ABSTRACT

Abnormally great thicknesses of Paleozoic sediments in the Massanutten and Greendale synclines in western Virginia indicate that gentle folding accompanied sedimentation. This folding was underway in Ordovician time. The major disconformity between Lower and Middle Ordovician limestones in the Valley-and-Ridge Province is locally absent. An example is the conformable and apparently gradational relationship of these limestones near the depression of a major syncline in the Shenandoah Valley where the basal Middle Ordovician limestone is abnormally thick. This is of particular significance because on the crest of an adjacent anticline the contact is sharp and the basal Middle Ordovician limestone is very much thinner.

Re-examination of evidence bearing on the “Taconic disturbance” in eastern Pennsylvania indicates, at most, mild deformation. Recrystallization and cleaving of the Martinsburg shale certainly did not occur prior to burial beneath Silurian and younger sediments, and the folds with the slaty cleavage must have been formed at the same time as the cleavage. The metamorphism appears to have been the result of the deformation that produced slaty cleavage in some of the near-by Devonian shales.

The recrystallization and cleavage exhibited by the slates formed from Late(?) Ordovician shales at Arvonia, Virginia, suggest that deposition in the Piedmont continued into at least middle Paleozoic time. The metamorphism of the shales may not have occurred before late Paleozoic time.

The structural features and some stratigraphic features of the Paleozoic rocks of Virginia appear to be not the result of periodic disturbances but the result of nearly continuous deformation throughout much of Paleozoic time.

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