Skip to Main Content
Skip Nav Destination
GEOREF RECORD

Preservation of giant anomalocaridids in silica-chlorite concretions from the Early Ordovician of Morocco

Robert R. Gaines, Derek E. G. Briggs, Patrick J. Orr and Peter Van Roy
Preservation of giant anomalocaridids in silica-chlorite concretions from the Early Ordovician of Morocco (in Lagerstaetten through time; a collection of exceptional preservational pathways from the terminal Neoproterozoic through today, James D. Schiffbauer (editor) and Marc Laflamme (editor))
Palaios (May 2012) 27 (5): 317-325

Abstract

The recently discovered Fezouata Biota, from the Early Ordovician (late Tremadocian to late Floian) of Morocco, preserves a diverse soft-bodied fauna. While preservation is mostly of Burgess Shale-type, giant anomalocaridids also occur in siliceous concretions. Petrographic and geochemical analyses of these concretions reveal their growth history and the circumstances that led to the fossilization of nonbiomineralized anatomy within them. The large (>1 m) concretions are homogeneous in composition and geochemical characteristics, suggesting rapid, pervasive growth of mineral frameworks during decay of the large animals at, or near, the sediment-water interface. Concretions are comprised of ultrafine-grained (2-20 mu m) authigenic quartz, Fe chlorite, and calcite, a composition unlike other described marine concretions. Abundant pyrite, now represented by oxide pseudomorphs, grew adjacent to the anomalocaridid carcasses, but rarely within the matrix of the concretions. This distribution indicates that sulfate reduction around the carcasses was vigorous within otherwise organic-poor sediments resulting in the establishment of prominent chemical gradients around the giant anomalocaridids that led to early precipitation of mineral overgrowth around nonbiomineralized tissues. Rapid precipitation of intergrown silica and Fe chlorite required an abundant source of silica, iron, and aluminum. These ions were likely derived from dissolution of volcanic ash in the sediments. Limited intergrown calcite (delta (super 13) C avg. -12.2 per mil, n=23) precipitated from bicarbonate that was generated largely by sulfate reduction of organic tissues of the carcasses. Whereas Burgess Shale-type preservation of fossils in the Fezouata biota required suppression of degradation, exceptional preservation of anomalocaridids within the siliceous concretions resulted from extensive microbial decomposition of a large volume of organic tissues. Rapid mineralization was facilitated by localization of microbial activity around the large carcasses and must have required an unusually reactive sediment composition.


ISSN: 0883-1351
Serial Title: Palaios
Serial Volume: 27
Serial Issue: 5
Title: Preservation of giant anomalocaridids in silica-chlorite concretions from the Early Ordovician of Morocco
Title: Lagerstaetten through time; a collection of exceptional preservational pathways from the terminal Neoproterozoic through today
Author(s): Gaines, Robert R.Briggs, Derek E. G.Orr, Patrick J.Van Roy, Peter
Author(s): Schiffbauer, James D.editor
Author(s): Laflamme, Marceditor
Affiliation: Pomona College, Geology Department, Claremont, CA, United States
Affiliation: Virginia Polytechnic Institute and State Univesity, Nanoscale Characterization and Fabrication Laboratory, Blacksburg, VA, United States
Pages: 317-325
Published: 201205
Text Language: English
Publisher: Society for Sedimentary Geology, Tulsa, OK, United States
Meeting name: Geological Society of America annual meeting
Meeting location: Denver, CO, USA, United States
Meeting date: 20101031Oct. 31-Nov. 3, 2010
References: 50
Accession Number: 2012-065524
Categories: Invertebrate paleontologyIsotope geochemistry
Document Type: Serial Conference document
Bibliographic Level: Analytic
Annotation: NSF grants EAR-1053247, DMR-0618417, and DUE-0942447
Illustration Description: illus. incl. 3 tables, geol. sketch map
N30°30'00" - N30°30'00", W05°49'60" - W05°49'60"
Secondary Affiliation: Smithsonian Institution National Museum of Natural History, USA, United StatesYale University, USA, United StatesUniversity College Dublin, IRL, Ireland
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: 201234
Close Modal

or Create an Account

Close Modal
Close Modal