PROVENANCE OF PENNSYLVANIAN-AGED STRATA FROM THE APPALACHIAN FORELAND BASIN IN EASTERN PENNSYLVANIA AND WESTERN MARYLAND

U-Pb ages of detrital zircons were derived from fluvial sandstones of the 1) Lower and Middle Pennsylvanian Pottsville Formation (Schuylkill and Sharp Mountain Members) in eastern Pennsylvania, 2) Middle and Upper Pennsylvanian Llewellyn Formation in eastern Pennsylvania, and the 3) Upper Pennsylvanian Conemaugh Group in southwestern Maryland. The detrital zircon signatures from three samples in Maryland (n=686) and four samples from Pennsylvania (n=401) exhibit similar characteristics. All samples contain a major peak (>20%) of grains interpreted to be derived from the Grenville Orogen (~900–1300 Ma). All except one sample contain a minor peak (5–20%) with ages equivalent to the Granite-Rhyolite Province (~1300–1500 Ma). Three of the samples from Pennsylvania also have a minor peak that may be derived from accreted Gondwanan terranes or synrift plutons (~530–750 Ma) and two of those samples also have a minor peak with Taconic ages (440–490 Ma). –The paucity of <380 Ma detrital ages (<2%) in all samples indicates little sediment flux from Acadian-Alleghanian synorogenic sources.

All of these detrital zircon signatures are typical of a northern Appalachian Mountains provenance. Detrital zircons with ages corresponding to the Grenville and Taconic orogenies may have been derived directly from igneous suites associated with those events or recycled from older passive margin or foreland basin strata. Detrital zircons with Granite-Rhyolite ages likely represent a recycled sediment contribution. Neoproterozoic grains (~530–750 Ma) were probably not derived from synrift plutons because they are very limited in extent in the field and are typically unconformably overlain by lower Paleozoic strata. Furthermore, existing detrital zircon signatures from synrift sediments do not contain Neoproterozoic ages as observed in the sampled strata. This suggests that accreted Gondwanan terranes, such as the Avalon terrane in the northern Appalachian Mountains, were contributing sediment to the Alleghanian foreland basin throughout Early to Late Pennsylvanian time.