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paleogene boundary and planktonic foraminifera in the flyschgosau (Eastern Alps, Austria)
Palaeogeography, Palaeoclimatology, Palaeoecology,
239
104 (1993): 239-252
Elsevier Science Publishers B.V.. Amsterdam
The Cretaceous/Paleogene boundary and planktonic foraminifera in the Flyschgosau (Eastern Alps, Austria) D. Peryt”, R. Lahodynskyb,
R. Rocchia” and D. Bocletc
aInstitute of Paleobiology, Polish Academy of Sciences, Al. Zwirki i Wigury 93,02-089 Warsaw, Poland bInstitut fur Geologie und Paldontologie, Universitiit Innsbruck, Innrain 52, A-6020 Innsbruck, Austria ‘Centre des Faibles Radioactivitks, Laboratoire Mixte CEA-CNRS, Avenue de la Terrasse, F-91198, Gifsur Yvette cedex, France
(Received
January
28, 1992; revised and accepted
May 24, 1992)
ABSTRACT Peryt, D., Lahodynsky, R., Rocchia, R. and Boclet, D., 1993. The Cretaceous/Paleogene boundary and planktonic foraminifera in the Flyschgosau (Eastern Alps, Austria). Palaeogeogr., Palaeoclimatol., Palaeoecol., 104: 239-252. The studied interval extends from 2.5 m below to 1 m above the Cretaceous/Paleogene (K/P) boundary and comprises the uppermost Maastrichtian marly limestone overlain by a boundary (rusty) layer-a dark yellow orange clay 5-10 mm thick, followed by a turbidite sequence of very fine sandstones and grey-brown marls. The following planktonic foraminiferal zones are distinguished: Abafhomphalus mayaroensis, PO (subzones: POaGuembelitria cretacea and POb-Globoconusa conusa), Pa or Parvularugoglobigerina eugubina and Pl (subzone: Pla or Subbotina pseudobulloides).
The distribution of iridium shows a relatively sharp rise to a maximum value of 7.176 ppb about 1.2 cm above the rusty layer, followed by a rapid drop to normal background levels. The Abathomphalus mayaroensis Zone exhibits a moderately diverse planktonic foraminiferal assemblage. The main extinction episode occurs within the rusty layer; only a few species survived. Survivors are small primitive forms. The first new Paleocene species evolved immediately after the major Cretaceous extinctions. Rapid extinction of planktonic foraminifers coincides with the iridium anomaly which suggests that, at this site, the source(s) of the iridium anomaly was (were) probably responsible for K/P extinctions.
Introduction
K/P transitions containing a boundary clay and geochemical anomalies in the Eastern Alps are only within the flyschoid Upper exposed Campanian-Lower Eocene Upper Complex of the Gosau Beds. The East-Alpine sections which have been studied in detail are: Wasserfallgraben/Lattengebirge, Bavaria (Herm et al., 1981), Elendgraben/Dachstein, Salzburg (Stradner et al., 1985; Preisinger et al., 1986; Lahodynsky, 1988), Knappengraben/Hochschwab, Styria (Stradner et al., 1987) and Rotwandgraben/Dachstein, Upper Austria (Lahodynsky, 1989). The purpose of this paper is to trace the changes 0031-0182/93/$06.00
in planktonic foraminiferal assemblages across the K/P boundary and to compare them with the iridium distribution in the Rotwandgraben section. Material and methods
A total of 22 samples were micropaleontologitally analyzed from the section 2.5 m below to 1 m above the K/P boundary. The section was sampled at 20-50 cm intervals below the K/P boundary and continuing sampling was done at l-2 cm intervals for the first 15 cm above the boundary, then at 10 cm intervals between 15-35 cm and at 20 cm intervals between 35 and 100 cm above the boundary. Samples were processed using the glauber salt.
0 1993 ~ Elsevier Science Publishers B.V. All rights reserved
240
D. PERYT
An aliquot of about 200-300 specimens from the >63 pm size fraction was used for the fauna1 analyses. Twenty-four samples were taken for geochemical analysis for the interval between 55 cm below the K/P boundary and 108 cm above the boundary. Iridium content was measured by Instrumental Neutron Activation Analysis (INAA) of bulk samples irradiated for a few hours in the 2 x 1014 ncm-’ s-l neutron beam of the Osiris reactor. Iridium was counted with a y-y spectrometer detecting the 3 16-468 keV y-ray coincidence resulting from the decay of lg21r. Geological setting The studied section is located in the Gosau area (Fig. 1) in the Northern Calcareous Alps which is the southernmost of the five major paleogeographic zones of the Eastern Alps which constitute a complex nappe system, consisting of the AustroAlpine, Flysch and Helvetic nappes. The Gosau basins were developed on a tectonically mobile Triassic to Jurassic carbonate platform that advanced northwards since the Early Cretaceous and evolved into a submarine plateau with trenchlike basins during the Late Cretaceous. These basins were loci of turbidite sedimentation during
the Campanian to Paleocene (Hesse and Butt, 1976; Butt, 1982; Preisinger et al., 1986). The K/P transition in the Rotwandgraben section is contained within the Zwieselalm Beds which range from Upper Maastrichtian to Upper Paleocene in the Gosau area. The Zwieselalm Beds consist of interbedded sandstones, siltstones, limestones, marly limestones and marls, which are partly turbiditic and partly hemipelagic (Fig. 2). Preservation
Planktonic foraminifers exhibit poor preservation, mostly with traces of dissolution and commonly fragmented. Uppermost Maastrichtian samples are noticeably enriched in dissolutionresistant foraminifers relative to dissolutionsusceptible species. In the lowermost Paleocene, the P/B ratio is very low, planktonic foraminiferal assemblages are taxonomically impoverished compared to other sections and tests are also very poorly preserved. The presence of only the most dissolutionresistant species in the uppermost Maastrichtian planktonic foraminiferal assemblages, low contribution of Paleocene planktonic foraminifers to the assemblages as well as poor preservation of calcareous benthic tests may be related to the accumula-
0
IJJJJHELVETIC ~FLVSCH ~NOATHERN IFJ
ET AL.
and KLIPPEN ZONE ZONE CALCAREOUS ALPS
GOSAU FORMATION
Fig. 1. Location of the studied section in the Eastern Alps and the geologic units (from Lahodynsky, 1989).
K/T BOUNDARY
AND
PLANKTONIC
FORAMINIFERA:
EASTERN
241
ALPS
Subbotina pseudobuhdes
H*lO21-
_
ll*,‘6=_--_15-
.-
.~~ __
7 \
Parvularugoglob,gerlna eugubtna ZOIE
20\ \ H.45 HI \ i ‘\ $9:
HZ3 14II21 -
_ _ -iii
‘\ [p: H1917-
HZ513= HZ612llHZ9
-
HZ9 10; IlAO 9“31 y 6n-555:
50cm
I
i-
0
Fig. 2. Lithological column across the K/T boundary in the Rotwandgraben
section.
S
t
242
D. PERYT
ET AL.
tion of the tests at and/or below the foraminiferal lysocline. Accumulation of the sediment from the studied section at and/or below the foraminiferal lysocline has changed the original foraminiferal assemblages and introduced some limitations in paleontological interpretations. However, it is thought that the lack of the smallest forms in the assemblages of the uppermost Maastrichtian did not distort the pattern of extinction of the Cretaceous foraminifers at the K/P boundary as the smallest forms have been interpreted as having survived the boundary crisis (cf. Brinkhuis and Zachariasse, 1988; Keller, 1988, 1989; Canudo et al., 1991). The assemblages of planktonic foraminifers from the lowermost Paleocene at this locality are not appropriate for the study of evolution of early Paleocene planktonic foraminifers and their taxonomy, but the presence of index forms provides criteria to distinguish biostratigraphic zones.
placed on dissolution susceptibility ranking lists (e.g. Berger, 1970; Coulbourn et al., 1980; Thunell and Honjo, 1981; Malmgren, 1983) are compared to their Cretaceous morphological equivalents, then heterohelicids and globigerinelloids should be the most dissolution-susceptible species and their absence may indicate accumulation of sediment at and/or below the foraminiferal lysocline. As the smallest tests undergo the fastest dissolution (Berger, 1970), it is evident why the smallest forms in the uppermost Maastrichtian are absent and why planktonic foraminifers in the lowermost Paleocene are almost lacking. Poorly preserved planktonic as well as calcareous benthic foraminifers in uppermost Maastrichtian and very rare planktonic foraminifers in the lower Paleocene imply that the bottom of the basin perhaps was located at and/or below the foraminiferal lysocline at a depth about 2000 m (cf. Butt, 1981).
Environment
Several biostratigraphical schemes for the Cretaceous/Paleogene boundary interval were published (e.g. Bolli, 1966; Berggren, 1969, 1978; Blow, 1979; Herm et al., 1981; Smit, 1982; Toumarkine and Luterbacher, 1985; Berggren and Miller, 1988; Brinkhuis and Zachariasse, 1988; Keller, 1988; Canudo et al., 1991; Fig. 3) but none was entirely applicable to the studied section. The following foraminiferal zones have been distinguished in the studied section: Abathomphalus mayaroensis, PO with two subzones: POa or Guembelitria cretacea and POb or Globoconusa conusa, Pa or Parvularugoglobigerina eugubina and Pl with Pla or Subbotinapseudobulloides Subzone.
According to Butt (1981), the Gosau Basin subsided to middle and upper bathyal depths and was above the CCD. Preisinger et al. (1986) and Lahodynsky (1989) also concluded that the sequence of the Maastrichtian and Paleocene sediments in Gosau Basin indicates sedimentation in a deep-sea environment above the CCD. The preservation of foraminiferal tests in the Rotwandgraben section indicates deposition above the CCD, but probably at and/or below the foraminiferal lysocline. Butt (198 1) considered Maastrichtian planktonic foraminiferal assemblages from the Gosau area that are mainly composed of globotruncanids and large and complex heterohelicids as indicators of mid- to lower bathyal depths. According to Butt (1981), the absence of smaller forms with globular, delicately ornamented tests in foraminiferal assemblages may be explained by environmental prefererence of this group. Planktonic foraminiferal species vary in their susceptibility to dissolution and in the structural changes that occur during dissolution. If morphotypes of recent species of planktonic foraminifers
Biostratigraphy
Abathomphalus
mayaroensis Zone (Bolli, 1966)
Interval of total range of Abathomphalus mayarof the zone has been identified with the K/P boundary (e.g., Bolli, 1957, 1966; Luterbacher and Premoli-Silva, 1964; Berggren, 1969; Blow, 1979; Herm et al., 1981; 1985). Brinkhuis and Smit, 1982; Caron, Zachariasse (1988) and Keller (1988, 1989) showed that Abathomphalus mayaroensis in shelf areas became extinct prior to the K/P boundary. oensis. The upper boundary
K:T BOUNDARY
AND PLANKTONIC
Fig. 3. Comparison
However, in recorded just Herm et al., Canudo et al.,
FORAMINIFERA:
of late Maastrichtian
EASTERN
243
ALPS
and early Paleocene
the open ocean the species was below the boundary (Bolli, 1966; 1981; Stradner and Rogl, 1988; 1991).
