对渭河盆地新生界及其年代的讨论

Discussion on the Cenozoic and Its chronology in the Weihe River basin

秦岭造山带北缘的渭河盆地,新生界十分发育,前人建立了盆地地层系统,随着地质成果的不断积累,原有的地层系统需要重新整理。在前人工作基础上,根据新的全球变化研究资料和数据,对渭河盆地新生界部分地层的年代做了重新认识。认为红河组形成于古近纪中始新世—晚始新世;白鹿塬组形成于古近纪晚始新世—早渐新世;冷水沟组形成于新近纪中新世早期;寇家村组形成于新近纪中新世中期;灞河组形成于新近纪中新世晚期。蓝田组和游河组不存在层位上下关系,它们可能是地史时期形成的同期异相沉积;三门组的上界年代在不同的地区各不相同,表明古三门湖的消亡时代不同的地区存有差异。蓝田组和游河组形成时期,研究区地形地貌发生分异,表现为地形凸起和凹陷并存,凸起堆积风成沉积,凹陷接受湖泊沉积,这一地貌格局很可能自7.3MaB.P.以来,一直持续到0.15MaB.P.,黄土高原的风尘堆积与古三门湖并存的地貌格局是新近纪晚中新世最晚期至0.15MaB.P.以来研究区重要的地质事件之一,它是当时研究区区域构造运动作用的结果。

The Weihe River basin lies in the northern margin of the Qinling orogenic belt, and the Cenozoic in the basin is very developed.The previous researchers have set up the stratigraphic system in this basin.With accumulation of the geological results,the original stratigraphic system needs to be rearranged. Based on the previous studies,according to the updated materials and datum of studies about the global change,this paper has reconsidered the Cenozoic in the Weihe River basin , and the chronology of some strata is stadied.The authors considered that the Honghe Formation formed during the Middle-Late Eocene Epoch of the Paleocene Period,the Bailuyuan Formation formed during the Late Eocene Epoch to the Early Oligocene Epoch of the Paleocene Period,the Lengshuigou Formation formed during the Early Miocene Epoch of the Neocene Period, the Koujiacun Formation formed during the Middle Miocene Epoch of the Neocene Period, and the Bahe Formation formed during the Late Miocene Epoch of the Neocene Period.The contact relationship between the Lantian Formation and Youhe Formation is not up and down,which implies that they may be formed in different sedimentary environments at the same time during the geological history.The geological age of the top part of Sanmen Formation varies in different regions, which states that the vanishing time of the ancient Sanmen Lake was different in studied area.As 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, and the lacustrine deposition heaped up in the depressions.This geomorphic pattern probably sustained during 7.3 Ma B.P. to 0.15 Ma B.P.,One of the important geological events is that the ancient Sanmen Lake and the eolian deposition of the Loess Plateau coexisted during the Latest period of the Late Miocene Epoch of the Neocene Period to 0.15 Ma B.P. in studied area,it reflects the regional tectonic Movement in Weihe River basin.