盐湖盆地沉积有机质中的脱羟基维生素E

脱羟基维生素E(DHVE)同系物及其异构体在盐湖盆地原油及生油岩的轻芳烃馏份中被检出。文章从有机立体化学角度对其结构进行了分析;并根据热力学原理,对该类化合物在地质体中的存在状态及演化规律进行了讨论。认为DHVE作为生物分子化石,不仅可反映有机质的热演化程度,而且也可作为膏盐沉积环境的特征生物标志。DHVE在原油中的检出,对业已发现的未成熟原油的存在又是一个新的证据。

DEHYDROXYL-VITAMIN E IN SEDIMENTARY ORGANIC MATTER IN SALT LAKE BASIN

The homologues of dehydroxyl-vitamin E (DHVE) and their isomers are determined in the light aromatics fraction of source rocks and crude oils in Qianjang depression, (Jianghan Salt Lake Basin, China ) which is the most complete distribution series of DHVE fornd in the geological body so far. DHVE come from VE by removing-OH group, and has three homologues: α, γ and δ types. According to the GC/ MS determination, it is found that every one of DHVE homologues has a pair of diastereomer-2R and 2S, These two configuration differ obversly in thermal stability because of their diference of the long side chain alkayl group in space arrangement. 2R-DHVE may be distroyed precedently under clay minerals catalysis and thermal stress effect, but 2S-DHVE is relatively more stable. DHVE exits mainly in immature-lower mature sedimentary organic matter (Ro0.6%), and there is higher content of 2R-DHVE in Ro 0.4% depth range. 2R-DHVE disappears and 2S-DHVE is predominent along with the increase of burial depth and the raise of temperature。 In the depth section, there is the stable alignment of δ γ α type or the transformed rela tion of α→γ→δ type among DHVE homoegues in source rocks and oils., δ / α, δ / γ and δ/ (α+γ) ratios show gradually increase trend in general change with depth of burial which indi cates mature degree of organic matter. Up to now, DHVE reported in geological body is mainly identified in gypseous salt sedimentary environment which is formed underdry scotching climate condition. Enough sunsb ing is more favourable to bio-photosynthesis, and so, both 1 lower livings and higher plants can synthesis abundent VE.Most sampls contain DHVE. They are gypseous, plastery, calcific mudstone with visiable plant trace, that locate at the Qianjiang depression margin in Jianghan Basin. Therefore it may be indicated that higher concentration of DHVE may be partly due to the contribution of conlinenbtal sources and the strong reduction nature and climate condition of saline environment that are more favourable to occuration preservation and transformation of VE and DHVE. The identification in sedimentary organic matter of DHVE shows that it is important composition of oil- generating matters. As a biomolecular fossil, DHVE may indicate sedimentary environment, mature degree of organic matter, and be another precursor of pristane and other isopenoid compounds. The appearance of DHVE in oils furnish more relia-bled evidence for existance of immature or lower mature oil, which has important theoretical value to further approching mechanism for organic matter to generate hydrocarbon.