Processes responsible for the development of soft-sediment deformation structures (SSDS) in the Paleoproterozoic Gordon Lake Formation, Huronian Supergroup, Canada

摘要

An exposure of the Paleoproterozoic Gordon Lake Formation in the Bruce Mines area, Ontario, Canada, contains abundant soft-sediment deformation structures (SSDS), including load casts, convolute bedding, pseudonodules, ball-and-pillow structures, flame structures and one dewatering pipe. These features are developed in siltstone to fine-grained sandstone beds and are between 1 and 120 cm in width and 3-78 cm high. The primary trigger mechanism is interpreted to be storm or tsunami activity, however seismic shock, overloading brought about by density inversions, or a combination of these processes, may have influenced the formation of SSDS to a lesser degree. Several beds also contain flat to wavy carbonaceous laminae, locally with a botryoidal texture and concentrations of heavy minerals, which are interpreted as relicts of microbial mats. Microbial mats may have played a minor role in the formation of SSDS, but do not appear to have been a prominent driving mechanism. Soft-sediment deformation structures observed in the Baie Fine, Flack Lake, and Cobalt plains regions of Ontario, are smaller and not as abundant as in the study area, suggesting that the deposits in the study area were either affected by local events or different magnitudes of sedimentary processes. In contrast to the tidal flat paleoenvironment interpreted for the Gordon Lake Formation in the Flack Lake area, the stratigraphically lower beds at the studied outcrop more closely resemble shallow shelf deposits.