Abstract

Middle Ordovician limestones of the Chazyan, Bolarian, and Trentonian series are exposed in the western anticlines in the Appalacian Mountains of West Virginia and in Virginia northeast of the New River. The term Western Anticlines is applied to those cove-breeched structures which contrast with the dominantly homoclinal, fault-bounded slices west of the New River.

The Chazyan comprises the Lurich and Lincolnshire formations. The Lurich has a persisting calcilutite, the Five Oaks, at its top; in the southwest it has a middle member, the Elway, a cherty limestone, overlying a lower, Blackford, member containing chert-pebble conglomerate. The Lincolnshire limestone has disconformities above and below, thins to local extinction, and is overlapped by younger beds northward in Pennsylvania.

The Bolarian rocks are in two groups. The lower has three limestone formations, Ward Cove, Peery, and Benbolt; the Peery persists as a cherty datum. The Ward Cove varies in lithic sequence and thins toward the northwest, probably by overlap and convergence. The Benbolt also has changing facies but is of more constant thickness. The upper Bolarian is of two newly named units, McGlone and McGraw limestones; the latter is particularly distinctive and disappears southeastward, probably beneath a regional unconformity.

Trentonian rocks lie with disconformity on the Bolarian. In the southwest the lower Trentonian is dominantly Moccasin reddish argillite; northeastward it changes into fossiliferous Nealmont limestone of a facies like that in Pennsylvania. In the southwest the Eggleston argillaceous shale has a basal quartz sandstone, and in the northwest it passes into the Onego argillaceous limestone which resembles the Oranda limestone of the Appalachian Valley. Volcanic ash beds persist in all three. The younger Trentonian has not been successfully divided and traced and is called the “Martinsburg,” though in the northeastern exposures it is essentially like the Salona limestone of Pennsylvania.

An erosion surface of low relief bevelled the lower Ordovician carbonate rocks. The Chazyan Lurich carbonate rocks blanketed the Western Anticlines and areas to the southeast, and the Lincolnshire covered most of the outcrop area in the Virginias. Differential deformation increased in Bolarian, for lower units thicken southeastward and become argillaceous and quartz-arenaceous. During late Bolarian there was gentle northwest tilting. In the south sources to the southeast were rejuvenated in early Trentonian, producing reddish clays and silts that filled the margins of an adjoining trench. In later Trentonian diastrophism was moderate, but calcareous facies in the Western Anticlines grade southeastward into argillaceous sediments.

Structural trends are similar to those in Pennsylvania and New York, although the tectonic events that most strongly influenced sedimentation were not synchronous along the whole Appalachian belt. Stable periods were interrupted by deformation of belts to the southeast.

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