File:Jasper-quartz pebble conglomerate (Lorrain Formation, Paleoproterozoic, ~2.3 Ga) 1.jpg
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English: Jasper-quartz pebble conglomerate from 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 quartzites were originally sandstones - they have been well cemented and somewhat metamorphosed into very hard rocks. The jasper-pebble conglomerates include clasts of white quartz and reddish jaspilites. Pebble shapes range from rounded to angular. 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: unrecorded, but possibly derived from north of the Bruce Mines area in Ontario, Canada; or possibly a crack sample from a Lorrain glacial erratic in America Some info. synthesized from: Hadley (1970) - Paleocurrents and origin of Huronian Lorrain Formation, Ontario and Quebec. American Association of Petroleum Geologists Bulletin 54: 850. |
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| Source | https://www.flickr.com/photos/47445767@N05/50711748027/ |
| 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@N05/50711748027. It was reviewed on 14 December 2020 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| current | 19:37, 14 December 2020 | | 2,739 × 1,936 (3.72 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/50711748027/ with UploadWizard |
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