Person: Smith, Emily
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Smith
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Emily
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Smith, Emily
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Publication Updated Definition and Correlation of the Lower Fifteenmile Group in the Central and Eastern Ogilvie Mountains(Yukon Geological Survey, 2012) Halverson, Galen P.; Macdonald, Francis; Strauss, Justin Vincent; Smith, Emily; Cox, Grant M.; Hubert-Théou, LucieOngoing mapping, chemostratigraphy, geochronology, and stratigraphic analysis of Neoproterozoic successions in the Ogilvie Mountains requires redefinition and correlation of the Fifteenmile Group across the Proterozoic inliers in Yukon. Here we present new stratigraphic logs through the lower Fifteenmile Group in the Coal Creek and Hart River inliers. Based on these data and new observations, we propose redefinition of the lower Fifteenmile Group. A succession dominated by sandstone, mapped as unit PPD1 in the Hart River inlier, is now recognized at the base of the Fifteenmile Group in the Coal Creek inlier. These strata unconformably overlie the Pinguicula Group and transition upward into a distinctive carbonate interval; together, these comprise the informally defined Gibben formation. The shallowing-upward carbonate sequence contains abundant oolitic grainstone and packstone and microbial laminated dolostone. It is capped by a distinct interval of mud-cracked maroon mudstone, siltstone, and fine-grained sandstone that forms the base of what we informally define as the Chandindu formation. The mud-cracked shale transitions upwards into interbedded shale, coarse-grained sandstone, and minor carbonate. The overlying informally defined Reefal assemblage consists of up to 1 km of complexly interbedded carbonate and shale, with variable truncation beneath the major angular unconformity at the base of the Callison Lake Dolostone. The lower Fifteenmile Group (now informally PPD1 through the Chandindu formation) likely correlates with the Hematite Creek Group in the Wernecke Mountains.Publication Early Neoproterozoic Basin Formation in Yukon, Canada: Implications for the Make-Up and Break-Up of Rodinia(Geological Association of Canada, 2012) Macdonald, Francis; Halverson, Galen P.; Strauss, Justin Vincent; Smith, Emily; Cox, Grant; Sperling, Erik A.; Roots, Charles F.Geological mapping and stratigraphic anaylsis of the early Neoproterozoic Fifteenmile Group in the western Ogilvie Mountains of Yukon, Canada, has revealed large lateral facies changes in both carbonate and siliciclastic strata. Syn-sedimentary NNW-side-down normal faulting during deposition of the lower Fifteenmile Group generated local topographic relief and wedge-shaped stratal geometries. These strata were eventually capped by platformal carbonate after the establishment of a NNW-facing stromatolitic reef complex that formed adjacent to the coeval Little Dal Group of the Mackenzie Mountains, Northwest Territories. Correlations between specific formations within these groups are tested with carbon isotope chemostratigraphy. As there are no known 830-780 Ma stratigraphic successions south of 62°N, the basin-forming event that accommodated the Fifteenmile and Little Dal Groups of the Ogilvie and Mackenzie Mountains and equivalent strata in the Shaler Supergroup of Victoria Island was restricted to the northwest margin of Laurentia. Therefore, this event does not represent widespread rifting of the entire western margin of Laurentia and instead we propose that these strata were accommodated in a failed rift generated by localized subsidence associated with the emplacement of the coeval Guibei (China) and Gairdner (Australia) large igneous provinces. The northern margin of Laurentia was reactivated by renewed extension at ca. 720 Ma associated with the emplacement of the Franklin large igneous province. Significant crustal thinning and generation of a thermally subsiding passive margin on the western margin of Laurentia may not have occurred until the late Ediacaran.Publication Constraints on Global Carbon Cycling, Basin Formation, and Early Animal Evolution During the Neoproterozoic and Early Cambrian(2015-09-25) Smith, Emily; Macdonald, Francis A.; Schrag, Daniel P.; Knoll, Andrew H.; Johnston, David T.Within this dissertation, I document different time intervals during the Neoproterozoic through the early Cambrian (1000 – 525 Ma), one of the most dynamic and non-uniformitarian intervals in the history of the Earth. This thesis focuses on two time periods of change within this time interval: 1) The pre-Cryogenian-Cryogenian transition (~800-635 Ma) and 2) the Ediacaran-Cambrian Transition (~551-525 Ma). To begin, I use a combination of detailed mapping, regional stratigraphy, and geochronology to reinterpret the depositional and tectonic setting of the ~750-730 Ma Beck Spring Dolomite and its bounding units in Death Valley, California. Instead of being deposited in an interior seaway in a long-lived aulacogen as Rodinia rifted apart, I suggest that this unit was accommodated by strike-slip motion that could have represented a margin-wide event along the west coast of Laurentia. The true rift to drift did not occur until the latest Ediacaran to earliest Cambrian. Late Ediacaran to early Cambrian datasets from the Great Basin in the western USA are integrated to refine the biological and environmental changes that occur across the Ediacaran-Cambrian Boundary. In my third chapter, two new horizons of exceptionally preserved Ediacaran fauna that include Conotubus and Gaojiashania are documented. These fossils were previously only known from South China. The Conotubus horizon occurs just below the most negative δ13C values in the basal Cambrian δ13C excursion, establishing it as the youngest Ediacaran fossil to date. These fossils are placed into a high-resolution δ13C chemostratigraphic framework, allowing for regional and global correlation. Three δ13C chemostratigraphic curves from the Great Basin combined with five sections from Western Mongolia show that instead of a single, rapid δ13C excursion at the Ediacaran-Cambrian Boundary, there is one broad excursion with more secondary structure than has been previously documented. Together, these data suggest the nadir of the δ13C excursion is younger than 541 Ma and provide a new framework to interpret Ediacaran-Cambrian biostratigraphy, chemostratigraphy, and U/Pb ash ages globally. The final chapter focuses on the earliest Cambrian in Southwest Mongolia. By using extensive field data, I construct a basin-wide facies model and age model for the Zavkhan Basin. I place the early Cambrian fossil horizons into this new framework and correlate the composite dataset from Mongolia with others globally. In doing so, I reinterpret the tempo and patterns of evolution during this critical interval in Earth history. The following chapters cover diverse events in Earth history that better constrain topics ranging from the breakup of the supercontinent Rodinia to environmental change across the Ediacaran-Cambrian Boundary to rates of evolutionary change during the early Cambrian. All of these topics, however, are united by a multidisciplinary approach that combines original field observations with geochemical, geochronological, stratigraphic, and paleontological datasets to constrain the origin and timing of the coevolution of life and the environment in the deep past.