Sandstones with cross-sets up to 1.5 m thick occur within the Copper Harbor Formation, most prominently at Five Mile Point. In contrast to intercalated sandstones with smaller scale cross-stratification or horizontal lamination, pebbles are very scarce in the large-scale cross-stratified sandstones and, where present, are restricted to set bases. The large-scale cross-stratified sandstones are better sorted than intercalated sandstones and show a mean palaeocurrent direction at 90° to the mean for the interbedded sandstones.The large-scale cross-stratified sandstones are interpreted as the product of fields of small transverse aeolian dunes that formed on dry parts of alluvial fans bordering the Keweenawan rift. The aeolian palaeocurrent mean is along the rift valley, and tentatively may be interpreted as the result of topographically constrained palaeo-tradewinds.

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