Graduate Student Lectures

Please join us for two graduate student lectures this Friday April 12 starting at 3:30 pm in rm 106 Biology:

3:30 pm

Lavie Nguyen, MSc Candidate

Automated identification of geodynamic features and associations in plate tectonic models

Plate tectonic reconstructions provide a framework within which one may better understand the association of geodynamic processes with mappable features and the symptoms of the processes. For instance, location of economic mineralisation is related not only to specific geodynamic processes but also to previous episodes of fertilisation of crust or mantle. Geological processes, plate boundaries and their locations through time also influence the interaction of atmosphere and hydrosphere, partially control the migration of species across continents and regional patterns of erosion and deposition. Accurate plate tectonic boundaries for any reconstruction model provide one mechanism for researchers to validate and improve plate models but also constrain the location of important geological processes. Currently, only a few reconstruction models implement continually closing plate boundary topologies. No detailed reconstruction models with this capability exist prior to the Mesozoic, in part because of the complexity of motion of multiple geodynamic unit (GDU) polygons representing preserved older crustal blocks. Manual identification of geodynamic boundaries is very time consuming. We report on methods being developed to automate the process of identifying and delineating zones of divergence (rifts and midocean ridges) and convergence (subduction zones) using a variety of open source software code and machine learning techniques. A number of approaches have been tested and compared to optimise time and memory for current desktop computer systems. This approach also opens up opportunities to integrate additional layers of geo-information so as to derive additional insights and constraints for the reconstruction models being developed.

4:00 pm

Meagan Gilbert, PhD Candidate

Ichnology and Depositional Environments of the Upper Cretaceous Dinosaur Park – Bearpaw Formation transition in the Cypress Hills region of Southwestern Saskatchewan, Canada

The upper Campanian Dinosaur Park Formation (DPF) is a south- and eastward-thinning fluvial to marginal-marine clastic wedge in the Western Canadian Sedimentary Basin. The DPF is overlain by the Bearpaw Formation (BF), a fully marine clastic succession representing the final major transgression of this epicontinental sea across western North America. In southwestern Saskatchewan, the DPF is comprised of marginal-marine coal, carbonaceous shale, and heterolithic siltstone and sandstone grading vertically into marine sandstone and shale of the BF. Historically these deposits have been interpreted as the record of fluvial delta systems along a paleocoastline. This study revisits this interpretation using integration of ichnologic, sedimentologic, and sequence stratigraphic concepts.

Detailed facies analysis indicates the upper DPF does not record sedimentation in a delta system, but rather was deposited in a low-relief coastal plain with a wave-dominated, tidally

influenced, fluvially modified shoreline. Marginal-marine facies, interpreted as lagoons, tidal flats and estuaries, are bioturbated, showing a typical brackish-water trace-fossil assemblage, including Asterosoma isp., Chondrites isp., Cylindrichnus concentricus, Teichichnus rectus, and Skolithos isp. Fine-grained sandstone was deposited in an estuarine mouth-bar and barrier-island complex that protected the coast from wave reworking. As the seaway transgressed across the coast, fully marine wave-dominated parasequences replaced those of the coastal plain. Typical trace fossils include Asterosoma isp., Chondrites isp., Diplocraterion isp., Nereites missouriensis, Phycosiphon incertum, Planolites isp., Rhizocorallium isp., and Zoophycos isp., reflecting open, fully marine conditions. This study provides new insights into the evolution of depositional environments in the Late Cretaceous of southwestern Saskatchewan, and provides a framework for further geological and paleontological studies ongoing in the region.