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青藏高原边界地区的研究,尤其是砾石研究,对探讨青藏高原的隆升过程及隆升机制具有重要意义。本文选取青藏高原东北部香山山前小洪沟剖面,对出露的新生界各层位的砾石进行统计。统计结果显示,该剖面寺口子组上段、红柳沟组下段、红柳沟组上段、第四系以及现今河床出露的砾石成分主要为砂岩和石英砂岩,这与香山地区岩性相符合;砾石主要呈次圆状和次棱角状;长短轴比主要为1～2之间,为近圆状;砾石主要集中在中砾和小砾类别;分选好至中等好。砾石粒径分布显示出向细粒成分偏的特征,主要呈尖峰正态分布。这些特征表明各层位砾石相似的搬运过程,为中距离山前河流冲积砾石。沉积分析表明该砾石与气候振荡无必然联系,为构造隆升的产物。砾石沉积年龄由邻区磁性地层定年结果来限定。砾石特征结合邻区沉积分析表明香山地区在寺口子组沉积时(始新世)已具有相当大的高程;至清水营组沉积时(渐新世),该山体被剥蚀夷平;到红柳沟组沉积时(中新世早、中期),香山经历了再次的隆升;至干河沟组沉积时(中新世晚期到上新世),构造趋于稳定;到更新世时,再次出现隆升事件。始新世香山山体可能与晚白垩世至新生代早期的构造事件有关,中新世的隆升时间可以作为印-藏碰撞效应到达香山地区的时限,显示青藏高原东北边界新生代的变形隆升时间较前人研究结果早,且存在多期隆升。
The research on the border area of the Qinghai-Tibet Plateau, especially the study of gravel, is of great significance for exploring the uplift process and uplift mechanism of the Qinghai-Tibet Plateau. In this paper, the Xiaoxiangou section of the Xiangshan piedmont in the northeastern Qinghai-Tibet Plateau is selected to make statistics on the gravels in the exposed Neozoic strata. The statistical results show that the upper part of the Teikokuzi Formation, the lower part of the Hongliugou Formation, the upper part of the Hongliugou Formation, the Quaternary, and the present gravelly interbeds are mainly sandstone and quartz sandstone, which are consistent with the lithology of the Xiangshan area. The main gravels Was sub-circular and sub-angular; long axis was mainly between 1 and 2, is nearly circular; gravel mainly in the gravel and small gravel categories; good to medium good. Gravel particle size distribution shows the characteristics of the partial composition of fine particles, the main spike normal distribution. These features indicate similar gravel-bearing removal processes at all levels, alluvial gravel for rivers at mid-distance. Sedimentary analysis shows that the gravel is not necessarily related to the climate oscillation and is the product of structural uplift. The gravel sedimentary age is defined by the dating results of the magnetic strata in the adjacent area. The gravel characteristics and the analysis of the adjacent areas show that the Xiangshan area has a considerable elevation at the time of the deposition of the Shikouzi Formation (Eocene); when it was deposited in the Qingshuiying Formation (Oligocene), the mountain was eroded and flattened; During the deposition of the Group (Early and Middle Miocene), Xiangshan experienced another uplift; the structure tended to be stable during the deposition of the Gansheou Formation (from the Late Miocene to the Pliocene), and again to the Pleistocene Rise event. The Eocene Fragrant Hills may be related to the tectonic events from the Late Cretaceous to the Early Cenozoic. The Miocene uplift time can be used as a time limit for the Indian-Tibetan collision effect to reach the Xiangshan area, indicating the Cenozoic uplift of the northeastern boundary of the Tibetan Plateau The results earlier than previous studies, and the existence of multiple uplift.