File:Asymmetrical ripple marks in quartzite (Baraboo Quartzite, upper Paleoproterozoic, ~1.7 Ga; southern shore of Devil's Lake, Devil's Lake State Park, Wisconsin, USA) 3 (18200165874).jpg

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Asymmetrical ripple marks in quartzite in the Precambrian of Wisconsin, USA.

The Baraboo Ranges of southern Wisconsin are dominated by a hard, erosion-resistant Precambrian metamorphic unit called the Baraboo Quartzite. These rocks were originally marine sandstones and have been subjected to metamorphism and structural folding. Original sedimentary structures are preserved, such as cross-bedding and ripple marks. Baraboo Quartzites vary in color from pinkish to dark reddish to grayish. During metamorphism, quartz overgrowths formed over the original quartz sand grains. Long-term, modern weathering can result in original sand grains being released.

This unit has economic significance - it has been quarried historically and in modern times. The quartzite is broken down into gravel-sized pieces for use as railroad ballast and erosion-control rip-rap.

The ridges on the rock shown above are asymmetrical ripples. Asymmetrical ripple marks have a long side and a short side, when viewed in cross-section. They form in a one-directional current by wind or water (in this case, water). The current direction was toward the short side of each ripple.

Stratigraphy: Baraboo Quartzite, upper Paleoproterozoic, ~1.7 Ga

Locality: loose block along the southern shore of Devil's Lake, Devil's Lake State Park, northern part of the South Range of the Baraboo Ranges, southeast of the town of Baraboo, eastern Sauk County, southern Wisconsin, USA
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Source Asymmetrical ripple marks in quartzite (Baraboo Quartzite, upper Paleoproterozoic, ~1.7 Ga; southern shore of Devil's Lake, Devil's Lake State Park, Wisconsin, USA) 3
Author James St. John

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This file is licensed under the Creative Commons Attribution 2.0 Generic license.
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/18200165874 (archive). It was reviewed on 22 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

22 October 2019

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current05:45, 22 October 2019Thumbnail for version as of 05:45, 22 October 20194,000 × 3,000 (4.15 MB)Rudolphous (talk | contribs)Transferred from Flickr via #flickr2commons

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