潜江凹陷古近系潜江组盐间泥岩地球化学特征及地质意义  

Geochemical Characteristics and Their Geological Significance of Intrasalt Mudstones from the Paleogene Qianjiang Formation in the Qianjiang Graben,Jianghan Basin,China

作　　者：徐崇凯 刘池洋[1] 郭佩[1] 黎茂稳[2] 黄雷[1] 赵岩[1] 潘银华 张益银 XU ChongKai;LIU ChiYang;GUO Pei;LI MaoWen;HUANG Lei;ZHAO Yan;PAN YinHua;ZHANG YiYin(State Kay Laboratory of Continental Dynamics / Department of Geology,Northwest University,Xi’an 710069,China;China State Key Laboratory of Shale Oil and Shale Gas Resources and Effective Development,SINOPEC Petroleum Exploration ＆ ProductionResearch Institute,Beijing 100083,China)

机构地区：[1]西北大学大陆动力学国家重点实验室,西北大学地质学系,西安710069 [2]页岩油气富集机理与有效开发国家重点实验室,中国石油化工股份有限公司石油勘探开发研究院,北京100083

出　　处：《沉积学报》2018年第3期617-629,共13页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(41330315);国家重点基础研究发展计划(973计划)项目(2014CB239101);西北大学优秀博士学位论文资助项目(YYB17024)

摘　　要：咸化湖盆盐间泥岩的地球化学特征对咸化烃源岩的形成环境及其共生盐岩的形成条件具有重要指示意义。利用江汉盆地潜江凹陷内潜三下段盐间泥岩的详细地球化学测试结果,并结合岩芯观察,分析了古近系潜江组沉积时湖盆的古盐度、氧化还原环境及古气候背景。该地层较高的Sr丰度、Sr/Ba值及钙芒硝的存在揭示潜江组泥岩沉积时水体盐度较高;氧化还原环境指标及一些敏感元素的含量变化指示潜江组沉积时期水体含氧量较低,处于底层水体中等分层厌氧环境;主量元素化学蚀变指数CIA、Mg/Ca比值及对膏盐层岩芯观察反映潜三下段泥岩沉积于气候相对潮湿期段,而膏盐层则沉积于气候相对干旱期。这种泥岩与膏岩互层出现的变化可能是由我国晚始新世频繁的气候变化导致的。而且,由气候干湿波动造成的淡化-咸化成盐序列,伴随着生物短期的爆发与死亡,将有利于有机质的生成与堆积;潮湿、缺氧的沉积环境有利于有机质的保存,整体上盐间泥岩具备形成较好烃源岩的条件。Geochemical characteristics of intrasalt mudstones have great implications for the sedimentary environmentof saline source rocks and the conditions for the symbiotic formation of halite ore. In this paper, 15 mudstone samplescollected continuously from the lower part of the 3rdmember of Qianjiang Formation in the Qianjiang Sag of the Jiang-han Basin have been analyzed for major, trace and rare earth elements, in order to obtain a better understanding ofthe paleosalinity, redox conditions and paleoclimatic background. The high Sr contents and Sr / Ba ratios, and also thepresence of glauberite indicate high-salinity conditions with organic-rich mudstones deposited. The redox indexes of V/Cr, V/ Ni, V/ （V＋Ni）, δCe、Ce / La、δU and Ceanom and the alteration of some redox-sensitive trace elements suchas V、U、Ni、Zn and Cr suggest low oxygen contents in water and the existence of water delamination with anaerobicconditions. The chemical index of alteration, Mg / Ca ratios and core observation indicate a semi-humid climate forsource rocks deposition and semi-arid one for halite formation. The frequent variations of source rocks and halite de-posits may indicate a fluctuated climate, probably corresponding well to the late Eocene doubt house climate. The in-ter-salt mudstones have a great potential to form high-quality source rocks. On the one hand, along with the alterna-tives of water freshening and salinizing due to climatic fluctuations, short pulses of feast and famine for living beingsare conductive to the formation and accumulation of organic matters. On the other hand, deep-water and anoxic condi-tions during the humid pulse provide an appropriate environment to preserve organic matters.

关 键 词：沉积环境 地球化学特征 潜江组 古近纪 古气候 

分 类 号：P618.13[天文地球—矿床学]