STRATIGRAPHY OF LOWER VOLGIAN DEPOSITS IN THE RUSSIAN PLATE AND CORRELATION BETWEEN VOLGIAN AND TITHONIAN STAGES

Abstract

A detailed biostratigraphic scale is suggested for the lower Volgian Substage of the Russian plate. The Ilowaiskya klimovi Zone is subdivided (from the base upward) into the Glochiceras (Lingulaticeras) solenoids and Neochetoceras steraspis beds underlying the Glochiceras (Paralingulaticeras) lithographicum efimovi Horizon, and Anaspidoceras neoburgense and Pseudovirgatites puschi horizons are discriminated within the Ilowaiskya pseudoscythica Zone. Data on distribution of sub-Tethyan ammonities (species of Glochiceras s.l., Neochetoceras, Pseudolissoceras, Anaspidoceras, and Pseudolissoceras genera) in the Russian plate are used to correlate the lower Volgian Substage with the Tithonian in accord with the following scheme: (1) the klimovi Zone corresponds to the lower half of the hybonotum Zone; (2) the sokolovi Zone is an equivalent of the upper portion of hybonotum Zone coupled with a basal interval of the darwini Zone; (3) the pseudoscythica Zone ranges from the upper portion of the darwini Zone to the top of semiforme Zone and even through the basal part of the fallauxi Zone so that the entire neoburgense Horizon falls into the semiforme Zone. Migration paths of thermophilic ammonities into the Central Russian sea are depicted. Ammonites of Poland actively migrated eastward during the klimovi phase, in the early sokolovi time, and at the moment corresponding to the puschi Horizon. The diverse sub-Tethyan ammonities present in the neoburgense Horizon point to progressing connections with the North Caucasian basin. Species Neochetoceras steraspis (Oppel, 1863), Glochiceras (Lingulaticeras) solenoids (Quenstedt, 1849), Pseudolissoceras sp. ind., and new subspecies Glochiceras (Paralingulaticeras) lithographicum efimovi Rogov, subsp. nov., which have been found in the Russian platform sections, are described for the first time. Images of some other ammonite species important for correlation are presented as well.