In situ stable isotopic constraints on dolomitizing fluids for the hydrothermally-originated saddle dolomites at Keping, Tarim Basin

Detailed characterization of diagenetic fluid behaviour and evolution is commonly hindered by shortage of appropriate and economic methods to carry out in situ analysis in the tiny diagenetic mineral crystals. Using micromill sampling method, this study presents in situ stable isotopic data for the growth zones of saddle dolomite crystals in the hydrothermally-altered dolostones of Upper Cambrian (Furongian) at Keping, Tarim Basin, NW China. These data show minor and large variations in δ13C ( 0.7‰ to 1.5‰ VPDB) and δ18O ( 8.3‰ to 13.8‰ VPDB), respectively, from the cores to outer rims of the dolomite crystals and suggest that saddle dolomites precipitated from dolomitizing fluids with similar carbon sources but oscillatory temperatures during different formation stages. This scenario is confirmed by microthermometry of fluid inclusions within the growth zones of dolomite crystals. This study indicates that in situ isotope analysis could provide more detailed information related to the source and pathway of dolomitizing fluids, facilitating better characterization of dolomitizing fluids and processes.     

Estimation of carbon sinks in chemical weathering in a humid subtropical mountainous basin

The fluvial geochemistry of the mainstream and tributaries of the Zengjiang River was investigated,and the mass balance approach and deduction methods were used to estimate the uptake of atmospheric CO2 through rock chemical weathering.The results showed that the chemical runoff mainly consisted of HCO3-,Ca2+,Na+,and dissolved Si,and that silicate mineral weathering was significant,but carbonate mineral weathering was a minor source of dissolved loads in the Zengjiang River basin because of the low amount o...