2006 Philadelphia Annual Meeting (2225 October 2006)
Paper No. 23-8
Presentation Time: 8:00 AM-12:00 PM

EXCEPTIONAL PRESERVATION OF MIDDLE CRETACEOUS (ALBIAN) THECAMOEBIANS (ARCELLACEANS): EVOLUTION OF A TRANSIENT LACUSTRINE ENVIRONMENT

VAN HENGSTUM, Peter J., School of Geography and Earth Sciences, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada, vanhenp@mcmaster.ca, REINHARDT, Eduard G., School of Geography and Earth Sciences, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4K1, Canada, and GROCKE, Darren R., Department of Earth Sciences, Durham University, South Road, Durham, DH1 3LE, United Kingdom

Thecamoebians (Arcellaceans) are testate Rhizopods that are ubiquitous in most freshwater to slightly brackish environments and have a test that is either self-secreted or made by agglutinating foreign particles using organic cement. Due to their test composition thecamoebian tests have a poor preservation potential through deep geologic time. Although some specimens have been found in Mesozoic and early Paleozoic sediments; limited preservation prevents detailed identification beyond the genus level resulting in a fragmented geologic record. Late Albian sediments from a regionally-variable shale deposit within the Dakota Formation (Nebraska, USA) have revealed exceptionally well-preserved thecamoebian tests that allow identification to the specific and even "strain" level. Identified species include abundant Difflugia oblonga, D. protaeiformis, Pontigulasia compressa, and Lesquereusia sp.. Previous regional paleoenvironmental research on the Dakota Formation suggests that during the late Albian a large extensive braided river system drained the North American craton into the Western Interior Seaway, westward of the Appalachian Basin. The recovered thecamoebian assemblage from the shale unit indicate deposition in a transient, quiescent lacustrine environment suggesting the presence of an oxbow lake setting, pond, or shallow lake transiently present in the ancient river system floodplain. These paleoenvironmental interpretations based on the recovered thecamoebians are consistent with similar Holocene environmental reconstructions.

2006 Philadelphia Annual Meeting (2225 October 2006)
General Information for this Meeting
Session No. 23--Booth# 31
Paleontology/Paleobotany (Posters) I: Paleoecology, Taphonomy, and Early Life
Pennsylvania Convention Center: Exhibit Hall C
8:00 AM-12:00 PM, Sunday, 22 October 2006

Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 64

© Copyright 2006 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.