DEPOSITIONAL ENVIRONMENT OF THE NORTHEAST SHALE MEMBER ALONG FOUR MILE CREEK, ERIE COUNTY, PENNSYLVANIA

The Northeast Shale Member of the Canadaway Formation is exposed along Four Mile Creek in northeastern Erie County. Based on 21.3m of strata, the North East Shale consists mainly of grey shale with episodic, thin, fine-grained sandstone beds. Primary structures include linguoid and sinuous ripples, and groove, prod and flute casts with an overall east to west paleocurrent direction (which during the Late Devonian was southeast to northwest). Other structures include wrinkle marks, bioturbated laminations and 1cm-2.5cm thick lenses of cone-in-cone structures. There are also sandstone beds containing liquefaction structures within the lower 7.6m of the strata. Body and trace fossils include: Ceratodictya Sp. (glass sponge), crinoid columnals, and horizontal burrows and trails of the Cruziana ichnofacies. Pyrite spheres ranging in size from 12µm-100µm diameter are present in medium and dark shale as well as amongst carbonized terrestrial plant debris which exists periodically throughout the section.

The asymmetrical ripples in the sandstone beds are indicative of episodic, high energy currents that interrupted low energy currents with slow sedimentation which prevailed during shale deposition. The sandstone beds were deposited rapidly, causing wrinkles to form in the underlying shale. Between the shale beds, calcareous beds were deposited which later formed cone-in-cone structures. The abundance and diversity of ichnofossils and bioturbation, along with the presence of fossil sponges and crinoids indicate that the water oxygen content at the bottom of the Kaskaskia Sea was sufficient to sustain diverse life. Sedimentary structures and fossils suggest that the water was warm and shallow with episodic currents which brought terrestrial organic matter to the marine environment. Below the sediment-water interface an oxygen deficiency produced a redox boundary, as suggested by the presence of spherical to sub-spherical pyritized bacterial colonies (framboids).