Jasper-quartz pebble conglomerate (Lorrain Formation, Paleoproterozoic, ~2.3 Ga) 7

            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

Provenance: Ontario, Canada

Locality: unrecorded (but probably from Ontario or possibly a crack sample from a Lorrain glacial erratic in America)
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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: May 27, 2024

Tags:

Lorrain

Formation

Proterozoic

Paleoproterozoic

conglomerate

puddingstone

quartz

jasper

jaspilite

banded

iron

BIF

pebble

pebbles

Ontario

Canada « 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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