File:Argillite (Coleman Member, Gowganda Formation, Paleoproterozoic, ~2.3 Ga; Straight Lake West roadcut, north of Temagami, Ontario, Canada) (47026090734).jpg

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Argillite in the Precambrian of Ontario, Canada.

The rocks here were originally mudrock (siliciclastic mudstone), but they have been lightly metamorphosed into argillite.

This is a clast-free portion of a tillite outcrop. Tillites are ancient, lithified tills (= unsorted, nonbedded, coarse-grained glacial deposits). This is part of the famous Gowganda Formation, a ~2.3 billion year old deposit in Ontario, Canada representing a very ancient Ice Age. Other glacially-deposited sedimentary rocks of Paleoproterozoic age have been reported from Wyoming, Finland, India, southern Africa, and Australia. The glaciation was likely a widespread event, and may have persisted for a long time. This ice age is hypothesized to have been triggered by decreasing levels of methane gas (CH4) in the atmosphere as oxygen gas (O2) levels increased (the methane oxidized to carbon dioxide). This lessened the effects of greenhouse warming, and resulted in climate cooling.

Stratigraphy: Coleman Member, Gowganda Formation, lower Cobalt Group, Huronian Supergroup, Paleoproterozoic, ~2.3 Ga

Locality: Straight Lake West outcrop - roadcut on the western side of Route 11, due west of Straight Lake, ~0.4 miles south of the Route 11-Roosevelt Forest Road/Anima Nipissing Road intersection & ~2.1 miles south of the town of Latchford & north of the town of Temagami, Ontario, southeastern Canada (47° 17’ 32.79” North latitude, 79° 47’ 29.17” West longitude)
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Source Argillite (Coleman Member, Gowganda Formation, Paleoproterozoic, ~2.3 Ga; Straight Lake West roadcut, north of Temagami, Ontario, Canada)
Author James St. John

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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/47026090734 (archive). It was reviewed on 6 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

6 December 2019

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current01:48, 6 December 2019Thumbnail for version as of 01:48, 6 December 20194,000 × 3,000 (6.85 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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