Abstract:

In Lower Cretaceous Luanping faulted basin is characterized as an alluvial fan—fan delta—lake depositional system. Different types of fan deltas develope under different tectonic settings during evey period of the basin evolution have been found in the outcrops.The fan delta is developed along the steep-slope belt of the faulted basin. The fan delta front is composed of front sheet sand,mouth bar，front channel and overbank sheet-flow deposits. The mouth bar and overbank sheet-flow microfacies are typical in the fan delta front, which are both controlled by periodically developed floods in the channels.Produced by the joint effects of sheet-flow (traction current or grain flow) out of channel mouth with high flow energy and lake waves or currents, the mouth bar is of relatively good reservoir quality.With poor reservoir quality, the overbank sheet-flow unit is deposited by the suspension-load flow over the distal-front channel's bank. Considering the regional distribution features of sedimentary sequence and deposition system, we propose that this type of fan delta progresses to the secondary fault zone along the steep-slope belt during the later period of fault basin uplifting. A depositional model of this kind fan delta has been established.

Key words: fan delta, mouth bar, sheet flow, fault basin, the Luanping faulted basin