Isoprenoid and Straight-chmn Alcohols in the Green River Formation,Wyoming
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摘要: 研究了美国绿河盆地的23个未成熟的露头油页岩样品,其中 13个样品取自Laney组,为半温湿半干燥气候下沉积于较浅的封闭水体的盐湖中心,含有丰富的有机质;另外 10个样品取自LumanTongue组,为潮湿气候下沉积于近岸的水体开放的淡水环境,其有机质含量较低。所有样品均富含从C11至C20 的同分异构体丰富的饱和类异戊二烯醇类化合物。此外还检出了一整套直链一元仲醇同系物,其碳数从 10至 33,而羟基可在任何理论上可能的碳位上。伯醇含量较低。研究结果表明,绿河油页岩中的有机质分别在沉积过程中和被抬升之后遭受了两次微生物降解。除伯醇的分布有生物来源特征外,其余的开链醇化合物是在绿河层系抬升至地表后微生物对其中烃类化合物降解的产物。文中将绿河油页岩有机质中异常高的氧指数归因于微生物降解,并探讨了其开链醇化合物的分布与物源、沉积环境及微生物降解程度的相关性。盐湖相Laney组的直链醇以低碳数组分为主,反映其有机质以菌藻为主的物源,与干燥的古气候相一致;淡水相LumanTongue组则以高碳数组分为主,有着明显优势的高等植物来源,与其潮湿的古气候相吻合。在沉积过程中,淡水相的LumanTongue组中的有机质遭受了比盐湖相的Laney组中的有机质更强的微生物降解,这意味着盐湖环境。Abstract: In this paper ocurrence and distribution patterns are presented of isoprenoid and straight chain alcohols in twenty three exposed rocks from the Eocene Green River Formation at the Trail Dugway and the Hiawatha Creek sections. The Trail Dugway section of the Laney Shale Member was deposited in the center of a shallow, hydrologically closed, alkaline to highly saline lake under semi humid to semi arid climatic conditions. This sediment contains alginite rich organic matter in high concentrations. The Hiawatha Creek section of the Luman Tongue Member, representing the lake center, shoreline and lake plain facies, was accumulated in a hydrologically open freshwater lake under humid climatic conditions. Both sections are located in the Washikie Basin, Wyoming, USA. Abundant isoprenoid alcohols with carbon number from 11 to 20 were dectected to be of diversity of isomers in all samples. Straight chain alcohols range from 10 to 33 with the hydroxyl group at every theoretically possible positions. The concenration of primary alcohols is low. The results show that the organic matter of the Green River Formation suffered two times from biodegradation, during the sedimentation and after the uplift, respectively. While primary alcohols show a dominant biogenic origin, the mid chain alcohols evidence the second biodegradation of alkanes after the sediments were uplifted to the present position. The notably high Oxygen Indices of the Green River Oil Shale is attributed to the second biodegradation. The distribution patterns of mid chain alcohols are related to the input of organic materials, sedimentary environments, and the degree of the first biodegradation. The mid chain alcohols of Laney Shale sediments are dominated by short chain components, which is consistent with the semi arid climate with insignificant terrestrial run off. On the other hand, a significant proportion of long chain constituents in the Luman Tongue section indicates that abundant higher plant material was swept into the lake during times of more humid climatic conditions. Data reveal that the saline sedimentary environment of Laney Shale is more favourable for preservation of organic matter from biodegradation than that of the freshwater Luman Tongue.
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