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Abstract: Stratigraphic Setting of New Vertebrate Fossil Discoveries: Lower Cretaceous Wayan Formation, Southeastern Idaho

S. C. Minkin, A. L. Ayres Jr., J. M. Bunzow, T. W. Reid, K. E. Wright, S. F. Robison

Recent strategraphic studies in Caribou County, Idaho, in the Lower Cretaceous Wayan Formation, have revealed vertebrate fossils in a rip-up clast conglomerate. The conglomerate is associated with a series of fluvial channel fill and floodplain deposits. The study area, located along Tincup Creek, is contained in the Absaroka thrust plate of the central Idaho-Wyoming thrust belt. The section is exposed in the east limb of a northwest trending syncline, subparallel to the regional thrust and fold strike belt. The thin fossil bearing conglomerate is provisionally located in the lower part of the Wayan Formation, correlative with the Thomas Fork Formation to the east. The section contains banded and variegated red, purple, brown and green mudstones; gray, tan, buff siltstone , and sandstones; and lenses of quartz-pebble conglomerate and rip-up clast conglomerate. The fossil bearing conglomerate is composed of fine grained calcareous siltstone, chert pebbles, sand grains, and mascerated plant material. Fossil material found in the conglomerate include dinosaur bone, teeth and eggshell; crocodilian teeth; turtle shell; ganoid fish scales; bivalve and gastropod molluscs; and unidentified plant debris. Studies to identify the dinosaur materials are in progress. Further work is necessary for a more detailed description of depostional environments and to determine stratigraphic position relative to the underlying Smiths Formation.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada