Depositional environment of terrestrial petroleum source rocks and geochemical indicators in the Songliao Basin

Abstract

To determine geochemical indicators for depositional environment favored by terrestrial petroleum source rocks, we selected 40 source rock samples from the Late Cretaceous Qingshankou Formation (K 2 qn) and the first member of Nenjiang Formation (K 2 n 1 ) in the Songliao Basin to qualify saturate fraction and aromatic fraction using GC-HRT (gas chromatography high resolution time-of-flight mass spectrometry) and quantify important biomarkers using GC-MS. The results reveal that source rocks from the 1st member of Qingshankou Formation (K 2 qn 1 ) are characterized by not only high contents of terpanes, regular steranes and 4-methylsteranes but also high contents of dinosteranes, C 31 steranes and aryl isoprenoids. Presence of specific biomarkers like elementary sulfur and lanostanes indicates a depositional environment of lagoon characterized by water stratification and high salinity. In the 2nd-3rd members of Qingshankou Formation (K 2 qn 2+3 ), source rocks contain lower contents of biomarkers, indicating a depositional environment of shallow fresh-water lake delta. Source rocks in the K 2 n 1 contain high contents of terpanes, regular steranes and 4-methylsteranes but lower contents of dinosteranes, C 31 steranes and aryl isoprenoids, indicating a depositional environment of fresh-brackish open lake characterized by low salinity and poor water stratification, where organic matter is seriously altered by bacteria. Overall analysis shows that primary geochemical indicators for terrestrial petroleum source rocks are as follows: 1) C 30 hopanes > 1500 ppm; 2) gammacerane >190 ppm; 3) C 27 steranes >200 ppm; 4) 4-methylsteranes >100 ppm; 5) aryl isoprenoids > 3 ppm; 6) dehydroxyl-vitamin E >10 ppm.Songliao Basin, source rock, depositional environment, geochemistry, biomarker Citation:Feng Z H, Fang W, Li Z G, et al. Depositional environment of terrestrial petroleum source rocks and geochemical indicators in the Songliao Basin.

Lithofacies and depositional setting of a highly prospective lacustrine shale oil succession from the Upper Cretaceous Qingshankou Formation in the Gulong sag, northern Songliao Basin, northeast China

“…Contributing to the worldwide growth in production of unconventional oil and gas, tight oil has also been discovered in the sandstones of the second and third members of the Qingshankou Formation (K 2 qn 2+3 ) in the Songliao Basin (Shi et al, 2015). The Qingshankou Formation contains shale oil layers with high TOC and high oil yield near the base of its first (lower) member (K 2 qn 1 ; Feng et al, 2011). For this reason, over the past two decades, highresolution studies of the potential for hydrocarbon generation and the reconstruction of paleoenvironmental changes have been undertaken (Zhou and Littke, 1999;Jia et al, 2013b;Xu et al, 2015).…”

Compound-specific carbon isotope study on the hydrocarbon biomarkers in lacustrine source rocks from Songliao Basin

“…The depositional environments and source of organic matter (OM) in Songliao source rocks has been extensively studied (Yang et al, 1981;Huang et al, 1998;Feng et al, 2009Feng et al, , 2011Chamberlain et al, 2013). Prior studies have shown that the Qiangshankou and Nenjiang Formations, the two major sets of OM-rich source rocks, were deposited in a deep freshwater lake, but under eutrophic and anoxic conditions Bechtel et al, 2012;Song et al, 2013).…”

Paleoenvironmental reconstruction of the Late Santonian Songliao Paleo-lake

“…Prior studies have shown that two large marine transgressions occurred during the Late Cretaceous, specifically during the Late Turonian (lower Qingshankou Formation) and the Late Santonianearly Campanian (lower Nenjiang Formation, K 2 n 1+2 ), depositing suites of dark mudstone, black shale, and oil shale (Yang et al, 1985;Feng et al, 2011). An increasing number of studies suggest that the formation of a hydrocarbon source rock in K 2 n 1+2 of the SLB relates to the marine transgression (Hou et al, 2000;Xi et al, 2011a;Huang et al, 2013;Hu et al, 2015).…”