The GSSP for the base of the Eocene Series is located at 1. 58 m above the base of Section DBH in the Dababiya Quarry, on the east bank of the Nile River, about 35 km south of Luxor, Egypt. It is the base of Bed 1 of the Dababyia Quarry Beds of the El Mahmiya Member of the Esna Formation, interpreted as having recorded the basal inflection of the carbon isotope excursion (CIE), a prominent (3 to 5%) geochemical signature which is recorded in marine (deep and shallow) and terrestrial settings around the world. The Paleocene/Eocene boundary is thus truly a globally correlatable chronostratigraphic level. It may be correlated also on the basis of 1) the mass extinction of abyssal and bathyal benthic foraminifera (Stensioina beccariiformis microfauna), and reflected at shallower depths by a minor event; 2) the transient occurrence of the excursion taxa among the planktonic foraminifera (Acarinina africana, A. sibaiyaensis, Morozovella allisonensis); 3) the transient occurrence of the Rhomboaster spp. -Discoaster araneus (RD) assemblage; 4) an acme of the dinoflagellate Apectodinium complex. The GSSP-defined Paleocene/Eocene boundary is approximately 0.8 my older than the base of the standard Eocene Series as defined by the Ypresian Stage in epicontinental northwestern Europe.
Recent discoveries of microtektite and related crystal bearing microspherule layers in deep‐sea sediments of the west equatorial Pacific DSDP Sites 292, 315A and 462, off‐shore New Jersey in Site 612 and in southern Spain have confirmed the presence of at least three microspherule layers in Late Eocene sediments. Moreover, these discoveries have extended the North American strewn field from the Caribbean and Gulf of Mexico region to the northwest Atlantic, and have established a third strewn field in western equatorial Pacific and Indian Ocean which may extend to the Mediterranean. Stratigraphically the oldest microspherule layer occurs in the planktonic foraminifer Globigerapsis semiinvoluta Zone about 0.5 m.y. prior to the closely spaced crystal bearing microspherule layer and North American microtektite layer in the Globorotalia cerroazulensis Zone. Major element composition of the G. semiinvoluta Zone layer and the crystal bearing microspherule layer overlap, but there is a clear trend towards higher Al2O3 and FeO values in SiO2 equivalent microspherules of the latter layer. The G. semiinvoluta Zone microspherules also contain a higher percentage of non‐crystalline spherules (microtektites) than the crystal bearing microspherule layer, but lower than the North American microtektite layer. Excess iridium due to an abrupt increase in supply is associated with the middle crystal bearing microspherule layer and to a lesser extent with the other two layers. But, Ir excess due to concentration as a result of carbonate loss was also observed at two sites (462, 612). The three late Eocene microspherule layers do not precisely coincide with planktonic foraminiferal species extinctions, but a major faunal assemblage change is associated with the G. semiinvoluta Zone layer. Abundant pyrite is present in the North American microtektite layer of DSDP Site 612 suggesting reducing conditions possibly due to a sudden influx of biologic matter (dead bodies) to the ocean floor, and the crystal bearing microspherule layer coincides with five radiolarian extinctions. All three microspherule layers are associated with decreased carbonate possibly due to sudden productivity changes, increased dissolution as a result of sea‐level and climate fluctuations, or the impact events.
ABSTRACT. --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.R~SUM~. -L'extinction en masse des foraminif~res planctoniques h travers la limite Cr6tac6/Tertiaire h Agost (Espagne) s'est produite au cours d'une certaine p6riode; 7 espbces disparaissant au Maastrichtien sup6rieur, 47 ~ la limite K/T et 16 au Danien inf6rieur. Les esp~ces ayant disparu h la limite K/T sont grandes et complexes, des formes vivant en milieux oc6aniques profonds tropicaux et subtropicaux, qui ne constituent qu'environ 20 % des individus de la population de taille sup6rieure h 63 microns. Cependant, leur disparition repr6sente l'6vbnement d'extinction le plus important et soudain de l'histoire des foraufinif~res planctoniques. Toutefois, les petites formes cosmopolites ayant une morphologie simple et vivant dans les eaux superficielles semblent avoir surv6cu et la phipart ont disparu progressivement darts la partie inf6rieure de la Biozone ~ P. pseudobuUoides. Ce module d'extinction des foraminif~res planctoniques peut ~tre consid6r6 comme une extinction en masse catastrophique eoncentr6e h la limite K/T et superpos6e h une extinction en masse graduelle qui avait commenc6 au Maastrichtien sup6rieur et continua jusqu'au Danien inf6rieur. Le module d'extinction catastrophique h la limite K/T est bien compatible avec les effets de l'in~pact d'un grand m6t6orite, tandis que le patron d'extinction graduelle au cours de la transition Maastrichtien-Danien l'est avec les changements de temp6rature et du nivean de lamer qui pourraient ~tre en rapport avec un volcanisme massif.
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