Stratigraphy and depositional history of the Pliocene Bianco section, Calabria, southern Italy

Palaeogeography, Palaeoclimatology, Palaeoecology, 76 (1989): 85 105 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

85

Stratigraphy and depositional history of the Pliocene Bianco section, Calabria, southern Italy D. RIO 1, R. T H U N E L L 2, R. SPROVIERI 3, D. BUKRY 4, E. DESTEFANO 3, M. HOWELL 2, I. RAFFI 1, C. SANCETTA 5 and A. SANFILIPPO 6 l Istituto di Geologia, Universita di Parma, 43100 Parma (Italy) 2Department of Geological Sciences, University of South Carolina, Columbia, SC 29208 (U.S.A.) 3Istituto di Geologia, Universita di Palermo, 90134 Palermo (Italy) 4U.S. Geological Survey, Menlo Park, CA 94025 (U.S.A.) 5Lamont-Doherty Geological Observatory, Palisades, N Y 10964 (U.S.A.) 6Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093 (U.S.A.) (Received January 30, 1989; revised and accepted June 27, 1989)

Abstract Rio, D., Thunell, R., Sprovieri, R., Bukry, D., DeStefano, E., Howell, M., Raffi, I., Sancetta, C. and Sanfilippo, A., 1989. Stratigraphy and depositional history of the Pliocene Bianco section, Calabria, southern Italy. Palaeogeogr., Palaeoclimatol., Palaeoecol., 76: 85-105. An integrated micropaleontological and geochemical study was carried out on the Pliocene-age Bianco section located in Calabria, southern Italy. This section is somewhat unique for the Pliocene of the Mediterranean region in that it contains abundant calcareous and siliceous microfossils. Based on the biostratigraphic findings, it ranges in age from approximately 3.7-3.0 Ma. The Bianco section is composed of marly mudstones intercalated with diatomites, with the diatomites being particularly common in the upper 50 m of the section (above 3.1 Ma). The diatomites contain an abundant benthic foraminiferal assemblage and have a low organic carbon content indicating that bottom waters were fairly welloxygenated during their deposition. Faunal and floral indicators suggest a cooling of surface waters in this region at 3.1 Ma. The diatom assemblages within the Bianco diatomites are very similar to those living in the Gulf of California, suggesting an upwelling origin for these silica-rich units. A model is proposed which attributes diatomite formation to upwelling induced by climatically controlled changes in local hydrography.

Introduction Plio-Pleistocene marine sediments outcrop extensively on the Ionian side of southern Calabria, in the foothills of the Aspromonte Mountains. Since being described in the last century by Seguenza (1880) and Cortese (1895), these late Neogene marine sequences have received little attention. In this paper we present the results of a micropaleontological and geochemical study of a previously undescribed Pliocene section located close to the 0031-0182/89/$03.50

village of Bianco (Reggio Calabria province) (Fig.l). The Bianco section was selected because it contains a fairly continuous record rich in calcareous and siliceous microfossils; the latter are not well documented in other time equivalent Italian sections. Our objectives in studying this section were both biostratigraphic and paleoenvironmental. From a biostratigraphic point of view, the Bianco section provides a rare opportunity to document the stratigraphic distribution of Pliocene

© 1989 Elsevier Science Publishers B.V.

86

D. RIO ET AL.

.... I

17' 20'E 39"20"N

1 Late Plalstocene-Holocene marine and contmenta~ sediments Late Miocene to middle Pleistocene marine sediments

Crystalhne and allochthonous untts of the C a l a b r l a n Arc t

10 Km

x~ il]iil]iii!!

x~ xx q. -k

c~

BIANCO section

CAPO SPARTIVENTO

15"E, 37"50'N

Fig.1. Geologicmap of Calabria showingthe location of the Bianco section. siliceous microfossils (diatoms, silicoflagellates and radiolaria) in the Mediterranean. From a paleoenvironmental point of view, we have attempted to reconstruct the paleoceanographic and paleoclimatic conditions which existed during the time interval represented by the Bianco section, and to evaluate the origin of the diatomites contained in the section. To meet these objectives we have carried out an interdisciplinary micropaleontological and geo-

chemical study. The microfossil groups studied include benthic and planktonic foraminifera, calcareous nannofossils, diatoms, radiolaria, silicoflagellates, and pollen.

Location, lithology and depositional setting The outcrop section studied is continuously exposed and is located approximately 3 km

STRATIGRAPHY OF PLIOCENE BIANCO SECTION, CALABRIA

inland from the Ionian coast of southern Calabria, west of the village of Bianco Nuovo (Reggio Calabria province) (Fig.l). The section is within a small late Neogene basin (Capo Spartivento Basin of Rossi and Sartori, 1982 and Ghisetti and Vezzani, 1982) spanning the Aspromonte sector of the Calabrian Arc thrustbelt, the most active element of the Alpine-Maghrebide diastrophic system. The general lithology of the Bianco section is illustrated in Fig.2. The marly mudstones are light grey in color while the intercalated diatomites are white. Neither lithology contains any distinctive sedimentary structures. This feature, together with the fact that an abundant and diversified benthic foraminiferal assemblage occurs throughout the section and that the organic carbon content is very low, suggests that bottom waters in the basin were fairly well ventilated during deposition. The autochthonous benthic foraminifera of the Bianco section are indicative of a lower epibathyal depositional environment. Specifically, the presence of Parrelloides robertsonianus, Dimorphina tuberosa, Eggerella bradyi, Epistomella exigua, Hoeglundina elegans, Laticarinina pauperata, Lingulina seminuda, Nuttalides rugosus convexus, Psammosphaera testacea and Ramulina globulifera point to an upper depth limit of about 500-700 m (Parker, 1958; Blanc-Vernet, 1969; Wright, 1978). The dominance of lagenids and the presence of Siphonina reticulata and Planulina ariminensis suggests a lower depth limit of about 1000 1300 m (Parker, 1958; Blanc-Vernet, 1969). The benthic foraminifera give no indication of any major paleobathymetric change during the deposition of the marls. We conclude that the unit was deposited on the slope (500-1000 m water depth) of a marginal basin, most likely below the oxygen minimum zone. Methods

Fifty-one samples from the Bianco section were utilized in the present study (Fig.2). Total carbonate content, as well as fine fraction (63 ~m) carbonate content, was determined

87

using a digestion technique similar to the one described by Jones and Kaiteris (1983). The organic carbon content of each sample was determined by first acidifying each sample with orthophosphoric acid and then combusting the carbonate-free samples in a Hewlett-Packard 185B CHN Analyzer. Biogenic silica determinations were made following the leaching method of DeMaster (1979), with the colorimetric analyses carried out on a Bausch and Lomb Spectronic 1001 spectrophotometer. Stable isotopic analyses (oxygen and carbon) of the planktonic foraminifer Globigerinoides ruber and the benthic foraminifer genus Planulina were carried out following the procedures of Williams and others (1977). All analyses were made utilizing a VG Isogas Sira-24 isotope ratio mass spectrometer and all values are expressed in ~-notation (%0) relative to the PDB standard. For the foraminiferal studies (benthic and planktonic), each sample was disaggregated, washed through a 63 ~tm sieve and dried. The dry residue was then sieved at 125 ~m for the benthic foraminifera and 150 ~m for the planktonic foraminifera and split into aliquots containing at least 300 benthic and planktonic specimens. Each specimen was identified and recorded as a percentage of the total assemblage. Calcareous nannofossil studies were carried out on smear slides using a light microscope (normal light and crossed nicols). For each sample 500 specimens greater than 3.5 ~tm were identified and the relative abundance of each taxa was determined. In some samples the nannofossil assemblage is dominated by small placoliths (<3.5 ~m) which are difficult to quantify. An examination of smear slides from all of the samples revealed that diatoms are only present in the diatomaceous mudstone samples. These samples were prepared using the method described by Sancetta and Silvestri (1984), which involves ultrasonic disaggregation in distilled water and repeated settling and decantation to remove clay-sized particles. An aliquot of this suspension was then dried on

