Upper Oligocene Sediments in the Ciscaucasus, Volga–Don, and Mangyshlak Regions (Central Part of the Eastern Paratethys): Communication 2. Facies–Paleogeographic Sedimentation Settings

Late Oligocene basins were very unusual in terms of sedimentation. The most remarkable example is the early Kalmykian basin that was characterized by the drastic morphological differentiation and deposition of substantially different lithofacies sediment types (shallow-water shelf to relatively deep-water facies in anoxic troughs). Slopes of the troughs and uncompensated areas are marked by the accumulation of thick sandy–silty–clayey (up to 1000 m) and thin calcareous–clayey (up to 100 m) sediments, respectively. The outer shelf zone with islands and shoals includes metalliferous fish bone detritus and iron sulfide deposits. This exotic feature of the Kalmykian basin has no genetic analogues among other formations of the world. This communication presents the first description of the late Kalmykian basin and its lithofacies map that demonstrates the abrupt transformation of the paleogeographic setting in the late Oligocene as a result of the general relative shoaling and basin bottom leveling. Consequently, metalliferous sediments ceased to accumulate in the northern shelf area, but bone–sulfide deposits could accumulate in the southern part of the basin along the Caucasian archipelago.