Ignacio Arenillas

The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary

The Fall of the Dinosaurs According to the fossil record, the rule of dinosaurs came to an abrupt end ∼65 million years ago, when all nonavian dinosaurs and flying reptiles disappeared. Several possible mechanisms have been suggested for this mass extinction, including a large asteroid impact and major flood volcanism. Schulte et al. (p. 1214) review how the occurrence and global distribution of a global iridium-rich deposit and impact ejecta support the hypothesis that a single asteroid impact at Chicxulub, Mexico, triggered the extinction event. Such an impact would have instantly caused devastating shock waves, a large heat pulse, and tsunamis around the globe. Moreover, the release of high quantities of dust, debris, and gases would have resulted in a prolonged cooling of Earths surface, low light levels, and ocean acidification that would have decimated primary producers including phytoplankton and algae, as well as those species reliant upon them. The Cretaceous-Paleogene boundary ~65.5 million years ago marks one of the three largest mass extinctions in the past 500 million years. The extinction event coincided with a large asteroid impact at Chicxulub, Mexico, and occurred within the time of Deccan flood basalt volcanism in India. Here, we synthesize records of the global stratigraphy across this boundary to assess the proposed causes of the mass extinction. Notably, a single ejecta-rich deposit compositionally linked to the Chicxulub impact is globally distributed at the Cretaceous-Paleogene boundary. The temporal match between the ejecta layer and the onset of the extinctions and the agreement of ecological patterns in the fossil record with modeled environmental perturbations (for example, darkness and cooling) lead us to conclude that the Chicxulub impact triggered the mass extinction.

The Cretaceous/Tertiary boundary mass extinction in planktic foraminifera at Agost, (Spain)

The planktic foraminiferal mass extinction across the Cretaceous/Tertiary boundary at Agost (Spain) occurred over an extended period, with 7 species disappearing in the late Maastrichtian, 47 species extinct at the K/T boundary and 16 ranging into the earliest Danian. The species that became extinct at the K/T boundary are large, complex tropical and subtropical forms dwelling in deep and intermediate water depths, which constitute only about 20 % of the individuals in the population larger than 63 microns. Nevertheless, their disappearance constitutes the major and sudden extinction event in the history of planktic foraminifera. However, the small cosmopolitan surface dwellers with simple morphologies appear to survive and the last of them gradually disappear in the lower part of the P. pseudobulloides Biozone. This planktic foraminiferal extinction model can be interpreted as a catastrophic mass extinction that centred at the K/T boundary, and was superimposed on a gradual mass extinction which began in the late Maastrichtian and continued into the early Danian. The catastrophic pattern of extinction at the K/T boundary is very compatible with the effect of a large meteorite impact, whereas the gradual and extended pattern of extinction across the Maastrichtian-Danian transition is compatible with temperature and sea level changes that may be related to massive volcanism.

A new high-resolution planktic foraminiferal zonation and subzonation for the lower Danian

A new planktic foraminiferal zonation has been established for the lower Danian, based on some of most expanded and continuous pelagic sections known to date (from Spain, Tunisia and Mexico). This biozonation is considered valid for low and middle latitudes. The maximum stratigraphical distribution of the index-species approximately coincides in all the studied sections. The index-species are abundant and easily recognizable. We propose the following biozones and subzones: Guembelitria cretacea Zone and the Hedbergella holmdelensis and Parvularugoglobigerina longiapertura subzones; the Parvularugoglobigerina eugubina Zone, which is subdivided into the Parvularugoglobigerina sabina and Eoglobigerina simplicissima subzones and the Parasubbotina pseudobulloides Zone with the Eoglobigerina trivialis and Subbotina triloculinoides subzones. A biomagnetostratigraphic correlation and calibration of the stratigraphical ranges of these species suggest that the biohorizons used to define the new biozonation are very isochronous, at least in the geographical areas analysed.

Slumping and a sandbar deposit at the Cretaceous-Tertiary boundary in the El Tecolote section (northeastern Mexico): An impact-induced sediment gravity flow

Slumps affecting uppermost Mendez Formation marls, as well as the spherulitic layer and basal part of the sandy deposits of the Cretaceous-Tertiary (K-T) boundary clastic unit, are described at the new K-T El Tecolote section (northeastern Mexico). These K-T clastic deposits represent sedimentation at middle-bathyal water depths in channel and nonchannel or levee areas of reworked materials coming from environments ranging from outer shelf to shallower slope via a unidirectional, high- to low-density turbidite flow. We emphasize the development and accretion of a lateral bar in a channel area from a surging low-density turbidity current and under a high-flow regime. The slumps discovered on land and the sedimentary processes of the K-T clastic unit reflect destabilization and collapse of the continental margin, support the mechanism of gravity flows in the deep sea, and represent important and extensive evidence for the impact effects in the Gulf of Mexico triggered by the Chicxulub event.

