HR: 1340h
AN: PP23A-1079    [Abstracts]
TI: Glacial and Periglacial Geology of the Egiin Davaa Region, Hangay Nuruu, Mongolia
AU: * Carson, R J
EM: carsonrj@whitman.edu
AF: Whitman College, Dept. of Geology, Walla Walla, WA 99362, United States
AU: Wegmann, K W
AF: Lehigh University, Dept. of Earth & Environmental Sciences, Bethlehem, PA 18015, United States
AU: Coggan, B D
AF: Whitman College, Dept. of Geology, Walla Walla, WA 99362, United States
AU: Skyles, E
AF: Fort Lewis College, Geosciences Dept., Durango, CO 81301, United States
AU: Pearson, A J
AF: Beloit College, Dept. of Geology, Beloit, WI 53511, United States
AB: A wide variety of glacial and periglacial landforms exist near Egiin Davaa (pass) in the Hangay Nuruu (mountains) of west-central Mongolia. Today this area has permafrost but no permanent snowfields. Glaciers originated on the north side of the divide separating Arctic-seeking streams from interior drainage toward the Gobi. The cirque glaciers flowed northerly and westerly, becoming valley glaciers, some of which coalesced to form a piedmont glacier in the Davaatiin and Chuluut valleys. The piedmont glacier blocked the Chuluut Gol (river) to form glacial Lake Chuluut which had a minimum volume of 0.3 km3. The glacial lake likely drained in one or more jökulhlaups due to ice-dam failure. Part of the glacier complex flowed (probably during OIS2) southwest over Egiin Davaa and reached (at LGM) to within 1-2 km of moraines deposited during an earlier glaciation (possibly OIS6). Here and elsewhere the older moraines can be distinguished from younger moraines based on surface boulder frequency, boulder height, and hillslope gradient. Glaciolacustrine sediment upvalley of a recessional moraine in the valley of Botgon Gol has a calibrated radiocarbon age of 13,155 ± 70 ybp. This recessional moraine, at an elevation of 2300 m, is 16 km downvalley from the cirque headwall and 11 km upvalley from the LGM terminal moraine. From a separate valley we also obtained cosmogenic ages of two granitic boulders on a recessional moraine at an elevation of 2600m, ~11 km downvalley from the cirques; the boulders are on top of the 8-m-high scarp of the Egiin Davaa Fault (normal dip-slip) and yielded surface exposure ages of 14,709 ± 1005 and 16,537 ± 1174 ybp. This recessional moraine is 15 km upvalley from the terminal LGM ice position. Periglacial features are widespread. Most impressive are extensive cryoplanation terraces with terrace sets hundreds of meters high and individual terrace risers 13-22 m high. Scattered across the landscape are blockfields, patterned ground, and aufeis, plus generations of solifluction lobes on valley sides and palsas on valley bottoms. Peat from the permafrost table (base of the 70-cm-thick active layer) has a calibrated radiocarbon age of 5,695 ± 26 ybp.
DE: 1105 Quaternary geochronology
DE: 1130 Geomorphological geochronology
DE: 1625 Geomorphology and weathering (0790, 1824, 1825, 1826, 1886)
DE: 9320 Asia
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting