Study On Tectonic Properties And Precision Interpretation Of Well Logging And Seismic Data In Guanzhong Basin

Guanzhong Basin is located between Ordos platform and Qinling Orogenic Belt.It has been in a status of imbalanced subsidence for a long period due to tectonic stress since Mesozoic-Cenozoic,thus the geological structure is quite complex and belongs to fault development,the stratum sedimentary is of high thickness,the differences between the north and the south part are obvious and the changes of depositional environment and lithologic composition are complex.The theory and means of sedimentology,structural geology,high resolution sequence stratigraphy are used in this paper,and based on the information of Seismic,gravity and magnetic,well logging,profile outcrop etc,the sedimentary filling characteristics are analyzed in the region and the types of sedimentary facies are divided;The structural profile features in the region and the structural relationship of the surrounding geological units are investigated;Through observing field geological profile,the structure of basal faciesthe are divided;Through analyzing controlling faults,the structural style of the basin was summarized;thus the tectonic sequence was established and the features of tectonic evolution was described;Finally,the stretching causes of Guanzhong Basin was investigated.The research shows that:(1)from a lateral view,the east end of the basin is wider than its west end;from a vertical view,the south part is deeper than its north part;the types of depositional system are mainly include the systems of alluvial fan(diluvial fan),of stream,of lake,of river-lake-delta,of fan-delta,etc.;(2)the basement lithology of the area is mainly consist of limestones from the Lower Palaeozoic group,clastic rocksfrom Upper Palaeozoic group,clastic rocksfrom Mesozoic group,metamorphic rocksfrom Proterozoic group,intrusions and granites from Archaeozoic group;(3)the target basin is a Cenozoic extensionalnormal fault basin,controlledfaults are mainly listric fault or graben-like fault,faults' dip angle is gradually slower when it comes deeper;tectonic pattern is normal fault patterns and their combination,which can be divided into flat type,seat type,shovel type,plough type,graben type,horsetail type,"y" type,stepped type,etc.;(4)the tectonic sequence can be divided into the following five interface with five stages:?SB1 stands for the unconformity generated by regional tectonic events between Palaeogene and Neogene;?SB2 stands for the sequence interfacedeveloped between the Pliocene Bahe group and Lantian group;?SB3 stands for the sequence interface between Tertiary and Quaternary system;?SB4 stands for upper limit of Sanmen;correspondingly,the terms of E2—E3,Ni—N21,Nat—N23,Ql,Q2 stand for five tectonic sequences;(5)under the east-west extrusion which derived from Pacific movement and Himalayan movement,the lateral dragging generated by mantle upwelling and also the high temperature expansion,the basin extended along the north-south-trending compressional lineation which generated before and inverse-rifted under the effect of later gravity adjustment,which eventually contribute the formation of such a extensional normal faulted basin today.