塔里木盆地西北缘二叠纪生物礁灰岩地球化学特征及其地质意义

Geochemical Characteristics and Geological Significance of Permian Reef Limestone in the Northwest of Tarim Basin

塔里木盆地西北缘早二叠世出露块状藻礁灰岩,是形成油气藏的重要目标层。为研究其地球化学特征,对藻礁灰岩的微量元素、稀土元素进行系统的测试。研究表明:研究区的藻礁灰岩样品中具有LREE亏损、负Ce异常、正Gd异常等较为典型的海水稀土配分型式,与现代浅海特征相似。Y/Ho值、Er/Nd值较高,Th极低,表明其未受到陆源碎屑的影响;δCe具有中等到弱的负异常,δU值<1、V/(V+Ni)值在0.16~0.20,V/Sc值在4.28~5.14,均表明藻礁灰岩形成于氧化环境。Sr/Ba为16.19~25.77,表明海水处于较咸化环境;Sr/Cu为176.42~361.54,指示了干旱的气候条件。综合各项地球化学特征认为塔里木盆地西北缘的藻礁灰岩形成于局限碳酸盐台地环境。

In the northwest of Tarim basin,the Early Permian section exposed thick layer of algae reef limestone,which is an important target layer for the oil-gas prospecting areas.The trace elements of the algae reef limestone showed a seawater-like pattern of LREE depletion,negative Ce anomaly and positive Gd anomaly.The high Y/Ho and Er/Nd,and the extremely low Th indicate that it was not affected by terrestrial debris.δCe had moderate to weak negative anomalies,δU<1,V/(V+Ni)between 0.16~0.20 and V/Sc between 4.28~5.14 indicate that algal reef limestone formed in an oxidizing environment.Sr/Ba is between 16.19~25.77,indicating that the seawater was in a saline environment.Sr/Cu is between 176.42~361.54,indicating the arid climatic condition.Based on various geochemical characteristics,it is inferred that the algae reef limestone in the northwest of Tarim basin was formed in a limited carbonate platform environment.