Ocean Sediments

Classification by Source

Biogenous:

Source: Organic accumulation of hard parts of some marine organisms

Examples: Calcarous and silaceous oozes

Distribution: Dominant on deep-ocean floor

Cosmogenous:

Source: Dust from space, meteorite debris

Examples: Tektite spheres, glassy nodules

Distribution: Mixed in very small proportion with more dominant sediments

Hydrogenous:

Source: Precipitation of dissolved minerals from water

Examples: Manganese nodules, phosphorus deposits

Distribution: Present with more dominant sediments

Terrigenous:

Source: Erosion of land, volcanic eruptions, blown dust

Examples: Quartz sand, clays, estuary mud

Distribution: Dominant on continental margins, abyssal plains, polar ocean floors

Beaches

Backshore:

The backshore is the area from the berm crest to the farthest point that sand has been deposited. This area is relatively inactive. The foreshore is the area from the berm crest to the sea. This is the active area of the beach.

Beach:

A beach is a zone of loose particles that cover all or part of a shore. The landward limit may be vegetation, a cliff, sand dunes, or a constructed seawall. The materials on it may be boulders, pebbles, gravel, sand, silt, shell debris and/or fragments of coral. Usually, the flatter the beach is, the finer the material is.

Berm:

The berm is an accumulation of sediment that runs parallel to the shore, marking the limit of the depositing of sand by the action of the waves. The berm crest is usually the highest point on the beach.

Ripples:

Ripples in the sand are caused by rushing currents. Rills are small depressions that channel water back to the ocean during a falling tide. Diamond-shaped backwash marks form when projecting shells or other objects interrupt the backwash during low tide.

Swash:

The swash, water washing onto the beach, carries particles onto the shore. The backwash carries materials back to the ocean. The beach will not become larger or steeper if the amount of particles going each way remains the same.

Features of Depositional Coasts

Barrier island:

A barrier island is a narrow, exposed sandbar that is parallel to, but separated from, the mainland.

Bay mouth bar:

A bay mouth bar forms when a sand spit closes off a bay, by attaching to the headland nest to the bay. An inlet may be cut through the bar by the action of the tide.

Estuary:

An estuary is a body of water partially surrounded by land where fresh water from a river mixes with ocean water.

Lagoon:

A lagoon is a long, shallow body of sea water isolated from the ocean. It is created when rising sea water breaks through sand dunes.

Sand spit:

A sand spit forms where the longshore current slows as it clears a headland and approaches a quiet bay. The slower current deposits sand and gravel in a line downcurrent from the headland.