MISSISSIPPIAN (CHESTERIAN) EOLIAN STRATA IN THE EASTERN UNITED STATES

In the eastern United States, eolian strata of Late Mississippian (Chesterian) age are present in the Appalachian and Illinois Basins. In the Appalachian Basin, mixed siliciclastic-carbonate strata of eolian origin have been identified in Pennsylvania (where they are mapped as the Loyalhanna Member of the Mauch Chunk Formation) and in West Virginia (where they are mapped informally as the “Greenbrier Big Injun” sandstone). Detailed studies of the Loyalhanna Member in Somerset County, Pennsylvania, have revealed the following four facies: (1) cross-stratified sandstone with grainfall and grainflow structures (interpreted as eolian dune deposits) and coarsening-upward laminations (interpreted as wind ripple deposits); (2) wavy, laminated sandstone interbedded with mm-scale silty laminations (interpreted as sabkha deposits); (3) nodular sandstone with carbonate micrite matrix, interbedded with discontinuous beds of micrite (interpreted as a calcrete paleosol); and (4) poorly sorted, coarse-grained sandstone with scoured base and few visible structures (interpreted as fluvial/wadi deposits). The lower half of the Loyalhanna Member consists of sabkha deposits, calcrete paleosols, and eolian dune and wind ripple strata that contain features suggestive of wet interdune areas (e.g., rare slumps in foresets and fluid escape structures). In contrast, the upper half of the Loyalhanna Member consists of several sets of eolian dune and wind ripple strata (with no evidence of wet interdune areas), capped by fluvial/wadi and sabkha deposits. In the Illinois Basin, carbonate oolitic grainstones of eolian origin have been identified in Indiana and Illinois within the Ste. Genevieve Limestone. Sedimentary structures include prominent cross-bedding and eolian wind ripple laminations, as well as micrite-clast breccias and cylindrical structures that are interpreted as calcrete pedogenic features. In both basins, these strata are thought to be of Chesterian age, within the Cavusgnathus-Gnathodus bilineatus conodont zone. In the Michigan Basin, strata of Chesterian age have not been identified but a possible candidate is the Parma Sandstone, a non-fossiliferous well sorted quartz sandstone (interbedded with siltstone in places) that rests on an unconformity above the Meramecian Bayport Limestone.