珠江口盆地珠三坳陷文昌组有机质碳同位素异常成因  

Origin of the abnormal carbon isotopic in organic matter of the Wenchang Formation,Zhu Ⅲ sub-basin,Pearl River Mouth basin

作　　者：何智同 尹相东 陈世加[1,2,3] 雷明珠 朱必清 刘杨 赵荣茜[1,2,3] 刘宇阳 HE Zhitong;YIN Xiangdong;CHEN Shijia;LEI Mingzhu;ZHU Biqing;LIU Yang;ZHAO Rongqian;LIU Yuyang(State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu,Sichuan 610500,China;Natural Gas Geology Key Laboratory of Sichuan Province,Southwest Petroleum University,Chengdu,Sichuan 610500,China;School of Geoscience and Technology,Southwest Petroleum University,Chengdu,Sichuan 610500,China;Hainan Branch of China National Offshore Oil Corporation Ltd,Haikou,Hainan 570311,China)

机构地区：[1]油气藏地质及开发工程国家重点实验室,西南石油大学,四川成都610500 [2]天然气地质四川省重点实验室,西南石油大学,四川成都610500 [3]西南石油大学,地球科学与技术学院,四川成都610500 [4]中海石油(中国)有限公司海南分公司,海南海口570311

出　　处：《地质学报》2024年第1期266-279,共14页Acta Geologica Sinica

基　　金：国家自然科学基金项目(编号42002176,41872165,42072185)资助的成果。

摘　　要：部分中国近海湖盆和大西洋裂谷盆地发现了腐泥型有机质碳同位素偏重的现象,并伴随异常高总有机碳含量和生烃潜力。本文依据泥岩有机碳测试、孢粉分析、主微量元素、泥岩和原油碳同位素及饱和烃色质色谱资料,并结合现代湖泊盘星藻发育特征,从有机质来源、古环境条件和有机质保存改造三个方面探讨了珠江口盆地珠三坳陷古近系文昌组碳同位素正偏移的成因机制。珠三坳陷文昌组碳同位素异常与气候、古生产力、古水深和藻类勃发等古环境因素有关。然而,从三级层序尺度看,古水深可能是一个不可忽视的重要因素:指示水深的Rb/K比值随深度加深而增加,与碳同位素和TOC含量变化趋势一致。同时现代湖泊研究也证实了盘星藻分布于不同水深范围,因此“深水型盘星藻”的繁盛很可能是珠三坳陷文昌组二段烃源岩碳同位素偏重的根本原因。The phenomenon of sapropelic organic matter with high carbon isotope values,coupled with an abnormally high abundance of total organic carbon and hydrocarbon potential,has been identified in certain offshore lacustrine basins in China and rifting basins in the Atlantic.In this paper,we aim to investigate the mechanism behind the positive deviation of carbon isotope values within the organic matter of the Paleogene Wenchang Formation.Our research approach involves analyzing the organic carbon content,pollen,major and trace elements,as well as the carbon isotope and gas chromatograph-mass spectroscopy(GC-MS)of saturated hydrocarbon in both source rocks and crude oils.We also consider the characteristics of pediastrum in modern lakes to gain insights into the sources of organic matter,ancient environmental conditions,and the preservation and transformation of organic matter.The carbon isotope anomaly observed in the Wenchang Formation appears to be closely linked to various ancient environmental factors,including paleoclimate,paleoproductivity,and flourishing algae in the Zhu Ⅲ sub-basin.However,paleobathymetry may be a non-negligible significant factor on the scale of the third-order sequence.The Rb/K ratio,indicating the water depth,exhibits an increasing trend with depth,which coincides with the variations observed in carbon isotope values and TOC content.Additionally,modern lake investigations confirm the distribution of pediastrum across different water depths.Therefore,the bloom of“deep water type of pediastrum”is considered a key factor contributing to the high carbon isotope values observed in source rocks within the 2nd Member of the Wenchang Formation in the Zhu Ⅲ sub-basin.

关 键 词：腐泥型有机质 碳同位素 古环境 盘星藻 珠三坳陷 珠江口盆地 

分 类 号：P618.13[天文地球—矿床学]