LATE PLIOCENE FLUVIAL SEDIMENTATION, SOIL DEVELOPMENT AND PALEOENVIRONMENTAL CHANGE AT THE TIGRE DORADO FOSSIL LOCALITY, SOUTHWESTERN KANSAS

The Meade Basin Rodent Project (MBRP) is a long-term research study examining rodent evolution in the Meade Basin of southwestern Kansas during the Plio-Pleistocene transition. One of the primary MBRP fossil localities is the Hibbard site, located on the eastern rim of Fox Canyon. While rodent fossils abound, the site has been significantly affected by post-depositional slump, making stratigraphic and paleoecological interpretation difficult. In 2005, the MBRP team serendipitously discovered a second fossil locale on the opposite site of the canyon, which they named Tigre Dorado due to the presence of saber-tooth cat remains preserved in a matrix of golden-colored sands. Unlike the Hibbard site, Tigre Dorado contained articulated remains of both carnivores (e.g., saber-tooth cats) and herbivores (e.g., camel, horse), indicating that the canyon may preserve an entire ecosystem. The stratigraphic sequence is intact, offering an ideal opportunity to reconstruct the depositional environment through time.

The objectives of this study are to 1) assess the hypothesis that Tigre Dorado and Hibbard’s site are part of the same geologic system; 2) reconstruct the geologic setting and investigate the large mammals’ cause of death; and 3) characterize paleoenvironmental change through time in order to provide an ecological context for the MBRP. A multi-proxy methodology utilizing particle size analysis, petrographic microscopy, and reflectance spectroscopy suggest that both sites were initially deposited by a high-energy fluvial system. Over time, the system lost energy and the coarse basal sands give way to fining upward sands and silts containing burrows infilled with gleyed mud. The uppermost sediments are carbonate-cemented silts intercalated by caliche lenses, indicating a transition from an unstable fluvial environment to a stable arid environment experiencing pedogenesis. The geologic framework developed here will enable MBRP biologists to examine mammalian population and morphological change within the broader context of fluctuating environmental conditions. Thus, this research represents an important interdisciplinary approach to questions regarding evolving mammalian response to shifting ecological conditions during the Plio-Pleistocene transition in southwestern Kansas.