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Interstitial Light Hydrocarbon Gases in Jumbo Piston Cores Offshore Indonesia: Thermogenic or Biogenic?

机译:印尼近海巨型活塞芯中的间隙性轻质烃类气体:是热成因还是生物成因?

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Interstitial light hydrocarbon gases were measured to 12 m below seabed in two Jumbo piston cores acquired in deepwatersediments offshore Indonesia. Determinations were made for dissolved methane, ethene, ethane, propene, propane, isobutane,n-butane, iso-pentane, and n-pentane, as well as for carbon dioxide. Stable carbon isotopic ratios of methane andethane were also measured. Such gas measurements are typically performed in deepwaters around the world as elements ofsurface geochemical exploration programs for the purpose of distinguishing biogenic from thermogenic sources in seepgases. Various gas source models have been developed in the literature to aid in accurate interpretation for systems that havebeen biodegraded, fractionated, and/or mixed during migration. In these models, assumptions are made about the ranges ofcomposition of the end-member gas types and maturities. The compositional ranges of the thermogenic and biogenic endmembers have been empirically derived from a large database of drilled-hole gas data and various theoretical considerations.In addition to this literature base, tens of thousands of near-surface marine sediment cores have been acquired worldwide andanalyzed for interstitial gases on a proprietary SGE basis over the last 35-40 years. Interpretation of these results has helpedto fine-tune the accepted end-member compositions of the source models. However, essentially all of the SGE sediment coreshave reached a maximum 5 m below the seabed. Our acquisition and analysis of cores down to 12 m has revealedinformation about gas compositions not apparent from the former SGE coring efforts. In particular, ethane concentrations arein the accepted thermogenic range, but their stable carbon isotopic compositions are not. Near-surface gases formerlyinterpreted to have an unambiguous thermogenic component are here shown to be purely biogenic. Our conclusions maychange the boundaries of the biogenic end member used for the indication of thermogenic gas traces in near-surfacesediments.
机译:在深水中采集的两个巨型活塞芯中,海床下的间隙轻质烃类气体被测量到海底以下12 m 印度尼西亚近海的沉积物。确定了溶解的甲烷,乙烯,乙烷,丙烯,丙烷,异丁烷, 正丁烷,异戊烷和正戊烷,以及二氧化碳。甲烷和甲烷的稳定碳同位素比 还测量了乙烷。这种气体测量通常是在世界各地的深水中进行的, 地表地球化学勘探计划,目的是区分渗流中的生物成因与热成因 气体。文献中已经开发了各种气体源模型,以帮助对具有以下特征的系统进行准确的解释: 在迁移过程中被生物降解,分馏和/或混合。在这些模型中,对 最终成员气体类型和成熟度的组成。热源端和生物源端的组成范围 这些成员是根据经验从大型的钻孔气体数据数据库和各种理论考虑中得出的。 除了这个文献基础之外,全世界还获得了数万个近地表海洋沉积物核,并且 在过去的35-40年中,使用专有的SGE对间隙气体进行了分析。这些结果的解释有助于 以微调源模型的可接受的最终成员组成。但是,基本上所有的SGE沉积物核 到达海床以下最多5 m。我们对低至12 m的岩心的采集和分析表明 从以前的SGE取芯工作中看不到有关气体成分的信息。尤其是乙烷浓度为 在可接受的产热范围内,但其稳定的碳同位素组成却没有。近地表气体 被解释为具有明确的生热成分的物质在此显示为纯生物成因的。我们的结论可能 更改用于指示近地表中的热气痕迹的生源末端成员的边界 沉积物。

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