A GLACIAL CLAST PAVEMENT IN DOOR COUNTY, WISCONSIN

Glacial sediments, exposed in the quarrying operation of Soil Specialists, one half mile south of Sturgeon Bay, Door County, Wisconsin, include sand and gravel covered by diamicton. The diamicton is clay-rich, reddish brown till of the late Wisconsin Kewaunee Formation. Ice-flow indicators suggest deposition by the Green Bay Lobe. Previous workers found one (Mickelson et al., 1984) or two (Schneider, 1989) members of the Kewaunee Formation in Door County. The diamicton is thickest along the south and west walls of the pit and is bisected by a clast pavement consisting of a single layer of primarily tabular, flat-lying cobble- to boulder-sized dolostone clasts, many of which have a striated upper surface. The clast pavement is also visible along the north and east walls of the pit, but in these areas, the clasts rest on sand and gravel.

Several hypotheses have been put forth to explain the development of clast pavements. The purpose of this study was to collect sedimentological evidence from the pit in an effort to identify the mechanism responsible for the development of the clast pavement. Till fabric and grain-size determinations of till above and below the pavement at the south end of the pit indicate the tills had different origins. The orientation of clast striations was found to be consistent with the fabric of the till above the pavement as well as with long-axes of nearby drumlins. The similarity in fabric and striation orientation, as well as the situation of the pavement at a till/sand interface along the north wall of the pit, may indicate that the pavement resulted from clast settling within a deforming till. A strong till fabric, as in the till above the pavement at this site, is indicative of a lodgement till, but recent laboratory experiments have shown that it is possible to induce a strong fabric within a deforming till.