinids Subhotma praeturritilina (Blow and Banner, 1962)
_~7
( = Glohigerina turritilina praeturritilina Blow and Banner). (Plate XVI, la c). See Blow and Banner (1962), pl.XIII, figs.A C. Subbotina gortanii (Borsetti, 1959) ( = Catapswtra.v gortanii Borsetti). (Plate XVI, 3a d). See Borsetti (1959),pl.l, figs.la lc. Very rare.
Genus Tenuitella Tenuitella clemenciae (Bermudez, 1961) ( : Turhorotalia clemenciae Bermudez). (Plate XVIII, la c, 4a c). See Bermudez (1961), pl.17, fig. 10. Intermediate forms between T. clemenciae and T. mumh~ are often present (Plate X V I I I . 3a d). Tenuitella g e m m a (Jenkins, 1971 ) ( = GIohorotalia (Turborotalia; g e m m a Jenkins). (Plate XVIII, 6a c). See Jenkins (1971), pl.10, figs.263 269. Tenuitella munda (Jenkins, 1966) (=Glohorotalia munda Jenkins). See Jenkins ( 1966), figs. 14 and 15.
Genus Tenuitellinata Tenuitellinata angustiumhilicata (Bolli, 1957) ( = Globigerina ciperoensis an~ustiumbilicata Bolli).
PLATE XIII (see p.254) la c. 2a c. 3a. 4a d. 5a c. 6a d.
Protentella sp. Sample 538A-2-CC. furhorola/ia pseudoampliapertura (Blow and Banner), Sample 538A-14-1, 0 2 cm. furhorotaiia pseudoampliapertura (Blow and Banner), Sample 538A-14-1, 0 2 cm, (a) side view: Protentella sp., Sample 538A-2-CC. "GIobi~,,erina"sp. Sample 538A-10-CC. This specimen is probably related to the "Globi~,erina" woodi group. "Glohi~erina"arnpliapertura Bolli, Sample 538A-10-CC. (a) Spiral view, (b) side view, (c) umbilical view. and (d) wall structure. except when differently specified. Figs.l, 2, and 5, 6, same magnification.
PLATE XIV (see p.255) la 2a 3a 4a 5a
c. b. b. b. c.
Pseudohasli~erina naguewichiensis (Myatliuk), Sample 538A-13-CC. Pseudohasti¢erina naguewichiensis (Myatliuk), Sample 538A-13-CC. P.;eudohastifzerinaharhadoensis Blow, Sample 538A-13-CC. P;eudohastigerina micra (Cole), Sample 538A-14-CC. Pseudohastigerinanaguewichiensis (Myatliuk), Sample 538A-13-CC. (a) Spiral view, (b) side view, and (c) wall structure, except when differently specified. All specimens, same magnification. Figs. lc and 5c, same magnification.
PLATE XV l a-c. 2a. 3a d. 4a b.
Suhhotina an~,iporoides minima (Jenkins), Sample 538A-13-1, 86 99 cm. Suhbotinaang'iporoides minima (Jenkins), Sample 538A-12-3.40 42 cm. Suhhotina angiporoides ang,iporoides (Hornibrook), Sample 538A-10-4, 95 97 cm. Subhotina an~ziporoides anf;iporoides (Hornibrook), Sample 538A-I I-CC, (a) Spiral view, (b) side view. (c) umbilical view, and (d) wall structure, except when differently specified.
258
PLATE
s. SPEZZAFERRI AND 1. PREMOLI SILVA
XVI
(for e x p l a n a t i o n see p.261)
()I_IGOCI NE P L A N K T O N I (
FORAMINIFERAL
PLATE XVII
(for explanation see p.261)
BIOSTRATIGRAPHY AND PALEOCLIMATIC INTERPRETATION
_39
260
P L A T E XVIII
S. S P E Z Z A F E R R I
A N D 1. P R E M O L I
SILVA
()1 I(iO( [ N I P L A N K I O N I C F ( ) R A M I N I F I RAL B I O S I R A I I G R A P H ' ~ , \ N I ) PAl I{()( I A M A I I ( [ N I I ( R P R I I A I ION
2t, l
PLA'FE XVI (see p.25S) I a c. Suht~otim~ praeturritilim~ (Blow and Banner), Sample 538A- 12-4, 40 42 cm, 2a d. f'arag, lohorolalia pseudocontinuosa (Jenkins), Sample 53,~A-10-2, 95 97 cm, 3a d. Suhholina jmrlanii (BorscHt), Sample 538A- 13-1, ~6 99.cm. 4a d. Suhhozina ulili.vindex (Jenkins and err), Sample 538A-13-I, 86 99 cm. {a) Spiral "view. (b) side viev., (c) umbilical xiew, and !d) wall structure, except when differently specitied. Figs.2d and 3d. same magnification.
