MIDDLE CAMBRIAN TO UPPER ORDOVICIAN STRATIGRAPHY AND PALEONTOLOGY ALONG THE CHESAPEAKE & OHIO CANAL NATIONAL HISTORICAL PARK, WESTERN MARYLAND

During a cooperative study of the geology of the Chesapeake & Ohio Canal National Historical Park corridor by the U.S. Geological Survey and the National Park Service, three separate but stratigraphically overlapping sections in western Maryland that expose a nearly continuous succession of shelf carbonate rocks ranging in age from the late Middle Cambrian to early Late Ordovician were described and sampled for macro- and microfossils. The three sections, labelled A – C, present a rare opportunity to examine, within stratigraphic context, the depositional, biostratigraphic, and evolutionary development of the central Appalachian basin for this time interval. Section A exposes strata of the Elbrook Formation and lower part of the Conococheague Formation. Trilobite zones recognized in this section include the Ehmaniella Zone of the Middle Cambrian, and the Cedaria and Crepicephalus Zones of the Marjuman and Steptoean Stages (respectively) of the Upper Cambrian. Section B exposes a nearly continuous section of the upper part of the Elbrook, and the entire Conococheague and Stonehenge Formations. Trilobites collected from this section indicate that it extends from the Marjuman Crepicephalus Zone into the Lower Ordovician (Skullrockian) Bellefontia Zone. The oldest conodonts recovered from section B indicate that it includes strata as old as the Proconodontus tenuiserratus Zone; the youngest collections represent the Rossodus manitouensis Zone. Section C also begins in the upper part of the Stonehenge within the Bellefontia trilobite Zone and extends with nearly continuous exposure to the top of the Chambersburg Limestone. Conodonts from section C show that it spans the Rossodus manitouensis to Amorphognathus tvaerensis conodont Zones. Thus, section C encompasses strata from the Lower Ordovician Skullrockian Stage to the Blackriveran Stage of the lower part of the Upper Ordovician. These exposures along the canal contain fossil microbial (bacterial) reefs and associated marine invertebrate faunas that inhabited this region roughly 500 million years ago. The major geological events recorded in this extensive exposure of soluble formations, typically poorly exposed in the region, add significantly to the historical uniqueness of the area and can be used to enrich the experiences of those who visit the park