File:Dropstones in argillite (Coleman Member, Gowganda Formation, Paleoproterozoic, ~2.3 Ga; Straight Lake West roadcut, north of Temagami, Ontario, Canada) 1 (46899361525).jpg
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Dropstones in argillite in the Precambrian of Ontario, Canada. Dropstones are granules or pebbles or larger gravel dropped into bodies of water by melting glaciers. Larger dropstones that fell into fine-grained sediments deform the underlying layers and can have arched, draping sediment layers above. Two dropstones are present here - one of them is the same color as the matrix, so it can be difficult to discern (click on the photo to zoom in). The host rock here was originally mudrock (siliciclastic mudstone), but it has been lightly metamorphosed into argillite. This glacial deposit 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) |
| Date | |
| Source | Dropstones in argillite (Coleman Member, Gowganda Formation, Paleoproterozoic, ~2.3 Ga; Straight Lake West roadcut, north of Temagami, Ontario, Canada) 1 |
| 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@N05/46899361525 (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. |
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| current | 01:49, 6 December 2019 | | 4,000 × 3,000 (7.26 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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