宁南盆地古近纪沉积岩地球化学特征对沉积环境的反映  

Geochemical Characteristics of Paleogene Sedimentary Rocks in Ningnan Basin and Their Implications for Sedimentary Environments

作　　者：赵岩[1,2] 刘池洋[1,2] 张东东[1,2] 邓辉 赵晓辰[1,2] Zhao Yan Liu Chiyang Zhang Dongdong Deng Hui Zhao Xiaochen(State Key Laboratory of Continental Dynamics Department of Geology, Northwest University, Xi＇an 710069,China Tianjin Branch of CNOOC Ltd. , Tianjin 300452, China)

机构地区：[1]西北大学大陆动力学国家重点实验室,西安710069 [2]西北大学地质学系,西安710069 [3]中海石油(中国)有限公司天津分公司,天津300452

出　　处：《地质科技情报》2016年第5期27-33,共7页Geological Science and Technology Information

基　　金：国家自然科学基金项目(41330315);中国地质调查局项目(12120113039900;12120114009201);西北大学大陆动力学国家重点实验室自主研究项目(BJ14264)

摘　　要：沉积物元素地球化学特征是盆地沉积环境变化的响应。通过分析沉积岩的微量元素和稀土元素含量变化特征,研究了宁南盆地古近纪气候条件、古盐度和氧化还原环境。Cu、Cs质量分数变化以及Rb/Sr比值、Sr/Cu比值特征,揭示寺口子组沉积时期至少存在一期由潮湿-干旱转变的气候事件,从寺口子组沉积末期到清水营组沉积初期,古气候由干旱变为潮湿。Sr/Ba比值和B/Ga比值反映清水营组沉积水体盐度与寺口子组相差不大,仅在石峡口水库处古盐度值极大,其他地区略有减小。寺口子组沉积过程中,水体盐度有所增加。氧化还原指标V/Cr、Ni/Co、U/Th、V/(V+Ni)、δU、δCe、Ce/La和Ce_(anom)以及氧化还原敏感元素V、U、Ni、Zn和Cr的质量分数变化指示清水营组沉积时期水体氧含量整体小于寺口子组沉积时期。寺口子组沉积环境以氧化环境为主,清水营组沉积水体为氧-贫氧环境。Element geochemistry characteristics of sediments are responses to the depositional environment.On the basis of field geological investigation,we studied the characteristics of trace and rare elements of the sedimentary rocks and probed into the features of paleoclimate,paleosalinity and redox conditions by analyzing the changes of the element components and ratios.The contents of Cu and Cs and the ratios of Rb/Sr and Sr/Cu as well obviously show that one humid-arid climate change event occurred during the deposition time of Sikouzi Formation,when the deposition entered into Qingshuiying Formation,the climate turned from arid to humid.The ratios of Sr/Ba and B/Ga reveal that the water during the period of Qingshuiying Formation contained a little less salinity than that of Sikouzi Formation except Shixiakou reservoir,where the salinity reached the peak.Also,the paleosalinity experienced an upward tendency during one specific period of Sikouzi Formation.The redox conditions of the sandstones and mudstones in Sikouzi Formation and Qingshuiying Formation were also investigated by means of element ratios of V/Cr,Ni/Co,U/Th and V/（V＋Ni）as well asδU,δCe,Ce/La and Ceanomand also some trace element concentrations such as V,U,Ni,Zn and Cr.The results show that the sedimentary environment was oxidation environment during Sikouzi Formation while oxidation-lean oxidation environment during Qingshuiying Formation.

关 键 词：沉积环境 地球化学特征 宁南盆地 古近纪 古气候 

分 类 号：P552[天文地球—构造地质学]