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Tremain, Emily S.1, Stephen T. Hasiotis1, Julie A. Maxson2 
(1) University of Kansas, Lawrence, KS 
(2) Gustavus Adolphus College, St. Peter, MN

ABSTRACT: Preliminary Report on the Ichnofossils of the Lower Cretaceous Cedar Mountain Formation, North-Central Utah

The Lower Cretaceous Cedar Mountain Formation (Albian) is a fluvial unit deposited at approximately 110 Ma. Vertebrate trace fossils, mainly tracks and trackways, have been the focus of previous ichnologic studies. Invertebrate trace fossils have not been investigated in any detail. This preliminary study examines several diverse assemblages of ichnofossils from the Cedar Mountain Formation in and around Dinosaur National Monument and the areas in and around Moab and Green River, in north-central Utah. 
Ichnofossils occur in sandstone, sandy siltstone, carbonate, and siltstone-mudstone facies. The sandstone facies, deposited by meandering fluvial channels, contains primarily post-depositional invertebrate traces. There are several size gradations of adhesive meniscate burrows, backfilled burrows, oligochaete burrows and trails, pelecypod burrows, snail trails, and horizontal branching burrows. U-shaped burrows and simple horizontal burrows were likely constructed during active deposition. The sandstone facies also preserves vertebrate tracks. The sandy siltstone facies was deposited by crevasse-splays, and has ichnofossils similar to the sandstone facies, with the exception of possible earthworm burrows, wasp cocoons, and dung beetle balls. The carbonate facies, deposited in palustrine and marginal lacustrine settings with varying degrees of pedogenesis, preserve several types of rhizoliths, adhesive meniscate burrows, crayfish burrows, and probable dung beetle nests or weevil cocoons. The siltstone-mudstone facies, deposited as overbank alluvial sediment with varying degrees of pedogenesis, contains adhesive meniscate burrows, ant nests, and termite nests. The termite nests are associated with rhizoliths of shrub-like plants. These facies represent the distal portions of the floodplain. 
Funding was provided to J. A. Maxson by NSF-REU (NSF grant #0139373) and Gustavus Adolphus College.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.