Abstract:

The fine analysis of deep-water gravity flow deposits in the Ordovician Lashenzhong Formation outcropping at the western margin of Ordos Basin， serves for revealing the evolutionary pattern and sedimentary model of deep-water gravity flow channel-lobe system， and then the reservoir distribution therein. The results show that the gravity flow depositional units in the study area include complex channels， migration channels， vertical aggradation channels with layered fill， distributary channels， as well as proximal and distal lobes， the evolution of which is closely related to the type and energy of gravity flow. At the initial stage， gravity flow is dominated by debris flows and turbidites， commonly leading to the development of complex channels. As the gravity flow gets waning in energy， turbidites become predominant， resulting in the formation of migration channels and vertical aggradation channels in succession through multi-stage erosion and sedimentation. Subsequently， distributary channels， proximal and distal lobes are generated in turn when the turbidites fade. In addition， the process of complex channel development could be divided into youthful， prime， and decline stages which are corresponding to the short-term gravity flow evolution processes. Complex channels in the prime stage， migration channels， and vertical aggradation channels are favorable reservoirs， with the storage capability declining in turn. The middle parts of channels are generally better compared with those at the flanks in terms of reservoir potential， and reservoirs of proximal lobes are superior to those of distributary channels.

Key words: turbidite, debris flow, gravity flow, channel-lobe system, depositional model, Lashenzhong Formation, Ordovician, Ordos Basin