PO Zone (Smit, 1982, emended Keller, 1988)
Originally the zone was defined as partial range zone of Guembelitria cretacea, from the extinction of the main mass of Cretaceous species to the entry of Globigerina minutula (Smit, 1982). Keller (1988) modified the range of the PO Zone as the interval from the K/P boundary to the first appearance of Parvularugoglobigerina eugubina. She subdivided it into two subzones: POa or Guembelitria cretacea Subzone-interval from the K/T boundary to the first appearance of Globoconusa conusa and POb or Globoconusa conusa Subzone-from the first appearance of the nominal species to the Parvularugoglobigerina appearance of first eugubina.
In this paper, PO Zone is the interval from the last occurrence of Abathomphalus mayaroensis and
planktonic
foraminiferal
zonations.
the main extinction level of Cretaceous planktonic foraminifers to the first occurrence of Parvularugoglobigerina
POa or Guembelitria 1988)
eugubina.
cretacea Subzone (Keller,
Originally the subzone was defined as the interval from the K/P boundary to the first appearance of Globoconusa conusa. In this paper, it is the interval from the last occurrence of Abathomphalus mayaroensis and the main extinction level of Cretaceous planktonic foraminifers to the first occurrence of Globoconusa conusa.
POb or Globoconusa 1988)
Interval Globoconusa eugubina.
between
conusa Subzone (Keller,
the
conusa and
first
occurrences
of
Parvularugoglobigerina
244
D. PERYT
Pa or Parvularugoglobigerina eugubina Zone (Luterbacher and Premoli-Silva, 1964, and Blow, 1979)
Luterbacher and Premoli-Silva (1964) established the zone as the total range zone of the nominate species. Later, the range of the zone was slightly changed to the interval between the first appearances of “Globigerina” eugubina and “Morozovella” pseudobulloides (e.g., Bolli, 1966; Herm et al., 1981; Brinkhuis and Zachariasse, 1988). In his numeric zonation Blow (1979), designated the interval between the first occurrences of Globorotalia (Turborotalia) longiapertura and Globorotalia (Turborotalia) pseudobulloides as his Pa Zone. We follow the opinion of Smit (1982) that Turborotalia longiapertura Blow is a junior synonym of Globigerina eugubina Luterbacher and in this paper Pa or Premoli-Silva and Parvularugoglobigerina eugubina Zone is used as defined by Blow (1979) and Bolli (1966).
PI Zone (Blow and Berggren in Berggren, 1969, emended Blow, 1979)
Originally the zone was established as the interval from the Globotruncana-Rugoglobigerina extinction datum (main extinction level of Maastrichtian planktonic foraminifera) to the first appearances of Globorotalia uncinata and G. spiralis. Berggren and Van Couvering (1974) changed the range of the zone to the interval between first of Globigerina eobulloides and appearances Globorotalia uncinata and G. spiralis. Blow (1979) proposed the lower boundary of the zone to correspond to the first appearance of Globorotalia (Turborotalia) pseudobulloides.
Pla or Subbotina pseudobulloides 1966, Blow, 1979)
Subzone (Bolli,
Interval from the first appearance of Subbotina pseudobulloides to the first appearance of Morozovella trinidadensis (Bolli, 1966). In his numeric zonation Blow (1979) included this interval in Subzone Pla. The Pla or Subbotina
ET AL.
pseudobulloides Subzone has been distinguished in
this work according 1966; Blow, 1979).
to these definitions
(Bolli,
Foraminiferal assemblages Abathomphalus
mayaroensis Zone
Samples l-9 represent the Abathomphalus mayforaminifers dominate the foraminiferal assemblages. P/B ratio ranges between 75 and 97%, and the number of species of planktonic foraminifers is 15-19 (Figs. 4 and 5). Large, massive, distinctly ornamented, mesoand bathypelagic forms, such as Globotruncana, aroensis Zone. Planktonic
Rosita, Globotruncanita, Abathomphalus, Pseudotextularia, Racemiguembelina, and Planoglobulina are present. The dominant species are Rosita contusa, Globotruncanita stuarti and Pseudotextularia spp. Rugoglobigerina is very rare. Hedbergella, Heterohelix, Globigerinelloides,
Guembelitria-representatives group-are lacking. Within the last 1 m
of the epipelagic of
the
uppermost
Abathomphalus mayaroensis Zone, the following extinctions are found: Globotruncanita pettersi in sample 4, Rugoglobigerina rotundata and Rosita patelliformis in sample 7, Globotruncanella petaloidea in sample 8 and Abathomphalus mayaroensis, Rosita contusa, R. waljishensis, Globotruncanita stuarti, G. angulata, G. stuartiformis, G. conica, Pseudotextularia brazoensis, Planglobulina deformis, P. elegans, Rugoglobigerina sp., R. milamensis, Racemiguembelina powelli, R. fructicosa, carseyae, multicamerata, P. Planoglobulina Globotruncana esnehensis, Hedbergella monmouthensis in sample 9 (Fig. 4). Sample 9 repre-
sents the main extinction level of Cretaceous planktonic foraminifers. It is difficult to determine whether the extinction of a few species of planktonic foraminifers in samples 4, 7 and 8 is background or related to the K/P boundary mass extinction. The distribution of iridium shows that these extinctions occurred considerably earlier than iridium anomaly (Fig. 4) and therefore they are regarded as having no
K/T BOUNDARY
AND PLANKTONIC
FORAMINIFERA:
EASTERN
245
ALPS
PPE
..
.
. .
IR
.
..
.
.
.
..... ..
. .. . ..
.. . .
.
1
........
20 50
. . .... .. ....
.
....
...
.
..
. . . . .. . . . ....
..
. . . .. . .... . . .
................. ..... ........
. .
30
.... .....
... . ..
. .
.... .. 5Qcm
!
l-
. . .
. . . .
.
.
.
.
.
. . .
Fig. 4. Distribution of planktonic foraminifers in uppermost Maastrichtian and lowermost Paleocene deposits in the Rotwandgraben section plotted against the succession and Ir distribution. Lithologies and other symbols are explained in Fig. 2.
246
D. PERYT
ET AL
Fig. 5. Contribution of the particular groups of foraminifers to the assemblages. Lithologies and other symbols are explained in Fig. 2.
relation to the events at the K/P boundary. However, the main extinctions occur in lower half of the iridium anomaly and appear to be directly related to the anomaly.
PO Zone-POa
or Guembelitria
cretacea Subzone
In the studied section the interval is 10 cm thick and consists of clay with l-cm-thick sandstone
K/T BOUNDARY
AND
PLANKTONIC
FORAMINIFERA:
EASTERN
intercalation (Figs. 3 and 4). The zone begins just above a 0.55l-cm-thick rusty layer. The greatest fauna1 and geochemical changes are related to the interval. Samples lo- 16 represent the Guembelitria cretatea Subzone (Fig. 4). Sample 10 is from the clay overlying the rusty layer where a considerable decrease of foraminiferal density and diversity is observed. P/B ratio decreases to 70% (Fig. 5), and the assemblage of planktonic foraminifers is represented by five species: Globotruncana arca, G. esnehensis, Planoglobulina carseyae, Racemiguembelina powelli and Pseudotextularia elegans. In the next sample, 11, the P/B ratio is
only 45%. Planktonic foraminifers of the uppermost Maastrichtian are absent. Significantly, very small, dwarfed heterohelicids and globigerinelloids such as Guembelitria cretacea, Heterohelix striata, H. globulosa, H. planata and Globigerinelloides aspera (Fig. 4) make their first local appearance. Prior to the K/P bc;mdary, these species were not present at the site. Such assemblages are characteristic of the earliest Danian and have been recorded from many other sections and described as K/T survivors (Brinkhuis and Zachariasse, 1988; Keller, 1988; Canudo et al., 1991; D’Hondt and Keller, 1991). In the upper part of the Guembelitria cretacea Subzone-in samples 12-16-both planktonic and benthic foraminifers are very rare. (The number of specimens from this part of the section was insufficient to use them for quantitative analyses; cf. Fig. 5). Planktonic foraminifers are represented by only three species: Globotruncana arca, G. esnehensis and Pseudotextularia elegans (Fig. 4) which are considered to be redeposited (Fig. 5). It is remarkable that even the dwarfed heterohelicids are lacking. Neither Paleocene planktonic foraminifers were recorded. PO Zone: POb or Globoconusa
247
ALPS
conusa Subzone
The interval is 50 cm thick and consists of intercalated fine-grained sandstones and clays. When compared to the Guembelitria cretacea Subzone, the increase in foraminiferal density in the sediment is observed. In the lower part of the subzone (sample 17), the assemblage of planktonic
foraminifers is composed of Cretaceous survivors, i.e. dwarfed heterohelicids and globigerinelloids, first Paleocene species-Globoconusa conusa and Eoglobigerina fringa, and relatively abundant reworked Maastrichtian species (Figs. 4 and 5). In the upper part of the subzone (samples 18 and 19) planktonic foraminiferal assemblages are composed only of reworked Maastrichtian species (Figs. 4 and 5). Pa or Parvularugoglobigerina
eugubina Zone
The interval is 47 cm thick and consists of intercalated calcareous marlstones, clays and sandstones. Two samples were examined (nos. 20 and 21). Planktonic foraminifers are very scarce (Fig. 5), represented by a few Paleocene planktonic species, e.g. Eoglobigerina fringa, Parvularugoglobigerina eugubina, Eoglobigerina sp. and dwarfed heterohelicids (Figs. 4 and 5) accompanied by rare and very poorly preserved, reworked globotruncanids. Within this subzone Cretaceous survivors became extinct (Fig. 4). Pl Zone: Pla or Subbotina pseudobulloides Subzone
Sample 22 is from the basal part of the subzone. Planktonic foraminifers are rare; they are represented by scarce, reworked Cretaceous forms and two Paleocene planktonic species-Subbotina pseudobulloides and Eoglobigerina sp. (Figs. 4 and 5). Geochemical anomaly The analysis of iridium content in clays of the K/P boundary indicates an abrupt enrichment in the 3-cm-thick interval above the marly limestone of the uppermost Maastrichtian, from 0.416 ppb 1.2 cm below the rusty layer, through 4.409 ppb and 5.326 ppb in the clay overlying the rusty layer, to 7.176 ppm 1.2 cm above the rusty layer. Above, an abrupt decrease of iridium content is observed (0.597 ppb 3 cm above the rusty layer). Four centimeters above the rusty layer the iridium content increases to 1.514 ppb, and higher in the section decreases gradually to 0.022 ppb in the Subbotina pseudobulloides Subzone (Figs. 4 and 6).
