GERTA KELLER PUBLICATIONS

High-resolution geochemical record of Cretaceous-Tertiary boundary sections in Mexico: New constraints on the K/T and Chicxulub events

TitleHigh-resolution geochemical record of Cretaceous-Tertiary boundary sections in Mexico: New constraints on the K/T and Chicxulub events
Publication TypeJournal Article
Year of Publication2005
AuthorsStüben, D, Kramar, U, Harting, M, Stinnesbeck, W, Keller, G
JournalGeochimica et Cosmochimica Acta
Volume69
Issue10
Pagination2559 - 2579
Date PublishedJan-05-2005
ISSN00167037
Abstract

The investigation of eight Cretaceous–Tertiary (K/T) sections in Mexico, based on major and trace element, platinum group element (PGE), stable isotope, and multivariate statistical analysis, reveals a complex depositional history across the Chicxulub and K/T boundary events. At the biostratigraphically determined K/T boundary, a minor but significant Ir-dominated PGE anomaly (0.2– 0.8 ng/g) is present in most sections. This Ir anomaly originated from an impact event and is always stratigraphically and geochemically decoupled from the underlying spherule-rich ejecta deposit related to the Chicxulub event. In all sections examined, one to three glass spherule ejecta layers and one or two chondrite-dominated PGE anomalies are separated by a bioturbated siliciclastic deposit and/or hemipelagic marl, which indicates the occurrence of at least two impact events separated by a considerable amount of time. In addition, bentonite layers and Pt and Pd-dominated PGE anomalies below and above the K/T boundary indicate volcanic activity. Above the K/T boundary, reduced bioproductivity is documented by a decrease in the biogenically bound fraction of nutrients and fluctuating ratios of immobile elements (e.g., Ti/Zr). Variations in detrital elements reflect changes in the depositional environment. Carbon and oxygen isotope and trace element distribution patterns indicate a gradually changing climate during the latest Maastrichtian, an abrupt change at the K/T boundary, and a slight recovery during the lowermost Paleocene.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0016703704008622
DOI10.1016/j.gca.2004.11.003
Short TitleGeochimica et Cosmochimica Acta

Basinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, NE Mexico: Comment and Reply: COMMENT

TitleBasinward transport of Chicxulub ejecta by tsunami-induced backflow, La Popa basin, NE Mexico: Comment and Reply: COMMENT
Publication TypeJournal Article
Year of Publication2005
AuthorsStinnesbeck, W, Schafhauser, A, Götz, S
JournalGeology
Volume33
Paginatione86
Abstract

Valley-fi ll deposits in the continental to shallow marine La Popa basin to the northwest of Monterrey, Mexico, are interpreted by Lawton et al. (2005) as the result of Chicxulub impact-induced tsunami backfl ow. There is little if any support for this notion in their paper and it contradicts their earlier publication on the same outcrops (Lawton et al., 2001).  PDF

URLhttp://geology.gsapubs.org/content/33/1/e86.short
DOI10.1130/0091-7613-33.1.e86

Disaster opportunists Guembelitrinidae: index for environmental catastrophes

TitleDisaster opportunists Guembelitrinidae: index for environmental catastrophes
Publication TypeJournal Article
Year of Publication2004
AuthorsKeller, G, Pardo, A
JournalMarine Micropaleontology
Volume53
Issue1-2
Pagination83 - 116
Date PublishedJan-10-2004
ISSN03778398
KeywordsGuembelitria blooms; Volcanism; impacts; K–T; late Maastrichtian
Abstract

