Tuscarora Formation
From Wikipedia, the free encyclopedia
The Silurian Tuscarora Formation (St) is a mapped bedrock unit in Pennsylvania, Maryland, Virginia and West Virginia. It is also sometimes referred to as the Tuscarora Sandstone or the Tuscarora Quartzite.
Contents |
[edit] Description
The Tuscarora is a thin- to thick-bedded fine-grained to coarse-grained orthoquartzite. It is a white to medium-gray or gray-green subgraywacke, sandstone, siltstone and shale, cross-stratified and conglomeratic conglomerate in parts, containing a few shale interbeds.[1][2][3] There is one named member of this formation: Castanea (Stc), occurring at the top, leaving the Lower and Middle Tuscarora Formation (Stlm) at the bottom.[4]
The Tuscarora is a lateral equivalent of the Minsi and Weiders members of the Shawangunk Formation in eastern Pennsylvania, New Jersey, and New York, and of the Massanutten Formation sandstone in Virginia. The Tuscarora and its lateral equivalents are the primary ridge-formers of the Ridge-and-Valley Appalachians in the eastern United States[5] It is typically 935 feet thick in Pennsylvania,[2] and in Maryland varies from 60 feet to 400 feet thick from east to west.[3]
[edit] Depositional Environment
The Tuscarora has always been intrepreted as molasse resulting from the Taconic orogeny. It is thought to represent a vast sand shoal along the margin of the Iapetus Ocean.
[edit] Fossils
Very few fossils exist in the Tuscarora, and most of them are trace fossils. Ripple marks are seldom found.
[edit] Age
Relative age dating of the Tuscarora places it in the Lower Silurian period, being deposited between 440 to 417 (±10) million years ago. It rests conformably atop the Juniata Formation and conformably below the Clinton Group in Pennsylvania.[6]
[edit] Economic uses
The Tuscarora may have been used as a ganister for making furnace liners in 19th century iron smelting blast furnaces of central Pennsylvania.[4]
[edit] References
- ^ Berg, T.M., Edmunds, W.E., Geyer, A.R. and others, compilers, (1980). Geologic Map of Pennsylvania: Pennsylvania Geologic Survey, Map 1, scale 1:250,000.
- ^ a b Jackson, Margaret S.; Hanley, Peter M.; and Sak, Peter B. (2007). Preliminary Bedrock Geologic Map of the Middle Portion of the Susquehanna River Valley, Cumberland, Dauphin, And Perry Counties, Pennsylvania (pdf). Open File Report OFBM-07-05.0. Pennsylvania Geological Survey. Retrieved on 2008-01-26.
- ^ a b Geologic Maps of Maryland:. Retrieved on 2008-01-26.
- ^ a b Doden, Arnold G. and Gold, David P.. "Bedrock Geologic Map of The Mc Alevys Fort Quadrangle, Huntingdon, Centre, and Mifflin Counties, Pennsylvania" (pdf). . Pennsylvania Geological Survey
- ^ Kempler, Steve (2007-01-19). Geomorphology : Chapter 2 Plate T-12 : Folded Appalachians. NASA, Goddard Earth Sciences (GES), Data and Information Services Center (DISC). Retrieved on 2008-03-16. “The major ridge makers are the Tuscarora (T), Pocono (Po), and Pottsville (Pt) Formations.”
- ^ Berg, T.M., et al., (1983). Stratagraphic Correlation Chart of Pennsylvania: G75, Pennsylvania Geologic Survey, Harrisburg, Pennsylvania.
