HR: 17:45h
AN: PP14A-08    [Abstracts]
TI: New Sections and Fossils From the Southern Bighorn Basin, Wyoming Document Faunal Turnover During the PETM
AU: * Bloch, J I
EM: jbloch@flmnh.ufl.edu
AF: University of Florida, Florida Museum of Natural History, PO Box 112710, Gainesville, FL 32611-2710 United States
AU: Boyer, D M
EM: dboyer@ic.sunysb.edu
AF: Stony Brook University, Department of Anatomical Science, Health Sciences Center, Stony Brook, NY 11794-8081 United States
AU: Strait, S G
EM: straitho@marshall.edu
AF: Marshall University, Department of Biological Sciences, Huntington, WV 25755 United States
AU: Wing, S L
EM: wings@si.edu
AF: Smithsonian Institution, Department of Paleobiology, Washington, DC 20560 United States
AB: Though earliest Eocene (Wa-0) mammals are known from the southern Bighorn Basin, late Paleocene mammals are not. Recent discovery of latest Paleocene mammals in section with new Wa-0 faunas and floras at Cabin Fork allows for the first studies of terrestrial biotic change across the Paleocene-Eocene boundary interval outside of the northern Bighorn Basin. A differential GPS was used to map the area and provide a framework for high-resolution biostratigraphy. Least squares interpolation of bedding planes from points marking outcrop of beds reveals high r$^{2}$ coefficients (0.97-0.98). This indicates that small scale folding is minimal and bed traces are smoothly planar. Beds in the study area strike N-NW ($355\deg$) and dip shallowly W-SW ($<$$1.0\deg$). Smaller scale undulations are present: to the NE beds strike NW and dip to the SW ($342\deg$/$1.0\deg$) whereas those to the SW strike NE and dip NW ($5\deg$/$1.0\deg$). Shallow dips allow us to approximate stratigraphic thickness with elevation. Paleocene mammals, including diagnostic Clarkforkian land-mammal age indicators, {\it Aletodon gunnelli}, {\it Apheliscus nitidus}, and {\it Haplomylus simpsoni}, were found in a ferruginous, grit-pebble conglomerate at the base of a channel sand at the top of the Fort Union Fm. The fossiliferous horizon is extensive and has produced over 200 specimens from more than 60 sites for which positions have been determined with sub-meter accuracy. Absence of {\it Plesiadapis cookei} and {\it Hyracotherium} spp., together with high relative abundance of {\it Phenacodus} and {\it Ectocion}, indicate this fauna is latest Clarkforkian ({\it Phenacodus-Ectocion} Range Zone, Cf-3). Earliest Eocene mammals, including diagnostic Wa-0 taxa {\it Arfia junnei}, {\it Copecion davisi}, {\it Hyracotherium sandrae}, and {\it Diacodexis ilicis}, are represented by more than 233 specimens from 70 sites at three levels in the lowest Willwood Formation. The lowest fossils come from paleosols and claygall accumulations in stringer sands approximately 3 meters above the top of the channel sand that is the top of the Fort Union Formation, and 8 meters above the Clarkforkian localities. The second level is a fossiliferous paleosol 6-8 meters above the top of the channel sand. The third level is a paleosol fossil accumulation approximately 22 meters above the top of the channel sand and 15 meters below a large and persistent red paleosol informally called ?Big Red.? In the Cabin Fork area, Big Red produces mammal fossils, including {\it Cardiolophus}, that have been used to define the succeeding Wa-1 faunal zone (although some Wa-0 taxa have been recovered from Big Red approximately 6 km to the east). The Wa-0 interval in the Cabin Fork area is 38-40 meters thick and bounded by distinct Cf-3 and Wa-1 faunas. Preliminary analyses of fossils from the Cabin Fork section show that the faunal shift marking the PETM was very similar to that seen in the northern Bighorn Basin. This suggests that previously documented differences between Wa-0 mammalian faunas in the southern and northern Bighorn Basin, including the absence of certain diagnostic Wa-0 taxa in the south, may reflect local sampling variation or artifacts rather than regional variation in faunal composition.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting