Earth s Seafloors. Ocean Basins and Continental Margins. Introductory Oceanography Ray Rector - Instructor

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1 Earth s Seafloors Ocean Basins and Continental Margins Introductory Oceanography Ray Rector - Instructor

2 OCEAN BASINS and CONTINENTAL PLATFORMS Key Concepts I. Earth s 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 regions Shallow continental margins Deep-sea oceanic basins III. Continental margins and Deep Ocean basins are fundamentally different Composition Structure Age Tectonic origin IV. Ocean basins are rugged and have a wide variety of topographic features Mid-oceanic ridges and Transform fracture systems Abyssal Hills and Plains Oceanic islands, Seamounts, and Guyots Trenches and Island Arcs

3 Marine Provinces

4 Earth s Solid-Surface Topography

5 Topography of Earth s Ocean Basins

6 Topography of Pacific Ocean Basin

Mean depth of ocean = 4 km below sea level 6.

7 Elevation Relief Profile of Earth Surface 1. Sea level 2. Continental shelf 3. Continental slope 4. The deep ocean floor 5. Mean depth of ocean = 4 km below sea level 6. Mean altitude of land = 1 km above sea level 7. Mt. Everest = 8848m 8. Marianas Trench = 11022m

8 Seafloor-Shoreline Mapping Methods

9 Four Principle Methods of Mapping the Ocean Bottom 1. Ship-based Sonar 2. Satellite-based Radar 3. Ship-based Seismic Reflection 4. Submersible Survey

10 Means of Mapping the Ocean Bottom Sonar

11 Means of Mapping the Ocean Bottom Satellite Radar Use of space-based radar to reflect off ocean surface, giving a very precise sea surface profile; sea surface profile anomalies closely mimic the underlying seafloor profile

12 Means of Mapping the Ocean Bottom Seismic Reflection Use of underwater explosions to penetrate seafloor with seismic waves that reflect back, providing a subsurface image

13 Means of Mapping the Ocean Bottom Deep Sea Drilling Use of underwater drilling to penetrate seafloor and recover core samples of seafloor down to depths of over 3000 meters

14 Two Primary Types of Earth Crust Oceanic Continental

15 Earth s Continents and Seafloors 1) 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.)

16 Cross Section: Oceanic Crust 1) Mafic-rich layers of rock made of olivine, pyroxene, calcium plagioclase and magnetite. 2) Formed at spreading centers 3) Ocean crust obducted onto continental edges called Ophiolite complexes 4) Worldwide, oceanic crust is fairly simple in structure and composition

17 Cross-Section Profile of an Ocean Basin Large-Scale 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

18 Cross-Section of the North Atlantic Ocean Basin

19 AGE OF EARTH S OCEAN BASINS

20 AGE PROFILE OF NORTH AMERICA Tectonic Provinces of North America: (Ages are in Billions of Years)

21 Continental Margins of the World Submerged continental margins are shown in pale orange color

Subdued coastline Little to no tectonic activity No Plate Boundary

22 Two Types of Continental Margins Passive = Constructive = Atlantic Type Active = Destructive = Pacific Type Passive Margins Broad shelves Subdued coastline Little to no tectonic activity No Plate Boundary Active Margins Narrow shelves Rugged coastline Tectonically active Plate Boundary

23 Active versus Passive Margins Excellent Example: South America Active = West Coast Passive = East Coast

24 Continental Margin Features Major Features Continental Shelf Continental Slope Slope Break Continental Rise Submarine Canyons

25 Turbidity Sedimentation

26 Passive Continental Margin Example: Eastern Siberia -- Arctic Ocean Basin

Plains Seamounts and Guyots Oceanic Islands and

27 Earth s Deep-Sea 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

28 Deep Ridges and Rises

Active faulting and volcanism Sea bottom is covered by rugged bedrock of

29 Mid-Ocean Ridge, Rises & Fracture Systems Key Points Mid-ocean ridge systems represent the most extensive chain of active mountains on Earth Active faulting and volcanism Sea bottom is covered by rugged bedrock of young pillow basalt Little to no pelagic sediment Site of active hydrothermal vents

