GERTA KELLER PUBLICATIONS

U-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction

TitleU-Pb constraints on pulsed eruption of the Deccan Traps across the end-Cretaceous mass extinction
Publication TypeJournal Article
Year of Publication2019
AuthorsSchoene, B, Eddy, MP, Samperton, KM, C. Keller, B, Keller, G, Adatte, T, Khadri, SFR
JournalScience
Volume363
Pagination862–866
Date Published02/2019
Abstract

Temporal correlation between some continental flood basalt eruptions and mass extinctions has been proposed to indicate causality, with eruptive volatile release driving environmental degradation and extinction. We tested this model for the Deccan Traps flood basalt province, which, along with the Chicxulub bolide impact, is implicated in the Cretaceous-Paleogene (K-Pg) extinction approximately 66 million years ago. We estimated Deccan eruption rates with uranium-lead (U-Pb) zircon geochronology and resolved four high-volume eruptive periods. According to this model, maximum eruption rates occurred before and after the K-Pg extinction, with one such pulse initiating tens of thousands of years prior to both the bolide impact and extinction. These findings support extinction models that incorporate both catastrophic events as drivers of environmental deterioration associated with the K-Pg extinction and its aftermath. PDF

URLhttps://doi.org/10.1126/science.aau2422
DOI10.1126/science.aau2422

Deposition and age of Chicxulub impact spherules on Gorgonilla Island, Colombia

TitleDeposition and age of Chicxulub impact spherules on Gorgonilla Island, Colombia
Publication TypeJournal Article
Year of Publication2019
AuthorsMateo, P, Keller, G, Adatte, T, Bitchong, AM, Spangenberg, JE, Vennemann, T, Hollis, CJ
JournalGSA Bulletin
Volume132
Pagination215–232
Date Published06/2019
Abstract

The end-Cretaceous mass extinction (66 Ma) has long been associated with the Chicxulub impact on the Yucatan Peninsula. However, consensus on the age of this impact has remained controversial because of differing interpretations on the stratigraphic position of Chicxulub impact spherules relative to the mass extinction horizon. One side argues that the impact occurred precisely at the Cretaceous-Paleogene boundary, thus coinciding with the mass extinction; the other side argues that the impact predated the Cretaceous-Paleogene boundary, based on the discovery of primary impact spherules deposits in NE Mexico and Texas near the base of planktic foraminiferal zone CF1, dated at 170 k.y. before the Cretaceous-Paleogene boundary. A recent study of the most pristine Chicxulub impact spherules discovered on Gorgonilla Island, Colombia, suggested that they represent a primary impact deposit with an absolute age indistinguishable from the Cretaceous-Paleogene boundary. Here, we report on the Gorgonilla section with the main objective of evaluating the nature of deposition and age of the spherule-rich layer relative to the Cretaceous-Paleogene boundary.

The Gorgonilla section consists of light gray-yellow calcareous siliceous mudstones (pelagic deposits) alternating with dark olive-brown litharenites (turbidites). A 3-cm-thick dark olive-green spherule-rich layer overlies an erosional surface separating Maastrichtian and Danian sediments. This layer consists of a clast-supported, normally graded litharenite, with abundant Chicxulub impact glass spherules, lithics (mostly volcanic), and Maastrichtian as well as Danian microfossils, which transitions to a calcareous mudstone as particle size decreases. Mineralogical analysis shows that this layer is dominated by phyllosilicates, similar to the litharenites (turbidites) that characterize the section. Based on these results, the spherule-rich layer is interpreted as a reworked early Danian deposit associated with turbiditic currents. A major hiatus (>250 k.y.) spanning the Cretaceous-Paleogene boundary and the earliest Danian is recorded at the base of the spherule-rich layer, based on planktic foraminiferal and radiolarian biostratigraphy and carbon stable isotopes. Erosion across the Cretaceous-Paleogene boundary has been recorded worldwide and is generally attributed to rapid climate changes, enhanced bottom-water circulation during global cooling, sea-level fluctuations, and/or intensified tectonic activity. Chicxulub impact spherules are commonly reworked and redeposited into younger sediments overlying a Cretaceous-Paleogene boundary hiatus of variable extent in the Caribbean, Central America, and North Atlantic, while primary deposits are rare and only known from NE Mexico and Texas. Because of their reworked nature, Gorgonilla spherules provide no stratigraphic evidence from which the timing of the impact can be inferred.  PDF

URLhttps://doi.org/10.1130/b35287.1
DOI10.1130/b35287.1

Cretaceous-Paleocene transition along a rocky carbonate shore: Implications for the Cretaceous-Paleocene boundary event in shallow platform environments and correlation to the deep sea

TitleCretaceous-Paleocene transition along a rocky carbonate shore: Implications for the Cretaceous-Paleocene boundary event in shallow platform environments and correlation to the deep sea
Publication TypeBook Chapter
Year of Publication2019
AuthorsSanders, D, Keller, G, Schlagintweit, F, Studeny, M
Book TitleMass Extinctions, Volcanism, and Impacts: New Developments
PublisherGeological Society of America
Abstract

The Cretaceous-Paleocene (K/P) boundary intervals are rarely preserved in successions of shallow-water limestones. Here, we describe a shallow rocky shore on the active orogenic wedge of the eastern Alps (Austria) fringed by a carbonate platform that was largely cannibalized by erosion. We compared this succession with similar nearshore environments globally, as well as the deep sea, to gain a better understanding of the environmental response to the K/P boundary transition. In the eastern Alps, Cretaceous and Paleocene lithofacies across the K/P boundary transition are separated by a hardground that formed during subaerial exposure and that terminates Upper Maastrichtian limestone with planktic foraminiferal assemblages deposited at neritic depth during zone CF3 (ca. 66.500 Ma). Above the hardground, there are beachrocks with early Danian zone P1a(1) assemblages, which indicate the hardground spans about ~600 k.y. of nondeposition and/or erosion. During the early Danian, the marine transgressive fringe fluctuated between “shoreface to emersion” environments, depositing limestones rich in bryozoans, rhynchonellids, coralline algae, and rare planktic foraminifera along with abraded, bored, and/or encrusted clasts eroded from older rocks. Repeated short subaerial exposure is marked by vadose diagenesis and hardgrounds, including an ~1.5 m.y. interval between magnetochrons C29n to C28n and planktic foraminiferal zones P1b to P1c(2).

Comparison with platform carbonate sequences from Croatia, Oman, Madagascar, Belize, and Guatemala, as well as nearshore siliciclastic environments of southern Tunisia, Texas, and Argentina, across the K/P boundary transition revealed surprisingly similar deposition and erosion patterns, with the latter correlative with sea-level falls and repeated subaerial exposure forming hardgrounds. Comparison with deep-sea depositional patterns revealed coeval but shorter intervals of erosion. This pattern shows a uniform response to the K/P boundary transition linked to climate and sea-level changes, whether in shallow nearshore or deep-sea environments, with climate change tied to Deccan volcanism in magnetochrons C29r-C29n. PDF

URLhttps://doi.org/10.1130/2019.2544(06)
DOI10.1130/2019.2544(06)

Environmental changes during the Cretaceous-Paleogene mass extinction and Paleocene-Eocene Thermal Maximum: Implications for the Anthropocene

TitleEnvironmental changes during the Cretaceous-Paleogene mass extinction and Paleocene-Eocene Thermal Maximum: Implications for the Anthropocene
Publication TypeJournal Article
Year of Publication2018
AuthorsKeller, G, Mateo, P, Punekar, J, Khozyem, H, Gertsch, B, Spangenberg, J, Bitchong, AMbabi, Adatte, T
JournalGondwana Research
Volume56
Pagination69–89
Date Publishedapr
Abstract

The Cretaceous-Paleogene boundary (KPB) mass extinction (~66.02 Ma) and the Paleocene-Eocene Thermal Maximum( PETM)(~55.8Ma) are two remarkable climatic and faunal events in Earth's history that have implications for the current Anthropocene global warming and rapid diversity loss. Here we evaluate these two events at the stratotype localities in Tunisia and Egypt based on climatewarming and environmental responses recorded in faunal and geochemical proxies. The KPBmass extinction is commonly attributed to the Chicxulub impact, but Deccan volcanism appears as amajor culprit.Newmercury analysis reveals thatmajor Deccan eruptions accelerated during the last 10 ky and reached the tipping point leading up to themass extinction. During the PETM, climatewarmed rapidly by ~5 °C,which is mainly attributed tomethane degassing from seafloor sediments during global warming linked to the North Atlantic Igneous Province (NAIP). Biological effectswere transient,marked by temporary absence ofmost planktic foraminifera due to ocean acidification followed by the return of the pre-PETM fauna and diversification. In contrast, the current rapid rise in atmospheric CO2 and climate warming are magnitudes faster than at the KPB or PETM events leading to predictions of a PETM-like response as best case scenario and rapidly approaching sixth mass extinction as worst-case scenario.  PDF

URLhttps://doi.org/10.1016/j.gr.2017.12.002
DOI10.1016/j.gr.2017.12.002

Deccan volcanism induced high-stress environment during the Cretaceous–Paleogene transition at Zumaia, Spain: Evidence from magnetic, mineralogical and biostratigraphic records

TitleDeccan volcanism induced high-stress environment during the Cretaceous–Paleogene transition at Zumaia, Spain: Evidence from magnetic, mineralogical and biostratigraphic records
Publication TypeJournal Article
Year of Publication2018
AuthorsFont, E, Adatte, T, Andrade, M, Keller, G, Bitchong, AMbabi, Carvallo, C, Ferreira, J, Diogo, Z, Mirão, J
JournalEarth and Planetary Science Letters
Volume484
Pagination53–66
Date Publishedfeb
Abstract

We conducted detailed rock magnetic, mineralogical and geochemical (mercury) analyses spanning the Cretaceous–Paleogene boundary (KPB) at Zumaia, Spain, to unravel the signature of Deccan-induced climate and environmental changes in the marine sedimentary record. Our biostratigraphic results show that Zumaia is not complete, and lacks the typical boundary clay, zone P0 and the base of zone P1a(1) in the basal Danian. Presence of an unusual ∼1m-thick interval spanning the KPB is characterized by very low detrital magnetite and magnetosome (biogenic magnetite) contents and by the occurrence of akaganéite, a very rare mineral on Earth in oxidizing, acidic and hyper-chlorinated environments compatible with volcanic settings. These benchmarks correlate with higher abundance of the opportunist Guembelitria cretacea species. Detrital magnetite depletion is not linked to significant lithological changes, suggesting that iron oxide dissolution by acidification is the most probable explanation. The concomitant decrease in magnetosomes, produced by magnetotactic bacteria at the anoxic–oxic boundary, is interpreted as the result of changes in seawater chemistry induced by surficial ocean acidification. Mercury peaks up to 20–50 ppb are common during the last 100 kyr of the Maastrichtian(zone CF1) but only one significant anomaly is present in the early Danian, which is likely due to the missing interval. Absence of correlation between mercury content (R2 = 0.009) and total organic carbon (R2 = 0.006) suggest that the former originated from the Deccan Traps eruptions. No clear relation between the stratigraphic position of the mercury peaks and the magnetite-depleted interval is observed, although the frequency of the mercury peaks tends to increase close to the KPg boundary. In contrast to Bidart (France) and Gubbio (Italy), where magnetite depletion and akaganéite feature within a ∼50cm-thick interval located 5 cm below the KPg boundary, the same benchmarks are observed in a 1m-thick interval encompassing the KPg boundary at Zumaia. Results reinforce the synchronism of the major eruptions of the Deccan Traps Magmatic Province with the Cretaceous–Paleogene (KPg) mass extinction and provide new clues to better correlate the Deccan imprint of the global sedimentary record.  PDF

URLhttps://doi.org/10.1016/j.epsl.2017.11.055
DOI10.1016/j.epsl.2017.11.055

Vegetation response to exceptional global warmth during Oceanic Anoxic Event 2

TitleVegetation response to exceptional global warmth during Oceanic Anoxic Event 2
Publication TypeJournal Article
Year of Publication2018
AuthorsHeimhofer, U, Wucherpfennig, N, Adatte, T, Schouten, S, Schneebeli-Hermann, E, Gardin, S, Keller, G, Kentsch, S, Kujau, A
JournalNature Communications
Volume9
Date Publishedsep
Abstract