88

D. RIO ET AL.

TOTAL ~o

CaCO 3 %

20

,o,

30

4o,

Fine fraction C a C O 3 % (Nennos tot. abundance)

,o

20

~o

,o

5o,

Organic 0

0 iI

C %

Oi 2

O3

SiO 2 % J

0

I

2

3

I

|

4

5

190,

180

/ / I

/ /

I

/

i

\ \ \

/

\

100

SO

r

m 10 I

[

I

I

I

I

l

I

I

Diatomites

Fig.2. Lithostratigraphic column for the Bianco section. Positions of the diatomites are indicted by the horizontal bars. Height in the section (m) and locations of samples are also shown. Carbonate, organic carbon and silica contents are plotted.

89

STRATIGRAPHY OF PLIOCENE BIANCO SECTION, CALABRIA

a cover slip and mounted on a glass slide with Permount medium. The slides were scanned at 500 x magnification for identification of stratigraphic indicator taxa and qualitative assessment of the assemblage. Approximately 200 specimens were then counted in a random traverse at 1250 x magnification, and used to calculate relative abundances of taxa. Samples for radiolarian study were acidified to remove carbonate and sieved at 44 ~m. Strewn slides were prepared and mounted in Canada balsam in the manner described by Sanfilippo and others (1985). Species abundances were estimated as percentages of the total number of specimens on the slide. A detailed taxonomic description of the radiolaria from the Bianco section is presented in Sanfilippo (1988). Samples for silicoflagellate study were acidified and strewn slides prepared for light microscope examination at 250x and 500x magnification. All specimens encountered were identified and relative abundances of individual taxa were determined based on counts of 200 specimens for each sample. Silicoflagellate paleotemperature values (Ts) were calculated according to the procedure described by Bukry (1981a) using the equation

Ts=Xw+0.5 X t

(1)

where Xw is the warm genera Corbisema and Dictyocha, and X, is the temperate genera Distephanus (quadrate) and Bachmannocena (quadrate).

Biostratigraphy and time f r a m e w o r k

Calcareous plankton biostratigraphy The calcareous plankton (planktonic foraminifera and calcareous nannofossils) provide the most reliable biochronologic framework for the Mediterranean Pliocene (Rio and Sprovieri, 1986; Rio et al., in press a; Channell et al., in press), and these groups provide the primary means of biostratigraphically dating the Bianco section. During the late Neogene the Mediterranean was a distinct biogeographic

province, and as a result regional biozonations have been developed for both the calcareous nannofossils (Schmidt, 1973; Ellis and Lohman, 1979; Raffi and Rio, 1979) and planktonic foraminifera (Bertolino et al., 1968; Cita, 1973 and 1975; Thunell, 1979 a; Spaak, 1983). In the present study we have utilized the planktonic foraminiferal zonations of Cita (1973 and 1975) and Spaak (1983) and the nannofossil scheme of Raffi and Rio (1979) emended by Rio et al. (in press a), which is easily correlated to the standard nannofossil zonations of Martini (1971) and Bukry (1973). This integrated calcareous plankton biostratigraphic scheme, and its correlation to the magnetic polarity time scale provides a high resolution time stratigraphic framework for the Pliocene of the Mediterranean (Fig.3). The main planktonic foraminiferal and nannofossil bioevents recognized in the Bianco section are shown in Fig.4. The presence of

D. asymmetricus, R. pseudoumbilica, Sphenolithus spp.and G. margaritae in the lowermost samples indicate that the basal part of the section can be assigned to the MPL3 Zone of Cita (1975) and the R.pseudoumbilica Zone of Raffi and Rio (1979). The top of the section is just above the last occurrence (S. seminulina and within the range of D. tamalis (Fig.4), thus placing the upper limit of the section in the MPL5 Zone and the D. tamalis Zone. Within the Bianco section the following bioevents can be recognized: (1) the last occurrence of G. m~trgaritae at approximately 28 m defines the MPL3/MPL4 boundary of Cita (1975); (2) the last occurrence of Sphenolithus spp. and the last common and continuous presence of R. pseudoumbilica are at approximately 62 m. While the extinction of Sphenolithus is easily recognized, the last occurrence of R.pseudoumbilica is more difficult to pinpoint because of reworking. Rio et al. (in press a) have demonstrated that these two events are stratigraphically close to each other. This level is stratigraphically equivalent to the NN15NN16 zonal boundary of Martini (1971) and the

90

D. RIO ET AL.

C A L C A R E O U S PL AN KT ON BIOSTRATIGRAPHY CHRONO~TRATIGRAPHY

POLARITY TIME SCALE MA

I

•. ' ~ / / / /

~

15-

~J

'

<

Z 2.0 -

ILl

uJ

o <

O O

C.

G. ocanlcs $.l.t_

MACINTYREI

" O. brouweri+

I '

"

I

3.0 ~

"

:

a

IX

D. triradiatus ~

I

m

D. pentllradiatus I-"

MpI R

d

"'"

D

C

N N 17'

~NTARADU0"US

--

CN12

'

Vl

=

i

<

I "mSphaemidinellopsis s p p .

o

~-JG. ~.o.~=s

¢ --

=

4.0. ' ~

MPL4

| 7

a V

Sphenolithus spp. t ' R. peeudoumbiiica f__~ ~ G . marg.rltae R. PSEUOOUM-i

MPL3

/

/

=

J.-I ~ /|

"J

Z

-

/G.

MPL2

MPL1

~////////~

NN16

!

f'

=

O

<..too

TAMALIS

L.-. G. puncticu ata

3.5-

-I

v,,

b

O. tamalisl'-

I

~NNI=

/ Lu

CN13 - -

v,,,

•

a.

NN19

O. PRODUCTUS

~

0.

"Z

IN3

b

D. BROUWERI N N 1 8 1

I

--

'm

•-J

~=~J~K,

.,J G. inflata

B

2.5

-

y//

MPL6

FORAMS

,

N

Z

"

NANNOFOSSILS RAFFI & RIO, M,~ffl OKAOA& 1979 (emend) NI, 1971 BUKRY, 19~0

C. maclntyrel ~

"G ~ c ~ r m a

I<

-

z

EVENTS

G, CARIACO EN$1S

~i < >.

III

FORAM$ CITA, t975 (emend.)

.,.,c, D. asymmetricgs C L punctlculatl

l 1 '°-m'°-

I

L

rNN14 CN11 / ° t

~--

'l'

c. RUGOSUS INN13 - - 7 - - I-?-

H. sell, ,._ A. pdmus+ r-" A. tdcomiculatull

I

IV

I

/ C I_ '-- -/

I '

TR,CO~iNCU-k,,H'~

CN10 / b

I-

l

......

,

5

~ / / / / / / / / / / / / / / / / / / / ~

II

I

6.0

Fig.3. Calcareous plankton biochronology used in this study. The correlations of the nannofossil and planktonic foraminiferal zonations to the polarity time scale is from Rio et al. (in press b).

