Provenance Of Neogene Eolian Red Clay Deposits In The Loess Plateau And Its Plateoclimate Implication

The study of the provenance of eolian deposit sequences is of great significance for revealing the paleoenvironment.Understanding the dust sources,transport dynamics and their temporal and spatial variations of the Eolian Red Clay sequence in the Loess Plateau will contribute to our paleo-environmental inversion work on larger temporal and spatial scales.This paper collected 27 Eolian Red Clay zircon U-Pb age samples from Qin'an-I,Dongwan,Chaona,Lingtai,Baodejingle,Shilou and Lantian Red Clay section on the Loess Plateau,representing the Red Clay Deposits from Diffient Spatial Regions on the Loess Plateau and 3~22Ma Red Clay Sediment in the Loess Plateau.Based on the zircon U-Pb ages of the Red Clay from diffient regions on the Loess plateau,we can find that except the edge area where is affected by surrounding orogenic belt,the Red Clay in the Loess Plateau exhibits spatial homogeneity.Based on the zircon U-Pb ages of the Red Clay deposited during 3~22Ma in the Loess Plateau,we can find the Eolian Red Clay exhibits significant temporal variation.the Eolian Red Clay sequences on the Loess Plateau can be divided into five sedimentary stages according to the diffience of material sources:(1)15~22Ma,the main sources were the Pamir and Tianshan Mountains(2)12Ma,the main sources were the Pamir ?Tianshan Mountains and Northern China Desert(3)8Ma,the Qaidam Basin was important contributor for Red Clay sequences.(4)6~7Ma,the main sources were Qilian Mountains and the North Mountain of the Hexi Corridor;(5)3~5.5Ma,the main sources were the Hexi Corridor?the Alxa area and the Tibetan Plateau.The origin and change of dust of the Eolian Red Clay in the Loess Plateau correspond to the retreat of Sub-Tethys Sea,the Mi-1 cooling event,the tectonic movements of the Tianshan Mountains,Pamir,and West Kunlun Mountains during the late Oligocene-early Miocene,the uplift of Tibetan Plateau at ~12Ma,the uplift of Tibetan Plateau at ~8Ma,the Messina Salinity Crisis at ~5.7Ma.The Evolution of dust source of the Red Clay in the Loess Plateau shows:(1)The retreat of the Sub-Tethys Sea is the beginning of aridity in Central and East Asia,which is the precipitating factor for the Red Clay deposition.the tectonic evolution of the Tibetan Plateau is the dominant factor affecting the regional climate environment;global climate events are also an important factor to participate in regional environmental changes.(2)The change of dust source from the west to the east,from single to multiple shows that the Aridification development is from the west to the east,from local to all-round in Central and East Asia since 22 Ma,which makes the regions of north and northwest China turn into dust supply areas successively.(3)The uplift of the Tibetan Plateau during the 8Ma blocked the transmission of near-surface Westerlies and strengthened the East Asian Winter Monsoon,Since then,the influence of near-surface Westerlies on the eolian deposits was weakened or disappeared,and the East Asian Winter Monsoon became the dominant force for dust transport.