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|Title:||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|
|Doctoral Committee Chair(s):||Langenheim, Ralph L., Jr|
|Department / Program:||Geology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||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.
|Rights Information:||Copyright 1990 Kluessendorf, Joanne|
|Date Available in IDEALS:||2011-05-07|
|Identifier in Online Catalog:||AAI9026232|
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