Definition: Red clay, also known as pelagic clay, accumulates in the deepest and most remote areas of the ocean. Containing less than 30% biogenic material, its composition is a varied mix of very fine quartz and clay minerals, authigenic deposits precipitated directly from seawater, and micrometeorites. Though called "red" because it sometimes takes the color of oxidized iron minerals, it is usually brownish in color. Its ultimate origin is uncertain, but red clay seems to be mostly derived from distant rivers, and windblown dust. Covering 38% of the ocean floor, it accumulates more slowly than any other sediment type, at only 0.1-0.5 cm / 1000 yr.
Definition: A wetland, featuring grasses, rushes, reeds, typhas, sedges, and other herbaceous plants (possibly with low-growing woody plants) in a context of shallow water.
Definition: Gravel is an environmental material which is composed of pieces of rock that are at least two millimeters (2mm) in its largest dimension and no more than 75 millimeters.