x. chemical components of sediment

Chemical components of sediment

X.

Introduction

• The sediments deposited in the ocean are an archive of historical information about the Earth

• They provide information about global biogeochemical cycles

• The distribution of sediments in the ocean is determined by biological and chemical processes

The origin of sediment

Sediments

Autochtonous (authigenic)precipitation

Hydrogenous Biogenous

AllochtonousSolid form

Lithogenous (clastic) Cosmogenous

Anthropogenic

Grain-size of sediments

http://www.virtual-geology.info/sediments-and-strata/grainsize.html

Grain-size distribution

Lithogenous sediment

• From the earth`s crust as a process of weathering and volcanic activity

• Terrigenous particles are the products of weathering of continental rocks

• It enters the ocean via rivers, glaciers, and winds

Volcanic activity

• Sediments from volcanic activity normally larger than clays

• In the ocean, the particles undergo weathering as a result of chemical attack by seawater

• Their mineralogy is primarily that of amphiboles, pyroxine , and olivine (rock-forming silicate minerals contain ions iron and magnesium in their structure)

AmphibolesOlivine

Pyroxine

Biogenous sediments

• Composed of detrital (nonliving) hard and soft parts formed by marine organisms

• The hard parts are fragments of structural components, including shell, endoskeletons, and exoskeletons

• The soft parts composed of organic matter, such as tissues, organic exoskeletons, and excretions (fecal pellets)

Examples

• Calcite (CaCO3) deposited by coccolithophorids (< 60 µm) and foraminiferans (< 2 mm)

• Opaline (SiO2) deposited by diatoms (mostly < 50 µm) and radiolarians ( 20-300 µm)

• Aragonite polymorphous with calcite• Barite (BaSO4)

• Celestite (SrSO4)• Carbonate-rich fluoroapatite minerals (francolite)

Hydrogenous sediments

• Sediments formed by the abiogenic precipitation of solutes from seawater

1. Evaporites: salt crystals that form when seawater evaporates

2. Metal sulfide deposits at mid-ocean ridges3. Manganese nodules4. Phosphorites5. Some clay minerals around mid-ocean ridges

Evaporites

Form when seawater evaporates and is not relaced with fresh water

Cosmogenous sediments

• Extraterrestrial material that is constantly entering earth`s atmosphere with particle diameter is less than 1 mm

• Composed primarily of fragments of comets and asteroids in the 5 to 50 µm size range

• Because of its small size, some of these particles are able to pass through earth`s atmosphere and reach the sea surface without melting

Calcareous oozes (CaCO3)

• Is calcium carbonate mud formed from the hard parts (tests) of the bodies of free floating animals

• the primary calcareous organisms are foraminifera (microscopic animals) and coccoliths (algae)

• When the planktonic organisms die their calcareous shells fall to the ocean bottom

Stability of CaCO3

http://www.utdallas.edu/~pujana/oceans/calcium.html

Siliceous oozes (SiO2)• made up of the tests of floating (planktonic)

organisms that extract silica from seawater to make their hard parts

• The most abundant of these are the diatoms (plants) and the radiolarians (animals)

DiatomsRadiolarians

Siliceous oozes