T17 Where Does the Wind Blow? Aeolian Systems in Time and Space I

Sunday, 4 November 2018
8:00 AM - 12:00 PM
Room 138-139

DRY TIMES IN THE CENTRAL COLORADO PLATEAU: PREHISTORIC DROUGHT RECORDED IN SOUTHERN UTAH DUNE FIELDS

Paper number: T17-10
Program: Technical Sessions
Time: 10:25 AM – 10:40 AM

Authors

Abstract

Sand dunes are threshold systems that are sensitive to sustained, decadal-scale aridity and can record past changes in effective moisture. Records of past aridity can inform us of natural climate variability and extremes in an area. These records provide data useful for refining climate models, and adaptive planning for land and watershed management in environmentally sensitive areas.

We use optically stimulated luminescence (OSL) dating and radiocarbon (14C) ages from charcoal to investigate eolian activity in two dune fields in southern Utah, located 250 km apart in the central Colorado Plateau. Dune forms in this semi-arid region have been mapped and OSL/14C samples collected from multiple eolian packages within each dune field. In addition to age control, chronostratigraphic reconstructions are based on geomorphic assessment and stratigraphic information from grain size analysis, geochemistry, organic and magnetic properties, and identification of paleosols (representing periods of dune stability).

Kanab dune field located 13 km northwest of Kanab, Utah, covers about 12.5 km2 and is oriented WSW. Dune forms include stabilized and partially active parabolic dunes and areas of sand sheets. San Rafael Desert dune field located approximately 25 km southwest of Green River, Utah is composed of multiple dune fields encompassing a greater area (>2500 km2). Sand ridges, oriented NNE, are prominent regionally, with scattered partially active dune fields composed of barchanoid and parabolic dunes. Twenty-four samples from Kanab and 17 samples from San Rafael dune fields have been obtained for OSL chronology. Preliminary OSL ages from both dune fields identify at least four periods of dune activity between 8 and 1 ka. There is also evidence of dune reactivation during the last 1ka.

We interpret coeval dune activity in these dune fields to represent persistent (at least decadal scale) regional droughts that lead to changes in threshold conditions for dune mobility. Further analyses will refine chronologies of both sites and will include comparison to records of aridity to refine a regional hydroclimate reconstruction.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-317847

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