Upper Oligocene Sediments of the Ciscaucasus, Volga–Don, and Mangyshlak Regions (Central Eastern Paratethys): Communication 1. Main Compositional and Structural Features

Upper Oligocene sediments of the Eastern Paratethys are distinguished in the Maikop Group owing to several characteristic features. They form a thick (1000–1200 m) sequence with specific composition and structure in different structural–facies zones of the basin. The development of “fish facies” is the most remarkable feature. It includes unique sediments composed of fish bone detritus (FBD) and iron sulfides with high contents of REE, U, Sc, Re, Ni, Co, Mo, and other elements. These elements form commercial uranium–base metal deposits so far unknown in other formations of the Earth. The structure of thick rock sequences in the deepest part of the Eastern Paratethys is also characterized by specific features. Deep-sea clayey fish-facies sediments intercalate with beds of fine-grained sandy and silty material. Their influx into the central part of the basin was responsible for the clinoform structure of the rock sequence revealed by seismostratigraphic studies. This communication presents new data on the distribution of bone detritus deposits, composition and structure of sediments, and summary characteristics of Upper Oligocene sediments that are essential for the further analysis of facies–paleogeographic sedimentation conditions in the central Eastern Paratethys.