The Cenomanian–Turonian Oceanic Anoxic Event (OAE2; ~94.5 million years ago) represents an episode of global-scale marine anoxia and biotic turnover, which corresponds to one of the warmest time intervals in the Phanerozoic. Despite its global significance, information on continental ecosystem response to this greenhouse episode is lacking. Here we present a terrestrial palynological record combined with marine-derived temperature data (TEX86) across an expanded OAE2 section from the Southern Provençal Basin, France. Despite high TEX86-derived temperature estimates reaching up to 38 °C, the continental hinterland did support a diverse vegetation, adapted to persist under elevated temperatures. A transient phase of climatic instability and cooling during OAE2 known as Plenus Cold Event (PCE) is marked by the proliferation of open, savanna-type vegetation rich in angiosperms at the expanse of conifer-dominated forest ecosystems. A rise in early representatives of Normapolles-type pollen during the PCE marks the initial radiation of this important angiosperm group.  PDF

URLhttps://doi.org/10.1038/s41467-018-06319-6
DOI10.1038/s41467-018-06319-6

Environmental changes during the Cetaceous-Paleogene mass extinction and Paleocene-Eocene thermal maximum: Implications for the Anthropocene

TitleEnvironmental changes during the Cetaceous-Paleogene mass extinction and Paleocene-Eocene thermal maximum: Implications for the Anthropocene
Publication TypeJournal Article
Year of Publication2017
AuthorsKeller, G, Mateo, P, Punekar, J, Khozyem, H, Gertsch, B, Spangenberg, J, Bitchong, A, Adatte, T
JournalGondwana Research
Date Publisheddec
Abstract

The Cretaceous-Paleogene boundary (KPB) mass extinction (~ 66.02 Ma) and the Paleocene-Eocene Thermal Maximum (PETM) (~ 55.8 Ma) are two remarkable climatic and faunal events in Earth's history that have implications for the current Anthropocene global warming and rapid diversity loss. Here we evaluate these two events at the stratotype localities in Tunisia and Egypt based on climate warming and environmental responses recorded in faunal and geochemical proxies. The KPB mass extinction is commonly attributed to the Chicxulub impact, but Deccan volcanism appears as a major culprit. New mercury analysis reveals that major Deccan eruptions accelerated during the last 10 ky and reached the tipping point leading up to the mass extinction. During the PETM, climate warmed rapidly by ~ 5 °C, which is mainly attributed to methane degassing from seafloor sediments during global warming linked to the North Atlantic Igneous Province (NAIP). Biological effects were transient, marked by temporary absence of most planktic foraminifera due to ocean acidification followed by the return of the pre-PETM fauna and diversification. In contrast, the current rapid rise in atmospheric CO2 and climate warming are magnitudes faster than at the KPB or PETM events leading to predictions of a PETM-like response as best case scenario and rapidly approaching sixth mass extinction as worst-case scenario.

URLhttps://doi.org/10.1016/j.gr.2017.12.002
DOI10.1016/j.gr.2017.12.002

Early to Late Maastrichtian environmental changes in the Indian Ocean compared with Tethys and South Atlantic

TitleEarly to Late Maastrichtian environmental changes in the Indian Ocean compared with Tethys and South Atlantic
Publication TypeJournal Article
Year of Publication2017
AuthorsMateo, P, Keller, G, Punekar, J, Spangenberg, JE
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume478
Pagination121–138
Date Published07/2017
Abstract

Planktic foraminiferal analysis, including species populations, diversity trends, high-stress indices and stable isotopes of the latest Campanian through Maastrichtian in the South Atlantic, Tethys and Indian oceans reveal four major climate and faunal events that ended with the Cretaceous-Paleogene (K/Pg), formerly Cretaceous-Tertiary (K/T), mass extinction. The prelude to these events is the late Campanian cooling that reached minimum temperatures in the earliest Maastrichtian (base C31r) correlative with low primary productivity and species diversity. Event-1 begins during the persistent cool climate of the early Maastrichtian (lower C31r) when primary productivity rapidly increased accompanied by rapid species originations, attributed to increased nutrient influx from increased upwelling, erosion during the sea-level fall ~70.6 Ma, and Ninety East Ridge volcanism. During Event-2 (upper C31r to lower C30n), climate rapidly warmed by 2–3 °C in deep waters and peaked at 22 °C on land, primary productivity remained high and diversification reached maximum for the entire Cretaceous. We attribute this climate warming to intense Ninety East Ridge volcanic activity beginning ~69.5 Ma, accompanied by rapid reorganization of intermediate oceanic circulation. Enhanced greenhouse conditions due to the eruption of Deccan Phase-1 in India resulted in detrimental conditions for planktic foraminifera marking the end of diversification. Global cooling resumed in Event-3 (C30n), species diversity declined gradually accompanied by dwarfing, decreased large specialized species, increased small ecologically tolerant taxa, and ocean acidification. Event-3 is mainly the result of enhanced weathering and volcanogenic CO2 adsorption by the oceans during the preceding warm Event-2 that led to cooling and lower pH in the surface ocean. Event-4 marks the last 250 kyr of the Maastrichtian (C29r), which began with the largest Deccan eruptions (Phase-2) that caused rapid climate warming of 4 °C in deep waters and 8 °C on land, acid rain and ocean acidification leading to a major carbonate crisis preceding the K/T mass extinction.  PDF

URLhttps://doi.org/10.1016/j.palaeo.2017.01.027
DOI10.1016/j.palaeo.2017.01.027

Comments on "Post-impact event bed (tsunamite) at the Cretaceous-Palaeogene boundary deposited on a distal carbonate platform interior"

TitleComments on "Post-impact event bed (tsunamite) at the Cretaceous-Palaeogene boundary deposited on a distal carbonate platform interior"
Publication TypeJournal Article
Year of Publication2017
AuthorsFont, E, Keller, G, Sanders, D, Adatte, T
JournalTerra Nova
Volume29
Pagination329–331
Date Published08/2018
Abstract

Korbar, McDonald, Fućek, Fuček, and Posilović (2017) report a tsunamite, triggered by the Chicxulub impact on Yucatan, from the Likva Cove carbonate platform of the Island of Brač, Croatia, which is similar to that in an earlier report from the nearby Island of Hvar (Korbar et al., 2015). If true, such deposits in the Adriatic Sea would be truly anomalous given that no tsunamites are identified in well-preserved Cretaceous–Palaeogene (K–Pg) sections from the Basque-Cantabric Basin (Bidart, Zumaia, Hendaye and Sopelana sections), which are located more proximal and towards the hypothetical tsunami wave propagation front. We strongly question the authors’ criteria for identifying the presumed “tsunamite” as well as the K–Pg boundary (KPB) age attributed to these deposits based on planktic foraminifera.  PDF

URLhttps://doi.org/10.1111/ter.12282
DOI10.1111/ter.12282

Upheavals during the Late Maastrichtian: Volcanism, climate and faunal events preceding the end-Cretaceous mass extinction

TitleUpheavals during the Late Maastrichtian: Volcanism, climate and faunal events preceding the end-Cretaceous mass extinction
Publication TypeJournal Article
Year of Publication2016
AuthorsKeller, G, Punekar, J, Mateo, P
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume441
Pagination137–151
Date Published01/2016
Abstract

The late Maastrichtian was a time of major climate, evolution and extinction extremes. Rapid climate warming of 2–3 °C in intermediate waters between 69.5 and 68 Ma (top C31r to base C30n) accompanied maximum evolutionary diversification (43% increase, zone CF5 to low CF4) in planktic foraminiferal history, followed immediately by a cluster of extinctions. During the last 250 ky of the Maastrichtian (C29r, zones CF2–CF1), rapid warming of 4 °C in intermediate waters and 8 °C on land resulted in high-stress environments ending in the mass extinction. The end-Cretaceous mass extinction is recorded in sediments between massive Deccan lava flows in India and attributed to SO2 and CO2 outgassing leading to ocean acidification. The early late Maastrichtian climate and faunal upheavals are not well known.

Here we document the faunal similarities of both events from the Indian Ocean through the Tethys and Gulf of Mexico. Results show that both extreme warm events are marked by high-stress environments characterized by decreased abundance and diversity of large specialized species and dwarfing, high abundance of low oxygen tolerant species, and disaster opportunist surface dweller Guembelitria blooms. The similarity in faunal response with the Deccan warming of C29r (CF2–CF1) suggests that volcanism was also responsible for the warming and faunal upheaval of the early late Maastrichtian. Major volcanic activity at this time included the onset of Deccan eruptions and Ninetyeast Ridge volcanism. The role of the Chicxulub impact appears to have been a contributing, rather than causal, factor in the mass extinction.   PDF

URLhttps://doi.org/10.1016/j.palaeo.2015.06.034
DOI10.1016/j.palaeo.2015.06.034

A multi-proxy approach to decode the end-Cretaceous mass extinction

TitleA multi-proxy approach to decode the end-Cretaceous mass extinction
Publication TypeJournal Article
Year of Publication2016
AuthorsPunekar, J, Keller, G, Khozyem, HM, Adatte, T, Font, E, Spangenberg, J
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume441
Pagination116–136
Date Publishedjan
KeywordsLow magnetic susceptibilityPlanktic foraminiferaCarbonate-dissolutionOcean acidificationDeccan volcanism
Abstract

Mass extinctions generally involve a complex array of interrelated causes and are best evaluated by a multi-proxy approach as applied here for the end-Cretaceous mass extinction. This study documents and compares the planktic foraminiferal records, carbonate dissolution effects, stable isotopes, and magnetic susceptibility in France (Bidart), Austria (Gamsbach) and Tunisia (Elles) in order to explore the environmental conditions during the uppermost Maastrichtian Plummerita hantkeninoides zone CF1 leading up to the mass extinction. Planktic foraminiferal assemblages at Bidart and Gamsbach appear to be more diverse than those at Elles, with unusually high abundance (20–30%) and diversity (~15 species) of globotruncanids in the two deep-water sections but lower abundance (b10%) and diversity (b10 species) at the middle shelf Elles section. Oxygen isotopes in zone CF1 of Elles record rapid climate warming followed by cooling and a possible return to rapid warming prior to the mass extinction. The onset of high stress conditions for planktic foraminifera is observed ~50–60 cm below the KTB at Bidart and Gamsbach, and ~4.5 m below the KTB at Elles due to much higher sediment accumulation rates. These intervals at Bidart and Gamsbach record low magnetic susceptibility and high planktic foraminiferal fragmentation index (FI) at Elles, Bidart and Gamsbach. An increased abundance of species with dissolution-resistant morphologies is also observed at Gamsbach. The correlative interval in India records significantly stronger carbonate dissolution effects in intertrappean sediments between the longest lava flows, ending with the mass extinction. Based on current evidence, this widespread dissolution event stratigraphically coincides with the climate cooling that follows the Late Maatrichtian global warming and may be linked to ocean acidification due to Deccan volcanism. The estimated 12,000–28,000 Gigatons (Gt) of CO2 and 5200–13,600 Gt of SO2 introduced into the atmosphere likely triggered the carbonate crisis in the oceans resulting in severe stress for marine calcifiers leading to mass extinction.  PDF

URLhttp://www.sciencedirect.com/science/article/pii/S0031018215004617
DOI10.1016/j.palaeo.2015.08.025

Mass wasting and hiatuses during the Cretaceous-Tertiary transition in the North Atlantic: Relationship to the Chicxulub impact?

