New results of OSL dating of Quaternary sediments in the Upper Katun’ valley (Gorny Altai) and adjacent area

Several sections have been studied to understand the distribution and interrelation of basic genetic types of Quaternary deposits in the Uimon basin and adjacent area. The OSL date of 101 ± 10 ka from the glaciolacustrine terrace on the northeastern rim of the basin corresponds to the cool substage of MIS 5. The glaciolacustrine sediments of the northern rim are covered with widespread diamictic flows of the outburst draining of the ice-dammed lake. The diamicts are overlain by a subaerial complex of loesses and three fossil soils. From the OSL loess dates in the range of 43 to 49 ka we infer that the complex formed from the early MIS 3 through the Holocene. This is also supported by radiocarbon dates from alluvial deposits incised into the glaciolacustrine terrace and into megaflood sediments of the final draining of the last paleolake. The OSL dates in the range of 77 to 89 ka from alluvial sediments indicate that postglacial downcutting of the present-day Katun’ valley probably started just after MIS 5. The discrepancy between the beryllium dates from dropstones and Holocene TL-dates of the Katun’ valley floods ranging from 23 to 6 ka can be explained if the younger floods are related to the draining of moraine- and rock slide dammed rather than ice-dammed lakes. The younger floods, though being less voluminous than the glacial megafloods, were capable of producing giant ripple marks.