Tilliitti

Tilliitti is a sedimentary rock composed primarily of unsorted glacial debris. It is formed from till, which is sediment deposited directly by a glacier. When this till is compacted and lithified over time, it becomes tillite. The rock typically contains a wide range of clast sizes, from fine clay and silt to large boulders, all embedded within a finer-grained matrix. The clasts are often angular and scratched, a characteristic known as striations, which are indicative of their transport and abrasion by glacial ice.

Tillite is a significant geological indicator of past glaciation. Its presence in the rock record suggests that the area was once covered by ice sheets. Geologists study tillite to understand ancient climates, the extent of past ice sheets, and the movement of glaciers. It can be found in many locations around the world, often in formations dating back to Precambrian, Paleozoic, and Neoproterozoic eras, periods known for significant glaciations. Notable examples include the Huronian glaciation deposits in Canada and the Sturtian and Marinoan glaciations in Australia and other parts of the world. The composition of the matrix in tillite can vary, but it is often composed of rock flour, sand, and clay derived from the grinding action of the glacier.