A STRANDED BEACH FAUNULE IN THE BALD EAGLE SANDSTONE (MID-UPPER ORDOVICIAN, CENTRAL PENNSYLVANIA)
The Bald Eagle gray sandstone (a protoquartzite Pettijohn ’57) is in the middle of the clastic wedge deposited westward from the rising Taconic highlands, sandwiched between the offshore Reedsville dark shales and the coastal-plain Juniata redbeds, and thus represents an ancient shoreline. Its low-angle cross-bedding and gently inclined planar laminations are consistent with a beach (or foreshore) paleohabitat, which seems confirmed by the kinds of fossils just found.
The medusae were collected from Bald Eagle float, 2.8 mi (4.5 km) N23°E from Milroy (N edge Burnham 7.5’ quad.; Mifflin Co.). The best preserved is a flat circular impression on a bedding plane, 28 mm in diameter, with a small central spot, 4 surrounding concentric rings, and an outermost irregularly granular rim. Because medusae in life are soft-bodied, identifying fossil ones is problematic, but a number are known scattered through the geologic column. The Bald Eagle specimens most closely resemble the older Protolyella radiata (Trts F155; USGS Mon 30 pl 28 fig 2). Other possible identifications include Lorenzinia, Palaeoscia, Cyclomedusa, and Madigania. Less likely alternatives are basal attachment disks (conularid or pennatulacean), algal cysts, or circular feeding marks.
The nautiloid was obtained from the upper Bald Eagle on the east side of Synagogue Gap, 2.8 mi (4.5 km) S8.5°W from Spring Mills (Spring Mills 7.5’ quad.; Centre Co.). It is preserved as a white-sand-filled cast 75 mm long, showing the base of the body chamber and 5 internal chambers. Its shell has been partially dissolved, making identification difficult, but its outline and proportions suggest an oncocerid like Metarizoceras or a barrandeocerid like Jolietoceras (Trts K287, 375, resp.).
Finally, both medusae and nautiloids wash up and strand on modern beaches; both kinds as fossils would be logical cast-ups on ancient counterparts. We envision Bald Eagle paleoenvironments as sandy beaches with occasional stranded jellyfish and tossed-up nautiloid shells. Sand-bottomed estuaries cutting through such beaches are also possibilities for shell burial.