Diamictite in the Precambrian of Virginia, USA.

The Snowball Earth Glaciations during the Neoproterozoic were the most significant ice ages that Earth ever experienced - two or three of them occurred in succession. The most extreme models describing Snowball Earth have glacial ice completely covering all continents and all oceans, even at the equator. Some models, called “Slushball Earth”, have Earth’s equatorial oceanic areas not completely frozen over. Each Snowball Earth Glaciation was followed by a super-greenhouse climate. The resulting sedimentary record of these “freeze-fry” events typically consists of glacial tillites and overlying cap carbonates. These units are preserved at many localities on Earth.

The Virginia outcrop shown above consists of a Snowball Earth glacial conglomerate (polylithic diamictite), with non-bedded matrix-supported clasts. This was originally a glacial till. With burial and lithification, till becomes tillite. The rocks in this area have been subjected to very low grade metamorphism, so the tillite is now a metatillite. The clasts vary in lithology, origin, and age. The most conspicuous clasts are speckled granites (dominated by quartz and potassium feldspar), derived from the 1.0 to 1.3 billion year old Cranberry Gneiss.

Stratigraphy: Konnarock Formation, Neoproterozoic, ~750 Ma