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Title:Synthesis of a Middle Pennsylvanian soft-bodied fauna from western Illinois
Author(s):Sroka, Steven Daniel
Doctoral Committee Chair(s):Blake, Daniel B.
Department / Program:Geology
Degree Granting Institution:University of Illinois at Urbana-Champaign
Abstract:Collection and examination of thousands of concretions from the Francis Creek Shale (Middle Pennsylvanian) of Fulton County, in western Illinois, has revealed a diverse euryhaline (Essex) assemblage of the Mazon Creek biota. Previous studies suggested the Essex fauna of western Illinois is of low diversity; however forty-one species are described here, including two new species of cnidarians (Solmacula fodina and Circularia gelataforma). The fauna is represented by cnidarians, polychaete worms, non-annelid worms, arthropods, a holothurian, numerous chordates (mainly fishes), and problematic fossils. Many species had been previously known only from the Mazon Creek area of northern Illinois. In an examination of 67 localities containing fossiliferous concretions from Illinois and Missouri, abundances and ranking were culled to determine the dominant animals for the Essex fauna. For western Illinois, represented in the analyses by a single strip mine and a newly discovered outcrop, the top ten dominant organisms or groups are Essexella asherae Foster, Belotelson magister (Packard), coprolites, Tullimonstrum gregarium Richardson, Esconichthys apopyris Bardack, indeterminate animals, trails, Etacystis communis Nitecki and Schram, Strobeus cf S. primigenius Conrad, and fish parts. The Fulton County concretions lack most of the benthic organisms found in the Mazon Creek area.
The fauna is significant because, as a whole, it compares well with modern tropical estuaries. For the first time, the Mazon Creek biota is subdivided into various groups representing environments of a general estuary. Lower paleoestuarine settings are recognized in western Illinois and they are best represented by the Sun Spot Mine. Fossils from this mine are dominated by euryhaline, planktonic, nektonic, or semi-nektonic animals (medusae, fishes, crustaceans, and problematic), with a small diverse group of benthonic forms (mainly crustaceans and some polychaetes). All of the animals in this group are members of the Essex fauna and most are predators or carrion feeders. Inferred stenohaline groups (barnacles, the horseshoe crab Paleolimulus, and crustaceans) are recognized, with many species of limited distribution, restricted to the lower paleoestuary.
Stratigraphic sections at several locations in Fulton County revealed that the Francis Creek Shale consists of laminated light gray silty mudstone, siltstone, and thin bedded sandstones, and large sandstone complexes and sandstone channels. The Francis Creek lithofacies displayed in these sections are similar to the thick facies that contains the Mazon Creek biota in northern Illinois. The basal portion of the Francis Creek ranges from a dark gray, pyritic, fossiliferous shale, not seen in the northern area, to a gray silty to sandy mudstone that grades upward into interlaminated shales and fine-grained argillaceous sandstones. This unit contains occasional vertical burrows, flaser bedding, and ripple marks. Fossiliferous concretions are restricted to the basal, light gray silty mudstones and are unevenly distributed.
Issue Date:1996
Rights Information:Copyright 1996 Sroka, Steven Daniel
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9625199
OCLC Identifier:(UMI)AAI9625199

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