248
D. PERYT
Fauna1 turnover The planktonic foraminiferal assemblages from the uppermost Abathomphalus mayaroensis Zone are very abundant and moderately diversified. They are mainly represented by large and complex species of deep and intermediate dwellers. Smaller, globular, epipelagic forms are very rare. Such composition of assemblages probably resulted from dissolution of delicate globular forms during accumulation of these deposits at and/or below the foraminiferal lysocline. In the uppermost part of Abathomphalus mayaroensis Zone, a few species became extinct, i.e. Rugoglobigerina rotundata, Rosita patelliformis, Globotruncanita pettersi and Globotruncanella petaloidea. Canudo et al. (199 1) reported Globotruncanella petaloidea as a species which become extinct in the Parvularugoglobigerina longiapertura Zone. In the studied section, the species is very rare and its earlier disappearance probably resulted from dissolution of tests on the sea floor. The main extinction level corresponds to the OS-l-cm-thick dark yellow orange clay-
Sample
ROTWANDGRABEN (Bulk) Ir content Sample position (cm) (ppb)
,
ET AL.
the rusty layer. Immediately below the K/P boundary, 14 of the 19 species became extinct. They represent a group of large and complex species of deep and intermediate water dwellers. Above the rusty layer, contribution of the planktonic assemblage drops from 92 to 70%. The five next Maastrichtian species became extinct at this level. In the basal PO Zone none of the species from the uppermost Abathomphalus mayaroensis Zone is present. Instead for the first time in the section an assemblage composed of small triserial and biserial heterohelicids appears, such as Guembelitria cretatea and dwarfed Heterohelix striata, H. globulosa, H. planata and Globigerinelloides aspera. These species are common in many latest Maastrichtian assemblages. However, they are 2-3 times larger than the earliest Paleocene ones. Dwarfed heterohelicids and globigerinelloids are considered to be the Cretaceous survivors (Brinkhuis and Zachariasse, 1988; Keller, 1988, 1989; Canudo et al., 1991; D’Hondt and Keller, 1991). They became extinct within the Parvularugoglobigerina eugubina Zone. The first Paleocene species appear 15 cm above the K/P boundary. In the studied section, earliest Paleocene planktonic foraminifers are very scarce and assemblages are taxonomically impoverished compared to other sites. This is due to the dissolution of very fine tests of earliest Paleocene planktonic foraminifers during accumulation at and/or below the foraminiferal lysocline. K/P boundary
Fig. 6. Iridium interval.
content
in deposits
from
the K/P
boundary
According to the decision of the Working Group on the Cretaceous/Paleogene boundary, the boundary is characterized by the major planktonic foraminiferal extinction event and/or the first appearance datum of Cainozoic species, and a major lithologic change, including the presence of a thin red layer at the base of the boundary clay, anomalies marked by various geochemical (Canudo et al., 1991). The Rotwandgraben section possesses all these characteristics. In Rotwandgraben section as well as in other Alpine K/P boundary sections (Elendgraben, Knappengraben, Lattengebirge), the major Cretaceous species extinctions occur in the rusty layer (Herm et al., 1981; Preisinger et al.,
KIT BOUNDARY
AND
PLANKTONIC
FORAMINIFERA:
EASTERN
ALPS
1986; Stradner and Rogl, 1988). Abathomphalus mayaroensis became extinct at the same level. In Rotwandgraben as well as in Knappengraben the first Paleogene species (Globoconusa conusa and Eoglobigerina fringa) are found 15 cm above the rusty layer (Stradner and Rogl, 1988); in Lattengebirge sections Elendgraben and Eoglobigerina fringa appears 6 cm above the boundary layer (Herm et al., 1981; Preisinger et al., 1986). Iridium enrichments were found within the K/P boundary layers and also within the turbidites Elendgraben, immediately above at the sites and Rotwandgraben Knappengraben (Preisinger et al., 1986; Stradner et al., 1987). In the Rotwangraben section, the highest iridium value was measured 1.2 cm above the rusty layer. Discussion
The Cretaceous/Paleogene boundary is recognized as representative of one of the greatest mass extinctions in Earth history. Mass extinctions of many groups of organisms were accompanied by, or caused by, different abiotic events: a large meteorite impact (Alvarez et al., 1980; Smit, 1982; Smit and Ten Kate, 1982; Preisinger et al., 1986; Rampino and Volk, 1988; Rocchia et al., 1990b; Bhandari and Shukla, 1991; Hildebrand, 1991) hot spot volcanism (Officer and Drake, 1985; Hansen et al., 1986; Olmez et al., 1986; Officer et al., 1987; Lahodynsky, 1989; Rocchia et al., 1990a), climate warming by 6”-8” (Rampino and Volk, 1988; Smit, 1990) extensive forest fires (Wolbach et al., 1986) and latest Maastrichtian regression (Haq et al., 1987; Brinkhuis and Zachariasse, 1988; Keller, 1988; Peryt, 1988). The abrupt extinction of Cretaceous planktonic foraminifers constitutes a major base-line to delimit the K/P boundary in marine sections. K/P boundary levels in the marine record are associated with a drop in 6i3C and 6l*O values (e.g., Thierstein and Berger, 1978; Hsii et al., 1982; Perch-Nielsen et al., 1982; Rampino and Volk, 1988; Keller and Lindinger, 1989; Smit, 1990) as well as in CaC03 content. K/P boundary levels are also characterized by an iridium anomaly (Alvarez et al., 1980, 1982; Smit, 1982; Smit and Ten Kate, 1982; Hansen et al., 1986; Preisinger
249
et al., 1986; Stradner et al., 1987; Rocchia et al., 1990a,b; Bhandari and Shukla, 1991; Robin et al., 1991). Iridium peaks strongly correlate with elemental carbon and aluminium oxide (Hansen et al., 1986; Preisinger et al., 1986). Officer et al. (1987) and Rocchia et al. (1988, 1990a,b) recorded that at several K/P sites the anomalous concentration of iridium is not limited to the boundary layer but extends over a thickness of about one meter. In the Gubbio section, Rocchia et al. (1990a) found that iridium concentrations stand out above background over almost 3 m of section, corresponding to half a million years based on magnetostratigraphy. This extended distribution most probably results from post depositional diffusion (Robin et al., 1991). The cause of the iridium anomaly in deposits at the K/P boundary has been explained by an extraterrestrial impact (Alvarez et al., 1980, 1982; Preisinger et al., 1986; Rocchia et al., 1990b; Hildebrand, 1991; Robin et al., 1991) hot spot volcanism (Officer and Drake, 1985; Hansen et al., 1986; Olmez et al., 1986; Lahodynsky, 1989; Rocchia et al., 1990a), and reducing conditions during sedimentation (Nazarov et al., 1982). Bhandari and Shukla (1991) having analyzed several sections from the Indian subcontinent, concluded that the Deccan volcanism which had been suggested as a possible source of geochemical anomalies at K/P boundary was too small to give rise to the iridium anomaly worldwide. The occurrence of increased iridium concentrations in a very thin (2 cm) layer in Rotwandgraben section indicates a rather shortlasting source of the anomaly. In other Alpine sections, the increased iridium content is recorded in intervals a few centimeters thick and interpreted as being due to an extraterrestrial impact (Preisinger et al., 1986; Stradner et al., 1987). It seems that the event was also responsible for the iridium enrichment in the Rotwangraben section. A distinctive correlation between the extinction of a majority of Cretaceous species of planktonic foraminifers and the iridium anomaly indicates that the two are closely associated. Keller and Lindinger (1989) and D’Hondt and Keller (199 1) concluded on the basis of the negative
250
excursion of 6i3C at the K/P boundary that the main extinction level of planktonic foraminifers coincides with the decrease in marine primary productivity. It seems that the iridium anomaly, the decrease in marine primary productivity and the mass extinctions of planktonic foraminifera are interrelated. If the iridium anomaly is caused by meteorite impact(s), then the following scenario seems probable: The impact-related dust clouds may have suppressed sunlight long enough that photosynthesis was temporarily reduced on a global scale and primary productivity in the oceans was rapidly diminished (e.g., Alvarez et al., 1980, 1982; Smit, 1982, 1990; Smit and Ten Kate, 1982). The darkness could be additionally increased by the smoke from the extensive forest fires (Wolbach et al., 1986). A rapid decrease of primary productivity caused essential perturbations in the food chain which resulted in extinction of specialized groups of planktonic foraminifers (Keller and Lindinger, 1989; Smit, 1990; D’Hondt and Keller, 1991). Also a substantial increase in volcanism at K/P time (Hansen et al., 1986; Officer et al., 1987; Lahodynsky, 1988) as well as great fires would supply a significant amount of CO2 to the atmosphere (Wolbach et al., 1986) which, in turn, could have caused a greenhouse effect, global temperature increase, acid rains and decrease in surface ocean alkalinity. In addition, there was a pronounced late Cretaceous regression of the sea lasting for a few million years (e.g., Brinkhuis and Zachariasse, 1988; Keller, 1988). Vertical and horizontal distribution of planktonic foraminifers in the water column depends on many factors e.g. temperature, salinity, pH, water depth, nutrients, oxygen (Boltvskoy and Wright, 1976; Hemleben et al., 1989). Major changes of these factors may have led to the extinction of the most sensitive groups. Large and more complex dwellers are more sensitive to the environmental changes than small and primitive forms. The latter live predominantly in the uppermost 50-m-layer of water column and may live in less saline waters. They can also survive better in a lower pH environment than larger forms of planktonic foraminifers (Boltovskoy and Wright, 1976), and an environment that is under-
D. PERYT
ET AL.
going change is selective toward smaller species as compared with a more stable environment. Small, primitive forms are also the first colonizers of new niches. Most of the K/P boundary events influenced the oceans which resulted in paleoceanographic changes that led to the extinction of large, highly specialized forms of planktonic foraminifers. The earliest Paleocene planktonic foraminifers exhibit a change from large and complex forms to small and simple ones. At the K/P boundary, the previous biogeographic provincial differences disappear. The earliest Paleocene planktonic foraminifer assemblages are characterized in both open-ocean and epicontinental environments by forms previously dominant in epicontinental environments i.e. small, generelized forms (cf. Herm et al., 1981; Smit, 1982, 1990; Brinkhuis and Zachariasse, 1988; Keller, 1988, 1989; Canudo et al., 1991; D’Hondt and Keller, 1991).
