Sedimentary Filling Of Xuanhua Basin And Its Indication Of Basin Nature,in The North Hebei Province

Xuanhua Basin is located at the intersection of the western part of the Yanshan fold belt and the northern section of the Taihang Mountains fold.Yanshan fold belt is subjected to folds and deformation in Mesozoic,and a large number of flexural basins are developed.Characteristic basin filling sequencesand sedimentary models develop in Xuanhua Basin under the control of the Mesozoic faults,especially the Jiulongshan Formation and the Tuchengzi Formation,two sets of coarse-grained terrigenous clastic deposits as typical representative.Based on the study of the relationship between basin sediments and basin sediments with basin margin tectonic structures,the sedimentary environment of the Late Jurassic to Early Cretaceous can be restored,and the tectonic setting of the basin filling is explored,and the discussionof the tectonic system of the Yanshan fold belt also is inspired.The paper is based on the field survey of outcrops in Xuanhua Basin.The sedimentary facies of the Jiulongshan Formation and the Tuchengzi Formation are divided.The main observation contents include the thickness of the sedimentary layer,the contact relationship between the sedimentary layers,the debris in the sedimentary layer Structure and distribution characteristics.The Jiulongshan Formation and the Tuchengzi Formation divided into 13 types of lithofacies.The sedimentary facies are deduced by the combinationof lithofacies.The fan-delta sedimentary system of Jiulongshan Formation and the lacustrine-braided river delta-alluvial fan sedimentary system of the Tuchengzi Formation result from identification of sedimentary facies.The sedimentary filling of the basin is the performance and product of the basin development process,while the basin development process is controlled by the basin-controlling faults and the regional tectonic setting.The development of alluvial fan in Tuchengzi Formation and fan delta in Jiulongshan Formation is a prominent manifestation of basin-orogeny control,but the key evidence that can reflect the tectonic nature of the basin is two sets of growth strata developed in the basin.The two sets of growth strata,respectively,are located in Lishicun and Guiyukou,which are controlled by the secondary thrust of the Xiahuayuan Thrusts.The growth strata in Liushicun is developed in the period of Tiaojishan Formation,while the growth strata in Guyukou is developed in the Tuchengzi period.The growth strata controlled by the thrust reflects the sedimentation basin controlled by the extrusion action.FromLate Jurassic to Early Cretaceous the Xuanhua basin is the product of regional extrusion background.And the squeeze background of this region is related to the tectonic setting of the eastern part of China.