Foraminiferal assemblages and zonations across the Lower - Middle Triassic boundary in Bulgaria

Abstract

Two types of Triassic sediments could be distinguished on the territory of Bulgaria: Tethyan and Peri-Tethyan. The Tethyan Triassic is allochthonous in its origin. It forms olistolites or rock fragments in breccia-conglomerates within olistostromes in East Stam Planina as well as thrust sheets in Strandzha Mountain. As a rule the Tethyan Triassic rests upon the autochthonous Peri-Tethyan Triassic - coastal shallow - marine sediments of diverse lithology. We summarized the data about foraminiferal contents and foraminifera sequences from Peri-Tethyan Triassic: Northeast Bulgaria (Dobrogea region), Moesian Platform, Central Forebalkan, Northwest Bulgaria, Southwest Bulgaria and St. Ilija Ridge of Sakar Mts. in Southeast Bulgaria. The analysis of the benthic foraminifers occurrence within the Dienerian ? - lowermost part of Pelsonian interval resulted in recognition of three interval biozones: Meandrospira cheni Interval Biozone, Meandrospira pusilla Interval Biozone and Meandrospira deformata Interval Biozone. The foraminifers of the Tethyan Triassic in East Balkan Mts. have always been of special interest because of the typical Tethyan character of the micro- and macrofossils in this region of Bulgaria. In this region were found foraminifers characterizing Meandrospira pllsilla Zone. Due to the absence of the index species Meandrospira deformata, the Zone of the same name in the Tethyan Triassic cannot be recognized.