basal till
Quick Summary
In geology, basal till is unsorted material deposited directly by glacial ice. It is often called boulder clay and can be composed of clay, boulders, or a mix of both. The rock fragments are typically angular and sharp, as they are deposited from the ice with minimal water transport. These fragments may be faceted and striated from grinding within the glacier. Basal till is carried at the base of a glacier and commonly laid down beneath it, distinguishing it from ablation till, which is carried on or near the glacier's surface. This type of deposit is often severely compressed and compacted, referred to as lodgment till.12
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