Response of Oceanic Organisms to Abiotic Events
in the Paleogene

M. S. Barash

Shirshov Institute of Oceanolgy, Russian Academy of Sciences, pr. Nakhimovskii 36, Moscow, 117997 Russia

E-mail: barashms@yandex.ru

Received April 14, 2008; in final form, May 25, 2008

Abstract—Climate fluctuations with the optimum in the Early Eocene and subsequent cooling were the main
abiotic factor that controlled the development of the oceanic biota in the Paleogene. The Paleogene represented
the transitional stage from the greenhouse climate of the Mesozoic to the partly glacial Neogene and was charac-
terized by changes in the distribution of the temperatures in the ocean with the replacement of the dominant lati-
tudinal thermal circulation by the largely meridional thermohaline one. The climate changes were also determined
by other factors: the opening and closure of seaways between basins, the position of major currents, volcanic activ-
ity, the sea-level fluctuations, the composition of the hydro- and atmosphere, and others. These changes were, in
turn, determined by factors of higher order, primarily, by tectonic movements: vertical and horizontal (motions of
lithospheric plates). The contribution of impact events to this process is also highly probable. All these factors
influenced, via the hydrological and hydrochemical parameters of the water column, the evolution of the oceanic
biota: their distribution areas, the sizes of the organisms, the diversity of the communities, the bioproductivity, and
the mass extinction (for example, the extinction of 30–50% of the benthic foraminifers at the Paleocene–Eocene
transition in response to the abrupt temperature increase). The Eocene–Oligocene transition (38 Ma ago) was
marked by a global biotic crisis, the most significant one in the Cenozoic, when the abyssal part of the ocean was
filled with cold water to form the psychrosphere. At least five major impact events, which preceded the Oligocene
mass extinction of the biota, occurred in the terminal Eocene (36–35 Ma ago).

DOI: 10.1134/S0001437009030114

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