A paper on the stratigraphy, sedimentology, age, and paleoclimate of the late Miocene Coffee Ranch mammal locality based partially on research in the Peppe lab was published in Palaeogeography, Palaeoclimatology, Palaeoecology this week. The first author of the paper is Baylor Geosciences graduate student Bill Lukens. Magnetostratigraphy analyses were conducted in the Baylor paleomagnetism lab by former undergraduate and senior thesis student Mike Loudermilk.
The results of the magnetostratigraphy indicate the section was deposited over ~ 277 kyr within chron C3An.2n from ~ 6.42–6.70 Ma. Sedimentology and stratigraphy analyses indicate a variable landscape with a variety of depositional environments including fluvial, palustrine, eolian, and paleosols. Paleoclimate reconstructions from paleosols indicate precipitation was ~900-1150 mm/yr, which is about double modern values. These precipitation estimates and features of the paleosols indicate that during the late Miocene there was a significant westward shift of the longitudinal precipitation gradient of several hundred kilometers. This in turn created climatic conditions in the southern midcontinent that were not sufficiently arid to select for C4 photosynthetic pathways over C3photosynthesis in the late Miocene.
Here’s a link to the paper: http://www.sciencedirect.com/science/article/pii/S0031018217303553.