Large-Scale Cross-Stratification in the St. Peter Sandstone
Large-scale cross-stratification is present in the St. Peter Sandstone of southern Wisconsin. Sets of cross-bedding are as much as 35 ft thick and are made up of thick master fore-set units which contain sets of smaller scale, internal cross-stratification. The master fore-set units occur as two types of cross-stratification: convex upward, planar and convex downward, tangential. Both the large-scale master fore-set bedding and the small-scale internal fore-set bedding dip toward the southwest, parallel to the regional paleocurrent pattern. The large-scale cross-stratification in the St. Peter Sandstone is the result of internal structures developed in large migrating sand waves, dunes, banks, or ridges.