Megaflood sedimentary valley fill: Altai Mounatins, Siberia

Carling, Paul A., Martini, Peter, Herget, Jurgen, Borodavko, Pavel and Parnachov, Sergei (2009) Megaflood sedimentary valley fill: Altai Mounatins, Siberia. In, Burr, Devon, Carling, Paul and Baker, Vic (eds.) Megaflooding on Earth and Mars. Cambridge, UK. Cambridge University Press, pp. 243-264.

Abstract

During the Quaternary, the Altai Mountains of south-central Siberia sustained ice-caps and valley glaciers. Glaciers or ice lobes emanating from plateaux blocked the outlet of the Chuja-Kuray intermontane basins and impounded meltwater to form large ice-dammed lakes up to 600 km3 capacity. On occasion the ice dams failed and the lakes emptied catastrophically. The megafloods that resulted were deep, fast-flowing and heavily charged with sand and gravel, the sediment being sourced from the lake basins and also entrained along the course of the flood-ways. The floods were confined within mountain valleys of the present-day Rivers Chuja and Katun, but large quantities of sediment were deposited over a distance of more than 70km from the dam site in tributary river-mouths, re-entrants in the confining valley walls (e.g. cirques) and on the inside of major valley bends. The main depositional units that resulted are giant bars which blocked the entrances to tributaries and temporarily impeded normal drainage from the tributaries into the main-stem valley such that minor lakes were impounded within the tributaries behind the bars. Fine sediment from the tributaries accumulated in these lakes as local lacustrine units. Later the bars were breached by the tributary flows and the local lakes were drained. Sections of the giant bar sediments and the local lacustrine units are used to describe the nature of the megaflood valley fill which was deposited primarily in Marine Isotope Stage 2. Although there is evidence of the Chuja-Kuray lake being in existence within Marine Isotope Stage 4 there are no flood sediments unequivocably ascribed to this period. Descriptions of the sedimentology and stratigraphy of the valley-fill are interpreted within a context of proposed flow mechanisms associated with deposition of the various facies and thus provide some indication of the flood dynamics

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