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Exceptional fossil preservation in the Conasauga Formation, Cambrian, northwestern Georgia, USA

David R. Schwimmer and William M. Montante
Exceptional fossil preservation in the Conasauga Formation, Cambrian, northwestern Georgia, USA
Palaios (July 2007) 22 (4): 360-372

Abstract

Mudstones and siliceous concretions in the middle Cambrian Conasauga Formation, northwestern Georgia, contain body and trace fossils showing nonmineralized preservation and represent two temporally and spatially different marine environments. Identifiable, nonbiomineralized taxa include components of a Burgess Shale-type biota with red and green algae, primitive sponges, and the arachnomorph arthropod Naraoia compacta. Also exceptionally preserved are the filamentous appendages of a large ptychopariid trilobite and assemblages of oriented hyolithid tests we interpret as priapulid coprolites and cololites. Exceptional preservation in the Conasauga Formation has multiple causes. The Conasauga contains superabundant siliceous concretions, many with skeletal, trace, and some nonbiomineralized fossils. Shale specimens, especially sponges with preserved details, and whole-body trilobite preservations, often have iron (Fe) oxide halos that resulted from a biochemical cascade including bioimmuration, decomposition gas anoxia, Fe-sulfide crystallization, and Fe oxidation. Preservation of soft tissue is also partly attributable to the well-sorted clay matrix of inner shelf Conasauga shales, which allowed mechanical imprinting of body fossils. Several nonbiomineralized fossils show algal overgrowths, suggesting an additional form of bioimmuration. Exceptional preservation in the Conasauga Formation is relatively poor compared with such better-known Cambrian Lagerstatten as the Burgess and Wheeler Shales; nevertheless, it is significant for three reasons. The siliceous concretions are a rare vehicle for exceptional preservation and feature three-dimensional fossils rather than the more common compressed specimens. The older Conasauga biota occupied a shallow-shelf environment, a setting in which exceptional preservation is poorly understood. The Conasauga Formation extends the geographic range of a Burgess Shale-type biota to the extreme southeastern USA.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 22
Serial Issue: 4
Title: Exceptional fossil preservation in the Conasauga Formation, Cambrian, northwestern Georgia, USA
Affiliation: Columbus State University, Department of Chemistry and Geology, Columbus, GA, United States
Pages: 360-372
Published: 20070701
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
References: 123
Accession Number: 2007-087612
Categories: Invertebrate paleontology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, sketch map
N34°04'60" - N34°34'60", W85°28'00" - W85°01'00"
Secondary Affiliation: Marsh USA, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by SEPM (Society for Sedimentary Geology), Tulsa, OK, United States
Update Code: 200739
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