The central region of the southern Junggar basin （Northwest China） is a key exploration target in this petroliferous basin. As there are four sets of potential source rocks （e.g., Permian, Jurassic, Cretaceous and Paleogene sequences）, petroleum migration and accumulation are likely complex. This study represents an attempt to understand this complexity in order to provide fundamental information for future regional petroleum exploration and geological studies. Based on petroleum geology and geochemistry, it is implied that there are mainly three types of hydrocarbons, including Cretaceous- and Paleogene-sourced oils （with the former being dominant） and Jurassic-sourced gas. The petroleum migration and accumulation mainly cover three stages. The first stage is the late period of the Early Pleistocene, in which the Cretaceous-sourced oils migrate and accumulate. Then, in the second stage （from the late period of the Middle Pleistocene to the early period of the Late Pleistocene）, the Cretaceous- sourced oils, together with the Paleogene-sourced oils, participate in the migration and accumulation. At last, in the end of the Late Pleistocene, large quantities of oils remigrate and accumulate, with gas （especially Jurassic- sourced gas） migrating along faults to accumulate. Thus, petroleum charge events in the area are complex, reflecting the control of complex tectonic evolution on petroleum migration and accumulation.
Whether benthic macroalga can be an important type of bio-precursor of source rocks is a contentious issue in source-rock studies,and has not been well understood.This paper represents a case study of Jurassic mudstone source rocks from the northern Qaidam Basin,northwestern China,in which the benthic macro red algae were recognized for the first time based on combined organic petrological and biomarker works.We found not only cystocarps in the algae,representative of rhodophyta,but also diahopanes,which are diagnostic biomarkers of such algae.Thus,as many reservoired oils in the northern Qaidam Basin contain abundant diahopanes,it may indicate that the red algae have contributed to hydrocarbon accumulation.This was confirmed by integrated geological and geochemical analyses.Hence,this study provides new evidence for macroalga-generated hydrocarbons.
CAO JianBIAN LiZengHU KaiLIU YunTianWANG LiQunYANG ShaoYongCHEN YanPENG XiaoQun
