QUATERNARY LACUSTRINE DEPOSITS IN HIGH-ENERGY SEMIARID MOUNTAIN ENVIRONMENT, KARAKORAM MOUNTAINS, NORTHERN PAKISTAN

Impressive Quaternary lacustrine deposits are present as terrace remna nts throughout the Karakoram Mountains, northern Pakistan. They are ma inly the result of damming of drainage systems during glacial advances or by catastrophic mass movement deposits. The longevity of most lake s is relatively short, in the order of years to tens of years, but sed imentation rates are extremely high as a consequence of the high sedim ent loads within the rivers. This results in deposits that frequently exceed 10 m in thickness. The sediments comprise dominantly planar bed ded, massive and, less commonly, planar laminated, silts, comprising d etrital quartz, feldspar, mica, calcite, chlorite and illite. A facies model for lacustrine sedimentation in a high-energy semi-arid high mo untain region is presented, using case studies from a glacially dammed palaeolake (Glacial Lake Gilgit) and a debris-flow dammed palaeolake (Lake Serat). The rapid deposition and absence of organic material res tricts the usefulness of these lacustrine sediments as proxies for pal aeoenvironmental reconstruction, but they are helpful in reconstructin g the former extent of glaciers and illustrating the importance of hig h-magnitude-low-frequency events, such as landsliding, as formative pr ocesses contributing to the evolution of the Karakoram landscape.