Sedimentary environments of the Upper Cretaceous in the Southwestern and Central Crimea

Research subject. Upper Cretaceous sections of the southwestern and central parts of Crimea, which are part of the Cretaceous-Palaeogene cover of the Scythian platform. Aim. Reconstruction of sedimentation and changes in paleogeography related to sea level fluctuations. Materials and methods . Outcrop descriptions and petrographical investigations of rocks were conducted. A range of methods including facial analysis and cyclic and sequence stratigraphic techniques were employed. Results . Six lithological types of beds were identified, with diagnostic characteristics and genetic interpretations proposed. A model of sedimentation environments has been developed that takes into account the diagenetic transformations of sediments under anoxic conditions in the outer ramp. This has made it possible to identify transgressive-regressive layer sequences (cyclothems), determine the position of maximum flooding surfaces, and transgressive surfaces. Based on this, the correlation structures have been refined and detailed. Traces of 12 regional sedimentation cycles have been established. The features of the structures of transgressive and highstand systems tracts from the Cenomanian-Coniacian and Santonian-Maastrichtian sequences were demonstrated. A series of paleogeographic schemes for short intervals of geological time has been compiled. Conclusions. In the Crimean part of the Late Cretaceous epicontinental basin, sedimentation took place under the conditions of an inner, middle, and outer terrigenous-carbonate ramp that moved northward during periods of transgression and migrated southward during regression (in modern coordinates). At the same time, on large areas, the bottom surface most often remained above the base of storm waves.