Sedimentology and Stratigraphy

Wellsville Formation (Woodruff, 1942)

Lithology.  The Wellsville Formation is comprised of interbedded gray silty shales and very thin fine-grained sandstones.  While generally similar to the interbedded sections of the Machias Formation, the main distinguishing characteristic for the Wellsville Formation is the lower abundance of sandstone beds.  There were three thicker sandstone lenses observed in the Wellsville Formation, which typically ranged 1 meter in thickness, but were not laterally extensive and cannot be traced west of the Allegany-Cattaraugus border area.  There were few sedimentary structures observed within the Wellsville Formation.  The thin sandstones within the main interbedded section were typically cross-bedded with irregular 3-dimensional ripples.  The thicker sandstone lenses were dominated by SCS, with thin coquinites present as internal lenses or basal lags.

Ichnology.  The Wellsville Formation contained very few observable trace fossils in the interbedded sections.  The thicker sandstone lenses contained a low-diversity Skolithos ichnofacies of Arenicolites and Skolithos.

Interpreted Depositional Environment.  The Wellsville Formation is interpreted as being deposited below storm wave base, most likely lower offshore.  The three sandstone lenses were interpreted as being deposited during large, hurricane-size storms that could briefly deposit the coarser grained sediments farther from shore and represent storm-generated shelf sandstones.


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