Conclusions (1) A few species of planktonic foraminifers became extinct in the uppermost part of the Abathomphalus mayaroensis Zone. (2) The main extinction level is related to the rusty layer; 14 of 19 species recorded in the rusty layer do not occur in the overlying layer. (3) The five remaining species became extinct above the rusty layer. (4) An entirely new assemblage composed of Guembelitria cretacea and dwarfed Heterohelix striata, H. globulosa, H. sp., and Globigerinelloides aspera appears 2 cm above the rusty layer. A similar composition is characteristic for assemblages found in the lowermost Paleocene in many sites and regarded as Cretaceous survivors. (5) Other species of Maastrichtian planktonic foraminifers which are found higher up in the section, are considered to be reworked. (6) The first Paleocene planktonic foraminifers appear 15 cm above the K/P boundary. (7) A very small taxonomic diversity of planktonic foraminifers and their scarcity in the lowermost Paleocene section is explained by the dissolution of the most part of assemblages during
K,‘T BOUNDARY
AND
PLANKTONIC
FORAMINIFERA:
EASTERN
251
ALPS
deposition on the sea bottom that was probably located at/below the foraminiferal lysocline. (8) There is a correlation between the extinction of planktonic foraminifers and the presence of the iridium anomaly. Thirty percent of the former assemblage occurs in the deposit containing more than 4 ppb of iridium, and the content of 7 ppb is associated with complete lack of more complex Maastrichtian planktonic foraminifers, and only very primitive, cosmopolitan and dwarfed forms of Guembelitria, Heterohelix and Globigerinelloides occur. These forms may survive stressed environmental conditions which eliminate other forms and accordingly they are the first colonizers. (9) The cause of the iridium anomaly in Rotwandgraben section is probably an extraterrestrial impact. Acknowledgements
We are grateful to Dr. D.H. McNeil and an anonymous reviewer whose comments and suggestions were very useful. Thanks are due to E. Hara for processing samples and to D. Slawik for the drawings. This is CFR contribution no. 1366. References Alvarez, L.W., Alvarez, W., Asaro, F. and Michel, H.W., 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science, 208: 1095-1108. Alvarez, W., Alvarez, L.W., Asaro, F. and Michel, H.W., 1982. Current status of the impact theory for the terminal Cretaceous extinction. Geol. Sot. Am. Spec. Pap., 190: 3055315. Berger, W.H., 1970. Planktonic foraminifera: selective solution and the lysocline. Mar. Geol., 8: 11 I-138. Berggren, W.A., 1969. Rates of evolution in some Cenozoic planktonic foraminifera. Micropaleontology, 15: 351-365. Berggren, W.A., 1978. Recent advances in Cenozoic planktonic foraminiferal biostratigraphy, biochronology and biogeography: Atlantic Ocean. Micropaleontology, 24: 337-370. Berggren, W.A. and Van Couvering, J.T., 1974. The late Neogene. Biostratigraphy, geochronology and paleoclimatology of the last 15 millions years in marine and continental sequences. Palaeogeogr., Palaeoclimatol., Palaeoecol., 16: I-215. Berggren, W.A. and Miller, K.G., 1988. Paleogene tropical planktonic foraminiferal biostratigraphy and magnetobiochronology. Micropaleontology, 34: 362-380. Bhandari, N. and Shukla, P.N., 1991. Geochemistry of K/T boundary sections in India. Symp. Event Markers in Earth History. Progr. Abstr., p, 17.
Blow, W.H., 1979. The Cainozoic Globigerinida. A Study of the Morphology, Taxonomy, Evolutionary Relationships and the Stratigraphical Distribution of Some Globigerinida (Mainly Globigerinacea). Brill, Leiden, 1413 pp. Bolli, H.M., 1957. The genera Praeglobotruncana, Rotalipora, Globotruncana and Abathomphalus in the Upper Cretaceous of Trinidad. Bull. U.S. Nat. Mus., 215: 51-60. Bolli, H.M., 1966. Zonation of Cretaceous to Pliocene marine sediments based on planktonic foraminifera. Asoc. Venez. Geol. Min. Petrol., Bol. Inform., 9: 2-32. Boltovskoy, E. and Wright, R., 1976. Recent Foraminifera. W. Junk, The Hague, 515 pp. Brinkhuis, H. and Zachariasse, W.J., 1988. Dinoflagellate cysts, sea level changes and planktonic foraminifers across the Cretaceous/Tertiary boundary at El-Haria, northwest Tunisia. Mar. Micropaleontol., 13: 153-191. Butt, A., 1981. Depositional environments of the Upper Cretaceous rocks in the northern parts of the Eastern Alps. Cushman Found. Foraminiferal Res. Spec. Publ., 20: 5-121. Canudo, J.I., Keller, G. and Molina, E., 1991. Cretaceous/Tertiary boundary extinction pattern and fauna1 turnover at Agost and Caravaca, S.E. Spain. Mar. Micropaleontol., 17: 319-341. Caron, M., 1985. Cretaceous planktic foraminifera. In: H.M. Bolli, J.B. Saunders and K. Perch-Nielsen (Editors), Plankton Stratigraphy. Cambridge Univ. Press, Cambridge, pp. 17786. Coulbourn, W.T., Parker, F.L. and Berger, W.H., 1980. Fauna1 and solution patterns of planktonic foraminifera in surface sediments of the North Pacific. Mar. Micropaleontol., 5: 329-399. D’Hondt, S. and Keller, G., 1991. Some patterns of planktic foraminiferal assemblage turnover at the Cretaceous-Tertiary boundary. Mar. Micropaleontol., 17: 777118. Hansen, H.J., Gwozdz, R., Hansen, J.M., Bromley, R.G. and Rasmussen, K.L., 1986. The diachronous C/T plankton extinction in the Danish Basin. In: O.H. Walhser (Editor), Global Bio-Events. Lecture Notes Earth Sci., 8: 381-384. Haq, B.U., Hardenbol, J. and Vail, P.R., 1987. Chronology of fluctuating sea level since the Triassic. Science, 235: 1156-l 166. Hemleben, Ch., Spindler, M. and Anderson, O.R., 1989. Modern Planktonic Foraminifera. Springer, New York, 363 pp. Herm, D., Von Hillebrandt, A. and Perch-Nielsen, K., 1981. Die Kreide/Tertiargrenze im Lattengebirge (Nordliche Kalkalpen) in mikropalaontologischer 82: 3 19-344.
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Hesse, R. and Butt, A., 1976. Paleobathymetry turbidite basins of the East Alps relative compensation level. J. Geol., 84: 505-533.
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Hildebrand, A.R., 1991. What evidence is required to establish that a large impact ended the Cretaceous period? Or that the impact caused the associated mass extinction? Is finding the K/T crater enough? Symp. Event Markers in Earth History. Progr. Abstr., p. 39. Hsii, K.J., McKenzie, J.A. and He, Q.X., Cretaceous environmental and evolutionary Sot. Am. Spec. Pap., 190: 317-328.
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252 Keller, G., 1988. Extinction, survivorship and evolution of planktic foraminifera across the Cretaceous/Tertiary boundary at El-Kef, Tunisia. Mar. Micropaleontol., 13: 239-263. Keller, G., 1989. Extended Cretaceous/Tertiary boundary extinctions and delayed population change in planktonic foraminifera from Brazos River, Texas. Paleoceanography, 4: 287-332. Keller, G. and Lindinger, M., 1989. Stable isotope, TOC and CaCO, record across the Cretaceous/Tertiary boundary at El Kef, Tunisia. Palaeogeogr., Palaeoclimatol., Palaeoecol., 73: 243-265. Lahodynsky, R., 1988. Lithostratigrapgy and sedimentology across the Cretaceous/Tertiary boundary in the Flyschgosau (Eastern Alps, Austria). Rev. Esp. Paleontol., No. Extraordinario, pp. 73-82. Lahodynsky, R., 1989. The K/T boundary and “Yellow Clay” Layers in the Gosau Group, Northern Calcareous Alps, Austria. In: J. Wiedmann (Editor), Proc. 3rd Int. Cretaceous Symp. Schweizer bart, Stuttgart, pp. 677-690. Luterbacher, H.P. and Premoli-Silva, I., 1964. Biostratigrafia de1 Limite Cretaceo-Terziario nell Appennino centrale. Riv. Ital. Paleontol. Stratigr., 70: 67-88. Malmgren, B.A., 1983. Ranking of dissolution susceptibility of planktonic foraminifera at high latitudes of the South Atlantic Ocean. Mar. Micropaleontol., 8: 183-191. Nazarov, M.A., Barsukova, L.D., Kolesov, G.M., Naidin, D.P., Alekseev, V.A. and Vernadsky, V.I., 1982. Extraterrestrial event at the C/T Boundary: New geochemical and mineralogical data. Lunar Planet. Sci. 13: 580-581. Officer, C.B. and Drake, C.L., 1985. Terminal Cretaceous Environmental Events. Science, 227: 1161-l 167. Officer, C.B., Hallam, A., Drake, C.L. and Devine, J.D., 1987. Late Cretaceous and paroxysmal Cretaceous/Tertiary extinctions. Nature, 326: 143-149. Olmez, I., Finnegan, D.L. and Zoller, W.H., 1986. Iridium emissions from Kilauea volvano. J. Geophys. Res., 91: 653-663. Perch-Nielsen, K., McKenzie, J. and He, Q.X., 1982. Biostratigraphy and isotope stratigraphy and the “catastrophic” extinction of calcareous nannoplankton at the Cretaceous-Tertiary boundary. Geol. Sot. Am. Spec. Pap., 190: 353-371. Peryt, D., 1988. Maastrichtian extinctions of planktonic foraminifera in Central and Eastern Poland. Rev. Esp. Paleontol., 3: 105-l 15. Preisinger, A., Zobetz, E., Gratz, A., Lahodynsky, R., Becke, M., Mauri&h, H.J., Eder, G., Grass, F., Rogl, F., Stradner, H. and Surenian, R., 1986. The Cretaceous/Tertiary boundary in the Gosau Basin, Austria. Nature, 322: 797-799. Rampino, M.R. and Volk, T., 1988. Mass extinctions, atmospheric sulphur and climatic warming at the K/T boundary. Nature, 332: 63-65.
