Original paper

Distribution of larger foraminifera near the Lower-Middle Eocene boundary in the Northeastern Peritethys

Zakrevskaya, E. Yu.

Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen Band 234 Heft 1-3 (2004), p. 335 - 360

22 references

published: Dec 22, 2004

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Abstract

The distribution of the larger foraminifera (nummulitids and orthophragminids) of the Lower-Middle Eocene transitional layers in sections in the Crimea, North Caucasus, Manghyshlak and North Peri-Aralian has been examined. The analysis of the larger foraminifera and the lithology has allowed to distinguish two horizons in the lower Lutetian. A gradual transition from the Ypresian to the Lutetian, marked by the appearance of isolated Lutetian Nummulitaceae is observed in the Crimea, the Northern Caucasus and the Northern Peri-Aral Region. In these regions, an abrupt facies change from nummulitic to marly limestones or clays and a decrease of diversity in the Nummulites is characteristic for the upper horizon of the lower Lutetian. In the Manghyshlak, the boundary between the Ypresian and the Lutetian is sharp and regressive, whereas the limit between the lower and upper horizons of the lower Lutetian corresponds to a transgressive event. A rapid decrease of the foraminiferal diversity coincides with the beginning of the Lutetian. The horizons recognized in the Crimea and southern Russia and Kazakhstan correspond to two subzones of the lower Lutetian in Schaub's scale (1981) or to Zone SBZ13 in the Tethyan scale (Serra-Kiel et al. 1998). The dynamics of the diversity of the Nummulitaceae near the Lower-Middle Eocene boundary is different in the Tethyan and the North-Eastern Peritethyan provinces, reflecting different trends in the paleoenvironmental evolution.

Kurzfassung

Die Entwicklung der Diversität der Nummulitiden und Orthophragminiden aus dem Übergangsbereich vom unteren zum mittleren Eozän der nordöstlichen Paratethys (Krim, Nord-Kaukasus, Mangyshlak, Aral-See) unterscheidet sich von derjenigen, die in der Tethys beobachtet wird. Diese Unterschiede sind wohl vor allem auf unterschiedliche Ablagerungsbedingungen zurückzuführen. In der Krim und im N-Kaukasus erfolgt der Übergang vom Ypresien zum Lutétien fließend, während diese beiden Stufen im Mangyshlak durch eine scharfe Grenze getrennt sind.

Keywords

foraminiferaLutetian NummulitaceaetransgressiveRussiaKazakhstan