Genesis of Turbidite Fan and Depositional Model in the Upper Member of Eh_3 of Deep Area of Biyang Depression

Through the research of lithologic combination,granularity analysis and seismic reflection characteristic in the deep area of Biyang Depression,it was considered that the slumping turbidite fan in the abyss was derived from Houzhuang braided delta,where lithology was dark grey and medium sandstone and fine sandstone,it was mainly of interlayer in the dark grey lake shale,was abruptly contacted with shale,and it had one section low-slope characteristics in granularity probability curve,with lens seismic reflection and progradation on the seismic section.The period when delta advanced fast forward and lobes extended farther away was a better time for forming the large quantity and volume of slumping turbidite fans.The water is shallow in northeastern delta front,in which exposures are instability due to buoyancy caused by the sudden falling down of lake surface,the local slump lake is produced.Wave was intensely eroded and the sediments of delta front around wave base plane were changed,and turbidity sand was further induced in the action of its reflux.Therefore,the falling down of lake surface is favorable for forming the flux-turbidite in delta front without outside trigger mechanism.