A Preliminary Stratigraphic Study of the Galena Group of Winneshiek County, Iowa

The rocks of the Galena Group have proved to be problematic in correlation. This problem is due to a variable lithofacies development. A preliminary investigation, although based upon exposures studied just within Winneshiek County, provides a method for field identification in Iowa of stratigraphic units currently used by the Illinois State Geological Survey within Illinois. Units under consideration at this time are restricted to the Dunleith, Wise Lake, and Dubuque Formations. Methods of identification and correlation employ in part such physical features as sequences of nodular chart bands, discontinuity surfaces, and sparry calcarenite bands. Investigation has disclosed a close relationship of these three features. A composite graphic column is provided, with key identification factors, for each of the subdivisions together with reference localities where the strata under investigation may be observed in sequence

Unusual Beach Deposits in Oolite Carbonate Environments Mississippian and Recent

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

New Flexible Crinoids from The Upper Devonian of North Central Iowa

Complete crinoid dorsal cups and crowns are virtually unknown from the Lime Creek Formation and Amana beds except for one partial crown of Dactylocrinus stellatimbasalis (Thomas) 1924. A partial and a complete crown and one dorsal cup belonging to Apodactylocrinus Strimple and Levorson, new genus, are described as A. keithi Strimple and Levorson, n. sp. and A. amanaensis Strimple and Levorson, n. sp

Additional Crinoid Specimens from the Shellrock Formation (Upper Devonian) of Iowa

Well preserved crinoids from the Shellrock Formation (Upper Devonian) of Iowa are extremely rare. Several well preserved specimens collected by one of us (Levorson) have led to new generic assignments of the species originally described as Nassoviocrinus goldringae Belanski, 1928, to Glossocrinus goldringae, n. comb., and of Hexacrinus springeri Thomas to Cerasmocrinus springeri, n. comb. The latter is the type species of Cerasmocrinus, new genus

Fossil crinoid studies

26 p., 9 fig.http://paleo.ku.edu/contributions.htm

Edrioasteroids (Echinodermata) of the Maquoketa Formation of Iowa

Two specimens of edrioasteroids have been found in the Maquoketa Formation, Richmond Group, Upper Ordovician of Iowa. This occurrence extends the geographic range of both genera, lsorophus Foerste (1917) and Edriophus Bell (1975) into Iowa which is the westernmost occurrence of these genera formerly recorded only east of Illinois. Isorophus was found in a horizon essentially barren of fossils but Edriophus is coexistent with more common echinoderms of the Maquoketa, including the crinoid genera Carabocrinus and Porocrinus

Stratigraphy of the Dubuque Formation (Upper Ordovician) in Iowa

The Dubuque Formation of Upper Ordovician age crops out in the Upper Mississippi Valley. It comprises interbedded carbonate and argillaceous rocks that are approximately 35 feet thick in Iowa and Illinois, but thicken to a maximum of approximately 45 feet in southern Minnesota. Three proposed informal subdivisions: Frankville, Luana, and Littleport beds, are differentiated on the basis of bed surface topography ranging upward from nearly planar beds in the Frankville to prominently undulose surfaces in the Littleport beds. The Frankville beds represent a transition from the massive dolomite of the underlying Stewartville Member of the Wise Lake Formation to the overlying interbedded carbonate rocks and shale of the upper Dubuque. The base of the Dubuque Formation in Iowa and Minnesota is placed at a prominent, approximately 8 inch thick, carbonate bed at the base of the Frankville beds. This \u27\u27marker bed\u27\u27 provides a more precise datum for lithostratigraphic correlation than the lowest prominent shale parting employed by previous workers to identify the base of the Dubuque