SEDIMENTOLOGY AND TAPHONOMY OF THE POLESLIDE MEMBER, BRULE FORMATION, BADLANDS NATIONAL PARK, SOUTH DAKOTA

Examination of several calcareous beds within the lower Poleslide Member of the Oligocene Brule Formation in Badlands National Park, South Dakota, suggests the presence of a carbonate pond in an eolian-dominated depositional system. Samples collected from several localities in the north unit of Badlands National Park contain abundant aquatic snails, charophytes, and clams. There is also a lateral change in limestone morphology from massive in the central part of the pond to laminated along the northern fringe. A subsequent increase in pond size is manifested as lacustrine carbonate on top of a former land surface that is marked by calcified dung balls, rhizolith-enriched A horizons, and sediment infilled burrows. This underlying A horizon has been laterally correlated to other resistant layers of similar lithology over a 2 km area. The development of rhizolith-enriched A horizons that can be traced throughout our study area suggest multiple periods of landscape stability within this eolian dominated system. The presence and degree of articulation of vertebrate fossils, which have been found within former A horizons and throughout the massive eolian units, can also be used to infer alternating periods of aggradation and landscape stability. The origin of the carbonate lacustrine deposits may be similar to the spring-fed carbonates observed at the Chadron-Brule formational contact lower in the section.