TitleMass wasting and hiatuses during the Cretaceous-Tertiary transition in the North Atlantic: Relationship to the Chicxulub impact?
Publication TypeJournal Article
Year of Publication2016
AuthorsMateo, P, Keller, G, Adatte, T, Spangenberg, JE
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume441
Pagination96–115
Date Published01/2018
Abstract

Deep-sea sections in the North Atlantic are claimed to contain the most complete sedimentary records and ultimate proof that the Chicxulub impact is Cretaceous-Tertiary boundary (KTB) in age and caused the mass extinction. A multi-disciplinary study of North Atlantic DSDP Sites 384, 386 and 398, based on high-resolution planktonic foraminiferal biostratigraphy, carbon and oxygen stable isotopes, clay and whole-rock mineralogy and granulometry reveals the age, stratigraphic completeness and nature of sedimentary disturbances. Results show a major hiatus across the KTB at Site 384 with Zones CF1, P0 and P1a missing, spanning at least ~ 540 ky, similar to other North Atlantic and Caribbean localities associated with tectonic activity and Gulf Stream erosion. At Sites 386 and 398, discrete intervals of disturbed sediments with mm-to-cm-thick spherule layers have previously been interpreted as the result of impact-generated earthquakes at the KTB destabilizing continental margins prior to settling of impact spherules. However, improved age control based on planktonic foraminifera indicates spherule deposition in the early Danian Zone P1a(2) (upper Parvularugoglobigerina eugubina Zone) more than 100 ky after the KTB. At Site 386, two intervals of white chalk contain very small (< 63 μm) early Danian Zone P1a(2) assemblages (65%) and common reworked Cretaceous (35%) species. In contrast, the in situ red-brown and green abyssal clays of this core are devoid of carbonate. In addition, high calcite, mica and kaolinite and upward-fining are observed in the chalks, indicating downslope transport from shallow waters and sediment winnowing via distal turbidites. At Site 398, convoluted red to tan sediments with early Danian and reworked Cretaceous species represent slumping of shallow water sediments as suggested by dominance of mica and low smectite compared to in situ deposition. We conclude that mass wasting was likely the result of earthquakes associated with increased tectonic activity in the Caribbean and the Iberian Peninsula during the early Danian well after the Chicxulub impact.  PDF

URLhttps://doi.org/10.1016/j.palaeo.2015.01.019
DOI10.1016/j.palaeo.2015.01.019

The Cretaceous–Palaeogene boundary at Gorgonilla Island, Colombia, South America

TitleThe Cretaceous–Palaeogene boundary at Gorgonilla Island, Colombia, South America
Publication TypeJournal Article
Year of Publication2016
AuthorsBermúdez, HD, García, J, Stinnesbeck, W, Keller, G, Rodríguez, JVicente, Hanel, M, Hopp, J, Schwarz, WH, Trieloff, M, Bolívar, L, Vega, FJ
JournalTerra Nova
Volume28
Pagination83-90
Abstract

The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well-preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size-grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit.  PDF

URLhttps://doi.org/10.1111/ter.12196
DOI10.1111/ter.12196

Mercury anomaly, Deccan volcanism, and the end-Cretaceous mass extinction

TitleMercury anomaly, Deccan volcanism, and the end-Cretaceous mass extinction
Publication TypeJournal Article
Year of Publication2016
AuthorsFont, E, Adatte, T, Sial, ANobrega, de Lacerda, LDrude, Keller, G, Punekar, J
JournalGeology
Volume44
Pagination171–174
Abstract

The contribution of the Deccan Traps (west-central India) volcanism in the Cretaceous-Paleogene (KPg) crisis is still a matter of debate. Recent U-Pb dating of zircons interbedded within the Deccan lava flows indicate that the main eruptive phase (>1.1 × 106 km3 of basalts) initiated ∼250 k.y. before and ended ∼500 k.y. after the KPg boundary. However, the global geochemical effects of Deccan volcanism in the marine sedimentary record are still poorly resolved. Here we investigate the mercury (Hg) content of the Bidart (France) section, where an interval of low magnetic susceptibility (MS) located just below the KPg boundary was hypothesized to result from paleoenvironmental perturbations linked to the paroxysmal Deccan phase 2. Results show Hg concentrations >2 orders of magnitude higher from ∼80 cm below to ∼50 cm above the KPg boundary (maximum 46.6 ppb) and coincident with the low MS interval. Increase in Hg contents shows no correlation with clay or total organic carbon contents, suggesting that the Hg anomalies resulted from higher input of atmospheric Hg species into the marine realm, rather than organic matter scavenging and/or increased runoff. The Hg anomalies correlate with high shell fragmentation and dissolution effects in planktic foraminifera, suggesting correlative changes in marine biodiversity. This discovery represents an unprecedented piece of evidence of the nature and importance of the Deccan-related environmental changes at the onset of the KPg mass extinction.  PDF

URLhttps://doi.org/10.1130/g37451.1
DOI10.1130/g37451.1

The Cretaceous-Palaeogene boundary at Gorgonilla Island, Colombia, South America

TitleThe Cretaceous-Palaeogene boundary at Gorgonilla Island, Colombia, South America
Publication TypeJournal Article
Year of Publication2016
AuthorsBermúdez, HD, García, J, Stinnesbeck, W, Keller, G, Rodríguez, JVicente, Hanel, M, Hopp, J, Schwarz, WH, Trieloff, M, Bolívar, L, Vega, FJ
JournalTerra Nova
Volume28
Pagination83–90
Date Published01/2016
Abstract

The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well-preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size-grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit. PDF

URLhttp://onlinelibrary.wiley.com/doi/10.1111/ter.12196/abstract
DOI10.1111/ter.12196

Maastrichtian to Eocene subsurface stratigraphy of the Cauvery basin and correlation with Madagascar

TitleMaastrichtian to Eocene subsurface stratigraphy of the Cauvery basin and correlation with Madagascar
Publication TypeJournal Article
Year of Publication2016
AuthorsKeller, G, Jaiprakash, BC, Reddy, AN
JournalJournal of the Geological Society of India
Volume87
Pagination5–34
Date Published01/2016
Abstract

Late Maastrichtian through middle Eocene planktic foraminiferal biostratigraphy and erosion patterns from three Cauvery basin wells are compared with the Krishna-Godavari basin, Madagascar and South Atlantic Site 525A. Maastrichtian sedimentation appears continuous at DSDP site 525A and substantially complete in the Cauvery basin and Madagascar for the interval from ~70.3 to 66.8 Ma (zones CF6-CF3). But the latest Maastrichtian through early Paleocene record is fragmented, except for some Krishna-Godavari and Cauvery basin wells protected from erosion by Deccan traps or graben deposition, respectively. Hiatuses are observed correlative with sea level falls at 66.8, 66.25, 66.10, 65.7, 63.8 and 61.2 Ma with erosion amplified by local tectonic activity including doming and uplift due to Deccan volcanism.

Throughout this region the Cretaceous-Paleogene transition (magnetochron C29r-C29n, 66.25-65.50 Ma) is preserved only in deep wells of the Krishna-Godavari basin where Deccan Traps protected intertrappean sediments from erosion. The late Paleocene to middle Eocene marine record was recovered from two Cauvery basin wells with hiatuses correlative with low sea levels at ~49.0-56.5 Ma (zones P4c-E6) and ~53.0-55.3 Ma (zones E1-E4) at the ridge well KALI-H. A nearly complete record was recovered from well AGA, including the PETM event (zones E1-E2), which marks this an excellent reference section for India.

Similarity in erosion and sedimentation patterns of the late Maastrichtian to middle Paleocene from India to Madagascar and South Atlantic is mainly attributed to climate changes and sea level falls, regional tectonic activity from the Bay of Bengal to Madagascar, and uplift and doming in the Cauvery and K-G basins as a result of Deccan volcanism. Directly correlative with Deccan volcanism are high stress environments for marine calcifiers, as observed by species dwarfing, reduced diversity and blooms of the disaster opportunist Guembelitria cretacea in magnetochron C30n (zones CF4-CF3) correlative with Deccan phase-1 and Ninetyeast Ridge volcanism, in C29r (zones CF2-CF1) correlative with Deccan phase-2 and in C29n (zone P1b) correlative with Deccan phase-3 marking volcanism as the most important stress factor in the end-Cretaceous mass extinction and delayed evolution of planktic foraminifera.  PDF

 

 

URLhttps://link.springer.com/article/10.1007/s12594-016-0370-4
DOI10.1007/s12594-016-0370-4

Mercury anomaly, Deccan volcanism and the end-Cretaceous Mass Extinction: (REPLY)

TitleMercury anomaly, Deccan volcanism and the end-Cretaceous Mass Extinction: (REPLY)
Publication TypeJournal Article
Year of Publication2016
AuthorsFont, E, Adatte, T, Keller, G, Abrajevitch, A, Sial, ANobrega, de Lacerda, LDrude, Punekar, J
JournalGeology
Volume44
Paginatione382–e382
Date Published02/2016
Abstract

We thank Jan Smit and colleagues (Smit et al., 2016) for giving us the opportunity to clarify some important points in our original manuscript (Font et al., 2016a) and to discuss the issues raised in their Comment. Their main critique centers on the origin of the mercury anomalies, which they argue are post-depositional and cannot be assigned to Deccan Traps activity. Their arguments center on the hypothesis of Lowrie et al. (1990) who invoked a process of downward infiltration by reducing waters to explain the origin of the white beds below the CretaceousPaleogene (KPg) boundary at Gubbio, Italy. Apparently Smit et al. are not aware of the work by Abrajevitch et al. (2015) or that this issue was addressed in our Geology paper. Here we provide more detailed explanations of why the comments by Smit et al. are out of date.  PDF

URLhttps://pubs.geoscienceworld.org/gsa/geology/article/44/3/e382/132066/mercury-anomaly-deccan-volcanism-and-the-end
DOI10.1130/g37717y.1

U-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction

TitleU-Pb geochronology of the Deccan Traps and relation to the end-Cretaceous mass extinction
Publication TypeJournal Article
Year of Publication2015
AuthorsSchoene, B, Samperton, KM, Eddy, MP, Keller, G, Adatte, T, Bowring, SA, Khadri, SFR, GERTSCH, BRIAN
JournalScience
Volume347
Pagination182–184
ISSN0036-8075
Abstract

The Chicxulub asteroid impact (Mexico) and the eruption of the massive Deccan volcanic province (India) are two proposed causes of the end-Cretaceous mass extinction, which includes the demise of nonavian dinosaurs. Despite widespread acceptance of the impact hypothesis, the lack of a high-resolution eruption timeline for the Deccan basalts has prevented full assessment of their relationship to the mass extinction. Here we apply uranium-lead (U-Pb) zircon geochronology to Deccan rocks and show that the main phase of eruptions initiated ~250,000 years before the Cretaceous-Paleogene boundary and that >1.1 million cubic kilometers of basalt erupted in ~750,000 years. Our results are consistent with the hypothesis that the Deccan Traps contributed to the latest Cretaceous environmental change and biologic turnover that culminated in the marine and terrestrial mass extinctions. PDF

URLhttp://science.sciencemag.org/content/347/6218/182
DOI10.1126/science.aaa0118

Early to late Maastrichtian environmental changes linked to Deccan Traps and Ninetyeast ridge volcanism: Case study of the Indian ocean

TitleEarly to late Maastrichtian environmental changes linked to Deccan Traps and Ninetyeast ridge volcanism: Case study of the Indian ocean
Publication TypeMiscellaneous
Year of Publication2015
AuthorsMateo, P, Keller, G, Punekar, J
Abstract

The Maastrichtian (C31-C30n) was a time of major environmental changes that record evolutionary diversification in planktic foraminifera as well as a minor extinction associated with climate change and high carbonate dissolution. Although these changes have been observed worldwide, their cause(s) remain speculative. Here we report on these events based on Ninetyeast Ridge sites, Indian Ocean, investigate their links to Deccan and Ninetyeast Ridge volcanism and correlate the results with sections around the world. Methods include high-resolution quantitative planktonic foraminiferal biostratigraphy and oxygen and carbon stable isotopes analysis. The Campanian cooling reached its maximum near the Campanian-Maastrichtian boundary (planktic foraminifera zone CF8, base C31r) and was followed by species diversification and a gradual increase in δ13C marking enhanced primary productivity (Event I, zones CF8-CF7). Volcanism associated with the Ninetyeast Ridge may have been an important source of nutrients that created favorable environmental conditions that led to this diversification. Maximum δ13C and negative δ18O values in zone CF6 (top C31r) mark high productivity and climate warming correlative with a rapid increase in species diversity (Event II). The subsequent cooling and decrease in δ13C marks maximum Cretaceous diversity around the CF5-CF4 transition (Event III, C31r-C30n transition). In zone CF4, rapid warming (top C31n) followed by cooling (base C30n) led to a rapid increase in the relative abundance of the most robust planktic and benthic species (large, thick walls) and gradual extinctions of Campanian survivor species (Event IV, C31n-C30n transition). In zone CF3 (top C30n), an increase in the relative abundance of generalist and disaster opportunist species, a rapid decrease in diversity, species dwarfing, high fragmentation index and decreased primary productivity indicate enhanced environmental stress conditions (Event V). During this time, both Ninetyeast Ridge and Deccan phase-1 volcanism were active, suggesting that the environmental changes were likely linked to intense volcanic eruptions that released large amounts of volcanogenic SO2 and CO2 poisoning the environment, causing ocean acidification and ultimately extinctions.  PDF

New geochemical constraints on the Paleocene–Eocene thermal maximum: Dababiya (GSSP), Egypt

TitleNew geochemical constraints on the Paleocene–Eocene thermal maximum: Dababiya (GSSP), Egypt
Publication TypeJournal Article
Year of Publication2015
AuthorsKhozyem, H, Adatte, T, Spangenberg, JE, Keller, G, Tantawy, AAziz, Ulianov, A
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Volume429
Pagination117–135
Date Published07/2018
Abstract