C N 1 1 - C N 1 2 zonal b o u n d a r y of O k a d a and B u k r y (1980); (3) the last o c c u r r e n c e of G. puncticulata at a p p r o x i m a t e l y 102 m defines the base of Interval V of S p a a k (1983); (4) the first o c c u r r e n c e of G. bononiensis at a p p r o x i m a t e l y 148m defines the b o u n d a r y b e t w e e n i n t e r v a l s V a n d VI of S p a a k (1983); (5) the last o c c u r r e n c e of Sphaeroidinellopsis spp. at a p p r o x i m a t e l y 178 m defines t h e M P L 4 M P L 5 zonal b o u n d a r y of Cita (1975). T h e d i s t r i b u t i o n s of P. lacunosa and D. pentaradiatus (Fig.4) in the B i a n c o s e c t i o n r e q u i r e some discussion. T h e first o c c u r r e n c e o f P. la-

cunosa in the M e d i t e r r a n e a n has been considered to o c c u r j u s t above the e x t i n c t i o n of R. pseudoumbilica (Raffi and Rio, 1979). In the B i a n c o section, w h e r e p r e s e r v a t i o n is good and s e d i m e n t a t i o n r a t e s are high, a distinct overlap of t h e s e two forms is observed in t h e lower p a r t of the section (Fig.4). D r i e v e r (1981) has s h o w n t h a t D.pentaradiatus was v i r t u a l l y a b s e n t from the M e d i t e r r a n e a n for a n i n t e r v a l d u r i n g the middle Pliocene. At Bianco, this p a r a c m e (absence i n t e r v a l ) extends from a p p r o x i m a t e l y the last o c c u r r e n c e of G. margaritae to the last o c c u r r e n c e of Globorotalia puncticulata (Fig.4). This d i s t r i b u t i o n agrees

STRATIGRAPHY

OF PLIOCENE

91

BIANCO SECTION, CALABRIA

~d t~

uealouez

ue!zu~e!c/

,2.

>

o=Z'~g7dY~

0 ~

P 7d14/ s ! l e w e j "G

m ~

o

I

e~

£ 7d~/ nopnasd

~

sgsueguouoq 9 Z

~

~°

0 o

o

5

i°

!/L

0

! Z

~

eesde°°JAqde9

Ile~u S

~ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ ~ _1 o

o_

°

Z z z

.g o

O u~

bE =

f

iit IIIIIIIIIIIII

III

II III

I

I

I

I I

I

I

II

IIII I II

III

E

92

well with the recent findings from ODP Leg 107 in the Mediterranean (Rio et al., in press a).

Siliceous plankton biostratigraphy The standard radiolarian zonations used in tropical and subtropical regions of the open ocean (Nigrini, 1971; Sanfilippo et al., 1985) are of limited utility in the Mediterranean area because of the absence or scarcity of the index fossils. Sporadic occurrence of a microfossil group considerably diminishes its value for establishing a detailed zonation, and this is a common feature of radiolarian distributions in the Mediterranean. Furthermore, some taxonomic difficulties are caused by a certain degree of morphological dissimilarity between taxa from the Mediterranean and those from the open ocean (e.g. Stichocorys peregrina and Theocorythium trachelium, see Sanfilippo, 1988). The last occurrence of Stichocorys peregrina is at the top of the Bianco section, between the upper two samples. The lack of samples above this level weakens the case for this being the true upper limit of the species, but on the other hand it is strengthened by the consistent occurrence of this species in large numbers in all lower radiolarian-bearing samples. The last occurrence of S. peregrina occurs at the top of the Gauss normal epoch in the topical Pacific (Theyer et al., 1978) and slightly earlier in the Kaena polarity event in the North Pacific (Hays, 1970; Kling, 1973; Foreman, 1975). The following additional radiolarian events can also be recognized within the Bianco section: (1) the last occurrence of Amphirhopalum virchowii at approximately 180 m; (2) the transition of A. virchowii to A. ypsilon between 140 and 150 m; (3) the first occurrence of T. trachelium and Anthocyrtidiumjenghisi at approximately 102 m. The first occurrences of T. trachelium is a time transgressive event shown to occur at 2.5 Ma in the western Indian Ocean (Szumakov, 1982; Nigrini, 1985), approximately one million years prior to its first appearance in the eastern equatorial Pacific (Johnson and Knoll,

D. RIO ET AL.

1975; Baker, 1983), as well as above the l a s t appearance of S.peregrina. In the Bianco section the earliest appearance of T. trachelium is even earlier based on its first appearance well below the last occurrence of S.peregrina (Sanfilippo, 1988). Most of the radiolarian species present in the Bianco section are long-ranged forms which do not permit zonal assignments. Some of the species present at Bianco whose ranges extend through all of the Pliocene include: Stylatrac-

tus universus, Didymocyrtis tetrathalmus, Tholospyris rhombus, Zygocircus piscicaudatus, Eucyrtidium calvertense, Lychnodictym audax and Pseudocubus vema. The late Miocene and Pliocene tropical index fossils Spongaster berminghami, S. pentas, S. tetras, Pterocanium primatium, Phormostichoartus doliolium and Didymocyrtis penultima are absent. Based on the co-occurrences of the above species and the listed events within the section, the best estimate is that the Bianco section corresponds to the late Spongaster pentas or the early Pterocanium prismatium Zone (Fig.5). Stratigraphically important diatom taxa are rare in all samples. The only useful taxa present are Thalassiosira convexa and Nitzschia jouseae (Fig.5). They occur throughout the section and indicate an age between 4.4 Ma (first occurrence of N.jouseae) and 2.2 Ma (last occurrence of T. convexa) (Burckle, 1978). Rhizosolenia praebergonii is absent, but it is not possible to determine whether the absence is ecologic or stratigraphic. If the absence is stratigraphic, the top of the Bianco section must be older than 3.0 Ma (Burckle, 1978). This agrees with the planktonic foraminiferal biostratigraphy which provides an age of approximately 3.0 Ma for the top of the section (Figs.3 and 4). The low latitude silicoflagellate zonation of Bukry (1981b) can be applied to the Bianco section (Fig.5). The first occurrence of Dictyocha stapedia stapedia is used to identify the upper Pliocene D. stapedia stapedia Zone overlying the Dictyocha fibula Zone. Dictyocha flexatella, an upper Pliocene guide species, occurs throughout the D. stapedia stapedia

93

STRATIGRAPHY OF PLIOCENE BIANCO SECTION, CALABRIA RADIO LARI A S, p e r e g r i n a % l

11o.

-

l

lo

i

i

20

D I AT OMS

SILICOFLAGELL ATES D, s t a p e d i a D. f i b u I a %

i

stapedia s

I

1,o

i

%

~

lo

l

20

J

SILICEOUS B I O Z O N ES 3o

i

Ppris.

-

(~

=

g o

100

~

"*~

o

m 50 10

i

1

1

,

i

i

i

i

.~ i

Fig.5. Distribution patterns of stratigraphicaHy important siliceous plankton. Biozones for radiolaria (Sanfilippo et al., 1985), diatoms (Burckle, 1972) and silicoflagellates (Bukry, 1981b) are indicated on the right. Zone sampled at Bianco. The presence of Dictyocha angulata, Dictyocha perfecta and Distephanus xenus, mainly in the D. fibula Zone, help to confirm this stratigraphic assignment.

