Depositional feature and mode of sand-conglomerate bodies in the lower third member of Shahejie Formation in Shengtuo area

The sand-conglomerate fans are the major depositional systems in the lower third member of Shahejie Formation in Shengtuo area,which formed in the deep lacustrine environment characterized by steep slope gradient,near sources and intensive tectonic activity.The near-shore subaqueous fans and its relative gravity channel and fluxoturbidite fan depositions were identified according to observation and description of cores combined with the numerous data of seismic and logging.The near-shore subaqueous fans mainly mingled within dark mudstones and located on the downcast side of the east Chennan fault in the horizontal direction.The grain size of the near-shore subaqueous fans became smaller from bottom to top in vertical direction.The bottom of those fans closely attached to the basement.The gravity channels and fluxoturbidite fans developed simultaneously.The gravity channels are the dark mudstones mingled with conglomerate and sandy conglomerate.The turbidity fan sequences are absent in the vertical direction.The fluxoturbidite fans have the linear provenance and fine grain size.The major channels are absent.The classic Bouma sequences developed in partial sandstones.The structural feature,palaeogeomorphology and provenance controlled the depositional system.The intense fault activity is the crucial factor for the formation of the complex depositional systems.