Thousands of small fossils were collected from unusual lenses within the Cyathophyllum Zone, Gilmore City Limestone (Mississippian) in a large quarry near Humboldt, Iowa. These rare lenses occur in an interval 1-2.5m thick that shows an extreme variability of facies. An intensive search of other Gilmore City outcrops revealed no similar lenses. The rest of the interval, outside the lenses, contained larger fossils and fossil fragments. The small fossils in the lenses are remarkably well preserved, the gastropods particularly so. Comparison of the Gilmore City Limestone with Recent oolitic deposits at Paradise Island in the Bahamas leads to the conclusion that these unusual lenses probably were a backshore deposit. The Bahamian deposits provide evidence for interpretation of these fossils as size-sorted rather than dwarfed. Early carbonate coating is hypothesized to explain the exceptional preservation of the Mississippian fossils
