Depositional Environment Of The Datangpo Formation In Manganese Forming Basin In Xiushan Area Of Chongqing

Xiushan is located in southeast of Chongqing City,at the junction of Hunan,Chongqing,Guizhou,which is is an important area of Datangpo type manganese ore Manganese deposit,the region has experienced Sturtian climate warming caused by glacial ablation,warm climate has obvious signs,save a lot of water limitation of sedimentary environment records,which is an ideal area to study Datangpo Formation of Nanhua System sedimentary environment,thus providing the basis for the study of environmental Datangpo type manganese ore deposition process.The Stratum of study area is mainly consisted by formations of Qianzimen,Dangtangpo,Nantuo.The Datangpo formation is epicontinental neritic sedimentary system of Platform deposit system which is dominated by mixed platform,diamictic continental shelf limited,continental slope.The sedimentary structures and sedimentary structures of the restricted shallow water facies in the continental margin mainly include wavy bedding,lenticular bedding,vein bedding and parallel bedding.It is inferred that the formation of the manganese deposit in the passive continental margin is a restricted shallow water deposit combined with SiO2/Al2O3,Al2O3 /(Al2O3Fe2O3),Fe2O3+TiO2 discrimination diagrams.By comparing the actual sedimentation rate of the modern or modern manganese forming basin,the target layer is rich in manganese,and the thickness of the single layer is larger,which indicates that the sedimentary rate of the early manganese rock may be slightly higher than that of the modern one.The research shows that the early Datangpo formation experienced many times of warm and wet to dry and cold climate change,Under the background of the whole stability of the slope,the hydrodynamic condition has the characteristics of early relative turbulence;The study on the redox condition of the ancient water body shows that the enrichment of manganese ore and the formation of the rock are more strict.According to V/Cr,Ni/Co and U/Th ratio,the area is the secondary oxygen enrichment to oxidation environment.The study on the enrichment regularity of Mo element also indicates that the manganese ore may have experienced a gradual change from oxidation to secondary oxidation.Concluded that the ancient water depth calculation in not considering thermal events,based on ancient seawater temperature most near continental margin basin should be Model-T at 20-23 ?,for some basin the seabed water temperature at 14?,due to the impact of seasonal oxygen rich ice water,rivers,flood,surface runoff injection,the sea water temperature will be lower in the early age of Datangpo Formation.The water temperature of the Model-P basin is relatively low,and the water level in the middle and upper reaches of the basin is about 13-22?,From the point of view of manganese,the bottom of the sea due to the continuous cycle by the sea water oxygen rich sea water,sea water temperature 4-13 ?.In the early stage of Datangpo formation,the sea water temperature may be lower than that of the glacial interglacial transition.According to the modern high latitude ocean survey,the formation of "tornado tornado like ice in the sea,sea water temperature to minus local rapid cooling.In this case,it is also possible to have a small ice age in low latitudes.Combined with modern marine research examples,the research on the ancient water salinity stratification shows obvious,surface water salinity is about 7.6-8.2‰,is obviously influenced by the continental margin of fresh water injection;high frequency oxygen or oxygen continuous salt water injection cycle,causing the bottom of the basin water salinity increased,but the overall survival in brackish water under the condition of salinity is about 11.3-16.1‰.During the period of evolution,the salinity is high,reaching 25.4-28.9‰.The organic carbon content of rhodochrosite was 1.42% ~ 2.48%,an average of 2.02%,carbon mudstone content is 0.61% ~ 4.19%,an average of 2.59%,indicating the presence of volcano evidence,volcano provides high geothermal sites,there are a large number of breeding microorganisms.The ratio of K/Na and Sr/Ba showed that the trend of salinity was in good agreement with that of manganese.