The Process And Cause Of Lake Transgression And Regression During The Late Quaterary In Linfen Basin, Shanxi

Linfen Basin is a faulted basin of the southern section of Shanxi garben system. It is located in the southern and eastern edge of Ordos plateau. This region is one of the areas where the new neotectonic movements of our country is very active. It is in favor of recognizing the major scientific issue that the regional uplift of the Tibetan Plateau and its environmental effects to focus research on Shanxi Linfen Basin from more extensive contacts with peripheral region.It also provided more persuasive evidence for phased uplift of Qinghai-Tibet Plateau.Since the late Quaternary the Pliocene neotectonic movement in the main rift subsidence increasingly enhanced,the rift subsidence area formed basin.The Linfen Basin has experienced a number of lake transgression and regression changes, continuous sedimentary strata formed of loess-paleosol series and layers of lacustrine sediments distribution in every situation, and there has been abundant paleoclimate change information.This paper based on magnetic susceptibility measurement of typical sections,geomorphological structure of the sediments and characteristics of the stratigraphic sequence revealed the changing progress of lake transgressions and regressions and further inferred the evolutionary mechanism of lake transgressions and regressions.Based on sedimentological analysis of beizhuang and Qinfucun section, data processing and integrated analysis of Linfen Basin lake sediments in magnetic susceptibility and stratigraphic sequences,combined with the actual observations of sedimentary structures and stratigraphic sequence features of danan village,cangdi village,sanlin Town,sanjiadian and nanzhou village,we concluded that a preliminary analysis of lake transgression and regression changes in Linfen Basin.We found that since the late Quaternary Linfen Basin has occurred three huge lake regressions;it took place at 0.55MaBP, 0.25 MaBP, 0.13 MaBP respectively in consistent with the development of palosoil S5,S2,S1.However it has taken place two slow lake transgression,the time is 0.47-0.278MaBP,0.25-0.14MaBP,corresponds respectively with the development of Loess L5 to L3 and S2 to L2. The height of the lake level after the slow lake transgression did not meet or exceed that of the early lake withdrew.According to the process of lake transgression and regression,we found that the model of the transgression and regression in Linfen Basin belongd to slow lake transgression and rapid lake regression.Combined with the physical data analysis about internal crust in Linfen Basin,the lake transgression and regression occurred mainly due to tectonic movements,the climate change did not play an important role. When tectonic movement was active,the upper mantle was strongly on the arch,pelvic floor relatively uplifted,the lake rapidly contracted,therefore the significant lake regression occurred; when tectonic movement was relatively stable,the upper mantle slowly cooled down and shrunk,the lake slowly expanded,therefore the lake transgression occurred slowly.So we concluded that Linfen Basin has taken palce three intense tectonic movements at 0.55MaBP,0.25MaBP,0.13MaBP respectively.The tectonic movements mainly caused by upper mantle magma movements active in Linfen Basin internal crust on the upper arch due to the phased uplift of Qinghai-Tibet Plateau.