Abstract:

Middle-Upper Cambrian dolomites in Shimen,Hunan Province,are mainly composed of anhedral micritic dolomite,euhedral and subhedral granular dolomites,grain dolomite.Different kinds of dolomites formed in different environments may have different models of dolomitization.The anhedral micritic dolomite shows a lower ordering degree (average 0.71),a higher CaCO₃ mole content (average 50.83%),higher δ¹³C and δ¹⁸O values (average+0.26‰ and-6.95‰PDB),a higher Sr²⁺ content and non luminescence.Grain dolomitehas a higher ordering degree (average 0.87),a lower CaCO₃ mole content (average49.4%),lower δ¹³C and δ¹⁸O values (average-0.87‰ and-9.5‰ PDB),and a lower Sr²⁺ content.The euhedral and subhedral granular dolomites,who's ordering degrees,δ¹⁸O and δ¹³C values,Sr²⁺ content are samilar to grain dolomite,has a dark red to red in lumi-nescence.All evidences show that there were three origins of the dolomites in the study area.Anhedral micritic dolomite formed in high-magnesium water in tidal flat;grain dolomite formed in shoal mixing water;euhedral and subhedral granular dolomites were the products of dolomitization in deep burial mixing water.