|WATER MASS EVOLUTION IN WESTERN IOWA, MID-CRETACEOUS|
FISHER, Cynthia G., GALLAGHER, Kimberly A., and REEVES, Kristy L., Geology and Astronomy, West Chester Univ, 750 S. Church Street, West Chester, PA 19383, firstname.lastname@example.org|
The Bridge Creek Limestone Member of the Greenhorn Formation is of late Cenomanian to early Turonian age and consists of alternating limestone and marl beds in the Western Interior Basin of the U.S.A. The Bridge Creek Limestone represents transgression, with the upper half representing maximum Greenhorn high-stand. Samples cored from near Hawarden and Grant City Iowa provide coverage from closer to the eastern shore. Assemblages of foraminifera indicate that as sea level rose in the latest Cenomanian into the Turonian more diverse planktonic foraminifers spread eastward. High fertility calcareous nannoplankton were pushed east (Grant City) as sea level rose and more diverse, oligotrophic assemblages replaced them to the west (Hawarden). An increase in planktonic foraminiferal porosity located in the upper Neocardioceras juddii ammonite zone has been identified at Hawarden and Grant City. This increase has also been found in Pueblo, Colorado, Deora, Colorado, and Hot Springs, South Dakota. We interpret this increase in Hedbergella delrioensis porosity as a decrease in water density. The decrease in water density was probably caused by an increase in sea level that brought warmer Tethyan water north and eastward.
Northeastern Section - 37th Annual Meeting (March 25-27, 2002)
General Information for this Meeting
|Session No. 31--Booth# 3|
Paleontology and Paleoceanography (Posters)
Sheraton Springfield: Ballroom North
8:00 AM-12:00 PM, Wednesday, March 27, 2002
© Copyright 2002 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.