English: Metatillite from the Precambrian of Ontario, Canada.

Tillites are ancient, lithified tills (= unsorted, nonbedded, coarse-grained glacial deposits). This sample is from of the famous Gowganda Formation, a ~2.3 billion year old deposit in Ontario, Canada representing a very ancient Ice Age. Other glacially-deposited sedimentary rocks of Paleoproterozoic age have been reported from Wyoming, Finland, India, southern Africa, and Australia. The glaciation was likely a widespread event, and may have persisted for a long time. This ice age is hypothesized to have been triggered by decreasing levels of methane gas (CH4) in the atmosphere as oxygen gas (O2) levels increased (the methane oxidized to carbon dioxide). This lessened the effects of greenhouse warming, and resulted in climate cooling.

Gowganda tillites have been somewhat metamorphosed, so a proper lithologic term is metatillite. Most of the included clasts are granitic.

Stratigraphy: Gowganda Formation, lower Cobalt Group, Huronian Supergroup, Paleoproterozoic, ~2.3 Ga

Locality: exposures beside Route 6, 1 to 2 miles south of Whitefish Falls & ~4 miles north of Roosevelt Memorial, just north of Manitoulin Island, southern Ontario, Canada