Sedimentary Environment Of The Present-day Tengger Desert And Its Implication For Dust Provenance To The Chinese Loess Plateau During Quaternary

Loess on the Chinese Loess Plateau is one of the significant archives of environmental and paleoclimatic change because of its extensive distribution,big thickness and successive deposition.And it is considered one of the most meaningful indicators in reconstruction of monsoon variability,aridity history and uplift of Tibetan Plateau.However,the provenance of loess,is still controversial,though researches attempted to solve this issue based on comparison from many tracers including physical and geochemical characteristics between loess Plateau and potential provenances.Therefore,this study attempts to test whether Tengger was possible to make actual contribution to the Chinese Loess Plateau thoroughout the Quaternary through detecting sedimentary environment in the present-day Tengger Desert,the proximal desert in upwind direction to the Chinese Loess Plateau.A core,BJ14,was obtained from the latest bank of the Baijian Lake within the Tengger Desert,and analysis of magnetostratigraphy,Electron Spin Resonance(ESR)dating,lithology,grain size and creature remnants were performed.Confined with limited ESR dating results,chronological framework of the core was established based on magnetostratigraphy.Sedimentary environment was reconstructed on the lithology,and creature remnants.The main conclusions of this thesis are listed as follows.(1)The strata of the 104-m-long core can be grouped into 6 units from bottom to up.Sediments of Unit 1,Unit 3 and Unit 5 mainly consist of brown clay and thin layers of grayish-green clay,which were intermingled with cinerous,brown and grayish-black sand.Sediments of Unit 2,Unit 4 and Unit 6 consist mainly of cinerous,brown and grayish-black sand intermingled with brown or grayish-green clay.In the grayish-black sand layers,parallel bedding and cross bedding developed.(2)Lithology of the core,including component,color,sedimentary structure,supports that almost all strata in core BJ14 formed in lake environments.And this recognition was further supported by creature remnants indicative of water envrionment in the representative strata,for example Gyrogonite of Charophyta were found in the clay layers at depths of 11.88 m,12.3 m,84.99 m and 96.36 m,Ostracodes shells were found in the clay layers at depths of 94.54 m and 102.24 m.Grain size analysis indicates that sediments are consisted mainly of <63 ?m particles(proportion nearly 90%)at the depths of 104-64.19 m,and of 100-250 ?m particles(proportion nearly 70%)which was considered transported mainly by wind at the depth of 64.19-0 m.(3)Constrained with limited ESR dating results,magnetostratigraphy of the core BJ14 definites polarity chrons of the Brunhes,Matuyama and Gauss,and the boundaries between Brunhes and Matuyama(B/M)and between Matuyama and Gauss(M/G)at depths of 44.57 m and 94.31 m respectively.The basal age of this core is older than 2.6 Ma.(4)Combined with the previous researches in the area and southwest Tengger Desert and south of Badain Jaran Desert,this study indicates that lakes occupied most area of the present Tengger Desert during early Pleistocene,and deserts started to develop from the marginal area of the basin since ?0.9 Ma.Therefore,Tengger Desert might have contributed limited dust to the Chinese Loess Plateau during early Pleistocene.