Record of glacial-eustatic sea-level fluctuations in complex middle to late Pennsylvanian facies in the Northern Appalachian Basin and relation to similar events in the Midcontinent basin

Magnitudes of highstand transgressions into this basin, deduced from the up-dip extent of marine and brackish fossil assemblages, were greatest for the Brush Creek, less so for the Upper Kittanning and Mahoning, and least for the Lower Freeport, Upper Freeport Leader, Piedmont, and Mason. The anomalous basin-wide fresh-water roofshales and equivalents of the Upper Freeport coal may reflect ponding of fresh water to the north by an elevated area that prevented marine encroachment at the southern opening of the basin along the Kentucky-Ohio border. Maximum thicknesses of IVF deposits in each cycle are used as a proxy for estimating the minimum depth of lowstand incision preceding transgression. While the thickness of IVF deposits in most cycles ranges from 6 to 20 m, the two thickest are 30+ m thick, one associated with the pre-Mahoning paleovalley and the other with the immediately post-Mahoning paleovalley. The extent of transgression of each cycle in the NAB is roughly equivalent to those of their age-correlative major marine cyclothems (Pawnee through Swope) in the Midcontinent. Moreover, the amount of incision between them is also roughly equivalent to the amount of regression between each of the roughly coeval cyclothems in the Midcontinent, with the deepest incisions in the NAB (pre-Mahoning and post-Mahoning) corresponding to the greatest southward withdrawals of the sea in the Midcontinent (Memorial and Seminole/Hepler) during this same interval.