THE WINNESHIEK LAGERSTÄTTE, STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE LOWER PORTION OF THE ST. PETER SANDSTONE

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THE WINNESHIEK LAGERSTÄTTE, STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENTS OF THE LOWER PORTION OF THE ST. PETER SANDSTONEHuaibao P. Lui, Robert M. McKay, and Brian WitzkeIowa Department of Natural ResourcesEAR-0921245Derek BriggsYale UniversityEAR-0922054ABSTRACTA remarkably preserved Middle Ordovician fossil fauna, the Winneshiek fauna, was recently discovered in a localized shale unit in the lower St. Peter Sandstone in northeast Iowa. Known from a single locality, the fauna displays exceptional fossil preservation, including soft tissues (a Konservat-Lagerstätte), and contains a variety of vertebrate and invertebrate fossils. The fauna, preserved in finely laminated dark shale, was deposited in a previously unknown Ordovician environment within an isolated basin along the margin of the tropical Laurentian seaway. There are few Ordovician Lagerstätten identified worldwide, and the Winneshiek fauna (the oldest known) has been recognized as one of the most important recent discoveries in Ordovician paleontology. The preservation, archiving, and study of these exceptional fossils are needed to ensure the scientific and paleontologic heritage of this unique and significant discovery. The fauna contains a variety of rare and poorly known taxa, including conodonts (many natural assemblages, some associated with soft-tissues), articulated jawless fish (among the rarest of Ordovician fossils), eurypterids and other chelicerates (among the oldest known), early phyllocarid crustaceans (many with soft-bodied preservation), ostracods, linguloid brachiopods, mollusks, and a variety of problematic organisms (especially ?worm-like? vermiforms). The exceptional preservation of the fauna will enable detailed studies of the anatomy and phylogenetic relationships of several poorly known groups early in their evolutionary history, particularly within the arthropods (chelicerates, crustaceans) and vertebrates (conodonts and stem gnathostomes). The funded research will study and describe the taxonomy and evolutionary relationships of the fauna, the sedimentology and taphonomy of the fossil occurrences, and the paleoenvironmental setting of this unique deposit.