EVIDENCE FOR MULTIPLE GLACIATIONS OF THE TANGGULA SHAN OF THE CENTRAL TIBETAN PLATEAU

Moraine mapping and cosmogenic radionuclide (CRN) model exposure ages of moraine boulders provide a preliminary chronology for multiple glaciations of the Tanggula Shan, central Tibetan Plateau. Mapping from satellite imagery shows that at least four groups of moraines are present in the Tanggula Shan. The most extensive moraines, of the Tanggula and Zhajiazangbu phases, probably formed during or before marine oxygen isotope stage 6 (MIS 6). During these phases large piedmont lobes extended from 16 to 26 kilometers from present glacier margins to elevations below 5050 m asl. At this time it is possible that most of the Tanggula Shan were covered by a large ice cap. The Basicuo phase occurred during or before MIS 3 based on minimum limiting CRN model exposure ages of 31,900 ± 3,400, and 41,400 ± 4,300 ¹⁰Be yr BP. Large discrete ice caps were present during the Basicuo phase and glaciers extended from 3 to 10 km from their present margins. The Longxiazai phase occurred between 31,900 ± 3,400 and 16,000 ± 1,700 ¹⁰Be yr BP based on two CRN model exposure ages. During MIS 2 glaciers advanced less than 3 kilometers from their present margins suggesting ice of limited extent in the central Tibetan Plateau at this time. Undated moraines within 1 km of the present margin could be Neoglacial or Little Ice Age in age. At present glaciers are restricted to the highest peaks above 5400 meters and have retreated at a rate of about 10 meters per year for the last 40 years.