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
EditionGSA Special Papers
PaginationPp. 29-55
PublisherGeological Society of America

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


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
Pagination885 - 907
Date Published01/2013
KeywordsChicxulub, impact spherules, KTB unconformity, North Atlantic

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

Short TitleGeol. Mag.

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
Pagination249 - 262
Date Published01/2013

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

Short TitleJournal of the Geological Society

KT Mass Extinction: theories and controversies - extended version

TitleKT Mass Extinction: theories and controversies - extended version
Publication TypeWeb Article
Year of Publication2010
AuthorsKeller, G
Access Year2010
Access DateMay 5
PublisherGeoscientist Online

The Cretaceous-Tertiary (KT) mass extinction is primarily known for the demise of the dinosaurs, the Chicxulub impact and the frequently rancorous 30 year-old controversy over the cause of this mass extinction. Since 1980 the impact hypothesis 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 multidisciplinary 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.

Most mass extinctions over the past 500Ma occurred during times of major volcanic eruptions, some occurred at times of multiple impacts (Fig. 1) and all were accompanied by major changes in climate, sea level and oxygenation levels of the water column. This first order test favours some direct or indirect causal relationship between mass extinctions, volcanism, large impacts, climate and sea-level changes. But among the five major mass extinctions, only the Cretaceous-Tertiary (KT) boundary mass extinction can be shown to have a close correspondence between an iridium anomaly commonly assumed to represent an impact, an impact crater (Chicxulub), a large igneous province (Deccan Traps) and major climate and sea level changes.  PDF


New evidence concerning the age and biotic effects of the Chicxulub impact in NE Mexico

TitleNew evidence concerning the age and biotic effects of the Chicxulub impact in NE Mexico
Publication TypeJournal Article
Year of Publication2009
AuthorsKeller, G, Adatte, T, Juez, AP, Lopez-Oliva, JG
JournalJournal of the Geological Society
Pagination393 - 411
Date PublishedJan-05-2009
KeywordsBiotic effects, Chicxulub impact, K-T Mass Extinction, Mexico

In the 1990s the Chicxulub impact was linked to the K–T boundary by impact spherules at the base of a sandstone complex that was interpreted as an impact-generated tsunami deposit. Since that time a preponderance of evidence has failed to support this interpretation, revealing long-term deposition of the sandstone complex, the K–T boundary above it and the primary impact spherule ejecta interbedded in Late Maastrichtian marls below. Based on evidence from Mexico and Texas we suggested that the Chicxulub impact predates the K–T boundary. Impact-tsunami proponents have challenged this evidence largely on the basis that the stratigraphically lower spherule layer in Mexico represents slumps and widespread tectonic disturbance, although no such evidence has been presented. The decades-old controversy over the cause of the K–T mass extinction will never achieve consensus, but careful documentation of results that are reproducible and verifiable will uncover what really happened at the end of the Crectaceous. This study takes an important step in that direction by showing (1) that the stratigraphically older spherule layer from El Peñon, NE Mexico, represents the primary Chicxulub impact spherule ejecta in tectonically undisturbed sediments and (2) that this impact caused no species extinctions.  PDF

Short TitleJournal of the Geological Society

The Chicxulub Impact and K-T Mass Extinction in Texas

TitleThe Chicxulub Impact and K-T Mass Extinction in Texas
Publication TypeReport
Year of Publication2007
AuthorsKeller, G
Series TitleBulletin of the South Texas Geol. Soc.
Document NumberXLVII (9)
Date Published05/2007
InstitutionSouth Texas Geol. Soc.
CitySan Antonio

The K-T sequences along the Brazos River of Falls County, Texas, provide the most important and critical information regarding the age and biotic effects of the Chicxulub impact outside of Mexico. New investigations based on outcrops and new cores drilled by DOSECC and funded by the National Science Foundation reveal a complex history of three tectonically undisturbed and stratigraphically well-separated events: the Chicxulub impact spherule ejecta layer, a sea-level lowstand sandstone complex, and the K-T mass extinction. The newly discovered Chicxulub impact spherule layer is the oldest of the three events and marks the time of the impact about 300,000 years before the K-T boundary (base of zone CF1), consistent with similar observations from NE Mexico and the Chicxulub crater core Yaxcopoil-l. The sea level lowstand sandstone complex predates the K-T boundary by about 100,000 years and contains clasts with Chicxulub impact spherules eroded from the original impact spherule layer. The third event is the K-T boundary mass extinction, which is not linked to the Chicxulub impact. These results indicate that a combination of impacts (Chicxulub and K-T), volcanism and climate changes caused increasingly stressful environmental conditions that culminated in the end-Cretaceous mass extinction.  PDF

