Water Provenance at the Old River Bed Inland Delta and Ground Water Flow from the Sevier Basin of Central Utah during the Pleistocene-Holocene Transition

Abstract

AbstractTo ascertain the provenance of water reaching wetlands in an area sustaining a population of Pleistocene–Holocene foragers, 87-strontium/86-strontium isotopic ratios (87Sr/86Sr) of mollusks from channels of the Old River Bed inland delta of central Utah were measured. Potential provenances examined included overflow from Pleistocene–Holocene Lake Gunnison, ground water flow from the Sevier basin, ground water discharge from piedmont aquifers infiltrated by Lake Bonneville, and ground waters from local regional aquifers. Old River Bed inland delta channels active from ~13.2 cal ka BP until ~11.2 cal ka BP have 87Sr/86Sr values of 0.70930–0.71049 that are consistent with water sourced from Lake Gunnison in the Sevier basin. Inland delta channels active from ~11.2 cal ka BP until shortly after ~9.3 cal ka BP have 87Sr/86Sr values of 0.70977–0.71033, suggesting ground water flowed from the Sevier basin during the early Holocene. Ratios of 87Sr/86Sr did not match known values for Lake Bonneville, but the youngest Old River Bed inland delta channel system has an 87Sr/86Sr ratio consistent with a local ground water source, perhaps Government Creek. Consistent ground water discharge may explain the persistence of foragers in the region despite the increasingly arid climate of the Great Basin.