GEOLOGICAL EVOLUTION OF NORTH USTYURT REGION AND ADJACENT AREAS IN TRIASSIC
The article considers the stages of tectonic - sedimentation evolution of the North - Ustyurt region in the Triassic. It has been established that palaeogeographic settings have repeatedly changed - from continental in the early Induan stage to marine in the Olenekian age and the middle Triassic epoch and again continental in the late Triassic. The most favorable for hydrocarbon generation are marine terrigenous - carbonate and terrigenous deep - water facies of the Olenekian stage and the Middle Triassic, as well as coastal - marine deposits of the Upper Triassic, which were formed in reducing or sharply reducing geochemical conditions that contributed to the accumulation and preservation of huge masses of organic matter. In the Early Triassic in the North Ustyurt sedimentation basin, at first, in the low - lying plains and then in the shallow -margine basin, were accumulated alternating clays, siltstones, and sandstones, that are replaced upstream by interlayers of marls or strongly carbonate rocks. In the Middle Triassic in the western part of the North - Ustyurt sedimentation basin, organogenic detritus, chemogenic limestones and finally black bituminous clays with relatively deep water accumulated. In the Eastern part, was located a low - lying hilly plain, where mainly terrigenous sand and siltstone differences were deposited, often red - colored, forming plumes of deluvial - proluvial sediments of the sub - mountain fan belt. In the Late Triassic, most of the North Ustyurt sedimentation basin was the scene of sedimentation of mostly sandy - clay sediments in a typical continental alluvial - lake plain. In the North-Ustyurt region in the Triassic, there are several phases of activation of volcanic activity - at the end of the Olenekian stage, in the Middle and Late Triassic, which actively influenced the nature of sedimentation.