Geoscience Education in the Mountain State:
CATS Geology Telecourse, Spring 1999,
Article--Three Miles Beneath West Virginia

Did you ever wonder what lies below the ground you stand on? What's underground is not only a curiosity--for many people it is a very practical matter. Each year, several thousand West Virginians drill wells to obtain water for their households. Each year, several hundred West Virginia individuals and companies drill wells in search of oil and gas. And, each day, thousands of West Virginians go to work in mines and quarries to extract coal, limestone, clay, sandstone, or sand and gravel. Directly or indirectly, we all have a stake in what lies below.

Rock Types

With the exception of small areas in Jefferson and Pendleton counties, the entire State is underlain by sedimentary rocks. Sedimentary is a general term applied to rocks which formed from the accumulation of sediments.* Examples of West Virginia's typical sedimentary rock types are given in Figure 1.

	Rock Type	Description of the Sediment	Examples of Depositional Environments
Rocks Formed From Inorganic Sediment	SANDSTONE	"sand-sized" mineral particles (1/16 - 2mm diameter); typical minerals include quartz, feldspar, micas, rock fragments	moving bodies of water (shorelines, riverbanks, etc.)
	SILTSTONE	"silt-sized" mineral particles (1/256 - 1/16 mm diameter); typical minerals include quartz, feldspar, micas	moving bodies of water (shorelines, riverbanks, etc.)
	SHALE	"clay-sized" mineral particles (less than 1/256 mm diameter); typical minerals include kaolinite, illite, quartz, feldspar	quiet bodies of water (ocean depths, swamps, lakes, lagoons, etc.)
Rocks Formed From Organic Sediment	LIMESTONE/DOLOMITE	typically the hard parts and waste products of marine organisms, plus some inorganically-derived material	shallow marine or fresh water (reefs, bays, platforms)
	COAL	partially decayed plant debris mainly from the woody and waxy parts of plants (peat)	swamps, marshes

Figure 1. West Virginia's typical sedimentary rock types, descriptions of the corresponding sediment types from which they formed, and examples of the types of environments under which they were deposited.

*Sediments are solid materials which have 1) settled from suspension in a liquid, 2) precipitated from solution, or 3) formed by the activity of organisms.

There is great variation across the State in the rocks present below the surface. The thickness, rock type, and depth of individual rock units change considerably from region to region, and in many instances over a distance as small as a few miles. How can we understand why these variations occur? The easiest way is to compare places where rock-forming sediments are accumulating today to similar environments that existed in West Virginia millions of years ago. We'll look at limestone, coal, sandstone, and shale.

Limestone. Excellent examples of contemporary limestone-forming areas include the Bahama Bank, Florida Bay, and the Persian Gulf. Here, warm shallow waters make a fine environment for corals, algae, and shellfish. These organisms provide calcium carbonate skeletons and waste products which accumulate as sediments and eventually become limestone. Under similar conditions, millions of years ago, some well-known West Virginia limestones and dolomites formed: the Greenbrier Limestone, Tomstown Dolomite, and Helderberg Limestone. (All are extensively quarried and used for highway construction, mine safety dust, lime manufacture, blast furnace flux, acid neutralization, and a variety of other purposes. Dolomite is similar to limestone, but is a calcium-magnesium carbonate, whereas limestone is primarily calcium carbonate.)

Coal. Today, coals of potentially commercial extent and quality are forming is the peat swamps of Borneo. In the United States, peat is currently accumulating in the Dismal, Okefenokee, and Mississippi Delta swamps, but the size and quality of these deposits will probably preclude their developing into commercial coals.

Similarly, West Virginia's 62 minable coal seams formed in huge swamps at a time when the Mountain State was a vast plain slightly above sea level. The swamps and flat topography were associated with a large delta complex (similar to the Mississippi delta) which covered much of what is now central Appalachia.

Sandstone. One of the best-known modern deltas exist where the Mississippi River enters the Gulf of Mexico. Here, over 500 million tons of sand, silt, and clay are deposited each year as moving river water slows and loses its ability to carry solids. The sand particles are the largest and therefore the most difficult for the river to carry. They typically accumulate as sand bars at the river mouth or along bends (points) in the river channel. Many of West Virginia's sandstones began as river-mouth or point-bar deposits.

Shale. Shale is composed of "clay-sized" mineral particles. Clay particles are tiny (less than 1/256mm) and are "dropped" from moving water when its velocity becomes too slow to carry them. These particles may be deposited on the floodplain when the river overflows its channel, or within the channel if the water velocity becomes slow enough, or may not settle out until they have been carried many miles beyond the river mouth.

Most of West Virginia's sandstones and shales were deposited as part of ancient delta systems. Exceptions include the Oriskany Sandstone and Tuscarora Sandstone, thought to have formed as beach deposits.

Geography and History

Looking at the earth today, we see that every ocean has it shore, and every swamp has its edge. The same was true millions of years ago, when West Virginia's rocks were formed. Thus, sandstones being formed along the beaches have a limited geographic extent, as do coal seams forming in swamps.

If, in 10,000,000 years, we could return to look at today's beaches, we might find that a rise in sea level has moved the beaches inland, creating new sandstone, or buried the coal-forming swamps under marine sediments, which form shales or limestones. In this way, sediments of completely different composition are layered one above another. Within each layer, composition and thickness variations show where beaches, deltas, and swamps began and ended, and where maximum deposition (or erosion) occurred in each environment.

Wells drilled today reveal West Virginia's geologic history and past geography. In a single well, changes in rock type as one drills downward reveal the history of environments at that location. In two or more wells, the past geography of these environments is also revealed, as we see the thickness (or even pressure) of individual layers changing from one location to another.

Today's Resources

The ancient swamps, reefs, and rivers have been gone for hundreds of millions of years, and we are now exploiting their deposits.

Some mineral production takes place in all of West Virginia's 55 counties. However, because the rocks vary statewide, the commodities produced also vary. Beckley, Parkersburg, and Elk Garden are examples of three areas where the surface and subsurface rocks are significantly different.

West Virginia's Basement

Although the sedimentary rocks beneath West Virginia are thousands of feet thick, they do have a lower limit. A few extremely deep oil-and-gas wells have been drilled in West Virginia and surrounding states, penetrating the entire sequence of sedimentary rocks and drilling into the "basement." These deep wells, referred to by geologists as "basement tests," reveal that West Virginia's basement consists of igneous and metamorphic rocks estimated to be about 900,000,000 years old.

Geologists have used basement tests and other information to estimate the depth of the basement throughout the State. These studies indicate that it ranges from less than 10,000 feet below sea level along the Ohio River, to nearly 30,000 feet below sea level in the eastern panhandle.

Although many factors influenced the eastward thickening of the sedimentary cover, the dominant one is simply that greater amounts of sediment were deposited there. This eastward thickening was actually greater millions of years ago, before several thousand feet of sedimentary rocks were eroded from parts of the eastern panhandle.

Further Reading

Geologic History of West Virginia: D.H. Cardwell, 1975, 63 p. Written for the layperson, this is a popular account of the geologic history of West Virginia. Extensively illustrated. Publication ED-10.

Correlation of Stratigraphic Units in North America, Northern Appalachian Region Correlation Chart: D.G. Patchen and others, 1984, American Association of Petroleum Geologists Correlation Chart Series (generalized correlation charts illustrating the stratigraphic sequence and nomenclature of various geographic areas.)

WVGES Education Specialist, Tom Repine (repine@wvgs.wvnet.edu)

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Page last revised: July 1999

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