Geochemical characteristics of the Upper Triassic Tanzhuang Formation in the Jiyuan sag, southern North China Block: Implications for the depositional environment and organic matter enrichment

IF 2
Wei-Qing Liu , Lu-Qi Chen , Hua-Ying Song , Yu Qiao , Su-Ping Li , Wei Wu , Chang-Song Lin , Jian-Xin Yao
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Abstract

The organic-rich black oil shales of the Upper Triassic Tanzhuang Formation represent important source rocks within the southern North China Block. However, the mechanism of organic matter enrichment remains unclear. Additionally, the climate evolution and driving factors of the Late Triassic in the southern North China Block are still unknown. This study explores the paleoclimate, paleohydrology, paleoenvironment, and organic matter accumulation mechanism of the section containing the Tanzhuang Formation in the Jiyuan area, utilizing its geochemical characteristics as a basis for analysis. The oil shales in the Tanzhuang Formation can be categorized into two types: organic-rich shales (with total organic carbon (TOC) contents varying between 1.61 % and 4.17 %) and organic-lean shales (with TOC contents varying between 0.29 % and 1.44 %). The paleoclimatic indices, the chemical alteration index (CIA) and the C value, suggest that the organic-lean shales were deposited under warm and semihumid paleoclimatic conditions, whereas the organic-rich black shales formed under warm and humid climate conditions. The positive correlation between the Hg/Al ratios and C values suggests that volcanic activity was the cause of paleoclimatic changes, which may have been associated with global climatic events that occurred during the Late Triassic Carnian period. The oxidation–reduction indices, V, U, and Mo contents and the Mo–U correlation diagram indicate that dysoxic conditions prevailed in the Jiyuan Basin during the deposition of the oil shales in the Tanzhuang Formation. The primary productivity indices (e.g., CuEF and ZnEF) suggest that higher primary productivity was observed during the deposition of the organic-rich shales. The positive correlations between the TOC contents and the CuEF and C values indicate that the enrichment of organic matter in the oil shales of the Tanzhuang Formation was influenced primarily by primary productivity and a warm and humid climate. The sedimentary model indicates that the elevated primary productivity may have originated from a warm and humid climate coupled with intense weathering caused by volcanic activity during the Late Triassic period, which formed a productivity model characterized by the accumulation of organic matter in the oil shales of the Tanzhuang Formation.
华北地块南部济塬凹陷上三叠统郯庄组地球化学特征:沉积环境与有机质富集意义
上三叠统郯庄组富有机质黑色油页岩是华北地块南部重要的烃源岩。然而,有机质富集的机制尚不清楚。此外,华北地块南部晚三叠世的气候演化及其驱动因素尚不清楚。本研究以济源地区滩庄组剖面的地球化学特征为基础,探讨了该剖面的古气候、古水文、古环境及有机质成藏机制。油页岩可分为富有机质页岩(总有机碳含量在1.61% ~ 4.17%之间)和贫有机质页岩(总有机碳含量在0.29% ~ 1.44%之间)。古气候指标、化学蚀变指数(CIA)和C值表明,贫有机质页岩形成于温暖半湿润的古气候条件下,富有机质黑色页岩形成于温暖湿润的古气候条件下。Hg/Al比值与C值的正相关表明火山活动是古气候变化的原因,这可能与晚三叠世卡尼期发生的全球气候事件有关。氧化还原指数、V、U、Mo含量及Mo - U对比图表明,济源盆地在滩庄组油页岩沉积时期处于缺氧状态。初级生产力指数(如CuEF和ZnEF)表明,富有机质页岩在沉积时期具有较高的初级生产力。TOC含量与CuEF和C值呈正相关,表明油页岩有机质富集主要受初级生产力和温暖湿润气候的影响。沉积模式表明,初产力的提高可能源于温暖湿润的气候,加上晚三叠世火山活动引起的强烈风化作用,形成了以油页岩有机质富集为特征的生产力模式。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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