GERTA KELLER PUBLICATIONS

The Paleocene-Eocene transition in the southern Tethys (Tunisia); climatic and environmental fluctuations

TitleThe Paleocene-Eocene transition in the southern Tethys (Tunisia); climatic and environmental fluctuations
Publication TypeJournal Article
Year of Publication1999
AuthorsBolle, MP, Adatte, T, Keller, G, von Salis, K, Burns, S
JournalBulletin de la Société Géologique de France
Volume170
Pagination661
Abstract

This study, based on a multidisciplinary approach including micropaleontology, sedimentology, mineralogy and geochemistry, evaluates the Paleocene-Eocene transition in Tunisia. At Foum Selja, sediment deposition occurred in the shallow, restricted Gafsa Basin influenced by the adjacent Saharan Platform. During the early Paleocene this area experienced a warm and humid climate that changed to warm but arid climatic conditions during the Paleocene-Eocene transition. At Elles the sediment deposition in the El Kef Basin occurred in an open marine environment connected to the Tethys. During the late Paleocene, the Tethyan region was submitted to a seasonal warm climate changing to a warm and humid climate across the P/E transition and becoming seasonal/arid in the early Eocene. From Africa to northern Europe, kaolinite, a strong marker of warmth and humidity disappeared diachronously suggesting a latitudinal shift in the source area of this mineral and consequently in the climatic zones, from lower to higher latitudes. The P/E transition observed at Elles corresponds to a 2.7 m thick clay layer and is marked by a drastic decrease in carbonate sedimentation, a negative delta 13 C excursion of 1.3 per mil and increased detrital input. The presence of a condensed interval, the accumulation of phosphate deposits after the P/E event, which obliterate the original isotopic signal and strong dissolution of the planktic fauna and flora in these phosphatic layers, all are criteria that prevent the Elles section to be a potential GSSP candidate for the P/E boundary.   PDF

URL+ http://dx.doi.org/

The Late Campanian and Maastrichtian in northwestern Tunisia: palaeoenvironmental inferences from lithology, macrofauna and benthic foraminifera

TitleThe Late Campanian and Maastrichtian in northwestern Tunisia: palaeoenvironmental inferences from lithology, macrofauna and benthic foraminifera
Publication TypeJournal Article
Year of Publication1999
AuthorsLi, L, Keller, G, Stinnesbeck, W
JournalCretaceous Research
Volume20
Pagination231–252
Date Publishedapr
Abstract

Late Campanian through Maastrichtian sea-level changes are examined based on lithology, macrofossils and benthic foraminifera at the Elles and El Kef sections in Tunisia. Six major sea-level regressions are identified during the late Campanian (74.4–74.2 Ma, 74.0–72.5 Ma), the Campanian-Maastrichtian transition (72.2–70.3 Ma), early Maastrichtian (69.6–69.3 Ma, 68.9–68.3 Ma), and late Maastrichtian (∼65.5 Ma). Correlation of the Maastrichtian sea-level regressions with the oxygen isotope record of DSDP Site 525 in the middle latitude South Atlantic reveals that they coincide with episodes of high latitude cooling and appear to be of eustatic origin.   PDF

URLhttps://doi.org/10.1006/cres.1999.0148
DOI10.1006/cres.1999.0148

Aspectos paleoceanográficos y paleoecológicos del límite Cretácico/Terciario en la Península de Mangyshlak (Kazakstan): inferencias a partir de foraminíferos planctónicos.

TitleAspectos paleoceanográficos y paleoecológicos del límite Cretácico/Terciario en la Península de Mangyshlak (Kazakstan): inferencias a partir de foraminíferos planctónicos.
Publication TypeJournal Article
Year of Publication1999
AuthorsPardo, A, Gerta, K
JournalRev. Esp. Micropal
Volume31
Issue2
Pagination265-278
Abstract

