Geochemical characteristics of Late Permian sediments in the Dalong Formation of the Shangsi Section, Northwest Sichuan Basin in South China: Implications for organic carbon-rich siliceous rocks formation

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• 作者：Hui Chen^a ; Xinong Xie^a ; ^{xnxie@cug.edu.cn} ; Chaoyong Hu^b ; Junhua Huang^b ; Hongjing Li^a
• 关键词：Hydrothermal contribution ; Paleo-depositional environment ; TOC content accumulation
• 刊名：Journal of Geochemical Exploration
• 出版年：2012
• 出版时间：January 2012
• 年：2012
• 卷：112
• 期：Complete
• 页码：35-53
• 全文大小：3135 K

文摘

The major processes responsible for the interplay of hydrothermal influence and paleo-depositional environments (paleoproductivity and plaeoredox condition) on the accumulation of organic matters can be better understood by integrating lithological and geochemical characteristics of samples from the well exposed Late Permian sediments in the Dalong Formation of the Shangsi Section, Northwest Sichuan Basin, South China: 1) The content of total organic carbon (TOC) ranging from 0.16 % to 14.6 % is closely related with the host lithology and high TOC contents prone to occur in intervals of siliceous rocks, dark shales, and laminated limestones that developed in deepwater intra-basin environments; 2) Non-detrital component elements and ratios (after Ti-normalized), e.g. Cu_xs, V_xs / (V_xs + Ni_xs), for all samples and their correlations with TOC contents imprint the control of paleoproductivity level and paleoredox condition on the accumulation of TOC contents; 3) Characteristics such as original contents of Al, Fe, Mn, Th, U and their non-detrital origin values, non-biogenic contribution values (TiO₂-normalized) of various elements, and the North America Shale Composite (NASC)-normalized Rare Earth Element (REE) Patterns of chert and shale samples are analyzed and compared to that of world average shales, classic hydrothermal and biogenic cherts, indicating hydrothermal contribution to siliceous rocks formation in the Dalong Formation of the Shangsi Section. Together with the discovery of volcanic ashes and bentonites in the Dalong Formation of the Shangsi Section, a new model has been proposed to explain the relationships of the hydrothermal activities and the organic matter accumulation process in the siliceous rocks in the Dalong Formation of the Shangsi Section: Hydrothermal contribution could cause a bio-thriving in surface water by providing nutrient elements and lead to a high primary productivity; With the organic matters sinking down, the anaerobic and anoxic conditions would control the organic matter accumulation during deposition and early diagenesis stage, which can imprint the organic carbon-rich siliceous rocks formation and the origin of high quality marine source rocks for hydrocarbon.