Biochronology, chronostratigraphy and sediment accumulation Utilizing the calcareous pl a nkt on biochronology for the M e d i t e r r a n e a n Pliocene (Fig.3),

the age of the base of the Bianco section can be placed between 3. 6Ma (R. pseudoumbilica LO) and 3.8 Ma (D. asymetricus FO). The age of the top of the section is slightly y o u n g e r t h a n 3.05 Ma (Sphaeroidinellopsis spp. LO). Pliocene c h r o n o s t r a t i g r a p h y for the Medit e r r a n e a n is presently in a state of flux due to the lack of agreement on its subdivision (bipartition vs. tripartition) and to strati-

94

D. RIO ET AL.

graphic problems in the stratotypes of both the Zanclean (Lower Pliocene) and Piacenzian (Late Pliocene) (Rio et al., in press b). Using the generally accepted proposal of Cita (1973) and Berggren and Van Couvering (1974), the lower part of the Bianco section (up to the G. margaritae LO and R.pseudoumbilica LO) should be placed within the Early Pliocene (Zanclean), with the remainder of the section being Late Pliocene (Piacenzian) in age (Fig.4). Workers utilizing a threefold subdivision of the Pliocene (i.e. Ruggieri and Selli, 1948) would place the lower Bianco section (up to the G. bononiensis FO) within the Early Pliocene and the upper 40 m of the section within the Middle Pliocene. Using the biochronology of Rio and others (in press b), an age-depth plot has been constructed for the Bianco section (Fig.6). This figure indicates that the rate of sediment accumulation was fairly constant, varying between 300 and 350 m/m.y.

Marine p a l e o e n v i r o n m e n t during deposition of the Bianco section The interval from 3.7 to 3.0 Ma was a time of significant change in climatic conditions in the Mediterranean region (Thunell et al., in press; Rio et al., in press c). A subtropical planktonic foraminiferal assemblage dominated the Mediterranean during most of this period (Ciaranfi and Cita, 1973; Thunell, 1979 b; Zachariasse and Spaak, 1983; Glacon et al., in press). At approximately 3.1 Ma a significant cooling began in the Mediterranean and is recorded in faunal (Thunell, 1979 b; Sprovieri, 1978; Van der Zwaan, 1983; Zachariasse and Spaak, 1983; Glacon et al., in press), pollen (Suc, 1984; Bertoldi et al., in press), and oxygen isotope records (Keigwin and Thunell, 1979; Thunell and Williams, 1983; Van der Zwaan and Gudjonsson, 1986; Thunell et al., in press). This cooling at 3.1 Ma is not a local or regional event, but has been observed globally (Shackleton and Opdyke, 1977; Keigwin, 1982, 1987;

MA 2,5

Sphaer LO

3.0 G b. FO

G.p LO 3 3 -3.~.~.

~."'~

- I m ~/

~_ ~'--30t)'''

GmLO R.p.LO ~ 3.5-36 " H I " ~ ' - -

3.5

350 m . . . .

GrnLO~Rp LO ~ S p h e n

10

5'0

LO

~Gp

100

LO

~Gb

150

FO

SphaerLO~

190 m

Fig.6. A g e - d e p t h plot for the Bianco section based on selected calcareous p l a n k t o n biostratigraphic events. The correlation of the calcareous p l a n k t o n events to the polarity time scale is from Rio and others (in press b). Sedimentation rates (m/m.y.) for different intervals of the section are indicated.

95

STRATIGRAPHY OF PLIOCENE BIANCO SECTION, CALABRIA

Leonard et al., 1984; Hodell et al., 1983; Prell, 1984) and probably reflects an intensification of glacial activity (Keigwin, 1987).

Surface water conditions Various indicators of surface water temperature and continental climate are presented in Fig.7. Relatively high abundances of the warm water planktonic foraminiferal genus Globi-

c~ISO

o?

i -;2,o

, -3,0

,

C 17

lo

•

s

W

Globigerino*do

$

$PP %

W

POLLEN % 50

,

I00

I

1go

Ioo

i -110

SILICOFL AGELL ATE PALEOTEMP %

C pelogicus %

(G r u b e r ) %o

gerinoides in the lower 140 m of the section suggest that surface water temperatures were moderately warm during this interval. The decrease of this genus and the increase of the cool-water coccolith species C.pelagicus (McIntyre and Be, 1967; Raffi and Rio, 1981) at 140m is interpreted as a cooling of surface waters. This cooling is also evident in the silicoflagellate paleotemperature record (Fig.7). These faunal and floral changes at

-1 --

!

Ig"4]l I l i i i

,12[]3

[iili

ill I I

4IE]IC],

Fig.7. Time series records of various surface water temperature and continental climate indicators. The calcareous nannofossil C. pelagicus is a cool-water indicator and the planktonic foraminiferal genus Globigerinoides is a warm water indicator. The silicoflagellate paleotemperatures were derived using the equation by Bukry (1981b). The pollen spectra symbols are as follows: (1) Taxodiaceae, (2) deciduous forest, (3) Mediterranean evergreen, (4) Pinaceae, (5) Picea-Abies, (6) other arboreal elements, and (7) non-arboreal plants.

96

140 m coincide with the first occurrence of the cool water planktonic foraminifera Globorotalia bononiensis (Fig.4) which has been dated at 3.15 Ma (Rio et al., in press b). The pollen record also reveals a significant vegetational change at this time (Fig.7). Specifically, the non-arboreal plants and Mediterranean evergreen declined, and the Picea-Abies group increased. These floral changes are indicative of the establishment of cool, humid climatic conditions in southern Calabria at around 3.15 Ma. These observations differ from those of Suc (1984) for the northwestern Mediterranean where a change to more arid conditions occurs at 3.1 Ma. This difference reflects the existence of a climatic gradient within the Mediterranean at this time. The G. ruber 5180 record is marked by a gradual decrease in values between approximately 90 and 140m (Fig.7), indicating a warming of surface waters. This warming in the 5180 record is stratigraphically equivalent to the interval between the last occurrence of G.puncticulata and t h e first occurrence of G. bononiensis (Fig.4). iThese two taxa are members of the cool water Globorotalia inflata group, and the gap in their stratigraphic distribution has been attributed to a climatic amelioration (Zachariasse and Spaak, 1983). At 2.5%0 increase in 5180 occurs between 140 and 150 m, reflecting a sudden cooling. Above 150m, the 5180 record displays a greater amount of variability than below this level (Fig.7), although this may be baised by different sampling densities. The timing of this increase in the Bianco 5180 record makes it roughly synchronous with a similar event observed in the open ocean (Shackleton and Opdyke, 1977; Keigwin, 1982, 1987). A major lithologic change is also associated with the cooler conditions that developed above 140 m. In the lower 140 m of the section, which represents approximately 500,000 years, there are only three diatomites (Fig.4). In contrast, eight diatomites were deposited in the 150,000 year period contained in the upper 50 m of the section. This considerable increase in the frequency of diatomite formation above

D. RIO ET AL.

140 m is a further indication of a major change in climatic/oceanographic conditions at approximately 3.1 Ma. Various aspects of our sedimentological and micropaleontological data can be used to evaluate the origin of the diatomites. In general, the distribution of opaline silica in deep sea sediments is primarily governed by surface productivity (Heath, 1974; Broecker and Peng, 1982; Calvert, 1983). Thus the relatively high biogenic silica content in the diatomites relative to the marls suggests that there was an increase in productivity during diatomite formation (Fig.2). The marls at Bianco are virtually barren of biogenic silica, implying lower productivity during their deposition. The most striking feature of the planktonic foraminiferal assemblages associated with the diatomites is the relatively high abundance of Globigerina bulloides and/or Neogloboquadrina spp. (Fig.8). Both of these forms are typical of highly productive upwelling areas in the northern Indian Ocean (Prell and Curry, 1981), in the Panama Basin (Thunell and Reynolds, 1984, off northwest Africa (Thiede, 1975; Berger et al., 1978), and off Peru (Thiede, 1983). According to Diester-Haas (1983) high abundances of the cool water species G. bulloides distinguish upwelling regions from areas of high productivity induced by river discharge. The coccolith genus Helicosphaera has also been reported to be associated with upwelling regimes (Perch-Nielsen, 1985) and is abundant within the diatomites (Fig.8). Based on these observations, we tentatively conclude that the Bianco diatomites are related to upwelling. The diatom assemblages found in Bianco provide perhaps the best means of deciphering the origin of the diatomites. Schrader and his colleagues (Schrader and Baumgartner, 1983; Schuette and Schrader, 1979, 1981a) have clearly demonstrated that the composition of diatom assemblages can be used to distinguish upwelling regions from normal oceanic environments. Within the diatomites, diatoms are abundant and well-preserved, and the

