Clay deposits are primarily moved by natural forces such as water, wind, and ice, which transport fine clay particles from their source to new locations where they are deposited. This process results in the formation of what are known as sedimentary or secondary clays.
These transported clays differ significantly from residual clays, which form in place from the weathering of parent rock. Sedimentary clays tend to be more plastic, with smaller, more uniform particles, and are often mixed with a variety of other materials during their journey.
Mechanisms of Clay Transport
The movement of clay particles across landscapes and into sedimentary basins is a continuous geological process, driven by various agents of erosion and deposition.
1. Water Transport
Water is a highly effective agent for moving clay. Rivers, streams, and ocean currents carry vast quantities of fine sediment, including clay particles, over long distances.
- Fluvial Transport (Rivers & Streams): Clay particles, being very fine and light, can remain suspended in water for extended periods, even in slow-moving currents. As the water velocity decreases (e.g., in floodplains, deltas, or lakes), these suspended clays settle out, forming layered deposits.
- Marine Transport (Oceans & Lakes): Ocean currents can redistribute clay particles across continental shelves and into deep-sea basins. Clays are a major component of marine sediments, accumulating slowly on the seafloor.
- Characteristics of Water-Transported Clays:
- Often well-sorted, meaning particles are of similar size.
- Can form extensive, stratified layers.
- Highly influenced by the energy of the water body.
2. Wind Transport
Wind, or aeolian processes, can also transport clay particles, especially in arid and semi-arid regions or during dust storms.
- Aeolian Transport: While larger sand grains are typically moved by rolling or saltation, fine clay and silt particles can be carried in suspension by wind for thousands of kilometers.
- Loess Deposits: A significant example of wind-transported clay and silt is loess, which forms thick, fertile deposits in many parts of the world, such as China and the Midwestern United States. These deposits are typically yellowish-brown and can be highly porous.
- Characteristics of Wind-Transported Clays:
- Usually extremely fine-grained.
- Can create widespread, relatively uniform deposits.
- Often associated with deserts, glacial outwash plains, or exposed floodplains.
3. Ice Transport (Glacial Movement)
Glaciers are powerful agents of erosion and transport, capable of moving enormous volumes of material, including clay.
- Glacial Till: As glaciers move, they scour the underlying bedrock and pick up sediment of all sizes, from boulders to fine clay. This unsorted mixture of material, known as glacial till, is deposited directly by the ice as it melts.
- Glacial Lake Sediments: When glaciers melt, the meltwater carries fine clay and silt into glacial lakes, where it settles to form stratified deposits called varves.
- Characteristics of Ice-Transported Clays:
- Typically mixed with a wide range of particle sizes (poorly sorted).
- Can be compacted and dense.
- Often found in regions that were historically glaciated.
Comparing Transported Clays
The table below summarizes the key agents of clay transport and their general characteristics:
| Transport Agent | Description | Typical Clay Characteristics | Examples of Deposits |
|---|---|---|---|
| Water | Rivers, streams, lakes, and ocean currents carry suspended clay particles. | Finer, often well-sorted, stratified. More plastic. | River deltas, lakebeds, marine shales, floodplains. |
| Wind | Strong winds lift and carry very fine clay particles over vast distances, especially in dry environments. | Extremely fine, uniform, often porous. | Loess deposits, dust layers. |
| Ice | Glaciers erode and transport a mix of sediments, including clay, which is deposited upon melting. | Poorly sorted (mixed with other particle sizes), dense, compacted. More plastic. | Glacial till, glaciolacustrine clays (varves). |
Understanding how clay deposits are moved is crucial for various fields, including geology, soil science, civil engineering, and ceramics, as the mode of transport directly influences the properties and distribution of these valuable earth materials. For more detailed information on geological processes, resources like the U.S. Geological Survey (USGS) offer extensive data.
