Enrichment mechanism of organic matter and silicon in lower Cambrian shale of the Yangtze Platform

• Published in: Palaeogeography, palaeoclimatology, palaeoecology Vol. 648; p. 112282
• Main Authors: Lin, Donglin, Xi, Zhaodong, Tang, Shuheng, Lash, Gary G., Li, Jin, Gou, Qiyang, Zhang, Ke, Mei, Xiaofan, Wang, Kaifeng
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.08.2024
• Subjects: Niutitang Formation; Organic matter enrichment; Shelf areas; Silica source; Upper Yangtze Platform; Organic matter enrichment; Silica source; Shelf areas; Upper Yangtze Platform; Niutitang Formation
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2024.112282

Early Cambrian time witnessed accumulation of high-quality organic-rich siliceous shale deposits that comprise an especially promising shale gas exploration target, especially in China. The present study of the Cambrian Niutitang Formation of the shelf area of the Upper Yangtze Platform utilizes mineralogical and elemental geochemical data to aide in the paleoenvironment reconstruction of these organic-rich deposits. We are especially interested in elucidating organic carbon and silicon enrichment mechanisms of the Niutitang Formation that will benefit shale gas exploration and development of these deposits. The Niutitang Formation can be subdivided into three intervals based on lithology, gamma ray (GR) signature, and TOC abundance. Enriched TOC (average = 6.7%) and nano-size authigenic microcrystalline quartz (Qn) contents of Interval I deposits likely reflect deposition in an environment that experienced persistent euxinic and elevated organic matter delivery associated with enhanced paleoproductivity driven by hydrothermal activity. Interval II shale is interpreted to have accumulated under euxinic-ferruginous conditions that experienced the effects of robust paleoproductivity and diminished terrigenous input related to persistently warm, humid climatic conditions. Enriched TOC (average = 4.9%) and moderate microcrystalline quartz content of these deposits were likely the result of redox conditions and elevated paleoproductivity. Interval III strata appears to have accumulated under oxygenated bottom conditions that experienced moderate paleoproductivity, brackish water and elevated terrigenous detritus input driven by the establishment of cold, dry climatic conditions. The combined results of these conditions are diminished TOC content (average = 0.7%) and enrichment of the sediment in terrestrial quartz. The elevated content of authigenic quartz appears to have diminished the reservoir capacity of Niutitang Formation shale. Interval II organic-rich siliceous shale deposits of Upper Yangtze Platform shelf areas, which have the comparable authigenic microcrystalline quartz content, reservoir performance, and greater organic matter abundance as the rift trough, appear to comprise the stratigraphic horizon with the greatest exploration and development potential. Results of the present study offer theoretical guidance for future shale gas exploration and development efforts in geologically similar regions. •The environment during the Niutitang shale sedimentation period are reconstructed.•Mechanism of organic matter and silica enrichment of the Niutitang shale are revealed.•Authigenic quartz significantly affects the reservoir capacity of the Niutitang shale.