Blooms of the disaster opportunist Guembelitria species are proxies for environmental catastrophes, whether impact orvolcanism, leading to severe biotic stress crises that may range from temporary exclusion of ecological specialists and generalists to mass extinctions. During the late Maastrichtian and early Danian (zones P0 and Pla), Guembelitria blooms show global distributions, but with the largest blooms (40–80% Guembelitria) in low and middle latitudes and only minor blooms (10–20%) in high latitudes. Late Maastrichtian Guembelitria blooms are, so far, known from the Indian Ocean and eastern Tethys. The most intense Guembelitria blooms (>60% Guembelitria) occurred in shallow continental shelf areas, slope/shelf margins and volcanic provinces of the Indian Ocean. What these environments have in common is high nutrient influx (eutrophication) either from continental runoff, upwelling along continental margins or volcanic input. At times of biotic crises, Guembelitria blooms may have spread rapidly to the exclusion of most or all other species, much like today’s red tides, but with near global distributions. A simple model can explain the ecological succession and recovery phases that follow major biotic perturbations caused by impacts or volcanism that lead to exclusion of specialist and most generalist species. Within such highly stressed environments, Guembelitria is the only genus to thrive, and without competition, rapidly reproduce and exponentially increase their populations. When nutrients are depleted, populations rapidly decrease, leading to ecologic niches for other generalists and ecosystem recovery. Small low-O2-tolerant heterohelicid populations mark this second stage, followed by small trochospiral and planispiral species. With further environmental recovery, increasing competition, niche development and restoration of a well-stratified water mass, oligotrophic conditions are restored, opening habitats for the highly specialized and diverse species and a return to normal diverse assemblages. This ecological succession is observed in association with mantle plume volcanism in the Indian Ocean and eastern Tethys during the late Maastrichtian, and in association with the K–T impact and volcanism during the early Tertiary.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0377839804000672
DOI10.1016/j.marmicro.2004.04.012
Short TitleMarine Micropaleontology

Yaxcopoil-1 and the Chicxulub impact

TitleYaxcopoil-1 and the Chicxulub impact
Publication TypeJournal Article
Year of Publication2004
AuthorsStinnesbeck, W, Keller, G, Adatte, T, Harting, M, Stüben, D, Istrate, G, Kramar, U
JournalInternational Journal of Earth Sciences
Volume93
Issue6
Pagination1042 - 1065
Date PublishedJan-12-2004
ISSN1437-3254
Abstract

CSDP core Yaxcopoil-1 was drilled to a depth of 1,511 m within the Chicxulub crater. An organic-rich marly limestone near the base of the hole (1,495 to 1,452 m) was deposited in an open marine shelf environment during the latest Cenomanian (uppermost Rotalipora cushmani zone). The overlying sequence of limestones, dolomites and anhydrites (1,495 to 894 m) indicates deposition in various carbonate platform environments (e.g., sabkhas, lagoons). A 100-m-thick suevite breccia (894–794 m) identifies the Chicxulub impact event. Above the suevite breccia is a dolomitic limestone with planktic foraminiferal assemblages indicative of Plummerita hantkeninoides zone CF1, which spans the last 300 ky of the Maastrichtian. An erosional surface 50 cm above the breccia/dolomite contact marks the K/T boundary and a hiatus. Limestones above this contact contain the first Tertiary planktic foraminifera indicative of an upper P. eugubina zone P1a(2) age. Another hiatus 7 cm upsection separates zone P1a(2) and hemipelagic limestones of planktic foraminiferal Zone P1c. Planktic foraminiferal assemblages of Zone Plc to P3b age are present from a depth of 794.04 up to 775 m. The Cretaceous carbonate sequence appears to be autochthonous, with a stratigraphic sequence comparable to late Cretaceous sediments known from outside the Chicxulub crater in northern and southern Yucatan, including the late Cenomanian organic-rich marly limestone. There is no evidence that these sediments represent crater infill due to megablocks sliding into the crater, such as major disruption of sediments, chaotic changes in lithology, overturned or deep dipping megablocks, major mechanical fragmentation, shock or thermal alteration, or ductile deformation. Breccia units that are intercalated in the carbonate platform sequence are intraformational in origin (e.g., dissolution of evaporites) and dykes are rare. Major disturbances of strata by the impact therefore appear to have been confined to within less than 60 km from the proposed impact center. Yaxcopoil-1 may be located outside the collapsed transient crater cavity, either on the upper end of an elevated and tilted horst of the terrace zone, or even outside the annular crater cavity. The Chicxulub site thus records a large impact that predates the K/T boundary impact and mass extinction.  PDF

