Marine sediments
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
