THE MARCELLUS (MIDDLE DEVONIAN) OF NEW YORK: OVERVIEW AND STRATIGRAPHIC REVISIONS

Cooper’s classic 1930s Hamilton Group stratigraphy defined four allostratigraphic formations, with the Marcellus at the base. Cooper’s work, as with most Marcellus studies, focused on its thin, black shale-dominated facies in central to western New York. The time-equivalent Marcellus of eastern New York is up to 580 meters thick, more varied through a range of basinal black shales to terrestrial facies, more depositionally complex, and mappable as several separate units. In modern sequence stratigraphy terms, each of Cooper’s upper formations consists of a single third order sequence. The Marcellus, combined with upper Onondaga Formation strata, however, comprises two third order sequences.

In contrast with previous New York Marcellus stratigraphy, outlined by Rickard (1975), revisions include (Ver Straeten and Brett, 2006): 1) the “Marcellus” is split into two divisions, bounded at a third order sequence boundary. These include three formation-level units (lower “Union Springs”, and upper, coeval “Oatka Creek” and “Mount Marion” formations); 2) the Marcellus is assigned to subgroup status (informal); 3) the mid-Marcellus formational boundary is placed at a generally thin limestone +/- shale package, the “Hurley Member”, at the mid-Marcellus sequence boundary; 4) member-level changes assign two members and seven members, respectively, to the Union Springs and coeval Oatka Creek-Mount Marion formations; 5) uppermost Marcellus strata in at least part of the Hudson Valley outcrop belt are terrestrial. Terrestrial tongues within marine strata are retained in the Mount Marion Formation; those continuous above with terrestrial facies are assigned to the Ashokan Formation; and 6) in contrast with Rickard (1975), upper Onondaga strata to the west are not time-correlative with lower Marcellus strata. Their contact is a drowning unconformity, formed due to combined global eustatic rise and regional tectonic subsidence processes.

Where upper Onondaga to lower Marcellus strata are relatively continuous, the contact falls a short distance above the Tioga B volcanic tephra bed, dated at 390 +/- 0.5 Ma (mid Eifelian stage). Marcellus strata straddle the Eifelian-Givetian stage boundary (lower Oatka Creek-Mount Marion formations), variably estimated in recent studies at about 387.5, 388.1, or 391.8 Ma.