Microbial, tidal, and storm activity in a macrotidal to shallow marine shelf environment during the Paleoproterozoic era

Abstract

The Gordon Lake Formation (GLF) of the Paleoproterozoic Huronian Supergroup is a siliciclastic-dominated succession ranging from 300 to 1100 m in thickness. Lithostratigraphic and sedimentological analyses of the formation in the Bruce Mines and Flack Lake areas, and Killarney and Lady Evelyn-Smoothwater provincial parks, Ontario, Canada, revealed seven lithofacies, which comprise three distinct lithofacies associations. The lithofacies associations are subtidal nearshore, subtidal to shallow shelf, and mixed intertidal flat. A variety of structures interpreted to be biogenic in nature, including microbially induced sedimentary structures (MISSs) and stromatolites, are preserved, which support local microbial colonization in a tidally influenced marine environment. Wave, current, and tide-generated sedimentary structures, including symmetrical ripples, trough cross-beds, flaser and lenticular bedding, and mudstone drapes, are abundant in all study areas. Storm influence is suggested by normally graded deposits, mudstone rip-up clasts, and soft-sediment deformation structures (SSDSs), including load casts, ball-and-pillow structures, convolute bedding, and pseudonodules. Interbedding and interlamination of sandstone and mudstone units are present throughout the GLF and represent fluctuations in water level and energy, related to tidal and storm processes. A lowermost carbonate-rich unit may represent a period of low clastic influx. The contacts with the underlying Lorrain and overlying Bar River formations appear gradational. The depositional environment can be visualized as an open coast, shallow marine shelf that was influenced by microbial mats, tides, and storms.