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Robin, E., Boclet, D., Bonte, Ph., Froget, L., Jehanno, C. and Rocchia, R., 1991. The stratigraphic distribution of N&rich spinels in Cretaceous-Tertiary boundary rocks at El Kef (Tunisia), Caravaca (Spain) and Hole 761C (Leg 122). Earth Planet. Sci. Lett., 107: 715-721. Rocchia, R., Boclet, D., Bonte, Ph., Buffetaut, E., OrueEtxebarria, X., Jaeger, J.-J. and Jehanno, C., 1988. Structure de l’anomalie en iridium a la limite Cretace-Tertiaire du site de SOPELANA (Pays Basque Espagnol). C.R. Acad. Sci. Paris, 307: 1217-1223. Rocchia, R., Boclet, D., Bonte, Ph., Jehanno, C., Yan Chen, Courtillot, V., Mary, C. and Wezel, F., 1990a. The Cretaceous-Tertiary boundary at Gubbio revisited: vertical extent of Ir anomaly. Earth Planet. Sci. Lett., 99: 206-219. Rocchia, R., Granier, B., Bellier, J.-P., Boclet, D., Bonte Ph., Fourcade, E., Galbrun, B., Jeharmo, C., Lambert, B., Rasplus, L. and Renard, M., 1990b. La limite cretace-tertiaire du site de Finestrat (province d’Alicante, Espagne). CR. Acad. Sci. Paris, 310: 391-397. Smit, J., 1982. Extinction and evolution of planktonic foraminifera after a major impact at the Cretaceous/Tertiary boundary. Geol. Sot. Am. Spec. Pap., 190: 329-352. Smit, J., 1990. Meteorite impact, extinctions and the Cretaceous-Tertiary Boundary. Geol. Mijnbouw, 69: 187-204. Smit, J. and Ten Kate, W.G., 1982. Trace element patterns at the Cretaceous-Tertiary boundary; consequences of a large impact. Cret. Res., 3: 307-332. Stradner, H. and Rogl, F., 1988. Microfauna and Nannoflora the Knappengraben (Austria) of across the Cretaceous/Tertiary Boundary. Ber. Geol. Bundesant., 15: 25-26. Stradner, H., Becke, M., Grass, F., Lahodynsky, R., Mauritsch, H.J., Preisinger, A., Rogl, F., Surenian, R. and Zobetz, E., 1985. The Cretaceous-Tertiary boundary in the Gosau Formation of Austria. Terra Cognita, 5: 247. Stradner, H., Eder, G., Grass, F., Lahodynsky, R., Mauritsch, H.J., Preisinger, A., Rogl, F., Surenian, R., Zeissl, W. and Zobetz, E., 1987. New K/T boundary sites in the Gosau Formation of Austria. Terra Cognita, 7: 212. Thierstein, H.R. and Berger, W.H., 1978. Injection events in ocean history. Nature, 276: 461-466. Thunell, R.C. and Honjo, S., 1981. Calcite dissolution and the modification of planktonic foraminiferal assemblages. Mar. Micropaleontol., 6: 169-182. Toumarkine, M. and Luterbacher, H.P., 1985. Paleocene and Eocene planktic foraminifera. In: H.M. Bolli, J.B. Saunders and K. Perch-Nielsen (Editors), Plankton Stratigraphy. Cambridge Univ. Press, Cambridge, pp. 155-262. Wolbach, W.S., Gilmour, I., Anders, E., Orth, C.J. and Brooks, R.R., 1986. Global wildfire at the Cretaceous-Tertiary boundary. Nature, 334: 665-667.
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104 (1993): 239-252
Elsevier Science Publishers B.V.. Amsterdam
The Cretaceous/Paleogene boundary and planktonic foraminifera in the Flyschgosau (Eastern Alps, Austria) D. Peryt”, R. Lahodynskyb,
R. Rocchia” and D. Bocletc
aInstitute of Paleobiology, Polish Academy of Sciences, Al. Zwirki i Wigury 93,02-089 Warsaw, Poland bInstitut fur Geologie und Paldontologie, Universitiit Innsbruck, Innrain 52, A-6020 Innsbruck, Austria ‘Centre des Faibles Radioactivitks, Laboratoire Mixte CEA-CNRS, Avenue de la Terrasse, F-91198, Gifsur Yvette cedex, France
(Received
January
28, 1992; revised and accepted
May 24, 1992)
ABSTRACT Peryt, D., Lahodynsky, R., Rocchia, R. and Boclet, D., 1993. The Cretaceous/Paleogene boundary and planktonic foraminifera in the Flyschgosau (Eastern Alps, Austria). Palaeogeogr., Palaeoclimatol., Palaeoecol., 104: 239-252. The studied interval extends from 2.5 m below to 1 m above the Cretaceous/Paleogene (K/P) boundary and comprises the uppermost Maastrichtian marly limestone overlain by a boundary (rusty) layer-a dark yellow orange clay 5-10 mm thick, followed by a turbidite sequence of very fine sandstones and grey-brown marls. The following planktonic foraminiferal zones are distinguished: Abafhomphalus mayaroensis, PO (subzones: POaGuembelitria cretacea and POb-Globoconusa conusa), Pa or Parvularugoglobigerina eugubina and Pl (subzone: Pla or Subbotina pseudobulloides).
The distribution of iridium shows a relatively sharp rise to a maximum value of 7.176 ppb about 1.2 cm above the rusty layer, followed by a rapid drop to normal background levels. The Abathomphalus mayaroensis Zone exhibits a moderately diverse planktonic foraminiferal assemblage. The main extinction episode occurs within the rusty layer; only a few species survived. Survivors are small primitive forms. The first new Paleocene species evolved immediately after the major Cretaceous extinctions. Rapid extinction of planktonic foraminifers coincides with the iridium anomaly which suggests that, at this site, the source(s) of the iridium anomaly was (were) probably responsible for K/P extinctions.
Introduction
K/P transitions containing a boundary clay and geochemical anomalies in the Eastern Alps are only within the flyschoid Upper exposed Campanian-Lower Eocene Upper Complex of the Gosau Beds. The East-Alpine sections which have been studied in detail are: Wasserfallgraben/Lattengebirge, Bavaria (Herm et al., 1981), Elendgraben/Dachstein, Salzburg (Stradner et al., 1985; Preisinger et al., 1986; Lahodynsky, 1988), Knappengraben/Hochschwab, Styria (Stradner et al., 1987) and Rotwandgraben/Dachstein, Upper Austria (Lahodynsky, 1989). The purpose of this paper is to trace the changes 0031-0182/93/$06.00
in planktonic foraminiferal assemblages across the K/P boundary and to compare them with the iridium distribution in the Rotwandgraben section. Material and methods
A total of 22 samples were micropaleontologitally analyzed from the section 2.5 m below to 1 m above the K/P boundary. The section was sampled at 20-50 cm intervals below the K/P boundary and continuing sampling was done at l-2 cm intervals for the first 15 cm above the boundary, then at 10 cm intervals between 15-35 cm and at 20 cm intervals between 35 and 100 cm above the boundary. Samples were processed using the glauber salt.
0 1993 ~ Elsevier Science Publishers B.V. All rights reserved
240
D. PERYT
An aliquot of about 200-300 specimens from the >63 pm size fraction was used for the fauna1 analyses. Twenty-four samples were taken for geochemical analysis for the interval between 55 cm below the K/P boundary and 108 cm above the boundary. Iridium content was measured by Instrumental Neutron Activation Analysis (INAA) of bulk samples irradiated for a few hours in the 2 x 1014 ncm-’ s-l neutron beam of the Osiris reactor. Iridium was counted with a y-y spectrometer detecting the 3 16-468 keV y-ray coincidence resulting from the decay of lg21r. Geological setting The studied section is located in the Gosau area (Fig. 1) in the Northern Calcareous Alps which is the southernmost of the five major paleogeographic zones of the Eastern Alps which constitute a complex nappe system, consisting of the AustroAlpine, Flysch and Helvetic nappes. The Gosau basins were developed on a tectonically mobile Triassic to Jurassic carbonate platform that advanced northwards since the Early Cretaceous and evolved into a submarine plateau with trenchlike basins during the Late Cretaceous. These basins were loci of turbidite sedimentation during
the Campanian to Paleocene (Hesse and Butt, 1976; Butt, 1982; Preisinger et al., 1986). The K/P transition in the Rotwandgraben section is contained within the Zwieselalm Beds which range from Upper Maastrichtian to Upper Paleocene in the Gosau area. The Zwieselalm Beds consist of interbedded sandstones, siltstones, limestones, marly limestones and marls, which are partly turbiditic and partly hemipelagic (Fig. 2). Preservation
Planktonic foraminifers exhibit poor preservation, mostly with traces of dissolution and commonly fragmented. Uppermost Maastrichtian samples are noticeably enriched in dissolutionresistant foraminifers relative to dissolutionsusceptible species. In the lowermost Paleocene, the P/B ratio is very low, planktonic foraminiferal assemblages are taxonomically impoverished compared to other sections and tests are also very poorly preserved. The presence of only the most dissolutionresistant species in the uppermost Maastrichtian planktonic foraminiferal assemblages, low contribution of Paleocene planktonic foraminifers to the assemblages as well as poor preservation of calcareous benthic tests may be related to the accumula-
0
IJJJJHELVETIC ~FLVSCH ~NOATHERN IFJ
ET AL.
and KLIPPEN ZONE ZONE CALCAREOUS ALPS
GOSAU FORMATION
Fig. 1. Location of the studied section in the Eastern Alps and the geologic units (from Lahodynsky, 1989).
K/T BOUNDARY
AND
PLANKTONIC
FORAMINIFERA:
EASTERN
241
ALPS
Subbotina pseudobuhdes
H*lO21-
_
ll*,‘6=_--_15-
.-
.~~ __
7 \
Parvularugoglob,gerlna eugubtna ZOIE
20\ \ H.45 HI \ i ‘\ $9:
HZ3 14II21 -
_ _ -iii
‘\ [p: H1917-
HZ513= HZ612llHZ9
-
HZ9 10; IlAO 9“31 y 6n-555:
50cm
I
i-
0
Fig. 2. Lithological column across the K/T boundary in the Rotwandgraben
section.
