Eustoquio Molina

Cretaceous/Tertiary boundary extinction pattern and faunal turnover at Agost and Caravaca, S.E. Spain

Abstract Planktonic foraminiferal extinctions at Caravaca and Agost occurred over an extended time period similar to El Kef and Brazos River. Some species disappeared well below the boundary. About 39–45% of the species, but less than 15% of the individuals in the population, became extinct at or near the K/T boundary. A second phase of extinction occurred at the top of the boundary clay (PO/Pla) and the remaining Cretaceous species (except G. cretacea ) disappeared in Subzone Pla. Species extinctions were selective eliminating geographically restricted large, complex and deeper dwelling forms first and favoring survival of cosmopolitan small, simple surface dwellers. Only surface dwellers survived the K/T boundary event, whereas all deeper dwelling species, as well as some surface dwellers, disappeared at the boundary. We interprete the selective abundance decline during the latest Cretaceous as a result of the seal level regression that reached a maximum just prior to the K/T boundary. The highly selective nature of the two-phased species extinctions at and above the boundary, we believe to be related to the major reduction in surface productivity and the breakdown in the water mass stratification that was associated with the rapid sea level transgression across the K/T boundary. A bolide impact however, may have hastened the demise of an already declining Cretaceous fauna.

High-resolution iridium, δ13C, δ18O, foraminifera and nannofossil profiles across the latest Paleocene benthic extinction event at Zumaya, Spain

In the expanded upper Paleocene-lower Eocene section (~ 30 m of Zone P5 sediments) at Zumaya, northern Spain, the highest occurrence of many late Paleocene deep-sea benthic foraminifera species (~40% extinction), coincides with a transition from marl to calcite-free clay. Our high-resolution studies (chemical elements, 613C, 6180, calcareous nannofossils, planktic and benthic foraminifera) show that below the marl-clay transition there is a 40-50 cm thick interval (corresponding to 10-20 kyr) containing a detailed record of a gradual succession of faunal and geochemical events culminating in the benthic extinctions. Planktic foraminiferal and nannofossil changes (e.g., the onset of demise in Fasciculithus genus) occur a few meters below the marl-clay transition. In the limestone 50 cm below the base of the clay, a prominent glauconite maximum indicates that sea-floor oxygenation suddenly decreased. Glauconite continues to be common until the onset of clay deposition. A whole-rock negative 613C shift (1.6%0), most likely reflecting an original sea-water trend, is gradually developed over the 40 cm of greenish brown marls immediately below the clay. At the base of these marls there is a small, significant iridium anomaly of 133 ppt Ir compared with an average background of 38 ppt. In the marls the demise of the Fasciculithus species accelerates, Gavelinella beccariiformis becomes extinct, and the abundance of Acarinina species begins to increase. The superjacent 4 m of clay is devoid of original calcite in its lower part and has a low calcareous content higher up. At calcareous levels in the clay an unusual planktic foraminifera fauna occurs, dominated by Acarinina species. When marl deposition returns, 613C gradually increases and then stabilizes at values about 0.5%o lower than before the isotopic excursion. The 613C excursion spans in total 5 m, probably corresponding to 200-400 kyr. The fasciculiths disappear shortly after the stabilization of 613C. Here we also present a whole-rock 6~3C profile through the entire Paleocene section at Zumaya. The profile is very similar to previous profiles registered in well preserved deep-sea material, suggesting that whole-rock 613C at Zumaya can be used for correlation.

Benthic foraminiferal turnover across the Cretaceous/Paleogene boundary at Agost (southeastern Spain): paleoenvironmental inferences

Abstract We studied Upper Cretaceous and Lower Paleogene benthic foraminifera from the Agost section (southeastern Spain) to infer paleobathymetrical changes and paleoenvironmental turnover across the Cretaceous/Paleogene (K/P) transition. Benthic foraminifera indicate uppermost bathyal depths at Agost during the Abathomphalus mayaroensis Biochron (from about 400 kyr before the K/P boundary) through the early Plummerita hantkeninoides Biochron (about 120–150 kyr before that boundary). The depth increased to middle bathyal for the remainder of the Cretaceous, and remained so for the Danian part of the studied section (Parasubbotina pseudobulloides Biochron, at least 200 kyr after the K/P boundary). There were no perceivable bathymetrical changes at the K/P boundary, where ∼5% of the species became extinct, and the species composition of the benthic foraminiferal fauna changed considerably. Below the boundary, infaunal morphogroups constitute up to 65–73% of the faunas. Directly above the boundary, in the black clays of the lower Guembelitria cretacea Biozone, benthic foraminifera are rare. Several opportunistic taxa (e.g. the agglutinant Haplophragmoides sp.) have short peaks in relative abundance, possibly reflecting low-oxygen conditions as well as environmental instability, with benthos receiving food from short-lived, local blooms of primary producers. Above the clays through the end of the studied interval, epifaunal morphogroups dominate (up to 70% of the assemblages) or there is an even mixture or epifaunal and infaunal morphogroups. Infaunal groups do not recover to pre-extinction relative abundances, indicating that the food supply to the benthos did not recover fully over the studied interval (about 200 kyr after the K/P boundary). The benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact, which severely destabilized primary producers and the oceanic food web that was dependent upon them.

