PLANT FOSSIL EVIDENCE FOR LATE PLEISTOCENE TUNDRA CONDITIONS IN SOUTH–CENTRAL PENNSYLVANIA

Initial studies of plant macrofossils from the lower portion of a sediment core have extended the record of late Pleistocene tundra vegetation in central Pennsylvania 144 km (89 mi) west-southwest of the previously known occurrence.

A 4.9-m sediment core from Kings Gap Pond #1, a vernal pond in Kings Gap State Park on the north flank of South Mountain in Cumberland County, Pennsylvania, was collected in January 2001. The pond developed in a depression, presumably a sinkhole, in thick sandstone colluvium over the Tomstown dolomite. The pond sediment in the core is predominantly silt and clay, with some sand and sparse organic material. Radiocarbon dates of 16,080 BP (organic sediment at 4.9 m) and 14,410 BP (twig at 2 m) correspond to a time when Wisconsinan ice had retreated north of Pennsylvania. The average sedimentation rate in the cored interval was approximately an order of magnitude greater before 14,410 BP than since that date.

Macrofossils from the bottom 1.45 m of the core include Dryas integrifolia (mountain avens), Salix (willow), Carex sp. (sedge), and both terrestrial and aquatic mosses. No remains of spruce or other trees were found in initial analysis. Watts documented similar tundra vegetation, of about 12,000 BP age, from Longswamp, Pa., 144 km east-northeast of Kings Gap. Sediments as old as 15,000 BP at Criders Pond, 28 km (17 mi) farther to the southwest, show no fossil evidence of tundra vegetation.

Confirmation of tundra conditions at Kings Gap increases our knowledge of plant succession in late Pleistocene Pennsylvania and adds credence to descriptions of periglacial features on South Mountain and other areas in south-central Pennsylvania well south of the glacial border.