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EarthEarth’’s Seafloorss SeafloorsOcean Basins and Continental MarginsOcean Basins and Continental Margins

Introductory OceanographyIntroductory OceanographyRay Rector - Instructor

OCEAN BASINS and CONTINENTAL PLATFORMSOCEAN BASINS and CONTINENTAL PLATFORMSKey ConceptsKey Concepts

I. EarthI. Earth’’s rocky surface covered by of two types of crusts rocky surface covered by of two types of crust Dense, thin, low-standing oceanic crust Light, thick, high-standing continental crust

II. Seafloor is divided into two topographic regionsII. Seafloor is divided into two topographic regions Shallow continental margins Deep-sea oceanic basins

III. Continental margins and Deep Ocean basins are fundamentallyIII. Continental margins and Deep Ocean basins are fundamentally differentdifferent Composition Structure Age Tectonic origin

IV. Ocean basins are rugged and have a wide variety of topographIV. Ocean basins are rugged and have a wide variety of topographic featuresic features Mid-oceanic ridges and Transform fracture systems Abyssal Hills and Plains Oceanic islands, Seamounts, and Guyots Trenches and Island Arcs

Marine ProvincesMarine Provinces

EarthEarth’’s Solids Solid--Surface TopographySurface Topography

Topography of EarthTopography of Earth’’s Ocean Basinss Ocean Basins

Topography of Pacific Ocean BasinTopography of Pacific Ocean Basin

Elevation Relief Profile of Earth SurfaceElevation Relief Profile of Earth Surface1. Sea level1. Sea level

2.2. Continental shelfContinental shelf

3. Continental slope3. Continental slope

4. The deep ocean floor4. The deep ocean floor

5. Mean depth of ocean5. Mean depth of ocean

= 4 km below sea level= 4 km below sea level

6. Mean altitude of land6. Mean altitude of land

= 1 km above sea level= 1 km above sea level

7. Mt. Everest = 8848m7. Mt. Everest = 8848m

8. Marianas Trench8. Marianas Trench

= 11022m= 11022m

SeafloorSeafloor--Shoreline Mapping MethodsShoreline Mapping Methods

Four Principle Methods ofFour Principle Methods ofMapping the Ocean BottomMapping the Ocean Bottom

2. Satellite2. Satellite--based Radarbased Radar1. Ship1. Ship--based Sonarbased Sonar

3.3. ShipShip--based Seismic Reflectionbased Seismic Reflection4. Submersible Survey4. Submersible Survey

Means of MappingMeans of Mappingthe Ocean Bottomthe Ocean Bottom

SonarSonar

Means of Mapping the Ocean BottomMeans of Mapping the Ocean BottomSatellite RadarSatellite Radar

Use of space-based radar to reflect off ocean surface,giving a very precise sea surface profile; sea surface profileanomalies closely mimic the underlying seafloor profile

Means of Mapping the Ocean BottomMeans of Mapping the Ocean BottomSeismic ReflectionSeismic Reflection

Use of underwater explosions to penetrate seafloor withseismic waves that reflect back, providing a subsurface image

Means of Mapping the Ocean BottomMeans of Mapping the Ocean BottomDeep Sea DrillingDeep Sea Drilling

Use of underwater drilling to penetrate seafloor and recovercore samples of seafloor down to depths of over 3000 meters

Two Primary Types of Earth CrustTwo Primary Types of Earth Crust

Oceanic Continental

EarthEarth’’s Continents and Seafloorss Continents and Seafloors1) Two Different Types of Crust

Continental – Granitic rock Oceanic – Basaltic rock

2) Continental Crust Lighter (2.7 g/ml) Thicker (30 km) High Standing (1 km elev.)

3) Oceanic Crust Denser (2.9 g/ml) Thinner (7 km) Low Standing (- 4 km elev.)

Cross Section: Oceanic Crust1) Mafic-rich layers of rock

made of olivine, pyroxene,calcium plagioclase andmagnetite.

