Palaeoenvironmental conditions during deposition of the Upper Cretaceous oil shale sequences in the Songliao Basin (NE China): Implications from geochemical analysis

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• 作者：Achim Bechtel^a ; ^{Achim.Bechtel@mu-leoben.at} ; Jianliang Jia^b ; Susanne A.I. Strobl^a ; Reinhard F. Sachsenhofer^a ; Zhaojun Liu^b ; Reinhard Gratzer^a ; Wilhelm Pü ; ttmann^c
• 刊名：Organic Geochemistry
• 出版年：2012
• 期刊代码：40_01466380
• 类别：pw
• 出版时间：May, 2012
• 卷：46
• 期：Complete
• 页码：76-95
• 文件大小：2513 K

摘要

Excellent hydrocarbon source rocks (oil shales), containing Type I organic matter (OM), were deposited in the continental Songliao rift basin during the Late Cretaceous. A major contribution of aquatic organisms (dinoflagellates, green algae, botryococcus) and minor input from macrophytes and land plants to OM accumulation is indicated by n-alkane distribution, steroid composition and 未¹³C values of individual biomarkers. Microbial communities included heterotrophic bacteria, cyanobacteria and chemoautotrophic bacteria, as well as purple and green sulfur bacteria. The presence of methanotrophic bacteria is indicated by ¹³C-depleted methyl hopane. The sediments were deposited in a eutrophic, alkaline palaeolake. Highly reducing (saline) bottom water conditions and a stratified water column existed during OM accumulation of the Qingshankou Formation and Member 1 of the Nenjiang Formation. This is indicated by low pristane/phytane, gammacerane index and MTTC ratios, and the presence of 尾-carotane and aryl isoprenoids. However, an abrupt change in environmental conditions during deposition of Member 2 of the Nenjiang Formation is indicated by significant changes in salinity and redox-sensitive biomarker ratios. A freshwater environment and suboxic conditions in the deep water prevailed during this period. Higher input of terrigenous OM occurred during deposition of the upper Nenjiang Formation.

Good oil-to-source rock correlation was obtained using biomarker fingerprints of oil-stained sandstone from the Quantou Formation and oil shales from the Qingshankou Formation. Based on the extent of isomerisation of C₃₁ hopanes, the oil was most probably derived from oil shales of the Qingshankou Formation in deeper parts of the basin.