FINDING THE ELUSIVE CATSKILL DELTA. THREE UNDERGRADUATE RESEARCH PROJECTS IDENTIFY DEVONIAN MARGINAL MARINE STRATA ON OYARON HILL, EAST-CENTRAL NEW YORK
The outcrop contains 3 scour-based, meter-scale bedsets made of conglomeratic greenish-gray sandstone beds that truncate subjacent cm-scale gray heterolithic (lenticular to flaser) wave-rippled sandstone and mudshale strata. A few sandstones within the heterolithic strata form graded beds and hummocky cross-stratified beds (tempestites) that bear a low-diversity marine faunal assemblage featuring abundant small bivalves, as well as common spirifierid and rhynchonellid brachiopods. The lowermost sandstone bedset: 1) fills small (up to 1.25 m thick and 3 m wide) channels above the heterolithic strata, 2) bears abundant coarse plant/wood fragments in the basal mud chip conglomerate, 3) and contains prominent thin gray shale beds or drapes between cross-stratified sandstone beds. The middle sandstone bedset exhibits prominent medium-scale trough cross strata with few shale partings. The uppermost sandstone bedset displays both planar bedding and medium-scale trough cross-stratification, locally preserving isolated dune bedforms. A recent rock fall from the upper sandstone bedset revealed the first known marine fossils from the bedsets; a low diversity transported assemblage very similar to fauna of the heterolithic strata. Large concentrations of small convex-up shells line the upper surfaces of multiple sandstone bed partings, and a few larger shells are found within basal mud chip-rich sandstone. The shells are mostly disarticulated but unfragmented.
We interpret the sandstone bedsets as storm- and tide-influenced distal delta distributary channel and channel mouth bar deposits. The heterolithic strata were likely storm-influenced tidal flats adjacent to the delta distributaries.