Controls on deposition of aquatic and terrestrial organic matter in the lacustrine Namling–Oiyug basin (Oligocene–Miocene, southern Tibet)

摘要: Abstract The Namling–Oiyug basin is the only Cenozoic lake that has hydrocarbon potential in southern Tibet, China. Coal was once exploited from early Miocene Mangxiang Formation, which also hosts oil-prone source rock layers. Herein, a combined investigation of sedimentological features and organic geochemistry performed on measured outcrop section Formation to study lake-basin types as well depositional history aquatic terrestrial matter (OM). There are two periods evolution history: balanced-fill overfilled stages. In stage, laminated shale deposited relatively deep environment, with total carbon (TOC) contents around 5 wt.%, HI values up 316 mg HC/g TOC, indicating hydrogen-poor Type II kerogen transition III kerogen. Comparison between maceral composition geochemical properties suggests relative low results thermal maturity. high value gammacerane index indicates water stratification lake. this sediment input approximately equaled accommodation, stable hosted large amounts lacustrine algae, accumulated OM an anoxic environment. After onset thrusting, accommodation decreased, volumes clastic sediments drained into surrounding area, resulting basin. During peat freshwater > 30 wt.% HI, OM. Pr/Ph (> 3) implies oxic conditions.