GERTA KELLER PUBLICATIONS

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
Issue2
Start Page78
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

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)

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
ChapterPart III, Pp. 165
EditionSpecial Publication
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

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
ChapterPart I, Pp. 1
EditionSpecial Publication
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
ChapterPart III, Pp. 243
EditionSpecial Publication
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

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.

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
ChapterPart III, Pp. 183
EditionSpecial Publication
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

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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

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

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

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

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