EXPLORING VARIATION IN MARINE INVERTEBRATE PALEOCOMMUNITIES IN THE DEVONIAN MAHANTANGO FORMATION USING NEW DATA FROM EASTERN PENNSYLVANIA

The Mahantango Formation of eastern Pennsylvania hosts sediments deposited into a foreland basin associated with the Acadian Orogeny during the Middle Devonian (~380-390 Ma). The unit’s offshore siliciclastic and carbonate marine depositional environment preserves a diversity of marine invertebrate fossils. Mahantango sediments represent a transition from deeper marine conditions in the Marcellus Formation into deltaic conditions including the overlying Catskill Formation. While much paleoecological and sedimentological work has been done across the unit’s exposures in south-central Pennsylvania and neighboring states, we explore two understudied sites in eastern Pennsylvania analyzing the paleoecological variation within and between exposures of the Mahantango.

Marine invertebrate census collections were made at two locations in eastern Pennsylvania; Beltzville State Park and north of Stroudsburg. Over 300 fossils were counted and identified in the field at each location in reference to published monographs of Mahantango and Hamilton Group assemblages. Collections were analyzed for diversity, evenness, and taphonomic condition. The Beltzville collection, in bedded and laminated claystone and siltstone facies, includes more than 25 genera with over 50% count abundance of articulate brachiopods with subordinate bryozoans and corals. The site north of Stroudsburg yielded over 80% abundance of rugose and tabulate corals with significantly lower overall genus diversity, and in coarser and thicker stratal horizons. Both collections are placed in the context of measured stratigraphic columns noting possible event beds in each succession.

The spatial variability of these study assemblages and their host lithologies may reflect a lateral gradient in depositional environment from coast proximal to offshore distal, from east (near Stroudsburg) to west (Beltzville). We compare our study sites with those described from further to the west in south-central Pennsylvania, addressing paleocommunity diversity and abundance as a function of time and/or water depth across the basin.