AGE CONTROL FOR THE BIG WATER MAMMOTH SITE, BIG WATER, UTAH

In the spring of 2017, a vertebrate fossil-bearing site was discovered along Buck Tank Draw (BTD), a tributary to Wahweap Creek and the Colorado River in southern Utah. Erosion of a grey-green silty clay deposit at the site has revealed mammoth tusks and molars as well as disarticulated remains of camel, horse, and a small canid.

Recent work on the site utilized optically stimulated luminescence (OSL) dating of sandy channel deposits above and below the mammoth remains to constrain the age of the mammoth bearing deposit to 120-130 ka. Sedimentology and stratigraphy of the deposits suggest a marshy wetland environment within the drainage, possibly due to alluvial damming of Buck Tank Draw. Reconnaissance work suggests that other tributaries to Wahweap Creek contain similar silty-clay deposits containing snail and bone fragments. These deposits may be of the same age and suggest a more expansive wetland environment surrounding Wahweap creek and its tributaries.

New stratigraphic descriptions, measurements, and OSL results will test the hypothesis that silty-clay deposits identified throughout the region are the same age as those at the Buck Tank Draw mammoth site. OSL dating provides a numerical age estimate for the last time sediment was exposed to light, this method has been widely applied to fluvial deposits and is applicable to an age range up to several hundred thousand years. Three samples were collected for dating, one from deposits along LWRC and two along a measured stratigraphic profile in BTD. Stratigraphic descriptions from the new sites and forthcoming ages from these samples will allow comparison to those from the mammoth site and provide additional age control for the surrounding area.

Not much is known about the climate and environment of Utah and the Southwestern US during the period 100-150 ka. Research from this site provides a unique opportunity to fill a key gap in our understanding and to establish a larger environmental context for the Pleistocene fauna within these deposits.