The Controlling Effect Of Fault System On The Dunhuang Basin

The Dunhuang basin is a Mesozoic-Cenozoic tectonic basin sandwiched between the Altyn fault zone and the Beishan orogenic belt,it superimposed on the pre-Jurassic metamorphic rock series.Previous drilling data show that the basin has large reserves of oil and gas resources and great exploration prospects.However,the exploration progress is slow.Oil and gas resources are only found in Wudun sag,mainly because of the weak basic geological research of the basin,which restricts the exploration and development of oil and gas resources in this area.The structural characteristics,active time limit and stress state of the fault system in and around the orogenic belt of the Dunhuang Basin play an important role in controlling the formation and evolution of the basin,the distribution range of the basin and sedimentary filling.Therefore,the study of the fault system in the Dunhuang Basin provides an important geological basis for the subsequent exploration and development of the basin.Based on field geological survey,indoor data processing and analysis,this paper studies the faults developed in and around the Dunhuang Basin by means of structural analysis and seismic profile interpretation,and analyses the spatial distribution law and formation mechanism of faults in order to reveal the structural evolution process of the Dunhuang Basin.At the same time,the sedimentary profiles of the outcrop area around the basin are measured and studied.Combined with the collected regional data,the sedimentary filling characteristics and basin attributes of the Jurassic in Wudun Sag,the Dunhuang Basin is analyzed in detail,and the following understandings are obtained.1)The Cenozoic activities in the fault system in the basin are mainly divided into three stages:the first stage is the normal fault formed by the NW-oriented extension stress during the Jurassic period.The second stage is the late Cretaceous-Paleogene near-NE extrusion.The thrust fault formed by the stress field,and the third stage is the left strike-slip fault of the Cenozoic subjected to the near NE thrust stress field,reflecting that the basin is subjected to the north-south compression stress at this time,and the Altyn main fault from the Miocene At the beginning of the activity,the Sanwei Mountain main fault and the Beishan fault began to operate from the Pleistocene.2)The Jurassic provenance of the basin is analyzed by means of zircon U-Pb dating,heavy mineral analysis and outcrop analysis.It is concluded that the Sanwei Mountain had been uplifted before Jurassic and provided sufficient sediment sources for the basins on both sides.It is the main provenance area of Jurassic sedimentation in the basin.3)The sedimentary depressions on both sides of the Sanwei Mountain in Jurassic were controlled by normal faults along both sides of the Sanwei Mountain in the same period.After Jurassic,they were reformed and controlled by multiple fault system activities in the later period.The thrust faults developed after early Cretaceous changed the basin from extensional to compressive uplift,and the basin changed from fault depression to depression.The fault system began in the late Tertiary.The whole left strike-slip movement eventually formed the present strike-slip pull-apart basin4)The Mesozoic-Cenozoic tectonic evolution of the Dunhuang Basin can be divided into six stages: the early Jurassic initial rifting stage,the peak of the middle Jurassic fault depression development stage,the late Jurassic fault depression development stage,the early Cretaceous depression basin development stage,the uplift of the late Cretaceous-early Tertiary basin and the formation of the Late Tertiary-Quaternary strike-slip pull-apart basin.