Abstract：Based on field investigation，petrographic observation，and related geochemical analysis，the characteristics and genesis of the hypergene dissolved algal framework dolostone in the Upper Cambrian in Keping area，Tarim Basin，were studied.In macro-scale，hummocky and lenticular algal reef dolostone sandwiched between the tidal-flat dolostones. A large number of supergene dissolution pores developed due to the differential dissolution.In micro-scale，the rocks are mainly composed of dark mud-silt-sized dolomite enriched in algae and light-colored sparry dolomite cement.Mud-silt-sized dolomite has subhedral-anhedral shaped mosaic structure，and display dark-orange red luminescence.They have high concentration of Na and K，but lower concentration of Fe.The δ13C ranges between -0.572‰ and 0.124‰，with an average value of-0.116‰;the value of δ18O ranges between -5.391‰ and -4.983‰，with an average of-5.240‰.These characteristics indicate that the mud-silt-sized dolomite was formed in contemporaneously stage under relatively oxidizing and higher salinity conditions.The sparry dolomite cements filling between algal framework，are anhedral-subhedral shaped and medium-coarse crystalline sized.They show dark cathodoluminescence or non-luminous.The contents of Na and K are low，whereas the content of Fe is high.δ13C values range between -0.662‰ and -0.251‰，with an average value of-0.460‰;δ18O values range between -6.639‰ and -5.939‰，with an average value of-6.267‰.These data indicate that the sparry dolomite cement formed in a relative reduction environment during burial stage.Both mud-silt-sized dolomite and sparry dolomite cements share similar REE patterns with finely crystalline limestone: LREE are enriched，HREE are depleted，and there are Eu negative anomalies.It suggests that both of them derived from seawater dolomitization fluid.In dissolution aspect，sparry dolomite cements are more easily dissolved than mud-silt-sized algal framework dolomite.In the supergene dissolution process，the major elements，Ca and Mg of the sparry dolomite cements，decreased significantly，and the Mg/Ca value declines from 0.955 to 0.007. Trace elements of Na and K were lost obviously.The Na/Ca value declines from 3.8×10-4 reduced to 1.9×10-4，K/Ca value declines from 1.1×10-3 to below the detection limit.Distribution pattern of rare earth elements were not changed.These features suggest that hypergene dissolution process is dedolomitization with salinity decreases，and there were nearly no gains and losses of rare earth elements.
He Kai,Zhu Jingquan,You Xuelian et al. Geochemistry characteristics and their implications of hypergenedissolved algal framework dolostone in the Upper Cambrianin Keping area，Tarim Basin[J]. JOPC, 2013, 15(1): 77-94.
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