97

STRATIGRAPHY OF PLIOCENE BIANCO SECTION, CALABRIA

:I¸

¢)

QI

c~

"l ~o u~

o ¢o ~ N ~5 e_

X o

ig

g~ u

¢D

2, .¢

,-d

;> c9

tJ

/ / 1 /

IIIIllllllll

I I Ill

II Illl

I

I

I

I I

Ill

I

III

I] Illill

J

I IF I I IF

r o E

t~ tt0

98

assemblage is a mixture of oceanic and neritic taxa. The Bianco diatomites contain relatively high abundances of Actinocyclus octonarius, Thalassionema nitzschioides, Thalassiosira spp. and Chaetoceros resting spores (Fig.8), all of which are characteristic of modern coastal upwelling areas (Schuette and Schrader, 1979, 1981a. A unique feature of the Bianco diatom assemblages is the occurrence of Thalassiosira simonsenii. This species was originally described from plankton tow material from the Gulf of California (Hasle and Fryxell, 1977), and has not previously been reported outside of this region. In fact, the general make-up of the Bianco diatom assemblages bears a strong resemblance to that found in the late Pleistocene Gulf of California. Typical assemblages for Bianco and the Gulf of California (DSDP Site 480, Guaymas Basin) were determined by averaging diatom species abundances for 10 samples from each location (Table I). Except for differences due to evolutionary events, the same taxa are found in both locations. The biggest difference between the two sites is the considerably higher abundance of A. octonarius in the Bianco section; otherwise, the taxa occur in fairly similar proportions (Table I). This floral similarity suggests that the Gulf of California may serve as a modern analog for the conditions which existed during the deposition of the Bianco section. This implies that the sequence at Bianco was deposited within a marginal basin that had somewhat restricted exchange with the open Mediterranean, and that periodic upwelling was responsible for diatomite formation. Bottom water conditions Upwelling during diatomite deposition resulted in a high organic carbon flux to the seafloor. However, the Bianco diatomites do not contain a higher organic carbon content than the surrounding marls, the values for the entire section range from 0.1 to 0.3% (Fig.9). This implies that during diatomite deposition bottom waters remained sufficiently oxygen-

D. RIO ET AL. TABLE I D i a t o m a s s e m b l a g e s of the Bianco Section and Gulf of California D S D P Site 480. The a v e r a g e a b u n d a n c e of t a x a in ten s a m p l e s from each section is s h o w n as a p e r c e n t a g e of t o t a l d i a t o m assemblage. Taxon

Actinocyclus curvatulus A. octonarius Actinoptychus senarius Asteromphalus spp. Azpeitia nodulifer Bacteriastrum spp. Chaetoceros spores Coscinodiscus gigas C. radiatus Cyclotella spp. Cymatosira spp. Hernidiscus cuneiforrnis Lithodesmium spp. Nitzschia reinholdii Paralia sulcata Pseudoeunotia doliola Rhizosolenia barboi R. bergonii Rhizosolenia spp. Roperia tesselata Stellarima microtrias Stephanopyxis turris Thalassionema nitzschioides Thalassiosira eccentrica T. leptopa T. oesstrupii T. simonsenii T. symbolophora Thalassiothrix longissima Shelf p e n n a t e s

Bianco

Site 480

(%)

(%)

2

3

26

1

6

9

-

2

5

8

<1 17

<1 25

<1 4

<1 4

-

1 1

-

3 <1 2

1 <1 Extinct

1 N o t evolved 1

1 6 Extinct

-

1 1

2

2 2 1

6 2 -

21

15

1 1 1 5 1 1

1 2 7 3 3

6

1

Notes: " S h e l f p e n n a t e s " r e p r e s e n t s a m i x t u r e of b e n t h i c genera, and indicates displaced material. T h e Bianco section is m o r e diverse, a n d h a s several o t h e r neritic taxa, each less t h a n 1~o.

ated to degrade the increased supply of organic matter to the seafloor. The species compositions of the benthic foraminiferal assemblages provide additional information regarding bottom water conditions. In the lower 140 m the lagenids are a major component of the benthic fauna, on average accounting for more than 25~/o of the assemblage (Fig.9). Above 140m there is a noticeable decrease in the abundance of this

STRATIGRAPHY OF PLIOCENE BIANCO SECTION, CALABRIA

99

u-

R

u -

;~ee

5 3 5

m ~

5

0

flUlllrrlll

i i ill

i i iiii

i

I

I

f

II

III

I

III

II

m

111111 I II I III

E

~

i00

group, which drops to 5-20% of the fauna. Throughout the Mediterranean, the lagenids are typically associated with upper bathyal, normal marine environments (Blanc Vernet, 1969; Van der Zwaan, 1982, 1983). The decrease in importance of the lagenids at 140m or approximately 3.1 Ma in the Bianco section has also been observed at other localities in the Mediterranean and has been attributed to the cooling that occurred at this time (Sprovieri, 1986). The benthic foraminiferal diversity record contains two important features (Fig.9). First, the diatomites are characterized by lower diversity than the marls. Second, there is a long term trend for a decrease in diversity through time. In particular, there is a distinct shift to lower diversity above 140 m. This drop in diversity reflects the benthic foraminiferal turnover previously described by Sprovieri (1986) and is coincident with the cooling observed at 3.15 Ma. The Cibicididae group contains two distinct components with different ecological meanings. The Cibicidoides species (C. bradyi, C. pachyderma and C. ungerianus) are deep water, epifaunal forms characteristic of a well-oxygenated environment (Corliss and Chen, 1988). These species are present in uniformily low abundances throughout the Bianco section (Fig.9). In contrast, Cibicides lobatulus and Cibicides refulgens are shallow water forms and are considered to be displaced where present in Bianco. It is important to note that the highest abundances of these shallow water Cibicides species occur within the marls and are suggestive of increased erosion of inner shelf sediments at these times. A number of benthic foraminiferal taxa including Bulimina, Bolivina and Uvigerina have previously been used as indicators of low oxygen environments (Douglas and Woodruff, 1981). In the Bianco section, high abundances (15-35~/o) of Bulimina species (B. costata type and B. aculeata type) are found within the diatomites (Fig.9). In contrast, the marls typically contain less than 5% of these species. Corliss (1985) and Corliss and Chen (1988)

D. RIO ET AL.

have reported that benthic foraminifera occupy distinct microhabitats, infaunal or epifaunal, and the predominance of one group over the other may be related to food availability. According to these workers, an epifaunal habitat would be most advantageous in an environment where the flux of organic carbon to the seafloor is low and food is a limiting factor. Conversely, infaunal forms are suggested to be more abundant in regions where there is a high flux of organic carbon to the bottom (Corliss, 1985; Corliss and Chen, 1988). The observed inverse distribution patterns of the Bulimina species and Cibicidoides species in the Bianco section may be explained in terms of this microhabitat model. The moderate abundances of the epifaunal Cibicidoides species in the marls are interpreted as reflecting a normal open marine environment in which the flux of organic carbon to the seafloor is relatively low and bottom waters are well oxygenated. Conversely, the high abundances of the infaunal Bulimina species in the diatomites may reflect an increased flux of organic carbon and possibly a decrease in bottom water oxygen content.

