BUILDING A STANDARD FOR GLOBAL CORRELATION: THE CLASSIC NEW YORK DEVONIAN SECTION AS AN EXEMPLAR OF AN INTEGRATED STRATIGRAPHIC APPROACH

Stratigraphers in New York State have long employed an allostratigraphic approach to subdivision of classic Devonian strata. Decades before the concepts of sequence stratigraphy had been formalized, G.A. Cooper subdivided the upper Hamilton Group into formations, the boundaries of which were marked by sharply based limestone and calcareous siltstone units (Skaneateles: Stafford/Mottville mbrs., Ludlowville: Centerfield Mbr.; Moscow: Portland Point/Tichenor mbrs.), which in modern parlance reflect condensed early transgressive systems tracts (TSTs) that overlie sequence boundaries (SBs). They are overlain by mudrock/siltstone successions, reflecting complex late TST-highstand successions. Lower Hamilton Group terminology has now been made consistent by splitting the former Marcellus Fm. into the Union Springs and Oatka Creek formations, based at condensed limestone intervals (upper Seneca Mbr, and Cherry Valley/Hurley mbrs., respectively). Moreover, Hamilton formations are further divisible into more than twenty members and submembers, most commencing at thin, condensed, carbonate-rich intervals and each displaying abrupt lithologic shifts at maximum-starvation surfaces flooring dark shales. Sequence boundaries, succeeded by skeletal limestones that record TST intervals, are now recognized in dominantly carbonate intervals, such as the Helderberg Group and Onondaga Fm. The Upper Devonian clastic wedge proved to be a nemesis to Ulrich’s extreme “layer cake” approach. Nonetheless, this wedge, while generally lacking TST carbonates, was successfully subdivided into time-parallel stratigraphic slices, by R. Sutton and colleagues, using through-going, sharply based, black shale tongues that reflect maximum highstand events. Upper Devonian strata are being refined into a hierarchy of formations and members based on different scales of shell-rich transgressive deposits dark shale tongues. Integration of this high-resolution sequence stratigraphy with refined biostratigraphy, event stratigraphy, magnetic susceptibility patterns, and carbon isotope chemostratigraphy, will lead to chronostratigraphic refinements, which can form a global standard for high-resolution correlation.