西湖凹陷始新统平湖组煤系烃源岩分子地球化学特征

60个饱和烃和芳烃组分的GC－MS分析资料表明，东海盆地西湖凹陷平湖组煤系烃源岩饱和烃中富含源于针叶树脂的二萜烷类生物标志物，甾烷中普遍以C₂₉ 化合物占优势（>45%），芳烃组分中惹烯、1，7-二甲基菲等陆源标志物含量异常高，这些结果反映该煤系烃源岩的成烃母质主要来源于陆源高等植物。相对于煤及碳质泥岩，暗色泥岩中C₂₇ 甾烷有较高含量，且正构烷烃呈双峰型分布，说明其有机质生物源中水生生物占有一定比例。该煤系烃源岩的Pr/Ph值大多分布在3.5~8.5，二苯并呋喃类化合物较多，指示这套烃源层主要形成于氧化性较强的湖沼相环境;部分暗色泥岩Pr/Ph值在1.5左右，可能属弱还原-弱氧化的半深湖相沉积。煤及碳质泥岩以高C₂₉ 甾烷（大于80%）、低伽马蜡烷（与C₃₀ 藿烷的比值低于0.05）与暗色泥岩形成区别。

Molecular geochemistry of Eocene Pinghu Formation coal-bearing source rocks in the Xihu Depression, East China Sea Shelf Basin

GC/MS analytical data of 60 saturated and aromatic fractions revealed that saturated hydrocarbons from Pinghu Formation coal-bearing source rocks in the Xihu Depression of the East China Sea Shelf Basin are characterized by abundant diterpenoid compounds originated from resins of coniferous trees and dominant C29 in steranes(>45%).Moreover,aromatic fractions are abnormally rich in terrigenous biomarkers,such as retene and 1,7-dimethylphenanthrene,indicating a predominant source of organic matter derived from terrigenous higher plants.Compared with coals and carbonaceous mudstones,dark mudstones show a relatively higher content of C27 sterane and a bimodal distribution in n-alkanes,suggesting a certain proportion of aquatic organism contributions in the organic matter source.Source rocks as a whole are believed to be deposited in an oxic limnetic-facies environment,as reflected by high Pr/Ph ratios ranging mostly from 3.5 to 8.5 and abundant dibenzofuranes.However,some dark mudstones show relatively lower Pr/Ph values(round 1.5),suggesting a weakly reducing to suboxic semi-deep lake setting.Coals and carbonaceous mudstones can be distinguished from dark mudstones by a higher relative concentration of C29 sterane(>80%) and lower gammacerane /C30 hopane ratio(<0.05).