Sedimentary Characteristics And Geological Significance Of The Upper Cretaceous Jingzhushan Formation In The Bange Area,Tibet

The Bangong Lake-Nujiang suture zone in the central part of the Qinghai-Tibet Plateau,where the study area is located,has long been considered as a combination zone between the Qiangtang block and the Lhasa block.Due to the collision between the two land masses,the sedimentary facies and petrological characteristics of the Banluyang marine strata and the Jingzhushan Formation overlying the unconformity have changed.Therefore,the highest marine strata below the unconformity surface and the terrestrial strata above the unconformity surface become important horizons for constraining continental collision time,and also the key to study whether the region has been transformed into an intracontinental sedimentary environment.The Jingzhushan Formation is a set of morainestones developed on the Bangonghu-Nujiang suture zone.Therefore,the study of the Jingzhushan Formation,the era of determining the orogenic effect of the Bangonghu-Nujiang suture zone,and the analysis of its structure The nature of the event is of great significance.The paper relies on the 1:50,000-day A-Geological Survey Project,taking the Jingshan Formation in the Bangor area as the research object.Through the field measurement and sample collection,combined with the microscopic identification of indoor samples,the Upper Cretaceous Jingzhushan Formation was studied.On the basis of the sedimentary facies and its environmental evolution,the Dickinson triangle projection map is used to explore the geotectonic background properties of the Jingzhushan Formation source area,and the following main achievements and understandings have been achieved:(1)Sedimentary facies division: According to the lithologic combination characteristics,sedimentary structure and sand body morphology of the Jingzhushan Formation,the sedimentary facies of the Jingzhushan Formation are studied in detail,which are divided into two types of sedimentary facies(fan delta facies).And meandering river delta),four types of sedimentary subfacies and 12 types of sedimentary microfacies.(2)Profile sedimentary cycle and phase mode: According to the natural sequence of the sedimentary facies on the section and the phase sequence structure change law,the Jingzhushan Formation in the study area is divided into two sedimentary cycles under the condition of the datum elevation and change,and according to The compositional characteristics of the main sedimentary facies types were established,and the sedimentary facies model diagrams of the fan delta and meandering river delta were established to reflect the sedimentary characteristics of different parts of the basin.(3)Analysis of provenance properties: According to the Dickinson QFL triangle diagram,combined with the maturity and structural maturity of sandstone components in different sections,the geotectonic background properties of the source-source debris area of the Jingzhushan Formation in the study area are discussed.The crumb material includes both terrigenous clastics from the circulated orogenic belt and volcanic debris from the uncut island arc.Different sections in different parts of the basin are different from each other due to different sources,and the source and maturity of each source are different.the same.(4)Regional comparison: The Jingzhushan Formation is distributed intermittently along the northwest-south eastward direction in the Bannu suture zone and its south side.Through the comparison of east-west deposition thickness and grain size,it is concluded that the eastern part represented by the Bango area has a large sediment thickness(greater than 1000m)and a coarse sedimentary grain size,while the western part represented by the Geji area has a small sediment thickness(generally 300m),the sedimentation granularity is relatively fine,so it is considered that the eastern region has faster uplift rate,higher elevation difference,obvious erosion,abundant source supply and faster deposition rate than the western region.