Comparison of planktic foraminiferal assemblages from sections at Koshak and Kyzylsai (boreal Paratethys) allows an analysis of the biotic crisis occurred during the Cretaceous-Tertiary transition (K-T) in the Mangyslak Peninsula. Foraminiferal assemblages in both sections are typically oligotaxic, with low species richness and a single dominant species (Chiloguembelina waiparaensis), through the late Maastrchtian and early Danian. In the latest Maastrichtian in the Koshak and Kyzylsai sections, a group of exotic planktic foraminifera from low latitudes appears in the assamblage, suggesting seawater warming and a rising sea level. These are tropical-subtropical, large and ornate planktic foraminifera that account for less than 25% of the assemblage and they disappear before or at the K/T boundary in both sections. The species that survive the K/T boundary are the endemic, small, cosmopolitan opportunists, they are biserial, triserial and trochospiral taxa of simple morphologies, mostly surface dwellers or able to tolerate low oxygen conditions. These survivor taxa account for more than 75% of the assemblage. Decreased primary productivity and oxygen during the latest Maastrichtian are suggested as the main factors for the K/T biotic crisis and its ecologic selectivity in the low latitudes. However, in high latitudes environmental conditions (including productivity) changed little and this resulted in a less catastrophic K/T boundary biotic event.

URLhttp://www.igme.es/Publicaciones/revistaMicro/vol32/rem29apardo.htm

Paleoenvironmental changes across the Cretaceous–Tertiary boundary at Koshak, Kazakhstan, based on planktic foraminifera and clay mineralogy

TitlePaleoenvironmental changes across the Cretaceous–Tertiary boundary at Koshak, Kazakhstan, based on planktic foraminifera and clay mineralogy
Publication TypeJournal Article
Year of Publication1999
AuthorsPardo, A, Adatte, T, Keller, G, Oberhänsli, H
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume154
Pagination247–273
Date Publishednov
Abstract

The Koshak section of the Mangyshlack Peninsula, Kazakhstan, is one of the most complete Cretaceous–Tertiary (K–T) transitions known from the boreal Paratethys. Cretaceous species richness is low (11 to 13 species), except for a peak of 20 species near the K/T boundary in the uppermost Maastrichtian (top 50 cm) that represents the temporary incursion of low-latitude taxa. This maximum species richness occurred during climatic warming associated with increased humidity, as suggested by clay mineral analyses. Biofacies analysis suggests external platform conditions at this time, followed by a more humid climate, a sea-level transgression, and deepening basinal facies in the lower Danian Subzone P1a. Shallower platform conditions resumed in Danian Subzones P1b and P1c, accompanied by a cooler and probably more arid climate. No abrupt mass extinction occurred at the Koshak K/T boundary which is marked by an Ir anomaly, a clay layer and the first appearance of Tertiary planktic foraminifera. The influx of lower-latitude species ends at or before the K/T boundary, whereas the majority of the indigenous Cretaceous assemblage survived into the Danian. These data suggest that long-term climatic changes may have been the principal factors in the progressive demise of the Cretaceous planktic foraminifera in the eastern boreal Paratethys.   PDF

URLhttps://doi.org/10.1016/s0031-0182(99)00114-5
DOI10.1016/s0031-0182(99)00114-5

Paleoecologic and paleoceanographic evolution of the Tethyan realm during the Paleocene-Eocene transition

TitlePaleoecologic and paleoceanographic evolution of the Tethyan realm during the Paleocene-Eocene transition
Publication TypeJournal Article
Year of Publication1999
AuthorsPardo, A, Keller, G, Oberhaensli, H
JournalThe Journal of Foraminiferal Research
Volume29
Pagination37-57
Abstract

Analyses of planktic foraminifera and stable isotopes from sections in Kazakstan (Kaurtakapy), Spain (Alamedilla, Zumaya) and the Bay of Biscay (DSDP Site 401) suggest similar overall paleoecologic, paleoceanographic and paleoclimatic patterns during the Paleocene-Eocene (P-E) transition, although regional differences are apparent. The major difference in delta 13 C values measured in benthic Cibicidoides spp. is seen in the gradual decrease of approximately 1 per mil in Subzones P5a and P5b in the Tethys and its absence elsewhere. In planktic foraminifera, regional differences are marked by changes in the relative abundances of warm water taxa and cool water subbotinids. Overall, the P-E transition is marked by the following sequence of faunal and isotopic events. Near the P-E boundary (Zone P5b) and coincident with the benthic foraminiferal extinction event and the delta 13 C excursion, warm water planktic foraminiferal assemblages (e.g., acarininids, igorinids and morozovellids) rapidly diversified, suggesting surface water warming. Thereafter (Zone P5b/P6a), increased abundance in cool-temperate planktic foraminifera (e.g., subbotinids) and a concomitant increase in the abundance of low oxygen tolerant chiloguembelinids, suggest cooling and hypoxic conditions at thermocline depths that may have been due to changes in watermass stratification and upwelling. This cooling is followed by a second more gradual warming, where acarininids slowly replace morozovellids as the dominant surface dwellers. The biozonation of Berggren and others (1995) has been modified by subdividing Zone P5 into Subzones P5a and P5b based on the first appearance of Acarinina sibaiyaensis and/or Acarinina africana. This modification of Zone P5 provides greater age control for the P-E event with the P5a/P5b boundary coincident with the BFEE and the delta 13 C excursion.