Depositional model Previous studies on the origin of late Neogene diatomites from the Mediterranean region have proposed that these facies were deposited either during times of increased continental run-off (Van der Zwaan, 1979; Gudjonsson and Van der Zwaan, 1985) or increased surface water productivity associated with upwelling (McKenzie et al., 1979). Our data for the Bianco section suggest an upwelling origin for these particular diatomites. The depositional and hydrographic conditions that we envision during the formation of both the Bianco marls and diatomites are illustrated in Fig.10. We propose that the Bianco marls were deposited under low productivity conditions (Fig.10). This is supported by the virtual absence of any biogenic silica in the marls

101

STRATIGRAPHY OF PLIOCENE BIANCO SECTION, CALABRIA

A. MARL DEPOSITION

Low

Productivity

B. DIATOMITE DEPOSITION

High P r o d u c t i v i t y

[: ; : : :l - D i a t o m i t e

Fig.10. Model for the deposition of the Bianco marls and diatomites.

(Fig.2d). The marls contain very little organic carbon and an abundant and diverse benthic foraminiferal fauna (Fig.9). These findings suggest that bottom waters were well-oxygenated during marl deposition. It is proposed that an anti-estuarine circulation existed in the Bianco basin during the deposition of the marls (Fig.10). In contrast to the marls, our micropaleontological and geochemical data suggest that the

Bianco diatomites were produced by upwelling and high productivity. The simple presence of these silica-rich layers is an indication of periodically increased productivity. More importantly, the diatom assemblage in the Bianco diatomites is very similar to that found in the Gulf of California and this suggests an upwelling origin. In addition, the diatomites are marked by increases in the abundances of G. bulloides and/or N. dutertrei, two plank-

102

tonic foraminifera characteristic of upwelling regions. The increased flux of organic matter to the seafloor during diatomite deposition resulted in greater oxygen utilization and most likely reduced bottom water oxygen concentrations (Fig.10). However, the lack of any significant organic carbon accumulation and the presence of a benthic foraminiferal fauna in the diatomites clearly indicates that bottom water did not become anoxic. We speculate that an estuarine circulation existed in the Bianco Basin during diatomite formation and that this facilitated the upwelling of nutrient-rich waters (Fig.10). Rapid changes in climatic conditions would appear to be the most plausible explanation for the alternation between anti-estuarine and estuarine flow patterns in the Bianco Basin. As previously discussed, the frequency of diatomite deposition increased significantly above 3.1 Ma and this was also the time at which there was an intensification of global glacial/ interglacial climatic contrasts (Keigwin, 1987). The glacial/interglacial climatic oscillations caused localized changes in hydrographic conditions in the Bianco region that led to alternating marl and diatomite deposition.

Acknowledgements This work was supported by CNR Grant 85.00993.05/115.00443 to D. Rio (Progetto Bilaterale Italia-USA), NSF Grant EAR-8506844 and NATO Grant 0119/87 to R. Thunell, and NSF Grants OCE-8508242 and OCE-8707417 to A. Sanfilippo. We thank E. Masini and E. Tappa for drafting the figures.

References Amodio-Morelli, L., Bonardi, G., Colonna, V. et al., 1976. L'arco Calabro-Peloritano nell'orogene AppenninicoMaghrebi. Mem. Soc. Geol. Ital., 17: 1-60. Baker, C., 1983. Evolution and hybridization in the radiolarian genera Theocorythium and Lamprocyclas. Paleobiology, 9: 341-354. Berger, W. H., Diester-Haas, L. and Killingley, J. S., 1978. Upwelling off northwest Africa: the Holocene decrease as seen in carbon isotopes and sedimentological indicators. Oceanol. Acta, 1: 3-7.

D. RIOET AL. Berggren, W. A. and Van Couvering, J. A., 1974. The Late Neogene. Palaeogeogr., Palaeoclimatol., Palaeoecol., 16: 1-216. Bertoldi, R., Rio, D. and Thunell, R., in press. PliocenePleistocene vegetational and climatic evolution of the south-central Mediterranean. Palaeogeogr., Palaeoclim., Palaeoecol. Bertolino, V. et al., 1967. Proposal for a biostratigraphy of the Neogene in Italy based on planktonic foraminifera. G. Geol., 35: 23-30. Blanc-Vernet, L., 1969. Contribution ~ l'~tude des foraminif~res de Mediterran~e. Rec. Trav. Stratigr. Mar. Endocime, 64: 1-281. Broecker, W. S. and Peng, T. H., 1982. Tracers in the Sea. Eldigio, New York, N.Y., 690 pp. Bukry, D., 1973. Low latitude coccolith biostratigraphic zonation. N. T. Edgar, J. B. Saunders et al., Initial Reports of the Deep Sea Drilling Project, 15. U.S. Government Printing Office, Washington, D.C., pp. 685-703. Bukry, D., 1981a. Silicoflagellate stratigraphy of offshore California and Baja California, Deep Sea Drilling Project Leg 63. In: R. Yeats, B. U. Haq et al., Initial Reports of the Deep Sea Drilling Project, 63. U.S. Government Printing Office, Washington, D.C., pp. 539-557. Bukry, D., 1981b. Synthesis of silicoflagellate stratigraphy for Maestrichtian to Quaternary marine sediments. Soc. Econ. Paleontol. Mineral. Spec. Publ., 32: 433-444. Burckle, L. H., 1978. Early Miocene to Pliocene diatom datum levels for the equatorial Pacific. Geol. Res. Devel. Cont. Rep. Indones. Spec. Publ., 1: 25-44. Calvert, S. E., 1983. Geochemistry of Pleistocene sapropels and associated sediments from the eastern Meditero ranean. Oceanol. Acta, 6: 225-267. Channell, J., Rio, D., Sprovieri, R. and G. Glacon, in press. Biomagnetostratigraphic correlations at Sites 650, 651, 652 and 654 (Leg 107 in the Tyrrhenian Sea). In: K. Kastens, J. Mascle et al., Proc. the Ocean Drilling Program, vol. 107B. Ciaranfi, N. and Cita, M. B., 1973. Paleontological evidence of changes in the Pliocene climates. In: W. B. F. Ryan, K. J. Hsu et al., Initial Reports of the Deep Sea Drilling Project, 13. U.S. Government Printing Office, Washington, D.C. Cita, M. B., 1973. Pliocene biostratigraphy and chronostratigraphy. In: W. B. F. Ryan, K. J. Hsu et al., Initial Reports of the Deep Sea Drilling Project, 13. U.S. Government Printing Office, Washington, D.C. Cita, M. B., 1975. Planktonic foraminiferal biozonation of the Mediterranean Pliocene deep sea record. A revision. Riv. Ital. Paleontol., 81: 527-594. Corliss, B. H., 1985. Microhabitats of benthic foraminifera within deep sea sediments. Nature, 314: 435-438. Corliss, B. H. and Chen, C., 1988. Morphotype patterns of Norwegian Sea deep-sea benthic foraminifera and ecological implications. Geology, 16: 716-719. Cortese, E., 1895. Descrizione geologica della Calabria. Mem. Descr. Carta Geol. Ital., 9: 1-310. Demaster, D. J., 1979. The marine budgets of silica and 32Si. Thesis. Yale Univ. New Haven, Conn., 307 pp.

