FUSULINID BIOZONATION AS A PROXY OF MILANKOVITCH CYCLICITY: THE RECORD FROM MOSCOVIAN-KASIMOVIAN TRANSITION IN DONETS BASIN (UKRAINE)

The Donets Basin of Eastern Europe contains one of the most complete global Carboniferous sedimentary successions with almost no gaps in its depositional record. Here we present new data from M and N Formations in Donets Basin. Nine biozones in the Moscovian – Kasimovian transition have been distinguished in DB, each of which reveals cyclicity in fusulinid assemblages. Analyses of the facies, microfacies and fusulinid biota in each biozone allow recognition of three distinct assemblages formed in different habitat probably depending on sea level fluctuations. The transgression episodes are represented by packstone or silstone microfacies with monospecific population of Hemifusulina. Highstand brings wackstone microfacies with assemblage of mature Beedeina, Neostaffella, Ozawainella specimens. The micritic matrix of these limestones comprised of degraded or decomposed calcite bioclasts, indicates the low sedimentation rate of such off-shore limestone, which are usually thin-bedded and formed when the maximum sea level stand reached stability. At the sea level lowstand most abundant and diverse population of fusulinids mainly Fusulinella and Schubertella species appears in the coarse biostatic sediments. Each biozone corresponds to one full cycle started with a beginning of transgression, the stressful episode for the majority of fusulinids, with exception of Hemifusulina, continued by the maximum flooding, characterized by Beedeina-dominant species, and completed by regression with abundant Fusulinella-Schubertella association. Beedeina species show the same evolution trend in the many regions of the Paleotethys and proposed zones are recognizable in the Moscow Basin, Central Asia, China, Southern Urals, Cantabrian Mountains. The diverse Fusulinella species reveal higher degree of provinciality that indicates their association with regression episodes, when the marine connection between provinces was interrupted by exposed land. The occurrence of Hemifusulina species, which marked a beginning of transgression, is restricted by few regions Donets and Moscow Basins, Central Asia and the Cantabrian Mountains and indicates the limits of transgression, the proximity of exposed land, the source of terrigenous input into transgressive seas.