CHAPTER 5:STRATIGRAPHY AND FACIES OF THE MIDDLE AND UPPER HAMILTON GROUP (MIDDLE DEVONIAN; GIVETIAN) IN NEW YORK STATE AND ADJACENT AREAS

The Middle Devonian (lower-middle Givetian) Hamilton Group of New York State is an iconic unit in North America, which has contributed key concepts in stratigraphy, sedimentary geology, paleoecology and evolution. This interval comprises a ~100 to 1000 m-thick clastic wedge, shed westward from the Acadian Mountains, with thin but persistent carbonates. Despite the diverse invertebrate fauna that consists of >300 species of corals, bryozoans, brachiopods, mollusks, echinoderms, and trilobites, the age of the Hamilton Group is rather poorly constrained in terms of chronostratigraphy owing to the rarity of biostratigraphically useful conodonts and goniatites. It apparently belongs to the Polygnathus timorensis to middle Pol. ansatus Conodont chronozones. The middle-upper Hamilton Group in New York State comprises three formations, the Skaneateles, Ludlowville, and Moscow, each defined as an interval delimited with a sharply based fossiliferous limestone-calcareous siltstone, interpreted as condensed transgressive deposits, and dominated by highstand to falling stage shales, mudstones/ siltstones, and sandstone. Marine eastern equivalents dominated by fine grained sandstones and siltstones, include two formations: Panther Mountain Fm, equivalent to the combined Skaneateles and Ludlowville formations, and the Cooperstown Fm, equivalent to the Moscow Fm. We review, revise and update a hierarchical framework of lithostratigraphic subdivisions of these formations, including some 23 members (4 new), some 45 submembers (more than half newly proposed or redefined), and more than 70 named beds, both formal and informal. As defined herein, members and most submembers represent high-frequency depositional sequences with basal shell-rich carbonates and abrupt flooding surfaces that mark the base of highstand deposits. Not only are most of the members and submembers traceable across western and central New York, but also to a lesser extent into adjacent regions that include southern Ontario, Ohio, the Michigan Basin, and northeastern Pennsylvania. This refined lithostratigraphy provides an excellent framework for studying the evolutionary paleoecology of the long-ranging Hamilton fauna, which represents ~3-4 million years of relative stability bounded by the global Kačák and Taghanic biocrises.