MICROBIALLY INDUCED SEDIMENTARY STRUCTURES (MISS) FROM THE PALEOPROTEROZOIC GORDON LAKE FORMATION, HURONIAN SUPERGROUP, CANADA

Microbially induced sedimentary structures (MISS) form as a result of the interaction between microbial mats and siliciclastic sediment during sedimentary processes in predominantly aquatic environments. These structures provide evidence for ancient ecosystems, and where found preserved in the sedimentary rock record, generally indicate a shallow water environment. Microbially induced sedimentary structures are found throughout the geologic record, from Archean successions up to and including modern-day environments. Growth, metabolism, destruction, and decay of microbial mats result in the development of MISS; the latter two categories are well represented in the Gordon Lake Formation of the ca. 2.45 – 2.22 Ga Huronian Supergroup. Mat destruction features include various types of sand cracks, microbial sand and silt chips, and torn mat fragments. Mat decay features include gas domes; additional mat decay features were identified in the overlying Bar River quartz arenite succession. The gradational contact relationship with the inferred tidal inlet deposits of the Bar River Formation, in addition to the types of MISS and associated rock types and sedimentary structures in the Gordon Lake Formation, support deposition on a tidal flat. The absence of burrowing and grazing organisms in the Precambrian enabled widespread microbial mat growth along continental margins that are now preserved as biosignatures in sedimentary rocks.