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川南五峰组—龙马溪组有机质富集规律 ——基于旋回地层学的研究

作    者:肖 强,张廷山,张 喜,李红佼,雍锦杰,刘宇龙,李潇雨
单    位:西南石油大学地球科学与技术学院
基金项目:本文受国家科技重大专项课题“多场耦合筇竹寺组页岩气资源富集区优选”资助
摘    要:
基于钻井、测井资料,应用旋回地层学、地球化学等方法,探讨天文轨道周期驱动下的海平面变化对川南地 区上奥陶统五峰组—下志留统龙马溪组页岩有机质聚集的影响。应用川南地区Y8井GR数据序列,对五峰组—龙马 溪组开展旋回地层学研究,识别了记录在沉积物中的斜率长周期(1.2 Ma)、长偏心率周期(405 ka)及短偏心率周期 (100 ka)信号,并建立了该地质历史时期浮动的天文时间标尺。地球化学分析表明,川南地区五峰组—龙马溪组底 部TOC较高,平均达3.16%,向上含量变低并趋于稳定。根据有机质碳同位素及微量元素指标(U/Th、V/Cr、Ni/Co、V/ (V+Ni)),恢复了晚奥陶世—早志留世海平面变化及古海洋沉积环境。全球海平面升降变化趋势与斜率长周期(1.2 Ma) 具有较好的相关性。川南地区五峰组—龙马溪组有机质聚集与斜率长周期驱动下的海平面升降变化及水体的氧化还原条件密切相关:川南地区凯迪早期、赫南特晚期、鲁丹早期海平面上升,半深海—深海环境有利于有机质的形成 和保存;观音桥层沉积期海平面下降,浅海环境不利于有机质的形成和保存。
关键词:天文轨道周期;海平面变化;古环境;有机质聚集;五峰组;龙马溪组;川南

Organic matter enrichment in Wufeng Formation-Longmaxi Formation in southern Sichuan: based on cyclostratigraphy

Author's Name: XIAO Qiang, ZHANG Tingshan, ZHANG Xi, LI Hongjiao, YONG Jinjie, LIU Yulong, LI Xiaoyu
Institution: 
Abstract:
Based on drilling and logging data, the law of organic matter accumulation in shale of Wufeng Formation and Longmaxi Formation in southern Sichuan was studied with cyclostratigraphic and geochemical methods. According to the GR series of Well Y8, the cyclostratigraphy of the Late Ordovician Wufeng Formation-Early Silurian Longmaxi Formation was studied. The long slope period (1.2 Ma), long eccentricity period (405 ka), and short eccentricity period (100 ka) signals recorded in sediments were identified, and the astronomical time scales floating in this geological history period were established. Geochemical analysis shows that the total organic carbon content (TOC) at the bottom of the Wufeng Formation-Longmaxi Formation is relatively high, with an average content of 3.16%, and becomes lower and tends to be stable upward. Combining organic carbon isotopes (δ13Corg) and trace element ratios such as U/Th, V/Cr, Ni/Co, V/(V+Ni), the sea level change and paleo-ocean sedimentary environment in Late Ordovician-Early Silurian were restored in southern Sichuan. The long slope period (1.2 Ma) has a good correlation with the trend of global sea level change in Late Ordovician-Early Silurian. The accumulation of organic matter in Wufeng Formation-Longmaxi Formation in southern Sichuan is closely related to the long-term fluctuation of sea level driven by the long slope period and the redox condition of water body: the sea level rises in the early Katian, late Hirnantian, and early Rhuddanian in southern Sichuan, and the semi deep-deep sea environment is favorable for the formation and preservation of organic matter; during the deposition of Guanyinqiao carbonate strata, the sea level dropped, and the shallow sea environment was not conducive to the formation and preservation of organic matter.
Keywords: astronomical orbital period; sea-level change; paleo-environment; organic matter accumulation; Wufeng Formation; Longmaxi Formation; southern Sichua
投稿时间:2020-08-26  
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