The Preliminary Analysis On Rock Association Characteristics Of Volcano-hydrothermal Venting-flowing Sedimentary In Pingdiquan Formation,Permian, Northeast Zhunggar Basin

The Permian Pingdiquan formation in the northeast of Zhunggar Basin is the important hydrocarbon source rocks and reservoir. Previous studies classified its rock types as formal sedimentary rocks. After detailed evaluation for the thin sections of the of Pingdiquan formation in the northeast of Zhunggar Basin and comprehensive basis studying for the rock and mineral assemblages, composition characteristics and genetic by a variety of testing methods, our research team find that the Pingdiquan formation has not only normal clastic rocks but also volcanic tuff, and widely develops transition rock types between tuff and chemical deposited carbonates. Taking the alkaline magmatic mineral clastic, such as quartz, alkali feldspar, dolomite, calcite, and first discovered aegirine, aegirine-augite, batisite and so on, as research object, combined with sedimentary rock characteristics of this rock, this paper explores the characteristics of a special volcanic-hydrothermal venting-flowing sedimentary rock combination,which develops in the sedim entary environments rich in magmatic and hydrothermal fluid in the Permian Pingdiquan formation in the northeast of Zhunggar Basin. In this study, we have obtained the achievements and recognitions as follows:(1)Rock characteristics:The Pingdiquan formation volcanic-hydrothermal venting-flowing sedimentary rock includes tuff, hydrothermal dolomitic, dolomitic tuffite, including tuffaceous micritic dolomite, little bioclastic limestone closely related to volcanic hydrothermal activity and analcite rocks with the characteristic of developing analcite. Tuff is lamellar distribution. Porphyritic dolomitic has "porphyritic texture" similar to extrusive rocks, and we first discover the alkaline magmatic mineral clastic, such as aegirine, aegirine-augite, batisite and so on,in some part of dolomite tuffites' stratum, so we Speculate that these rocks may be formed from ultrabasic alkaline tuff eruption(2)Mineralogical characteristics. Quartz and feldspar in volcano-hydrothermal venting-flowing sedimentary association exist in the form of volcanic clastic minerals, with fine particle size, sharp angular shape, fresh-clear surface, irregular crack and harbour-diss olution in the Pingdiquan formation in the northeast of Zhunggar Basin, and the type of the feldspar is mainly alkali feldspar with sky blue color in cathodoluminescence and the magma genesis. Carbonate particles'interfere color is bright. Part of the (iron) dolomite has clear fog center-light edge structure and its mode of occurrence is similar to eruptive rock's "phenocryst", and is extremely similar to the hydrothermal dolomite that the domestic and foreign has confirmed, combined with determination of strontium isotope.(3)Sedimentary environment characteristics:. The sedimentary environment of the Pingdiquan formation in the northeast of Zhunggar Basin is high salinity lake environment and exists local gravity flow deposits, while the intermittent magmatic-hydrotherma 1 fluids frequently participate in the deposition process.The middle Permian of northeast of Zhunggar Basin is intracontinental downfault-rift environment, and stretch background caused deep faults, which provides upwelling of deep hydrothermal fluids for the sedimentary and forms the special volcano-hydrothermal venting-flowing sedimentary rock association.