Marine clay

Marine clays are fine-grained sedimentary deposits composed primarily of clay minerals that accumulate in coastal environments. They are typically derived from the weathering of continental rocks, transported to an ocean, where they settle and consolidate on the seabed. Marine clays commonly contain minerals such as illite, smectite, kaolinite, and chlorite, along with varying amounts of silt, organic matter, and biogenic materials. The saline conditions during deposition influence their structure and bonding, often producing high natural water contents, and low permeability. Marine clays exhibit high sensitivity, meaning their internal structure is fragile and can lose much of its strength when disturbed.

The structure and properties of Marine clays depend on regional geological conditions such as tectonic activity, erosion, and sediment deposition. In addition to their sources, marine clays are shaped by their stress history and environmental factors, including interactions between water and minerals, fluctuations in water levels caused by tides or climate change, and variations in salinity and acidity.

USDA classifies marine clay particles as being less than 0.002 millimetres (7.9×10⁻⁵ in) in diameter. Particles can become suspended in water; heavier sand settles quickly, while finer silt and clay particles remain suspended longer. Marine clay particles, being very small and often negatively charged, can resist settling and sometimes stay suspended indefinitely, this is also known as turbidity, in which suspended particles create a murky brown color.

Once the clay is deposited on the ocean floor it can change its structure through a process known as flocculation, process by which fine particulates are caused to clump together or floc. In estuarine systems, the changes in physicochemical conditions from the river side to the sea side triggers flocculation and leads to estuarine siltation. This is one of the main causes for the dredging activities in harbors. Organic matter in particular plays a major role in marine clay flocculation as it can adhere to marine clay particles. Particles can also be aggregated or shifted in their structure besides being flocculated.