The Paleocene-Eocene Thermal Maximum (PETM) shows an extraordinary drop in the δ13C of carbonate and organic matter across the globe, suggesting massive release of 13C-depleted carbon dioxide into the ocean and atmosphere over a very short time interval (probably < 20ky). We report a geochemical and mineralogical study of 106 samples spanning the most expanded PETM at the Dababiya Global Stratotype Standard section and Point (GSSP) near Luxor, Egypt. The field and laboratory observations reveal that the deposition occurred in a submarine channel extended laterally about 200 m with the deepest part (~ 0.88 m) at the designated GSSP, although all bio-zones are present. Stable isotope records of both carbonate and organic carbon show decreases starting 0.6 m below the Paleocene-Eocene boundary (PEB) and culminating at the erosion surface. A persistent shift in δ15Norg values to near zero reflects a gradual increase in bacterial activity. High Ti, K and Zr and low Si contents at the PEB coincide with increased kaolinite contents, which suggests intense chemical weathering under more humid conditions at the PETM onset. Two negative Ce-anomalies indicate intervals of anoxic conditions during the lower and middle PETM (base and top of zone E1). The first anoxic event is represented by a negative Ce-anomaly, high V/C rand V/V + Ni ratios, negative Mn* and an abundance of idiomorphic pyrite crystals that indicate anoxic to euxinic conditions. The anoxic event (middle PETM) is marked by high U, Mo, V, Fe and abundant small sized (2–5 μm) pyrite framboids, increased Cu, Ni, and Cd at the same level suggesting anoxic conditions linked to high surface water productivity. Above this interval, oxic conditions returned as indicated by the precipitation of phosphorus and barium. These data reveal an expanded PETM interval marked by intense weathering as a crucial parameter during the recovery phase.  PDF

URLhttps://doi.org/10.1016/j.palaeo.2015.04.003
DOI10.1016/j.palaeo.2015.04.003

Deccan volcanism, the Chicxulub impact, and the end-Cretaceous mass extinction: Coincidence? Cause and effect?

TitleDeccan volcanism, the Chicxulub impact, and the end-Cretaceous mass extinction: Coincidence? Cause and effect?
Publication TypeBook Chapter
Year of Publication2014
AuthorsKeller, G
Book TitleVolcanism, Impacts, and Mass Extinctions: Causes and Effects
Volume505
EditionGSA Special Papers
PaginationPp. 29-55
PublisherGeological Society of America
CityBoulder
Abstract

The recent discovery of the direct link between Deccan volcanism and the end-Cretaceous mass extinction also links volcanism to the late Maastrichtian rapid global warming, high environmental stress, and the delayed recovery in the early Danian. In comparison, three decades of research on the Chicxulub impact have failed to account for long-term climatic and environmental changes or prove a coincidence with the mass extinction. A review of Deccan volcanism and the best age estimate for the Chicxulub impact provides a new perspective on the causes for the end­Cretaceous mass extinction and supports an integrated Deccan-Chicxulub scenario. This scenario takes into consideration climate warming and cooling, sea-level changes, erosion, weathering, ocean acidification, high-stress environments with opportunistic species blooms, the mass extinction, and delayed postextinction recovery.The crisis began in C29r (upper CF2 to lower CF1) with rapid global warming of 4 °C in the oceans and 8 °C on land, commonly attributed to Deccan phase 2 eruptions. The Chicxulub impact occurred during this warm event (about 100–150 k.y. before the mass extinction) based on the stratigraphically oldest impact spherule layer in NE Mexico, Texas, and Yucatan crater core Yaxcopoil-1. It likely exacerbated climate warming and may have intensified Deccan eruptions. The reworked spherule layers at the base of the sandstone complex in NE Mexico and Texas were deposited in the upper half of CF1,  50–80 k.y. before the Cretaceous-Tertiary (K-T) boundary. This sandstone complex, commonly interpreted as impact tsunami deposits of K-T boundary age, was deposited during climate cooling, low sea level, and intensified currents, leading to erosion of nearshore areas (including Chicxulub impact spherules), transport, and redeposition via submarine channels into deeper waters. Renewed climate warming during the last  50 k.y. of the Maastrichtian correlates with at least four rapid, massive volcanic eruptions known as the longest lava flows on Earth that ended with the mass extinction, probably due to runaway effects. The kill mechanism was likely ocean acidification resulting in the carbonate crisis commonly considered to be the primary cause for four of the five Phanerozoic mass extinctions.  PDF

URLhttp://specialpapers.gsapubs.org/content/early/2014/06/10/2014.2505_03.1.abstract
DOI10.1130/2014.2505(03)

Effects of Deccan volcanism on paleoenvironment and planktic foraminifera: A global survey

TitleEffects of Deccan volcanism on paleoenvironment and planktic foraminifera: A global survey
Publication TypeJournal Article
Year of Publication2014
AuthorsPunekar, J, Mateo, P, Keller, G
JournalGeological Society of America Special Papers
Volume505
Abstract

Deccan volcanism, one of Earth's largest flood basalt provinces, erupted  80% of its total volume (phase 2) during a relatively short time in the uppermost Maastrichtian paleomagnetic chron C29r and ended with the Cretaceous-Tertiary boundary mass extinction. Full biotic recovery in the marine realm was delayed at least 500 k.y. or until after the last Deccan eruptions in C29n (phase 3, 14% of the total Deccan volume). For over 30 yr, the mass extinction has been commonly attributed to the Chicxulub impact, and the delayed recovery remained an enigma. Here, we demonstrate that the two phases of Deccan volcanism can account for both the mass extinction and delayed marine recovery.In India, a direct correlation between Deccan eruptions (phase 2) and the mass extinction reveals that  50% of the planktic foraminifer species gradually disappeared during volcanic eruptions prior to the first of four lava megaflows, reaching  1500 km across India, and out to the Bay of Bengal. Another 50% disappeared after the first megaflow, and the mass extinction was complete with the last megaflow. Throughout this interval, blooms of the disaster opportunist Guembelitria cretacea dominate shallow-marine assemblages in coeval intervals from India to the Tethys and the Atlantic Oceans to Texas. Similar high-stress environments dominated by blooms of Guembelitria and/or Globoconusa are observed correlative with Deccan volcanism phase 3 in the early Danian C29n, followed by full biotic recovery after volcanism ended. The mass extinction and high-stress conditions may be explained by the intense Deccan volcanism leading to rapid global warming and cooling in C29r and C29n, enhanced weathering, continental runoff, and ocean acidification, resulting in a carbonate crisis in the marine environment.  PDF

URLhttp://specialpapers.gsapubs.org/content/early/2014/08/21/2014.2505_04.abstract
DOI10.1130/2014.2505(04)

Late Maastrichtian–early Danian high-stress environments and delayed recovery linked to Deccan volcanism

TitleLate Maastrichtian–early Danian high-stress environments and delayed recovery linked to Deccan volcanism
Publication TypeJournal Article
Year of Publication2014
AuthorsPunekar, J, Keller, G, Khozyem, H, Hamming, C, Adatte, T, Tantawy, AAAM, Ponte, J
JournalCretaceous Research
Volume49
Pagination63 - 82
Date PublishedJan-05-2014
ISSN01956671
Abstract

Deccan volcanism occurred in three intense phases of relatively short duration: phase 1 spanning the paleomagnetic chron C30r/C30n boundary (planktic foraminiferal CF4), phase 2 in the latest Maastrichtian C29r (zones CF1–CF2), and phase 3 in the early Danian C29n (P1b). This study explores the nature of paleoenvironmental changes correlative with the three volcanic phases in central Egypt and the Sinai based on planktic foraminifers, stable carbon and oxygen isotopes.

Results show that high-stress assemblages dominated by Guembelitria blooms are prominent in, but not exclusive to, all three volcanic phases. These blooms are well known from the aftermath of this mass extinction in zones P0–P1a, the intertrappean interval between volcanic phases 2 and 3. Guembelitria blooms in CF4 (phase 1) are relatively minor (<45%) although they comprise a substantial component of the planktic foraminiferal assemblages. Maximum Guembelitria blooms (>80% of the total assemblage) are observed in CF1, which spans the last 160 ka of the Maastrichtian marked by rapid global climatic warming and cooling correlative with phase 2. Major Guembelitria blooms (50–75%) are also observed in P1b, which is marked by climate warming (Dan-C2 event) and a major negative carbon isotope excursion correlative with phase 3. This high-stress event precedes full marine biotic recovery after the mass extinction.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0195667114000056
DOI10.1016/j.cretres.2014.01.002
Short TitleCretaceous Research

Atmospheric halogen and acid rains during the main phase of Deccan eruptions: Magnetic and mineral evidence

TitleAtmospheric halogen and acid rains during the main phase of Deccan eruptions: Magnetic and mineral evidence
Publication TypeBook Chapter
Year of Publication2014
AuthorsFont, E, Fabre, S, Nedelec, A, Adatte, T, Keller, G, Veiga-Pires, C, Ponte, J, Mirao, J, Khozyem, H, Spangenberg, JE
Book TitleGeological Society of America Special Papers
Pagination353–368
PublisherGeological Society of America Special Papers
Abstract

 

Environmental changes linked to Deccan volcanism are still poorly known. A major limitation resides in the paucity of direct Deccan volcanism markers and in the geologically short interval where both impact and volcanism occurred, making it hard to evaluate their contributions to the mass extinction. We investigated the low-magnetic-susceptibility interval just below the iridium-rich layer of the Bidart (France) section, which was recently hypothesized to be the result of paleoenvironmental perturbations linked to paroxysmal Deccan phase 2. Results show a drastic decrease of detrital magnetite and presence of scarce akaganeite, a hypothesized reaction product formed in the aerosols derived from reaction of a volcanic plume with water and oxygen in the high atmosphere. A weathering model of the consequences of acidic rains on a continental regolith reveals nearly complete magnetite dissolution after ~31,000 yr, which is consistent with our magnetic data and falls within the duration of the Deccan phase 2. These results highlight the nature and importance of the Deccan-related environmental changes leading up to the end- Cretaceous mass extinction.  PDF

URLhttps://doi.org/10.1130/2014.2505(18)
DOI10.1130/2014.2505(18)

The Paleocene-Eocene GSSP at Dababiya, Egypt – Revisited

TitleThe Paleocene-Eocene GSSP at Dababiya, Egypt – Revisited
Publication TypeJournal Article
Year of Publication2014
AuthorsKhozyem, H, Adatte, T, Keller, G, Tantawy, AAAM, Spangenberg, JE
JournalEpisodes
Volume37
Start Page78
Issue2
Date Published06/2014
Abstract

We investigated the Paleocene-Eocene boundaryGSSP (Dababiya quarry) near Luxor, Egypt, in twonearby (25m and 50m) sequences based on high-resolution biostratigraphy, lithostratigrapy, mineralogyand geochemistry. Results confirm the many positiveaspects of the Dababiya GSSP but also show potentiallyserious limiting factors: (1) the GSSP is located in thedeepest part of a ~200 m wide submarine channel, whichlimits its use as global type section. (2) Some lithologicunits identified at the GSSP are absent or thin out anddisappear within the channel and beyond. (3) The P-Eboundary is placed at the base of a clay layer above anerosion surface with variable erosion of latest Paleoceneand earliest Eocene sediments. (4) The current definitionof the P-E boundary as marked by the abrupt onset ofthe carbon isotope excursion at the base of a clay layeris not supported at the GSSP because 50m to the leftthe excursion begins gradually 60cm below the P-Eboundary and reaches minimum values in the boundaryclay. With awareness of these limiting factors andrecognition of the gradual onset of the PETM excursionthe GSSP can contribute significantly to a more completeunderstanding of this global warm event.  PDF

URLhttp://www.researchgate.net/publication/264417759_The_Paleocene-Eocene_GSSP_at_Dababiya_Egypt__Revisited

Micropaleontology in Multi-disciplinary research: Applications to OAE2 and KTB

TitleMicropaleontology in Multi-disciplinary research: Applications to OAE2 and KTB
Publication TypeBook Chapter
Year of Publication2013
AuthorsKeller, G
Book TitleProceedings of XXIII Indian Colloquium on Micropaloentology and Stratigraphy and International Symposium on Global Bioevents in Earth's History
Volume1
EditionSpecial Publication
ChapterPart I, Pp. 1
PublisherGeological Society of India
CityBangalore
ISBN978-93-80998-08-04
Keywordsapplications
URLhttp://www.geosocindia.com/index.php?page=shop.product_details&flypage=flypage-ask.tpl&product_id=227&category_id=20&option=com_virtuemart&Itemid=6

Multiproxy evidence of main Deccan Traps pulse near the Cretaceous-Tertiary boundary

TitleMultiproxy evidence of main Deccan Traps pulse near the Cretaceous-Tertiary boundary
Publication TypeBook Chapter
Year of Publication2013
AuthorsAdatte, T, Keller, G
Book TitleProceedings of XXIII Indian Colloquium on Micropaloentology and Stratigraphy and International Symposium on Global Bioevents in Earth's History
Volume1
EditionSpecial Publication
ChapterPart III, Pp. 243
PublisherGeological Society of India
CityBangalore
ISBN978-93-80998-08-4
KeywordsGlobal Bioevents, KTB, PE
Abstract

Recent studies indicate that the bulk (80%) of Deccan trap eruptions occurred over a relatively short time interval in magnetic polarity C29r, whereas multiproxy studies from central and southeastern India place the Cretaceous-Tertiary (KT) mass extinction near the end of this main phase of Deccan volcanism suggesting a cause-and-effect relationship. Beyond India multiproxy studies also place the main Deccan phase in the uppermost Maastrichtian C29r below the KTB (planktic foraminiferal zones CF2-CF1), as indicated by a rapid shift in 187Os/188Os ratios in deep-sea sections from the Atlantic, Pacific and Indian Oceans, coincident with rapid climate warming, coeval increase in weathering, a significant decrease in bulk carbonate indicative of acidification due to volcanic SO2, and major biotic stress conditions expressed in species dwarfing and decreased abundance in calcareous microfossils (planktic foraminifera and nannofossils). These observations indicate that Deccan volcanism played a key role in increasing atmospheric CO2 and SO2 levels that resulted in global warming and acidified oceans, respectively, increasing biotic stress that predisposed faunas to eventual extinction at the KTB.

