A CRETACEOUS SANDSTONE AND LEAF FOSSIL LOCALITY IN WESTERN WISCONSIN

In the fall of 2007, an excavation for a house foundation on an upland site in Pierce County, Wisconsin temporarily exposed an unusual ferruginous sandstone. This fine-grained quartz-arenite ranges from soft to very hard and from light orange-yellow to medium-gray to nearly-black, both corresponding to variable amounts of iron-oxide mineralization. It lies stratigraphically well above the highest quartzose sandstone (St. Peter Sandstone) in the flat-lying Early Paleozoic bedrock sedimentary sequence of the area. It is capped by Pre-Wisconsinan tills typical of the region.

Isolated deposits such as this in western Wisconsin have been assigned to the Windrow Formation, and given a Cretaceous age based on lithologic and stratigraphic similarities with better-known and better-dated deposits to the west in Minnesota. We tentatively accept this age assignment, and further support it with the recovery of imprints of two leaves and numerous wood fragments in the sandstone. One leaf has tentatively been identified as belonging to the Lauraceae, which is a fairly common element in Cretaceous floras. To our knowledge, this is the first report of Cretaceous leaf fossils from Wisconsin.