Graduate Student Seminars

Please join us for the graduate student seminars this Friday September 21 in rm 155 Geology:

3:30 pm

Philip Adene, PhD candidate

Assessment of Unconformity-Related Uranium prospectivity of the Hawk Rapids Area, Southeastern Athabasca Basin, Canada

Hawk Rapids is the name of an unconformity-related uranium exploration project located in the southeastern part of the Athabasca Basin, Canada, host to high-grade unconformity-related uranium deposits. There are seven historical drill holes on the property that intersect Athabasca Group sandstones and the Cable Bay Shear Zone (CBSZ), which forms the contact between the Mudjatik and Virgin River Domains of the Athabasca basement. Petrographic observations show that pre-Athabasca alteration of the basement is recorded by muscovite and chlorite alteration. Early diagenetic alteration in the Athabasca Group sandstones is represented by early hematite and quartz overgrowths, whereas peak to late diagenetic alteration is marked by dickite and illite. This is followed by hydrothermal alteration represented by dravite, kaolinite and later pyrite, coffinite, uraninite, and siderite that also affected the basement rocks. Post-hydrothermal alteration is represented by kaolinite as a result of influx of meteoric water. There are three isotopically distinct fluids associated with these alteration events. Modified seawater in equilibrium with pre-Athabasca clinochlore and sudoite had δ18O values near +8 per mil and δ2H values near -10 per mil. Diagenetic illite in the sandstones formed from basinal fluids with δ18O values near +6 and δ2H values near -40 per mil, indicative of regional-wide basinal brines. Dravite that formed during a hydrothermal event represents a mixture of basinal brines and modified seawater in the basement, having δ18O values near +3 and δ2H values near -20 per mil, and indicative of mixing required for the formation of an unconformity-related uranium deposit seen elsewhere in the basin. Diagenetic illite gives 40Ar/39Ar ages coincident with fluid movement during the East Kootenay Orogeny (1360 Ma) and a later event related to the emplacement of the McKenzie dikes at 1280 Ma, indicating that fluids were still present in this area after the deposits in the basin formed at ca. 1600 Ma. These events mobilized radiogenic Pb into the Athabasca Group sandstones and basement rocks in the area. The radiogenic Pb in these rocks, which was measured using a weak acid leach method, is derived from the breakdown of detrital zircon, monazite and apatite in some samples, but is also derived from a uranium-rich external source in several other samples, thereby targeting some areas of Hawk Rapids as most prospective.

4:00 pm

Brittany Laing, PhD candidate

A protracted Ediacaran-Cambrian transition: an ichnologic ecospace analysis of the Fortunian in Newfoundland, Canada.

The transition between the seemingly disparate Ediacaran and Cambrian faunas is both enigmatic and body-fossil poor. The Chapel Island Formation on the Burin Peninsula, Newfoundland, Canada, contains a rich diversity of ichnofossils, providing new insight into the nature of the Ediacaran-Cambrian transition and early Fortunian ecosystems. Currently, the Global Boundary Stratotype Section and Point (GSSP) for the basal Cambrian boundary is located 2.4 m above the base of member 2 of the CIF, delineated by the lowest observed appearance of the Treptichnus pedum Ichnofossil Assemblage Zone (IAZ). Through a bed-by-bed study, the ichnotaxonomy of the T. pedum IAZ was revised, and a stratigraphic section was created. Twenty ichnospecies comprising thirteen ichnogenera were observed. The ichnospecies were grouped into five ichnoguilds, which were utilized to conduct an ecospace analysis of the section. The ichnofauna revealed a more gradual explosion of ichnofossil diversity at the boundary, and a more protracted transition between Ediacaran and Cambrian ecosystems than previously envisioned. The T. pedum IAZ in the CIF marks the appearance of novel methods of interacting with the substrate as documented by sub-horizontal branching burrows (Treptichnids), equilibrium structures (Bergaueria isp.), and complex vertical burrows (Gyrolithes ichnoguild). Additionally, it marks the evolution of novel body plans, as revealed by the presence of arthropod scratch marks (Dimorphichnus ichnoguild). Notably, remnants of Ediacaran matground ecology are also present—chemichnial feeding styles are utilized by the Gyrolithes ichnoguild, and mat grazing (Helminthoidichnites ichnoguild) remains a common feeding style. The revision of the CIF T. pedum ichnotaxa, as presented above further illuminates the depth and rate at which this new lifestyle evolved, shedding light on the evolution of Cambrian mixground ecology.