晋县凹陷未熟蒸发岩沉积物中C22-C27甾烯和C24-C30四环萜烷的检出

晋县凹陷赵芯2井（2459m，Ezk）低熟蒸发岩样品中检出了异常分布的C22-C27甾烯和C24-C30四环萜烷（17，21-断藿烷），但在同井更深、成熟度相对更高的沉积物中并未检出。实测镜质组反射率R^0=0．43％以及芳烃馏分中有高丰度的苯并噻吩和多烷基化的二苯并噻吩，说明热催化作用成因是不可能的，微生物参与成为最可能的生成途经。沉积抽提物未显示出常规生物降解的痕迹，因此这些化合物很可能是在早期成岩阶段特定微生物作用的结果。该区油样中检出的C21-C29甾烷的特征与同时检出的C22-C27甾烯特征一致，进一步表明微生物作用的可能性；高丰度的C24-C30四环萜烷（17，21-断藿烷）和常规藿烷、甲基藿烷相匹配，以及高丰度的C22-C27甾烯和规则甾烷缺失相匹配，特别是芳烃馏分中多取代二苯并噻吩类有机含硫化合物的检出，均表明异常分布的C22-C27甾烯与C24-C30四环萜烷类似，很可能是早期成岩阶段微生物改造作用下的产物。

Occurrence of C22-C27 sterenes and C24-C30 tetracyclic terpanes in an immature evaporitic sediment from the Jinxian Sag, North China

An unusual distribution of C22 - C27 sterenes and C24 - C30 tetracyclic terpanes （ 17, 21-secohopane） have been detected in an immature evaporitic marl sample from the Zhaoxin2 well （2459 m, E2k） in the Jinxian Sag, Bohai Bay Basin, North China. These compounds were not detected in the deeper and relatively more mature sediments suggesting that thermocatalytic generation is an unlikely mode of formation, leaving microbial mediation as the likely formation pathway. The broader molecular profiles of these sediments showed no traditional evidence of biodegradation, so these products may be the result of selective microbial processing during the early stages of diagenesis. The identification of C22 - C27 sterenes is consistent with the of C21 - C29 steranes detected in several crude oils sourced in this region, suggesting the possibility of a microbially-related diagenetic relationship. The coincidence of high abundances of C24 - C30 tetracyclic terpanes （ 17, 21-secohopanes） and regular hopanes, together with high abundance of C22 - C27 sterenes and the absence of common regular C27 - C29 steranes, also suggests the unusual C22- C27 sterenes, similarly to C24- C30 tetracyclic terpanes, might be product of microbial transformation in the early diagenetic stage.