Early generation of 20S-5α(H),14α(H),17α(H)- and 5α(H),14β(H),17β(H)-steranes in low salinity lacustrine shales

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• 作者：Li ; Maowen ; Larter ; Steve R. ; Mei ; Bowen
• 关键词：20S isomers ; biomarkers ; immature sediments ; sterane diagenesis ; Liaohe Basin ; lacustrine environment
• 刊名：Organic Geochemistry
• 出版年：1994
• 出版时间：December, 1994
• 年：1994
• 卷：22
• 期：6
• 页码：893-902
• 全文大小：809 K

文摘

A quantitative sterane biomarker study was conducted on a series of paralic freshwater lacustrine shale samples ranging in maturity from immature to near oil window maturity taken from Section 3 of the Shahejie Formation (Es3) in the Liaohe Basin, N.E. China. Concentrations of 5α(H),14α(H),17α(H)-20S and 5α(H),14β(H),17β(H)-steranes remain nearly constant throughout the sample suite. However, the decrease in the absolute concentrations of the 20R-5α(H),14α(H),17α(H)-C₂₉ steranes with increasing maturity results in an increase in the conventionally defined maturity parameters, 20S/(20S + 20R)-ααα and αββ/(ααα + αββ) sterane ratios. In addition, the data suggest that relatively early generation of 5α(H),14α(H),17α(H)-20S and 5α(H),14β(H),17β(H)-steranes has occurred in lacustrine sediments with a vitrinite reflectance 0.3 % (R_o). The data provide strong support for the major importance of relative thermal stability of epimers, but do not exclude the possibility of isomerization as a viable mechanism for production.