藏北羌塘盆地胜利河油页岩干酪根特征及碳同位素指示意义

Characteristics of Kerogens and Their Carbon Isotope Implications for the Shengli River Oil Shale in Qiangtang Basin, Northern Tibet

胜利河油页岩位于北羌塘盆地南部,走向长超过34km,宽9km。笔者对该油页岩各岩系干酪根进行了分离、镜鉴、元素分析和碳同位素分析,结果表明,该油页岩干酪根为Ⅱ型干酪根,油页岩中干酪根含量较高,介于15.79%~20.37%,具有富氢少氧的特征,其H/C和O/C比率分别为1.11~1.19和0.08~0.25,为胜利河地区非常好的烃源岩。油页岩层干酪根13C相对富集,具有相对较高的δ13CPDB值(-20.79‰^-21.78‰),与胜利河地区油页岩母源为较单一的藻类有关。藻类的大量繁殖造成了该类生物死亡埋藏速率远大于氧化速率,在还原环境下大部分藻类还未被氧化就被埋藏,从而保留了原始藻类略富13C的特征。胜利河油页岩的空间展布以及规模明显受古泻湖环境的控制。

The Shengli River oil shale in the southern part of northern Qiangtang depression within northern Tibet plateau has a EW-extending length of more than 34 km and a width of 9 m in the north-south direction. Such oil shale is of great importance in the assessment of oil and gas resources in Qiangtang basin. The oil shale has high kerogen contents and H/C ratios （1.11-1.19） and low O/C values （0.08-0.25）, implying a fairly ideal source rock. The oil shale and interbedded marl from the Shengli River area in Qiangtang basin have a remarkably heavy Ckerogen isotopic composition, ranging in δ^13 values of the bulk organic matter from -20.79‰ to -21.78‰. The enrichment of ^13C in the Shengli River oil shale can be attributed to a combination of the high growth rate and the sedimentary environment, with the paleo-lagoon environment obviously controlling the spatial distribution and size of oil shale.