Formation And Evolution Of The Weihe River Basin And Uplift Of The Eastern Qinling Mountains

The sedimentary sequence, the structural patterns, and tectonic subsidence of the Weihe basin have been discussed in this paper, according to the work done by previous researchers, a lot of information obtained from field working and in office, the coupled relationship of the erogenic belt and the basin. The Chronology of the Cenozoic in the Weihe basin has also been probed into and the uplift rate of the eastern Qinling mountains from the time of 1.2 MaB.P. is estimated in this paper. Researches on the sedimentary sequence and the structural patterns of the Weihe basin indicate the basin a complicated superimposed basin, and revealed the characteristics of the coupled relationship between the Weihe River basin and the eastern Qinling mountains, thus creating a new way for inversion of oroginic uplifting from the sedimentation of the basin.The Cenozoic Era is the major Period of the growth of the Weihe River basin,this basin underwent three stages of the tectonic evolution, i.e. the Early Period of the "passive" rifting stage(from the late of Middle Eocene to the Late Miocene ); the Middle Period of the strike slip-extensional stage(from the latest of Late Miocene to the late of Early Pleistocene);the late Period of the compressional-uplifting stage(from the late period of the Early Pleistocene to the present). It reflects that the topographic evolution of the basin underwent three times of uplift and two times of denudation since the late of Middle Eocene, i.e. "uplift-denudation-uplift-denudation-uplift" , in which the major uplift phase in the Eastern Qinling happened in Miocene and the geological and the topographic framework of the Eastern Qinling in the latest of Miocene has been quite similar to that of present. From 7.3 Ma B.P to 1.2 Ma B.P., the topography of the Weihe basin and the Eastern Qinling appeared in confrontation with small difference between the elevation of mountain and basin. In 1,2Ma B.P., the Eastern Qinling and the Weihe River basin uplifted together and from that time, the well-known ancient Sanmen Lake vanished gradually.Five grades of terrace developed in the Weihe basin indicate new characteristics of gradually and intermittently uplifting of the Eastern Qinling since 1.2Ma B.P. on, with a increase trend of uplift speed.In addition, the curves of tectonic subsidence indicated the "curve patterns" with multiple phases and also a great difference to those typical continental rifted basins in the world.It reflects the specific and complicated features of the Weihe River basin.Based on the latest researches, this paper has redetermined the geological age of some Cenozoic strata in the Weihe basin, such as the Honghe Formation formed in the late of Middle Eocene to the Late Eocene,the Bailuyuan Formation formed in the Late Eocene to the Early Oligocene,the Lengshuigou Formation formed in the Early Miocene, the Koujiacun Formation formed in the Middle Miocene ,and the BaheFormation was formed in the Late Miocene, and the contact relationship between the Lantian Formation and Youhe Formation is not up and down. Perhaps they are the sediments of synchronous but heteropic facies .The geological age of the Sanmen Formation varies in different regions.it states that the vanishing time of the ancient Sanmen Lake was different in studied area.During the period which the Lantian Formation and the Youhe Formation formed,the topographic and geomorphic pattern was divided into protrusions and depressions.the eolian deposition piled up on the protrusions, the lacustrine deposition heaped up in the depressions.This geomorphic pattern probably sustained from 7.3Ma B.P. to 1.2Ma B.R.One of the important geological events is that the ancient Sanmen Lake and the eolian deposition of the Loess Plateau coexisted from 7.3Ma B.P.lasted to 1.2Ma B.P. in studied area.it might be the result of regional tectonic movement in the Weihe River basin.The result of the calculation of the paleosalinity of the ancient Sanmen Lake in the Weihe River basin demonstrates that the Sanmen Formation belongs to a low sa...