MICROFAUNAL COMPLEXES AND MICROFACIAL DESCRIPTION OF THE LATE VISEAN CARBONATE ROCKS OF THE SOUTH DONETS BASIN

Abstract

A detailed study on the microfacies and microfossils of the Upper Visean carbonate rocks exposed in the South Donets Basin (the Mokra Volnovakha and Calmius rivers) were conducted. The studied material included limestone samples collected from the sections of the Donetsk Suite (the upper part of the Mokrovolnovakha Series) stratotypical area. Special attention in the microscopic study was given to microfauna (foraminifera) and algoflora since foraminifera and algae associations primarily reflect the environments and sedimentation conditions. Two distinguished microfaunal complexes correspond with two subdivisions of the Donetsk Suite. The lower complex included foraminifera Globoendothyra globula, Vissariotaxis exilis, Vissariotaxis compressa longa, Endothyranopsis compressa. Foraminifera from the upper complex are Howchinia, Omphalotis omphalota, Bradyina, Palaeotextulariidae, Loeblichia, Eostaffella ikensis, Eostaffella proikensis, Аrchaediscus gigas, Endotiranopsis crassa. Correspondingly to Dunham classification were recognized nine carbonate microfacies of limestone. The identified microfacies are bioclastic grainstone, foraminiferal grainstone, oolitic grainstone with bioclasts, foraminifera-algae grainstone, bioclastic packstone, foraminiferal packstone, microbial peloidal packstone, wackstone/packstone and packstone/grainstone. The recognized microfacies associations were correlated with standart microfacies associations (SMA) which were suggested by Wilson and Flügel. This shows that the studied rocks were deposited within the shallow marine environment of the carbonate platform zone. The alternation in sections of the identified facies types reflects cyclic changes of the paleobasin level. Similar conditions are typical for carbonate sedimentation of North of West Europe, Caspian region and Iran carbonate platforms, where Mississippian deposits are composed mainly of carbonate rocks.