Paleoenvironment of Carboniferous Conglomerate, Kharkhiraa Uul

Jo Nissenbaum

Whitman College, Walla Walla WA 99362



Located in the Black Marmot coal mine area of the northeastern Kharkhiraa Mountains, a thick accumulation of conglomerates represents a depositional environment that fluctuated between marine and terrestrial conditions. Approximately 35 diverse conglomerate units demonstrate cyclical variance in grain size, fabric, rounding, color, matrix, and cement. Shale, coarse-grained sandstones, coal beds, and welded tuff make up approximately 15 interbeds. Clasts in the conglomerates consist mostly of quartzite, quartz, sandstone, greenstone, and conglomerate clasts though a few units have limestone and volcanic clasts as well. Rocks similar to those found in the conglomerates make up the older Paleozoic terrane in this area. The interbedded conglomerate coal/shale sequence suggests an estuarine setting subject to frequent flooding from local highlands.