Effects of Volcanic Activity on Organic Matter Sources and the Paleoenvironment: Geochemical Evidence from Upper Carboniferous Source Rocks(Batamayineishan Formation) in Eastern Junggar, NW China

The mudstone, gray tuffite and carbonaceous shale in the Upper Carboniferous Batamayineishan Formation（Bashan Formation） are essential source rocks for the volcanic reservoir in eastern Junggar, northwestern China. The kerogen components, vitrinite reflectance, Rock-Eval pyrolysis, lipid biomarkers and isotope compositions were measured to understand the provenance and depositional environment of Bashan Formation under the background of volcanic activities. There were 10 and 4 periods of volcanic eruptions identified in the wells CS and DZ, respectively. The source rocks developed in the late or intermittent phase of volcanic activity. The original island arcs of the Early Carboniferous evolved into the Wucaiwan sag and the Dishuiquan sag in the Bashan Formation. The Wucaiwan sag inherited the restricted, closed residual sea, which had a slightly anoxic and hypersaline environment. The Dishuiquan sag was generally an oxidizing lacustrine environment, influenced by a marine transgression that may have occurred at the end of the DZⅢ period during the Late Carboniferous. Although the total organic matter decreased due to the volcanic eruption, ash could cause an increase of aquatic organisms, coinciding with increases in salinity and reducibility in the Dishuiquan sag.