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Santa Fe, NM, United States

Hall S.A.,Red Rock Geological Enterprises | Goble R.J.,University of Nebraska - Lincoln
Geomorphology | Year: 2015

The Strauss sand sheet occurs in south-central New Mexico, USA, and northern Chihuahua, Mexico, covering an area of about 4740km2. Its chronology is determined by 19 OSL ages. The sand sheet formed primarily during three phases of eolian deflation and deposition, each phase with a separate sand source and under different climatic and environmental circumstances. The first phase of eolian sedimentation occurred 45 to 15ka with the deposition of unit 1. The sand source for the first phase was beach-related features along the eastern shoreline of pluvial Lake Palomas in Mexico. The glacial-age climate was cool, wet, and windy because of the southern path of the jet stream at that time. After 15ka, with the onset of warmer conditions of the Bølling-Allerød, the shutting down of the Palomas sand source, and wet conditions of the Younger Dryas, the sand sheet stabilized with weak soil development in unit 1. By 11ka, the climate shifted to Holocene drying conditions and the second phase of sand accumulation began, forming unit 2; the sand source was the local deflation of the previously deposited unit 1 sand. The sand sheet stabilized again by 1.9ka with slightly wetter late Holocene climate; a weak soil formed in unit 2 sand. About A.D. 1500 and extending to about A.D. 1850 or later, an A horizon formed on the sand sheet, probably in response to a desert grassland vegetation during the period of wet climate of the Little Ice Age. In an anthropogenic third phase of eolian activity, after A.D. 1850, the vegetation was likely disturbed by overgrazing; and the unit 2 and A horizon (unit 3) sands were deflated, resulting in the deposition of a thin layer of massive eolian sand (unit 4) across the sand sheet. By about A.D. 1900 mesquite shrubs had increased in abundance; and deflated sand, largely from unit 2, began to accumulate around the shrubs, forming coppice dunes (unit 5). Mesquite coppice dunes continued to increase in number and volume during the twentieth century and at present dominate most of the sand sheet. This third phase of eolian deflation-deposition is ongoing today. © 2015 Elsevier B.V. Source

Hall S.A.,Red Rock Geological Enterprises | Penner W.L.,Parametrix | Palacios-Fest M.R.,Terra Nostra Earth science Research | Metcalf A.L.,University of Texas at El Paso | Smith S.J.,Northern Arizona University
Quaternary Research | Year: 2012

A thick alluvial sequence in central New Mexico contains the Scholle wet meadow deposit that traces upstream to a paleospring. The wet meadow sediments contain an abundant fauna of twenty-one species of freshwater and terrestrial mollusks and ten species of ostracodes. The mollusks and ostracodes are indicative of a local high alluvial water table with spring-supported perennial flow but without standing water. Pollen analysis documents shrub grassland vegetation with sedges, willow, and alder in a riparian community. Stable carbon isotopes from the wet meadow sediments have δ 13C values ranging from -22.8 to -23.3‰, indicating that 80% of the organic carbon in the sediment is derived from C 3 species. The wet meadow deposit is AMS dated 10,400 to 9700 14CyrBP, corresponding to 12,300 to 11,100calyrBP and overlapping in time with the Younger Dryas event (YD). The wet meadow became active about 500yr after the beginning of the YD and persisted 400yr after the YD ended. The Scholle wet meadow is the only record of perennial flow and high water table conditions in the Abo Arroyo drainage basin during the past 13ka. © 2011 University of Washington. Source

Hall S.A.,Red Rock Geological Enterprises | Goble R.J.,University of Nebraska - Lincoln
New Mexico Geology | Year: 2011

The Mescalero sand sheet that covers most of the Mescalero Plain is formed by two eolian sand bodies, the Lower and Upper units. New and revised OSL ages indicate that the Lower unit accumulated 90-50 ka and the Upper unit was deposited 18-5 ka. Both eolian units are dominated by massive, well-sorted, fine quartz sand. The Lower sand directly overlies the eroded surface of the calcic Mescalero paleosol. The top of the Lower sand incorporates the Berino paleosol, a red argillic soil that formed on the sand sheet during the comparatively wet and cool environment of the late Wisconsinan. The Lower sand and the Berino paleosol are buried by the Upper eolian sand. An unnamed Bw paleosol at the top of the Upper sand formed during the past 5 ka. Locally, archaeological sites younger than 3,000 B.C. are on the surface, whereas older sites are buried within the Upper sand. During the twentieth century, the shrub grassland vegetation of the Mescalero sand sheet was disturbed, leading to the formation of many coppice and parabolic dunes. Source

Hall S.A.,Red Rock Geological Enterprises | Riskind D.H.,Texas Parks and Wildlife Department
Journal of Arid Environments | Year: 2010

Pollen analysis of two woodrat middens from Hueco Tanks, El Paso County, Texas, dated 10,140 ± 70 and 7170 ± 70 14C years BP, shows late persistence of the regional glacial-age Artemisia steppe vegetation in what is historically desert shrub grassland of the northern Chihuahuan Desert. Local populations of Pinus were gone by the end of the Pleistocene, and creosotebush (Larrea) and mesquite (Prosopis) appeared in the local vegetation by mid-Holocene time. Juniperus can be strongly over-represented in midden pollen assemblages due to harvesting of cone-bearing twigs by woodrats. AMS radiocarbon dates on very small samples of midden matrix used for pollen analysis are 3400 and 2200 14C years younger than dates on plant macrofossils from the same middens. Juniperus over-representation in pollen percentages and age differences between pollen and macrofossil content must be taken into account when interpreting the palynology of woodrat middens. © 2009 Elsevier Ltd. All rights reserved. Source

Hall S.A.,Red Rock Geological Enterprises
Palynology | Year: 2010

Pollen concentrations containing abundant Zea mays pollen grains are AMS radiocarbon dated 3940±40 to 2450±4014C years BP. The maize pollen is from two prehistoric woodrat (Neotoma) middens that occur in fractures in the south-facing sandstone cliff at Chaco Culture National Historical Park. The diameters of the Archaic-age maize pollen grains are significantly larger than Puebloan and modern maize pollen. The size distributions of the earliest Zea grain populations are not normal, suggesting the possibility that more than one variety of maize is represented by the pollen. The occurrence of large numbers of maize pollen grains as well as pollen from weedy plants indicates the nearby presence of an Archaic cornfield, now buried in alluvial fill adjacent to the cliff. It was also found that the AMS radiocarbon ages of the pollen concentrations differ significantly from the age of twigs from the same woodrat middens. Because of the strong age differences of components of woodrat middens, pollen assemblages should be dated independent of plant macrofossils. © 2010 AASP-The Palynological Society. Source

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