Study on feature and origin of dolomite of late palaeozoic in Youjiang basin

During the sedimetary evolution of Late Paleozoic in Youjiang Basin, the dolomite formed in every era or horizon. But the scale of dolomite has evident difference in different horizon. In macroscopic, the shapes in profiles show in lay,parapsoriasis,lentoid,ataxitic and fissured,etc. In microcosmic, the shapes of dolomite include idiomorphic granular-hypautomorphic, automorphic, hypautomorphic-anhedral irregular, granular-hypautomorphic stylolite line, anhedral biopak filling, idiomorphic granular-anhedral biologic organize and anhedral veiny, etc. On the base of above study, this paper discusses the petrological feature of dolomite which included relic structure dolomite, relic-free structure dolomite, intense replacement dolomite and silica dolomite, expounded dolomite-forming environments which include carbonate plateform, carbonate plateform margin reef, slope and basin. The sedimentary environment has affected the macroscopic feature of occurrence which includes thick-bedded(platform), mediumbed(margin reef), ataxitic(slope), thin layer or interlayer(basin). So the origin model has been built. Through the research of dolomite in this area, it can be concluded that dolomite is the result of diagenetic replacement. But the origin mechanics and process are different for dolomite with different feature in macroscopic.They can be divided into two types: one is formed through dolomitization in deepwater, the other is formed through dolomitization in shallow water.