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Application of the isotope (stable and strontium) geochemistry and fluid inclusion microthermometry to studies of dolomitization of the deeply buried Cambrian carbonate successions in the West-central Tarim Basin, NW China

Ngong Roger Ngiaa,b,c,d, MingyiHua,b,c*DaGaoa,c, ZhongguiHua,c, ChunYan Sun a,b,c
aSedimentary Basin Research Center, Yangtze University, Wuhan 430100, China;bHubei Cooperative Innovation Center for Unconventional Oil and Gas, Wuhan 430100, China;cKey Laboratory of Exploration Technologies for Oil and Gas Resources of the Ministry of Education, Yangtze University, Wuhan 430100, China;dDepartment of Geology, University of Bamenda, P.O. Box 39, Bambili-Bamenda, Cameroon


Abstract: Detail petrographic, geochemical (O-C-Sr isotopes) and fluid inclusion studies of the deeply buried Cambriancarbonatesin the West-central Tarim Basin revealed three types of crystalline dolomites (fine-crystalline, nonplanar-a(s), dolomite (RD1), fine-to medium-crystalline, planar-e(s) dolomite (RD2), and medium-to coarse-crystalline, nonplanar-a dolomite (RD3)), medium-to coarse-crystalline, nonplanar-a saddle dolomite cement (CD)and early and later-stage calcite cement.The occurrence of RD1 along low-amplitude stylolites points to link with pressure dissolution by which minor Mg ions were likely released for replacivedolomitization during early-tointermediate-burial seawaterdolomitization. The increasing crystal sizes of RD2 and RD3 with irregular overgrowth rims suggests intense recrystallization and replacement upon the RD1 or remaining precursor limestonesby dolomitizing fluids during late intermediateburialdolomitization.The overlap of δ18O, δ13C and87Sr/86Sr values of RD1-RD3and CD dolomitewith coeval seawater values,suggests that the principal dolomitizing fluids that precipitated these dolomites was connate (Cambrian) seawater preserved in the host limestones/dolomites. Their high 87Sr/86Sr ratios suggest influx of radiogenic strontium into the Cambrian seawater.Two regimes of fluid floware recognized in the study area: firstly, influx of magnesium-rich higher-temperature basinal brines along deep-seated faults/fractures, resulting in cementation by CD dolomite. Secondly, the incursion of meteoric waters, mixing with ascending higher-temperature basinal brines, and an increase in Ca2+/Mg2+ ratio in the fluids probably resulting in the precipitation of calcite cement in vugs and fractures.


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Keywords:Cambrian dolomites, C-O-Sr isotopes, Burial dolomitization, West-central, Tarim Basin, Fluid flow regimes

DOI: 10.1007/s12583-017-0954-y
CLC number:
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