Late-holocene earthflows of the Willard playa/dune complex, Estancia Valley, New Mexico: a geomorphic response to climatic change

摘要

Late-middle to late Holocene dune sediment that overlies Pleistocene lacustrine sediment marks the onset of xeric conditions in the Estancia Valley, central New Mexico. Incised into the underlying lacustrine sediments, the modern deflation basins are enclosed by parabolic dunes composed of clay and gypsum derived from the underlying sediment.Located on the in-facing dune slopes of the deflation basins, the most striking geomorphic feature of this dune complex are numerous elongated scars. These relict scars document a geomorphically distinct earthflow event. Arroyos that cut into flow scars expose eolian earthflow sediment overlying lacustrine deposits. In the zone of depletion, erosional-flow evidence reveals flamed-load structures, channels, and rip-up clasts of lacustrine sediments. In the zone of accumulation, depositional flow evidence reveals laminations and lithic-rich horizons derived from the underlying lacustrine section.The large number of geomorphically similar earthflow scars are believed to represent a mesic climatic fluctuation within the late Holocene of the Estancia Valley.