File:Jasper-quartz pebble conglomerate (Lorrain Formation, Paleoproterozoic, ~2.3 Ga; Ottertail Lake Northeast roadcut, near Bruce Mines, Ontario, Canada) 69 (47709592711).jpg
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Jasper-quartz pebble conglomerate in the Precambrian of Ontario, Canada. Southeastern Canada's ~2.3 billion year old Lorrain Formation includes some beautiful rocks that rockhounds have nicknamed "puddingstone". This refers to whitish-gray quartzites having common pebbles of red jasper. The Lorrain Formation is somewhat heterolithic. Published studies mention that the unit has arkoses, subarkoses, quartzites, and jasper-pebble conglomerates. The latter two lithologies are present at the glacially-eroded outcrop seen here. The quartzites were originally sandstones. They have been well cemented and somewhat metamorphosed into very hard rocks. The jasper-pebble conglomerates, or "puddingstones", include clasts of white quartz and reddish jaspilites. Jaspilite is a type of BIF (banded iron formation). BIFs only formed on Earth during the Precambrian - most are Paleoproterozoic in age. They are the # 1 source of iron ore for the world's steel industry. Numerous specific types of BIFs are known. Jaspilite consists of alternating laters of red and silvery-gray, iron-rich minerals. The red layers are hematite or jasper (= hematitic chert). The silver-gray layers are usually rich in magnetite and/or specular hematite. Jaspilite BIFs outcrop in many areas around Lake Superior, for example in Michigan's Upper Peninsula, Minnesota, and Ontario. During the Paleoproterozoic, BIFs were subaerially exposed as paleo-outcrops and eroded, producing BIF sediments, including many red jasper pebbles. These mixed with quartz-rich sediments. Regional studies indicate that the Lorrain Formation was deposited in ancient shallow ocean, lake, delta, and shoreline environments. Stratigraphy: Lorrain Formation, upper Cobalt Group, Huronian Supergroup, Paleoproterozoic, ~2.3 Ga Locality: Ottertail Lake Northeast Roadcut - glacial knob on the eastern side of Rt. 638, northeast of Ottertail Lake & southeast of Rock Lake, north-northeast of the town of Bruce Mines, southern Ontario, southeastern Canada (46° 23' 30.59" North latitude, 83° 43’ 10.94" West longitude) Some info. synthesized from: Hadley (1970) - Paleocurrents and origin of Huronian Lorrain Formation, Ontario and Quebec. American Association of Petroleum Geologists Bulletin 54: 850. |
| Date | |
| Source | Jasper-quartz pebble conglomerate (Lorrain Formation, Paleoproterozoic, ~2.3 Ga; Ottertail Lake Northeast roadcut, near Bruce Mines, Ontario, Canada) 69 |
| 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@N05/47709592711 (archive). It was reviewed on 10 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 01:34, 10 October 2019 | | 4,000 × 3,000 (5.93 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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