URLhttp://jfr.geoscienceworld.org/content/29/1/37.abstract

Beloc, Haiti, revisited: multiple events across the KT boundary in the Caribbean

TitleBeloc, Haiti, revisited: multiple events across the KT boundary in the Caribbean
Publication TypeJournal Article
Year of Publication1999
AuthorsStinnesbeck, W, Keller, G, Adatte, T, Stüben, D, Kramar, U, Berner, Z, Desremeaux, C, Moliere, E
JournalTerra Nova
Volume11
Issue6
Pagination303 - 310
Date PublishedOct-12-1999
ISSN0954-4879
Abstract

Examination of new expanded K/T boundary sections near Beloc, Haiti, reveals deposition of a glass spherule-rich deposit (SRD) and two (PGE) anomalies (one Ir-dominated and one Pd-dominated) during the early Danian Parvularugoglobigerina eugubina Zone [Pla(l)]. The presence of the Haiti SRD within the early Danian is interpreted as being due to reworking. Ir is only slightly elevated within the SRD but forms an anomaly at the top of the SRD extending into the overlying pelagic limestones. It is unclear at present whether this Ir anomaly results from mechanical reworking of an impact at the K/T boundary, or an additional impact event in the early Danian. The second PGE anomaly upsection is dominated by Pd and Pt and is more compatible with a magmatic origin. This suggests a multi-event scenario consistent with one (and possibly two) impact(s), followed by a PGE-enriched volcanic event in the Caribbean.  PDF

URLhttp://doi.wiley.com/10.1046/j.1365-3121.1999.00263.x
DOI10.1046/j.1365-3121.1999.00263.x
Short TitleTerra Nova

The Paleocene-Eocene transition in the southern Tethys (Tunisia); climatic and environmental fluctuations

TitleThe Paleocene-Eocene transition in the southern Tethys (Tunisia); climatic and environmental fluctuations
Publication TypeJournal Article
Year of Publication1999
AuthorsBolle, MP, Adatte, T, Keller, G, von Salis, K, Burns, S
JournalBulletin de la Societe Geologique de France
Volume170
Pagination661-680
Abstract

This study, based on a multidisciplinary approach including micropaleontology, sedimentology, mineralogy and geochemistry, evaluates the Paleocene-Eocene transition in Tunisia. At Foum Selja, sediment deposition occurred in the shallow, restricted Gafsa Basin influenced by the adjacent Saharan Platform. During the early Paleocene this area experienced a warm and humid climate that changed to warm but arid climatic conditions during the Paleocene-Eocene transition. At Elles the sediment deposition in the El Kef Basin occurred in an open marine environment connected to the Tethys. During the late Paleocene, the Tethyan region was submitted to a seasonal warm climate changing to a warm and humid climate across the P/E transition and becoming seasonal/arid in the early Eocene. From Africa to northern Europe, kaolinite, a strong marker of warmth and humidity disappeared diachronously suggesting a latitudinal shift in the source area of this mineral and consequently in the climatic zones, from lower to higher latitudes. The P/E transition observed at Elles corresponds to a 2.7 m thick clay layer and is marked by a drastic decrease in carbonate sedimentation, a negative delta 13 C excursion of 1.3 per mil and increased detrital input. The presence of a condensed interval, the accumulation of phosphate deposits after the P/E event, which obliterate the original isotopic signal and strong dissolution of the planktic fauna and flora in these phosphatic layers, all are criteria that prevent the Elles section to be a potential GSSP candidate for the P/E boundary.