2) Formed at spreadingcenters

3) Ocean crust obductedonto continental edgescalled “Ophiolite” complexes

4) Worldwide, oceanic crustis fairly simple in structureand composition

CrossCross--Section Profile of an Ocean BasinSection Profile of an Ocean Basin

LargeLarge--Scale Ocean Bottom FeaturesScale Ocean Bottom Features Continental shelf, slope, and rise

Abyssal plains and hills

Mid-ocean ridge and rift valley

Oceanic islands, seamounts, and guyots

Ocean trench

CrossCross--Section of the NorthSection of the NorthAtlantic Ocean BasinAtlantic Ocean Basin

AGE OF EARTHAGE OF EARTH’’S OCEAN BASINSS OCEAN BASINS

AGE PROFILE OF NORTH AMERICAAGE PROFILE OF NORTH AMERICA

Tectonic Provinces of North America: (Ages are in Billions of Years)

Continental Margins of the WorldContinental Margins of the World

Submerged continental margins are shown in paleorange color

Passive MarginsPassive Margins Broad shelves

Subdued coastline

Little to no tectonicactivity

No Plate Boundary

Active MarginsActive Margins Narrow shelves

Rugged coastline

Tectonically active

Plate Boundary

Two Types of Continental MarginsTwo Types of Continental Margins PassivePassive = Constructive = Atlantic Type= Constructive = Atlantic Type ActiveActive = Destructive = Pacific Type= Destructive = Pacific Type

Active versus Passive MarginsActive versus Passive MarginsExcellent Example:South America

Active = West CoastActive = West Coast

Passive = East CoastPassive = East Coast

Continental Margin FeaturesContinental Margin FeaturesMajor FeaturesMajor Features Continental Shelf

Continental Slope

Slope Break

Continental Rise

Submarine Canyons

TurbidityTurbiditySedimentationSedimentation

Passive Continental Margin

Example: Eastern Siberia -- Arctic Ocean Basin

EarthEarth’’s Deeps Deep--Sea Basin FeaturesSea Basin Features Mid-Oceanic Ridge, Rises and

Transform Fracture Systems

Abyssal Hills and Plains Seamounts and Guyots Oceanic Islands and Plateaus Trenches and Island Arcs

Profile: North Atlantic Ocean Basin

Deep Ridges and Rises

Mid-Ocean Ridge, Rises & Fracture Systems MidMid--ocean ridge systemsocean ridge systemsrepresent the most extensive chainrepresent the most extensive chainof active mountains on Earthof active mountains on Earth

Active faulting and volcanismActive faulting and volcanism

Sea bottom is covered by ruggedSea bottom is covered by ruggedbedrock of young pillow basaltbedrock of young pillow basalt

Little to no pelagic sedimentLittle to no pelagic sediment

Site of active hydrothermal ventsSite of active hydrothermal vents

Key PointsKey Points

Mid-Ocean Ridge and Fracture Systems MidMid--ocean ridge systemsocean ridge systemsrepresent the most extensive chainrepresent the most extensive chainof active mountains on Earthof active mountains on Earth

Active faulting and volcanismActive faulting and volcanism

Sea bottom is covered by ruggedSea bottom is covered by ruggedbedrock of young pillow basaltbedrock of young pillow basalt

Little to no pelagic sedimentLittle to no pelagic sediment

Site of active hydrothermal ventsSite of active hydrothermal vents

Key PointsKey Points

Mid-Ocean Ridge Hydrothermal Vents

Seamounts, Islands, and Tablemounts

Excessive basaltic volcanism at spreading centers create seamouExcessive basaltic volcanism at spreading centers create seamountsntsand islands along midand islands along mid--ocean ridge.ocean ridge.

Over time, seamounts and islands move off the elevated ridges aOver time, seamounts and islands move off the elevated ridges and intond intodeeper and deeper water as oceanic crust becomes older, cooler,deeper and deeper water as oceanic crust becomes older, cooler, denserdenser

Eroded flatEroded flat--topped islands eventually sink below sea level to becometopped islands eventually sink below sea level to becometablemounts or guyots. Tops of guyots deeper with distance fromtablemounts or guyots. Tops of guyots deeper with distance from ridgeridge

Seamounts, and guyots eventually become buried beneath thickeniSeamounts, and guyots eventually become buried beneath thickeningngpelagic sediment pile to become part of the abyssal plains and hpelagic sediment pile to become part of the abyssal plains and hillsills

Abyssal Plains and Hills

Thick pelagic sedimentThick pelagic sedimentcovers a rugged subsurfacecovers a rugged subsurfacebedrock of basaltbedrock of basalt

Abyssal plains are theAbyssal plains are theflattest, most featurelessflattest, most featurelessprovinces on Earthprovinces on Earth

Abyssal hills are tops ofAbyssal hills are tops ofseamounts sticking outseamounts sticking out

Abyssal plains and hillsAbyssal plains and hillscover the most extensivecover the most extensivetracts of ocean seafloortracts of ocean seafloor

