Sediments

What to Watch for?You will see the true face of the ocean floorCovered by sediments, gravel, silt and mudSediment particles from land, from biological activity, and even from spaceSediments can help us define what occurred in recent history in the ocean basinSediment thickest at continental margins

Thinnest over active oceanic ridgesSedimentary “memory” of ocean basin is shortThink about

Movement, transport, how did the sediment arrive, where did it come from, and how can we tell the story of the ocean basin

Think about daily contact with marine sedimentBuilding materials, pool filters, toothpaste, oil, natural gas, paint

SedimentParticles of organic or inorganic matter that accumulates in a loose, unconsolidated form.

Major Sediment Input to the Oceans

Source Estimated Amount (109 tons/yr)

Rivers 18.3

Glaciers and ice sheets 2.0

Wind blown dust 0.6

Coastal erosion 0.25

Volcanic debris 0.15

Groundwater <0.48

What do sediments look like?Depends where you are

Atlantic ridge Sponges and corals may be growing over the dusting of sediment

Smooth ocean floor Brittle stars feed off surface bacteria and fallen particles of organic sediment

May see ripples if the bottom has swift currentsColors differ

Biological• Often white or cream colored

Silica deposits• Often gray

Clays on the ocean floor • Red due to oxidation• Chocolate brown

Sediment ClassificationsOrigin

SizeGravel - Bigger than 2 mm Sand – .062 – 2 mm, Big in Ocean TermsSilt – .004 - .062 mm, Gritty on TeethClay - <.004 mm

• Use Size to Determine the Energy of the Environment

Well sorted sedimentsSediments mixture that contains sediments of one size

Poorly sorted sedimentsSediments mixtures that contains a variety of of sizes

Sediment Type Diameter (mm)

Gravel Boulder >256

Cobble 65-256

Pebble 4-64

Granule 2-4

Sand Very coarse 1-2

Coarse 0.5-1

Medium 0.25-0.5

Fine 0.123-0.25

Very fine 0.0625-0.125

Mud (silt & clay) 0.0002-0.004

Deep Sea SedimentationThe Deep sea has two main sources of

sediment:

1. External- terrigenous material transported to oceans via rivers and wind

2. Internal-biogenic and authigenic from the sea.

Origin of the Particles (Genetic)Proposed by Sir John Murray and A.F. Renard while studying sediments during the Challenger expeditionTerrigenous/Lithogenous – terra = Earth, generare = to produce

From EarthBiogenous – Bio = life, generare = to produce

From lifeZebra MusclesDiatoms

Hydrogenous/ Authigenic – Hydro = life, generare = to producePrecipitates chemically from sea waterIron Stains in Sink in regular water

Cosmosgenous – cosmos = universe, generare = to produceComes from Outer SpaceMicro meteorites

•Terrigenous: Sands and mud produced by weathering and erosion of rocks on land.

•Biogenic: CaCO3 (calcium carbonate) and SiO2 (silica) muds and oozes composed of hard parts of organisms.

•Authigenic: formed by precipitation of minerals in seawater (Manganese (Mn) and Phosphorus (P) nodules).

•Volcanogenic: ejected from volcanoes (ash).

•Cosmogenous: pieces of meteorites that survive trip thru atmosphere.

Origin Classification

Terrigenous ParticlesComing from islands or nearby continentsMost abundant = Granite

Sources of quartz and clay in the oceansEarth’s crust is made of minerals

Inorganic crystalline materials that have a specific chemical composition

Both particles are small enough that they get transported to deep ocean floorTransportation?? How did they get there what was the Transport Agent…

Rivers – Clay Sand Mississippi River Delta: Birds Foot Trapped Near the Continents

How sediments reach deep oceanTurbidity Currents

Density and Gravity pull particles down SlopeCauses flatness of the abyssal plains

Resistant sandstone - rubble Turbidity current deposit rubble

Terrigenous ParticlesWind (Eolian)

Covers Long Distances Small Grain Sizes Slow Accumulation

Africa's West Coast:

Sediments that wind transports from the Sahara

Desert

Terrigenous ParticlesTransportation

Glaciers Deposits of sediment only happens when glaciers reach

sea level Iceberg Rafting

Rivers and streamsEloation

Biogenous Particles2nd Most abundant source for sedimentsSkeletal Components

Sediment Rich in skeletal material “ooze” Sample must contain more than 30% biogenic material

Two Major Players CaCO3 Calcium Carbonate: Plants Foraminifera: Animals

To make an “ooze” Production ~ Same everywhere Preservation ~ More soluble at high pressure and low temperature

