鄂尔多斯盆地东北部上古生界煤系烃源岩17α(H)-重排藿烷类的分布及成因探讨

鄂尔多斯盆地东北部上古生界10个典型煤系烃源岩样品中检测出三类重排藿烷，分别为17α(H)-重排藿烷、18α(H)-新藿烷以及未知结构的早洗脱重排藿烷。烃源岩样品中藿烷类具有两种分布型式:①以C₃₀藿烷为主峰的C₂₇~C₃₅(缺C₂₈)藿烷类常规分布型式，含少量17α (H)-重排藿烷和18α(H)-新藿烷；②以富含17α(H)-重排藿烷和C₃₀早洗脱重排藿烷为特征。含有高~异常高相对丰度17α(H)-重排藿烷的烃源岩样品，其17α(H)-重排藿烷的绝对浓度也明显较高。从烃源岩生源构成、有机质丰度及其赋存状态、成熟度以及沉积与成岩环境4个方面探讨了高丰度17α(H)-重排藿烷的成因。研究结果表明，烃源岩中高丰度的17α(H)-重排藿烷的形成与高等植物生源有一定联系、亚氧化-氧化的扇缘泥炭沼泽相是形成高~异常高丰度17α(H)-重排藿烷的有利沉积相带；而烃源岩显微组分、有机质丰度及其赋存状态以及有机质成熟度的影响尚不确定。

Origin of 17α (H)-Rearranged Hopanes in Upper Palaeozoic Coal Bearing Source Rocks in Northeast Ordos Basin

Geochemical characteristics of saturated hydrocarbons have been discussed on the basis of GC/MS analysis for the 10 typical coal-bearing source rock samples in northeast Ordos Basin. Three series of rearranged hopanes, 17α (H)-diahopanes, 18α (H)-neohopanes and unidentified early eluting rearranged hopanes, were detected. The analytical  results showed that the hopane series compounds have two different distribution patterns. One is conventional pattern, which has high abundance of regular hopanes, low abundance of 17α (H)-diahopanes and 18α (H)-neohopanes, represented by source rock samples from Yu 20 and Shuang 1 well. The other one is unconventional model, characterized by abnormally rich in 17α (H)-diahopanes and a C₃₀-early-eluting rearranged hopane, represented by source rock samples from Su 27 well. The source rocks from Su 27 well  high relative abundance of 17α (H)-diahopanes and also  high absolute concentration. The main controlling factors of extremely abundant 17α (H)-diahopanes are discussed from the composition of organic materials, maceral, the abundance of organic matters and its occurrence, maturity, depositional  and diagenetic environment. The result shows that the origin and accumulation of high abundance of 17α (H)-diahopanes in source rocks has a close relationship with higher plants source materials. Weak oxidation to oxidation fan marginal peat bog facies is a favorable sedimentary facies for forming a significant proportion of 17α (H)-diahopanes. However,  the influences of maceral, maturity, the abundance of organic matters and its occurrence are not sure.