THE EMSIAN AND LOWER EIFELIAN STAGES (UPPER LOWER AND LOWER MIDDLE DEVONIAN) OF NEW YORK: OVERVIEW, RECENT FINDINGS AND CONSEQUENT REVISIONS

Upper Lower and lower Middle Devonian strata of the Emsian and lower Eifelian stages in NY are represented by the Esopus, Schoharie and Onondaga fms. Recent geochronologic studies indicate a long Emsian Stage, with estimates ranging between 9.5 to 17.2 m.y. in duration. The Eifelian is interpreted to be shorter, between 3.8 to 6.5 m.y. long; the Onondaga Fm. likely comprises about one half of that. An active to quiescent phase of orogenesis along the Laurentian margin through the Emsian to lower Eifelian resulted in initial deposition of synorogenic clastics and airfall volcanic tephras in a narrow proximal trough (Esopus) which transitions upward to widely deposited carbonates (Onondaga).

Historically, the Onondaga Ls. has been the focus of numerous studies, while the Esopus and Schoharie fms. received little attention. Recent studies in NY and beyond better delineate their character, correlations, and geological histories. The Emsian-lower Eifelian succession contains six third order depositional sequences/T-R Cycles, and the initial TST of a seventh sequence. These include three in the Esopus (Sequences Ib₁ to Ib₃), two in the Schoharie (Sequences Ib₄ to Ib₅), and one in the Onondaga (Sequence Id) fms., plus an initial TST in the upper Onondaga (Sequence Ie). All sequences are regionally and globally correlatable. As now defined, the Esopus Fm. consists of the Spawn Hollow, Quarry Hill and Wiltwyck members. The Schoharie Fm. is subdivided into the Gumaer Island, Aquetuck and Saugerties mbrs. in eastern NY; and undifferentiated silt- to sandstones of the Carlisle Center Mbr., into east-central NY. Members of the Onondaga Fm. remain largely the same.

Poor biostratigraphic control remains a long-standing issue for the Emsian of NY and the Appalachian Basin; new work by the co-authors (e.g., palynomorphs, dacryoconariids, goniatites) is in process. Lower Eifelian biostratigraphy is better constrained. In NY and eastern North America, the position of the stage boundaries are not well defined. This is especially true of the lower (Pragian-Emsian) boundary, where a lack of biostratigraphic control is also complicated by international issues (i.e., which conodont defines the boundary). The Emsian-Eifelian stage boundary falls within the lower (Edgecliff) member of the Onondaga Ls., close to or at its base.