What happens when the ocean is overheated? The foraminiferal response across the Paleocene–Eocene Thermal Maximum at the Alamedilla section (Spain)

The global warming and major perturbation of the global carbon cycle that occurred during the Paleocene–Eocene Thermal Maximum (PETM) have been investigated in the lower bathyal–upper abyssal Alamedilla section (Spain). Geochemical anomalies and dramatic faunal changes (including the globally recognized extinction event of deep-sea benthic foraminifera and the rapid evolutionary turnover of planktic foraminifera and calcareous nannofossils) are associated with the PETM at Alamedilla. Biotic changes in the plankton and benthos indicate environmental instability ∼11–14 k.y. before the onset of carbon isotope excursion that marks the Paleocene/Eocene boundary. The reorganization of the planktic ecosystem points to warm and oligotrophic conditions in surface waters during the earliest Eocene, whereas faunal and geochemical data indicate that the extinctions of benthic foraminifera occurred over an interval with a high CaCO3 content and oxic conditions at the seafloor. The proliferation of disaster taxa ( Glomospira spp.) after the extinctions has been related to a potential source of isotopically light carbon in the western Tethys and North Atlantic. Significant changes in foraminiferal test size are documented across the PETM. We suggest that increased temperatures played an important role in benthic foraminiferal test size, increasing their metabolic rates and, consequently, their food requirements. Decreased planktic foraminiferal test size may be related to decreased nutrient availability or surface-water density. However, the differences in test size evolution among different species of both benthic and planktic foraminifera may be related to interspecific competition and ecological adaptations to direct or indirect consequences of the carbon addition during the PETM.

Cretaceous-Paleogene boundary deposits at Loma Capiro, central Cuba: Evidence for the Chicxulub impact

A newly discovered Upper Cretaceous to lower Paleogene section at Loma Capiro (central Cuba) has provided new evidence for a Cretaceous-Paleogene boundary age for the Chicxulub impact. The studied sediments at Loma Capiro consist of a foraminifera-rich marl and sandstone hemipelagic sequence, and a 9.6-m-thick intercalated clastic complex. Planktic foraminifera indicate an upper Maastrichtian age for the sediments below the clastic complex and a lowermost Danian age for those just above this complex. Small benthic foraminifera from below and above the clastic complex indicate deposition at middle to lower bathyal depths. The fining-upward clastic complex consists of a basal breccia that is overlain by microconglomerates and coarse- to fine-grained sandstones. The clastic complex contains reworked foraminifera from different ages and different paleoenvironments and, toward the top, impact material such as altered microtektites, shocked quartz, terrestrial chondrules, and accretionary lapilli. These microfacies suggest deposition from gravity flows that eroded sediments from upper-slope and shelf settings and redeposited them in deeper bathyal environments. We suggest that the origin of the clastic complex may be linked to the collapse of the Cuban platform, triggered by the Cretaceous-Paleogene impact at Chicxulub.

La estabilidad evolutiva de los foraminíferos planctónicos en el Maastrichtiense Superior y su extinción en el límite Cretácico/Terciario de Caravaca, España

El estudio bioestratigrafico y cuantitativo con foraminiferos planctonicos del transito Cretacico/Terciario (K/T) del corte de Caravaca permite comprobar la continuidad estratigrafica y la estabilidad evolutiva de las especies en la parte superior del Maastrichtiense. En Caravaca, el patron de extincion de foraminiferos planctonicos es en masa catastrofico, en el que el 74% de las especies se extinguen en coincidencia con el limite K/T y las evidencias de impacto meteoritico. Este patron es similar al identificado en otros cortes del Tetis y, por esta razon, se considera que las supuestas extinciones en el Maastrichtiense Superior identificadas por otros autores en Caravaca pueden ser causadas por el efecto Signor-Lipps. En este trabajo se han considerado 17 especies cretacicas como posibles supervivientes al evento del limite K/T, cuya abundancia relativa desciende bruscamente desde el limite K/T (curva ARECS). Este descenso puede ser una consecuencia del declive progresivo en abundancia de las especies cretacicas que sobrevivieron, debido a la competencia biologica con las nuevas especies terciarias, o simplemente el descenso de la proporcion relativa de ejemplares cretacicos retrabajados. No obstante, independientemente de que algunas especies sobrevivieran al evento del limite K/T, la existencia de un patron gradual de extincion en la parte inferior del Daniense no refuta la hipotesis de un evento catastrofico en coincidencia con el limite K/T. La extincion en masa catastrofica de mas del 70% de las especies de foraminiferos planctonicos en coincidencia con este limite es muy compatible con la hipotesis del impacto de un asteroide y sus efectos a corto, medio y largo plazo

El límite Cretácico/Paleógeno del corte de Agost revisado: reconstrucción paleoambiental y patrón de extinción en masa

