Type sedimentary Other conglomerate Region Appalachian Mountains Overlies Juniata Formation Parent range Appalachian Mountains | Sub-units Castanea Member Named by Darton and Taff Named for Tuscarora Mountain Underlies Clinton Group | |
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Primary quartzarenite (sandstone) Extent Pennsylvania, Maryland, West Virginia, Virginia | ||
The Silurian Tuscarora Formation — also known as Tuscarora Sandstone or Tuscarora Quartzite — is a mapped bedrock unit in Pennsylvania, Maryland, West Virginia, and Virginia, USA.
Contents
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. There is one named member of this formation: Castanea, occurring at the top, leaving the Lower and Middle Tuscarora Formation at the bottom. This formation has been called the "White Medina Sandstone" in West Virginia.
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, a 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 It is typically 935 feet thick in Pennsylvania, and in Maryland varies from 60 feet to 400 feet thick from east to west.
Depositional environment
The depositional environment of the Tuscarora has always been interpreted as mostly terrestrial or shallow marine deposits resulting in a molasse sequence produced by the Taconic orogeny. It is thought to represent a vast sand shoal along the margin of the Iapetus Ocean.
Ripple marks are seldom found, but do support interpretation as a shallow marine depositional environment.
Age
Relative age dating of the Tuscarora places it in the Lower Silurian period, being deposited between 440 and 417 (±10) million years ago. It rests conformably atop the Juniata Formation and conformably below the Clinton Group in Pennsylvania.
Fossils
Very few fossils exist in the Tuscarora, and most of them are trace fossils.
At least two hughmilleriid Eurypterids (sea scorpions) have been discovered in the Tuscarora.
Notable exposures
The Tuscarora Formation is commonly exposed on various ridge crests and in many water gaps in the Ridge and Valley physiographic province of the Appalachians of Pennsylvania, Maryland, and West Virginia, particularly along the Wills Mountain Anticline.
In Pennsylvania, the Tuscarora is exposed along US 30 on the north and south sides of the Narrows in central Bedford County, where it is nearly vertical. It is also well-exposed in the core of Jack's Mountain in Jack's Narrows, where the Juniata River cuts through the mountain, just west of Mount Union. The Standing Stone Trail traverses this cut, and many of the "Thousand Steps" here are Tuscarora quartzite.
In Maryland, the National Road (US 40) passes arched Tuscarora sandstone outcrops in the Cumberland Narrows in Allegany County.
In West Virginia, the River Knobs along the North Fork of the South Branch of the Potomac River in Pendleton County include dramatic outcrops of nearly vertical Tuscarora sandstone. Some of the better known of these exposures are Seneca Rocks, Champe Rocks, Judy Rocks, and Nelson Rocks. These cliffs are clearly visible along U.S. Route 33 and West Virginia Routes 28 and 55. North Fork Mountain, to the east of the River Knobs, is a long Ridge and Valley anticline ridge capped by Tuscarora sandstone.
Two of the most complete exposures of the Tuscarora Formation are in two quarries at the crest and south end of Canoe Mountain (Spruce Creek Quadrangle).
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.
The Tuscarora has become very important to the tourism industry of eastern West Virginia, where the formation has many conspicuous outcrops visible from such roads as U.S. Routes 33 and 50 and West Virginia Routes 28 and 55. Tuscarora-capped North Fork Mountain and various Tuscarora cliffs are prominent in scenic views from such sites as Spruce Knob and Dolly Sods.
Seneca Rocks in Pendleton County, West Virginia, has become a world-renowned rock climbing location. It is the only "true peak" (a peak inaccessible except by technical rock climbing techniques) on the East Coast of the United States. Two climbing schools near the outcrop and many other guide services offer guided climbing trips on the 300+ climbing routes on the west-facing cliff. Seneca Rocks is managed by the U.S. Forest Service, and is located within the Spruce Knob-Seneca Rocks National Recreation Area of the Monongahela National Forest.
The Nelson Rocks Preserve, located near Circleville, West Virginia, is a privately owned and operated nature preserve dedicated to preserving Nelson Rocks and the surrounding environment as a cultural, educational, and recreational resource. The preserve offers a via ferrata climbing trail, one of six in the United States.