LAUSR

Bohai Bay Basin is a Cenozoic rift basin containing abundant oil and gas resources in northeastern China. By combining 3D seismic data and well logs, three composited sequences are identified from regional unconformity relationships, and seven sequences can be further identified from local unconformities. Major depositional systems include fan delta, braided delta, fluvial delta, shallow lake, deep lake, and sublacustrine fan. Through identifying onlap points in the ramp of the Liaoxi depression, a lake level change curve is constructed. Pollen and algae data are used to analyze paleoclimate which shows two large cool-warm cycles in Paleogene Liaoxi depression. Lake level change is controlled by both tectonic subsidence and climate change. Paleoclimate change is the main factor controlling lake level during stable tectonic periods, while tectonic subsidence is the main controlling factor controlling lake level during active tectonic periods. Depositional evolution corresponds with lake level change, which indicates that lake level stays relatively high with deep or shallow lacustrine and delta front deposits developed, and lake level stays relatively low with alluvial fan, braid delta plain, fan delta, and shallow lacustrine deposits developed.