Geochemical characteristics in the Longmaxi Formation (Early Silurian) of South China: Implications for organic matter accumulation
Geochemical characteristics in the Longmaxi Formation (Early Silurian) of South China: Implications for organic matter accumulation
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DOI：
10.1016/j.marpetgeo.2015.04.016
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发表时间：
2015-08
影响因子：
4.2
通讯作者：
Detain Yan;Hua Wang;Q. Fu;Zhonghong Chen;Jinyou He;Zhan Gao
中科院分区：
文献类型：
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作者：
Detain Yan;Hua Wang;Q. Fu;Zhonghong Chen;Jinyou He;Zhan Gao
扬子地台早志留世龙马溪组富含有机质，是华南地区主要烃源岩之一。为了探讨有机质成藏机理，本文采用多种地球化学指标，包括氧化还原参数（S/C和微量元素比值）、生产力指标（P和Ba含量）和碎屑岩侵入指标（Ti/Al比值）。龙马溪沉积物TOC含量较高（3.00- 10.85%，平均值），5.63硫铁矿硫含量低（平均0.42- 1.14%）。0.59%）、高磷（0.02- 0.44%，平均值）、低磷（0.02%-0.44%，平均值）、低磷（0.02%-0.44%，平均值）。0.12%）和钡含量（576.65-2542.43 ppm，平均值. 1592.17 ppm）。计算的S/C、Th/U、Ni/Co、V/Cr和V/（V + Ni）比值为0.05-0.24（平均值）。0.12），0.23-9.86（平均值）2.30）、2.65-46.24（平均15.46），0.27-14.42（平均3.75）和0.36-0.96（平均值）。0.75）。S/C和微量元素比值以及黄铁矿形态表明，龙马溪段沉积过程中普遍处于缺氧/缺氧环境，这主要是冈瓦纳冰川融化后全球海侵造成的。生产力代用指标表明，龙马溪沉积物中有机质含量较高，主要沉积在中-高初级生产力水体中。一致的Ti/Al比表明碎屑供应具有相当均匀的性质。地球化学数据对有机质的聚集和相关的海洋环境提供了很好的约束。缺氧条件和相对较高的生产力可能是龙马溪组富有机质沉积物堆积的原因。
The organic-rich Early Silurian sediments (Longmaxi Formation) on the Yangtze platform are considered to be one of the main source rocks in South China. In order to investigate the mechanism of organic accumulation, multiple geochemical proxies, including redox parameters (S/C and trace-element ratios), productivity indices (P and Ba contents) and clastic influx indicator (Ti/Al ratios), are presented here from the Hehua section, Yichang, Hubei province. The Longmaxi sediments have high TOC contents (3.00–10.85 %, avg. 5.63 %), low Pyrite sulfur contents (0.42–1.14 %, avg. 0.59 %), high P (0.02–0.44 %, avg. 0.12 %) and Ba contents (576.65–2542.43 ppm, avg. 1592.17 ppm). Calculated S/C, Th/U, Ni/Co, V/Cr and V/(V + Ni) ratios are 0.05–0.24 (avg. 0.12), 0.23–9.86 (avg. 2.30), 2.65–46.24 (avg. 15.46), 0.27–14.42 (avg. 3.75) and 0.36–0.96 (avg. 0.75), respectively. S/C and trace–element ratios, together with pyrite morphology, suggest dysoxic/anoxic conditions prevailed during deposition of the Longmaxi intervals, which was mainly caused by a worldwide marine transgression after the melting of Gondwana glaciation. Productivity proxies indicate that the organic-rich Longmaxi sediments were deposited in moderate to high primary productivity water columns. The consistent Ti/Al ratios suggest a rather homogeneous nature for the detrital supply. Geochemical data provide a good constraint on the accumulation of organic matter and relevant oceanic environment. Anoxic conditions, together with relatively high productivity, were likely responsible for the accumulation of organic-rich sediments during the Longmaxi interval.