Analyses of lithology assemblage

grain size and seismic reflection characteristics of the upper third member of Hetaoyuan Formation reveal that the provenance of slump turbidite fan in the deep lake came from Houzhuang braided river delta in the northeast. The slump turbidite fans are characterized by grey medium-fine sized sandstones

interbedding with dark grey lacustrine mudstone in sharp contact

coexistence of lens and progradation reflection on the seismic profile

as well as low slope and one segment of grain-size probability curve. The drop of lake level was favorable for the formation of slump turbidite fan in delta front without external triggering mechanism. As water in northeast delta front was shallow

when the lake level dropped

part of the delta front exposed and lost stability due to the lost of buoyancy

resulting in local slumping. Wave action could strongly corrode and modify delta front sediments near the wave base and resulted in the formation of turbidite sandbody due to wave back flow. All the slump turbidite fans were developed in the lake mudstones between braised river delta and nearshore subaqueous fan. When the delta pushed forward rapidly and the lobes protruded long forward

it was easy to form slump turbidite fans large in both number and area. The number of slump turbidite fans increases and their area enlarges near the delta lobes.