URLhttp://bsgf.geoscienceworld.org/content/170/5/661.abstract

Variability in Late Cretaceous climate and deep waters: evidence from stable isotopes

TitleVariability in Late Cretaceous climate and deep waters: evidence from stable isotopes
Publication TypeJournal Article
Year of Publication1999
AuthorsLi, L, Keller, G
JournalMarine Geology
Volume161
Issue2-4
Pagination171 - 190
Date PublishedJan-10-1999
ISSN00253227
KeywordsMaastrichtian; Stable isotopes; Climate; Deep-water
Abstract

Strong climatic and temperature fluctuations mark the Late Campanian and Maastrichtian as indicated by stable isotope records from the equatorial Pacific (Site 463) and middle and high latitude South Atlantic (Sites 525, 689 and 690). The first major global cooling decreased intermediate water temperatures (IWT) by 5–6°C between 73–70 Ma. At the same time, sea surface temperature (SST) decreased by 4–5°C in middle and high latitudes. Intermediate waters (IW) temporarily warmed by 2°C in low and middle latitudes between 70–68.5 Ma. Global cooling resumed between 68.5–65.5 Ma when IWT decreased by 3–4°C and SST by 5°C in middle latitudes. About 450 ka before the Cretaceous–Tertiary boundary rapid global warming increased IWT and SST by 3–4°C, though SST in the tropics changed little. During the last 200 ka of the Maastrichtian, climate cooled rapidly with IWT and SST decreasing by 2–3°C. During the global cooling at 71–70 Ma and possibly at 67–65.5 Ma, the sources of cold intermediate waters in the equatorial Pacific, Indo-Pacific and South Atlantic were derived from the high latitude North Pacific. In contrast, during the global climate warming between 65.2–65.4 Ma, the middle latitude South Atlantic was closest to the source of IW production and implies that the low latitude Tethys played a major role in global climate change. Climate changes, sea-level fluctuations and associated restricted seaways appear to be the most likely mechanisms for the alternating sources of IW production.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S002532279900078X
DOI10.1016/S0025-3227(99)00078-X
Short TitleMarine Geology

Diversification and extinction in Campanian-Maastrichtian planktic foraminifera of northwestern Tunisia

TitleDiversification and extinction in Campanian-Maastrichtian planktic foraminifera of northwestern Tunisia
Publication TypeJournal Article
Year of Publication1998
AuthorsLi, L, Keller, G
JournalEclogae Geologicae Helvetiae
Volume91
Issue1
Start Page75 - 102
Abstract

Investigation of Campanian-Maastrichtian planktic foraminifera in north Tunisia reveals that the late Maastrichtian not only ends with a mass extinction, but also attains maximum species diversity during theirevolutionary history. Maximum species diversity is reached during global cooling in the early late Maastrichtian over a 600 kyr interval (69.1-69.7 Ma) when species richness nearly doubled with the evolution of many rugoglobigerinids and globotruncanids. No species extinctions occur at this time and there is little change in the relative abundanceof existing species, whereas new species did not evolve into numerically large populations during the succeeding late Maastrichtian. This suggests that species originations did not result in major competition and that the early-late Maastrichtian climatic cooling may have resulted in increased habitats and nutrient supply for marine plankton. The onset of the permanent decline in Cretaceous species richness began at65.9 Ma and accelerated during the last 50-100 kyr of the Maastrichtian, culminating in the mass extinction of all tropical and subtropicaltaxa at the end of the Maastrichtian. Climate changes appear to be responsible for both the rapid evolutionary activity in the early late Maastrichtian, as well as the gradual decline in species richness near the end of the Maastrichtian, although the additional stress imposed on the ecosystem by a bolide impact is the likely cause for the final demise of the tropical and subtropical fauna at the K-T boundary.

URLhttp://serials.unibo.it/cgi-ser/start/it/spogli/df-s.tcl?prog_art=5567963&language=ITALIANO&view=articoli

Abrupt deep-sea warming at the end of the Cretaceous

TitleAbrupt deep-sea warming at the end of the Cretaceous
Publication TypeJournal Article
Year of Publication1998
AuthorsLi, L, Keller, G
JournalGeology
Volume26
Pagination995-998
Abstract

