Pediment near the Western Liupan Mountain and Its Implication on the Neotectonic Uplift
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摘要: 晚新生代青藏高原的隆升对其周围地貌格局和沉积产生了重大影响。地处高原东北构造边界的六盘山受其影响产生明显的地貌分异，造成黄土高原东西两部分巨大的风成沉积差异。最近对位于六盘山西侧陇中盆地东北边缘黄河最高阶地之上的山麓剥蚀面上的黄土磁性地层学研究表明该剥蚀面形成于约1.8 MaBP，与陇中盆地西南隅的兰州、临夏两地山麓剥蚀面的年龄一致〔1〕，表明在约1.8 MaBP 以前六盘山以西普遍遭受剥蚀，可能形成一级统一 的山麓剥蚀面，即所谓的甘肃期准平原，并指示在约1.8 MaBP 时，六盘山和青藏高原曾产生进一步强烈抬升，该剥蚀面发育结束，黄河出现，黄土开始堆积〔1，2〕。Abstract: The late Cenozoic uplift of the Tibetan Plateau played a great role in the geomorphic and depositional evolution of its adjacent areas. This effect has brought about the Liupan Mountain at the northeastern tectonic margin of the Tibetan Plateau developed with quite different geomorphology in its two sides, resulting in large differences in wind-blown depositional environment between the eastern and western parts of the Chinese Loess Plateau. A well-preserved pediment, covered by 235 m thick loess, was recently found at the western side of the Liupan Mountain, which stands above the highest terrace of the Yellow River in the northeastern Longzhong Basin. The paleomagnetism of the loess section shows that the pediment developed at ～1.8 Ma BP, so did that of the pediments in Lanzhou-Linxia region in the southwestern Longzhong Basin. This implies that the Longzhong Basin to the west of the Liupan Mountain had been subject to long term denudation before ～1.8 Ma BP, and wight have finally developed a joined pediment or so-called Gansu Peneplain covering the whole Longzhong Basin. The large incision of the pediment and start of deposition of loess on the pediment at ～1.8 Ma BP suggest that the Tibetan Plateau and the Liupan Mountain rose strongly at that time, causing not only the end of the pediment but also the subsequent appearance of the Yellow River in the Basin.
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Key words:
- Liupan Mountain /
- loess /
- pediment /
- Tibet uplift /
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