PLATE XVI1 (see p.25% [ a d . l)ento~lohi~,,erma aft. D. larmeui tAkers), Sample 538A-4-CC 2a d. I)ento~dohi~,eriml aft. D. larmeui tAkers), Sample 538A-6-CC. 3a d. l)ento~,/(~k,~,,erina aft'. D. /armeui tAkers), Sample 538A-6-CC 4a b. l)enlo~,/rd,~,,erina aft. O. larnu, ui tAkers). Sample 538A-6-C('. (a) spiral side slightly oblique. (b) umbilical side wilh a broken chamber. 5 a b. l)enlo,el¢,hi~erma aft. D. larmeui takers), Sample 538A-6-CC.(b) umbilical view. 6a. I)enlo,e/ol,i~,,eriml aff. D. larmeui (Akers), Sample 538A-6-CC. la) Spiral view, (b) side vie'-*, (c) umbilical xicv,, and (d) v, all structure with particulars of teeth, except when differently specified. All specimens, same magnification: Eigs.2d and 3d. same magnilicalion.
PLATE XVIII [ U C.
2a 3a 4a 5a 6a
d. d. c. d. c
71,m~itel/a ~lemem'iae (Bermudez), Sample 538A-12-4, 40 42 cm. Tem~itel/inam an~u~tiumhilicala (Bolli), Sample 53SA- I I -CC. 7~'#mitella ch,tm,nciae (Bermudez), T, mumta (Jenkins) intermediate l\)rm, Samplc 538A 7-4, 40 42 cm. 7~,mdtella clemem'iae (Bermudez), Sample 538A-12-4, 40 42 cm, (a) umbilical view, (b) side xiew. and Ic) wall structure, Tem~ile//inala an~,,u.sliumhilicala (Bolli), Sample 53SA- 10-CC. Te,uilella ,£,cmma (Jenkins), Sample 538A-10-5, 2 3 cm. (a) Spiral view, (b) side view, (c) umbilical viex~, and (d) wall structure, except when difl'crenlly specified Figs.2d and 3d. same magnification.
(Plate XVIII, 2a d, 5a d). See Li Qianyu (1987), pl.2. figs. 15, 17 19. Genus Turborotalia Turhorotalia increbescens (Bandy, 1949) ( = Glohi,~erina increhe.wens Bandy). See Bolli and Saunders (1985). fig. 14 (5). Very, rare. Turhorotalia pseudoampliaperlura (Blow' and Bannor, 1962) ( = Gloh~,,erina pseudoampliapertura Blow' and Banner). (Plate XIII, 2a c, 3a). See Bolli and Saunders 1985), tig. 1 (4). References Adams, (7. G., Bunerlin, J. and Samanta, B. K., 1986. Larger foraminifera and events at the Eocene/Oligocene boundary in the Indo-West Pacitic region. In: C. Pomerol and 1. Premoli Siha (Editors), Terminal Eocene Events (Dev. Paleontol. Stratigr. 9). Elsevier, Amsterdam, pp. 237 252. Barren..1. A.. l_arsen. B., Baldauf, J. G. el al., 1989. Proximal and distal evidence of the history of the East Antarctic ice sheet: Result,',, from O D P Leg 119. In: 3rd Int. Conf. Palcoceanogr... Cambridge. T E R R A abstr., I: 3.
