Sediment characteristics and formation age of ancient dammed lakes in Wudongde Reservoir Area

Abstract

The lacustrine sediments of the ancient dammed lakes contain important information reflecting the evolution of the geological environment. Through the study of lacustrine sediments, the formation and extinction process of the ancient barrier lake in the Wudongde Reservoir Area can be further revealed. The lacustrine sediments in the Wudongde Reservoir Area in the lower reaches of the Jinsha River are taken as the research object, and the spatial distribution, grain size sequence characteristics and formation age of lacustrine sediments in this area are discussed through field investigation, grain size test and OSL dating. The results show that:(1)The elevation of lacustrine sediments visible in the Wudongde Reservoir Area ranges from 908 m to 1 038 m, mainly exposed in the broad valley and convex bank area;(2)The C-M diagram shows that at the end of deposition, the hydrodynamic conditions changed dramatically and the hydraulic transport capacity became stronger, and the superposition relationship between the “top layer” lacustrine sediments and fluvial sand and pebble beds in many places can reflect that the end of deposition process corresponded to a large-scale disastrous flood event;(3)The results of OSL dating indicated that formation time of sediments(the time to block the river) is 34 ka BP, and the end time of lacustrine sediment deposition(the time to break the dam) is about 20 ka BP.

Keywords

ancient dammed lake / lacustrine sediments / sedimentary characteristics / outburst flood / OSL dating