Study On The Evolution Of Sedimentary Systems And Accommodation Space In Shahejia Formation In Luojia Area

Luojia area is located in Luojia nose structure zone of Chenjiazhuang uplift, which belongs to northern part of Jiyang depression Zhanhua subdepression. The Shahejie formation is an important pay layer in this area. The evolution of sedimentary systems and accommodation space in Luojia area were studyed based on the integrated analysis of lithology, loggings and seismic data etc.Six sedimentary systems including alluvial fan, fan delta, delta, beach and bar deposits, saline lake, normal lake developed in Luojia area. The source area(provenance) of different periods were defined according to the analysis of seismic data, components of sandstone and content of both sandstone and conglomerate. Chenjiazhuang uplift was the source area during the period from lower Sha4 member to lower Sha3 member. With the weakening of Chenjiazhuang uplift, Gudao uplift acted as the main source area in both middle Sha3 member and upper Sha3 Member. Gudao uplift dominated in lower Sha2 member, which is characterised by weak supplyment.The distribution characteristics of different members were defined through the paleogeography reconstruction method of"single factor analysis, muti-factors integrated mapping". Lower Sha4 member is characterised by alluvial fan. Fan delta with saline lake developed in upper Sha4 member, semi-deep lake and deep lake largely developed in lower Sha3 member, with small fan delta around Chenjiazhuang uplift. Delta of fine grain size dominated in both eastern and southwest parts of this area in middle Sha3 member, but only eastern delta continued in upper Sha3 member. Lower Sha2 member is characterized by beach and bar deposits.The variation of accommodation space in different periods were defined under the instruction of sedimentology. Three main factors including basement subsidence, sediment supply and eustacy affect the accommodation space, structure dominated in the evolution of both the accommodation and sedimentary facies. Certain sedimentary facies only devoloped in certain backgroud, which is controlled by accommodation space, both sediment supply and accommodation background controlled the sedimentary facies systems developed in certain period or area. Besides, gradient, sediment supply and climate can also affect the development of sedimentary facies.