Study On Structural Characteristics And Genetic Mechanism Of Barrier Folds In Eastern Sichuan

The barrier fold in eastern Sichuan Basin is located in the eastern side of Huayingshan fault.There are many high-steep anticlines with NE and NNE strike in the area.The strata exposed in the core of the anticline are mainly Triassic with asymmetrical wings.The dip angle of the gentle wing strata is between 20 and 30 degrees.The dip angle of the steep wing strata is between 40 and 70 degrees or vertical inversion.The dip between the anticlines is broad and gentle syncline.The outcropped strata are mainly Jurassic and anticline.Obliquely closed,wide and gentle syncline,showing a typical barrier fold style.By studying the structural characteristics and genetic mechanism of the barrier folds in eastern Sichuan,we can provide a reference for the interpretation of geological data of the barrier folds in eastern Sichuan and the next step of oil and gas exploration and research.Based on basic geological data,two-dimensional seismic profile interpretation and drilling data,this paper studies and analyses the structural characteristics,evolution and genetic mechanism of barrier folds in eastern Sichuan by using balanced profile technology and structural physical simulation experiments:There are three sets of detachment layers developed in the barrier fold caprock in eastern Sichuan.The structural deformation of the upper and lower strata of the detachment layers is obviously different,which can be divided into three structural deformation layers:(1)the lower structural deformation layer is the lower Cambrian and its underlying strata,the strata are not involved in deformation and the structure is simple;(2)the middle structural deformation layer is the gypsum salt rock of Cambrian Gaotai Formation to the gypsum salt rock of Triassic Jialingjiang Formation,and the deformation is mainly concentrated.In this structural layer,the structural deformation is complex and the fault pole is well developed.3.The upper structural deformation layer is above the Triassic Jialingjiang Formation.The fault of this structural layer is less developed,and only small-scale faults,steep anticline and even stratum inversion are developed in some areas.The formation and evolution of the barrier fold structural belt in eastern Sichuan mainly underwent four stages: Caledonian to Hercynian extension,Indosinian fold embryonic,Yanshanian strong deformation and Himalayan fold transformation and finalization.In the process of formation,the barrier fold structural belt in eastern Sichuan experienced early tension and later was subjected to multi-stage compression.In the early stage of fold deformation,the overburden strata of the detachment layer developed detachment folds under compression.With the increase of backlog,faults developed in the detachment layer of the fold wing.Fault-spreading folds developed in the upper wall of the shallow fault.The north-west wing of the anticline was gentle and the south-east wing was steep,which resulted in the westward inclination of the anticlinal axis and formed the present structural characteristics.Many sets of detachment layers in the barrier-type fold cover in eastern Sichuan are the main factors controlling the structural change.The burial depth of the detachment layer controls the upper structural style,and the barrier-type folds develop in the upper overburden of the Shallow-buried detachment layer.The westward inclination of the barrier fold axis may be related to the block of Chuanzhong block on the west side of Huayingshan fault.