羌塘盆地东部三叠系阿堵拉组烃源岩古沉积环境的地球化学证据

Geochemical evidence of paleo-depositional environment of Triassic Adula Formation source rocks of eastern Qiangtang Basin

刘栩 刘中戎 庄新兵 范志伟 马泽良 彭金宁 李风勋 李吉鹏 李兴强

LIU Xu LIU Zhongrong ZHUANG Xinbing FAN Zhiwei MA Zeliang PENG Jinning LI Fengxun LI Jipeng LI Xingqiang

1. 中国石化油气成藏重点实验室, 江苏 无锡 214126; 2. 中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126; 3. 中国石化 勘探分公司, 成都 610041

1. Key Laboratory of Hydrocarbon Accumulation, SINOPEC, Wuxi, Jiangsu 214126, China; 2. Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China; 3. SINOPEC Exploration Company, Chengdu, Sichuan 610041, China

上三叠统阿堵拉组泥岩是羌塘盆地重要烃源岩系之一，目前对其古沉积环境的认识存在较大争议。通过对羌塘盆地东部雀莫错地区鄂尔托陇巴剖面阿堵拉组开展岩石学、有机地球化学和元素地球化学分析等系统研究，探讨阿堵拉组烃源岩古沉积环境及其对烃源岩发育的影响。阿堵拉组泥岩总有机碳(TOC)含量为0.27%~3.46%，平均为1.60%，总体为好烃源岩，局部发育优质烃源岩；阿堵拉组下段陆棚相泥岩形成于海平面上升时期，水体较深且贫氧，古气候为半干燥—半湿润气候，化学风化程度中等，陆源输入较低，水体盐度较高；上段泥岩沉积期处于盆地萎缩消亡阶段，沉积环境逐渐由陆棚相转变为三角洲相，水体较浅且富氧，经历了干燥—半干燥—半湿润的古气候变化，陆源输入相应增多，为咸水—半咸水环境，受到淡水输入的影响。阿堵拉组的源岩为长英质火山岩，源区构造背景以大陆岛弧为主，可能来自早—中三叠世金沙江缝合带岛弧源区。阿堵拉组下段陆棚相泥岩TOC含量与氧化还原条件指标具有较好的正相关性，表明烃源岩发育主要受到海平面上升时贫氧水体控制；上段陆棚—三角洲相泥岩TOC含量与古环境参数无明显相关性，TOC含量大于2%的泥岩沉积期具有较高陆源输入和相对湿润的古气候，综合分析认为烃源岩发育受到古气候、陆源输入等多种因素综合影响。

The mudstone within the Upper Triassic Adula Formation constitutes a crucial hydrocarbon source rock reservoir in the Qiangtang Basin, yet there is considerable debate regarding its paleo-depositional environment. Through systematic studies, including petrology, organic geochemistry, and elemental geochemistry analyses of the Adula Formation at the Eertuolongba section in the Quemocuo area of the eastern Qiangtang Basin, this study investigated the paleo-depositional environment of the Adula Formation source rocks and its impact on hydrocarbonsource rock development. The total organic carbon (TOC) content of the Adula Formation mudstone ranges from 0.27% to 3.46%, with an average of 1.60%, indicating overall favorable source rocks with locally deve-loped high-quality source rocks. The shelf facies mudstone in the lower section of the Adula Formation was formed during a phase of sea-level rise, characterized by deeper, oxygen-poor water, a semi-arid to semi-humid paleoclimate, moderate chemical weathering, minimal terrigenous input, and higher salinity. The deposition of the upper section occurred during a phase of basin contraction and demise, suggesting a transition from shelf facies to delta facies. This period was marked by relatively shallower, oxygen-rich water and a shift from arid to semi-arid to semi-humid paleoclimate, with increased terrigenous input and a saline to semi-saline water environment influenced by freshwater input. The source rocks of the Adula Formation are felsic volcanic rocks, primarily from a continental island arc tectonic setting, likely sourced from the island arc source domain in the Jinsha River suture zone during the Early to Middle Triassic. In the lower section of the Adula Formation, the TOC content of shelf facies mudstone shows a robust positive correlation with redox condition indicators, suggesting that source rock development was mainly controlled by oxygen-poor water conditions during sea-level rise period. In contrast, no significant correlation was observed between TOC content and paleo-environmental parameters in the upper shelf delta facies mudstones. Mudstones with TOC content greater than 2% were likely deposited during periods of high terrigenous input and relatively humid paleoclimate, indicating that source rock development was influenced by multiple factors such as paleoclimate and terrigenous input.

中国石化科技攻关项目(P22197、P22198)资助。

https://doi.org/10.11781/sysydz202403601