Lithostratigraphy of Upper Devonian Scherr-Foreknobs and Lockhaven Formations near Allegheny Front of Central Pennsylvania: ABSTRACT

Abstract

Five well-exposed sections (at Madley, New Baltimore, Altoona, Milesburg, and Lockhaven) of Upper Devonian marine strata were measured and analyzed to refine lithologic and temporal correlations along the Allegheny Front of Pennsylvania. The members of the Scherr and Foreknobs formations (Minnehaha Springs, Mallow, Briery Gap, Blizzard, Pound, and Red Lock) are recognized as far north as Altoona. Farther north at Milesburg and Lockhaven, the lithology of the upper parts of the Lockhaven Formation are markedly different from the contiguous Foreknobs Formation, but the Minnehaha Springs member of the basal Scherr and lower-middle Lockhaven Formations is recognized in all sections studied. The Minnehaha Springs member (a 50 to 100-ft, resistant, medium-gray to red-gray sandy silt unit) is considered to be the result of a brief sea level lowering and is therefore nearly isochronous. The isochronous nature of the Minnehaha Springs member is substantiated by biostratigraphic data; therefore, it is considered the most reliable datum for correlating the sections of this study. The lithologic information of the six measured sections was augmented by 38 wells logs of oil and gas wells of the region. From the combined lithologic data, three generalized lithofacies cross sections were generated. These cross sections clearly indicate that:more » (1) the strike of the paleoshoreline was nearly parallel with the Allegheny Front; (2) a major delta lobe existed in central Pennsylvania during the Late Devonian; but (3) the size and influence of the delta on depositional environments was not constant through space and time.« less