Paleoecological interpretation and age of an interstadial lake bed in western New York

Abstract

Pollen assemblages from a 6.6-m exposure of Pleistocene lake silt in central western New York consist of anomalous mixtures dominated by spruce, pine, and sedge but with a significant representation of deciduous forest elements. Leaves of Dryas integrifolia and plants of the terrestrial moss Distichium from the lake silt yielded AMS ages of 24,900 ± 1000 and 24,180 ± 900 yr B.P., indicating that the silt was deposited during the middle Wisconsinan Plum Point interstade and that the pollen of beech, hickory, and other deciduous trees was recycled from an interglacial deposit. Caution therefore must be exercised in the paleoecological interpretation of interstadial lake deposits. Plant macrofossil assemblages (seeds, fruits, mosses) from the silt also probably are mixtures of primary and secondary fossils. Scanning electron microscopy of surface features of fruits and seeds revealed two classes of preservation. The best-preserved fossils had intact surface microfeatures and are considered of primary origin. Those with the outer cell layer degraded or absent probably have been recycled. The distributions of species represented in the latter category center on the Great Lakes region and southward, whereas those of the primary fossils are more northern and indicate tundra and spruce-jack pine forest. The late Wisconsinan Kent ice margin advanced across central western New York after ca. 24,500 yr B.P. into a mosaic of tundra and conifer forest.