Marine sediments

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What determines the global distribution of marine sediments?

Formation and transport mechanisms

What are biogenic sediments?

Formed from marine organisms (mainly planktonic in origin)

Where are diatoms most prevelant?

In cold, nutrient-rich waters

Where can carbonate oozes be found?

In the Atlantic

Where are radiolarians most prevalent?

In warmer waters

What 5 classes can marine sediments be sorted into?

Lithogenous, authigenic (hydrogenous), biogenic, volcanogenic, cosmogenic

What are calcareous sediments composed of?

Mainly calcite from coccolithophores, foraminifera and pteropods

What are silicous sediments composed of?

Mainly composed of opal, derived from diatoms and radiolarians

What is the distribution and type of biogenic oozes determined by?

Marine productivity, species composition, bathymetry and ocean chemistry

What are ferromanganese nodules found?

Nodules are often found on top of red clay deposits where deposition of red clay is a low

What are biogenic oozes?

Sediment containing of >30% of biogenic material

What are sediment reflection profiles of turbidites used for?

Used to dstinguish turbidite deposits, as you get distorted layers of sediments often due to the transport mechanisms

What is the preservation of biogenic calcite in sediment controlled by?

solubility

What are pteropods?

A group of molluscs

what are coccolithophores?

A single-celled marine flagellate that secretes a calcareous shell, forming an important constituent of phytoplankton

Ice-raft debris (IRD)

A terrigenous material transported within the matrix of ice, and then deposited into the marine environment as sediment as the ice matrix gradually melts

How can lithogenous sediments be distinguished?

By methods of dispersion

Types of biogenic sediments

Calcareous sediments and siliceous sediments

Lysocline

Depth at which calcite starts to dissolve, seawater is understaurated in calcite under the lysocline

What are the 3 methods of dispersion for lithogenous sediments?

Riverine sediments, glacial-marine sediments, aeolian dust deposits

What is opal?

Silicious sediments (SiO2)

Carbonate compensation depth (CCD)

The water depth at which the rate of supply of calcium carbonates from the surface is equal to the rate of dissolution.

What are sediment slumps caused by?

Turbidite deposits from turbidity currents create fast-moving currents of sediment-water (sludge) from top of continental slope - often triggered by seismic activity

Depth of CCD

between 4000-5000m

Types of authigenic sediments

ferromanganese nodules

What can the distribution of biogenic calcite in sediments be caused by?

seafloor spreading

What is the distribution of opal controlled by?

sedimentation rate and solubility

What are foraminifera?

single-celled marine plankton


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