79 Soil, Dust, and Everything in Between: Current, Quaternary and Earlier Geological Processes and Records

This session will explore research on the interaction between soils, dust deposits (e.g., loess), dust emission and landscape evolution in modern and geological time scales.

Monday, 20 October 2025
8:00 AM - 12:00 PM
HBGCC, 212AB

Desert Loess Deposition During the Last Glacial Period, White River Badlands, South Dakota, USA

Paper number: 79-4
Program: Technical Sessions
Time: 9:00 AM – 9:15 AM

Authors

Abstract

We report on the age and characteristics of the basal sequence of the Red Dog Loess, a desert loess from the Last Glacial Period located within the White River Badlands of southwestern South Dakota. At its type section at Red Dog Table, the Red Dog Loess consists of  24 m of massive loess, with at least one interbedded paleosol. Using OSL and radiocarbon dating of loess paleosols and fossil snails, we determined absolute ages of 5 ka to present for the uppermost loess (0 to 6 m), 13 ka for the paleosol (7 m), and ~25–22 ka for the lower loess section (8 to 21 meters). However, the age of the basal sequence (22 to 24 m) remained unknown due to ambiguous OSL results and absence of fossil snails.  A new survey of the basal sequence revealed two clusters of small mammal bones at similar stratigraphic levels, a few meters apart. These included remains of eastern pocket gophers (Geomys) and either thirteen-lined ground squirrels (Ictidomys tridecemlineatus) or Franklin’s ground squirrels (Poliocitellus franklinii), species typical of open grassland ecosystems. Radiocarbon dating of the bones found no datable carbon due to poor preservation.  However, additional snail fossils were found near the basal horizon and processed for radiocarbon analysis.  These snails consist of the minute terrestrial genus Pupilla, and the aquatic genera Gyraulus, and Galba, which may suggest seasonal ponding.  Field observations show the Red Dog Loess rests unconformably on fluvial terrace deposits, consisting of silt with stringers of channel gravel. While of unknown age, fluvial deposits likely accumulated in low energy streams after the Cheyenne River captured east-flowing high-energy streams from the Black Hills uplift, post-665 ka. A switch from stream aggradation to incision formed the Red Dog Table mesa, which allowed loess to accumulate. Age data and fossil inferences from the loess and fluvial deposits in the White River Basin provide insights into Late Pleistocene paleoecology and loess accumulation rates, as well as constraints on climate change models for midcontinental North America during the Last Glacial Maximum.  Results from the new set of snail and mammal fossils will be presented.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-412335

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