URLhttp://www.geosocindia.com/index.php?page=shop.product_details&flypage=flypage-ask.tpl&product_id=227&category_id=20&option=com_virtuemart&Itemid=6

Biostratigraphy and foraminiferal paleoecology of the Early Eocene Naredi Formation, SW Kutch, India

TitleBiostratigraphy and foraminiferal paleoecology of the Early Eocene Naredi Formation, SW Kutch, India
Publication TypeBook Chapter
Year of Publication2013
AuthorsKeller, G, Khozyem, H, Adatte, T, Spangenberg, J
Book TitleProceedings of XXIII Indian Colloquium on Micropaloentology and Stratigraphy and International Symposium on Global Bioevents in Earth's History
Volume1
EditionSpecial Publication
ChapterPart III, Pp. 183
PublisherGeological Society of India
CityBangalore
ISBN978-93-80998-08-4
KeywordsGlobal Bioevents, KTB, PE
Abstract

The Naredi Formation in southwestern Kutch overlies the last Deccan Trap deposited during the early Paleocene. The lower part of the Naredi Formation (2.8-4.2 m from base) is of early Eocene (Ypresian) age (SBZ8, E4) based on larger foraminifera and rare planktic foraminifera, whereas the upper part (9.3-11 m, including the Assilina limestone) is of late early Eocene age (SBZ11, E6). There is no age control for the basal 0-2.8 m and between 4.2-9.3 m because microfossils are rare or absent. Small benthic and rare planktic foraminifera are common in three short intervals and indicate deposition in a brackish to normal marine inner shelf environment (SBZ8, E4), brackish environment (middle of section, no age control) and inner shelf to marginal marine environment (SBZ11, E6). Two phases of marine transgressions can be identified with the maximum transgressions in each phase coincident with the lower and upper foraminiferal assemblages. A paleosol indicated by root traces and burrows (5.9 m) represents a regression and possibly sequence boundary.  PDF

URLhttp://www.geosocindia.com/index.php?page=shop.product_details&flypage=flypage-ask.tpl&product_id=227&category_id=20&option=com_virtuemart&Itemid=6

Chicxulub impact spherules in the North Atlantic and Caribbean: age constraints and Cretaceous–Tertiary boundary hiatus

TitleChicxulub impact spherules in the North Atlantic and Caribbean: age constraints and Cretaceous–Tertiary boundary hiatus
Publication TypeJournal Article
Year of Publication2013
AuthorsKeller, G, Khozyem, H, Adatte, T, Malarkodi, N, Spangenberg, J, Stinnesbeck, W
JournalGeological Magazine
Volume150
Issue05
Pagination885 - 907
Date Published01/2013
ISSN0016-7568
KeywordsChicxulub, impact spherules, KTB unconformity, North Atlantic
Abstract

The Chicxulub impact is commonly believed to have caused the Cretaceous-Tertiary boundary (KTB) mass extinction and a thin impact spherule layer in the North Atlantic and Caribbean is frequently cited as proof. We evaluated this claim in the seven best North Atlantic and Caribbean KTB sequences based on high-resolution biostratigraphy, quantitative faunal analyses and stable isotopes. Results reveal a major KTB unconformity spans most of Danian subzone P1a(1) and Maastrichtian zones CF1-CF2 (~400 kyr) in the NW Atlantic Bass River core, ODP Sites 1049A, 1049C and 1050C. In the Caribbean ODP Sites 999B and 1001B the unconformity spans from the early Danian zone P1a(1) through zones CF1-CF4  (~3 myr). Only in the Demerara Rise ODP Site 1259B is erosion relatively minor and restricted to the earliest Danian zone P0 and most of subzone P1a(1) (~150 kyr). In all sites examined Chicxulub impact spherules are apparently reworked into the early Danian subzone P1a(1) about 150-200 kyr after the mass extinction. A similar pattern of erosion and redeposition of impact spherules in Danian sediments has previously been documented from Cuba, Haiti, Belize, Guatemala, south and central Mexico. This pattern can be explained by intensified Gulf stream circulation at times of climate cooling and sea level changes. The age of the Chicxulub impact cannot be determined from these reworked impact spherule layers, but can be evaluated based on the stratigraphically oldest spherule layer in NE Mexico and Texas, which indicates this impact predates the KTB by about 130-150 kyr.  PDF

URLhttp://www.journals.cambridge.org/abstract_S0016756812001069
DOI10.1017/S0016756812001069
Short TitleGeol. Mag.

Palaeoenvironmental and climatic changes during the Palaeocene–Eocene Thermal Maximum (PETM) at the Wadi Nukhul Section, Sinai, Egypt

TitlePalaeoenvironmental and climatic changes during the Palaeocene–Eocene Thermal Maximum (PETM) at the Wadi Nukhul Section, Sinai, Egypt
Publication TypeJournal Article
Year of Publication2013
AuthorsKhozyem, H, Adatte, T, Spangenberg, J, Tantawy, AAAM, Keller, G
JournalJournal of the Geological Society
Volume170
Pagination341-352
Abstract

The Palaeocene–Eocene Thermal Maximum (PETM) interval at the Wadi Nukhul section (Sinai, Egypt) is represented by a 10 cm thick condensed clay-rich layer corresponding to the NP9a–NP9b nannofossil subzone boundary. The Wadi Nukhul Palaeocene–Eocene boundary (PEB) is characterized by (1) an abrupt negative excursion in carbonate and organic carbon isotope ratios (−6‰ in δ13Ccarb and −2‰ δ13Corg), (2) an abrupt persistent negative shift in organic nitrogen isotope values (δ15Norg), (3) a significant increase in phosphorus concentrations just above the carbon isotope excursion, (4) a decrease in carbonate content and significant increase in kaolinite and (5) high vanadium and low manganese contents coincident with the occurrence of framboidal pyrite. The abrupt correlative isotopic excursions of δ13Ccarb, δ13Corg and δ15N suggest that the lowermost part of the PETM is missing. The decrease in carbonate content indicates dilution by high detrital input triggered by acid weathering and carbonate dissolution in response to increased atmospheric CO2 resulting from the oxidation of methane. The sudden increase in kaolinite content reflects a short-lived change to humid conditions. The δ15N values close to 0‰ above the PEB suggest a bloom of N2-fixing cyanobacteria. Increased bacterial activity may be either the cause or the result of the anoxia locally associated with the PETM.

URLhttp://jgs.lyellcollection.org/content/170/2/341.abstract
DOI10.1144/jgs2012-046

Paleoclimate and Paleoenvironment of the Naredi Formation (Early Eocene), Kutch, Gujarat, India

TitlePaleoclimate and Paleoenvironment of the Naredi Formation (Early Eocene), Kutch, Gujarat, India
Publication TypeBook Chapter
Year of Publication2013
AuthorsKhozyem, H, Adatte, T, Keller, G, Spangenberg, J, Saravanan, N, Bajpai, S
Book TitleProceedings of XXIII Indian Colloquium on Micropaloentology and Stratigraphy and International Symposium on Global Bioevents in Earth's History
Volume1
EditionSpecial Publication
ChapterPart III, Pp. 165
PublisherGeological Society of India
CityBangalore
ISBN978-93-80998-08-4
KeywordsGlobal events, KTB, PE
Abstract

The Naredi Formation of Kutch, Gujarat, India, is early Eocene in age and marks the first marine transgression above the last Deccan traps. Sediment deposition occurred in a shallow inner shelf environment that varied from a brackish lagoon to brackish, normal inner shelf and to marginal marine environments. The section can be divided into 2 main transgressive cycles interrupted by a regression phase that is marked by a well-defined sequence boundary marked by a root-bearing paleosoil. Three intervals yielded common to abundant benthic foraminiferal assemblages. Planktic foraminifera are few to rare and restricted to the top of the section, except for Chiloguembelina trinitatensis. An early Eocene age can be attributed to the Naredi section based primarily on larger benthic foraminifera (SBZ8 to SBZ11, equivalent to planktic foraminiferal biozones E4 to E6), rare planktic foraminifera, the stable isotope curve and its correlation with marine sections and sequence stratigraphy. Sediments of the transgression/regression cycles were derived from physical and chemical-weathering processes of basaltic rocks as indicated by the different geochemical proxies. Carbon isotope analyses of bivalve shells and organic matter reveal a negative excursion that is correlative with the global Early Eocene excursion. The presence of fish bones, fish teeth and organic matter can be related to the Early Eocene climatic optimum. Clay mineral data from the Naredi Formation indicate variably hot humid to arid climate conditions. 

URLhttp://www.geosocindia.com/index.php?page=shop.product_details&flypage=flypage-ask.tpl&product_id=227&category_id=20&option=com_virtuemart&Itemid=6

The Cretaceous-Tertiary boundary (KTB) transition in NE Brazil

TitleThe Cretaceous-Tertiary boundary (KTB) transition in NE Brazil
Publication TypeJournal Article
Year of Publication2013
AuthorsGertsch, B, Keller, G, Adatte, T, Berner, Z
JournalJournal of the Geological Society
Volume170
Issue2
Pagination249 - 262
Date Published01/2013
ISSN0016-7649
Abstract

The Cretaceous-Tertiary boundary (KTB) transition of the Poty Quarry near Recife, NE Brazil, is the most distant locality (7800 km from Yucatan) with reported Chicxulub impact-tsunami deposits, impact spherules and Ir anomaly. Investigations based on sedimentology, biostratigraphy, mineralogy, stable isotopes and elemental geochemistry failed to confirm these reports. The KTB is at an unconformity marked by erosion and bioturbation. Latest Maastrichtian planktic foraminiferal zones CF1 below the unconformity and early Danian zone P1a(1) above indicates a short hiatus with the KTB clay (zone P0), Ir anomaly and characteristic negative d13C excursion missing. Above the unconformity is an upward-fining micro-conglomerate with abundant reworked Cretaceous foraminifera, sub-angular phosphate clasts, calcitic and phosphatic spheroids along with an early Danian zone P1a(1) assemblage.