• As it sinks carbonate needs shallower waters ~ 3500 – 4500 m starts to dissolve• When carbonate no longer can be preserved = CCD carbonate compensation

depth Little Dilution – Rapid input of Something else

• Get away from terrigenous areas

Coccolithophorid

Foraminifera

Foraminifera (zooplankton with CaCO3 shell)

White Cliffs of Dover

Biogenous ParticlesSilica

Opal – SiO2 . n H2O Zooplankton

• Diatoms – Plants

Radiolarians Zooplankton

To make a Siliceous “ooze” Production ~ High Productivity Zones they Do Well Preservation ~ Entire Ocean is Under saturated with Silica

• Once animal dies it starts to be dissolved• Preservation takes place with over whelming the system

– Make a lot so a Few can Survive– Getting to the sediment is the key– Micro environment once diatom reaches sediment won’t dissolve because others

already have been and water is saturated with silica

Diatoms (phytoplankton with SiO2 shell)

Cleaning agents and toothpaste often contain diatoms because of their sharp surfaces

Biogenous Sediments Soft Tissue

Gas Hydrates Near continental Margins A lot of methane stored in sediments Might be a useful source of fuel Possible Problems

• Limited Stability Range • Methane is much greater green house gas = AGGRESSIVE

– Large Gaseous Emissions!

Hydrogenous/Authigenic SedimentsFormed by chemical or biochemical reactions on ocean floor/ formed in the place they now occupyNodules of ferromanganese (Fe and Mn) or phosphorite (P).

Mn found deep sea bedsP found continental margins

Concentric layers of metal oxides accrete on particles over millions of years (1-4 mm per 106 y).Contain economically important metals Cu, Zn, Co and Pb. (but too expensive to harvest).Origin uncertain (biological?)

Ferromanganese nodules

Floor of South Pacific Ocean. Nodule size 1-5 cm diameter

Ferromanganese nodules

Cross-section

HydrogenousPebble like

Manganese Nodulesmm per million years, they grow slow

Evaporites – Hydrogenous deposit, precipitates out as water evaporates

Salts: Evaporates from isolated arms of the ocean Sea salts

• Red sea• Persian Gulf

Gypsum

Oolite sands – Calcium carbonate precipitates from shell fragments, white and rounded

Abundant in many warm, shallow waters• Bahamas

Deep Sea Sedimentation Process

Distribution of Sea SedimentsNeritic sediments: consist of primary terrigenous material

Found normally along continental shelf's

Distribution of Deep Sea SedimentsPelagic sedimentation: Sediments of the slope, rise, and deep-ocean that originate in the ocean

Pelagic: Inorganic red or brown clays

and silt• Fine-grained (0.0002 –

0.0004 mm)• Dominate below waters

with little planktonic production.

Deep Sea Sedimentation–Pelagic:

•Oozes

–Deep ocean sediment that has at least 30% of debris from planktonic organisms

–Named after the dominate remnant organism

–Calcareous oozes (CaCO3)

»Shells of foraminifera & pteropods (zooplankton) and coccolithophorids (phytoplankton).

»Accumulate on seafloor above CCD.

»Forms hard limestone under pressure

–Siliceous oozes (SiO2)

»Shells of radiolaria (zooplankton) and diatoms (phytoplankton).

»Accumulate on seafloor below CCD.

»Accumulate below regions of high diatom production (equator, poles, upwelling areas)

Deep Sea Sedimentation Distribution

TYPE COMPO-SITION

ATLANTIC (%)

PACIFIC (%)

INDIAN (%) GLOBAL (%)

Foram. ooze Carbonate 65 36 54 47

Pteropod ooze Carbonate 2 0.1 - 0.5

Diatom ooze Silica 7 10 20 12

Radiolarian ooze

Silica - 5 0.5 3

Red clay Aluminum silicate

26 49 25 38

Atlantic BasinSediments as thick as 1 km (3,300 feet)Small areaGreat numbers of rivers spilling sediments into ocean

The Atlantic basin contains a “two-layer-cake” stratigraphy–a thick basal layer of carbonate ooze overlain by a

layer of mud.

Pacific BasinLess than .5 km in thickness Large areaPacific has many trenches that the sediment gets trapped

Pacific plate moves across latitudes…

The Pacific basin contains a “five-layer-cake” stratigraphy, because unlike the Atlantic its sea floor as it spreads crosses the equator where the CCD is lowered to the ocean bottom.