URLhttp://link.springer.com/10.1007/s00531-004-0431-6http://www.springerlink.com/index/pdf/10.1007/s00531-004-0431-6
DOI10.1007/s00531-004-0431-6
Short TitleInt J Earth Sci (Geol Rundsch)

Age and paleoenvironment of the Cenomanian–Turonian global stratotype section and point at Pueblo, Colorado

TitleAge and paleoenvironment of the Cenomanian–Turonian global stratotype section and point at Pueblo, Colorado
Publication TypeJournal Article
Year of Publication2004
AuthorsKeller, G, Pardo, A
JournalMarine Micropaleontology
Volume51
Issue1-2
Pagination95 - 128
Date PublishedJan-04-2004
ISSN03778398
Abstract

Biostratigraphy and stable isotopes indicate that the global stratotype section and point (GSSP) at Pueblo contains an essentially complete sedimentary record across the global ocean anoxic event (OAE 2) and the Cenomanian–Turonian boundary. The OAE 2 δ13C shift occurred over a period of about 90 ky and was accompanied by a major sea level transgression, which at its peak was marked by an incursion of oxygen-rich waters creating a benthic oxic zone that lasted about 100 ky. A mid-Cenomanian δ13C shift, sea level transgression and faunal turnover occurred about 2 my before OAE 2. δ18O values of the planktic foraminifer Hedbergella planispira and its relative abundance changes reveal cyclic variations in surface salinity due to alternating freshwater influx and marine incursions, whereas dominance by the low oxygen tolerant Heterohelix species indicates a well-developed oxygen minimum zone (OMZ) for most of the middle to late Cenomanian and early Turonian.

Profound faunal changes accompanied these oceanographic events, including the extinction of 30% of the species assemblage and an equal gain in evolutionary diversification, though the overall combined relative abundances of outgoing and incoming species were less than 2% and 4%, respectively, of the total assemblages. The faunal turnover began with the sea level transgression and rapid increase in δ13C values, and accelerated with the influx of oxygen-rich deep water, increased water mass stratification and competition during the benthic oxic zone. The incursion of oxygen-rich deep waters at this time was also observed in Morocco and may represent a global event of a still unknown source.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0377839803001051
DOI10.1016/j.marmicro.2003.08.004
Short TitleMarine Micropaleontology

La météorite innocentée

TitleLa météorite innocentée
Publication TypeJournal Article
Year of Publication2004
AuthorsGerta, K
JournalLa Recherche
Volume379
Pagination30-36
Abstract

L'impact de Chicxulub n'est pas responsable de l'extinction en masse qui a vu disparaître les dinosaures et de nombreux organismes marins. Il précéderait celle-ci d'au moins 300 000 ans. Reste à trouver un autre cratère, encore plus grand, ou d'autres causes.

Depuis sa découverte dans la péninsule du Yucatán, au Mexique, au début des années quatre-vingt-dix, le cratère de Chicxulub est considéré comme la preuve indéniable qu'un astéroïde a provoqué une extinction en masse en percutant la Terre, il y a 65 millions d'années [1]. À la limite entre le Crétacé* et le Tertiaire*, les dinosaures et de nombreuses autres espèces auraient ainsi disparu dans une apocalypse de feu, suivie d'une période d'obscurité et de tsunamis géants. Mais ce scénario, parfait pour la télévision et largement diffusé, dans la littérature scien-tifique comme dans la presse grand public, ne repose pas sur des preuves convaincantes.

URLhttp://www.larecherche.fr/1-la-m%C3%A9t%C3%A9orite-innocent%C3%A9e

Suche nach der Ursache des Massensterbens vor 65 Millionen Jahren

TitleSuche nach der Ursache des Massensterbens vor 65 Millionen Jahren
Publication TypeJournal Article
Year of Publication2004
AuthorsGerta, K
JournalWerdenberger Jahrbuch
Pagination189-200
Abstract

