Biostratigraphy and paleoecology of the Givetian Hamilton group in Pennsylvania and New York

Revisions to previous chronostratigraphic correlations (cf. Ellison 1966, Willard 1939, Brett and Baird 1994, Slattery 1995) of the rocks at the sections studied within Pennsylvania to those of New York are proposed that include: (1) The Montebello and Sherman Ridge Members of the Mahantango Formation in the Harrisburg, Pennsylvania area are correlative with the Kashong Shale and Windom Shale Members, respectively of the Moscow Formation of New York; (2) The upper part of the Mahantango Formation at Bowmanstown is equivalent to the New Lisbon and Windom Shale Members of the Moscow Formation of New York. However, the uppermost portion previously referred to as the Mahantango Formation is now recognized as correlative to the Tully Mesosequence. In particular, fossil assemblages associated with the distinct Nis Hollow Member of Pennsylvania indicate this unit to be correlative with the Taunton Beds of the Windom Shale of New York; (3) The portion of the Port Jervis section is recognized as older than previously indicated by Slattery (1995). Historically the differentiation of the Mahantango Formation within Pennsylvania has proven difficult due to thick beds of sediments dominated by fine-textured clastics. The use of sequence stratigraphic concepts in conjunction with sedimentary, biostratigraphic, paleoecologic, and subtle lithologic differences of beds has provided a basis for the correlations proposed in this study. The term “Tully Mesosequence” is proposed for recognizing penecontemporaneous beds with a wide array of lithologies that are correlative with the classic Tully Limestone of central New York.; This work reports the first occurrence of a unique pyritized microfauna from the Lower Member of the Tully Mesosequence at Lock Haven, Pennsylvania. This “small shelly fauna” (sensu Dzik 1993) consists of minute, postlarval specimens of pelecypods, gastropods, and dacryoconarids. Also present are the first reported specimens of Jinonicella from North America and a ctenosome bryozoan showing unusual body preservation.