2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 9
Presentation Time: 3:45 PM


YANS, Johan1, STRAIT, Suzanne G.2, SMITH, Thierry3, DUPUIS, Christian1, STEURBAUT, Etienne4 and GINGERICH, Philip D.5, (1)Fundamental and Applied Geology, Mons Engineering, Rue de Houdain 9, Mons, B7000, Belgium, (2)Biological Sciences, Marshall University, Huntington, WV 25755, (3)Paleontology, Royal Belgian Institute of Natural Sciences, Rue Vautier 29, Brussels, B-1000, Belgium, (4)Department of Paleontology, Royal Belgian Institute of Natural Sciences, Vautierstraat 29, Brussels, B-1000, Belgium, (5)Department of Geological Sciences and Museum of Paleontology, The Univ of Michigan, Ann Arbor, MI 48109-1079, gingeric@umich.edu

The Paleocene-Eocene boundary is defined chemostratigraphically by the onset of a global carbon isotope excursion (CIE), recognized in marine and continental strata in both carbonates and dispersed organic carbon (DOC). In continental sections the CIE is important as a proxy for climate change affecting mammalian faunal succession during the Paleocene-Eocene thermal maximum (PETM). At Polecat Bench in the northern Bighorn Basin, Wyoming, the CIE spans four faunal zones from latest Clarkforkian Cf-3, through earliest Wasatchian Meniscotherium or Wa-M, Wa-0, and Wa-1. The CIE at Polecat Bench has been studied at high resolution in both pedogenic carbonate and DOC, where there is good agreement between records in both. Here we report a new high resolution study of the CIE in relation to Wa-M and Wa-0 faunal change in the Honeycombs area of the southern Bighorn Basin.

In the Honeycombs area 46 isotope sample sites span a vertical section of 52 meters, including a Meniscotherium-and-perissodactyl-bearing interval at Halfway Hill (UCMP V99557), the rich Wa-0 wash site of Castle Gardens (UCMP V99019), and a higher Wa-0 site of UCMP V99557 with the small perissodactyl Hyracotherium sandrae. The latter site is at the base of the most salient marker bed in the sequence, a thick, deeply weathered red paleosol called Big Red. Total organic carbon is in the range of 0.1-0.3% and CaCO3 is notably lacking except in the wash site interval where it reaches ca. 3%. Pre-excursion values range from δ13C (PDB) = -26.2 to -24.7‰ and excursion values range from δ13C = -28.8 to -25.9‰. As at Polecat Bench, the Meniscotherium zone in the Honeycombs area is in the brief initial onset of the CIE, and the Wa-0 sites are in the longer recovery during or after the maximum negative excursion.

The Honeycombs area is important because the Halfway Hill locality is the first to yield a perissodactyl from the Meniscotherium zone, and the Castle Gardens wash site is the first to yield abundant evidence of Wa-0 microvertebrates. This area is different from Polecat Bench in preserving mammals in channel deposits.