Reports
Revision of stratigraphic nomenclature of the Glenarm Series in Maryland
1967, Southwick, D.L. and Fisher, G.W.
Report of Investigations 6
Abstract
As originally defined by Knopf and Jonas (1922; 1923), the Glenarm Series (probably Late Precambrian in age) included from the base upwards, the Setters Formation, the Cockeysville Marble, the Wissahickon Formation, the Peters Creek Schist, the Cardiff Conglomerate, and the Peach Bottom Slate. Subsequent work required removal of the Cardiff Conglomerate and the Peach Bottom Slate, and addition of the Laurel and Sykesville Formations. The Setters Formation and the Cockeysville Marble are easily mapped units, and should be retained as defined. The rocks above the Cockeysville are difficult to subdivide into mappable formations because of their uniformity and poor exposure, the lensing, interfingering habit of locally distinct lithologies, the complex structure, and the variable intensity of metamorphism. Subdivisions currently in use are based on a synclinal interpretation of regional structure, and are not easily adaptable to other structural interpretations. In order to keep the system of stratigraphic nomenclature as free of structural interpretation as possible, to avoid creating a stratigraphic column with one formation sandwiched between two parts of another, and to avoid drawing formation contacts where no lithologic boundary exists, we propose that the present Wissahickon, Peters Creek, Laurel, and Sykesville Formations be included in a single formation, the Wissahickon; and that the Wissahickon Formation be subdivided into five informal lithofacies, defined on the basis of original lithology. The lithofacies defined are the lower pelitic schist; the boulder gneiss; the metagraywacke; the metaconglomerate; and the upper politic schist. These units have generally consistent geometric relationships to one another throughout the original basin of deposition, but are not time-stratigraphic.
