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Discovery of seismites in the first member of the Kelaza Formation in central Taibei Sag of Tuha Basin and its geological significance
Pages: 345-354
Year: Issue:  2
Journal: Oil & Gas Geology

Keyword:  seismiteYanshan movementKelazha FormationLate JurassicBogeda MountainTaibei SagTuha Basin;
Abstract: Tuha Basin is a polycyclic composite basin with dual base and foreland structures.The Yanshan movement du-ring the Late Jurassic controlled and affected the sedimentation of the Kelaza Formation in the basin.Based on observations of cores from more than 20 wells drilled in the Formation,we recognized for the first time some deformed structures of soft sediments originated from seismicity,including sandstone veins (dikes),liquefied breccias,liquefied crinkling deformation,ball-pillow shaped structures,liquefied homogeneous layers and load structures of liquefaction origin;lamellar crinkling deformation,mound-trough structures,annular layers and vibration collapse structures of hydroplastic deformation origin;and seismite breccias,echelonment micro-faults and V-shaped ground fractures of brittle deformation origin.A vertical succession of seismites was established based on the deformation features of seismites recognized in the first member of the Formation.It indicates frequent and intensive seismic activities during the formation of the member.By comparing the spatial and temporal distributions of seismites,we found that the intensity of seismic activities weakened along the Shengbei area at the northern foreland to the Honglian area at the southern margin of the basin,indicating the Bogeda orogenic belt being the earthquake source.A Dickinson triangle chart also revealed that the belt was the provenance of the sandstone in the first member.The widely-distributed seismites (a special sedimentary response between basins and mountains) in the member also indicated that the Bogeda Mountain was strongly uplifted during the sedimentation of the first member in the Later Jurassic due to the second phase of the Yanshan movement.
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