江陵凹陷古新世盐湖沉积碳酸盐碳氧同位素组成及其环境意义  

Carbon and Oxygen Isotopes Characteristics of Palaeocene Saline Lake Facies Carbonates in Jiangling Depression and Their Environmental Significance

作　　者：王春连[1] 刘成林[1] 徐海明[1] 王立成[1] 张林兵[2] 

机构地区：[1]中国地质科学院矿产资源研究所,国土资源部成矿作用与资源评价重点实验室,北京100037 [2]中国地质大学(北京)地球科学与资源学院,地质过程与矿产资源国家重点实验室,北京100083

出　　处：《地球学报》2013年第5期567-576,共10页Acta Geoscientica Sinica

基　　金：国家"973"计划项目(编号:2011CB403000);中国地质调查局计划项目(编号:1212010011808);国家自然科学基金青年基金(编号:41202059)联合资助

摘　　要：江陵凹陷位于江汉裂谷盆地西部, 古新世是该区富钾卤水形成的主要时期, 研究该时期古气候的演化, 对下一步找钾有重要的理论和实际意义。古新统沙市组和新沟嘴组湖相碳酸盐岩分析结果显示, 沙市组沉积碳酸盐岩δ13CPDB值介于–4.8‰ ~ –1.0‰之间, 平均值为–3.4‰; δ18OPDB值介于–5.6‰ ~ –0.6‰之间, 平均值为–3.3‰; 新沟嘴组碳酸盐岩δ13CPDB值介于–10.8‰ ~ –8.8‰之间, 平均值为–9.3‰; δ18OPDB值介于–10.2‰ ~ –6.7‰之间, 平均值为–8.6‰。沙市组碳酸盐岩样品的δ13CPDB和δ18OPDB之间具有良好的正相关性, 表明它们发育在蒸发作用明显的相对封闭的咸水湖泊体系中; 而新沟嘴组δ13CPDB和δ18OPDB之间相关性差, 指示该时期是水体滞留时间较短的开放型湖泊系统。碳氧同位素, Sr/Ba值和Mg/Ca值均说明沙市组沉积时期古盐度和蒸发/降雨大于新沟嘴组沉积时期; 古新世的岩相古地理演化说明了沙市组沉积时期古湖水面小于新沟嘴组沉积时期。江陵凹陷古新统湖泊沉积碳酸盐碳氧同位素组成的变化指示了区域古气候条件由沙市期的干热向新沟嘴期的湿润转变。显示古新统沙市组到新沟嘴组江陵凹陷古气候格局发生了重大变化, 这一变化对于沙市组时期古盐湖演化和成钾十分有利。Abstract：The Jiangling depression is located in the west of Jianghan rift basin, and potassium-rich brine was mainly formed in Palaeocene. The study of the palaeoclimate evolution in Palaeocene has great theoretical and practical significance for further potash survey. The δ13CPDB values of carbonate in Shashi Formation of Jiangling depression vary between –4.8‰ and –1.0‰ with an average of –3.4‰; the δ18OPDB values are between –5.6‰ and –0.6‰ with an average of –3.3‰; the δ13CPDB values of carbonate in Xingouzui Formation of Jiangling depression are in the range of –10.8‰ ~ –8.8‰ with an average of –9.3‰; the δ18OPDB values are between –10.2‰ and –6.7‰ with an average of –8.6‰. The δ13CPDB and δ18OPDB values of micrite in Shashi Formation show good positive correlation, suggesting a relative closed salt lake system with apparent evaporation. However, in Xingouzui Formation, the relationship between δ13CPDB and δ18OPDB is indistinct, implying an open lake system whose water was stagnant only for a short time. The carbon and oxygen isotopes as well as Sr/Ba and Mg/Ca ratios reveal that Shashi Formation had relatively high paleosalinity and evaporation/raining ratio. The paleo-lake surface is higher in Xingouzui Formation than in Shashi Formation. The differences of carbon and oxygen isotope compositions of the Palaeocene lake in Jiangling depression reveal the change from dry-hot climate in Shashi Formation to wet climate in Xingouzui Formation. It is thus inferred that the palaeoclimate changed greatly from Shashi Formation to Xingouzui Formation in Jiangling depression throughout the Paleogene period. This change was favorable for the salt lake evolution and potassium deposition in Shashi Formation.

关 键 词：江陵凹陷 古新统 湖相碳酸盐岩 稳定同位素 古气候 古环境 

分 类 号：P597.2[天文地球—地球化学] P588.245[天文地球—地质学]