VIRGIANID BRACHIOPODS OF THE MICHIGAN BASIN, AND ITS IMPLICATIONS FOR POST-EXTINCTION DIVERSIFICATION OF THE SILURIAN PENTAMERIDE FAUNA IN LAURENTIA

Three virgianid genera are present in the Michigan Basin. The oldest, Virgiana mayvillensis Savage from the Mayville Dolomite, is upper Rhuddanian in age and coeval with the same species on Anticosti Island in eastern Canada. “Virgiana” major Savage, 1916, from the uppermost Lime Island (uppermost Rhuddanian), has an incipient cruralium supported anteriorly by a low median ridge, for which Virgianoides gen. nov. is proposed in this study. Platymerella in the Elwood  Formation (uppermost Rhuddanian) was the most southerly virgianid occurrence in the American mid-continent. The early evolution of the Brevilamnulella-Viridita-Virgiana lineage was represented by the early-middle Rhuddanian fossil record of Anticosti Island. Available fossil data indicate that the Virgiana invasion into intracratonic basins did not begin until late Rhuddanian time, represented by the excellent record of V. mayvillensis in the Michigan Basin, and V. decussata in the Hudson Bay and Williston basins. Despite its late arrival, virgianids thrived for a somewhat longer geological time in the Michigan Basin, represented by Virgianoides and Platymerella in the latest Rhuddanian, when virgianids largely became extinct in other basins of Laurentia

The classic Silurian reefs of the Chicago area

Previously published by Western Michigan University for the 27th Annual Meeting, North Central Section, Geological Society of America, April 1994.Geological Field Trip 4: April 24, 1999.Includes bibliographical references (p. 39-42)

The Silurian Geology and Stone Industry of Jersey County, Illinois

Illinois Association of Aggregate Producers 2002 Science Teachers' Workshop. Pere Marquette State Park, August 13-14, 2002.Ope

Tri-State Geological Field Conference

Includes bibliographical references

The implications of a Silurian and other thylacocephalan crustaceans for the functional morphology and systematic affinities of the group

Background: Thylacocephala is a group of enigmatic extinct arthropods. Here we provide a full description of the oldest unequivocal thylacocephalan, a new genus and species Thylacares brandonensis, which is present in the Silurian Waukesha fauna from Wisconsin, USA. We also present details of younger, Jurassic specimens, from the Solnhofen lithographic limestones, which are crucial to our interpretation of the systematic position of Thylacocephala. In the past, Thylacocephala has been interpreted as a crustacean ingroup and as closely related to various groups such as cirripeds, decapods or remipeds. Results: The Waukesha thylacocephalan, Thylacares brandonensis n. gen. n. sp., bears compound eyes and raptorial appendages that are relatively small compared to those of other representatives of the group. As in other thylacocephalans the large bivalved shield encloses much of the entire body. The shield lacks a marked optical notch. The eyes, which project just beyond the shield margin, appear to be stalked. Head appendages, which may represent antennulae, antennae and mandibles, appear to be present. The trunk is comprised of up to 22 segments. New details observed on thylacocephalans from the Jurassic Solnhofen lithographic limestones include antennulae and antennae of Mayrocaris bucculata, and endites on the raptorial appendages and an elongate last trunk appendage in Clausocaris lithographica. Preserved features of the internal morphology in C. lithographica include the muscles of the raptorial appendage and trunk. Conclusions: Our results indicate that some `typical' thylacocephalan characters are unique to the group; these autapomorphies contribute to the difficulty of determining thylacocephalan affinities. While the new features reported here are consistent with a eucrustacean affinity, most previous hypotheses for the position of Thylacocephala within Eucrustacea (as Stomatopoda, Thecostraca or Decapoda) are shown to be unlikely. A sister group relationship to Remipedia appears compatible with the observed features of Thylacocephala but more fossil evidence is required to test this assertion. The raptorial appendages of Thylacocephala most likely projected 45 degrees abaxially instead of directly forward as previously reconstructed. The overall morphology of thylacocephalans supports a predatory mode of life

Depositional and taphonomic aspects of a Silurian (Brandon Bridge, Llandovery-Wenlock) Fossil Konservat Lagerstatte from Waukesha, Wisconsin (U.S.A.), predictability of North American Silurian Fossil Konservat Lagerstatten, and some insights into ichnofacies

Chapter I demonstrates that a discontinuity surface occurs between the Silurian Plaines Member of the Kankakee Dolomite and Brandon Bridge Member of the Joliet Dolomite of Illinois and their stratigraphic equivalents in Wisconsin. Enigmatic pits on the Plaines surface are determined to be biogenic structures, which are important in interpreting this surface and the laterally-adjacent unconformity as paleokarst.Chapter II addresses preservation of Fossil Konservat Lagerstatten, utilizing Lagerstatte from the Brandon Bridge strata (late Llandovery-early Wenlock) at Waukesha, Wisconsin. This Lagerstatte occurs in a localized area of restricted circulation adjacent to a paleoscarp within a peritidal setting. Preservation is controlled by anoxic conditions, possible brackish water influence, and early diagenetic mineralization. Composed primarily of arthropod exuviae, which were washed into a sediment-trap formed by paleoscarp topography, the organisms in this Lagerstatte are unified more by their hydrodynamic properties than by any living association. This hydrodynamically-controlled taphonomic accumulation of exuviae represents a new category of Lagerstatten.Chapter III examines predictability of North American Silurian Fossil Konservat Lagerstatten. Eight Lagerstatten are grouped on the basis of Q-mode cluster analysis, employing biotic components and sedimentary features as characters. Two main clusters result: (1) EP biotas (eurypterid and/or phyllocarid-dominated), which are restricted geographically to areas surrounding the Michigan Basin, stratigraphically to the Upper Silurian, and ecologically to arid, hypersaline conditions; and (2) DG biotas (dendroid graptolite-characterized), which are taxonomically more diverse and less restricted geographically, ecologically, and stratigraphically. Therefore, the location of EP biotas is easier to predict based on readily recognized features, supporting the contention that Lagerstatte prospecting is possible.Chapter IV compares ichnofacies of parallel modern siliciclastic and carbonate marine depositional environments in order to determine what differences exist because of sediment composition. Sedimentation rate, cementation history, grain properties, and grain-size distribution all may vary with sediment type, and these affect the distribution of bioturbation patterns. Consequently, the widely-used siliciclastic ichnofacies model may not apply to carbonate settings in all cases.U of I OnlyETDs are only available to UIUC Users without author permissio

Calcareous and ferruginous oolites at the Ordovician-Silurian boundary in Illinois

Typescript.Thesis (B.S.) in Geology--University of Illinois at Urbana-Champaign, 1983.Bibliography: leaves 39-44

Calcareous and ferruginous oolites at the Ordovician-Silurian boundary in Illinois

Typescript.Thesis (B.S.) in Geology--University of Illinois at Urbana-Champaign, 1983.Bibliography: leaves 39-44

Silurian reefs of the Chicago area. Part I : field trip for the 1992 Eastern Section meeting, American Association of Petroleum Geologists, Champaign, Illinois, September 19, 1992

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