No description available.

No description available.

No description available.

No description available.

There is no abstract available for this thesis.

The quarry of Western Indiana Aggregates, Inc., south of Francesville, Indiana, was examined to determine the relation off its stratigraphy and paleontology to that of other Silurian (Niagaran) outcrops of northern Indiana. Lithologic analysis and paleoecologic interpretations of 25 genera of fossils found in the quarry were utilized in the investigation.Strata exposed at the Francesville locality belong to the Liston Creek Member of the Wabash Formation. The exposure reveals a reef core, reef-flank and back-reef platform which are identified by their attitude and fossil content. The coral Ealysites is interpreted as being a deep-water (low reef-flak dweller while the rugose coral, Strombodes is a rough water (reef core) form. Distribution of pentamerids and trilobites also yields evidence of selective zoning. The occurrence of a coquina of the pentamerid Kirkidium is significant. The bed is believed to have formed as the result of a storm lowering wave base sufficiently to expose the living Kirkidium colony and subjecting it to surf activity. Detailed examination of individual specimens within the unit reveal the storm approached the reef from the south-southwest. Normal (non-storm) current direction was also from the south-southwest, as demonstrated by the location of the back water reef platform north of the reef core.Ball State UniversityMuncie, IN 47306

Regional study of the Silurian Amabel and Guelph (including the Eramosa Member) formations in the subsurface on the Bruce Peninsula provides petrographic details of these pervasively dolomitized rocks, defines lithofacies changes within each formation, and demonstrates the use of ground-penetrating radar as a tool for shallow subsurface stratigraphic mapping. Detailed stratigraphic logging of core provides insight on the complex depositional history of the pervasively dolomitized Amabel and Guelph formations by highlighting lateral facies changes that are not readily observable in outcrop. <br /><br /> The Lions Head and Colpoy Bay members of the Amabel Formation are continuous in core across the Bruce Peninsula. These members contain characteristic dark grey mottles which are the result of increased porous zones and pyrite, and/or concentrations of undifferentiated organics. Chert nodules and the abundance of silica is most abundant in the upper Lions Head Member where silica-replaced fossils are recognized within the surrounding dolomite. Typical Wiarton Member crinoidal lithofacies from the upper Amabel Formation are more common in the southern half of the Peninsula. The Eramosa Member is more laterally continuous on the Bruce Peninsula than previously assumed. Although there is a lack of bituminous argillaceous Eramosa lithofacies within core, the laminated Eramosa Member is thick near Wiarton which suggests that a large restricted less-oxygenated area existed in that vicinity during the Silurian. Thick accumulations of tan-brown fossiliferous undifferentiated Guelph Formation dolostones occur at both the northern and southern ends of the Peninsula. <br /><br /> Petrographic analyses reveal that the Amabel and Guelph formations are dolomitized with no precursor limestone observed. Four types of dolomite were observed within these formations and differentiated based on crystal size. These dolomites are characterized by a uniform dull red luminescence, and range from inclusion-rich anhedral very finely (< 5 µm) crystalline dolomite to clearer euhedral coarsely (> 250 µm) crystalline dolomite. Petrographic analyses also revealed secondary minerals such as pyrite, calcite (and dedolomite), silica, sphalerite, fluorite, and glauconite. <br /><br /> Ground-penetrating radar surveys provided high-resolution data, which combined with detailed geologic observations of accessible quarry outcrops and borehole logs, support the conclusion that GPR is a useful tool for locating karstic features, vuggy porosity, and lateral and vertical facies changes in carbonate rocks. Radar profiles may have important implications for the aggregate and building-stone industries as a tool to locate carbonate units of exploration interest or to avoid zones with high impurities.

Regional study of the Silurian Amabel and Guelph (including the Eramosa Member) formations in the subsurface on the Bruce Peninsula provides petrographic details of these pervasively dolomitized rocks, defines lithofacies changes within each formation, and demonstrates the use of ground-penetrating radar as a tool for shallow subsurface stratigraphic mapping. Detailed stratigraphic logging of core provides insight on the complex depositional history of the pervasively dolomitized Amabel and Guelph formations by highlighting lateral facies changes that are not readily observable in outcrop. <br /><br /> The Lions Head and Colpoy Bay members of the Amabel Formation are continuous in core across the Bruce Peninsula. These members contain characteristic dark grey mottles which are the result of increased porous zones and pyrite, and/or concentrations of undifferentiated organics. Chert nodules and the abundance of silica is most abundant in the upper Lions Head Member where silica-replaced fossils are recognized within the surrounding dolomite. Typical Wiarton Member crinoidal lithofacies from the upper Amabel Formation are more common in the southern half of the Peninsula. The Eramosa Member is more laterally continuous on the Bruce Peninsula than previously assumed. Although there is a lack of bituminous argillaceous Eramosa lithofacies within core, the laminated Eramosa Member is thick near Wiarton which suggests that a large restricted less-oxygenated area existed in that vicinity during the Silurian. Thick accumulations of tan-brown fossiliferous undifferentiated Guelph Formation dolostones occur at both the northern and southern ends of the Peninsula. <br /><br /> Petrographic analyses reveal that the Amabel and Guelph formations are dolomitized with no precursor limestone observed. Four types of dolomite were observed within these formations and differentiated based on crystal size. These dolomites are characterized by a uniform dull red luminescence, and range from inclusion-rich anhedral very finely (< 5 µm) crystalline dolomite to clearer euhedral coarsely (> 250 µm) crystalline dolomite. Petrographic analyses also revealed secondary minerals such as pyrite, calcite (and dedolomite), silica, sphalerite, fluorite, and glauconite. <br /><br /> Ground-penetrating radar surveys provided high-resolution data, which combined with detailed geologic observations of accessible quarry outcrops and borehole logs, support the conclusion that GPR is a useful tool for locating karstic features, vuggy porosity, and lateral and vertical facies changes in carbonate rocks. Radar profiles may have important implications for the aggregate and building-stone industries as a tool to locate carbonate units of exploration interest or to avoid zones with high impurities.

