Abstract

The upper Pleistocene-Holocene sequence in southeastern White Sands Missile Range was deposited in an eolian sand-sheet environment that interacted with gravel-depositing arroyos near the Jarilla Mountain piedmont and with mud-depositing arroyo-mouth ponds and more extensive lakes on the basin floor. The sand sheet contains ridge and swale, coppice dune, and deflation depression subenvironments. Three distinctive and locally exhumed buried soils occur within these eolian, alluvial, and lacustrine deposits. The youngest buried soil is characterized by an A to Bw to Bk (stage I) profile; the second, by a Btk (stage II) to Bk (stage I) profile; and the third, by a Btk (stage II) to K (stage III or IV) to Bk (stage II) profile. The tops of these buried soils, which in most cases are truncated, represent easily identifiable regional bounding surfaces. They separate the stratigraphic sequence into four units with approximate time spans of 0 to 100 yr B.P. (unit Q4), 100 to 7300 yr B.P. (unit Q3), 9400 to 15,000 yr B.P. (unit Q2), and about 50,000 to 250,000 yr B.P. (unit Q1). Lateral variations in unit thickness delineate eolian depocenters and areas of maximal erosion during these time spans.

The stratigraphic sequence records three cyclic alternations between landscape instability, during which erosion and sedimentation took place, and landscape stability, during which the soil profiles became well developed. The initiation of the earliest two episodes of landscape instability, represented by erosion of, or deposition upon, the lower two buried soils, is attributed to climatic change toward drier conditions, which caused the breakup of the sediment-binding vegetative cover. The most recent landscape destabilization episode was initiated about 100 yr B.P. by the destruction of the desert grassland cover by cattle overgrazing.

Prehistoric Holocene cultural remains largely are restricted to unit Q3 and the surface of unit Q2, or to the present surface at localities where units Q2 or Q1 are exhumed. Remains found within distinct eolian lag accumulations or within bedded arroyo sediments likely are removed from their original context, the degree to which can be estimated by the extent of incision into the soil-profile horizons. Prehistoric habitants occupied a landscape containing the ridge and swale and deflation depression eolian topography but without the current hummocky mesquite coppice dunes.

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