Marine Sediments

Ocean sedimentVarious materials settle through the water column and accumulate on the ocean floorLayers represent a record of Earth history, including:

Movement of tectonic platesPast changes in climateAncient ocean circulation patternsCataclysmic events

The 4 main types of sediment

1. Lithogenous = composed of fragments of pre-existing rock material

2. Biogenous = composed of hard remains of once-living organisms

3. Hydrogenous = formed when dissolved materials come out of solution (precipitate)

4. Cosmogenous = derived from outer space

Origin of lithogenous sedimentForms by:

Weathering = breakup of exposed rockTransportation = movement of sedimentDeposition = settling and accumulation

Sediment-transporting media

Lithogenous sediment composition

Most lithogenous sediment is composed of quartz, which is:

AbundantChemically stableDurable

Lithogenous sediment textureTexture includes:

Grain sizeSortingRoundingMaturity

Distribution of lithogenous sediment

Lithogenous sediment occurs as:Neritic (nearshore) deposits

BeachesContinental shelvesTurbiditesGlacial-rafted debris

Pelagic (deep ocean floor) depositsAbyssal clay

Origin of biogenous sedimentOrganisms that produce hard parts dieMaterial rains down on the ocean floor and accumulates as:

Macroscopic shells, bones, teethMicroscopic tests (shells)

If comprised of at least 30% test material, called biogenous ooze

Biogenous sediment compositionMicroscopic biogenous tests are composed of 2 main chemical compounds:

1. Silica (SiO2) including opal (SiO2 · nH2O)Diatoms (algae)Radiolarians (protozoan)

2. Calcium carbonate or calcite (CaCO3)Coccolithophores (algae)Foraminifers (protozoan)PteropodGlobigerina

Examples of silica-secreting microscopic organisms

Diatom Radiolarian

Siliceous oozeSilica-secreting organisms accumulate to form siliceous ooze (>30% siliceous test material)

Examples of calcite-secreting microscopic organisms

Coccolithophores Foraminifers

Calcareous oozeCalcite-secreting organisms accumulate to form calcareous ooze (>30% calcareous test material)

Biogenous ooze turns to rockWhen biogenous ooze hardens and lithifies, can form:

Diatomaceous earth (if composed of diatom-rich ooze)Chalk (if composed of coccolith-rich ooze)

Chalk cliffs of southern England

Distribution of biogenous oozeMost biogenous ooze found as pelagic depositsFactors affecting the distribution of biogenous ooze:

Productivity (amount of organisms in surface waters)Destruction (dissolving at depth)Dilution (mixing with lithogenous clays)

Distribution of siliceous oozeSilica slowly but steadily dissolves in seawaterSiliceous ooze found where it accumulates faster than it dissolves

Distribution of calcareous oozeCalcite dissolves beneath the calcite compensation depth (CCD) at 4.5 kmCalcareous ooze can be found below the CCD if it is buried and transported to deep water

Biogenous ooze as environmental indicator

Siliceous ooze Calcareous oozeSurface water temperature

Cool Warm

Main locations found

Sea floor beneath cool surface water in high latitudes; upwelling areas

Sea floor beneath warm surface water in low latitudes; not too deep (CCD)

Origin of hydrogenous sedimentHydrogenous sediment forms when dissolved materials come out of solution (precipitate)Precipitation is caused by a change in conditions including:

Changes in temperatureChanges in pressureAddition of chemically active fluids

Types of hydrogenous sedimentManganese nodulesPhosphatesCarbonatesMetal sulfidesEvaporite salts

Mining manganese

nodules

Evaporite salts

Cosmogenous sedimentCosmogenous sediment is composed of material derived from outer spaceTwo main types:

1. Microscopic space dust2. Macroscopic meteor debrisForms an insignificant proportion of ocean sediment

Microscopic cosmogenous

spherule

MixturesMost ocean sediment is a mixture of sediment typesOne type of sediment usually dominates, allowing it to be classified as primarily:

LithogenousBiogenousHydrogenousCosmogenous

Worldwide distribution of neritic and pelagic sediment

Figure 4-17

Ocean sediments as a resourceOcean sediments contain many important resources, including:

PetroleumGas hydratesSand and gravelEvaporative saltsPhosphoriteManganese nodules and crusts

Offshore drilling rig