CHAPTER 4. LOWER MIDDLE DEVONIAN (EIFELIAN-LOWER GIVETIAN) STRATA OF NEW YORK STATE: THE ONONDAGA FORMATION AND MARCELLUS SUBGROUP

Lower Middle Devonian strata of the Eifelian and lower Givetian stages in NY are assigned the names Onondaga and Marcellus. For >80 years these represent time-significant allostratigraphic units, that cut across lithologic boundaries. The Onondaga Fm. is a relatively tabular, limestone-dominated unit throughout NY. Strata thin from both east and west into thinner basinward facies in central NY. In contrast, the “Marcellus subgroup” of the lower part of the Hamilton Group forms an eastward-thickening and coarsening wedge of siliciclastic-dominated facies related to onset of renewed Acadian (“Neoacadian”) orogenesis. Marcellus strata range from less than seven meters in the western NY subsurface to an estimated 580 meters in the Hudson Valley. Marine Marcellus strata are assigned to a lower Union Springs Fm.; and to coeval upper Oatka Creek and Mount Marion fms. The latter two represent distal, basinal mudrocks and proximal, sand-dominated facies, respectively. In easternmost outcrops near Catskill, uppermost Marcellus strata pass into terrestrial facies.

Southward through the Appalachian Basin, Onondaga correlatives are assigned to: 1) Onondaga Fm., eastern PA; 2) upper Needmore Fm, central PA to the middle VA-WV border area; and 3) upper part of the Huntersville Chert Fm. further southwest along the VA-WV border. South of NY, the term Marcellus is applied lithostratigraphically, not allostratigraphically. There, the base of Marcellus ranges from mid-Onondaga-age to the base of the Marcellus as in NY. The top of the Marcellus south of NY ranges from middle Union Springs-equivalent strata at the base of Turkey Ridge Mbr., central PA to post-NY Marcellus strata correlative with parts of the Skaneateles Fm. in NY.

Onondaga and Marcellus strata form three third-order depositional sequences. Devonian Sequences Ic, Id, and Ie (or Eif-1, Eif-2, and Eif-Giv) consist, respectively, of 1) lower to middle Onondaga; 2) upper Onondaga and Union Springs; and 3) coeval Oatka Creek-Mount Marion fms. Three distinct Eifelian-lower Givetian faunal assemblages represent the Onondaga, Stony Hollow, and Hamilton Ecological-Evolutionary Subunits (Brett et al., 2009). Changes from fauna to fauna in part relate to shifts of global climate and Marcellus transgression over the Laurentian transcontinental arch.