Quaternary landscape evolution in the eastern Hindu Kush, Pakistan

摘要

The eastern Hindu Kush in northern Pakistan is among the most dynamically active tectonic and geomorphic areas in the world. During the Quaternary, valley-fill sediments of great thickness have been deposited by glacial, fluvial, eolian and mass-movement processes. Fluvial incision eroded these sediments and formed terraces. Their development was controlled by tectonic and climatic factors, and therefore they record information about the Quaternary landscape evolution and glaciations. Investigations included the mapping of landforms, especially the terraces, and sedimentological analyses on valley-fill deposits. This resulted in a classification with six main types of terraces: morainic, glaciofluvial, fluvial, lacustrine, mass-movement debris, and fan terraces. Tectonic terraces were not recognized, but tectonically influenced sediments have been found near the Shyok Suture Zone. This classification corresponds with results from the nearby Karakoram. Two major Late Pleistocene glaciations are recognized during marine isotopic stage 3 (MIS-3) (Drosh Glacial Stage) and in the MIS-2/Early Holocene (Pret Glacial Stage). Moraines from the Neoglacial (Shandur Glacial Stages Ⅰ and Ⅱ) and the Little Ice Age (Barum Glacial Stage Ⅰ) are located near the contemporary glaciers. During deglaciations, huge terraces were formed: the upper terrace or Broz Fan Formation and the middle terrace or Ayun Fan Formation between the Drosh and Pret Glacial Stages, and the lower terrace or Urghuch Fan Formation after the Pret Glacial Stage. The chronology presented in this paper shows that there was only limited glaciation in the eastern Hindu Kush during the global Last Glacial Maximum (LGM).