Seit der Entdeckung des ChicxulubAsteroidenkraters auf der südmexikanischen Halbinsel Yucatán im Jahr l990 (Abb. 1) wird dieser Krater für das Aussterben der Dinosaurier und zahlreicher weiterer Tiergruppen verantwortlich gemacht. Der Einschlag (Impakt2 ) vor rund 65 Millionen Jahren soll eine weltweite Feuerwalze und gigantische Flutwellen verursacht haben, und der aufgewirbelte Staub und Russ soll zur totalen Verdunkelung der Atmosphäre geführt haben. Zurück blieb der Todeskrater. – Ein wunderbares Skript, wie gemacht für Film und Fernsehen. Und so fand die Story in den letzten 15 Jahren Eingang in die öffentliche Meinung und wurde so auch in der wissenschaftlichen Literatur oft als Faktum dargestellt. Aber entspricht sie der Wahrheit? Reichen die wissenschaftlichen Belege aus, um diese Theorie zu untermauern?   PDF

URLhttp://www.sunorbit.net/Belege/K_23.pdf

More evidence that the Chicxulub impact predates the K/T mass extinction

TitleMore evidence that the Chicxulub impact predates the K/T mass extinction
Publication TypeJournal Article
Year of Publication2004
AuthorsKeller, G, Adatte, T, Stinnesbeck, W, üben, D, BERNER, ZSOLT, Kramar, U, Harting, M
JournalMeteoritics & Planetary Science
Volume39
Issue7
Pagination1127 - 1144
Date PublishedJan-07-2004
ISSN10869379
Abstract

Yaxcopoil-1 (Yax-1), drilled within the Chicxulub crater, was expected to yield the final proof that this impact occurred precisely 65 Myr ago and caused the mass extinction at the Cretaceous-Tertiary (K/T) boundary. Instead, contrary evidence was discovered based on five independent proxies (sedimentologic, biostratigraphic, magnetostratigraphic, stable isotopic, and iridium) that revealed that the Chicxulub impact predates the K/T boundary by about 300,000 years and could not have caused the mass extinction. This is demonstrated by the presence of five bioturbated glauconite layers and planktic foraminiferal assemblages of the latest Maastrichtian zone CF1 and is corroborated by magnetostratigraphic chron 29r and characteristic late Maastrichtian stable isotope signals. These results were first presented in Keller et al. (2004). In this study, we present more detailed evidence of the presence of late Maastrichtian planktic foraminifera, sedimentologic, and mineralogic analyses that demonstrate that the Chicxulub impact breccia predates the K/T boundary and that the sediments between the breccia and the K/T boundary were deposited in a normal marine environment during the last 300,000 years of the Cretaceous.  PDF

URLhttp://blackwell-synergy.com/doi/abs/10.1111/maps.2004.39.issue-7http://doi.wiley.com/10.1111/j.1945-5100.2004.tb01133.x
DOI10.1111/maps.2004.39.issue-710.1111/j.1945-5100.2004.tb01133.x

Chicxulub impact predates the K-T boundary mass extinction

TitleChicxulub impact predates the K-T boundary mass extinction
Publication TypeJournal Article
Year of Publication2004
AuthorsKeller, G, Adatte, T, Stinnesbeck, W, Rebolledo-Vieyra, M, J. Fucugauchi, U, Kramar, U, Stüben, D
JournalProceedings of the National Academy of Sciences
Volume101
Issue11
Pagination3753 - 3758
Date PublishedApr-03-2005
ISSN0027-8424
Abstract

Since the early l990s the Chicxulub crater on Yucatan, Mexico, has been hailed as the smoking gun that proves the hypothesis that an asteroid killed the dinosaurs and caused the mass extinction of many other organisms at the Cretaceous-Tertiary (K-T) boundary 65 million years ago. Here, we report evidence from a previously uninvestigated core, Yaxcopoil-1, drilled within the Chicxulub crater, indicating that this impact predated the K-T boundary by ≈300,000 years and thus did not cause the end-Cretaceous mass extinction as commonly believed. The evidence supporting a pre- K-T age was obtained from Yaxcopoil-1 based on five independent proxies, each with characteristic signals across the K-T transition: sedimentology, biostratigraphy, magnetostratigraphy, stable isotopes, and iridium. These data are consistent with earlier evidence for a late Maastrichtian age of the microtektite deposits in northeastern Mexico. PDF