Chicxulub impact predates K–T boundary: New evidence from Brazos, Texas

TitleChicxulub impact predates K–T boundary: New evidence from Brazos, Texas
Publication TypeJournal Article
Year of Publication2007
AuthorsKeller, G, Adatte, T, BERNER, ZSOLT, Harting, M, Baum, G, Prauss, M, Tantawy, A, Stüben, D
JournalEarth and Planetary Science Letters
Pagination339 - 356
Date PublishedJan-03-2007

Multidisciplinary studies, including stratigraphy, sedimentology, mineralogy and geochemistry, of the new core Mullinax-1 and outcrops along the Brazos River and Cottonmouth Creek, Falls County, Texas, reveal the complex history of the Chicxulub impact, the event deposit and the K–T boundary event. The K–T boundary, as identified by the negative δ13C shift, first occurrence of Danian planktic foraminifera and palynomorphs occurs 80 cm above the event deposit in core Mullinax-1. The underlying 80 cm interval was deposited in a shallow low oxygen environment during the latest Maastrichtian, as indicated by high stress microfossil assemblages, small shells and burrows infilled with framboidal pyrite. The underlying event deposit, commonly interpreted as K–T impact tsunami, consists of a basal conglomerate with clasts containing Chicxulub impact spherules, repeated upward fining units of spherule-rich sands, followed by hummocky cross-bedded and laminated sands, which are burrowed by Thalassinoides, Planolites and Ophiomorpha and truncated by erosion. This suggests a series of temporally separated storm events with recolonization of the ocean floor by invertebrates between storms, rather than a series of waning tsunami-generated waves. The lithified clasts with impact spherules at the base of the event deposit provide strong evidence that the Chicxulub impact ejecta layer predates the event deposit, but was eroded and re-deposited during the latest Maastrichtian sea level lowstand. The original Chicxulub ejecta layer was discovered in a 3 cm thick yellow clay layer interbedded in undisturbed late Maastrichtian clay- and mudstones 40 cm below the base of the event deposit and near the base of planktic foraminiferal zone CF1, which spans the last 300 kyr of the Maastrichtian. The yellow clay consists of cheto smectite derived from alteration of impact glass, as indicated by rare altered glass spherules with similar chemical compositions as reworked spherules from the event deposit and Chicxulub impact spherules from NE Mexico and Haiti. The Brazos sections thus provide strong evidence that the Chicxulub impact predates the K–T boundary by about 300 kyr, consistent with earlier observations in NE Mexico and the Chicxulub crater core Yaxcopoil-1.  PDF

Short TitleEarth and Planetary Science Letters

Multiple impacts across the Cretaceous–Tertiary boundary

TitleMultiple impacts across the Cretaceous–Tertiary boundary
Publication TypeJournal Article
Year of Publication2003
AuthorsKeller, G, Stinnesbeck, W, Adatte, T, üben, D
JournalEarth-Science Reviews
Pagination327 - 363
Date PublishedJan-09-2003
KeywordsMultiple impacts; Maastrichtian–Danian; Microtektites; Microkrystites; Ir; PGE anomalies

The stratigraphy and age of altered impact glass (microtektites, microkrystites) ejecta layers from the Chicxulub crater are documented in Late Maastrichtian and Early Danian sediments in Mexico, Guatemala, Belize and Haiti. In northeastern Mexico, two to four ejecta layers are present in zone CF1, which spans the last 300 ky of the Maastrichtian. The oldest ejecta layer is dated at 65.27F0.03 Ma based on sediment accumulation rates and extrapolated magnetostratigraphy. All younger ejecta layers from the Maastrichtian and Early Danian Parvularugoglobigerina eugubina zone Pla(l) may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity. The K/T boundary impact event (65.0 Ma) is not well represented in this area due to widespread erosion. An Early Danian Pla(l) Ir anomaly is present in five localities (Bochil, Actela, Coxquihui, Trinitaria and Haiti) and is tentatively identified as a third impact event at about 64.9 Ma. A multiimpact scenario is most consistent with the impact ejecta evidence. The first impact is associated with major Deccan volcanism and likely contributed to the rapid global warming of 3–4 °C in intermediate waters between 65.4 and 65.2 Ma, decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations. The K/T boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species. The Early Danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity. PDF

Short TitleEarth-Science Reviews

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

TitlePost-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
Date Published08/2018

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


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
Date Published01/2018

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