Studies On Middle Jurassic Mixing Of Siliciclastic Carbonate-sediments In The Eastern Part Of The Qiangtang Basin, Tibet, China

The paper give particular studies on sedimentology, stratigraphy, especial characteristics of mixed sedimentation siliciclastics and carbonate in the east basin of Qiangtang bon base of plentiful real materials,which get following results:1. According to combinations and structure of grains and interstitial substance, the siliciclastic rock can be divided into quartzose sandstone, feldspar quartz sandstone, lithic arkose and lithic quartz arkose. Dickinson chart shows that it is mainly origin from sources of orogenic belt,few parts is from craton; According to structure and conglobation froom Dunham(1962), 10 main types of corbonate microfacies are distinguished in the deposits. They are lime mudstone, containing radial specula packstone, pellet micrite-sparite packstone,pellet micrite-sparite packstone,bioclastic wackstone, bioclastic packstone, lamellar power-mud limestone, calcarenite, pellet micrite-sparite packstone,oncoid lump packstone,bioclastic wackstone, bioclastic mudstone, bioclastic packstone, brachia enrichment packstone, oosparite grainstone.2. By means of two units taxonomy(siliciclastic and carbonate) , mixed siliciclastic and carbonate rock can be divided into 9 main types,they are, bioclastic sandy limestone, sandy limestone, lime sandstone, containing siliciclastic intraclast lime mudstone, lamellar silt mud limestone, argillaceous limestone, argillaceous silt limestone, calcareous shale and breccia siliciclastic limestone. four sets can be identifyied, they are siliciclastic rock- carbonate rock set,siliciclastic rock- mixed siliciclastic and carbonate rock set,carbonate rock- mixed siliciclastic and carbonate rock set and mixed siliciclastic and carbonate rock- mixed siliciclastic and carbonate rock set.3. The Middle Jurassic series in eastern of Qiangtang basin, Tibet can be recognized into following facies: littoral facies, carbonate slamp carbonate facies, delta facies, tidal falt-lagoon facies et al. by means of studies of characteristics of mixed sedimentation siliciclastics and carbonate, four sequences can be recognized in the Middle Jurassic series, which improve the precision of stratigraphic division in eastern of Qiangtang basin. 4. It dicuss relations of mixed siliciclastics and carbonate sedimentation and sequences, as a whole, under circumstance of dominating siliciclastics, mixed sedimentation mainly occurs ealry stage of TST and HST. under circumstance of dominating carbonates, mixed sedimentation mainly occurs LST and late stage of HST. It occurs dicuss controlling factoes of mixed sedimentation of siliciclastics and carbonate on tectonic solution, sea level variations, condition of climate, resources and hydrodynamic.5. It discuss the geological evolutions of Middle jurassic epoch in research area, found charasterics of lithofacies and paleogeography as well as mixed sedimentary pattern of Bajocian Bathonian and Callovian age.