Paper No. 21-14
Presentation Time: March 25, 2003 1:00 PM-5:00 PM (Session No. 21--Booth# 22)
THE ALTAMONT FORMATION (MIDDLE PENNSYLVANIAN) AT THE I-170 OUTCROP IN ST. LOUIS, MISSOURI
KING, Norman R., Geosciences, Univ of Southern Indiana, Evansville, IN 47712, nking@usi.edu and SUTTON, Barry G., 265 St. Eugene Ln, Florissant, MO 63033

Pennsylvanian strata spanning the Desmoinesian-Missourian boundary have been preserved in the St. Louis area due to a local downwarp called the St. Louis basin. The upper Desmoinesian (Middle Pennsylvanian) Altamont Formation is extensively exposed along both sides of the southbound lanes of I-170 near the St. Louis metropolitan airport. The Altamont Formation includes three members, including (ascending) the Amoret Limestone, Lake Neosho Shale, and Worland Limestone. In terms of Midcontinent cyclostratigraphy, the Amoret Limestone is the transgressive limestone of the Altamont cyclothem, the Lake Neosho Shale is the phosphatic core shale of the cyclothem, and the Worland Limestone is the regressive limestone. All three of these members have been reported at the I-170 exposure. A brightly-colored claystone paleosol that has been identified as the Bandera Shale is at the base of the exposure.

Our work shows that the shale underlying the Worland Limestone Member at I-170 actually includes two phosphatic shales separated by a paleosol, and therefore represents two depositional cycles. Conodonts in these units indicate the lower phosphatic zone correlates with the unnamed core shale of the Farlington cyclothem, and only the upper phosphatic shale is the true Lake Neosho Shale. The so-called Amoret at I-170 underlies both phosphatic shales, and therefore must be older than the Amoret at its type locality, correlating instead with the Farlington Limestone; there is no Amoret equivalent at the I-170 exposure. Since the Bandera Shale in its type area lies between the Farlington Limestone and the Lake Neosho Shale, the paleosol between the two phosphatic zones at I-170 must have formed at the time of Bandera Shale deposition. The more prominent paleosol beneath the Farlington-equivalent limestone at I-170 formed during an earlier depositional cycle. Data collected at this site are crucial for proper correlation of strata along the Midcontinent outcrop belt to the west with those in the Illinois basin to the east.

North-Central Section - 37th Annual Meeting (March 2425, 2003)
General Information for this Meeting
Session No. 21--Booth# 22
Geochemistry, Petrology and Tectonics (Posters)
Kansas City Airport Hilton: Shawnee A
1:00 PM-5:00 PM, Tuesday, March 25, 2003
 

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.

Click Here to Go-Back