Graptolites from the Martinsburg Formation, Lehigh Gap, Eastern Pennsylvania
Graptolites collected from the uppermost part of the Martinsburg Formation (Pen Argyl Member) at and near the contact with the overlying Shawangunk Formation at Lehigh Gap, Pa., indicate that the uppermost Martinsburg is as young as Edenian to early Maysvillian (upper subzone [Climacograptus spiniferus subzone] of zone 13 | Orthograptus truncatus intermedius zone]). The Martinsburg gradationally overlies the Jacksonburg Limestone of late Middle Ordovician age, suggesting a lower age limit for the Martinsburg.
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