Climatic and oceanographic variations during the last 2 m.y. of the Maastrichtian inferred from high-resolution (10 k.y.) stable isotope analysis of the mid-latitude South Atlantic Deep Sea Drilling Project Site 525 reveal a major warm pulse followed by rapid cooling prior to the Cretaceous-Tertiary boundary. Between 66.85 and 65.52 Ma, cool but fluctuating temperatures average 9.9 and 15.4 °C in intermediate and surface waters, respectively. This interval is followed by an abrupt short-term warming between 65.45 and 65.11 Ma, which increased temperatures by 2–3 °C in intermediate waters, and decreased the vertical thermal gradient to an average of 2.7 °C. This warm pulse may be linked to increased atmospheric pCO2, increased poleward heat transport, and the switch of an intermediate water source from high to low-middle latitudes. During the last 100 k.y. of the Maastrichtian, intermediate and surface temperatures decreased by an average of 2.1 and 1.4 °C, respectively, compared to the maximum temperature between 65.32 and 65.24 Ma.  PDF

URLhttp://geology.gsapubs.org/content/26/11/995.abstract
DOI10.1130/0091-7613(1998)026<0995:ADSWAT>2.3.CO;2

Maastrichtian climate, productivity and faunal turnovers in planktic foraminifera in South Atlantic DSDP sites 525A and 21

TitleMaastrichtian climate, productivity and faunal turnovers in planktic foraminifera in South Atlantic DSDP sites 525A and 21
Publication TypeJournal Article
Year of Publication1998
AuthorsLi, L, Keller, G
JournalMarine Micropaleontology
Volume33
Issue1-2
Pagination55 - 86
Date PublishedJan-02-1998
ISSN03778398
Abstract

Stratigraphic, faunal and isotopic analyses of the Maastrichtian at DSDP sites 525A and 21 in the South Atlantic reveal a planktic foraminiferal fauna characterized by two major events, an early late Maastrichtian diversification and end-Maastrichtian mass extinction. Both events are accompanied by major changes in climate and productivity. The diversification event which occurred in two steps between 70.5 and 69.1 Ma increased species richness by a total of 43% and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity. The onset of the terminal decline in Maastrichtian species richness began at 67.5 Ma and the first significant decline in surface productivity occurred at 66.2 Ma, coincident maximum cooling to 13°C in surface waters and the reduction of the surface-to-deep temperature gradient to less than 5°C. Major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the Maastrichtian. Between 200 and 400 kyr before the K/T boundary surface and deep waters warmed rapidly by 3–4°C and cooled again during the last 100 kyr of the Maastrichtian. Surface productivity decreased only moderately across the K/T boundary. Species richness began to decline during the late Maastrichtian cooling and by K/T boundary time, the mass extinction had claimed 66% of the species. Viewed within the context of Maastrichtian climate and productivity changes, the K/T mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0377839897000273
DOI10.1016/S0377-8398(97)00027-3
Short TitleMarine Micropaleontology

Biostratigraphy, mineralogy and geochemistry of the Trabakua Pass and Ermua sections in Spain : Paleocene-Eocene transitions

TitleBiostratigraphy, mineralogy and geochemistry of the Trabakua Pass and Ermua sections in Spain : Paleocene-Eocene transitions
Publication TypeMiscellaneous
Year of Publication1998
AuthorsKeller, G, Bolle, M-P, Adatte, T
Abstract

Isotopie, geochemical and bulk mineralogical analyses in the Trabakua and Ermua sections. Basque Basin, reveal major changes across the Paleocene- Eocene transition. Expanded sedimentary records exhibit a gradual decrease of 1.0 %o in 5 "C values in the lower part of Zone P5 followed by a more rapid 3 %o negative excursion. The 3 %si S l3C excursion is associated with an abrupt decrease in carbonate sedimentation, increased detrital flux and decreased grain size which suggest changes in marine/atmospheric currents and/or size and structure of the ocean carbon reservoir. The clays recognized at Trabakua record a deep burial diagenesis as indicated by two generations of chlorite. the presence of mixed-layers chlorite-smectite and illite-smectite. the absence of smectite and the near absence of kaolinite. The very low 5 "O values (<-3.5%o) throughout the Trabakua and Ermua sections reflect diagenetic al¬ teration rather than paleotemperatures. Because of deep burial diagenesis and very poorly preserved microfossils. the Trabakua Pass and Ermua sections are not optimal potential stratotypes for the Paleocene-Eocene boundary.  PDF

DOI10.5169/seals-168405

The K/T mass extinction, Chicxulub and the impact-kill effect

TitleThe K/T mass extinction, Chicxulub and the impact-kill effect
Publication TypeJournal Article
Year of Publication1998
AuthorsKeller, G, Li, L, Stinnesbeck, W, Vicenzi, E
JournalBulletin de la Société Géologique de France
Volume169
Pagination485
Abstract

