川西南和川北地区震旦系顶不整合形成古环境研究  

Paleoenvironmental study on the formation of stratigraphic unconformities on the top of the Sinian in the Southwest and North Sichuan Basin

作　　者：马行陟[1,2] 姜林 鲁雪松[1,2] MA Xingzhi;JIANG Lin;LU Xuesong(PetroChina Research Institute of Exploration and Development,Beijing 100083,China;Key Laboratory of Basin Structure and Petroleum Accumulation,China National Petroleum Corporation,Beijing 100083,China)

机构地区：[1]中国石油勘探开发研究院,北京100083 [2]中国石油天然气集团有限公司盆地构造与油气成藏重点实验室,北京100083

出　　处：《世界石油工业》2025年第1期54-64,共11页World Petroleum Industry

基　　金：中国石油天然气股份有限公司科学研究与技术开发项目“全油气系统理论与非常规油气成藏机理”(2021DJ0101);中国石油天然气股份有限公司重大科技专项“叠合盆地中下组合油气成藏与保持机制研究”(2023ZZ02)。

摘　　要：四川盆地安岳气田震旦系灯影组气藏的形成受寒武系与震旦系地层不整合的控制,研究震旦系顶部不整合形成古环境对于天然气成储、成藏的影响具有重要意义。对四川盆地西部震旦系灯影组地质露头剖面进行勘查,选取川西南的张村和川北国华等剖面震旦系顶部的风化黏土层及其上覆和下伏地层岩石样品,开展岩石微量元素、主量元素以及同位素的分析,探讨桐湾运动时期寒武系与震旦系地层不整合形成的古环境。研究结果表明,川西南张村风化黏土层与川北国华风化黏土层的特征有着差异显著,前者是以氧化铝和二氧化硅为主的淡蓝色铝土风化壳,后者则是以氧化铝为主的褐黄色铁质风化壳。川西南张村风化黏土层钍铀比和铷锶比分别为3.61和26.45,川北国华风化黏土层的钍铀比和铷锶比分别为0.31和0.26,差别巨大,分别反映了潮湿和干旱的古环境。风化黏土层处均表现为明显的碳、氧同位素低负值,指示大气淡水成岩环境。在稀土元素含量和分布方面,发现存在负铕异常和负铥异常,且川西南剖面的负铕异常大于川北国华剖面,开放的氧化环境和湿润气候条件导致铕和铥损失,沉积岩具有负铕和负铥异常特征。由此推测川西南和川北地区震旦系顶不整合分别形成于雨量充沛湿热环境和雨量较少的炎热环境,也反映了川西南—川中地区的沉积环境更有利于震旦系灯影组岩溶储层的形成。The formation of Dengying Formation of Sinian gas reservoir in Anyue gas field is obviously controlled by unconformity in the Sichuan Basin.It is of great significance to study the formation and paleoenvironment of top unconformity of Sinian.This study explored the geological outcrop profile of Sinian Dengying Formation in Western Sichuan Basin.Samples from Zhangcun section in Southwest Sichuan and Guohua section in Northwest Sichuan are selected.The analysis of trace elements,major elements and isotopes in samples are carried out to explore the Paleoenvironment of the unconformity.Results show that there is an obvious weathered clay layer between Sinian and Cambrian strata in Zhangcun section.Zhangcun's sample is light blue bauxite weathering crust dominated by Al_(2)O_(3) and SiO_(2),while Guohua's sample is maroon iron weathering crust dominated by Fe2O3.In the trace element composition,the biggest difference between Southwest Zhangcun weathered clay layer and Northwest Sichuan Guohua weathered clay layer is that the Th/U ratio and Rb/Sr ratio of the former are 3.61 and 26.45,while the Th/U ratio and Rb/Sr ratio of the latter are 0.31 and 0.26.Which reflects the different formation environment.The samples of the two sections have low negative values of carbon and oxygen isotopes,indicating the diagenetic environment of atmospheric fresh water.The REE content show that there are negative europium anomaly and negative thulium anomaly.The negative europium anomaly of the sample from Zhangcun section is bigger than that of Guohua section in northwest Sichuan. Open oxidation environment and humid climate conditions lead to the loss of europium and thulium. Europium and thulium losses are also related to tectonic setting, sedimentary diagenetic age, hydrothermal action and source rock type. It is inferred that the Sinian top unconformity in southwest Sichuan and north Sichuan is formed in hot and humid environment with abundant rainfall and hot environment with low rainfall respectively. It also reflects that the se

关 键 词：四川盆地 震旦系 不整合 古环境 风化壳 

分 类 号：TE121.3[石油与天然气工程—油气勘探]