This deposit has previously been interpreted as impact-tsunami with impact spherules. However, the spheroids are common throughout the late Campanian-Maastrichtian and appear to be chamber infillings of the benthic foraminifer Dentalina alternata. The unconformity coincides with the latest Maastrichtian sea level fall, which is widely recognized globally. The upward fining micro-conglomerate is likely a gravity-flow deposit associated with the early Danian sea level rise. Two minor Ir anomalies (<0.7 ppb) in thin clay layers of zone Pla are unrelated to the Chicxulub impact. Although there is no evidence of the Chicxulub impact in the Poty Quarry, this section remains a very important distant example of the complex global environmental and sea level changes, including gravity flows, observed in KT sequences from North America through Mexico, Central America and the Caribbean and commonly misinterpreted as impact tsunami event.  PDF

URLhttp://jgs.geoscienceworld.org/cgi/doi/10.1144/jgs2012-029
DOI10.1144/jgs2012-029
Short TitleJournal of the Geological Society

Volcanism, impacts and mass extinctions (Long Version)

TitleVolcanism, impacts and mass extinctions (Long Version)
Publication TypeWeb Article
Year of Publication2012
AuthorsKeller, G, Armstrong, H, Courtillot, V, Harper, D, Joachimski, M, Kerr, A, MacLeod, N, Napier, W, Palfy, J, Wignall, P
Access Year2012
Access DateNovember
PublisherThe Geological Society
CityLondon
Type of MediumOnline version
Keywordsclimate change, Impacts, Mass extinctions, ocean anoxia, Phanerozoic, Volcanism
Abstract

The nature and causes of mass extinctions in the geological past have remained topics of intense scientific debate for the past three decades.  Central to this debate is the question of whether one or several large bolide impacts, the eruption of large igneous provinces (LIPS), or a combination of the two were the primary mechanism(s) driving the environmental and habitat changes that are universally regarded as the proximate causes for four of the five major extinction events.  Recent years have seen a revolution in our understanding of both the interplanetary environment and LIPS eruptions and their environmental effects such that the current impact-kill scenario no longer seems adequate for the KT (KPg) or any other mass extinction.  Massive sequential volcanic eruptions and the breakup of giant comets leading to rapid climate change, ocean anoxia and ozone destruction emerge as the leading causes in major mass extinctions.  PDF

URLhttp://www.geolsoc.org.uk/Geoscientist/Archive/November-2012/Volcanism-impacts-and-mass-extinctions-2
Alternate TitleVolcanism, impacts and mass extinctions (long version)

The Cretaceous–Tertiary Mass Extinction, Chicxulub Impact, and Deccan Volcanism

TitleThe Cretaceous–Tertiary Mass Extinction, Chicxulub Impact, and Deccan Volcanism
Publication TypeBook Chapter
Year of Publication2012
AuthorsKeller, G
Book TitleEarth and Life
Pagination759 - 793
PublisherSpringer Netherlands
CityDordrecht
ISBN Number978-90-481-3427-4
KeywordsChicxulub impact, Cretaceous, Danian, deccan volcanism, Foraminifers, Maastrichtian, Mass extinctions, Paleogene
Abstract

After three decades of nearly unchallenged wisdom that a large impact (Chicxulub) on Yucatan caused the end-Cretaceous mass extinction, this theory is facing its most serious challenge from the Chicxulub impact itself, as based on evidence in Texas and Mexico and from Deccan volcanism in India. Data generated from over 150 Cretaceous–Tertiary (KT) boundary sequences to date make it clear that the long-held belief in the Chicxulub impact as the sole or even major contributor to the KT mass extinction is not supported by evidence. The stratigraphic position of the Chicxulub impact ejecta spherules in NE Mexico and Texas and the impact breccia within the crater on Yucatan demonstrate that this impact predates the KTB by about 300,000 years. Planktic foraminiferal and stable isotope analyses across the primary impact ejecta layer reveal that not a single species went extinct as a result of this impact and no significant environmental changes could be determined. The catastrophic effects of this impact have been vastly overestimated. In contrast, recent advances in Deccan volcanic studies indicate three volcanic phases with the smallest at 67.5 Ma, the main phase at the end of the Maastrichtian (C29r), and the third phase in the early Danian C29r/C29n transition (Chenet et al. 2007). The main phase of eruptions occurred rapidly, was marked by the longest lava flows spanning 1500 km across India, and ended coincident with the KT boundary. The KT mass extinction may have been caused by these rapid and massive Deccan lava and gas eruptions that account for ∼80% of the entire 3500 m thick Deccan lava pile.

URLhttp://link.springer.com/content/pdf/10.1007/978-90-481-3428-1_25
DOI10.1007/978-90-481-3428-110.1007/978-90-481-3428-1_25

Stratigraphy of the Cenomanian–Turonian Oceanic Anoxic Event OAE2 in shallow shelf sequences of NE Egypt

TitleStratigraphy of the Cenomanian–Turonian Oceanic Anoxic Event OAE2 in shallow shelf sequences of NE Egypt
Publication TypeJournal Article
Year of Publication2011
AuthorsEl-Sabbagh, A, Tantawy, AAAM, Keller, G, Khozyem, H, Spangenberg, J, Adatte, T, Gertsch, B
JournalCretaceous Research
Volume32
Issue6
Pagination705 - 722
Date PublishedJan-12-2011
ISSN01956671
Abstract

Two shallow water late Cenomanian to early Turonian sequences of NE Egypt have been investigated to evaluate the response to OAE2. Age control based on calcareous nannoplankton, planktic foraminifera and ammonite biostratigraphies integrated with δ13C stratigraphy is relatively good despite low diversity and sporadic occurrences. Planktic and benthic foraminiferal faunas are characterized by dysoxic, brackish and mesotrophic conditions, as indicated by low species diversity, low oxygen and low salinity tolerant planktic and benthic species, along with oyster-rich limestone layers. In these subtidal to inner neritic environments the OAE2 δ13C excursion appears comparable and coeval to that of open marine environments. However, in contrast to open marine environments where anoxic conditions begin after the first δ13C peak and end at or near the Cenomanian–Turonian boundary, in shallow coastal environments anoxic conditions do not appear until the early Turonian. This delay in anoxia appears to be related to the sea-level transgression that reached its maximum in the early Turonian, as observed in shallow water sections from Egypt to Morocco.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0195667111000474
DOI10.1016/j.cretres.2011.04.006
Short TitleCretaceous Research

The Sandstone Complex in the Brazos Riverbed Section: Geochemical Contraints on Genesis and Depositional Conditions

TitleThe Sandstone Complex in the Brazos Riverbed Section: Geochemical Contraints on Genesis and Depositional Conditions
Publication TypeBook Chapter
Year of Publication2011
AuthorsMunsel, D, Berner, Z, Stuben, D
Book TitleSEPM, Special Publication
VolumeNo. 100
Pagination281-295
ISBN978-1-56576-308-1
Abstract

The origin and deposition of spherule-bearing, dominantly sandy beds in a sandstone complex (also called ‘‘event deposit’’) below the biostratigraphic Cretaceous–Tertiary (KT) boundary plays a key role in models linking the KT mass extinction to the Chicxulub impact. This study, which focuses on the chemostratigraphy of this complex exposed in a ca. 60-cm-thick succession along the Brazos River, Falls County, Texas, U.S.A., aims to constrain the source of the material as well as the depositional conditions and postdepositional history of this highly controversial stratigraphic unit. Major and trace elements, as well as the isotopic composition of the Ca carbonate, contrast sharply with the underlying Corsicana Formation, indicating a dramatic change in the source of material and depositional conditions. Evaluation of geochemical data by principal-component analysis permits identification of (1) siliciclastic components, (2) ejecta material, consisting of altered impact-glass spherules, and (3) Ca carbonate. The ejecta material, originally represented chiefly by glass spherules with carbonate infill, is strongly altered to clay minerals with dominantly smectitic composition and is characterized by the element association Al2O3, TiO2, Fe2O3, P2O5, and SO2 and the trace elements (TE) V, Cr, Ni, Cu, Zn, Ga, and Mo. The occurrence of two moderately high Ir peaks (0.2 and 1.1 μg/kg) suggests the presence of tiny amounts of extraterrestrial material within the sandstone complex. Based on the contrasting abundance of Ni and Cu in chondritic meteorites and middle crust, the Ni/Cu ratio was used to trace the portion of extraterrestrial material in the sequence. The distribution of this ratio reflects changes in the amount of siliciclastic components added during deposition of the sandstone complex rather than variations in the amount of meteoritic material. The disagreement between evidence suggesting a prevalence of reducing conditions during the alteration of the ejecta material (pyrite inclusions in spherules; accommodation of Mn2+ by secondary calcite) and sedimentologic features which indicate that the sandstone complex was deposited in a dominantly oxic, high-energy environment strongly supports the case that the ejecta material in these deposits was subjected to reworking. PDF

 

Biostratigraphy, Age of Chicxulub Impact, and Depositional Environment of the Brazos River KTB Sequences

TitleBiostratigraphy, Age of Chicxulub Impact, and Depositional Environment of the Brazos River KTB Sequences
Publication TypeBook Chapter
Year of Publication2011
AuthorsKeller, G, Abramovich, T, Adatte, T, Berner, Z
Book TitleThe End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSEPM, Special Publication
Pagination81-122
PublisherSEPM (Society for Sedimentary Geology)
CityTulsa
ISBN978-1-56576-308-1
KeywordsBiostratigraphy, Brazos, Chicxulub impact, Cretaceous-Tertiary, d13C shift, Evolution, Ir anomaly, mass extinction, Sandstone complex, Sea level, Texas
Abstract

Integrated biostratigraphy, sedimentology and stable isotopes of 11 outcrops and wells along the Brazos River of Falls County, Texas, U.S.A., reveal the stratigraphic separation and sequential depositional history of the Chicxulub impact, followed by the sandstone complex and associated sea-level fall, which in turn was followed by the Cretaceous-Tertiary boundary (KTB). The KTB was identified up to 1 m above the sandstone complex based on three global standard criteria: the mass extinction in planktic foraminifera, the evolution of first Danian species and the negative d13C shift. No Ir anomaly is associated with the KTB or the Chicxulub impact-ejecta layers. Late Maastrichtian sediment deposition occurred in a middle-shelf environment that shallowed to inner-shelf depth at the time of deposition of the sandstone complex. At this time, Brazos sections show distinct shallowing from inner neritic in the north to subtidal and lagoonal at Cottonmouth Creek, with further shallowing to intertidal swamp or marsh conditions in the Darting Minnow Creek area to the south. The sandstone complex is the most prominent feature of the Brazos sections. At the base of this unit are reworked Chicxulub impact spherules and lithified clasts with impact spherules and mud cracks that bear witness to erosion of an older primary spherule deposit. This primary Chicxulub impact-ejecta layer was discovered between 45 and 60 cm below the sandstone complex in a (3 cm thick) impact-glass layer that is diagenetically altered to yellow clay. The sandstone complex, the reworked impact spherules, the spherule-rich clasts, and the yellow clay layer all clearly predate the KTB. PDF

Deccan volcanism linked to the Cretaceous-Tertiary boundary mass extinction: New evidence from ONGC wells in the Krishna-Godavari Basin

TitleDeccan volcanism linked to the Cretaceous-Tertiary boundary mass extinction: New evidence from ONGC wells in the Krishna-Godavari Basin
Publication TypeJournal Article
Year of Publication2011
AuthorsKeller, G, Bhowmick, PK, Upadhyay, H, Dave, A, Reddy, AN, Jaiprakash, BC, Adatte, T
JournalJournal of the Geological Society of India
Volume78
Issue5
Pagination399 - 428
Date PublishedJan-11-2011
ISSN0016-7622
Abstract

A scientific challenge is to assess the role of Deccan volcanism in the Cretaceous-Tertiary boundary (KTB) mass extinction. Here we report on the stratigraphy and biologic effects of Deccan volcanism in eleven deep wells from the Krishna-Godavari (K-G) Basin, Andhra Pradesh, India. In these wells, two phases of Deccan volcanism record the world’s largest and longest lava mega-flows interbedded in marine sediments in the K-G Basin about 1500 km from the main Deccan volcanic province. The main phase-2 eruptions (∼80% of total Deccan Traps) began in C29r and ended at or near the KTB, an interval that spans planktic foraminiferal zones CF1–CF2 and most of the nannofossil Micula prinsii zone, and is correlative with the rapid global warming and subsequent cooling near the end of the Maastrichtian. The mass extinction began in phase-2 preceding the first of four mega-flows. Planktic foraminifera suffered a 50% drop in species richness. Survivors suffered another 50% drop after the first mega-flow, leaving just 7 to 8 survivor species. No recovery occurred between the next three mega-flows and the mass extinction was complete with the last phase-2 mega-flow at the KTB. The mass extinction was likely the consequence of rapid and massive volcanic CO2 and SO2 gas emissions, leading to high continental weathering rates, global warming, cooling, acid rains, ocean acidification and a carbon crisis in the marine environment.

