The Geochemistry Character Of The Xuanlong Iron Deposit In Chuanlinggou Formation And Its Sedimentary Environment Significance

The geochemistry character of sediment is quite important to the research of the evolution of sedimentary basins, depositional environment and the resource of sedimentary rocks, which is very well for tracing. Some signals of the changes of marina environment,with the reformation of complicated bio-geochemistry process, will be preserved in the deposition finally. Neo-Mesoproterozoic strata in North China Craton is the most well-growing area in Pre-Cambrian strata. It has recorded the process of earth’s revolution and biological evolution in Cambrian, which has high research value.The turning point of North China Craton changing from littoral-neritic sedimentary system which mainly consists of detrital deposition to epicontinental oceanic sedimentary system which mainly consists of carbonate deposition is Mesoproterozoic Chuanlinggou Formation. It came into being from the divergent initial period of Columbia super-continent. From the changing of vertical sedimentary facies, it reflects an important process of marine transgression, during which the terrigenous sediment of baisin reduces, the rate of sedimentation remains low, the main sedimentary system tends to take shape in reductant environment.The famous Xuanlong Iron Deposits grow in the lower of the Chuanlinggou Formation and take shape of unique oolith and reniform. It represents the palaeohydrodynamic condition that forms the environment is characterized of periodicity. The discovery of fossil bacteria in ore-forming belt implies the co-relationship of the ore-forming environment and the early earth’s ecosystem. The chemical characteristics of earth reflects that ooid-form hematite takes shape in the bio-chemistry sedimentary depositit in foreshore-shoreface beach, reniform hematite takes shape in the bio-adhesive depositit in lower shoreface. We can tell from the traits of trace elements, the most possible source of Fe element is deep-sea hydrothermal.Apart from the sediments of iron rocks, the Chuanlinggou Formation also fosters the earliest sediments of fossil bacteria, which grows out of deep water anoxic zones. Its material resource mainly is mafic basement with the characteristic of passive continental margin. We can estimate from paleocurrent directio that the east block of North China Craton is most likely to be where the detrital material came from.According to the evidence of vertical lithologic characteristic, redox sensitive trace elements, the proxies for paleoredox and vertical changing, the ocean stratification theory which means the surface of seawater was oxic and under the chemical change layer which was intermittent anoxic(partial euinxic) are beneath shallow shore will be support.