Robert Speijer

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.

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.

Turnover of larger foraminifera during the Paleocene-Eocene Thermal Maximum and paleoclimatic control on the evolution of platform ecosystems

The larger-foraminifera turnover (LFT) during the Paleocene-Eocene transition constitutes an important step in Paleogene larger-foraminifera evolution, involving a rapid increase in species diversity, shell size, and adult dimorphism. A platform-to-basin transect in Egypt provides new data on timing and causal mechanisms through correlation with planktic biozonations and through integration with regional paleoenvironmental data. The LFT coincides with the boundary between shallow benthic biozones SBZ4 and SBZ5 and closely correlates with the Paleocene-Eocene Thermal Maximum (PETM). Enhanced oligotrophy from the late Paleocene onward favored the diversification of K-strategist larger foraminifera. We suggest that a short-term eutrophication during the PETM led to a temporary decline of extreme K-strategist larger-foraminifera species, providing opportunities for new taxa with different ecological strategies to develop. During post-PETM oligotrophic conditions, these new taxa were able to evolve rapidly and soon dominated early Eocene larger-foraminifera assemblages, whereas many Paleocene taxa gradually disappeared. The success of larger foraminifera during the early Paleogene appears climatically controlled. Because of the vulnerability of corals to high surface-water temperatures, the late Paleocene to early Eocene global warming may have favored larger foraminifera at the expense of corals as the main carbonate-producing component on carbonate platforms at lower latitudes.

Ostracode turnover and sea-level changes associated with the Paleocene-Eocene thermal maximum

The ostracode response to oceanographic changes during the Paleocene-Eocene thermal maximum (PETM, ca. 55 Ma) is largely unknown. The Gebel Duwi section (Egypt) provides a detailed ostracode record across the PETM in a middle neritic setting. Quantitative analysis of this record reveals two significant results. (1) The PETM is marked by a sharp faunal turnover, as indicated by abundance changes, local extinctions, and immigrations. This turnover punctuated a gradual basin-wide faunal transition. (2) During the ∼60 k.y. period prior to the PETM, relative sea level fell rapidly by ∼15 m. This sea-level fall was followed by an ∼20 m sea-level rise during the PETM. A possible eustatic control on these fluctuations suggests the presence of a cryosphere and variations in its size during this time of global warmth.

Latest Paleocene benthic extinction event on the southern Tethyan shelf (Egypt): Foraminiferal stable isotopic (δ13C, δ18O) records

The dramatic global extinction of 35%–50% of benthic foraminifera species in the deep sea in the latest Paleocene and associated negative excursions in δ 13 C and δ 18 O may be related to spreading of warm, saline bottom water from subtropical Tethyan shallow regions over the sea floor worldwide. Our study of neritic sections in Egypt shows that in the southern shallow Tethys, a prominent long-term change in bottom-water chemistry, sedimentation, and benthic foraminifera fauna was initiated at the time when the deep-sea benthic extinction event (BEE) took place. Bottom-water δ 13 C values on the Tethyan shelf show a sudden 3.0‰ negative shift at this event; however, contrary to the deep sea, in which the δ 13 C excursion was of short duration, Tethyan δ 13 C values did not fully return to preboundary values, but remained depressed by ∼1.5‰ for at least 1 m.y. The δ 13 C values at the Egyptian shelf during the BEE are much lower than would be expected if this was a source region for global deep water. The δ 18 O values indicate no significant change in bottom-water salinity or temperature at the BEE. The long-lasting environmental changes that began on the Egyptian shelf at the BEE may be related to, for example, gateway reorganization along the Tethyan seaway. Paleogeographic changes possibly also triggered a change in the loci of global deep-water formation; however, these loci must be sought in another part of the Tethys.

Stratigraphy of late Palaeocene events in the Middle East: implications for low‐ to middle‐latitude successions and correlations

We have investigated the upper Palaeocene stratigraphical record in four sections in Egypt and one in Israel. The sections are arranged on a depth transect across the southern Tethyan margin. In all sections, a δ13C excursion and benthic foraminiferal extinctions coincide at a level within planktic foraminiferal Zone P5. In three sections, a bed (sapropelic in two of the deeper profiles) contains extraordinarily transient benthic and planktic foraminifera assemblages. These planktic assemblages are dominated by Acarinina and contain rare to common Morozovella allisonensis and Globanomalina luxorensis, but unusually few other Morozovella. The extremely restricted stratigraphical range of M. allisonensis to the lower part of the δ13C excursion enables: (1) a three‐fold subdivision of Zone P5, (2) accurate correlation to the best sections spanning the δ13C excursion in the Atlantic and Pacific and (3) assessment of stratigraphical completeness over the δ13C excursion in other (sub)tropical successions. Discontinuities and especially dissolution intervals in many low‐ to middle‐latitude marine successions elsewhere, as in two Middle East sections, preclude an accurate correlation within the lower part of the δ13C excursion (= M. allisonensis Zone P5b). Three studied sections can provide the best coverage of the sequence of events over the onset and early part of the δ13C excursion in the Middle East, but as in most known sections, probably none constitutes a complete upper Palaeocene–lower Eocene record.