Belanger, P. E. and Manhews, R. K., 1984. The forammilLqal isotope record across the EoceneOligocene boundary at Deep Sea Drilling Project Site 540. In: R T. Buffier, W. Schlager et al., lnit. Rep. DSDP, 77:589 593. Bermudez, P. J.. 1961. ('ontribuci6n al cstudio de las Globigerinidae de la region Caribe-Anfillana tPaleoceneRecientc). Memorias de la Ill Congreso Geologico Venezolane, tome I11. Soc. (}eel. Venez., Bol. Geol., Publ. Espec., 3: [119 139~. Bcrmudcz. P. J. and Seiglie, B. S., 1967. A new gellUS and species of foraininifcr from the early Miocene of Puerto Rico. Tulane Stud. Geol.. 5(3): 177 [79. Biolzi, M . . 1983. Stable isotopic stud,, of Oligocenc Miocene sediments from DSDP Site 354, Equatorial Atlantic. Mar. Micropaleontol., 8:121 I39 Biolzi, M., 1985. The Oligocene Miocene boundar', m sclectcd Atlantic, Mediterranean and Paratethyan sections based on stratJgraphic and stable isotope evidence. Mere. Sci. Geol. Padova, 37:303 378. Blow, W. H.. I969. Late middle Eocene to Recent planktonic l\mmfiniferal biostratigraphy In: Prec. l:irst Int. ('onf. Planktonic MicrotBssils. Geneva. Bri!l. I.ciden, I, pp. 199 422. Blow. W. It., 1979. The Cainozoic (}lobigerinida. BM1, Leiden. 1410 pp. Blow. W. H. and Banner. F. T_ 1962. The Mid-Tertiary (Upper
262 Eocene to Aquitanian) Globigerinacea. In: F. E. Eames, F. T. Banner, W. H. Blow and W. J. Clarke (Editors), Fundamentals of Mid-Tertiary Stratigraphical Correlation. Cambridge Univ. Press, pp. 61 151. Boersma, A., 1977. Cenozoic planktonic foraminifera, DSDP Leg 39, South Atlantic. In: P. R. Supko, K. Perch-Nielsen et al., Init. Rep. DSDP, 39: 643-656. Boersma, A. and Premoli Silva, 1., 1983. Paleocene planktonic foraminiferal biogeography and the paleoceanography of the Atlantic Ocean. Micropaleontology, 29(4): 355-381. Boersma, A. and Premoli Silva, I., 1986. Terminal Eocene events: planktonic foraminifera and isotopic evidence. In: C. Pomerol and I. Premoli Silva (Editors), Terminal Eocene Events (Dev. Paleontol. Stratigr., 9). Elsevier, Amsterdam, pp. 213-224. Boersma, A. and Premoli Silva, I., 1988. Boundary conditions of Atlantic oxygen minimum zones. Riv. Ital. Paleontol. Stratigr., 93(4): 479-506. Boersma, A. and Premoli Silva, I., 1989. Atlantic Paleogene biserial heterohelicids and oxygen minima. Paleoceanography, 4(3): 271 286. Boersma, A., Premoli Silva, I. and Shackleton, N. J., 1987. Atlantic Eocene planktonic foraminiferal paleohydrographic indicators and stable isotope paleoceanography. Paleoceanography, 2(3): 287-331. Boersma, A. and Shackleton, N. J., 1977. Tertiary oxygen and carbon isotope stratigraphy, Site 357 (mid latitude South Atlantic). In: P. R. Supko, K. Perch-Nielsen et al., lnit. Rep. DSDP, 39:911 924. Boersma, A. and Shackleton, N. J., 1978. Oxygen and carbon isotope record through the Oligocene Site 366, Equatorial Atlantic. In: Y. Lancelot, E. Seibold et al., lnit. Rep. DSDP, 41:957 962. Bollk H. M., 1957. Planktonic Foraminifera from the Oligocene-Miocene Cipero and Lengua formations of Trinidad, B.W.1. Bull. U.S. Natl. Mus., 215:97 124. Bolli, H. M. and Saunders, J. B., 1985. Oligocene to Holocene low latitude planktic foraminifera. In: H. M. Bolli, J. B. Saunders and K. Perch-Nielsen (Editors), Planktic Stratigraphy. Cambridge Univ. Press, pp. 155 262. Borsetti, A. M., 1959. Tre nuovi Foraminiferi plantonici dell'Oligocene piacentino. G. Geol., 27:205 212. Buffier, R. T., Schlager, W. et al., 1984. Init. Rep. DSDP, 77, 747 pp. Chaproniere, G. C. H., 1988. Globigerina woodi from the late Oligocene and early Miocene of southeastern Australia. J. Foraminiferal Res., 18(2): 124 129. Cita, M. B., Vergnaud-Grazzini, C., Robert, C., Chamley, H., Ciaranfi, N. and D'Onofrio, S., 1977. Paleoclimatic record of a long deep sea core from the Eastern Mediterranean. Quat. Res., 8:205 235. Cifelli, R., 1982. Early occurrences and some phylogenetic implications of spiny, honeycomb textured planktonic Foraminifera. J. Foraminiferal Res., 12:105 115. Douglas, R. G. and Savin, S. M., 1978. Oxygen isotope evidence for the depth stratification of Tertiary and Cretaceous planktonic foraminifera. Mar. Micropaleontol., 3: 175 196. Fleisher, R. L., 1974. Cenozoic planktonic foraminifera and biostratigraphy, Arabian Sea Deep Sea Drilling Project, Leg
