Sedimentary facies in the Lulehe Formation, Pingtai area, Qaidam Basin, Qinghai

The Qaidam Basin is a giant Mesozoic-Cenozoic petroleum basin in northwestern China. The present paper deals, on the basis of core examination, SEM, well logs and laboratory data, with sedimentary structure, grain size, sedimentary sequence and sedimentary facies types in the Lulehe Formation, Pingtai area, Qaidam Basin, Qinghai. The Lulehe Formation constrained by the proximal sediments is primarily built up of conglomerates, gravelly coarse-grained sandstones, muddy siltstones and mudstones with trough and tabular cross-beddings, and poor compositional and textural maturity. The grain size probability accumulation curves for the coarse-grained clastic rocks cited above are characteristic of the fluvial deposits composed of suspension and saltation populations, and indicate relatively strong hydrodynamic conditions during the deposition of the Lulehe Formation. The sedimentary microfacies consist mainly of channel lag deposits and channel bar deposits in the channel subfacies, and overbank deposits and flood plain deposits in the flood subfacies. This study will provide reliable geological data for the future petroleum exploration in the study area.