Continental MarginsRivers and Erosion allow for a lot of the terrigenous sediment transported to the marginsOrderly sorting of particles from finest to large grains

Large grains stay near shoreSmall grains get carried into the deep ocean

Biogenous Sediments also accumulate in this regionProductivity of near shore waters is normally high

Some sediments are lithified due to the pressure of overlying sediments.

ExceptionsShelf deposits are subject to erosion as the sea level fluctuates.

Ice ages Exposed shelf leads to further erosion

Studying SedimentsClamshell sampler - Shallow sediment sampler

Piston CorerDevice capable of punching through as much as 25 m of sediment and returning an intact plug of material

Scientist Sample Sediments

Coring Preserves deep Straitigraphy, or Layering

StratigraphyAnalysis of layered sedimentary deposits in the ocean (or on land) Paleo-oceanogrpahy- Study of the Ocean’s past

Interpret ocean and climate history from evidence in deep-sea sediments

Started in 1930’s

Andrill

JOIDES: Deep-Sea Drilling Program (DSDP)

1978Drills into the ocean floor to take core samples24 a day50 scientists65 crew peopleStatistics

Economic ImportanceTaken from sedimentary deposits of continental shelves and rises

36% of the world’s crude oil28% of its natural gas

125 billion dollars

Sand and gravel estimated over 480 million dollars

Chapter 5 VocabularySilt- Sediment particle between 0.004 and 0.062 mm in diameterSand- Sediment particle between 0.062 and 2 mm in diameter.Clay- Sediment particle smaller than 0.004 mm in diameter the smallest sediment size category.Well-sorted sediments- A sediment in which particles are of uniform size.Poorly-sorted sediments- A sediment in which particles of many sizes are found.Terrigenous Sediments- Sediment derived form the land and transported to the ocean by wind and flowing water

Biogenous Sediments- Sediment of biological origin. Organisms can deposit calcareous (calcium-containing) or siliceous (silicon-containing) residue.Hydrogenous Sediments- A sediment formed directly by precipitation from seawater; also called authigenic sediment.Authigenic sediments- Sediment formed directly by precipitiaon from seawater; also called hydrogenous sediment.Cosmogenous sediments- Sediment of extraterrestrial origin.Microtektites- Translucent oblong particles of glass, a component of cosmosgenous sediment.Neritic sediments- Continental shelf sediment consisting primary of terrigenous material.Pelagic sediments- Sediments of the slope, rise, and deep-ocean floor that originate in the ocean.

Turbidites- A terrigenous sediment deposited by a turbidity current; typically, coarse-grained layers of nearshore origin interleaved with finer sediments.Siliceous Ooze- Ooze composed mostly of the hard remains of silica-containing organisms.Calcareous Ooze- Ooze composed mostly of the hard remains of organisms containing calcium carbonate.Foraminifera- One of a group of planktonic amoeba-like animals with a calcareous shell, which contributes to biogenous sediment.Pteropods- A small planktonic mollusk with a calcareous shell, which contributes to biogenous sediments.

Radiolarian- One of a group of usually planktonic amoeba-like animals with a siliceous shell, which contributes to biogenous sediments.Diatoms- Earth’s most abundant, successful, and efficient single celled phytoplankton. Diatoms possess two interlocking valves made primarily of silica. The valves contribute to biogenous sediments.Nodule- Solid mass of hydrogenous sediment, most commonly manganese or ferromanganese nodules and phosphorite nodules.Evaporite- Deposit formed by the evaporation of ocean water.Oolite sands- Hydrogenous sediment formed when calcium carbonate precipitates from warmed seawater as pH rises, forming rounded grains around a shell fragment or other particle.

Piston Corer- A seabed-sampling device capable of punching through up to 25 m (80 feet) of sediment and returning an intact plug of materialStratigraphy- The branch of geology that deals with the definitions and description of natural divisions of rocks; specifically, the analysis of rock strata.Paleoceanography- The study of the ocean’s past.Coccolithophores- A very small planktonic alga carrying discs of calcium carbonate, which contributes to biogenous sediment.Calcium Carbonate Compensation Depth (CCD)- The depth at which rate of accumulation of calcareous sediments equals the rate of dissolution of these sediments. Below this depth, sediment contains little or no calcium carbonate.

Clam shell sampler- A sampling device used to take shallow samples of the ocean bottom.Minerals- A naturally occurring inorganic crystalline material with a specific chemical composition and structure.Lithification- Conversion of sediment into sedimentary rock by pressure or by the introduction of a mineral cement.

Homework with in Chapter 5 - BookRead Chapter 5 take notesMake flashcards of vocab termsPg. 142 Review Questions – 1, 2, 3Pg. 142 Critical Thinking Questions – 1, 2