The Fluvio-lacustrine Landform Development And Environmental Change In The Sanmenxia Section Of The Yellow River

Plenty of structure and climate information was concluded by the development of Fluvio-lacustrine Landform. There are abroad distributed Fluvio-lacustrine physiognomies in the Yellow River basin between Shanxi and Henan which are the right carrier for the research about the dynamic interaction among the formation, climate and surface change of the Earth. So the deeply research of the Yellow River basin in this region is very important for the theoretics and realism.The physiognomic character along the Yellow River between Shanxi and Henan is basin-mountain interphase. Depended on the detailed measurement of terraces within eleven sections in different physiognomic positions, the formation dates of typical terraces and their sequences were established. Based on the analysis of granularity and magnetization rate, the sediment structures of the Wangyuan and Yuantuping terrace were identified, and the evolvement process of paleoclimate and paleoenvironment in the researched area was rebuilt. In the end, the influence of the Fluvio-lacustrine landform development in this region on the responding relationship between tectonic movement and environmental change was discussed.From the field observation, it was found that there are many terraces (river terraces/lacustrine-deposit mesas) in the research region and the terraces are mainly distributed on the sides of the basins. Based on the research of systemic chronology by the optically stimulated luminescence (OSL) dating and electron spin responance (ESR) signal, it was confirmed that there are nine terraces of lacustrine-deposit mesas or river terraces in the area. These terraces were formed sequentially at 2.0 Ma B.P. (T9), 1.62 Ma B.P. (T8), 1.25Ma B.P. (T7), 0.87Ma B.P. (T6), 0.63Ma B.P. (T5), 0.25Ma B.P. (T4), 0.15Ma B.P. (T3), 86～63Ka B.P. (T2) and 41～22Ka B.P. (T1).From the character analysis of granularity, it was indicated that the sediment contents of the lacustrine and floodplain deposits in the underlayers of the Wangyuan mesas and Yuantuping terraces were from eolian deposits or resediment of the deposits, and the sediment structure of the terraces from lacustrine to floodplain deposit and then to eolian deposit recorded a tectonic movement, the drop of water level and the sequentially depositing process from water to air. The deposit transfers of Wangyuan mesas were happened at 2.21 Ma B.P. and 2.00Ma B.P., and the transfers of Yuantuping terraces were at 1.84MaB.P. and 1.62Ma B.P..The loess granules of eolian deposit which larger than 32μm showed the intensities of the winter monsoon. The section recording of Wangyuan mesas and Yuantuping terraces indicated that intensities of the winter monsoon from 2.0Ma B.P. were whole enhanced and there were two gradually enhanced phases at 1.83～0.8 7Ma B.P. and 0.87 Ma B.P.The evolutional charactars of the winter monsoon is coupled with the change of the global ice content, which esplained that the paleoclimate of research region had responded to the global climate change, and the change of global ice content was the driving factor of the paleoclimate evolution in this area.From the loess records of Wangyuan and Yuantuping profiles, it was shown that the paleoclimate in these regions was markedly conversed at 1.83Ma B.P. 1(L₂₅/S₂₅), 1.65Ma B.P. (S₂₃/L₂₄), 1.15Ma B.P. (L₁₅/S₁₅), 0.87Ma B.P. (S₈/L₉), 0.66Ma B.P. (S₅/L₆) and 0.19 Ma B.P. (L₂/S₂). The change phases and characters of the paleoclimate were consisted with the records of Luochuan loess sections in Loess Plateau. The consistence of the climate change phases in researched region and the eras of the quickly phasic uplift in Tibetan Plateau showed that the phased uplift of Tibetan Plateau is the main factor which influenced the paleoclimate change in the researched area.The coupling relationship among the formation age of the step-like physiognomy of lacustrine-deposit mesas and river terraces between Shanxi and Henan, the evolvement phases of the winter monsoon recorded by loess, the global change phases of ice volume, and the eras of the quickly phased uplift in Tibetan Plateau indicated that the landform development and paleoclimate evolution were mainly controlled by the regional environmental changes and the global climate evolution acted just as trending background.The suddenly increment of loess grains larger than 63μm in the L₁₅, L₉, L₆, and L₂ sections of Wangyuan mesas and Yuantuping terraces indicated four environment events happened. The results showed that there formed some terraces during the environment events in this Yellow River basin, and the age was consisted with the starting times of the uplifts of "Kun-Huang movement" and "Republican movement" in Tibetan Plateau. All of these indicated that the suddenly increment of loess grains larger than 63μm could reflect the regional tectonic movement.