THE DISTRIBUTION OF LITHOLOGIC TRAPS OF EOGENE IN THE DONGYING SAG OF THE BOHAI BAY BASIN

There are mainly three genetic types of lithologic trap mode in the Dongying Sag of the Bohai Bay Basin during Eogene time,which are turbidite(fan) trap related to delta,near-shore subaqueous fan-turbidite fan trap and palaeo-geomorphic platform beach-bar trap.Controlled by genetic types of delta,the turbidite(fan) traps are related to flood lakes.So they are often developed during rising hemicycle of medium-term base-level.Near-shore subaqueous fan-turbidite fan traps are controlled by the palaeo-geomorphology,the characteristics of the faults,the fracture intensity,fracture combination styles,etc.The development of the subaqueous fan is often closely related to trough-valley,fault order,continuous movement of the fault.Controlled by the provenance,palaeo-geomorphology and lake strandline,palaeo-geomorphic platform beach-bar traps lies on the palaeo-geomorphic platform in front of or beside the coarse grained lithosomic body,and develops the rising time of the long-term base-level.In the high-frequency sequence frame,bar sand mainly forms during fall time of the middle-term base-level,while beach sand mainly in rise time of the middle-term base-level.