Abstract

Sharon conglomerate crops out in three separate areas in Ohio and in all of these the formation has similar characteristics and is the basal Pennsylvanian bed resting unconformably on Mississippian sandstone or shale. This paper is concerned chiefly with the larger area of outcrop in northeastern Ohio which lies west of the type area at Sharon, Pennsylvania. The formation is dominantly a pure (96+% SiO2), medium-grained, quartz sandstone (orthoquartzite) with a few pebble layers or scattered pebbles. Laterally this rock grades into a series of narrow, conglomerate belts 1000± feet wide and 10–50 feet thick. Trend of these belts, and, in the whole formation, dip of cross-bedding, dip of the initial slope, direction of overturning of tops of cross-beds, imbricate structure, and north-south changes in sedimentary features, mechanical analyses, and chemical analyses all indicate a northern source for the clastic material of the Sharon conglomerate and also suggest a deltaic type of depositional environment. In older literature the pebbles of the Sharon are described as “vein quartz” suggesting an igneous rock source. Fossils as pebbles, and pebbles of sandstone, and conglomerate indicate rocks that were in part sedimentary. Almost no minerals are present except quartz and most of the quartz grains show secondary growth, indicating that the individual grains have been through more than one cycle of sedimentation. Although igneous rocks were doubtlessly the original source of many of the multicycle particles, the lack of pebbles of igneous rock and grains of igneous rock accessory minerals strongly suggests that the sediments of the Sharon are several cycles removed from the original source rocks. This concept is confirmed by examination of thin sections. Most pebbles show ghost granular structure and the inclusions in both pebbles and sand grains are characteristic of quartz derived from a metamorphic source.

The fossils, most of which are tabulate corals, prove that at least part of the source was Middle Devonian (Onondaga-Hamilton). The writer concludes that the Sharon sediments originated in a Canadian highland composed of a mixture of sedimentary and metamorphic rocks some of which were of Middle Devonian age, and that these sediments were transported by streams of considerable competency and were ultimately deposited as a delta in a shallow basin developed on Mississippian rocks.

The characteristics of the Sharon in southern Ohio indicate a similar origin but the clastic components were apparently derived from the southeast as shown by direction of dip of cross-beds and trend of conglomerate belts.

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