Forming Mechanism Of Fengcheng Formation Of Lacustrine Hydrothermal Dolomite In The Junggar Basin In Urho

The research of hydrothermal sedimentary rocks have been the focus of research all overthe world. The domestic research mainly concentrated in the marine hydrothermalsedimentary rocks while researches on terrigenous hydrothermal sedimentary rocks are few,especially the research of lacustrine hydrothermal dolomite is extremely rare. Based onprevious research and on the basis of core observation, thin section analysis, scanningelectron microscope, X ray diffraction and geochemical analysis experimentalmethods, dolomite of Fengcheng formation in Urho Area, Junggar Basin is more less commonhydrothermal sedimentary rock, sedimentary environment and formation mechanism of thecomprehensive research obtains the following results and understanding:1)Fengcheng formation in Urho rock type is mainly dolomite which include dolomiticsiltstone, argillaceous dolomite，calcite dolomite and dolomitic mudstone, settinggraydolomite and dolomitic mudstone, the dolomite is more developed in P1f2and P1f3, moreenriched in the south generally,2) The dolomite formation sedimentary structure type is rich, including horizontalbedding, common convolute bedding, banded and crumpled deformation formed in normaldeep water environment, small step synsedimentary tectonic, clastic structure and stockworkstructure of hydrothermal exhalative sedimentary system.3) Deposition of Fengcheng formation and hydrothermal activity are closely related,Fengcheng formation sedimentary facies are mainly semi deep lake-deep lake subfacies,secondly are shore shallow lake facies. The semi deep lake-deep lake subfacies includevolcano ash plume microfacies, hydrothermal pulsation exhalative microfacies andlow-density turbidite sand microfacies.4) A set of alkaline salt minerals such as reedmergnerite, shortite of dolomite formationare found, saline minerals are distributed mainly in P1f1, P1f2vertically, and of moreenrichment in plain. The mineralization materials mainly comes from the middle-high salinedeep hot fluid and the formation belongs to deep basin hot brine water exhalativesedimentation-salification.5) Deposition of Fengcheng formation and hydrothermal activity are closely related, microcrystalline dolomite mud lake which is a hydrothermal precipitation causes, powder-fine crystalline dolomite is buried hydrothermal dolomitization product,the Fengchengformation epicontinental offshore lake hot liquid internal-exogenous jet flow mixedsedimentary model are established.