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Faulted interbedded metagraywacke-slate (Lake Vermilion Formation, Neoarchean, 2.695-2.722 Ga; Pike River Bridge outcrop, just north of Peyla, Minnesota, USA) | by James St. John
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Faulted interbedded metagraywacke-slate (Lake Vermilion Formation, Neoarchean, 2.695-2.722 Ga; Pike River Bridge outcrop, just north of Peyla, Minnesota, USA)

Faults in turbidites (interbedded metagraywacke and slate) in the Precambrian of Minnesota, USA.

 

Whitish-gray layers = metagraywacke

Dark gray layers = slate

 

The Lake Vermilion Formation is a Precambrian stratigraphic unit in northeastern Minnesota, USA. It consists of low-grade metamorphosed volcaniclastic sedimentary rocks that were deposited in a moderately deep water marine environment.

 

The outcrop shown above is a Pleistocene-glaciated knob of Lake Vermilion Formation turbidites, which consist of interbedded graywackes ("dirty sandstones") and shales - these have since been metamorphosed to metagraywackes and slates. Turbidites are deposits laid down by turbidity currents - underwater sediment slides. Such slides commonly occur in continental slope settings. Turbidity current deposits typically accumulate in the continental rise, at the base of the slope. Turbidites consist principally of interbedded coarse-grained and fine-grained siliciclastic sedimentary rocks that show graded bedding, climbing ripple cross-stratification, flame structures, flute casts, and soft-sediment deformation.

 

Stratigraphy: Lake Vermilion Formation, Neoarchean, 2.695-2.722 Ga

 

Locality: Pike River Bridge Outcrop - glaciated low outcrop on the western side of County Road 77, immediately north of bridge over the Pike River, just north of the town of Peyla, north-central St. Louis County, Minnesota, USA (47° 47’ 30.89” North, 92° 22’ 07.68” West)

 

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Taken on June 10, 2015