Deccan volcanism phase-3 began in the early Danian near the C29R/C29n boundary correlative with the planktic foraminiferal zone P1a/P1b boundary and accounts for ~14% of the total volume of Deccan eruptions, including four of Earth’s longest and largest mega-flows. No major faunal changes are observed in the intertrappeans of zone P1b, which suggests that environmental conditions remained tolerable, volcanic eruptions were less intense and/or separated by longer time intervals thus preventing runaway effects. Alternatively, early Danian assemblages evolved in adaptation to high-stress conditions in the aftermath of the mass extinction and therefore survived phase-3 volcanism. Full marine biotic recovery did not occur until after Deccan phase-3. These data suggest that the catastrophic effects of phase-2 Deccan volcanism upon the Cretaceous planktic foraminifera were a function of both the rapid and massive volcanic eruptions and the highly specialized faunal assemblages prone to extinction in a changing environment. Data from the K-G Basin indicates that Deccan phase-2 alone could have caused the KTB mass extinction and that impacts may have had secondary effects.

URLhttp://link.springer.com/article/10.1007%2Fs12594-011-0107-3
DOI10.1007/s12594-011-0107-3
Short TitleJ Geol Soc India

Nature of the KTB Controversy

TitleNature of the KTB Controversy
Publication TypeBook Chapter
Year of Publication2011
AuthorsKeller, G, Adatte, T
Book TitleThe End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSEPM, Special Publication
ISBN978-1-56576-308-1
Abstract

One of the liveliest debates among scientists concerns potential causes of catastrophic extinction events, but none have garnered the imagination of scientists and public alike as the Cretaceous–Tertiary boundary (KTB) mass extinction including the demise of the dinosaurs 65 million years ago. Over three decades ago the discovery of anomalous concentrations of iridium in a thin clay layer between Cretaceous limestones and Tertiary claystones led Alvarez and collaborators to propose that a large meteorite crashed into Earth and caused the KTB mass extinction (Alvarez et al., 1980). Because iridium is rare on Earth’s surface, relatively common deep in Earth’s interior where it can surface via volcanic eruptions, but most abundant in some meteorites, this hypothesis rapidly gained support. With the discovery of the 175 km diameter Chicxulub impact crater on Yucata´n in 1991 (Hildebrand et al., 1991), followed by discoveries of impact glass spherule ejecta throughout the Caribbean, Central America, and North America in stratigraphic proximity of the KTB mass extinction (Izett et al., l99l; Swisher et al., l992; Smit et al., 1992) there seemed little doubt that the smoking gun had been found in the Chicxulub impact crater and that the impact-kill hypothesis was all but proven. For many scientists, the impact-kill hypothesis became a Eureka moment—a beautiful theory that could be expanded with many corollaries to account for virtually all observations. It was reconfirmed by 41 scientists in a recent Science article (Schulte et al., 2010) and expressed well by Birger Schmitz (2011) in his review of Ted Nield’s new book Incoming—Or why we should stop worrying and learn to love the meteorite. Nield (2011) writes a riveting account on meteorites that begins with fascinating historical facts, heresy, and beliefs through the ages before leading into the scientific geological account of the meteorite theory and an objective treatment of the controversy based on evidence inconsistent with this theory. There is nothing worse than destroying a beautiful theory with facts. Schmitz takes issue with Nield’s suggestion that doubters like Gerta Keller and her small team may have a point—the impact harmed nature, but the mass extinction had more varied causes. Schmitz considers this a compromise that belongs in politics, not in science. He goes on to state that he started his career in the 1980s as a non-believer of the impact theory, but has now seen the KTB clay layer in over 50 localities ‘‘where the iridium enriched layer always occurs exactly at the level at which the microscopic foraminifera typical of Cretaceous oceans disappear almost completely . . . The precise coincidence of these two events is so compelling that it is difficult to understand how anyone can doubt the direct relationship between them’’ (Schmitz, 2011).  PDF

Environmental effects of Deccan volcanism across the Cretaceous–Tertiary transition in Meghalaya, India

TitleEnvironmental effects of Deccan volcanism across the Cretaceous–Tertiary transition in Meghalaya, India
Publication TypeJournal Article
Year of Publication2011
AuthorsGertsch, B, Keller, G, Adatte, T, Garg, R, Prasad, V, Berner, Z, Fleitmann, D
JournalEarth and Planetary Science Letters
Volume310
Issue3-4
Pagination272 - 285
Date Published01/2011
ISSN0012821X
Abstract

The Um Sohryngkew section of Meghalaya, NE India, located 800–1000 km from the Deccan volcanic province, is one of the most complete Cretaceous–Tertiary boundary (KTB) transitions worldwide with all defining and supporting criteria present: mass extinction of planktic foraminifera, first appearance of Danian species, δ13C shift, Ir anomaly (12 ppb) and KTB red layer. The geochemical signature of the KTB layer indicates not only an extraterrestrial signal (Ni and all Platinum Group Elements (PGEs)) of a second impact that postdates Chicxulub, but also a significant component resulting from condensed sedimentation (P), redox fluctuations (As, Co, Fe, Pb, Zn, and to a lesser extent Ni and Cu) and volcanism. From the late Maastrichtian C29r into the early Danian, a humid climate prevailed (kaolinite: 40–60%, detrital minerals: 50–80%). During the latest Maastrichtian, periodic acid rains (carbonate dissolution; CIA index: 70–80) associated with pulsed Deccan eruptions and strong continental weathering resulted in mesotrophic waters. The resulting super-stressed environmental conditions led to the demise of nearly all planktic foraminiferal species and blooms (> 95%) of the disaster opportunist Guembelitria cretacea. These data reveal that detrimental marine conditions prevailed surrounding the Deccan volcanic province during the main phase of eruptions in C29r below the KTB. Ultimately these environmental conditions led to regionally early extinctions followed by global extinctions at the KTB.

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0012821X11004791
DOI10.1016/j.epsl.2011.08.015
Short TitleEarth and Planetary Science Letters

Defining the Cretaceous-Tertiary Boundary: A Practical Guide and Return to First Principles

TitleDefining the Cretaceous-Tertiary Boundary: A Practical Guide and Return to First Principles
Publication TypeBook Chapter
Year of Publication2011
AuthorsKeller, G
Book TitleThe End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSEPM, Special Publication
Number of Volumes23-42
PublisherSEPM (Society for Sedimentary Geology)
CityTulsa
ISBN978-1-56576-308-1
KeywordsCretaceous-Tertiary, d13C shift, Evolution, Guide, Ir anomaly, KT Definition, mass extinction
Abstract

The Cretaceous-Tertiary boundary (KTB) is one of the easiest epoch boundaries to identify, whether based on lithological changes in the field, geochemical analysis in the laboratory, or fossil content. A set of five KTB-identifying criteria, originally proposed by the ICS working group during 1980 -1990s, have proven globally applicable and independently verifiable: (1) mass extinction of Cretaceous planktic foraminifera, (2) evolution of the first Danian species, (3) KTB clay and red layer, (4) Ir anomaly, and (5) δ13C shift. Despite this successful track record, it was recently proposed to reduce the five KTB-identifying criteria to just two, the mass extinction and impact signals, based on the assumption that the Chicxulub impact caused the mass extinction and therefore defines the KTB. Because this assumption is contradicted by stratigraphic data in many places, this has led to contentious arguments, whereas defining the Chicxulub impact as KTB in age has led to circular reasoning. This study demonstrates the contradictions, pitfalls, and erroneous assumptions that accompany the use of these reduced impact-event-based KTB criteria. Returning the definition of the KTB to its GSSP based on all five criteria, and where this is not possible based on the mass extinction, the first appearance of Danian species, and the δ13C shift provide the most reliable KT boundary markers.   PDF

Cretaceous-Tertiary Mass Extinction in Marginal and Open Marine Environments: Texas, U.S.A., and Tunisia

TitleCretaceous-Tertiary Mass Extinction in Marginal and Open Marine Environments: Texas, U.S.A., and Tunisia
Publication TypeBook Chapter
Year of Publication2011
AuthorsKeller, G
Book TitleThe End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSEPM, Special Publication
Pagination197-226
PublisherSEPM (Society for Sedimentary Geology)
CityTulsa
ISBN Number978-1-56576-308-1
KeywordsChicxulub impact, d13C shift, Depositional environment, Evolution, high stress, Ir anomaly, KT Mass Extinction, Sandstone complex, Sea level, Shallow Environment, Texas, Tunisia. Cretaceous-Tertiary
Abstract

The Cretaceous-Tertiary boundary (KTB) sequences along the Brazos River, Texas, U.S.A., have been controversial for over two decades. At issue is whether the KTB and the mass extinction should be placed at the base of a sandstone complex based on the presence of Chicxulub impact spherules or at the mass extinction. This issue goes to the very core of the KTB controversy – did the Chicxulub impact cause the KTB mass extinction? Faunal, stable isotope, platinum group elements (PGEs), and lithological analyses of six Brazos cores and outcrop sections, and comparison of these data with the Elles, Tunisia, parastratotype shed empirical light on these issues. The KTB is well marked by the mass extinction of planktic foraminifera, the first appearance of Danian species, and the δ13C negative shift, which occurs up to 1 m above the sandstone complex that contains two to three impact spherule layers at its base. There is no Ir anomaly at the KTB and mass extinction, but minor Ir enrichments are present in condensed intervals within and slightly above the sandstone complex. Clasts at the base of the sandstone complex contain impact spherules that reveal earlier deposition, lithification, erosion and redeposition. The Chicxulub impact thus predates not only the KTB, but also the sandstone complex. A yellow clay layer consisting of altered impact glass 45-60 cm below the sandstone complex (zone CF1) may represent the original Chicxulub impact ejecta fallout.

 The mass extinction pattern in the Brazos sections appears gradual or progressive compared with patterns documented from open-ocean environments. This is largely the result of high sediment accumulation rates in inner-neritic depositional settings coupled with the sea-level fall that culminated with deposition of the sandstone complex. Comparison of various extinction parameters, such as overall species richness, species abundances, life strategies, and separation into opportunists vs. specialists reveals that the shallow Brazos environment excluded the specialized larger and deeper dwelling species (~40%) that suffered the most abrupt mass extinction at the KTB. The Brazos extinction pattern thus reflects the mass extinction in the most hardy and environmentally most tolerant assemblages, which include several KTB survivors. Similar patterns are observed in shallow-water environments of southern Tunisia, Egypt, Denmark and Argentina. These data strongly show that the Chicxulub impact predates the KTB and caused no species extinctions at the KTB or at the earlier time of the impact.   PDF

Nature and timing of extinctions in Cretaceous-Tertiary planktic foraminifera preserved in Deccan intertrappean sediments of the Krishna–Godavari Basin, India

TitleNature and timing of extinctions in Cretaceous-Tertiary planktic foraminifera preserved in Deccan intertrappean sediments of the Krishna–Godavari Basin, India
Publication TypeJournal Article
Year of Publication2011
AuthorsKeller, G, Adatte, T, Bhowmick, PK, Upadhyay, H, Dave, A, Reddy, AN, Jaiprakash, BC
JournalEarth and Planetary Science Letters
Volume341-344
Pagination211 - 221
Date PublishedJan-08-2012
ISSN0012821X
Abstract

In C29r below the Cretaceous-Tertiary boundary (KTB) massive Deccan Trap eruptions in India covered an area the size of France or Texas and produced the world’s largest and longest lava megaflows 1500 km across India through the Krishna–Godavari (K–G) Basin into the Bay of Bengal. Investigation of ten deep wells from the K–G Basin revealed four lava megaflows separated by sand, silt and shale with the last megaflow ending at or near the KTB. The biologic response in India was swift and devastating. During Deccan eruptions prior to the first megaflow, planktic foraminifera suffered 50% species extinctions. Survivors suffered another 50% extinctions after the first megaflow leaving just 7–8 species. No recovery occurred between the next three megaflows and the mass extinction was complete with the last mega-flow at or near the KTB. The last phase of Deccan volcanism occurred in the early Danian C29n with deposition of another four megaflows accompanied by delayed biotic recovery of marine plankton. Correlative with these intense volcanic phases, climate changed from humid/tropical to arid conditions and returned to normal tropical humidity after the last phase of volcanism. The global climatic and biotic effects attributable to Deccan volcanism have yet to be fully investigated. However, preliminary studies from India to Texas reveal extreme climate changes associated with high-stress environmental conditions among planktic foraminifera leading to blooms of the disaster opportunist Guembelitria cretacea during the late Maastrichtian.  PDF

URLhttp://linkinghub.elsevier.com/retrieve/pii/S0012821X12003056
DOI10.1016/j.epsl.2012.06.021
Short TitleEarth and Planetary Science Letters

