Extensive accumulation of organic matter in the Late Permian Dalong Formation, Western Hubei Trough, Southern China

IF 5.6 2区工程技术 Q2 ENERGY & FUELS

International Journal of Coal Geology Pub Date : 2025-02-19 DOI:10.1016/j.coal.2025.104727

Lulu Xu , Saipeng Huang , Dameng Liu , Zhiwei Liao , Kui Wu , Miankun Chen , Xianghui Zhou , Yanlin Zhang , Bei Liu , Minglong Li

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Abstract

The black shale in the Upper Permian Dalong Formation in the Western Hubei (WH) Trough is characterized by its extreme organic matter accumulation (OMA), and its vertical heterogeneity necessitates more nuanced research. The characteristics of the lithology, conodont, total organic carbon (TOC), mineral composition, silica origin, palaeoenvironmental evolution, and the OMA mechanisms of the Dalong Formation were systematically studied. The results indicate that the Dalong Formation can be subdivided into six distinct members, primarily composed of argillaceous siliceous rocks, siliceous dolomite, siliceous shales, calcareous siliceous rocks, and siliceous limestone, respectively. The silica in the organic-rich shale is predominantly of mixed biogenic and terrigenous origin, with localized contributions from hydrothermal sources. The organic-rich shale (ORS) is primarily distributing below the Wuchiapingian and Changhsingian boundary (WCB), which is deposited under moderate terrigenous input, semi-humid to semi-arid climate, euxinic conditions in a semi-open to the semi-restricted basin, and high palaeoproductivity caused by the upwelling setting and high-frequency volcanic ash layers. The WCB is characterized by the arid climate, oxic conditions in a strongly restricted basin, and low palaeoproductivity. Palaeoproductivity is identified as the principal controlling factor for the OMA. Additionally, the hydrothermal silica is commonly deposited under euxinic conditions, which are conducive to the preservation of organic matter. Evidence suggesting that thicker volcanic ash layer during the Changhsingian Stage may be one of the reasons for the mass extinction in the Late Permian. The north-central of the WH Trough exhibits a higher TOC content (> 4 %), overmature source rock with the vitrinite reflectance (R_o) ranging from 2 % to 3 %, and an euxinic conditions, suggesting more beneficial to shale gas enrichment.

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鄂西海槽晚二叠世大龙组有机质广泛富集

鄂西坳陷上二叠统大龙组黑色页岩具有有机质极端聚集（OMA）特征，其垂向非均质性需要进一步深入研究。系统研究了大龙组的岩性特征、牙形石特征、总有机碳特征、矿物组成特征、硅质成因特征、古环境演化特征及OMA机制。结果表明，大龙组可划分为6段，主要由泥质硅质岩、硅质白云岩、硅质页岩、钙质硅质岩和硅质灰岩组成。富有机质页岩中的二氧化硅主要为生物源和陆源混合成因，局部有热液源的贡献。富有机质页岩（ORS）主要分布在五家坪—长兴界线（WCB）以下，形成于陆源输入适中、半湿润—半干旱气候、半开放—半封闭盆地的缺氧条件下，上升流背景和高频火山灰层形成的高古生产力条件下。西孟加拉湾气候干旱，盆地缺氧，古生产力低。古生产力是OMA的主要控制因素。此外，热液二氧化硅通常在缺氧条件下沉积，有利于有机质的保存。有证据表明，长兴期较厚的火山灰层可能是导致晚二叠世大灭绝的原因之一。WH海槽中北部TOC含量较高(>；镜质组反射率（Ro）在2% ~ 3%之间，烃源岩过成熟，为富氧条件，更有利于页岩气的富集。

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来源期刊

International Journal of Coal Geology 工程技术-地球科学综合

CiteScore

11.00

自引率

14.30%

发文量

145

审稿时长

38 days

期刊介绍： The International Journal of Coal Geology deals with fundamental and applied aspects of the geology and petrology of coal, oil/gas source rocks and shale gas resources. The journal aims to advance the exploration, exploitation and utilization of these resources, and to stimulate environmental awareness as well as advancement of engineering for effective resource management.