Planktic foraminiferal turnover and δ13C isotopes across the Paleocene-Eocene transition at Caravaca and Zumaya, Spain

Abstract Biostratigraphic and faunal analysis of planktic foraminifera and benthic foraminiferal isotopes at Zumaya and Caravaca sections in Spain indicate that Zumaya has a continuous record with high sediment accumulation rates across the Paleocene-Eocene transition whereas Caravaca has a hiatus with the uppermost Zone P4, Zone P5 and the lower part of Zone P6 missing. Both sections contain nearly continuous and expanded records of the global δ13C excursion at Zumaya and Caravaca respectively. The δ13C excursion is associated with dark grey shale deposition in a dysaerobic benthic environment. This δ13C event is associated with a major planktic foraminiferal turnover marked by the gradual extinction and evolution of 33% and 18% of the species respectively. A rapid change in the relative abundances of these taxa occurs at the δ13C excursion coincident with the extinction of 50% of the small benthic foraminiferal taxa. The entire water column was affected by this faunal turnover (surface, intermediate, deep dwellers), but in contrast to benthic foraminifera there was no net loss of habitats since species extinctions of planktic foraminifera were largely replaced by originations.

Benthic foraminifera at the Cretaceous-Tertiary boundary around the Gulf of Mexico

Cretaceous-Tertiary (K-T) boundary sections in northeastern Mexico contain marly formations separated by a controversial clastic unit. Benthic foraminifera in seven sections indicate middle and lower bathyal depths of deposition for the marls, with the exception of the upper bathyal northernmost section. Mixed neritic-bathyal faunas were present in the clastic unit, indicating redeposition in the deep basin by mass-wasting processes resulting from the K-T bolide impact in the Gulf of Mexico. Benthic foraminifera in the Mexican sections, and at other deep-sea locations, were not subject to major extinction at the time of impact, but there were temporary changes in assemblage composition. Benthic faunas indicate welloxygenated bottom waters and mesotrophic conditions during the late Maastrichtian and increased food supply during the latest Maastrichtian. The food supply decreased drastically just after the K-T boundary, possibly because of the collapse of surface productivity. Cretaceous and early Paleogene benthic foraminifera, however, did not exhibit the benthic-pelagic coupling of present-day faunas, as documented by the lack of significant extinction at the K-T collapse of surface productivity. Much of the food supplied to the benthic faunas along this continental margin might have been refractory material transported from land or shallow coastal regions. The decrease in food supply at the K-T boundary might be associated with the processes of mass wasting, which removed surface, food-rich sediment. Benthic faunas show a staggered pattern of faunal recovery in the lowermost Paleogene, consistent with a staged recovery of the vertical organic flux but also with a gradual buildup of organic matter in the sediment.

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.

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.

Paleoenvironmental Recovery After the Cretaceous/ Paleogene Boundary Crisis: Evidence From the Marine Bidart Section (SW France)

Abstract The study of Upper Cretaceous and Lower Paleogene benthic foraminifera from the Bidart section (SW France) provides detailed data on the paleobathymetry as well as paleoenvironmental conditions across the Cretaceous/Paleogene (K/Pg) boundary. A quantitative analysis of benthic foraminiferal assemblages from the Upper Maastrichtian Abathomphalus mayaroensis Biozone and the Danian Guembelitria cretacea, Parvularugoglobigerina eugubina, and Parasubbotina pseudobulloides Biozones was performed. Benthic foraminifera indicate that the upper Maastrichtian and lower Danian sediments at Bidart were deposited in the upper–middle part of the slope. Benthic foraminiferal assemblages indicate mesotrophic conditions during the late Maastrichtian and a strong decrease in the food supply to the sea floor coincident with the K/Pg boundary. This change in the trophic regime was related to the collapse of the food web triggered by the mass extinction of calcareous primary producers. Benthic assemblages in the lower Danian are strongly dominated by few species, and suggest that primary productivity was dominated by blooms of non-calcareous primary producers, creating a stressful environment for the benthic fauna. The faunal turnover, together with the geochemical evidence, is compatible with an asteroid impact scenario. Benthic foraminiferal assemblages suggest that primary productivity had not completely recovered more than 200 kyr after the K/Pg boundary event.

Planktic foraminiferal turnover across the Paleocene-Eocene transition at DSDP Site 401, Bay of Biscay, North Atlantic

Abstract Planktic foraminifera across the Paleocene-Eocene transition at DSDP Site 401 indicate that the benthic foraminiferal mass extinction occurred within Subzone P 6a of Berggren and Miller (1988), or P5 of Berggren et al. (1995) and coincident with a sudden 2.0%. excursion in δ13C values. The benthic foraminiferal extinction event (BFEE) and δ13C excursion was accompanied by a planktic foraminiferal turnover marked by an influx of warm water species (Morozovella and Acarinina), a decrease in cooler water species (Subbotina), a sudden short-term increase in low oxygen tolerant taxa (Chiloguembelina), and no significant species extinctions. These faunal changes suggest climatic warming, expansion of the oxygen minimum zone, and a well stratified ocean water column. Oxygen isotope data of the surface dweller M. subbotina suggest climate warming beginning with a gradual 0.5%. decrease in δ18O in the 175 cm preceding the benthic foraminiferal extinction event followed by a sudden decrease of 1%. (4 °C) at the BFEE. The δ13C excursion occurred over 27 cm of sediment and, assuming constant sediment accumulation rates, represents a maximum of 23 ka. Recovery to pre-excursion gd13C values occurs within 172 cm, or about 144 ka. Climate cooling begins in Subzone P 6c as indicated by an increase in cooler water subbotinids and acarininids with rounded chambers and a decrease in warm water morozovellids.