S
t
242
D. PERYT
ET AL.
tion of the tests at and/or below the foraminiferal lysocline. Accumulation of the sediment from the studied section at and/or below the foraminiferal lysocline has changed the original foraminiferal assemblages and introduced some limitations in paleontological interpretations. However, it is thought that the lack of the smallest forms in the assemblages of the uppermost Maastrichtian did not distort the pattern of extinction of the Cretaceous foraminifers at the K/P boundary as the smallest forms have been interpreted as having survived the boundary crisis (cf. Brinkhuis and Zachariasse, 1988; Keller, 1988, 1989; Canudo et al., 1991). The assemblages of planktonic foraminifers from the lowermost Paleocene at this locality are not appropriate for the study of evolution of early Paleocene planktonic foraminifers and their taxonomy, but the presence of index forms provides criteria to distinguish biostratigraphic zones.
placed on dissolution susceptibility ranking lists (e.g. Berger, 1970; Coulbourn et al., 1980; Thunell and Honjo, 1981; Malmgren, 1983) are compared to their Cretaceous morphological equivalents, then heterohelicids and globigerinelloids should be the most dissolution-susceptible species and their absence may indicate accumulation of sediment at and/or below the foraminiferal lysocline. As the smallest tests undergo the fastest dissolution (Berger, 1970), it is evident why the smallest forms in the uppermost Maastrichtian are absent and why planktonic foraminifers in the lowermost Paleocene are almost lacking. Poorly preserved planktonic as well as calcareous benthic foraminifers in uppermost Maastrichtian and very rare planktonic foraminifers in the lower Paleocene imply that the bottom of the basin perhaps was located at and/or below the foraminiferal lysocline at a depth about 2000 m (cf. Butt, 1981).
Environment
Several biostratigraphical schemes for the Cretaceous/Paleogene boundary interval were published (e.g. Bolli, 1966; Berggren, 1969, 1978; Blow, 1979; Herm et al., 1981; Smit, 1982; Toumarkine and Luterbacher, 1985; Berggren and Miller, 1988; Brinkhuis and Zachariasse, 1988; Keller, 1988; Canudo et al., 1991; Fig. 3) but none was entirely applicable to the studied section. The following foraminiferal zones have been distinguished in the studied section: Abathomphalus mayaroensis, PO with two subzones: POa or Guembelitria cretacea and POb or Globoconusa conusa, Pa or Parvularugoglobigerina eugubina and Pl with Pla or Subbotinapseudobulloides Subzone.
According to Butt (1981), the Gosau Basin subsided to middle and upper bathyal depths and was above the CCD. Preisinger et al. (1986) and Lahodynsky (1989) also concluded that the sequence of the Maastrichtian and Paleocene sediments in Gosau Basin indicates sedimentation in a deep-sea environment above the CCD. The preservation of foraminiferal tests in the Rotwandgraben section indicates deposition above the CCD, but probably at and/or below the foraminiferal lysocline. Butt (198 1) considered Maastrichtian planktonic foraminiferal assemblages from the Gosau area that are mainly composed of globotruncanids and large and complex heterohelicids as indicators of mid- to lower bathyal depths. According to Butt (1981), the absence of smaller forms with globular, delicately ornamented tests in foraminiferal assemblages may be explained by environmental prefererence of this group. Planktonic foraminiferal species vary in their susceptibility to dissolution and in the structural changes that occur during dissolution. If morphotypes of recent species of planktonic foraminifers
Biostratigraphy
Abathomphalus
mayaroensis Zone (Bolli, 1966)
Interval of total range of Abathomphalus mayarof the zone has been identified with the K/P boundary (e.g., Bolli, 1957, 1966; Luterbacher and Premoli-Silva, 1964; Berggren, 1969; Blow, 1979; Herm et al., 1981; 1985). Brinkhuis and Smit, 1982; Caron, Zachariasse (1988) and Keller (1988, 1989) showed that Abathomphalus mayaroensis in shelf areas became extinct prior to the K/P boundary. oensis. The upper boundary
K:T BOUNDARY
AND PLANKTONIC
Fig. 3. Comparison
However, in recorded just Herm et al., Canudo et al.,
FORAMINIFERA:
of late Maastrichtian
EASTERN
243
ALPS
and early Paleocene
the open ocean the species was below the boundary (Bolli, 1966; 1981; Stradner and Rogl, 1988; 1991).
PO Zone (Smit, 1982, emended Keller, 1988)
Originally the zone was defined as partial range zone of Guembelitria cretacea, from the extinction of the main mass of Cretaceous species to the entry of Globigerina minutula (Smit, 1982). Keller (1988) modified the range of the PO Zone as the interval from the K/P boundary to the first appearance of Parvularugoglobigerina eugubina. She subdivided it into two subzones: POa or Guembelitria cretacea Subzone-interval from the K/T boundary to the first appearance of Globoconusa conusa and POb or Globoconusa conusa Subzone-from the first appearance of the nominal species to the Parvularugoglobigerina appearance of first eugubina.
In this paper, PO Zone is the interval from the last occurrence of Abathomphalus mayaroensis and
planktonic
foraminiferal
zonations.
the main extinction level of Cretaceous planktonic foraminifers to the first occurrence of Parvularugoglobigerina
POa or Guembelitria 1988)
eugubina.
cretacea Subzone (Keller,
Originally the subzone was defined as the interval from the K/P boundary to the first appearance of Globoconusa conusa. In this paper, it is the interval from the last occurrence of Abathomphalus mayaroensis and the main extinction level of Cretaceous planktonic foraminifers to the first occurrence of Globoconusa conusa.
POb or Globoconusa 1988)
Interval Globoconusa eugubina.
between
conusa Subzone (Keller,
the
conusa and
first
occurrences
of
Parvularugoglobigerina
244
D. PERYT
Pa or Parvularugoglobigerina eugubina Zone (Luterbacher and Premoli-Silva, 1964, and Blow, 1979)
Luterbacher and Premoli-Silva (1964) established the zone as the total range zone of the nominate species. Later, the range of the zone was slightly changed to the interval between the first appearances of “Globigerina” eugubina and “Morozovella” pseudobulloides (e.g., Bolli, 1966; Herm et al., 1981; Brinkhuis and Zachariasse, 1988). In his numeric zonation Blow (1979), designated the interval between the first occurrences of Globorotalia (Turborotalia) longiapertura and Globorotalia (Turborotalia) pseudobulloides as his Pa Zone. We follow the opinion of Smit (1982) that Turborotalia longiapertura Blow is a junior synonym of Globigerina eugubina Luterbacher and in this paper Pa or Premoli-Silva and Parvularugoglobigerina eugubina Zone is used as defined by Blow (1979) and Bolli (1966).
PI Zone (Blow and Berggren in Berggren, 1969, emended Blow, 1979)
Originally the zone was established as the interval from the Globotruncana-Rugoglobigerina extinction datum (main extinction level of Maastrichtian planktonic foraminifera) to the first appearances of Globorotalia uncinata and G. spiralis. Berggren and Van Couvering (1974) changed the range of the zone to the interval between first of Globigerina eobulloides and appearances Globorotalia uncinata and G. spiralis. Blow (1979) proposed the lower boundary of the zone to correspond to the first appearance of Globorotalia (Turborotalia) pseudobulloides.
Pla or Subbotina pseudobulloides 1966, Blow, 1979)
Subzone (Bolli,
Interval from the first appearance of Subbotina pseudobulloides to the first appearance of Morozovella trinidadensis (Bolli, 1966). In his numeric zonation Blow (1979) included this interval in Subzone Pla. The Pla or Subbotina
ET AL.
pseudobulloides Subzone has been distinguished in
this work according 1966; Blow, 1979).
to these definitions
(Bolli,
Foraminiferal assemblages Abathomphalus
mayaroensis Zone
Samples l-9 represent the Abathomphalus mayforaminifers dominate the foraminiferal assemblages. P/B ratio ranges between 75 and 97%, and the number of species of planktonic foraminifers is 15-19 (Figs. 4 and 5). Large, massive, distinctly ornamented, mesoand bathypelagic forms, such as Globotruncana, aroensis Zone. Planktonic
Rosita, Globotruncanita, Abathomphalus, Pseudotextularia, Racemiguembelina, and Planoglobulina are present. The dominant species are Rosita contusa, Globotruncanita stuarti and Pseudotextularia spp. Rugoglobigerina is very rare. Hedbergella, Heterohelix, Globigerinelloides,
Guembelitria-representatives group-are lacking. Within the last 1 m
of the epipelagic of
the
uppermost
Abathomphalus mayaroensis Zone, the following extinctions are found: Globotruncanita pettersi in sample 4, Rugoglobigerina rotundata and Rosita patelliformis in sample 7, Globotruncanella petaloidea in sample 8 and Abathomphalus mayaroensis, Rosita contusa, R. waljishensis, Globotruncanita stuarti, G. angulata, G. stuartiformis, G. conica, Pseudotextularia brazoensis, Planglobulina deformis, P. elegans, Rugoglobigerina sp., R. milamensis, Racemiguembelina powelli, R. fructicosa, carseyae, multicamerata, P. Planoglobulina Globotruncana esnehensis, Hedbergella monmouthensis in sample 9 (Fig. 4). Sample 9 repre-
sents the main extinction level of Cretaceous planktonic foraminifers. It is difficult to determine whether the extinction of a few species of planktonic foraminifers in samples 4, 7 and 8 is background or related to the K/P boundary mass extinction. The distribution of iridium shows that these extinctions occurred considerably earlier than iridium anomaly (Fig. 4) and therefore they are regarded as having no
K/T BOUNDARY
AND PLANKTONIC
FORAMINIFERA:
EASTERN
245
ALPS
PPE
..
.
. .
IR
.
..
.
.
.
..... ..
. .. . ..
.. . .
.
1
........
20 50
. . .... .. ....
.
....
...
.
..
. . . . .. . . . ....
..
. . . .. . .... . . .
................. ..... ........
. .
30
.... .....
... . ..
. .
.... .. 5Qcm
!
l-
. . .
. . . .
.
.
.
.
.
. . .
Fig. 4. Distribution of planktonic foraminifers in uppermost Maastrichtian and lowermost Paleocene deposits in the Rotwandgraben section plotted against the succession and Ir distribution. Lithologies and other symbols are explained in Fig. 2.
246
D. PERYT
ET AL
Fig. 5. Contribution of the particular groups of foraminifers to the assemblages. Lithologies and other symbols are explained in Fig. 2.
relation to the events at the K/P boundary. However, the main extinctions occur in lower half of the iridium anomaly and appear to be directly related to the anomaly.