URLhttp://www.pnas.org/cgi/doi/10.1073/pnas.0400396101
DOI10.1073/pnas.0400396101
Short TitleProceedings of the National Academy of Sciences

Cenomanian–Turonian and δ13C, and δ18O, sea level and salinity variations at Pueblo, Colorado

TitleCenomanian–Turonian and δ13C, and δ18O, sea level and salinity variations at Pueblo, Colorado
Publication TypeJournal Article
Year of Publication2004
AuthorsKeller, G, BERNER, ZSOLT, Adatte, T, Stüben, D
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume211
Issue1-2
Pagination19 - 43
Date PublishedJan-08-2004
ISSN00310182
Abstract

Stable isotopes of the surface dwelling planktic foraminifera Hedbergella planispira, its abundance variations, and mineralogical analysis of the Cenomanian–Turonian at Pueblo, CO, reveal cyclic variations in surface salinity due to changes in precipitation, freshwater influx, marine incursions and long-term sea-level fluctuations. Hedbergella planispira is a proxy for salinity variations, as indicated by 2–4x more negative δ18O values in intervals of peak abundances as compared to intervals with reduced populations. Negative δ18O values reflect periods of brackish surface waters caused by freshwater influx during wet humid periods, accompanied by increased clastic transport. More positive δ18O values reflect more normal marine salinities as a result of arid periods and/or marine incursions and correlate with intervals of increased biogenic carbonate deposition. The magnitude of salinity variations during the low sea-level of the Hartland Shale is twice that during the sea-level transgression of the Bridge Creek Limestone. The rapid positive δ13C shift that marks the onset of Oceanic Anoxic Event 2 (OAE 2) at Pueblo occurred over a period of about 100 ky (93.90–94.00 Ma), and coincided with the major sea level transgression that culminated in the deposition of the basal Bridge Creek Limestone. A positive δ13C shift also occurred in the Rotalipora cushmani zone prior to OAE 2 and coincided with a sea level rise and enhanced preservation of terrestrial organic matter. The likely cause for OAE 2 is depletion of 12C in the water column as a result of high primary productivity, whereas an earlier R. cushmani zone event was primarily caused by increased input of terrigenous organic matter. Both δ13C events are associated with enhanced organic matter preservation and anoxic or dysoxic bottom waters.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0031018204002007
DOI10.1016/j.palaeo.2004.04.003
Short TitlePalaeogeography, Palaeoclimatology, Palaeoecology

Low-Diversity, Late Maastrichtian and Early Danian Planktic Foraminiferal Assemblages of the Eastern Tethys

TitleLow-Diversity, Late Maastrichtian and Early Danian Planktic Foraminiferal Assemblages of the Eastern Tethys
Publication TypeJournal Article
Year of Publication2004
AuthorsKeller, G
JournalThe Journal of Foraminiferal Research
Volume34
Issue1
Pagination49 - 73
Date PublishedJan-01-2004
ISSN0096-1191
Abstract

The eastern Tethys, from Israel to Egypt, experienced unusually adverse environmental conditions for planktic foraminifera during the last two million years of the Maastrichtian, as evident by very low species richness, blooms of opportunistic Guembelitria species in surface waters, dominance of low-oxygen-tolerant heterohelicids in subsurface waters, and near absence of deeper dwelling globotruncanids. Comparison of southern Israel (Mishor Rotem section) with central Egypt (Gebel Qreiya section) reveals that adverse conditions intensified towards the south with foraminiferal assemblages mimicking stress conditions of the early Danian, dominated (75– 90%) by Guembelitria blooms. Faunal assemblages indicate an expanded oxygen minimum and dysoxic zone throughout the region, though at the greater depths represented by localities of southern Israel, bottom waters remained aerobic. Primary productivity was extremely low, as indicated by stable isotopes and low total organic content in sediments. These adverse environmental conditions are likely related to the regional paleobathymetry of the tectonically active Syrian Arc that spans Syria to Egypt. The paleorelief of intra-shelf and intra-slope basins of the Syrian Arc, with their differential rates of subsidence and sedimentation, active folding and faulting, likely controlled the intensity of circulation, upwelling, watermass stratification and the extent of the oxygen minimum zone. The late Maastrichtian rapid climate and sea level changes exacerbated these conditions.  PDF

