Mesozoic and Cenozoic Geologic History and Surface Topography of the Northwestern Altai-Sayan Area

摘要

Middle Mesozoic and Cenozoic tectonic events on the periphery of the West Siberian Plain and in the flanking mountains of the northwestern Altai-Sayan province produced highland topography over a part of southeastern West Siberia. The activity stages were separated by a long lull from Late Cretaceous through middle Paleogene, when the Mesozoic mountains were denuded to the base level corresponding to the level of the West Siberian epicontinental sea. The sea of that time was connected to the World Ocean, and its level fell in several successive events. The periods of stable sea level are marked by surfaces at 200, 250, and 300 m above sea level (in the present reference of elevations) and correlate with global sea level changes according to Haq and Vail. The stability surfaces were revealed during geomorphological surveys in the Salair Range and in the Bugotak-Sokur upland. Their elevations have not changed since the origin in the studied part of the Bugotak-Sokur area, but the SW tilting Salair block delineated by thrust faults in the north and in the east has been uplifted at 0.1 mm/year. In the course of neotectonic activity, the line of mountain growth shifted notably to the southeast, leaving behind the Fore-Altai plain and the Bugotak-Sokur upland, which were occupied by high mountains in the Jurassic. The lack of post-Mesozoic molasse in the Kuznetsk Basin and in the Chulym plain indicates that the present Kuznetsk Alatau and Salair Ranges are considerably lower than their middle Mesozoic precursors.