Sediments. What to Watch for? You will see the true face of the ocean floor Covered by sediments,...
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Transcript of Sediments. What to Watch for? You will see the true face of the ocean floor Covered by 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
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 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
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
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?)
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
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
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
Piston CorerDevice capable of punching through as much as 25 m of sediment and returning an intact plug of material
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
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.