Key PointsKey Points

Subsurface imaging of abyssal plains and hills from seismic refSubsurface imaging of abyssal plains and hills from seismic reflectionlectionstudies and deep sea drillingstudies and deep sea drilling

Abyssal Plains and Hills Abyssal sediments areAbyssal sediments arepredominately clays and oozespredominately clays and oozes

Soft pelagic sediment isSoft pelagic sediment isloaded with benthic organismsloaded with benthic organisms

Benthic organisms crawlBenthic organisms crawlover and and burrow throughover and and burrow throughthe sediment = Bioturbationthe sediment = Bioturbation

Key PointsKey Points

PLATE TECTONICS and the SEAFLOORPLATE TECTONICS and the SEAFLOOR Seafloor Spreading

Subduction

Transform Faulting

Continental Rifting and Collision

Hot Spots

Seafloor Ridge and Trench MapSeafloor Ridge and Trench Map

Earth Processes That Create Seafloor FeaturesContinental Margins

1) Features resulting from Continental RiftingContinental Rifting Continental Shelf and Slope

Deep-Sea Oceanic Basins1) Features generated by Seafloor SpreadingSeafloor Spreading

Mid-Ocean Ridges and Fracture Systems

Oceanic Islands, Seamounts and Plateaus

2) Features generated by SubductionSubduction Trenches and Island Arcs

Forearc Islands

3) Features resulting from Sedimentary processesSedimentary processes Abyssal Plains and Hills

Continental Rises

Submarine Canyons

OCEAN BASINS and CONTINENTAL PLATFORMSOCEAN BASINS and CONTINENTAL PLATFORMSSummary of ConceptsSummary of Concepts

I. EarthI. Earth’’s rocky surface covered by of two types of crusts rocky surface covered by of two types of crust Dense, thin, low-standing oceanic crust Light, thick, high-standing continental crust

II. Seafloor is divided into two topographic regionsII. Seafloor is divided into two topographic regions Shallow continental margins Deep-sea oceanic basins

III. Continental margins and Deep Ocean basins are fundamentallyIII. Continental margins and Deep Ocean basins are fundamentally differentdifferent Composition Structure Age Tectonic origin

IV. Ocean basins are rugged and have a wide variety of topographIV. Ocean basins are rugged and have a wide variety of topographic featuresic features Mid-oceanic ridges and Transform fracture systems Abyssal Hills and Plains Oceanic islands, Seamounts, and Guyots Trenches and Island Arcs

OCEAN BASINS and SEAFLOORSOCEAN BASINS and SEAFLOORSDiscussionDiscussion

Seafloor SedimentsSeafloor SedimentsSeafloor Sediments

Shallow Underwater Carbonate Sand Dunes - Bahamas

Ocean Basins are Vast Sinks for SedimentOcean Basins are Vast Sinks for Sediment

Two Major Types of Marine SedimentTwo Major Types of Marine SedimentDepositional EnvironmentsDepositional Environments

Shallow Margin = Littoral and Neritic

Deep Sea = Pelagic

NeriticPelagic

Littoral

Seafloor Sediment ProvincesSeafloor Sediment Provinces

Continental shoreline = Littoral Province

Continental shelf = Neritic Province

Continental slope to rise = Transitional

All deep sea regions = Oceanic or Pelagic

CrossCross--Section Profile of an Ocean BasinSection Profile of an Ocean Basin

Four Compositional TypesFour Compositional Typesof Seafloor Sedimentsof Seafloor Sediments

1. TerrigenousTerrigenous Sources: Erosion of land; volcanic eruptions; wind-blown dust

Material: Gravels, Sands, Silts, and Clays

2. BiogenousBiogenousSources: Organic; accumulation of plant and animal hard parts

Material: Calcareous and Siliceous Oozes

3. HydrogenousHydrogenous

Sources: Precipitation of minerals from solution

Material: Carbonates, Metal Oxides and Sulfides

4. CosmogenousCosmogenous Sources: Extraterrestrial dust and meteorites

Material: Tektite particles, Glassy spheres, Silicate dust

Type and Locality of Marine SedimentsType and Locality of Marine Sediments

Marine Sediment Sampling MethodsMarine Sediment Sampling Methods

Piston Coring

Bucket-Scooping

Submersible

Drilling

Marine Sediment Sampling ToolsMarine Sediment Sampling Tools

Camel Grab Box Core

Drill Core Piston Core

Core Sample Processing and AnalysisCore Sample Processing and Analysis

Marine Sediment Sampling LocationsMarine Sediment Sampling Locations

Terrigenous SedimentsSources: Erosion of land; volcanic eruptions; wind-blown dust; icebergsMaterial Comp: Quartz, Feldspar, Mica, Amphibole, Fe Oxide, & ClaysMaterial Size: Cobbles, Gravels, Sands, Silts, and Clays