URLhttp://jfr.geoscienceworld.org/cgi/doi/10.2113/0340049
DOI10.2113/0340049
Short TitleThe Journal of Foraminiferal Research

Biotic effects of impacts and volcanism

TitleBiotic effects of impacts and volcanism
Publication TypeJournal Article
Year of Publication2003
AuthorsKeller, G
JournalEarth and Planetary Science Letters
Volume215
Issue1-2
Pagination249 - 264
Date PublishedJan-10-2003
ISSN0012821X
KeywordsBiotic effects, Cretaceous–Tertiary, DSDP Site 216, Impacts, Maastrichtian, Volcanism
Abstract

The biotic effects of late Maastrichtian mantle plume volcanism on Ninetyeast Ridge and Deccan volcanism mirror those of the Cretaceous–Tertiary (KT) mass extinction and impact event. Planktonic foraminifera responded to high stress conditions with the same impoverished and small-sized species assemblages dominated by the disaster/opportunists Guembelitria cretacea, which characterize the KT mass extinction worldwide. Similar high stress late Maastrichtian assemblages have recently been documented from Madagascar, Israel and Egypt. Biotic effects of volcanism cannot be differentiated from those of impacts, though every period of intense volcanism is associated with high stress assemblages, this is not the case with every impact. The most catastrophic biotic effects occurred at the KT boundary (65.0 Ma) when intense Deccan volcanism coincided with a major impact and caused the mass extinction of all tropical and subtropical species. The Chicxulub impact, which now appears to have predated the KT boundary by about 300 kyr, coincided with intense Deccan volcanism that resulted in high biotic stress and greenhouse warming, but no major extinctions. The unequivocal connection between intense volcanism and high stress assemblages during the late Maastrichtian to early Danian, and the evidence of multiple impacts, necessitates revision of current impact and mass extinction theories.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0012821X0300390X
DOI10.1016/S0012-821X(03)00390-X
Short TitleEarth and Planetary Science Letters

Planktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A

TitlePlanktonic foraminiferal response to the latest Maastrichtian abrupt warm event: a case study from South Atlantic DSDP Site 525A
Publication TypeJournal Article
Year of Publication2003
AuthorsAbramovich, S, Keller, G
JournalMarine Micropaleontology
Volume48
Issue3-4
Pagination225 - 249
Date PublishedJan-07-2003
ISSN03778398
Abstract

An abrupt global warming of 3-4°C occurred near the end of the Maastrichtian at 65.45-65.10 Ma. The environmental effects of this warm event are here documented based on stable isotopes and quantitative analysis of planktonic foraminifera at the South Atlantic DSDP Site 525A. Stable isotopes of individual species mark a rapid increase in temperature and a reduction in the vertical water mass stratification that is accompanied by a decrease in niche habitats, reduced species diversity and/or abundance, smaller species morphologies or dwarfing, and reduced photosymbiotic activity. During the warm event, the relative abundance of a large number of species decreased, including tropical^subtropical affiliated species, whereas typical mid-latitude species retained high abundances. This indicates that climate warming did not create favorable conditions for all tropical^subtropical species at mid-latitudes and did not cause a massive retreat in the local mid-latitude population. A noticeable exception is the ecological generalist Heterohelix dentata Stenestad that dominated during the cool intervals, but significantly decreased during the warm event. However, dwarfing is the most striking response to the abrupt warming and occurred in various species of different morphologies and lineages (e.g. biserial, trochospiral, keeled globotruncanids). Dwarfing is a typical reaction to environmental stress conditions and was likely the result of increased reproduction rates. Similarly, photosymbiotic activity appears to have been reduced significantly during the maximum warming, as indicated by decreased δ13C values. The foraminiferal response to climate change is thus multifaceted resulting in decreased species diversity, decreased species populations, increased competition due to reduced niche habitats, dwarfing and reduced photosymbiotic activity.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0377839803000215
DOI10.1016/S0377-8398(03)00021-5
Short TitleMarine Micropaleontology

Pages