STRATIGRAPHYOF PLIOCENEBIANCOSECTION,CALABRIA Diester-Haass, L., 1983. Differentiation of high oceanic fertility in marine sediments caused by coastal upwelling and/or river discharge off northwest Africa during the late Quaternary. In: J. Thiede and E. Seuss, (Editors), Coastal Upwelling - - Its Sediment Record. Plenum, New York, N.Y., pp. 399-420. Douglas, R. and Woodruff, F., 1981. Deep-sea benthic foraminifera. In: C. Emiliani, (Editor), The Sea. Wiley, New York, N.Y., 7, pp. 1233-1327. Driever, B., 1981. A quantitative study of Pliocene associations of Discoasters from the Mediterranean. Proc. K. Ned. Akad. Wet., 84: 437-455. Ellis, C. and Lohman, W. H., 1979. Neogene calcareous nannoplankton biostratigraphy in eastern Mediterranean deep-sea sediments (DSDP Leg 42A, Sites 375 and 376). Mar. Micropaleontol., 4: 61-84. Foreman, H. P., 1975. Radiolaria from the North Pacific; Deep Sea Drilling Project, Leg 32. In: R. L. Larson, R. Moberly et al., Initial Reports of the Seep Sea Drilling Project, 32. U.S. Government Printing Office, Washington, D.C. pp. 579-676. Ghisetti, F. and Vezzani, L., 1982. Different styles of deformation in the Calabrian arc (southern Italy): implications for seisotectonic zoning. Tectonophysics, 85:149 165. Gudjonsson, L. and Van der Zwaan, G. J., 1985. Anoxic events in the Pliocene Mediterranean: stable isotope evidence of run-off. Proc. K. Ned. Akad. Wet., Ser. B, 88: 69~82. Hasle, G. R. and Fryxell, G. A., 1977. The genus Thalassiosira: some species with a linear areola array. Nova Hedwigia Beih., 54: 15-66. Hays, J. D., 1970. Stratigraphy and evolutionary trends of Radiolaria in North Pacific deep sea sediments. In: J. D. Hays, (Editor), Geological Investigations of the North Pacific. Geol. Soc. Am. Mem., 126: 185-218. Heath, G. R., 1974. Dissolved silica and deep-sea sediments. Soc. Econ. Paleontol. Mineral. Spec. Publ., 20: 77-93. Hodell, D. A., Kennet, J. P. and Leonard, K. A., 1983. Climatically-induced changes in vertical water mass structure of the Vema Channel during the Pliocene: evidence from DSDP Sites 516A, 517 and 518. In: Initial Reports of the Deep-Sea Drilling Project, 72. U.S. Government Printing Office, Washington, D.C. Johnson, D. A. and Knoll, A. H., 1975. Absolute ages of Quaternary radiolarian datum levels in the equatorial Pacific. Quat. Res., 5: 99-110. Jones, G. A. and Kaiteris, P., 1983. A vacuum-gasometric technique for rapid and precise analysis of calcium carbonate in sediments and soils. J. Sediment. Petrol., 53: 655-660. Keigwin, L. D., 1982. Stable isotope stratigraphy and paleoceanography of Sites 502 and 503. In: W. L. Prell, J. V. Gardner et al., Initial Reports of the Deep Sea Drilling Project, 68. U.S. Government Printing Office, Washington, D.C., pp. 445-453. Keigwin, L. D., 1987. Pliocene stable isotope record of DSDP Site 606: sequential events of 180 enrichment beginning at 3.1 Ma. In: Initial Reports of the Deep Sea

103 Drilling Project, 94. U.S. Government Printing Office, Washington, D.C. Keigwin, L. D. and Thunell, R. C., 1979. Middle Pliocene climatic change in the western Mediterranean from faunal and oxygen isotopic trends. Nature, 282: 292-296. Kling, S. A., 1973. Radiolaria from the eastern Pacific, Deep Sea Drilling Project Leg 18. In: L. D. Kulm, R. von Huene et al., Initial Reports of the Deep Sea Drilling Project, vol. 18. U.S. Government Printing Office, Washington, D.C., pp. 617-671. Leonard, K. A., Williams, D. F. and Thunell, R. C., 1984. Pliocene paleoclimatic and paleoceanographic history of the South Atlantic Ocean: stable isotopic records from Leg 72 DSDP Sites 516A and 517. In: Initial Reports of the Deep Sea Drilling Project, 72. U.S. Government Printing Office, Washington, D.C. Martini, E., 1971. Standard Tertiary and Quaternary calcareous nannoplankton zonation. In: A. Farinacci, (Editor), Proc. 2nd. Plankton Conf, Roma, 2, pp. 739-785. Malinverno, A. and Ryan, W. B, F., 1986. Extension in the Tyrrhenian Sea and shortening in the Appenines as a result of arc migration driven by sinking of the lithosphere. Tectonics, 5 (2): 227 245. McIntyre, A. and Be, A. W. H., 1967. Modern coccolithophoridae of the Atlantic Ocean. Deep-Sea Res., 14: 561-597. McKenzie, J., Jenkyns, H. and Bennet, G., 1979. Stable isotopic study of the cyclic diatomite-claystones from the Tripoli formation, Sicily: a prelude to the Messinian Salinity Crisis. Palaeogeogr., Palaeoclimatol., Palaeoecol. 29, 125-141. Nigrini, C. A., 1971. Radiolarian zones in the Quaternary of the equatorial Pacific Ocean. In: B. M. Funnell and W. R. Riedel, (Editors), The Micropaleontology of Oceans. Cambridge Univ. Press, pp. 443-461. Nigrini, C. A., 1985. Radiolarian biostratigraphy in the central equatorial Pacific, Deep Sea Drilling Project Leg 85. In: L. Mayer, F. Theyer et al., Initial Reports of the Deep Sea Drilling Project, 85. U.S. Government Printing Office, Washington, D.C., pp. 511-551. Okada, H. and Bukry, D., 1980. Supplementary modification and introduction of code numbers to the low latitude coccolith biostratigraphic zonation. Mar. Mieropaleontol., 5: 321-325. Parker, F. L., 1958. Eastern Mediterranean foraminifera. Rep. Swed. Deep-Sea Exped. 1947-1948, 4: 217-283. Perch-Nielsen, K., 1985. Cenozoic calcareous nannofossils. In: H. M. Bolli, J. B. Saunders and K. Perch-Nielsen, (Editors), Plankton Stratigraphy. Cambridge Univ. Press, pp. 427-554. Prell, W. L., 1984. Covariance patterns of foraminiferal 1sO: An evaluation of Pliocene ice volume changes near 3.2 million years ago. Science, 226: 692-694. Prell, W. L. and Curry, W. B., 1981. Faunal and isotopic indicators of monsoonal upwelling in the Arabian Sea. Oceanol. Acta, 4: 91-98. Rio, D. and Sprovieri, R., 1986. Biostratigrafia integrata del Pliocene-Pleistocene inferiore Mediterraneo in un ottica di stratigrafia sistemica. Boll. Soc. Paleontol. Ital., 25: 65-85.

