Ocean Deposits

INTRODUCTION

The Ocean deposit which cover the ocean floor like a blanket include unconsolidated sediments extracted from various sources at the sea floor. By far the greater part of the deposits on the continental shelf and slope consists of material brought down from the land by rivers, on the one warm form its edge by the sea.

The larger fragments in the deposits one found close to the, as it is only in the shallow water that to none  them.  The finest particles on the other hand may be found at a considerable distance away from shore to sea. The ocean deposits spread over the floors of the ocean like carpet. By far the greater part of the deposits on the continental shelf and slope consists of material brought down form the land by rivers or worn from its edge by the sea.

The larger fragments are laid down close to the shore, for it is only in shallow water that the waves and currents have power to move them, but the finer particles  may be borne a considerable distance out to sea and the more minute they are the farther they can can be carried.

The sediments derived from weathering and erosion of continental rocks are transported to the oceans by rivers, winds etc. Weathering and erosion of continental rocks, results in the formations of sediments which are transported the ocean by rivers, winds, volcanic eruptions etc. The decomposition of plants and animals also contribute to the ocean deposits eruptions also provide sediments. Besides, the decay and decomposition of marine organisms (both plants and animals) also contribute sediments to ocean deposits. Thus to a certain extent the material is sorted according to size.

Sources of Ocean Deposits

There are four sources of ocean deposits. It is, therefore, convenient to study them under the following four  heading:-

Ocean deposits have different sources of origin which can be divided into four heads.

i) Terrigenous Sediments: These deposits found on land are formed due to the works of rivers, sea waves, winds and glaciers. The disintegration of decomposition of continental rocks leads to the formation of fine- course sediments. The sediments formed due to disintegration of continental rock are called terrigenous sodium. Due to the variation in size and shape of the terrigenous materials the courses and larger sediments are deposited the coast and the finer ones away from the coast.

The continental rocks are disintegrated and decomposed d of weathering and gradation of these due to the various types of weathering and thus fine to coarse sediments are formed. These sediments of continental origin are called terrigenous materials which ae brought to the rivers through surface wash, rainwash, rills, gullies and small rivulets.

The process and extent of disintegration depends  on the nature of rock material, climate and time taken. The larger particles of the terrigenous deposits are found near the shore and the finer ones are carried deeper. The extent to which they are carried outwards on the size of rock material and the strength of sea waves and currents.

As there is much variation in the size and shape of terrigenous materials, there is marked gradation of these materials, when they are deposit in the oceans i.e. coarser and larger sediments becomes smaller and finer away from the coast. On the size, composition and chemical  characteristics terrigenous sediments are divided into gravels, sand and silt clay and muds.

Gravels: the diameter of gravels ranges from 2 mm to 256 mm. There is marked gradation in the size of gravels. The following are subtypes of gravels. The following are subtypes of gravels on the basis of diameter of particles boulders (256 mm), cobbles (64 mm), pebbles (4mm), granules (2mm) etc. Since, these sediments are very large in size, these are deposited near the coast on the continental shelves.

Sands: The sediments varying in diameter from 1 mm to 1/16 mm are termed sands. On the basis of size of grains, sands are classified into five types i.e. 

1.  Very coarse sands (1 mm)
2. Coarse sands (0.5 mm)
3. Medium sands (0.25 mm)
4. Fine sands (0.125 mm)
5. Very fine sands (0.0625 mm)

There is marked gradation of sand deposits in the oceans i.e. coarser sands are deposited close to the coast while the sands are deposited away from the coast.

Silt, Clay and Mud : The finer sediments ranging to diameter from 1/32 mm to 1/8192  mm are grouped under the category silt, clay and mud. Clay and mud are deposited in calm seawater. Generally, these deposits are found at the depth of 100 to 1000 fathoms.

Mud refers to the finest particles, which comprise the minute particles of rock forming materials, principally quartz. Murray has classified the mud deposits into the green and red types, based on the color of constituents.

• Blue muds includes the materials derived through the disintegration of rocks rich in iron sulphide and organic elements. They are generally found at greater depth of the continental shelves. Blue mud predominates in the Atlantic Ocean, Mediterranean sea, Arctic Sea, and enclosed seas.
• Red muds are the sediments are derived through the communication of rocks rich in Iron Oxide. The reddish color is due to the dominance of Iron content. The deposit of red mud is confined mostly to the yellow Sea., Brazilian coast and the floors of the Atlantic Ocean.
• Green mud is formed due to chemical weathering wherein the color of blue mud is changed to green mud due to reaction of seawater.