Quartzite & pebbly quartzite with jasper (Lorrain Formation, Paleoproterozoic, ~2.3 Ga; Ottertail Lake Northeast roadcut, near Bruce Mines, Ontario, Canada) 1

            Quartzite & pebbly quartzite 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)
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Some info. synthesized from:

Hadley (1970) - Paleocurrents and origin of Huronian Lorrain Formation, Ontario and Quebec.  American Association of Petroleum Geologists Bulletin 54: 850.

Some rights reserved

Taken on: July 17, 2012

Tags:

Lorrain

Formation

Proterozoic

Paleoproterozoic

Ontario

Canada

quartzite

quartzites

jasper

quartz

pebble

pebbles

red

chert

conglomerate

pebbly

puddingstone « less

Sets appears in: • Ontario Rocks, Minerals, Geology • Lorrain Formation (Paleoproterozoic, ~2.3 Ga; Ontario, Canada) more » • Paleoproterozoic Rocks & Fossils « less

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