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: