GSA Connects 2021 in Portland, Oregon

Paper No. 55-12
Presentation Time: 2:30 PM-6:30 PM


JIANG, Hehe, Department of Earth Sciences, University of Toronto, 22 Ursula Franklin Street, Toronto, ON M5S 3B1, Canada and CHU, Xu, University of Toronto Department of Earth Science, 22 Ursula Franklin St, Toronto, ON M5S 3B1, CANADA

Clastic dikes occur in a wide variety of depositional environments. The injection of clastic dikes is due to forceful emplacement of remobilized sediments in response to overpressure that might be triggered by seismic activity, tectonic stress, rapid sediment deposition, and variation in pore fluid pressures. In this study, we investigated the clastic dikes crosscutting the glacial-interglacial section of the Quirke Lake Group within the Paleoproterozoic Huronian supergroup (2.45-2.2 Ga) near Espanola, Ontario, Canada. The Bruce Formation at the lowest of Quirke Lake Group consists of glaciogenic diamictites representing the second pulse of Huronian Glacial Event. The overlying Espanola Formation consists of lower limestone units and upper siltstone-argillite-dolomite units, and is considered to deposit in interglacial shallow marine or lacustrine environments. Sandstone and conglomerate dikes are commonly seen in the Espanola Formation. The petrography and geochemistry of these clastic dikes show close affinity with the underlying Bruce formation, suggesting upward injection of the unconsolidated sediments shortly after deposition of the Bruce Formation. Cobble-sized clasts concentrate in the center of the dikes within a granule-to-silt matrix. This alignment suggests liquefaction and a laminar flow profile for the process of injection. We modeled plug flow in a channel assuming that the suspension flow behaves as a Herschel-Bulkley fluid, and calculated the velocity profile using different viscosities. Model results show that the drag force exerted on a ~6cm clast is large enough to overcome the gravitational force with relatively small disturbance or overpressure (~2000 Pa/m). The gradient of overpressure can possibly be attributed to sub-permafrost instabilities during the unloading of glacial ice sheets. Thus, we conclude that the deglaciation of the Bruce Glacial Event was rapid. The Bruce-Espanola boundary is featured by drastic changes of a range of geochemical proxies, which are cited by researchers to argue for the synchronicity of oxygenation and glacial-interglacial cycles within the Huronian Glacial Event. Rapid interglacial thawing would lead to a sudden flux of nutrients into the oceans, which might have stimulated the blooms of oxygenic photosynthesis.