The Chicxulub structure on Yucatan is now commonly believed to have been formed by the Cretaceous/Tertiary (K/T) boundary bolide impact that caused the catastrophic extinction of organisms from dinosaurs to microplankton. However, the mass extinction began well before the K/T boundary and the kill-effect that may be directly attributed to a K/T impact is relatively small (only planktonic foraminifera and nannoplankton affected), highly selective (only tropical-subtropical species extinct) and restricted to low latitudes. Moreover, key evidence cited in support of Chicxulub as K/T impact crater is still controversial (e.g., impact origin of glass), or contradictory : the so-called "impact-generated megatsunami deposits" in northeastern Mexico contain burrowing horizons that indicate deposition occurred over an extended period of time. This database suggests a multi-event scenario that includes a pre-K/T event (impact or volcanism) that formed the spherule deposits in northeastern Mexico and a K/T event (Ir anomaly, mass extinction) with both events coinciding with climatic and sea level fluctuations during the last 200-300 kyr of the Maastrichtian.  PDF

URL+ http://dx.doi.org/

The Cretaceous-tertiary transition on the shallow Saharan Platform of southern tunisia

TitleThe Cretaceous-tertiary transition on the shallow Saharan Platform of southern tunisia
Publication TypeJournal Article
Year of Publication1998
AuthorsKeller, G, Adatte, T, Stinnesbeck, W, Stüben, D, Kramar, U, Berner, Z, Li, L, Perch-Nielsen, Kvon Salis
JournalGeobios
Volume30
Pagination951–975
Date Published01/1998
Abstract

A multidisciplinary approach to the study of a K/T boundary section on the Saharan Platform based on planktic and benthic foraminifera, calcareous nannofossils, lithology, stable isotopes, mineralogy and geochemistry reveals a biota stressed by fluctuating hyposaline, hypoxic littoral and nearshore environments, productivity changes, and a paleoclimate altering between seasonal warm to temperate and warm/humid conditions. Benthic formaminifera indicate that during the last 300 kyr of the Maastrichtian (CF1, Micula prinsii) deposition occurred in a inner neritic (littoral) environment that shallowed to a near-shore hyposaline and hypoxic environment during the last 100–200 kyr of the Maastrichtian. These conditions were accompanied by a seasonal warm to temperate climate that changed to warm/humid conditions with high rainfall, by decreasing surface productivity, and significantly decreasing planktic and benthic foraminiferal species richness. The K/T boundary is marked by an undulating erosional contact overlain by a 10 cm thick sandstone layer which is devoid of any exotic minerals or spherules. Their absence may be due to a short hiatus and the fact that the characteristic clay and red layer (zone P0) are missing. During the earliest Danian (Pla), low sea-levels prevailed with continued low oxygen, low salinity, high rainfall, high erosion and terrigenous sediment influx, accompanied by low diversity, low oxygen and low salinity tolerant species. These environmental conditions abruptly ended with erosion followed by deposition of a phosphatic siltstone layer that represents condensed sedimentation in an open (transgressive) marine environment. Above this layer, low sealevels and a return to near-shore, hyposaline and hypoxic conditions prevailed for a short interval [(base of Plc(2)] and are followed by the re-establishment of normal open marine conditions (inner neritic) comparable to the late Maastrichtian. This marine transgression is accompanied by increased productivity, and the first diversified Danian foraminiferal assemblages after the K/T boundary event and represents the return to normal biotic marine conditions. Though the K/T Seldja section represents one of the most shallow marginal sea environments studied to date for this interval, it does not represent isolated or atypical conditions. This is suggested by the similar global trends observed in sea-level fluctuations, hiatuses, as well as faunal assemblages. We conclude that on the Saharan platform of southern Tunisia, longterm environmental stresses beginning 100–200 kyr before the K/T boundary and related to climate, sea-level, nutrient, oxygen and salinity fluctuations, were the primary causes for the eventual demise of the Cretaceous fauna in the early Danian. The K/T boundary bolide impact appears to have had a relatively incidental short-term effect on this marine biota.  PDF

URLhttps://doi.org/10.1016/s0016-6995(97)80218-5
DOI10.1016/s0016-6995(97)80218-5

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