QUATERNARY MESA STRATIGRAPHY IN THE WHITE RIVER BADLANDS OF SOUTH DAKOTA, USA

The White River Badlands are well known for Tertiary strata and fossils. However, there are also significant Quaternary sediments there. These include: 1) Holocene eolian cliff-top deposits and eolian sand with millennial-scale cyclicity, 2) Pleistocene eolian sand, and 3) fluvial and lacustrine deposits that predate the initiation of Badlands erosion. Mesas containing and covered by these Quaternary deposits occur at ~830 and 950 m elevation.

Eolian cliff-top deposits are typical on mesa edges in the study area. They contain Holocene soils that were buried at ~ 1300, ~2500 and ~3700 ¹⁴C yrs BP. Soils beneath the cliff-top deposits are early Holocene on higher elevation mesas, and late Holocene on lower elevation mesas. Holocene millennial-scale periodicity evidenced here correlates temporally to that seen in Greenland ice cores and North Atlantic sediment cores (i.e. to “Bond Cycles”).

Parabolic dunes also occur on mesa surfaces in the study area. An exposure sampled on an 830 m mesa has seven buried Holocene A-C soils that range in age from ~9600 to 800 ¹⁴C yrs BP. One optical luminescence age estimate from the base of the eolian sand is ~12,500 cal yr BP (11,000 ¹⁴C yrs BP) old (i.e. the Younger Dryas). These deposits also evidence a periodicity similar to the cliff-top deposits. Parabolic dunes on the higher 950 m surface contain older Pleistocene age sand.

All mesas in the study area have fluvial, colluvial, and lacustrine strata beneath the eolian deposits. These include the Red Dog Loess, which is probably a fluvial deposit. A thermal luminescence sample taken near the base of this deposit at Sheep Mountain Table yielded a minimum age estimate of 171,460±23,810 yrs ago. Continued dating of these deposits is aiding in the interpretation of the long-term evolution of the White River Badlands.