Breanne Beh MSc Thesis Abstract

Thesis Title: 
Depositional Processes Operating on the Paleoproterozoic Gowganda Ice Margin

Glacial sedimentary rocks of the Huronian Supergroup crop out along the north shore of Lake Huron and were likely deposited on what is thought to have been a divergent continental margin (Fralick and Miall, 1981; 1989). The rocks of the Gowganda Formation record one of three glacial events preserved in the Supergroup and are therefore of interest for developing further glaciomarine models (Puffett, 1974) and furthering understanding of this early stage in Earth's history. Data has been collected in five main study areas in an attempt to cover as much of the ancient continental margin as possible.  The study areas include Espanola, Elliot Lake, Thessalon and Cobalt, Ontario and Marquette, Michigan. There are two glaciogenic formations in the Marquette area of Paleoproterozoic age, the Reany Creek Formation and the Enchantment Lake Formation.  The Enchantment Lake Formation has been chronostratigraphically correlated to the Huronian Supergroup based on U-Pb age determination on detrital zircon, 2317±6 Ma, and diagenetic xenotime, 2133±11 Ma (Vallini et al., 2006).  As these formations are present in such close proximity to each other, and there are no Archean glacial events recorded in the rest of the Canadian Shield, it is reasonable to correlate them with the Gowganda Formation, the thickest and most commonly preserved of the three Huronian glacial events.

Stratigraphic sections were compiled in each of the study areas and the sedimentary rocks were grouped into seven lithofacies associations (LA): 1) Planar Cross-Stratified Sandstone LA, 2) Basal Breccia LA, 3) Diamictite LA, 4) Interlayered Siltstone and Fine-Grained Sandstone LA, 5) Slump LA, 6) Heterogeneous Sandstone LA and 7) Quartz-Rich Sandstone LA.  These lithofacies associations likely represent a sequence of depositional environments on a shallow continental shelf.  Initially, the shelf was dominated by what were likely large-scale, low-angle sandwaves, interbedded with successions of wavy bedding and possible hummocky cross-stratification indicating an open-water setting with tidal and storm processes reworking the sediments.  The shelf then gradually evolved into an environment dominated by diamicite layers.  The diamictite layers have dropstones as well as evidence of current activity indicating outsized clasts were likely being introduced into the environment as ice-rafted debris.  Resedimentation events in the form of debris flows are thought to account for conglomeratic layers that are common in the Diamictite LA.  The Interlayered Siltstone and Fine-Grained Sandstone LA, along with the Slump LA, seem to indicate deposition from suspension in a prodelta setting where large slump events are common.  The gradual transition into a more sandstone dominated LA, with an abundance of current-related sedimentary structures, is indicative of the shallowing and coarsening upwards succession common to deltaic deposits.  A final transition into the Quartz-Rich Sandstone LA indicates a return to a sandy, current-dominated open continental shelf environment with abundant tidally generated sedimentary structures such as herringbone cross-stratification.  The Cobalt study area differs from this overall model in that evidence of grounded ice is present.  Less exposure in the Marquette study area makes it difficult to draw overall conclusions on the evolution of the continental shelf but deposition in a subaqueous glacial outwash fan is hypothesized.

A copy of the thesis can be downloaded here