Abyssal plains

Whelan, J.K. 1977. Amino acids in surface sediment core of the Atlantic abyssal plain. Geochimica et Cosmochimica Acta 41 803-810. 

Table 14.3 Average % Composition of <2 xm Fraction in Sediments of the Abyssal Plains. Carbonate-Free Size...

The slowest growth rates are found in the Fe-Mn oxides that have formed predominantly by precipitation of solutes from seawater, being on the order of 1 to a few millimeters per million years. Because of slow formation rates, these hydrogenous precipitates tend to form only in areas where sedimentation rates are slow, such as the abyssal plains of the mid-Pacific Ocean, or where bottom currents are strong enough to prevent sediment accumulation, such as on submarine seamounts and plateaus. 

The hydrothermal-vent and cold-seep communities are dramatically different from the ecosystems typical of the abyssal plains. First, they are sites of high productivity supported by the abundant reduced chemicals in the hydrothermal fluids. Thus, these communities are independent of the skimpy flux of POM created in the surface waters that survives to settle on the seafloor. On the other hand, these communities have had to adapt to survival in hydrothermal systems that are ephemeral, disjunct, and characterized by extreme conditions, such as high temperatimes, high concentrations of reduced metals and sulfur, and low pH. As a result, vent communities have high rates of endemism. Of the 712 recorded vent species, 71% are found in no other setting ... 

Figure 20.1 illustrates that the major sediment type on the abyssal plains are the abyssal clays with some local exceptions, including equatorial radiolarian oozes, manganese nodifles, and metalliferous sediments. 

The abyssal clays are composed primarily of clay-sized clay minerals, quartz, and feldspar transported to the siuface ocean by aeolian transport. Since the winds that pick up these terrigenous particles travel in latitudinal bands (i.e., the Trades, Westerlies, and Polar Easterlies), the clays can be transported out over the ocean. When the winds weaken, the particles fell to the sea siufece and eventually settle to the seafloor. Since the particles are small, they can take thousands of years to reach the seafloor. A minor fraction of the abyssal clays are of riverine origin, carried seaward by geostrophic currents. Despite slow sedimentation rates (millimeters per thousand years), clay minerals, feldspar, and quartz are the dominant particles composing the surface sediments of the abyssal plains that lie below the CCD. Since a sediment must contain at least 70% by mass lithogenous particles to be classified as an abyssal clay, lithogenous particles can still be the major particle type in a biogenous ooze. 

Latitudinal patterns in clay mineral distributions are pronounced in abyssal plain sediments as illustrated in Figures 14.8 through 14.11. These latitudinal bands reflect the... 

The model provided in Figure 20.1 is for an ocean basin whose abyssal plains all lie below the CCD. This most closely resembles the conditions in the North Pacific, whereas the rest of the ocean basins have a significant portion of their abyssal plains lying above the CCD, and, hence, contain some calcareous oozes. From a global perspective, calcareous oozes are more abundant than siliceous oozes. This is caused by two phenomena (1) all seawater is undersaturated with respect to opal, whereas all surface waters and 20% of the deep waters are saturated with respect to calcite, and (2) siliceous plankton are dominant only in upwelling areas. 

Because of the relative scarcity of lithogenous particles and fast seafloor spreading rates, metalliferous sediments are common around the East Pacific Rise and very high densities of manganese nodules are present on the abyssal plains, especially in the Southern Hemisphere. In these locations, the weathering products of volcanic detritus, such as montmorillonite, phillipsite, nontronite, and celadonite, are also found in great abimdance. 

Like the Atlantic, the Indian Ocean is characterized by foram oozes along its mid-ocean ridge and most of its abyssal plains. Only in basins where the water depths exceed 5000 m are abyssal clays abundant. 

Pelagic sedimentation Sedimentation that occurs at rates less than 1 cm/lOOOy. This is characteristic of sediment on the abyssal plains and mid-ocean ridges. 

The Ustica island (0.75-0.13 Ma) occurs in the southern Tyrrhenian Sea, west of the Aeolian volcanic arc, along the southern margin of the Tyrrhenian abyssal plain, probably at the intersection between E-W and NW-SE trending faults (e.g. Boccaletti et al. 1984). The recently discovered Pro-meteo submarine lava field is located a few km southeast of Ustica (Trua et al. 2003). 

Barberi F, Bizouard H, Capaldi G, Ferrara G, Gasparini P, Innocenti F, Joron JL, Lambert B, Treuil M, Allegre C (1978) Age and nature of basalts from the Tyrrhenian Abyssal Plain. In Hsu K, Montadert L, et al. (eds) Init Rep Deep Sea Drilling Project. Washington, 42 pp 509-514... 

The sediments of the abyssal plain of the central Black Sea region are mostly biogenic and are enriched with organic matter. The floor of the deepwater depression is covered with coccolith oozes. In peripheral zones, in addition, terrigenous lowly calcareous oozes and carbonate-free silts are observed. 

Marine sediments cover the ocean floor to a thickness averaging 500 m. The deposition rates vary with topography. The rate may be several millimetres per year in nearshore shelf regions, but is only from 0.2 to 7.5 mm per 1000 years on the abyssal plains. Oceanic crustal material is formed along spreading ridges and moves outwards eventually to be lost in subduction zones, the major trenches in the ocean. Because of this continual movement, the sediments on the seafloor are no older than Jurassic in age, about 166 million years. 

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