Relict deltas of well-sorted and well-drained sands are among numerous strand-line deposits that mark the former shoreline positions of glacial Lake Iroquois in northern New York. In this study, ground penetrating radar (GPR) was used to image the subsurface architecture of four Late Pleistocene lacustrine deltas to provide information about their depositional environment. The surveyed deltas indicate two distinct glacial Lake Iroquois water levels, the Frontenac and Trenton water phases. A pulseEKKO 100 GPR unit and a 400 Vtransmitter, combined with 50 and 100 MHz antennas are used to provide a better understanding of the internal structures, delta thickness, and distinct facies units. Delta thickness varies generally from 10 to >20 m. High-resolution GPR profiles exhibit variable reflection continuity. Depositional patterns of four distinct radarfacies are described as being characteristic of foreset bed, braided channel, channel cut and fill, and lacustrine clay, in addition to fine-grained till deposits. Facies units reflect an environment of a braided delta in which high sediment volumes and unstable directions of deposition dominated. Larger boulders of nonriverine origin that are located within deltaic sediments are interpreted as dropstones. Waterlevels of glacial Lake Iroquois appear to be stable during the relatively short periods of delta formation. Deltas of glacial Lake Iroquois exhibit lobate morphology typical of a constructive environment.

Abstract The New York bluffs of Lake Erie, which stretch northeastward 100 km from the Pennsylvania border, and those of Lake Ontario, which extend eastward 212 km from the Niagara River along the south shore of the lake, expose one of the most continuous sets of glacial drift in the northeast. The Erie bluffs are predominantly Devonian shale. However, the shale is mantled by sandy-silt till remarkable for its lateral uniformity in texture, but with distinct “down-ice” trends in lithologic properties relating to the regional bedrock or glacial reworking. Proglacial lacustrine silt, clay, and sand, deposited in 90 to 50 m of water in glacial Lakes Whittlesey and Warren between 13.5 and 12 ka, overlie the till. The bluffs of Lake Ontario are cut only sparingly in Ordovician red sandstone and shale and expose three major lithostratigraphic units. A lower red or pink sandy-till sheet is overlain by widespread gray and red glaciolacusrrine silt and clay. These fines provide major input to a younger, sillier, purplish-gray or gray till marked by both massive basal facies and upper subaqueous-flow or basal melt-out diamicton. A blanketing glaciolacustrine sequence occurring in the lower, nondrumlin areas is largely related to glacial Lake Iroquois. Locally, proglacial sands, lenses of flow till, or stone concentrations indicate a short readvance during lake formation. The two major tills of the Lake Ontario bluffs correlate with a similar sequence in adjacent Ontario, Canada. These, in turn, are tied to the Halton Till of the Port Huron advance. The lower till sheet of the United States Erie shore is related to a preceding advance, which is tentatively identified as the Lake Escarpment glaciation, and the Wentworth Till of nearby Canada.