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Sorted and Eroded
As glaciers move across the land, debris is picked up, exposed to intense pressure for hundreds of miles and deposited in other areas. The heaviest of this fluvio-glacial sediment sinks first as the flow of glacial runoff slows and loses strength. Over time the slowing of the water continues to deposit sediment in vertical layers, stratified, determined by the weight of the material.
Outwash Plains
Broad, flat outwash plains form of the sand, gravel and other sediments (dependant on the region) that the meltwater streams cannot carry. The rapidly moving meltwaters also bring and deposit layers of stratified materials from the advance of multiple glaciers. These plains form large areas of flat, or very lightly rolling, land that often has quite a bit of unstratified material under the stratified outwash deposits.
Contents
Most stratified outwash deposits consist mainly of gravel and sand, but multiple continental glaciers encountered huge areas of sandstone and crystalline bedrock across areas such as the northern parts of Wisconsin and Michigan. Fragments, sometimes as large as volcanic boulders, were integrated into the ice, worn down, stratified and deposited further south. Stratified materials containing calcium magnesium carbonate left deposits that are rich in clay, chalky and consist almost exclusively of calcium carbonate.
Ice-Contact Stratified Drift
Sediment that was formerly beneath the glacier (subglacial) forms the first layer in river beds shaped by meltwater. Chunks of ice containing sediment that was inside (englacial) or that stayed on top or near the surface of the glacier (supraglacial) are sheared off and trapped under layers of other sediment in the glacial meltwater streams. The melting of these chunks of ice is greatly slowed, and as each finally melts additional stratified layers are deposited.