QUATERNARY GEOLOGY OF THE TAMANMYUN HILLS AREA OF THE JARAI GOL, KHOVSGOL, MONGOLIA

The Jarai Gol, a river located in northern Mongolia, flows eastward out of a glacial trough and into the Darhad depression. Landforms in this area reflect a complex history of major late Quaternary processes (glacial, periglacial, lacustrine, eolian, fluvial, and mass wasting). This area is, in effect, a microcosm of Quaternary processes in the whole of the 3500-km²-Darhad depression.

Of primary interest are the interaction and timing of glacial and lacustrine processes. The Tamanmyun Hills, two end moraine complexes, record a history of approximately two glacial advances. The outer moraine complex is composed of two sections of differing morphology and elevation. Kettles in the higher moraine section and the inner moraine complex indicate ice stagnation. The lower moraine section, on the other hand, has a much smoother and more subdued morphology.

Shorelines and lake sediments indicate that a lake filled the Darhad depression at least once. Wave modification of the outer moraine complex suggests the lake to be coeval with and/or to post-date moraine formation. Lacustrine modification may be responsible for the differing outer moraine morphologies. Shoreline elevations (max of 1665 m) suggest the lake overtopped only the lower section of the moraine complex (max elev. of 1640 m, base at 1575 m) but not the higher section. (max elev. of 1680 m) The morphology of the inner moraine complex suggests there has been no wave modification; the lake level must have dropped before its construction.

Evidence for periglacial processes is found as patterned ground. Wind has used the abundant supply of lacustrine and glacial sediments to deposit large parabolic dunes. The Jarai Gol incised the moraine complexes, leaving terraces. Oversteepened slopes enhance mass wasting of incompetent lakebeds.