New Mexico Geological Society Annual Spring Meeting — Abstracts

Near the northernmost floor of the Tularosa Basin, the demarcated Capitol Peak SE 7.5’- quadrangle is at the junction of three drainages (upper Salt Creek-Mound Springs, Carrizozo valley, and Three Rivers fan) and a western piedmont slope. This junction, along with an uncommon, sulfate-precipitating planar wetland, created a low-gradient surface that stalled the Carrizozo Malpais lava flow. The 5,200-year-old lava flow overrode alluvium and a complex environment of evaporite deposition and eolian features. In turn, these contrasting depositional processes continued after the lava flow and buried its margins and kipukas by up to 3 m of alluvial, evaporite, and loessal sediments. Post-lava alluvium accumulates on top of several types of groundwater-discharge gypsum and has spread out across the north-central part of the quadrangle. To the west, the broad valley of Salt Creek is incised up to 13 m below the level of maximum basin fill. The valley borders of Salt Creek consist of sparse, wind-deflated basin-fill exposures of fine-grained clastic and gypsic beds and cross-bedded pebbly sand channels, and moist fine-grained alluvial/eolian slopes where groundwater seeps just below the surface. The southwestern quarter of the quadrangle consists of a complex string of marshes, playas, blowouts, eolian dunes, and alluvial channels with discontinuous outcrops of basin fill. Stripped exposures of basin fill exhibit rare trackways of Pleistocene megafauna (mammoths?). Evidence of subsurface dissolution includes karst features and tilted basin-fill. The two endemic populations of White Sands pupfish (Cyprinodon tularosa) live in Salt Creek and Malpais Spring and salt marsh on the quadrangle. In addition to gypsum, the modern brackish-to-saline springs, streams, and wetland environments precipitate halite, hexahydrite, thenardite and other soluble salts as widespread efflorescent surface accumulations, which are periodically removed by re-dissolution and wind deflation. The uncommon surficial features related to accumulation by gypsum precipitation include megamounds, meandering raised-levee streams, platform marshes, raised-rim marshes, and hummocky rolling plains that appear to represent modification of previously deposited gypsum by eolian and/or dissolutional processes.