Underground mapping of Pennsylvanian paleokarst exposed in Linwood Mine, Scott Co., Iowa has revealed two distinct types of sediment infilling: (1) a finely laminated to thinly bedded karst facies consisting of claystone, siltstone, and very fine sandstone, and (2) a massive, unsorted, and heterolithic karst facies that preserves abundant fossil debris. Type 1 deposits are characterized by discrete laminations and bedding which are individually fairly well-sorted and often truncated in cut-and-fill structures. Type 1 bedding ranges from horizontal to steeply inclined and carbonaceous debris and well-preserved macrospores are abundantly preserved on bedding planes. The stratigraphy of these fills suggest settling from suspension. Type 2 fills are composed of unsorted and weakly cemented claystone, siltstone, and fine to coarse sandstone with rounded pebble to cobble-sized chert, limestone, and sandstone clasts. The sedimentology of this fill type is consistent with a dumped, sinkhole type deposit. Fossils recovered from Type 2 fills include silicified Devonian invertebrates, Devonian ptyctodont dental plates and scales, indistinguishable rounded bone material, and two potentially identifiable Pennsylvanian? tetrapod bones (limb and vertebra). Time-averaged Type 2 fossil assemblages, which reflect reworking of fossiliferous Devonian bedrock by Pennsylvanian fluvial processes, offer a unique opportunity to sample small tetrapods of Pennsylvanian age in Iowa.
Jacob S. Benner, ’97
Sponsor: Ray Rogers