Biogenous sediments oozes

In the event of a decline in sea level, the supratidal zone will move seaward, causing evaporites to deposit on top of old lagoonal sediments. When sea level rises back, it drowns these evaporites. These low-amplitude fluctuations in sea level build up laminated sediments in which layers of biogenic oozes and organic-rich muds alternate with evaporites. 

While rapid burial enhances preservation, the type of sediment produced is determined by the relative particle composition of the deposit. For example, rapid burial of biogenic silicate by clay minerals helps protect the shells against dissolution, but the resulting deposit is classified as an abyssal clay, rather than a siliceous ooze, if the sediment is less than 30% by mass BSi. Thus, prediction of the sediment type likely to be found at a given location requires knowledge of the relative magnitudes of the accumulation rates of all particle types. 

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. 

As shown in Table 20.1, biogenous oozes are the most common type of pelagic oceanic sediment, with calcareous oozes dominating. 

Biogenous ooze Sediments that contain more than 30% by mass hard or soft parts that were synthesized by marine organisms. 

Ooze A sediment that contains greater than 30 percent detrital biogenic hard parts by mass. 

A special type of sediment is formed at the foot of the continental slope of the Black Sea in the zone of discharge of turbidity flows. In the western part of the sea and in the Crimean sector, the sediments of the base of the continental slope are represented by finely stratified biogenic or organogenic oozes. In the eastern and southern parts of the basin, a terrigenous component of clayey sediments becomes more significant [6,14]. 

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. 

The Crimean region is characterized by alongshore variations in the sediments of the underwater slope. West of the Tarkhankut Peninsula up to Evpatoriya, biogenic coquina deposits dominate they cover the limestone bedrock. On the Crimean shelf, terrigenous sediments are also observed represented by boulders and pebbles in the near-shore zone, sands at depths down to 7-10 m, and fine sands and silty oozes at greater depths. Meanwhile, at depths of about 30 m, there exists a sandy-pebbly bar formed by extreme waves. 

Typical biogenic ooze strength profiles. (From Chaney, R., and Fang, H.Y., Static and dynamic properties of marine sediments A state of the art. In Marine Geotechnology and Nearshore/Offshore Structures. STP 923, Chaney, R.C., and Fang, H.Y., eds., ASTM Press, Philadelphia, PA, pp. 74-111,1986. Reprinted with permission. Copyright ASTM.)... 

---