Site Locations: 

Cumberland Valley Camp, mileage 95.40

     Nearest Access: Falling Waters Road, mileage 94.44

 Near the middle of the Shenandoah Valley are clastic sediments that are surrounded by the carbonate precipitates.  This is the Martinsburg that identifies a significant change in the geologic processes governing the deposition of rock formations.  The Martinsburg is an assemblage of siltstone and graywacke layers.  Its earliest member, the Stickley Run, marks the termination of carbonate deposition of the Cambrian and Ordovician geologic periods and the beginning of an extensive sequence of sandstone and siltstones (shales) deposited through much of late Ordovician and Silurian time.  The basal portions of the Stickley Run contain volcanic ash (referred to as metabentonite) that attests to the evidence of an island arc system of volcanoes to the east.  The environment can be visualized as remarkably similar to that of today’s Japanese islands configuration of volcanoes and seas.

  While the carbonate sequence was being deposited, the environment was that of a shallow sea surrounded by low lying hills that were not conducive sources for clastic sediments.  With time, the basin began to deepen and to produce a more open marine environment.  At the same time, plate tectonic forces were at work to create a volcanic arc that provided a source for wind-deposited ash as well as a source for clastics.  The Martinsburg marks the earliest incursion of clastic sediments derived from an eastern source and deposition in an ocean basin that exhibited shelf and slope components in its profile similar to today’s eastern margin of the Atlantic.  The graywacke (muddy sand) component of the Martinsburg suggests that turbidity currents were active in the depositional process just as they are today off the New Jersey shore.

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