Cenozoic Tectonic Of Luliangshan And Adjacent Areas - Sedimentary Evolution

Reconstruction of Cenozoic thermal history and the uplift processes of mountains is the important research field of the Cenozoic geology.L(u|¨)liang Mountain which uplifted in Cenozoic divided the Pre-Ordos Basin into Ordos Basin and Qinshui Basin.Comparative study the evolution of L(u|¨)liang Mountain and Ordos Basin and Qinshui Basin in Cenozoic can provide new information for the study of basin reformation.In addition,L(u|¨)liang Mountain is the first mountain ranges across the northeastern border of Qinghai-Tibet Plateau.Research on the Cenozoic uplift of L(u|¨)liang Mountains could constrain the eastern border of Qinghai-Tibet Plateau lateral spread from time viewpoint.Composition,spatial distribution and sedimentary environment of Cenozoic sedmnetary in front of L(u|¨)liang Mountain are the keys to study uplift of L(u|¨)liang Mountains and the formation and evolution of Yellow River.In this thesis we subject different methods for the uplift of L(u|¨)liang Mountain from the view of foreland basin and Mountain Body.Based on qualitative study,the L(u|¨)liang Mountain can be divided into three parts(north,middle and south).In Mountain,fission track dating analysis are used in diffirent parts of L(u|¨)liang Mountain to get the information of times and amplitude of the uplift,which can provide information to study the time stage and regional characteristic of uplift.For the foreland basin,Lithofacies analysis and Paleomagnetic dating are the main methods to constraint the process of uplift and denudation of L(u|¨)liang Mountain. Together with the study of foreland basin and Mountain Body,We reconstruct the Cenozoic history of tectonic-sedimentation in L(u|¨)liang Mountain and its adjcient area.Fission track study on Different parts of L(u|¨)liang Mountain shows that there are at least four times intermittent uplift(58Ma,49-53Ma,38-43Ma and 26Ma) in Cenozoic and the amplitude is different in the north,middle and the south part.The middle part of L(u|¨)liang Mountain uplifted in 58Ma firstly which has not sweep other parts.In 49-53Ma,both north and the middle part of L(u|¨)liang Mountain uplift.The upift amplitude of middle part was larger the north.38-43Ma and 26Ma,the whole L(u|¨)liang Mountain experienced two rapid uplifts and the latter established the main pattern of L(u|¨)liang Mountain.Gravel's spatial distribution characteristics in a wider range,gravel composition and adjacent bedrock's composition and research of typical profile sedimentology tell us that the gravel bed in front of the L(u|¨)liang mountains is the product of L(u|¨)liang Mountains's uplift in Cenozoic. Paleomagnetic age(10-6.5Ma) of gravel bed is the uplift date of L(u|¨)liang Mountains. Further research on Liulin Section reveals the relation between red clay and fluvial accumulation.Togeteh with other researcher's results,the conclusion can be drawn:fluvial deposits wedge red clay base like an asymmetric wedge.The discovery of red clay and calcium nodule transported can provide new information for the cause of red clay. Magnetostratigraphic result reveals that red clay and calcium nodule transported is aged about 8Ma,which indicates that the red clay older than it must exist before 8Ma.Based on study on Neogene Stratigraphy in Liulin profile,together with other researcher's results,it is concluded that the sandy gravel layer in the lower pre-Baodean is fluvial deposits,but the upper sequence of brownish red clay and brownish yellow calcite nodule interbedded with each other are aeolian clay layers;The middle part is thought to be the transition zone of the lower aqueous deposit and upper interbedding of red clay and calcite nodule.In other words,pre-Baode Formation includes fluvial deposits and aeolian clay layers, which is not accord with the definition of Formtion by the《The Stratigraphic Guide of China and Its Explaination》and should be disassembled.We named fluvial deposits of Pre-Baode Formation as Luzigou Formation and aeolian clay layers as Baode Formation.Luzigou Formation is Equivalent to the original difintion of"luzigou Gravel".L(u|¨)liang Mountain and the Ordos Basin have kept in uplift-denudation condition Since the Cenozoic and missed Paleogene strata.At 10-6.5Ma,L(u|¨)liang Mountain uplifted rapidly and formed the luzigou Formation.At 8Ma,Loess Plateau Region(in the west part of L(u|¨)liang Mountains began to accumulate Aeolian clay layers extensively.The Yellow River transfixion the north and south Cenozoic graben in 1.6Ma,then it intermittent cut and cut into the bedrock.