Information

 

Geology of the Neighborhood

Editor's Note: Reprinted with the permission of the Moorefield Examiner. At the Examiner's request, geologists

Katherine Lee Avary and Dr. Ronald McDowell of the West Virginia Geological and Economic Survey in

Morgantown, on May, 6, 2005, examined strata exposures created by construction of Corridor H between

Moorefield and Wardensville. Much of what they observed can be seen from the roadway, particularly when

seasonal conditions minimize vegetation overgrowth. Here is Dr. McDowell's report:

 

West Virginia Geological and Economic Survey

The majority of the strata examined along this segment of Corridor H are Devonian (370

million years old) in age and are part of the wedge of eroded sediment that spread westward

from the predecessors of the Appalachian Mountains during the late Paleozoic Era.

The structural geology along these stretches of the highway is well exposed and displays the

full range of effects of compressive stresses on the rocks of the area. While some, relatively

undisturbed, flat-lying strata are observed, combinations of folding and faulting are more

typical. Strata appear to first have been folded as more and more force was applied from the

east. These folds either closed shut, were pushed over on their side, or both. In any event, many

of the folded structures are asymmetrically gently sloping on the east side and steeply tilted on

the west.

In addition, the different types of rock present behaved differently as they were compressed.

The finer grained shale, siltstones, and mudstones containing clay minerals generally folded

very easily. The sandstones, usually a much stronger type of rock, were not so easy to fold and

in many instances would bend only so far before breaking along a fault surface. As more and

more pressure was applied, the sandstones adjusted to it by shifting positions along these faults.

Dark Red Color

We looked at well-exposed sandstones, shale, siltstones, and mudstones of the Hampshire

Formation. The Hampshire is probably most notable for its predominantly dark red coloration

and for the general lack of fossils other than plant debris. The red coloration, and that of the

occasional, pale green, intercalated layers as well, is due to the chemical nature of the iron

compounds present in the rock. In the presence of oxygen or groundwater containing oxygen,

iron compounds usually take on a red color; when oxygen content is low or nonexistent, iron

compounds may be green or black in color.

Pale Green Interbeds

In addition, iron compounds that form in one set of conditions may change color as chemical

conditions change with time. This appears to have been the case with the Hampshire, as the

dominantly dark red sediment suggests the pervasive presence of oxygen during deposition. The

thin, pale green interbeds suggest that after burial of sediment by overlying deposits, the oxygen

content of groundwater was greatly reduced and iron compounds in the buried sediment were

altered along with their coloration.

Surprise Finding

As anticipated, the Hampshire yielded a large, but well dispersed volume of plant material,

primarily preserved as coalified fragments. None of this debris was identifiable by the

investigators. However, we were surprised to find trace fossils in the Hampshire, probably

attributable to activities of insect larvae. In nearly ten years of examination of Hampshire strata,

this is the first time that we have observed indisputable signs of the presence of animals in this

unit.

Ocean Bottom Fossils

We looked briefly at an exposure of the Foreknobs Formation, the next older rock unit below

the Hampshire. After several minutes of searching, we were able to locate body fossils and

traces of marine animals that lived during the deposition of the Foreknobs.Unlike the

Hampshire, the Foreknobs is thought to have been developed by deposition on a shallow ocean

bottom Ð markedly different from the river and floodplain system that generated the

Hampshire.

Important Discovery

We also had the opportunity to examine an exposure of Lower Silurian (425 million year old)

Tuscarora Sandstone. We noticed immediately that the Tuscarora, normally known as an

extremely strong white quartz sandstone with only rare shale layers, had a number of well

developed, dark grey to black shale interbeds. This is of importance because elsewhere rocks of

Lower Silurian age have been found to contain some of the earliest land plant fossils. A cursory

examination of the one of the dark shale layers yielded numerous black fragments that are

undoubtedly plant remains! This is an important discovery and the locality will require an

extended investigation by plant paleontologists. Their findings may help add to our knowledge

of the earliest development of plant life on Earth.

 

Geology of the Neighborhood

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