SURFICIAL GEOLOGY OF A LATE PLEISTOCENE PROBOSCIDEAN-TUSK SITE NEAR SHESEQUIN, BRADFORD COUNTY, PENNSYLVANIA, WITH REFERENCE TO SOME MAMMOTH/MASTODON OCCURRENCES IN NEARBY AREAS OF PENNSYLVANIA AND NEW YORK

In late May 2009 equipment operators excavated pieces of a proboscidean tusk from Late Pleistocene sand and gravel in Eastern Industries’ Shesequin Quarry, north-central Bradford County, PA. The fragmented tusk was relatively solid, ~3 ft in total length, and occurred 6 ft below the top of the deposit. Though the fossil is still clearly recognizable as proboscidean, the tusk has since spalled and weathered to the point where it is now no longer possible to identify it as mastodon or mammoth.

The Eastern Industries gravel pit is located on the east side of the North Branch Susquehanna River, 4.5 mi south of Athens, in Shesequin Twp. It is situated on the “Valley Heads” outwash terrace of Peltier (1949) at an elevation of ~445 ft, 1.8 mi south of Tioga Point, the confluence of the Chemung River and the North Branch. The sand-and-gravel deposit in the terrace is ~40 ft thick, ~30 ft lying above the water table (i.e., river level). Conspicuous in the main highwall is a 2-5 ft-thick bed of coarse, carbonate-cemented gravel, 20 ft below the top of the terrace. An undetermined thickness of gray, plastic clay encountered below the gravel suggests the prior existence of a proglacial lake at the site.

The Shesequin tusk is just the latest of numerous proboscidean fossils discovered in Bradford County and adjacent Chemung County, New York. “Chemung” in the Amerindian Delaware language translates as “big horn,” which 19^th-century ethnologist Henry Rowe Schoolcraft interpreted as referring to the tusks of mammoths and mastodons found in the region since pre-Colonial times, the earliest documented, however, being in 1794. Just after the Hurricane Agnes Flood of 1972 a mammoth molar was found in an excavation on the west side of the Chemung River near Sayre, PA. More recent and more spectacular was the 1982 discovery of the “Newton Mammoth” at Spring Lake, a late Wisconsinan kettle pond in Asylum-Terry Twps., Bradford Co., 17 mi to the SSE, where most of the skull, a tusk, the mandible (with molars) and other bones were collected and dated at ~14,240 ¹⁴C-yr BP. Deposition of the gravel terrace at Shesequin and burial of the tusk probably occurred somewhat earlier, i.e., at about the time the late Wisconsinan ice stood at the Outer Valley Heads moraine in central New York (35 mi to the north), 14,350 to >15,200 ¹⁴C-yr BP (Ridge, 2003).