CORRELATING DEVONIAN TERRESTRIAL STRATA IN THE APPALACHIAN BASIN: CHALLENGES AND ISSUES

Devonian progradation of Acadian synorogenic sediment into the Appalachian Basin led to diachronous filling of the basin and sea level regression creating fluvial-dominated terrestrial environments. Timing of filling varies greatly along the outcrop belt. In eastern New York, earliest Devonian terrestrial strata containing Earth’s oldest known fossil forests occur at ~385 Ma, when co-deposition of Oatka Creek black shale occurred further to the west. In northeastern West Virginia, the first terrestrial strata were deposited near the Frasnian-Famennian boundary in the Upper Devonian Foreknobs Formation, at ~371 Ma. This marine-terrestrial transition is traceable north into Pennsylvania; however, between central Pennsylvania and eastern New York the thickness of terrestrial strata greatly expands, and further correlation is unclear. The ~2.5 km of Givetian to Frasnian terrestrial strata of the Catskill Mountains of eastern New York present difficulties of correlation and hide lateral lithostratigraphic and allostratigraphic relationships. Several significant issues hinder successful correlation and nomenclature of these strata including complexities of terrestrial deposition and erosion, homogenous facies, generally low lateral continuity, great thickness in some areas, and few unique widespread marker units, combined with issues of extensive cover, broad distribution, and rugged terrain.

Fortunately, lidar imagery revolutionizes correlation of both terrestrial and shallow marine facies in mountainous to hilly terrain. Lidar imagery viewed in 3D shows resistant stratigraphic horizons that can be traced mountain to mountain. Lateral changes in lithology seen in lidar patterns across broad lateral expanses can distinguish between proximal and distal settings (e.g., sandstone versus mudrock bodies). Lithologic-related changes of lidar patterns in vertical successions may denote terrestrial sequence stratigraphic development controlled by changes in eustatic base level, climate, and/or tectonic/orogenic activity. In addition, lidar patterns may also portray erosional incision into lower strata, marking changes in alluvial plain slope, related to similar processes. Current work on these strata includes a fusion of lithostratigraphic and allostratigraphic analyses.