Types of seafloor sediments and factors controlling their distribution

Sea Sediment Types and Their Distribution

For ages mankind has struggled to map the geologic features of its surroundings, scaling tall peaks to measure elevation and traversing deadly deserts to expand the horizons of cartography, but the exploration of land typically ended where the sand met the sea. Although seafaring ships have allowed humanity to navigate the ocean's surface for millennia, the ability to accurately map and analyze the seafloor is a relatively modern innovation. The advent of sonar-aided bathymetric techniques, in the early 20th century, and satellite altimeters today, has allowed scientists and researchers to develop highly accurate, adaptable maps of the seafloor which reflect the shifts in sediment patterns caused by underwater currents. Deep sea exploration through the use of submarine vehicles has also enabled the scientific community to closely analyze the properties and physical makeup of the various strata of seafloor sediment resting thousands of feet, and sometimes many miles, below the surface of the sea. We now know that "seafloor sediments can be classified according to their origin into three broad categories: (1) terrigenous ('derived from land'), (2) biogenous ('derived from organisms'), and (3) hydrogenous ('derived from water')" (Lutgen, Tarbuck & Tasa, 2011), while each type of sediment is distributed across the seafloor due to a confluence of external factors.

The spread of terrigneous sediment throughout the seafloor is caused primarily by weathering and wind, as grains of stone from rocks on land are eroded and carried via wind currents, before being deposited into the sea and sinking to the seafloor. The largest particles of terrigenous sediment, such as sand and gravel, are typically heavy enough to resist ocean currents, settling near the shore to form beaches, while the smaller particles can be distributed via ocean currents for years before eventually settling. Terrigenous sediment settles very slowly on the deepest parts of Earth's seafloor, accumulating at the rate of 1 centimeter of abyssal clay every 50,000 years, while rapidly building up heavy deposits of material along continental margins near the mouths of large rivers (Lutgen, Tarbuck & Tasa, 2011).

The production of biogenous sediment is a continual process, as oceanic organisms shed their shells or skeletons after death, leaving the organic debris to sprinkle steadily along the seafloor. Research focused on the study of biogenous sediment properties has consistently observed that "the most common biogenous sediment calcareous (CaCO3) ooze, which, as the name implies, has the consistency of thick mud" (Lutgen, Tarbuck & Tasa, 2011). While the calcareous tests, or shells, of organic matter is fairly prevalent throughout the ocean's warmer surface waters, this material dissolves as it sinks deeper into the carbon dioxide (CO2) rich colder waters of the deep sea. Due to this property of calcareous ooze, biogenous sediment is rarely found at depths greater than 15,000 feet.