Using <Emphasis Type="Italic">in situ</Emphasis> REE analysis to study the origin and diagenesis of dolomite of Lower Paleozoic,Tarim Basin |
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| Authors: | XiaoLin Wang ZhiJun Jin WenXuan Hu JunTao Zhang YiXiong Qian JingQuan Zhu Qing Li |
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| Institution: | (1) State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing, 210093, China;(2) Petroleum Exploration and Development Institute of SINOPEC, Beijing, 100083, China;(3) SINOPEC Northwest Oil Field Branch, Urumqi, 830011, China;(4) Institute of Geology and Geophysics, Chinese Academy of Science, Beijing, 100029, China |
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| Abstract: | In situ REE concentrations of various dolomites from Tarim Basin were obtained by LA-ICP-MS analysis, and the data were normalized
to standard seawater (Seawater Normalized=SWN). Most of the samples have a ΣREE range of less than 20 ppm. All samples show
similar REESWN distributions with heavy REE depletion, and positive Ce anomaly, which indicates that they have the same dolomitization fluids
(seawater). According to the origin and diagenetic process of dolomite, two types of dolomite are determined and described
as follows: 1) syndepositional dolomite, with the highest REE concentrations (more than 20 ppm), the cores of which are more
enriched in REE compared with their cortexes, indicating that they underwent the dolomitization of calcareous sediments by
hypersaline and subsequent diagenesis decreased the REE content of the cortex because of the low REE concentration of the
diagenetic fluids; 2) diagenetic dolomite, which can be subdivided into four groups. (1) burial dolomite which has higher
REE concentrations than limestone, but lower than syndepositional dolomite. This shows that pore fluids with high salinity
dolomitized the pre-existing limestone; (2) void filling dolomite which has the similar REE patterns with the matrix dolomite.
In addition, the Eu anomaly is not obvious, suggesting that the dolomitization fluids originated from the diagenetic fluids;
(3) recrystallized dolomite, whose REE concentration was obviously decreased, indicating that the REE concentration was decreased
during the recrystallization processes; and (4) hydrothermal altered void-filling dolomite, which has the lowest REE concentration,
but obvious positive Eu anomaly, reflecting its hydrothermal activity related origin. Thus, the diverse REE signatures, which
were recorded in different dolomites, retain the information of their formation conditions and subsequent diagenetic processes.
In situ REE analysis of dolomite is an effective probe into the origin and diagenetic process of dolomite.
Supported by National Basic Research Program of China (Grant No. 2005CB422103) |
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| Keywords: | dolomite origin diagenesis in situ REE distribution Lower Paleozoic Tarim Basin |
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