Structural Feature Of Beier Depression And Its Controlling Effects On Sedimentary Characteristics

The systematic study on the structural feature of Beier Depression in HailaerBasin and its controlling effects on sedimentary characteristics is based on previousresearch, comprehensive analysis and collation of the existing geology, drilling andseismic data. The theory of structural geology, seismic stratigraphy, and fault-relatedfold were fully used in the study.Through the contrast of seismotectonic sequence, conclusions that the formationand the development of Beier Depression has experienced three processes: faultedperiod, fault-depressed diversionary period, depression period are drawn. There arethree tensile-torsional structural deformations and one inverse structural deformation.Beier Depression is classified into three main structural layers: the rifted layers (theTongbomiao Formation and Nantun Formation), rifted-depressed conversional layers(the Damoguaihe Formation and Yimin Formation), the depressed layers (the UpperCretaceous Qingyuangang Formation and the Paleo gene).There are three kinds of structural types in Beier Depression: extension,strike-slip and inversion. It can be seen through the fault complex type, in theextension background developing normal fault patterns such as step faults,graben-horst faults, domino faults and fault-related folds such as rollover anticline,fault-drag folds. Strike slip structural patterns mainly are resembling negative flowerstructure pattern and positive flower structure pattern. There are many reverse faultsin Beier Depression because it suffered extrusion pressure in late Paleogene whichwas nearly in the east west direction. Yimin Formation and Qingyuangang Formationwere in fold deformations and NE-trending overturned structure zones occurred.From the study of fracture types, fracture distribution characteristics, fractureactivity characteristics of Beier Depression, the conclusions are that the tectonicactivities were frequent and strong, the fracture systems were complex and thefracture characteristics were in great variation. NE-trending and NEE-trending normalfault combinations were well-developed. Tongbomiao Formation-Nantun Formationperiod was the primary stage. Hailaer Basin is a superimposed basin and the fractures can be classified into six period: faulted period, the late1st section of Nantunformation period, the late2nd section of Nantun formation period, fault-depresseddiversionary period, late Yimin formation period, inversion period.There are many half graben rifts, fault trough and half graben rift combinationsin the formation period of Beier Depression.There are three constructing patterns ofthe rifted layers in Beier Depression: mono-faulted pattern, single-faulted terracepattern, single-faulted trough pattern. There are two constructing patterns of therifted-depressed layers: non-faulted pattern and faulted pattern. The reconstructionmode of Beier Depression can be classified into three patterns: rotary pattern,decollement pattern, graben fault pattern.Beier Depression was composed by a lot of half graben rifts that were controlledby a series of NEE-trending faulted zones such as Suderte, Huoduomoer faulted zonesand NE-trending faulted zones such as Beizhong sub-depression faulted zones. Inaddition, there were NW-trending faults developing in Beier Depression such asBayantala faulted zones. There were also many faults nearly in the north southdirection developing in Beier Depression because it was effected by regional stressfield which was nearly in the east west direction. It can be seen that there are manyperiods of tectonic deformation in Beier Depression and it has today’s tectonicframework after the superimposed reformation.Four types of sedimentary facies were developing in Beier Depression: lacustrinefacies，delta facies（braided river delta facies）, fandelta facies, alluvial fan facies. Inthe sedimentary period of Nantun Formation, the distribution of fans was controlledby slopes and controlling-depression faults. The distribution of fans was along thetendency of slopes and controlling-depression faults and it was like a series of pearls.The developing positions of fans were controlled by gorges andcontrolling-depression faults’ transforming positions.