Sediment from rivers

Ash fromvolcaniceruptions

Wind-blown material Sediment-filled glacial ice flows

Biogenous SedimentsSources: Carbonate reefs; Benthic shelled-animals; PlanktonMaterial Comp: Calcium carbonate and SilicaMaterial Size: Gravel, Sand, Silt, and Clay

Coral andSpongeReefs

Microscopic PlanktonBenthic shelled-animals

Type and Locality of Marine SedimentsType and Locality of Marine Sediments

Continental Margins of the WorldContinental Margins of the World

Seafloor that includes shoreline, continental shelf and slope

Submerged continental margins are shown in pale orangecolor

Continental Margin SettingsContinental Margin Settings

Seafloor that includes shoreline, continental shelf and slope

Key Points1) Shallow marine sediments that deposit along shorelinesand offshore shelf are termed littoral and neritic

2) Coast and shelf sediments are of two types:

Land-derived inorganic rock and mineral fragments ofgravel, sand, silt, and clay

Organic carbonate and silica materials of marine lifeskeletons from reefs and sea bottom habitats

Carbonate, silica and phosphate seawater precipitates

3) Shelf sediments mostly arrive via rivers

4) Coastal sediments may reach deep waters via turbiditycurrents moving down submarine canyons

Shallow Marine SedimentsShallow Marine SedimentsShallow Marine Sediments

Deep Ocean Basins of the World

Deep seafloor excluding the continental shelf and slope

From continental rise to mid-ocean ridge

1) Deep ocean sediments are1) Deep ocean sediments aretermedtermed pelagicpelagic

2) Pelagic sediments are2) Pelagic sediments arepredominately very finepredominately very fine--grainedgrained

3) Two types of pelagic sediments3) Two types of pelagic sediments Inorganic claysInorganic clays –– from landfrom land

Biogenic oozesBiogenic oozes –– from planktonfrom plankton

4) Two types of biogenic oozes4) Two types of biogenic oozesCalcareousCalcareous

SiliceousSiliceous

5) Abundant benthic organisms5) Abundant benthic organismscrawl over and burrow throughcrawl over and burrow throughthe sediment =the sediment = BioturbationBioturbation

Key PointsKey Points

Deep MarineDeep MarineSedimentsSediments

Calcareous Ooze SedimentsCalcareous Ooze Sediments Accumulation of calcium carbonate hard parts from dead microscopic plankton

Mainly consists of cocolithophores and foraminifera tests

Calcite-shelled plankton abundant in warmer surface waters

Accumulate above the Carbonate Compensation Depth (CCD)

cocolithophoresforaminifera

Distribution of Calcareous Ooze Sediments

1) Calcareous oozes principally deposit in relativelyshallow, low- to mid-latitude regions of deep ocean

2) Concentrated on tops and flanks of mid ocean ridges

Silica Ooze Sediments Accumulation of silica hard parts from dead plankton

Mainly consists of diatoms and radiolarian tests

Abundant in deeper, cooler surface waters – high latitude

Silica Ooze Sediments Accumulation of silica hard parts from dead plankton

Mainly consists of diatoms and radiolarian tests

Abundant in cooler surface waters – high latitude

Comparing Silica and Carbonate OozesComparing Silica and Carbonate Oozes

Types of Hydrogenous Sediment Sources:Sources: Precipitation of minerals from solution

Material:Material: Carbonates, Metal Oxides and Sulfides

ManganeseNodules

Black SmokerChimneys

Types of Cosmogenous Sediment Sources:Sources: Extraterrestrial rock, dust ,and debris

Material:Material: Silicates, glass, and metals

Tektite Strewn Fields

Microtektites

Type and Distribution of Marine Sediments

Percentage Distribution of Pelagic Sediments

1) Calcareous OozesCalcareous Oozes = covers 48% of deep seafloor

2) Abyssal ClaysAbyssal Clays = covers 38% of deep seafloor

3) Siliceous OozesSiliceous Oozes = covers 15% of deep seafloor

Rates of Deposition of Marine SedimentsRates of Deposition of Marine Sediments

Total Sediment Thickness in OceanTotal Sediment Thickness in Ocean

MARINE SEDIMENTSMARINE SEDIMENTSDiscussionDiscussion