The Trollheim alluvial fan and facies model revisited

摘要: Widely held, fundamental alluvial-fan facies concepts generated in past literature based on the Trollheim fan, Deep Springs Valley, California, are inconsistent with actual characteristics of this fan. Previous publications have established, mostly without field study, that fan consists debris-flow, sieve lobe, sheetflood, and channel facies; debris-flow deposits comprise proximal area, giving way to or sheetflood distally. Contrary these views, clayey gravelly, matrix-supported, dominate all parts exposures, suggesting has been built almost exclusively by mass-wasting events. Channel-fill constitute only a small component most restricted area where they an inset relationship sequences. The laterally restricted, clast-supported gravel lenses formed primarily through winnowing fines streamflow. widespread surface is mantle varnished, matrix-free pebbles, cobbles, boulders commonly distributed radially oriented lobes levees characteristic deposits. This was produced surficial fine-fraction from overland water flow. In contrast previous conclusions, were not identified anywhere Additionally, many depicted widely cited "Trollheim vertical profile," including ripple-bedded sand, cross-bedded overbank mud, present on, stratigraphic cuts of, after which profile named.