CHARACTERIZATION OF THE INCEPTISOLS IN HOLOCENE SOD TABLES, BADLANDS NP, SD

We characterize the paleosols present in the sod tables, which are incised into late Holocene pediments, as inceptisols. Herein we describe these paleosols and their geomorphic context. The field setting lies upon the upper prairie, immediately north of Norbeck Pass, between mile posts nine and ten on the Loop Rd., easily accessible from the Fossil Trail parking lot. Sod tables are remnants of pediments, which have been incised and are bounded by arroyo walls, and typically exhibit a graded, sod-covered, flat top, of a few meters relief. Paleosols, or buried relict soils, are characterized by field description of soil profiles and a suite of ensuing laboratory analyses. Observations of grain size support a fining-distally progression from the bedrock source, Oligocene Brule ‘castles’, fining from sandy-silt to silt. The color of organic-rich paleosol horizons are typified by Munsell 10yr ⁵/₃, while inorganic horizons are Munsell 7.5 yr ⁴/₃ to 10yr ⁵/₃. Paleosol horizon structure within the studied sod tables was classified as angular-blocky to crumb. The results of a TOC (total organic carbon) analysis reveal a LOI (loss on ignition) of 4.2% within horizon Ab from CT-01-08. The underlying and overlying horizons (C and 2C respectively) reveal a LOI of 1.5% and 3.6%, justifying the results to proceed with radiocarbon dating. Similar trends in results were also found for CT-03-08. We have previously published radiocarbon dates from bulk humate fractions of paleosols in the age range of 530 and 1280 RCYBP from this locale. We have found that the LOI should exceed 3.6% to yield successful radiocarbon dates. The intervals of soil formation we have recorded for alluvial pediments are synchronous with those reported on forming upon Aeolian sediments in the Badlands.