Magnetostraitigraphy Chronology Of The Cretaceous In The Northwest Tarim Basin

Cretaceous played an important role in the long evolution history of the earth. A lot of global tectonic and environmental events happened in this period. Tarim basin is the biggest petroliferous superimposed basin in China, and it is also one of a few regions which have developed Cretaceous and Cenozoic marine strata. The Cretaceous marine strata is more complete in western tarim basin. There are plenty of marine fossils and various types of rocks. This region is a desirable place for researching tectonic and sediment evolutionary of tarim basin and evolution of Neo Tethys. After a lot of researches and scholar’s decades research, a great progress has been gained on Cretaceous strata partition and the regional paleontology in western tarim basin. However, Cretaceous strata absolute chronology sequence has not gained any concern. Further thorough research in this area was deterred by lacking of absolute chronology material.The study has chosen the Kuzigongsu section in Kashgar region northwestern Tarim basin as subject. Through Cretaceous Magnetostraitigraphy chronology studies, and the control of Palaeontology fossil macroscopical age, Magnetostraitigraphy age sequence of Cretaceous strata in Kuzigongsu section has been acquired. Meanwhile, under the control of strata chronology, we try to rebuild the evolution process of basin-orogen patterns by researching and analyzing the details of Tarim baisn, which includes Cretaceous strata sequence, sedimentary character, sedimentary facies combinations and deposition rate. We mainly obtained the following conclusions through our research:1.We have established the chronology sequence of Kuzigongsu strata spans from 145Ma to 65.5Ma through Magnetostraitigraphy studies and the control of Palaeontology fossil macroscopical age. The age of lower cycle kizilsu Gr, upper cycle kizilsu, Kukebai Fm,Wuytak Fm, and Yigeziya Fm are 145-125Ma、125-93.5Ma、93.5-33.5Ma、83.5-67.61Ma、67.61-65.5Ma, respectively.2.After researching lithology, sedimentary character and tectonic structure, we have stratified the whole Kuzigongsu region of northwestern Tarim basin into three sedimentary facies:fluvial facies, beach facies andtidal plat facies.3.After studying deposition rate, sedimentary facies combinations, depositional provenance, contact relationship of strata and basin-mountain coupling, we have found that Kuzigongsu region of NW Tarim basin has undergone four sedimentary evolution stages:The beginning subside and fluvial deposit period ranging from 145 Ma to 127.25Ma, the seawaterinvasion period ranging from 127.25 Ma to 124.2Ma, the great marine transgression ranging from 124.2 Ma to 83.5 Ma, and the marine regression and marine transgression period ranging from 83.5 Ma to 65.5Ma.The research above has significance to find out evolution of Neo Tethys in Cretaceous, clarify the relationship among palaeoenvironment, a large scale to form source rock in Tarim basin of Cretaceous and great geological events.