The Cretaceous-Tertiary Mass Extinction: Theories and Controversies

TitleThe Cretaceous-Tertiary Mass Extinction: Theories and Controversies
Publication TypeBook Chapter
Year of Publication2011
AuthorsKeller, G
Book TitleEnd-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSpecial Publication
Pagination7-22
PublisherSEPM (Society for Sedimentary Geology)
CityTulsa
Abstract

The Cretaceous-Tertiary (KT) mass extinction is primarily known for the demise of the dinosaurs, the Chicxulub impact and the frequently rancorous 30 years old controversy over the cause of this mass extinction. Since 1980 the impact hypothesis has steadily gained support that culminated in 1990 with the discovery of the Chicxulub crater on Yucatan as the KT impact site and ‘smoking gun’ that proved this hypothesis. In a perverse twist of fate this discovery also began the decline of this hypothesis because for the first time it could be tested directly based on the impact crater and impact ejecta in sediments throughout the Caribbean, Central and North America. Two decades of multi-disciplinary studies amassed a database with a sum total that overwhelmingly reveals the Chicxulub impact as predating the KT mass extinction in the impact crater cores, in sections throughout NE Mexico and in Brazos River sections of Texas. This chapter recounts the highlights of the KT controversy, the discovery of facts inconsistent with the impact hypothesis and the resurgence of the Deccan volcanism hypothesis as the most likely cause for the mass extinction.  PDF

Age and Origin of the Chicxulub Impact and Sandstone Complex, Brazos River, Texas: Evidence from Lithostratigraphy and Sedimentilogy

TitleAge and Origin of the Chicxulub Impact and Sandstone Complex, Brazos River, Texas: Evidence from Lithostratigraphy and Sedimentilogy
Publication TypeBook Chapter
Year of Publication2011
AuthorsAdatte, T, Keller, G, Baum, G
Book TitleThe End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSEPM, Special Publication
Pagination43-80
PublisherSEPM (Society for Sedimentary Geology)
CityTulsa
ISBN978-1-56576-308-1
Abstract

Multidisciplinary investigations based on the lithology, sedimentology, mineralogy and biostratigraphy of upper Maastrichtian to lower Danian boundary (KTB) sequences along 3.5 km of the Brazos River in Falls County, Texas, reveal depositonal sequences, including an impact spherule-rich sandstone complex, characteristic of sequence stratigraphic models applied to shallow shelf areas, such as incised valleys, lag conglomerate, storm deposits and repeated bioturbation. The top of the Corsicana Formation coincides with a channel, which we interpret as incised valley. The erosion surface marks a major depositional sequence boundary (SB) associated with the latest Maastrichtian sea-level fall. Initial channel deposits consist of coarse shelly glauconitic sand with large lithified clasts containing impact spherules and large bored and encrusted phosphatized concretions, which we interpret to indicate that the Chicxulub impact occurred well prior to the lithification, erosion and redeposition at the base of the channel. The primary Chicxulub ejecta layer lies about 40-65 cm below the sandstone complex in a 3 cm-thick yellow clay layer that consists of cheto smectitie (altered impact glass) interbedded in claystones of the Corsicana Formation. Above the sandstone complex, claystones and mudstones are burrowed and correspond to a condensed interval interpreted as a maximum flooding surface (MFS).Based on biostratigraphy and the δ13C shift, the KT boundary is up to 1 m (50-100 ky) above the sandstone complex and coincides with increased sediment accumulation during the early Danian sea level rise (HST). No impact signals are observed in KT deposits. These features are inconsistent with a single catastrophic bolide impact on Yucatan and associated mega-tsunami deposition as commonly interpreted.

 The biostratigraphy and KT characteristic δ13C shift of the Brazos sections indicate that the KTB, sandstone complex and the Chicxulub impact occurrred as three different stratigraphic events during the late Maastrichtian planktic foraminiferal zone CF1. These are represented by : 1) the Chicxulub impact sequence deposited about 200-300 ky prior to the KTB ;  2) the sandstone complex with reworked impact spherules deposited in incised valleys during the latest sea level fall about 100-150 ky prior to the KTB, and 3) the KTB event during the subsequent HST and following the condensed MFS.   PDF

Maastrichtian Planktic Foraminiferal Biostratigraphy and Paleoenvironment of Brazos River, Falls County, Texas, U.S.A.

TitleMaastrichtian Planktic Foraminiferal Biostratigraphy and Paleoenvironment of Brazos River, Falls County, Texas, U.S.A.
Publication TypeBook Chapter
Year of Publication2011
AuthorsAbramovich, S, Keller, G, Berner, Z, Cymbalista, M
Book TitleThe End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSEPM Special Publication
Pagination123-156
ISBN978-1-56576-308-1
Abstract

Investigation of late Maastrichtian faunal and environmental changes in three subsurface wells spanning over 3 km along the Brazos River, Texas, reveals similar minimum diversity high-stress assemblages associated with shallow shelf conditions. Upper Maastrichtian sediments recovered span planktic foraminiferal (CF) zones CF1 to CF4 in well Mullinax-1 to the north and well KT3 at Cottonmouth Creek, and zones CF1-CF2 in Mullinax-3 at Darting Minnow Creek. Biotic stress conditions are demonstrated by the minimum species richness, near exclusion of larger specialized species, dwarfing, and dominance of small generalist taxa.  Faunal assemblages dominated by alternating abundances of the disaster opportunist Guembelitria cretacea (Cushman) (particularly in zones CF4 and CF2-CF1) and heterohelicid species [e.g., Heterohelix globulosa (Ehrenberg), H. planata (Cushman), Paraspiroplecta navarroensis (Loeblich)].. Other small surface and subsurface mixed layer dwellers are rare to common (e.g., hedbergellids, globigerinellids, pseudoguembelinids).

The coincidence of Guembelitria blooms with lithological changes and oxygen and carbon stable isotope excursions may represent discrete episodes of freshwater runoff related to short -term pulses of the latest Maastrichtian (zone CF1-CF2) global climate warming. Climate warming ended in the upper part of zone CF1 with the return to a cooler climate, lower sea level and the formation of incised valleys in a coastal-lagoonal environment. With the subsequent early transgression, incised valleys were infilled by a sandstone complex with reworked impact spherules, as well as lithified clasts with impact spherules up to 80 cm below the K-Pg Boundary. In this environment the shallow inner neritic setting superimposed by sea level and climate changes is the most probable cause for the observed high biotic stress conditions preceding the K-Pg Boundary in the Brazos area.  PDF

De México a India en busca de las causas del ocaso de los dinosaurios

TitleDe México a India en busca de las causas del ocaso de los dinosaurios
Publication TypeJournal Article
Year of Publication2011
AuthorsPardo, A, Keller, G, Adatte, T
JournalEnseñanza de las Ciencias de la Tierra
Volume19.2
Issue149
Pagination149-161
ISSN1132-9157
Abstract

The Cretaceous-Tertiary (K/T) mass extinction that wiped out dinosaurs 65.5 million years ago is the last of five major biological crises that occurred in the history of life on Earth.

Each of them and the subsequent evolution of new life forms profoundly altered the planet up to the current expansion of the human species throughout the planet.

After proposing that the extinction of the K/T could be due to a bolide impact, the search of its impact crater began. Its discovery in Yucatan led scientists to direct their attention to Mexico in search of evidence. But what they found questioned that the impact would coincide in time with the K/T or caused any extinction.

In four of the five major mass extinctions, major volcanic episodes have taken place, including the K/T mass extinction. Thus, as it was becoming evident that the Chicxulub impact did not cause the demise of the dinosaurs, some scientists have investigated the massive Deccan volcanism in India as a possible cause of the K/T mass extinction.

Currently, there is a large database that suggests that the last great biological extinction could have been caused by our planet�s own geological dynamics.

URLhttps://dialnet.unirioja.es/servlet/articulo?codigo=4043251

Platinum Group Element (PGE) Geochemistry of Brazos Sections, Texas, U.S.A.

TitlePlatinum Group Element (PGE) Geochemistry of Brazos Sections, Texas, U.S.A.
Publication TypeBook Chapter
Year of Publication2011
AuthorsGertsch, B, Keller, G, Adatte, T, Bartels, D
Book TitleThe End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSEPM, Special Publication
Pagination227-249
PublisherSEPM (Society for Sedimentary Geology)
CityTulsa
ISBN978-1-56576-308-1
KeywordsBrazos River, Iridium, K-T boundary, PGE, Texas
Abstract

Geochemical and sedimentological analyses of Platinum Group Element (PGE) patterns across the Cretaceous/Tertiary (K-T) transition of 8 sections along the Brazos River, Texas, reveal possible sources and processes responsible for PGE enrichments. Of the five global KT boundary-defining characteristics (mass extinction in planktic foraminifera, first appearance of Danian species, negative δ13C excursion, Ir anomaly, thin (0.5 cm) red clay layer), the Ir anomaly and red clay layer are not present at the KTB in the Brazos sections. Instead, PGEs and especially Ir show several minor enrichments within the sandstone complex with the largest peak at the top or just above it. Possible mechanisms of PGE enrichments include, low sedimentation rates or sediment starvation that concentrates Ir and other PGEs. Absence of Ir at the KTB is likely linked to dilution effects caused by high sedimentation rates, and other still unknown processes. The source of PGEs remains elusive, but may be linked to an increased input of extraterrestrial dust during the late Maastrichtian, or reworked PGEs from the Chicxulub impact that predates the KTB in these sections.  PDF

Trace-Element Geochemistry of Brazos Sections, Texas, U.S.A.

TitleTrace-Element Geochemistry of Brazos Sections, Texas, U.S.A.
Publication TypeBook Chapter
Year of Publication2011
AuthorsGertsch, B, Keller, G, Adatte, T, Bartels, D
Book TitleThe End-Cretaceous Mass Extinction and the Chicxulub Impact in Texas
VolumeNo. 100
EditionSEPM, Special Publication
Pagination251-279
PublisherSEPM (Society for Sedimentary Geology)
CityTulsa
ISBN978-1-56576-308-1
KeywordsBrazos, K-T boundary, Texas, Trace Elements
Abstract

A geochemical study of major (MEs) and trace (TEs) elements across the Cretaceous-Tertiary (KT) transition was carried out on 2 sections of the Brazos area to investigate signals of the Chicxulub impact, as well as redox conditions and weathering processes in these shallow-water environments. Results show that ME and TE patterns are primarily affected by the type of lithology, including claystones, mudstones, a 3 cm thick yellow clay layer, a sandstone complex with 2-3 spherule-rich layers and alternating hummocky cross-bedded and laminated sandstone layers. In the yellow clay layer, TEs (Mn, Ni, Cr, Na) concentrations are comparable to the spherules-rich layers and geochemistry of spherules. Relative abundance of MEs (Al, Ca, Fe, Mg) in both spherule-rich layers and the yellow clay layer shows also a good correlation. This indicates that the yellow clay layer is likely an alteration product of a spherule-rich layer. No other evidence of the Chicxulub impact could be determined based on MEs and TEs values. In the claystone/mudstone intervals, TE concentrations are constant and slightly enriched in redox-sensitive TE (Mo, U, V), which indicates that dysoxic conditions prevailed. Occurrence of rare large pyrite framboids (30-50 μm) below the sandstone complex confirms that redox conditions were dysoxic in the shallow-water Brazos environments. High values for Al and weathering indices show high detrital input dominated by chemical weathering. These results reveal that persistent high stress conditions and high continental runoff prevailed through the late Maastrichtian-early Danian transition. No significant geochemical and environmental change due to the Chicxulub impact is detected. Sudden increases in trace elements (Co, Cr, Ni) possibly related to an impact, are observed only in reworked intervals within the sandstone complex.  PDF

KT Mass Extinction: theories and controversies

TitleKT Mass Extinction: theories and controversies
Publication TypeWeb Article
Year of Publication2010
AuthorsKeller, G
Access DateMay 2010
PublisherGeoscientist Online
CityLondon
Abstract

Most mass extinctions that have afflicted life on Earth during the past 500 million years have occurred during times of major volcanic eruption and all were accompanied by major changes in climate, sea level and oxygenation levels in the ocean.  Among the five major mass extinctions, only the end-Cretaceous (KT) displays a close coincidence of four factors - an iridium anomaly (commonly assumed to represent an impact), an impact crater (Chicxulub), a large igneous province (the Deccan Traps) and major climate and sea level changes (Fig. 2). The KT mass extinction also differs in that it follows the longest period (145-65.5Ma) of low background extinction (Fig. 2). Throughout the Cretaceous, generic diversity had increased, accelerating during the Campanian and peaking during the late Maastrichtian, prior to the mass extinction.  PDF

URLhttp://www.geolsoc.org.uk/keller

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