Original paper

The benthonic foraminifera turnover at the Paleocene/Eocene Thermal Maximum Event (PETM) in the southwestern Nile Valley, Egypt

Aref, Mahmoud; Youssef, Mohamed

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 234 Heft 1-3 (2004), p. 261 - 289

82 references

published: Dec 22, 2004

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ArtNo. ESP155023400007, Price: 29.00 €

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Abstract

The end of the Paleocene (55 Ma) was marked by a sudden global climatic change, upsetting oceanic and atmospheric circulation and leading to the extinction of numerous deep-sea benthonic foraminifera. Biotic and geochemical anomalies observed world-wide relate to high latitudinal warming (subtropical conditions prevailed at Antarctica!) and a reversal in oceanic circulation. During a short period (< 100 k.y.), dense warm and salty water, formed in low latitude basins (e. g. tethyan margins), is thought to have filled the oceanic basins. this period is known as the paleocene/eocene thermal maximum (= petm). the perturbations of the middle-outer neritic benthonic foraminiferal assemblages from the southwestern nile valley, egypt are described. the observations provide strong evidence that the benthonic extinction event (= bee) marking the petm cannot be considered as a deep-sea phenomenon, suggesting that the neritic benthonic ecosystems were at the same time severely perturbed. however, the relative and absolute numbers of extinctions clearly decrease towards shallower sites at the southern tethyan margin. Gavelinella rubiginosa, Angulogavelinella avnimelechi, Dorothia oxycona, Dorothia buletta, Spiroplectinella knebeli/esnaensis and Neoflabellina jarvisi have their LO in the upper part of Zone P5, with a drop in the benthonic simple diversity at the same level (48 species). In the study area, the extinctions of two well known taxa are clearly linked to the faunal turnover of the deep-sea event: Angulogavelinella avnimelechi, Neoflabellina jarvisi are known to have had a widspread (Tethyan to cosmopolitan) distribution before becoming extinct in the latest Paleocene. In the Egyptian outer neritic deposits, where the typical deep-water taxa (e. g. Gavelinella beccariiformis) are rare or absent, the extinction of A. avnimelechi would appear to be a good alternative marker for the BEE in the Tethyan Realm. The benthonic faunal assemblages reflect low-food, high-oxygen conditions in P1c-P4 when assemblages were mostly dominated by Cibicidoides spp. and almost devoid of buliminids. The majority of oligotrophic conditions coincided with maximum paleodepth. Intermediate trophic conditions started to prevail at the end of Biochron P4, where Bulimina farafraensis enters the record. After the BEE, trophic levels increased while oxygenation decreased (peaks of Bulimina midwayensis) dysoxic conditions and maximum food levels prevailed after the P/E boundary, as indicated by assemblages dominated by high food/low oxygen index (buliminids; Lenticulina spp.; Stainforthia spp.; Valvulinera scrobiculata).

Kurzfassung

Am Ende des Paleozäns führt eine abrupte globale Erwärmung zu kurzzeitigen biotischen und geochemischen Anomalien, die nicht nur den bathyalen, sondern auch den neritischen Bereich erfassen und auch in diesem zum Aussterben mehrer Leitformen von benthonischen Kleinforaminiferen führen. Im oberen Paleozän herrschen gut durchlüftete oligotrophe Bedingungen vor. Nach dem Aussterbe-Event an der Paleozän/Eozän-Grenze (BEE) nehmen eutrophische Bedingungen zu und die Sauerstoff-Versorgung in Bodennähe nimmt ab. Ausgeprägte disoxysche Bedingungen und ein hohes Nährstoffangebot finden sich unmittelbar über dem BEE.

Keywords

climatic changeperturbationecosystemsbuliminidsfaunal assemblagesPaleocene/Eocene Thermal MaximunPETM