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New Mexico Water Research Symposium, Socorro, 16 August, 2005

Abstract:

Two hydrologic systems determine the landforms and sedimentary facies preserved in the northern Tularosa Basin: 1) the surface water runoff and clastic sediment delivery system of Malpais drainage, Salt Creek, and Three Rivers and their tributaries, and 2) the sulfate-laden groundwater system that dissolves Permian gypsum and reprecipitates it in extensive springs, marshes, and lakes.  The relative dominance of Quaternary springs, wetland habitats, rivers, and lakes in the northern basin has undergone extensive spatial and temporal changes as indicated by both clastic and precipitated sedimentary deposits and landforms. The present-day gypsum buildups of Mound Springs complex occupy the western flank of an earlier and much larger accumulation of spring gypsum, covering an area of at least 16 km2.  Similar extensive spring deposits are present to the northeast and southwest of the Mound Springs area.  Lacustrine evaporite and siliciclastic sediments indicate that shallow saline lakes occupied the floor of the Tularosa basin below an elevation of ~3960 ft (1207 m) by at least ~35 kyrs B.P. (radiocarbon age). The lake experienced large influxes of siliciclastic sediment during the last glacial maximum (LGM).  LGM lake expansions represent times when fluvial and lacustrine systems and wetland habitats in contributing watersheds to the north (e.g. Salt Creek, Malpais, and Three Rivers watersheds) were integrated and produced an extensive fluvio-deltaic complex along the northern margin of late Pleistocene Lake Otero. Laterally extensive surface deposits of gypsum along the present-day Salt Creek drainage were deposited in a large, gypsum-precipitating wetland area covering at least 50 km2.  The gypsum deposits, up to 3 m thick, contain abundant fossil ostracodes and aquatic, pulmonate gastropods, and apparently accumulated after desiccation of Lake Otero during a latest Pleistocene-early Holocene (Younger Dryas?) episode of comparatively wet climate. Extensive deflation, eolian sheets and dunes, erosion of arroyo channels in the piedmont aprons and along salt Creek modified the landscape in Holocene time. The snout of the Carrizozo lava flow, with a cosmogenic age of 5200 years, covered earlier gypsic spring, marsh, and playa deposits.

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