Recalibration of the Tethyan shallow-benthic zonation across the Paleocene-Eocene boundary: the Egyptian record

The Galala Mountains in Egypt provide an excellent platform-basin transect with deposits spanning the Paleocene/ Eocene (P/E) boundary. These interfingering deposits enable a recalibration between platform and open marine biostratigraphic schemes. We investigated 18 sections from a shallow-water carbonate platform margin, dominated by larger benthic foraminifera, to basinal marls with pelagic and deep marine biota. The Late Paleocene to Early Eocene development of larger foraminifera is well recorded in the Galala transect, in particular the Tethyan evolutionary event known as the larger foraminifera turnover (LFT). This turnover distinguishes Paleocene assemblages dominated by glomalveolinids, miscellanids and ranikothalids typical for shallow benthic Zone 4 (SBZ4) from those of SBZ5, dominated by alveolinids, nummulitids, and orbitolitids. Our data agree with previous studies that suggested that the larger foraminifera turnover (LFT) coincides with the Paleocene/ Eocene boundary, delineated by the carbon isotopic excursion (CIE) and that it correlates with the boundary between calcareous nannofossils subzones NP9a/b, the benthic extinction event in smaller benthic foraminifera and the boundary between planktic foraminifera Biozones P5/E1.

Biostratigraphy of the Danian/Selandian transition in the southern Tethys. Special reference to the Lowest Occurrence of planktic foraminifera Igorina albeari

The P3a/P3b subzonal boundary is delineated by the lowest occurrence of Igorina albeari. Using literature, identification of the first representatives of I. albeari appeared to be very confusing. In this study descriptions of I. albeari are compared and a consistent definition is proposed. Igorinid specimens with an incipient keel are considered to be I. albeari. Flattening of the last chambers and the fusion of muricae on the peripheral margin may indicate such a slight keel. This keel enables an unambiguous distinction between I. pusilla and the first form of I. albeari and is in keeping with the original descriptions without introducing an intermediate species. In the southern Tethys, the lowest occurrence of I. albeari occurs just prior to the pinkish-brown marl bed in Egypt and immediately overlies the glauconitic bed in Tunisia. Furthermore, the NTp7A/NTp7B subzonal boundary, delineated by the lowest occurrence of Chiasmolithus edentulus, is in close correlation with these marker beds. In Egypt C. edentulus appears 1 m below the entry of I. albeari, whereas in Tunisia they coappear. This implies significant erosion at the glauconitic bed in the studied parts of the Tunisian Trough and a more complete succession at the dark-brown marl bed in the Nile Valley. These marker beds can also be correlated to a level of minor lithologic change in the upper part of the Danian Limestone Formation in the Zumaia section through the lowest occurrence of Chiasmolithus edentulus. The distinct lithologic change in Zumaia, from the Danian Limestone to the Itzurun Formation, however, appears to be ~600 kyr younger than what we now call upper Danian event beds, in Tunisia and Egypt.

A multi-proxy record of the Latest Danian Event at Gebel Qreiya, Eastern Desert, Egypt

The Latest Danian Event (LDE) is a proposed early Palaeogene transient warming event similar to the Paleocene–Eocene Thermal Maximum, albeit of smaller magnitude. The LDE can be correlated with a carbon isotope excursion (‘CIE-DS1’) at Zumaia, Spain, and the ‘top Chron C27n event’ defined recently from ocean drilling sites in the Atlantic and Pacific, supporting a global extent. Yet, records of environmental change during the LDE (e.g. warming and sea-level fluctuations) are still rare. In this study, we focus on the micropalaeontology (calcareous nannofossils and benthic foraminifera), mineralogy and trace element geochemistry of the LDE in the Qreiya 3 section from the southern Tethyan margin in Egypt. In this section, the LDE is characterized by the occurrence of anomalous beds intercalated within upper Danian shales and marls. The event beds of the LDE are situated above an unconformity on top of a shallowing-upwards sequence deposited in a well-oxygenated outer neritic to upper bathyal marine palaeoenvironment. The lower LDE bed is barren of benthic foraminifera, but contains pyrite and fish remains, and is interpreted as an anoxic level formed during rapid relative sea-level rise. Incursion of a Neoeponides duwi (Nakkady, 1950) benthic assemblage in LDE bed II is interpreted as repopulation of the seafloor after anoxia. The sea-level cycle associated with the LDE is estimated at about 50 m maximum in the Qreiya 3 section. The environmental changes at Qreiya 3 are of supra-regional extent, since a similar sequence of events has been observed at other southern Tethyan locations. Supplementary material: A table of floral, faunal and geochemical data is available at: http://www.geolsoc.org.uk/SUP18497

Upper Paleocene biostratigraphy in the Mediterranean region: Zonal markers, diachronism, and preservational problems

The Paleocene‐Eocene transition is one of the most interesting and intensively investigated time intervals because of the significant changes in global climate and in oceanic circulation that occurred and due to unresolved controversies related to the search for a Global Stratotype Section and Point (GSSP) for the P/E boundary. In order to characterize and understand these changes, numerous sections have been studied in the former Tethys region, an area characterized by sedimentary sequences with fairly continuous sedimentation and rich microfossil contents. The integrated stratigraphy obtained has provided a high-resolution biostratigraphy and important data for paleoenvironmental reconstructions of this time interval. Many of the studied sections are located in Spain (Zumaya, Alamedilla, Caravaca, and Tra