Glacial Processes:
During the last ice age, which occurred about 10,000 to 12,000 years ago, the Canadian Shield was covered by a thick ice sheet. As glaciers moved across the landscape, they eroded and scoured the surface, grinding down bedrock and creating a mixture of rock debris known as till.
Weathering of Bedrock:
The Canadian Shield is predominantly composed of Precambrian igneous and metamorphic rocks, such as granite and gneiss. Over time, these rocks weather and break down under the influence of various environmental factors, including temperature changes, moisture, and chemical reactions. This weathering process produces fine-grained clay minerals.
Formation of Clay Belts:
As the glaciers retreated at the end of the ice age, they deposited their load of till across the Canadian Shield. In areas where the till was relatively fine-grained and contained a significant amount of clay minerals, it formed distinct clay belts. These clay belts typically occur in low-lying areas or along river valleys.
Types of Clay Belts:
There are two main types of clay belts in the Canadian Shield:
1. Glaciolacustrine Clay Belts: These clay belts were formed when glacial meltwater accumulated in large proglacial lakes. As the water drained away, it deposited fine-grained sediments, including clay, that settled on the lake bottom.
2. Glaciofluvial Clay Belts: These clay belts were formed by meltwater streams and rivers that flowed from the melting glaciers. The moving water carried and deposited clay-rich sediments along its course, creating clay belts alongside river valleys.
The clay belts of the Canadian Shield vary in size and thickness, and they can be several kilometers long and hundreds of meters wide. They are an important natural resource, supporting agriculture, forestry, and various industrial activities in the region.