Generations,geochemistry characteristics and their precipitation conditions of cave fillings of the Middle Cambrian penecontemporaneous dolostone in Keping area,Tarim Basin
Liu Ling1,2 Zhu Jingquan2 You Xuelian1,2 He Kai1
1 Graduate University of Chinese Academy of Sciences,Beijing 100049;
2 Institute of Geology and Geophysics,Chinese Academy of Sciences, Beijing 100029
In order to rationally analyze and evaluate the developing and preserving condition of penecontemporaneous dolostone caves related with evaporation in burial diagenetic environment,the petrology and geochemistry of the Middle Cambrian dolomites and their cave fillings in the Keping area,Tarim Basin have been studied in details,and the precipitation conditions of the cave fillings have been recovered.It has been discovered that the cave fillings show obvious generational features.There are at least four generations of fillings from the bedrock to the center of the cave:(1) ivory granular calcite;(2)iron dipped variegated columnar calcite;(3)achromatic transparent quartz;(4)purple fluorite.The analytical data of carbon and oxygen stable isotope,trace elements and REE compositions show that the host dolomite has these characteristics such as high Sr/Ba ratio 5.47,low U/Th ratio -0.2954<0.7,high Zr/Hf ratio 36.86,relatively high total REE,relatively high δ18O -7.444‰,salinity index Z was 120.56,which show a relatively lower temperature,oxygen rich and relatively high saline environment. The calcite fillings of the first generation has these characteristics such as low Sr/Ba 2.33,high U/Th 1.3>1.25,low Zr/Hf ratio 20.857,moderate total REE,relatively low δ18O -13.758‰,salinity index Z was 105.35<120,which shows a relatively higher temperature,hypoxia and relatively lower saline environment. The second generation has these characteristics such as relatively low Sr/Ba 2.77,high U/Th 1,in the range 0.75~1.25,relatively lower Zr/H ratio 32.08,moderate total REE,relatively low δ18O -11.344‰,salinity index Z was 116.51<120,which also shows a relatively high temperature,Oxygen-poor and low saline condition. The fluorite fillings of the fourth generation has these characteristics such as relatively low Sr/Ba 3.15,relatively high U/Th 0.8666,in the range 0.75~1.25,relatively low Zr/Hf ratio 31.875,low total REE,and the REE pattern is similar to that of the magmatic origin fluorite,which also shows a relatively high temperature,oxygen-poor and low saline precipitation condition.The precipitation conditions of cave fillings reflect that this set of strata experienced a process of burial-uplift-and then buried-and ultimately uplifting to the surface after the penecontemporaneous dolomitization.
About author: Liu Ling,born in 1986, is a candidate for Ph.D.degree in Institute of Geology and Geophysics,Chinese Academy of Sciences. She majors in petroleum geology.E-mail:liuling522@sohu.com. About the corresponding author Zhu Jingquan,born in 1956,is a research professor in Institute of Geology and Geophysics,Chinese Academy of Sciences.He is mainly engaged in sedimentology,reservoir sedimentology and sedimentary geology.
Cite this article:
Liu Ling,Zhu Jingquan,You Xuelian et al. Generations,geochemistry characteristics and their precipitation conditions of cave fillings of the Middle Cambrian penecontemporaneous dolostone in Keping area,Tarim Basin[J]. JOURNAL OF PALAEOGEOGRAPHY, 2012, 14(6): 757-766.
Liu Ling,Zhu Jingquan,You Xuelian et al. Generations,geochemistry characteristics and their precipitation conditions of cave fillings of the Middle Cambrian penecontemporaneous dolostone in Keping area,Tarim Basin[J]. JOPC, 2012, 14(6): 757-766.
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