2003 Seattle Annual Meeting (November 25, 2003)
Paper No. 30-6
Presentation Time: 8:00 AM-12:00 PM


NESBITT, Elizabeth A. and GOEDERT, James L., Burke Museum, Univ of Washington, Box 353010, Seattle, WA 98195-3010, lnesbitt@u.washington.edu

Reworked concretions containing fossils Crustacea have been recovered from mid-Cenozoic conglomerate deposits in western Washington State, U.S.A. The best known and most diverse of these crab assemblages is from outcrops of the late Eocene Hoko River Formation, northern Olympic Peninsula. Conglomerates containing abundant fossiliferous concretions occur in five other middle Eocene to late Oligocene units in western Washington: the Humtulips, Lincoln Creek and Pysht formations, the conglomerate at Point Ellice on the Columbia River, and in the ?Aldwell Formation at Pulali Point. In some of these deposits, the calcite-cemented concretions are lithologically similar even though the crabs are derived from a mix of paleo-habitats. In other strata, the crabs apparently represent a fauna from one habitat type but the concretions show lithological diversity. Entrainment of the conglomerates within debris flows transported them all into outer shelf/slope submarine fans of a very narrow continental shelf. Such modes of transport do not adequately explain the taxonomic composition of all of these faunal assemblages. In some instances, crabs from the same conglomerate differ significantly in geochronologic age and the most taxonomic diverse assemblages are the least likely to represent a single temporal grouping. Just as they are today, allochthonous concretions may be eroded from sedimentary strata (even from shoreline subaerial outcrops) and be redeposited multiple times. Each redeposition event adds more taxonomic diversity to the assemblage. Paleodepth analysis and taxonomic faunule descriptions from such crustacean collections have a high probability of being erroneous. We suggest that conglomerates in other marine strata worldwide may contain similarly mixed lithologies and mixed temporal fossil assemblages, and that this has been overlooked.

2003 Seattle Annual Meeting (November 25, 2003)
Session No. 30--Booth# 89
Fossil Decapod Crustacean Paleobiogeography, Systematics, and Evolution Over the Past 20 Years: In Honor of Ross and Marion Berglund (Posters)
Washington State Convention and Trade Center: Hall 4-F
8:00 AM-12:00 PM, Sunday, November 2, 2003

Geological Society of America Abstracts with Programs, Vol. 35, No. 6, September 2003, p. 56

© Copyright 2003 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.