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A N D 1. P R E M O L I S I L V A
23A. In: R. B. Whitmarsh, O. E. Weser, D. A. Ross et al., Init. Rep. DSDP, 23: 1001-1072. Haq, B. U., Premoli Silva, I. and Lohmann, G. P., 1977. Calcareous plankton paleobiogeographic evidence for major climatic fluctuations in the Early Cenozoic Atlantic Ocean. J. Geophys. Res., 82: 3861-3876. Hardenbol, J. and Berggren, W. A., 1978. A new Paleogene numerical time scale. In: G. Cohee, M. Glaessner and H. Hedberg (Editors), Contributions to the Geologic Time scale. AAPG, Tulsa, OK, pp. 213 234. Harwood, D. N., Webb, P. N. and Barrett, P. J., 1989. Multiple Cenozoic glaciations of Antarctica from terrestrial and continental shelf data. In: 3rd Int. Conf. Paleoceanogr., Cambridge, TERRA Abstr., 1: 2. Hemleben, C. H., Spindler, M. and Anderson, O. R., 1988. Modern Planktonic Foraminifera, Springer, New York, NY, 363 pp. Hornibrook, N. de B., 1965. Globigerina angiporoides n. sp. from the Upper Eocene and Lower Oligocene of New Zealand and the status of Globigerina angipora Stache, 1865. N. Z. J. Geol. Geophys., 8(6): 834-838. Jenkins, D. G., I966. Planktonic foraminiferal zones and new taxa from the Danian to Lower Miocene of New Zealand. N. Z. J. Geol. Geophys., 8: I088-1126. Jenkins, D. G., 1971. Cenozoic planktonic foraminifera of New Zealand. N. Z. Geol. Surv. Paleontol. Bull., 42:1 278. Jenkins, D. G., 1985. Southern mid-latitude Paleocene to Holocene planktic foraminifera. In: H. M. Bolli, J. B. Saunders and K. Perch-Nielsen (Editors), Plankton Stratigraphy. Cambridge Univ. Press, pp. 263-282. Jenkins, D. G. and Orr, W. N., 1973. Globigerina utilisindex n. sp. from the Upper Eocene-Oligocene of the eastern equatorial Pacific. J. Foraminiferal Res., 3(3): 133-135. Kennett, J. P. and Srinivasan, M. S., 1983. Neogene Planktonic Foraminifera. A Phylogenetic Atlas. Hutchinson and Ross, Stroudsburg, PA, 265 pp. Li, Qianyu, 1987. Origin, phylogenetic development and systematic taxonomy of the Tenuitella plexus (Globigerinitidae, Globigerinina). J. Foraminiferal Res., 17(4): 298-320. Molina, E., 1979. Oligocene-Mioceno inferior por medio de foraminiferos planctonicos en el sector central de las Cordilleras Beticas (Espana). Thesis, Univ. Granada and Zaragoza. Palmer, D. K., 1934. The foraminiferal genus Guembelina in the Tertiary of Cuba. Mem. Soc. Cubana Hist. Nat., 8: 73-76. Poore, R. Z. and Matthews, R. K., 1984. Late Eocene-Oligocene oxygen- and carbon-isotope record from South Atlantic Ocean, Deep Sea Drilling Project Site 522. In: K. J. Hsu, J. L. LaBreque et al., Init. Rep. DSDP, 73: 725-736. Premoli Silva, I. and Boersma, A., 1988. Atlantic Eocene planktonic foraminiferal historical biogeography and paleohydrographic indices. Palaeogeogr., Palaeoclimatol., Palaeoecol., 67(3/4): 315-356. Premoli Silva, I. and Boersma, A., 1989. Atlantic Paleogene planktonic foraminiferal bioprovincial indices. Mar. Micropaleontol., 14: 357-371. Premoli Silva, I. and Spezzaferri, S., 1990. Paleogene planktonic foraminifer biostratigraphy and paleoenvironmental remarks of Paleogene sediments from Indian Ocean Sites, Leg 115. In: J. Backman, R. A. Duncan et al., Proc. ODP Sci. Reports, 115:277 314.
()[ IG()( I NI ['LANKIONIC FORAMINIF[RAL BIOSTRATIGRAPHYAN[) PALEO('IIMAII( IN II RPRI IAI ION Shackleton. N. J., ttall. M. A. and Boersma, A., 1984. Oxygen and carbon isotope data from Leg 74 foraminifers. In: T. C. Moore Jr., P. D. Rabinowitz et al., lnit. Rep. DSDP. 74: 509 612. Spezzaferri. S., m press. Evolution and taxonomy of the Paragloborotalia kugleri (Bolli) lineage. J. Foraminiferal Res.
26~
Thunell, R. C. and Reynolds, 1,. A.. 19S4. Se(limentation oF plantktonic foraminifera: Seasonal changes in species flux in the Panama Basin. Micropaleontology, 30(3): 243 262. Toumarkine, M. and Luterbacher, H. P.. 19S5. Paleocenc and Eocene planktic Foraminifera. l n : H . M . Bolli, J B. Saunders and K. Perch-Nielsen (Edilors). Planktonic Stratigraphy Cambridge Univ. Press, pp. 87 154.