PO Zone-POa
or Guembelitria
cretacea Subzone
In the studied section the interval is 10 cm thick and consists of clay with l-cm-thick sandstone
K/T BOUNDARY
AND
PLANKTONIC
FORAMINIFERA:
EASTERN
intercalation (Figs. 3 and 4). The zone begins just above a 0.55l-cm-thick rusty layer. The greatest fauna1 and geochemical changes are related to the interval. Samples lo- 16 represent the Guembelitria cretatea Subzone (Fig. 4). Sample 10 is from the clay overlying the rusty layer where a considerable decrease of foraminiferal density and diversity is observed. P/B ratio decreases to 70% (Fig. 5), and the assemblage of planktonic foraminifers is represented by five species: Globotruncana arca, G. esnehensis, Planoglobulina carseyae, Racemiguembelina powelli and Pseudotextularia elegans. In the next sample, 11, the P/B ratio is
only 45%. Planktonic foraminifers of the uppermost Maastrichtian are absent. Significantly, very small, dwarfed heterohelicids and globigerinelloids such as Guembelitria cretacea, Heterohelix striata, H. globulosa, H. planata and Globigerinelloides aspera (Fig. 4) make their first local appearance. Prior to the K/P bc;mdary, these species were not present at the site. Such assemblages are characteristic of the earliest Danian and have been recorded from many other sections and described as K/T survivors (Brinkhuis and Zachariasse, 1988; Keller, 1988; Canudo et al., 1991; D’Hondt and Keller, 1991). In the upper part of the Guembelitria cretacea Subzone-in samples 12-16-both planktonic and benthic foraminifers are very rare. (The number of specimens from this part of the section was insufficient to use them for quantitative analyses; cf. Fig. 5). Planktonic foraminifers are represented by only three species: Globotruncana arca, G. esnehensis and Pseudotextularia elegans (Fig. 4) which are considered to be redeposited (Fig. 5). It is remarkable that even the dwarfed heterohelicids are lacking. Neither Paleocene planktonic foraminifers were recorded. PO Zone: POb or Globoconusa
247
ALPS
conusa Subzone
The interval is 50 cm thick and consists of intercalated fine-grained sandstones and clays. When compared to the Guembelitria cretacea Subzone, the increase in foraminiferal density in the sediment is observed. In the lower part of the subzone (sample 17), the assemblage of planktonic
foraminifers is composed of Cretaceous survivors, i.e. dwarfed heterohelicids and globigerinelloids, first Paleocene species-Globoconusa conusa and Eoglobigerina fringa, and relatively abundant reworked Maastrichtian species (Figs. 4 and 5). In the upper part of the subzone (samples 18 and 19) planktonic foraminiferal assemblages are composed only of reworked Maastrichtian species (Figs. 4 and 5). Pa or Parvularugoglobigerina
eugubina Zone
The interval is 47 cm thick and consists of intercalated calcareous marlstones, clays and sandstones. Two samples were examined (nos. 20 and 21). Planktonic foraminifers are very scarce (Fig. 5), represented by a few Paleocene planktonic species, e.g. Eoglobigerina fringa, Parvularugoglobigerina eugubina, Eoglobigerina sp. and dwarfed heterohelicids (Figs. 4 and 5) accompanied by rare and very poorly preserved, reworked globotruncanids. Within this subzone Cretaceous survivors became extinct (Fig. 4). Pl Zone: Pla or Subbotina pseudobulloides Subzone
Sample 22 is from the basal part of the subzone. Planktonic foraminifers are rare; they are represented by scarce, reworked Cretaceous forms and two Paleocene planktonic species-Subbotina pseudobulloides and Eoglobigerina sp. (Figs. 4 and 5). Geochemical anomaly The analysis of iridium content in clays of the K/P boundary indicates an abrupt enrichment in the 3-cm-thick interval above the marly limestone of the uppermost Maastrichtian, from 0.416 ppb 1.2 cm below the rusty layer, through 4.409 ppb and 5.326 ppb in the clay overlying the rusty layer, to 7.176 ppm 1.2 cm above the rusty layer. Above, an abrupt decrease of iridium content is observed (0.597 ppb 3 cm above the rusty layer). Four centimeters above the rusty layer the iridium content increases to 1.514 ppb, and higher in the section decreases gradually to 0.022 ppb in the Subbotina pseudobulloides Subzone (Figs. 4 and 6).
248
D. PERYT
Fauna1 turnover The planktonic foraminiferal assemblages from the uppermost Abathomphalus mayaroensis Zone are very abundant and moderately diversified. They are mainly represented by large and complex species of deep and intermediate dwellers. Smaller, globular, epipelagic forms are very rare. Such composition of assemblages probably resulted from dissolution of delicate globular forms during accumulation of these deposits at and/or below the foraminiferal lysocline. In the uppermost part of Abathomphalus mayaroensis Zone, a few species became extinct, i.e. Rugoglobigerina rotundata, Rosita patelliformis, Globotruncanita pettersi and Globotruncanella petaloidea. Canudo et al. (199 1) reported Globotruncanella petaloidea as a species which become extinct in the Parvularugoglobigerina longiapertura Zone. In the studied section, the species is very rare and its earlier disappearance probably resulted from dissolution of tests on the sea floor. The main extinction level corresponds to the OS-l-cm-thick dark yellow orange clay-
Sample
ROTWANDGRABEN (Bulk) Ir content Sample position (cm) (ppb)
,
ET AL.
the rusty layer. Immediately below the K/P boundary, 14 of the 19 species became extinct. They represent a group of large and complex species of deep and intermediate water dwellers. Above the rusty layer, contribution of the planktonic assemblage drops from 92 to 70%. The five next Maastrichtian species became extinct at this level. In the basal PO Zone none of the species from the uppermost Abathomphalus mayaroensis Zone is present. Instead for the first time in the section an assemblage composed of small triserial and biserial heterohelicids appears, such as Guembelitria cretatea and dwarfed Heterohelix striata, H. globulosa, H. planata and Globigerinelloides aspera. These species are common in many latest Maastrichtian assemblages. However, they are 2-3 times larger than the earliest Paleocene ones. Dwarfed heterohelicids and globigerinelloids are considered to be the Cretaceous survivors (Brinkhuis and Zachariasse, 1988; Keller, 1988, 1989; Canudo et al., 1991; D’Hondt and Keller, 1991). They became extinct within the Parvularugoglobigerina eugubina Zone. The first Paleocene species appear 15 cm above the K/P boundary. In the studied section, earliest Paleocene planktonic foraminifers are very scarce and assemblages are taxonomically impoverished compared to other sites. This is due to the dissolution of very fine tests of earliest Paleocene planktonic foraminifers during accumulation at and/or below the foraminiferal lysocline. K/P boundary
Fig. 6. Iridium interval.
content
in deposits
from
the K/P
boundary
According to the decision of the Working Group on the Cretaceous/Paleogene boundary, the boundary is characterized by the major planktonic foraminiferal extinction event and/or the first appearance datum of Cainozoic species, and a major lithologic change, including the presence of a thin red layer at the base of the boundary clay, anomalies marked by various geochemical (Canudo et al., 1991). The Rotwandgraben section possesses all these characteristics. In Rotwandgraben section as well as in other Alpine K/P boundary sections (Elendgraben, Knappengraben, Lattengebirge), the major Cretaceous species extinctions occur in the rusty layer (Herm et al., 1981; Preisinger et al.,
KIT BOUNDARY
AND
PLANKTONIC
FORAMINIFERA:
EASTERN
ALPS
1986; Stradner and Rogl, 1988). Abathomphalus mayaroensis became extinct at the same level. In Rotwandgraben as well as in Knappengraben the first Paleogene species (Globoconusa conusa and Eoglobigerina fringa) are found 15 cm above the rusty layer (Stradner and Rogl, 1988); in Lattengebirge sections Elendgraben and Eoglobigerina fringa appears 6 cm above the boundary layer (Herm et al., 1981; Preisinger et al., 1986). Iridium enrichments were found within the K/P boundary layers and also within the turbidites Elendgraben, immediately above at the sites and Rotwandgraben Knappengraben (Preisinger et al., 1986; Stradner et al., 1987). In the Rotwangraben section, the highest iridium value was measured 1.2 cm above the rusty layer. Discussion
The Cretaceous/Paleogene boundary is recognized as representative of one of the greatest mass extinctions in Earth history. Mass extinctions of many groups of organisms were accompanied by, or caused by, different abiotic events: a large meteorite impact (Alvarez et al., 1980; Smit, 1982; Smit and Ten Kate, 1982; Preisinger et al., 1986; Rampino and Volk, 1988; Rocchia et al., 1990b; Bhandari and Shukla, 1991; Hildebrand, 1991) hot spot volcanism (Officer and Drake, 1985; Hansen et al., 1986; Olmez et al., 1986; Officer et al., 1987; Lahodynsky, 1989; Rocchia et al., 1990a), climate warming by 6”-8” (Rampino and Volk, 1988; Smit, 1990) extensive forest fires (Wolbach et al., 1986) and latest Maastrichtian regression (Haq et al., 1987; Brinkhuis and Zachariasse, 1988; Keller, 1988; Peryt, 1988). The abrupt extinction of Cretaceous planktonic foraminifers constitutes a major base-line to delimit the K/P boundary in marine sections. K/P boundary levels in the marine record are associated with a drop in 6i3C and 6l*O values (e.g., Thierstein and Berger, 1978; Hsii et al., 1982; Perch-Nielsen et al., 1982; Rampino and Volk, 1988; Keller and Lindinger, 1989; Smit, 1990) as well as in CaC03 content. K/P boundary levels are also characterized by an iridium anomaly (Alvarez et al., 1980, 1982; Smit, 1982; Smit and Ten Kate, 1982; Hansen et al., 1986; Preisinger
249
et al., 1986; Stradner et al., 1987; Rocchia et al., 1990a,b; Bhandari and Shukla, 1991; Robin et al., 1991). Iridium peaks strongly correlate with elemental carbon and aluminium oxide (Hansen et al., 1986; Preisinger et al., 1986). Officer et al. (1987) and Rocchia et al. (1988, 1990a,b) recorded that at several K/P sites the anomalous concentration of iridium is not limited to the boundary layer but extends over a thickness of about one meter. In the Gubbio section, Rocchia et al. (1990a) found that iridium concentrations stand out above background over almost 3 m of section, corresponding to half a million years based on magnetostratigraphy. This extended distribution most probably results from post depositional diffusion (Robin et al., 1991). The cause of the iridium anomaly in deposits at the K/P boundary has been explained by an extraterrestrial impact (Alvarez et al., 1980, 1982; Preisinger et al., 1986; Rocchia et al., 1990b; Hildebrand, 1991; Robin et al., 1991) hot spot volcanism (Officer and Drake, 1985; Hansen et al., 1986; Olmez et al., 1986; Lahodynsky, 1989; Rocchia et al., 1990a), and reducing conditions during sedimentation (Nazarov et al., 1982). Bhandari and Shukla (1991) having analyzed several sections from the Indian subcontinent, concluded that the Deccan volcanism which had been suggested as a possible source of geochemical anomalies at K/P boundary was too small to give rise to the iridium anomaly worldwide. The occurrence of increased iridium concentrations in a very thin (2 cm) layer in Rotwandgraben section indicates a rather shortlasting source of the anomaly. In other Alpine sections, the increased iridium content is recorded in intervals a few centimeters thick and interpreted as being due to an extraterrestrial impact (Preisinger et al., 1986; Stradner et al., 1987). It seems that the event was also responsible for the iridium enrichment in the Rotwangraben section. A distinctive correlation between the extinction of a majority of Cretaceous species of planktonic foraminifers and the iridium anomaly indicates that the two are closely associated. Keller and Lindinger (1989) and D’Hondt and Keller (199 1) concluded on the basis of the negative
250
excursion of 6i3C at the K/P boundary that the main extinction level of planktonic foraminifers coincides with the decrease in marine primary productivity. It seems that the iridium anomaly, the decrease in marine primary productivity and the mass extinctions of planktonic foraminifera are interrelated. If the iridium anomaly is caused by meteorite impact(s), then the following scenario seems probable: The impact-related dust clouds may have suppressed sunlight long enough that photosynthesis was temporarily reduced on a global scale and primary productivity in the oceans was rapidly diminished (e.g., Alvarez et al., 1980, 1982; Smit, 1982, 1990; Smit and Ten Kate, 1982). The darkness could be additionally increased by the smoke from the extensive forest fires (Wolbach et al., 1986). A rapid decrease of primary productivity caused essential perturbations in the food chain which resulted in extinction of specialized groups of planktonic foraminifers (Keller and Lindinger, 1989; Smit, 1990; D’Hondt and Keller, 1991). Also a substantial increase in volcanism at K/P time (Hansen et al., 1986; Officer et al., 1987; Lahodynsky, 1988) as well as great fires would supply a significant amount of CO2 to the atmosphere (Wolbach et al., 1986) which, in turn, could have caused a greenhouse effect, global temperature increase, acid rains and decrease in surface ocean alkalinity. In addition, there was a pronounced late Cretaceous regression of the sea lasting for a few million years (e.g., Brinkhuis and Zachariasse, 1988; Keller, 1988). Vertical and horizontal distribution of planktonic foraminifers in the water column depends on many factors e.g. temperature, salinity, pH, water depth, nutrients, oxygen (Boltvskoy and Wright, 1976; Hemleben et al., 1989). Major changes of these factors may have led to the extinction of the most sensitive groups. Large and more complex dwellers are more sensitive to the environmental changes than small and primitive forms. The latter live predominantly in the uppermost 50-m-layer of water column and may live in less saline waters. They can also survive better in a lower pH environment than larger forms of planktonic foraminifers (Boltovskoy and Wright, 1976), and an environment that is under-
D. PERYT
ET AL.
