THE PALEOGENE SEDIMENTARY SYSTEM AND EVOLUTION CHARACTERISTICS OF LENGHU STRUCTURAL BELT IN NORTHERN QAIDAM BASIN

The Paleogene sedimentary system and evolution characteristics of Lenghu structural belt are studied based on the core observation, analysis of heavy mineral, logging data and seismic data of key exploratory wells in the west section of northern Qaidam Basin. The results indicate that the alluvial fan-braided river-braided river delta-lacustrine sedimentary system is developed in the Paleogene strata, with the provenance from the nearby Xiaosaishitengshan and Saishitengshan in the northeast. The braided river and braided river delta plain were mainly developed during the depositional stage of Paleogene Lulehe Formation (E₁₊₂), with only a few alluvial fan deposits near the piedmont. There were mainly braided river, braided river delta plain, braided river delta front and shore-shallow lake deposits in the sedimentary period of Xiaganchaigou Formation (E₃). The Paleogene Lenghu structural belt is shown as a large-scale transgression process with obvious vertical depositional inheritance, which well records the sedimentary evolution. The sedimentary system and evolution process are favorable for the alternating deposition of coarse and fine clastics and form good reservoir-cap association, which provides reliable geological basis for further oil-gas exploration in Lenghu structural belt of Qaidam Basin.