Late-Ediacaran Resumption of Extension on the Western Laurentian Margin near Jasper, Alberta, Canada

English Abstract:

The timing and nature of renewed latest-Ediacaran extension on the western Laurentian margin remains controversial after decades of study. Lower-greenschist facies sedimentary rocks with Namacalathus-Cloudina fossils near Jasper, Alberta, Canada present an attractive prospect for improving geochemical understanding of the key end-Proterozoic time, yet remain poorly studied due to correlation difficulties. Two pulses of sedimentation have been interpreted to record major episodes of extension: 1) Cryogenian intracontinental rift sediments, the Miette Group of the Windermere Supergroup, a 9km thick siliciclastic-dominated shallowing-up succession; 2) late-Ediacaran extension resumption accommodating 6km of carbonate-dominated passive margin sediments through the lower-Paleozoic, beginning with fluvio-marine and fluvial coarse-grained sandstones of the >2.2km thick Hamill-Gog (locally Gog) Group. At it's base, an erosional hiatus of widespread extent and non-uniform stratigraphic removal, the sub-Gog Unconformity, has complicated correlations of upper Miette strata, as have the lack of biostratigraphic clues in the Gog, indications of extension diachroneity, and a paucity of rocks suitable for absolute-dating methods. In the Jasper area, however, extension contemporaneous with the sub-Gog surface provides a locally-continuous record of Miette through Gog sedimentation in fault-bounded basins. Our sequence-stratigraphic correlations, complemented by biostratigraphic and high-resolution carbonate chemostratigraphic data, permit study area correlation across a complex paleotopography with several hundreds of meters of stratigraphic variability, and to age-constrained rocks globally. We establish a new age-constraint on Jasper-area margin collapse: it begins no earlier than ~552Ma and before 542 ± 0.3Ma, at odds with the sole regional U-Pb radiometric date of 569.6 ± 5.3Ma from the 150km-distant Hamill Group, confirming strong diachroneity along the margin.