going change is selective toward smaller species as compared with a more stable environment. Small, primitive forms are also the first colonizers of new niches. Most of the K/P boundary events influenced the oceans which resulted in paleoceanographic changes that led to the extinction of large, highly specialized forms of planktonic foraminifers. The earliest Paleocene planktonic foraminifers exhibit a change from large and complex forms to small and simple ones. At the K/P boundary, the previous biogeographic provincial differences disappear. The earliest Paleocene planktonic foraminifer assemblages are characterized in both open-ocean and epicontinental environments by forms previously dominant in epicontinental environments i.e. small, generelized forms (cf. Herm et al., 1981; Smit, 1982, 1990; Brinkhuis and Zachariasse, 1988; Keller, 1988, 1989; Canudo et al., 1991; D’Hondt and Keller, 1991).
Conclusions (1) A few species of planktonic foraminifers became extinct in the uppermost part of the Abathomphalus mayaroensis Zone. (2) The main extinction level is related to the rusty layer; 14 of 19 species recorded in the rusty layer do not occur in the overlying layer. (3) The five remaining species became extinct above the rusty layer. (4) An entirely new assemblage composed of Guembelitria cretacea and dwarfed Heterohelix striata, H. globulosa, H. sp., and Globigerinelloides aspera appears 2 cm above the rusty layer. A similar composition is characteristic for assemblages found in the lowermost Paleocene in many sites and regarded as Cretaceous survivors. (5) Other species of Maastrichtian planktonic foraminifers which are found higher up in the section, are considered to be reworked. (6) The first Paleocene planktonic foraminifers appear 15 cm above the K/P boundary. (7) A very small taxonomic diversity of planktonic foraminifers and their scarcity in the lowermost Paleocene section is explained by the dissolution of the most part of assemblages during
K,‘T BOUNDARY
AND
PLANKTONIC
FORAMINIFERA:
EASTERN
251
ALPS
deposition on the sea bottom that was probably located at/below the foraminiferal lysocline. (8) There is a correlation between the extinction of planktonic foraminifers and the presence of the iridium anomaly. Thirty percent of the former assemblage occurs in the deposit containing more than 4 ppb of iridium, and the content of 7 ppb is associated with complete lack of more complex Maastrichtian planktonic foraminifers, and only very primitive, cosmopolitan and dwarfed forms of Guembelitria, Heterohelix and Globigerinelloides occur. These forms may survive stressed environmental conditions which eliminate other forms and accordingly they are the first colonizers. (9) The cause of the iridium anomaly in Rotwandgraben section is probably an extraterrestrial impact. Acknowledgements
We are grateful to Dr. D.H. McNeil and an anonymous reviewer whose comments and suggestions were very useful. Thanks are due to E. Hara for processing samples and to D. Slawik for the drawings. This is CFR contribution no. 1366. References Alvarez, L.W., Alvarez, W., Asaro, F. and Michel, H.W., 1980. Extraterrestrial cause for the Cretaceous-Tertiary extinction. Science, 208: 1095-1108. Alvarez, W., Alvarez, L.W., Asaro, F. and Michel, H.W., 1982. Current status of the impact theory for the terminal Cretaceous extinction. Geol. Sot. Am. Spec. Pap., 190: 3055315. Berger, W.H., 1970. Planktonic foraminifera: selective solution and the lysocline. Mar. Geol., 8: 11 I-138. Berggren, W.A., 1969. Rates of evolution in some Cenozoic planktonic foraminifera. Micropaleontology, 15: 351-365. Berggren, W.A., 1978. Recent advances in Cenozoic planktonic foraminiferal biostratigraphy, biochronology and biogeography: Atlantic Ocean. Micropaleontology, 24: 337-370. Berggren, W.A. and Van Couvering, J.T., 1974. The late Neogene. Biostratigraphy, geochronology and paleoclimatology of the last 15 millions years in marine and continental sequences. Palaeogeogr., Palaeoclimatol., Palaeoecol., 16: I-215. Berggren, W.A. and Miller, K.G., 1988. Paleogene tropical planktonic foraminiferal biostratigraphy and magnetobiochronology. Micropaleontology, 34: 362-380. Bhandari, N. and Shukla, P.N., 1991. Geochemistry of K/T boundary sections in India. Symp. Event Markers in Earth History. Progr. Abstr., p, 17.
Blow, W.H., 1979. The Cainozoic Globigerinida. A Study of the Morphology, Taxonomy, Evolutionary Relationships and the Stratigraphical Distribution of Some Globigerinida (Mainly Globigerinacea). Brill, Leiden, 1413 pp. Bolli, H.M., 1957. The genera Praeglobotruncana, Rotalipora, Globotruncana and Abathomphalus in the Upper Cretaceous of Trinidad. Bull. U.S. Nat. Mus., 215: 51-60. Bolli, H.M., 1966. Zonation of Cretaceous to Pliocene marine sediments based on planktonic foraminifera. Asoc. Venez. Geol. Min. Petrol., Bol. Inform., 9: 2-32. Boltovskoy, E. and Wright, R., 1976. Recent Foraminifera. W. Junk, The Hague, 515 pp. Brinkhuis, H. and Zachariasse, W.J., 1988. Dinoflagellate cysts, sea level changes and planktonic foraminifers across the Cretaceous/Tertiary boundary at El-Haria, northwest Tunisia. Mar. Micropaleontol., 13: 153-191. Butt, A., 1981. Depositional environments of the Upper Cretaceous rocks in the northern parts of the Eastern Alps. Cushman Found. Foraminiferal Res. Spec. Publ., 20: 5-121. Canudo, J.I., Keller, G. and Molina, E., 1991. Cretaceous/Tertiary boundary extinction pattern and fauna1 turnover at Agost and Caravaca, S.E. Spain. Mar. Micropaleontol., 17: 319-341. Caron, M., 1985. Cretaceous planktic foraminifera. In: H.M. Bolli, J.B. Saunders and K. Perch-Nielsen (Editors), Plankton Stratigraphy. Cambridge Univ. Press, Cambridge, pp. 17786. Coulbourn, W.T., Parker, F.L. and Berger, W.H., 1980. Fauna1 and solution patterns of planktonic foraminifera in surface sediments of the North Pacific. Mar. Micropaleontol., 5: 329-399. D’Hondt, S. and Keller, G., 1991. Some patterns of planktic foraminiferal assemblage turnover at the Cretaceous-Tertiary boundary. Mar. Micropaleontol., 17: 777118. Hansen, H.J., Gwozdz, R., Hansen, J.M., Bromley, R.G. and Rasmussen, K.L., 1986. The diachronous C/T plankton extinction in the Danish Basin. In: O.H. Walhser (Editor), Global Bio-Events. Lecture Notes Earth Sci., 8: 381-384. Haq, B.U., Hardenbol, J. and Vail, P.R., 1987. Chronology of fluctuating sea level since the Triassic. Science, 235: 1156-l 166. Hemleben, Ch., Spindler, M. and Anderson, O.R., 1989. Modern Planktonic Foraminifera. Springer, New York, 363 pp. Herm, D., Von Hillebrandt, A. and Perch-Nielsen, K., 1981. Die Kreide/Tertiargrenze im Lattengebirge (Nordliche Kalkalpen) in mikropalaontologischer 82: 3 19-344.
Sicht. Geol. Bavarica,
Hesse, R. and Butt, A., 1976. Paleobathymetry turbidite basins of the East Alps relative compensation level. J. Geol., 84: 505-533.
of Cretaceous to the calcite
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