The carbonate storm-dominated sedimentary succession superbly exposed on Anticosti Island in Eastern Canada represents one of the most complete and well-preserved paleotropical stratigraphic records spanning the Ordovician-Silurian (O-S) boundary. We sampled the nearly continuous coastal outcrop exposed at low tide along the west coast of Anticosti Island for high-resolution δ13C and δ18O chemostratigraphy. These new isotopic curves comprise more than 500 data points spaced at ~0.6 m intervals; for a total of 320 m of strata across the O-S boundary. The δ13C curve displays two distinctive positive excursions in the Hirnantian Ellis Bay Formation; a small lower excursion (+2.5‰) and an upper larger excursion (+4.5‰). These two positive isotopic carbon excursions provide a distinctive chemostratigraphic signature for regional and global correlations with other Hirnantian sections. The continuing descending δ13C trend, at least 30 m above the currently interpreted O-S boundary, suggests a readjustment of that boundary on the Anticosti succession. The δ18O curve, similarly to the Quaternary δ18O marine curve, is tightly coupled with multi-order cyclic facies changes. Our tightly coupled lithological and oxygen isotopic data suggest that the Anticosti succession was influenced by glacio-eustatic fluctuations during the end-Ordovician. Furthermore, the estimated duration of these multi-order cycles supports an astronomical forcing. A primary isotopic signal record is also supported by the lack of significant covariance between δ13C and δ18O, by the excellent microfabric preservation of both macro and microfossils in petrographic, cathodoluminescence, and SEM microscopy, and by little or no diagenetic resetting as suggested by the trace element geochemistry, which is unusual in the deep geological time.

The transition from the end of the Ordovician to the beginning of the Silurian Period is characterized by the glaciation of the Gondwana paleocontinent, eustatic sea level change, a perturbation to the global carbon cycle and one of the ve major mass extinctions of the Phanerozoic Eon. Due to signi cant sea level fall, the Ordovician-Silurian (O-S) boundary is often marked by hiatus and exposure in the shallow marine geologic record (e.g., Copper et al. [2013]). Two locations that host stratigraphic succession close to the boudary are Anticosti Basin of Quebec (Canada, e.g., Desrochers et al. [2010]), and the carbonate mounds of the Siljan ring district (Dalarna County, Sweden, e.g., Ebbestad et al. [2015]). The exact timing and dynamics of the glaciation and mass extinction are yet to be understood. Similarly, the interplay between those events and the carbon cycle perturbation are still unclear. As a result, there is a serious need for radiometric age constraints in this crucial part of the Paleozoic Era. The acquisition of more radiometric dates, achieved in this study, aims to address the present dearth of absolute dates close to the boundary. The dates produced in this study represent the first modern geochronologic constraints on the O-S boundary, leveraging the development of the EARTHTIME initiative and the latest U-Pb dating techniques that have improved accuracy and allowed for dating of single zircon crystals at <=0.1% precision level. Here I present two new U-Pb zircon ages obtained via bentonite dating. The first bentonite, 443.61+-0.52 Ma (2, including analytical, tracer calibration and decay constant uncertainties) was collected from the base of the Lousy Cove Member, Ellis Bay Formation (Anticosti Island, Quebec, Canada). The second one, 443.28+-0.50 Ma (including analytical, tracer calibration and decay constant uncertainties) comes from a karstic void within the Boda Core Facies of the Boda Formation (Dalarna County, Sweden). U-Pb geochronology (chemical abrasion, isotope dilution, thermal ionization mass spectrometry: CA-ID-TIMS) on single zircons was used to obtain these ages. These results are the closest radiometric ages to the current O-S boundary (compared to any time constraints in the 2012 Geologic Time Scale) and allow to signifcantly reduce the uncertainty of the current age boundary (443.8+-1.5, Cohen et al. [2018]). Furthermore these absolute ages have been used to make models that explore drivers of Earth system change, such as an end-Ordovician global carbon cycle perturbation. / Graduate / 2022-07-07