104 Rafli, I. and Rio, D., 1979. Calcareous nannofossil biostratigraphy of DSDP Site 132- Leg 13 Tyrrhenian Sea (Western Mediterranean). Riv. Ital. Paleontol. Stratigr., 85: 127-172. Rio, D., Rafli, I. and Villa, G., in press a. Calcareous nannofossil quantitative distribution patterns during the Pliocene and Pleistocene in the western Mediterranean. In: K. Kastens, J. Mascle et al., Proc. Ocean Drilling Program, 107 (B). Rio, D., Sprovieri, R., Thunell, R., Vergnaud-Grazzini, C. and Glacon, C., in press b. Pliocene-Pleistocene paleoenvironmental history of the western Mediterranean: a synthesis of ODP Site 653. In: K. Kastens, J. Mascle et al., Proc. Ocean Drilling Program, 107B. Rossi, S. and Sartori, R., 1982.A seismic reflection study of the external Calabrian arc in the northern Ionian Sea (eastern Mediterranean). Mar. Geophys. Res., 4: 403-426. Ruggieri, G. and Selli, R., 1949. I1 Pliocene e il postPliocene dell Emilia. G. Geol., 20: 1-14. Sancetta, C. and Silvestri, S., 1984. Diatom stratigraphy of the late Pleistocene (Bruhnes) subarctic Pacific. Mar. Micropaleontol. 9: 263-274. Sanfilippo, A., 1988. Pliocene radiolaria from Biancc, Calabria, Italy. Micropaleontology, 34: 159-180. Sanfilippo, A., Westberg-Smith, M. J. and Riedel, W. R., 1985. Cenozoic Radiolaria. In: H. M. Bolli, K. PerchNielsen and J. B. Saunders, (Editors), Plankton Stratigraphy. Cambridge Univ. Press, pp. 631-712. Schmidt, R. R., 1973. A calcareous nannoplankton zonation for the Upper Miocene-Pliocene deposits from the southern Aegean area, with a comparison to Mediterranean stratotype localities. Proc. K. Ned. Akad. Wet., 76: 287-310. Schrader, H. and Baumgartner, T., 1983. Decadal variation of upwelling in the Central Gulf of California. In: J. Thiede and E. Seuss, (Editors), Coastal Upwelling - - Its Sediment Record. Plenum Press, New York, N.Y., pp. 247-276. Schuette, G. and Schrader, H., 1979. Diatom taphocoenoses in the coastal upwelling area of western South America. Nova Hedwigia, 64: 359-378. Schuette, G. and Schrader, G., 1981a. Diatom taphocoenoses in the coastal upwelling area off southwest Africa. Mar. Micropaleontol., 6: 131-155. Schuette, G. and Schrader, H., 1981b. Diatoms in surface sediments: a reflection of coastal upwelling. In: F. A. Richards, (Editor), Coastal Upwelling. Am. Geophys. Union, Washington, D.C., pp. 372-380. Seguenza, G., 1880. Le formazioni terziarie nella provincia di Reggio (Calabria). R. Accad. Lincei Mem., 4: 1-446. Shackleton, N. J. and Opdyke, N. D., 1977. Oxygen isotope and paleomagnetic evidence for early Northern Hemisphere glaciation. Nature, 270: 216-219. Speak, P., 1983. Accuracy in correlation and ecological aspects of the planktonic foraminiferal zonation of the Mediterranean Pliocene. Utrecht Micropaleontol. Bull., 28: 1-160. Sprovieri, R., 1978. I foraminifieri bentonici della sezione Plio-Pleistocenica di Capo Rossello (Agrigento, Sicily). Boll. Soc. Paleontol. Ital., 17: 68-97.

D. RIOET AL. Sprovieri, R., 1985. Paleotemperature changes and speciation among benthic foraminifera in the Mediterranean Pliocene. Boll. Soc. Paleontol. Ital., 24: 13-21. Sprovieri, R., Thunell, R. and Howell, M., 1986. Paleontological and geochemical analysis of three laminated units of late Pliocene-early Pleistocene age from the Mont San Nicola section in Sicily. Riv. Ital. Paleontol. Stratigr., 92: 401-434. Suc, J. P., 1984. Origin and evolution of the Mediterranean vegetation and climate in Europe. Nature, 307: 429-432. Szumakow, L., 1982. Radiolarian biostratigraphy of the central equatorial Indian Ocean. Thesis. Brown Univ. Theyer, F., Mato, C. and Hammond, S., 1978. Paleomagnetic and geochronologic calibration of latest Oligocene to Pliocene radiolarian events, equatorial Pacific. Mar. Micropaleontol., 3: 377-395. Thiede, J., 1975. Distribution of foraminifera in surface waters of a coastal upwelling area. Nature, 253: 712-714. Thiede, J., 1983. Skeletal plankton and nekton in upwelling water masses off northwestern South America and northwest Africa. In: J. Thiede and E. Seuss, (Editors), Coastal Upwelling - - Its Sediment Record. Plenum Press, New York, N.Y., pp. 183-208. Thunell, R. C., 1979a. Mediterranean Neogene planktonic foraminiferal biostratigraphy: Quantitative results from DSDP sites 125, 132 and 372. Micropaleontology, 25: 412-437. Thunell, R. C., 1979b. Pliocene-Pleistocene paleotemperature and paleosalinity history of the Mediterranean Sea: results from DSDP Sites 125 and 132. Mar. Micropaleontol., 4: 173-187. Thunell, R. C. and Williams, D. F., 1983. The stepwise development of Pliocene-Pleistocene paleoclimatic and paleoceanographic conditions in the Mediterranean: oxygen isotopic studies of DSDP Sites 125 and 132. Utrecht Micropaleontol. Bull., 30: 11-128. Thunell, R. C. and Reynolds, L., 1984. Sedimentation of planktonic foraminifera: seasonal changes in species flux in the Panama Basin. Micropaleontology, 30: 241-260. Thunell, R., Williams, D., Tappa, E., Rio, D. and Ram, I., in press. Pliocene-Pleistocene stable isotope record for ODP Site 653, Tyrrhenian Sea: implications for the paleoenvironmental history of the Mediterranean. In: K. Kastens, J. Mascle et al., Proc. Ocean Drilling Program, 107 (B). Van der Zwaan, G. J., 1979. The pre-evaporite late Miocene environment of the Mediterranean: stable isotopes of planktonic foraminifera from section Falconara, Spain. K. Ned. Akad. Wet. Ser., B 82: 487-502. Van der Zwaan, G. J., 1982. Paleoecology of Late Miocene Mediterranean foraminifera. Utrecht Micropaleontol. Bull., 25: 1-202. Van der Zwaan, G. J., 1983. Quantitative analyses and the reconstruction of benthic foraminiferal communities. Utrecht Micropaleontol. Bull. 30, 49-69. Van der Zwaan, G. and Gudjonsson, L., 1986. Middle Miocene-Pliocene stable isotope stratigraphy and paleoceanography of the Mediterranean. Mar. Micropaleontol., 10: 71-90.

STRATIGRAPHYOF PLIOCENEBIANCOSECTION,CALABRIA Williams, D. F., Sommer, M. A. and Bender, M. L., 1977. Carbon isotopic compositions of recent planktonic foraminiferal of the Indian Ocean. Earth Planet. Sci. Lett., 36: 391-403. Wright, R., 1978. Neogene paleobathymetry of the Mediterranean based on benthic foraminifers from DSDP Leg 42A. In: K. Hsu, W. Ryan et al., Initial Reports of the

105 Deep Sea Drilling Project, 42A. U.S. Government Printing Office, Washington, D.C., pp. 837-846. Zachariasse, W. J. and Spaak, P., 1983. Middle Miocene to Pliocene paleoenvironmental reconstruction of the Mediterranean and adjacent Atlantic Ocean: planktonic foraminiferal record of southern Italy. Utrecht Micropaleontol. Bull., 30:91 110.