ocean basins and continental marginsseascisurf.com/seafloors.pdf · and islands along mid-ocean...
TRANSCRIPT
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