El evento del limite Cretacico/Paleogeno (K/Pg) ha sido intensamente estudiado en el corte espanol de Agost, que contiene uno de los transitos Cretacico-Paleogeno mas continuos y expandidos en el area del Tetis. Por este motivo, se considera como una seccion clasica del limite K/Pg, y ha sido detalladamente analizada por numerosos especialistas desde el punto de vista micropaleontologico, paleoicnologico, magnetoestratigrafico, mineralogico y geoquimico. Los sedimentos del Cretacico Superior (Biozonas de Abathomphalus mayaroensis y de Plummerita hantkeninoides) y del Paleogeno inferior (Biozonas de Guembelitria cretacea, de Parvularugoglobigerina eugubina y de Parasubbotina pseudobulloides) corresponden a una secuencia principalmente margosa rica en microfosiles, depositada en la parte superior y media del talud, tal y como indican las asociaciones de foraminiferos bentonicos. En el Daniense basal se identifica una capa arcillosa oscura que contiene evidencias de impacto. Los foraminiferos planctonicos muestran un patron de extincion en masa catastrofico en coincidencia con el limite K/Pg, situado en la base de esta capa arcillosa. El 70% de las especies se extinguieron claramente en coincidencia con en el limite K/Pg. Muy pocas especies parecen extinguirse en el Maastrichtiense final y podrian interpretarse como parte del patron de extincion de fondo o el remanente efecto Signor-Lipps. Algunas especies cretacicas parecen sobrevivir el evento y desaparecer gradualmente en el Daniense, tal vez como resultado de los efectos a mas largo plazo del impacto meteoritico. Sin embargo, su presencia en el Daniense tambien podria ser interpretada como resultado de la reelaboracion. Teniendo en cuenta estas consideraciones, el porcentaje de especies de foraminiferos planctonicos que se extinguieron en el evento del limite K/Pg alcanzaria el 90%. A pesar de que los foraminiferos bentonicos, al contrario que los foraminiferos planctonicos, no sufrieron una extincion en masa, la drastica reorganizacion de sus asociaciones en coincidencia con el limite refleja importantes cambios paleoambientales, compatibles con los efectos catastroficos causados por el impacto de un asteroide justo en el limite Cretacico/Paleogeno.

Correlation between the Paleocene-Eocene boundary and the Ilerdian at Campo, Spain

Abstract The Ilerdian is a well-established Tethyan marine stage, which corresponds to an important phase in the evolution of larger foraminifera not represented in the type-area of the classical Northwest-European stages. This biostratigraphic restudy of its parastratotype in the Campo Section (northeastern Spain) based on planktic foraminifera, calcareous nannofossils, dinoflagellate cysts and the distribution of the stable isotopes ∂13C and ∂18O is an attempt to correlate the Paleocene/Eocene boundary based on a characteristic carbon isotope excursion (CIE) marking the onset of the Initial Eocene Thermal Maximum (IETM) and the Ilerdian stage. The base of this ∂13C excursion has been chosen as the criterion for the recent proposal of the Global Stratotype Section and Point (GSSP) of the base of the Eocene (= base of the Ypresian) in the Dababiya Section (Egypt) to which an age of 54.9 Ma has been attributed. This level is also characterized by a marked extinction among the deep-water benthic foraminifera (Benthic Foraminifera Extinction Event, BFEE), a flood of representatives of the planktic foraminiferal genus Acarinina and the acme of dinoflagellate cysts of the genus Apectodinium. In the Campo Section, detailed biozonations (planktic foraminifera, calcareous nannofossils, dinoflagellate cysts) are recognized in the Lower and Middle Ilerdian. The correlation with the Ypresian stratotype is based on dinoflagellate cysts and calcareous nannofossils. The base of the Ilerdian is poor in planktic microfossils and its precise correlation with the redefined Paleocene/Eocene boundary remains uncertain.

Cretaceous-Tertiary boundary planktic foraminiferal mass extinction and biochronology at La Ceiba and Bochil, Mexico, and El Kef, Tunisia

Micropaleontology studies across the Cretaceous-Tertiary (K-T) boundary from sections at La Ceiba, Bochil, Mexico, and El Kef, Tunisia, suggest a close cause and effect relationship between the Chicxulub impact and the K-T planktic foraminiferal mass extinction. The K-T planktic foraminiferal biostratigraphy and assemblage turnover in Mexico was examined and the approximate deposition timing of K-T-related material (clastic unit) was estimated. On the basis of established biomagnetochronologic calibrations, the first appearance datum (FAD) of Parvularugoglobigerina longiapertura occurred 3.5–5 k.y. after the K-T boundary, and the FADs of Parvularugoglobigerina eugubina, Eoglobigerina simplicissima, and Parasubbotina pseudobulloides occurred 15–17.5 k.y., 28–31 k.y., and 45–55 k.y., respectively, after the K-T boundary. According to estimated average sedimentation rates and estimated age, the K-T red layer at El Kef was probably formed in 20 yr and the deposition of the K-T clastic unit in the Gulf of Mexico was geologically instantaneous. The last appearance of most Maastrichtian species is just below the K-T impact-generated bed, clearly implying a catastrophic planktic foraminiferal mass extinction.