Mid-Ocean Ridge and Fracture Systems Key Points

covered by rugged bedrock of young pillow basalt

30 Mid-Ocean Ridge and Fracture Systems Key Points Mid-ocean ridge systems represent the most extensive chain of active mountains on Earth Active faulting and volcanism Sea bottom is covered by rugged bedrock of young pillow basalt Little to no pelagic sediment Site of active hydrothermal vents

31 Mid-Ocean Ridge Hydrothermal Vents

32 Seamounts, Islands, and Tablemounts Excessive basaltic volcanism at spreading centers create seamounts and islands along mid-ocean ridge. Over time, seamounts and islands move off the elevated ridges and into deeper and deeper water as oceanic crust becomes older, cooler, denser Eroded flat-topped islands eventually sink below sea level to become tablemounts or guyots. Tops of guyots deeper with distance from ridge Seamounts, and guyots eventually become buried beneath thickening pelagic sediment pile to become part of the abyssal plains and hills

of seamounts sticking out Abyssal plains and hills cover the most extensive tracts of ocean

33 Abyssal Plains and Hills Key Points Thick pelagic sediment covers a rugged subsurface bedrock of basalt Abyssal plains are the flattest, most featureless provinces on Earth Abyssal hills are tops of seamounts sticking out Abyssal plains and hills cover the most extensive tracts of ocean seafloor Subsurface imaging of abyssal plains and hills from seismic reflection studies and deep sea drilling

34 Abyssal Plains and Hills Key Points Abyssal sediments are predominately clays and oozes Soft pelagic sediment is loaded with benthic organisms Benthic organisms crawl over and and burrow through the sediment = Bioturbation

35 PLATE TECTONICS and the SEAFLOOR Seafloor Spreading Subduction Transform Faulting Continental Rifting and Collision Hot Spots

36 Seafloor Ridge and Trench Map

Earth Processes That Create Seafloor Features Continental Margins 1) Features

Oceanic Basins 1) Features generated by Seafloor Spreading Mid-Ocean Ridges

generated by Subduction Trenches and Island Arcs Forearc Islands 3) Features

37 Earth Processes That Create Seafloor Features Continental Margins 1) Features resulting from Continental Rifting Continental Shelf and Slope Deep-Sea Oceanic Basins 1) Features generated by Seafloor Spreading Mid-Ocean Ridges and Fracture Systems Oceanic Islands, Seamounts and Plateaus 2) Features generated by Subduction Trenches and Island Arcs Forearc Islands 3) Features resulting from Sedimentary processes Abyssal Plains and Hills Continental Rises Submarine Canyons

38 OCEAN BASINS and CONTINENTAL PLATFORMS Summary of Concepts I. Earth s 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 regions Shallow continental margins Deep-sea oceanic basins III. Continental margins and Deep Ocean basins are fundamentally different Composition Structure Age Tectonic origin IV. Ocean basins are rugged and have a wide variety of topographic features Mid-oceanic ridges and Transform fracture systems Abyssal Hills and Plains Oceanic islands, Seamounts, and Guyots Trenches and Island Arcs

39 OCEAN BASINS and SEAFLOORS Discussion

40 Seafloor Sediments Shallow Underwater Carbonate Sand Dunes - Bahamas

41 Ocean Basins are Vast Sinks for Sediment

42 Two Major Types of Marine Sediment Depositional Environments Shallow Margin = Littoral and Neritic Deep Sea = Pelagic Littoral Pelagic Neritic

43 Seafloor Sediment Provinces Cross-Section Profile of an Ocean Basin Continental shoreline = Littoral Province Continental shelf = Neritic Province Continental slope to rise = Transitional All deep sea regions = Oceanic or Pelagic

Four Compositional Types of Seafloor Sediments 1.

wind-blown dust Material: Gravels, Sands, Silts, and Clays 2.

hard parts Material: Calcareous and Siliceous Oozes 3.

Material: Carbonates, Metal Oxides and Sulfides 4.

44 Four Compositional Types of Seafloor Sediments 1. Terrigenous Sources: Erosion of land; volcanic eruptions; wind-blown dust Material: Gravels, Sands, Silts, and Clays 2. Biogenous Sources: Organic; accumulation of plant and animal hard parts Material: Calcareous and Siliceous Oozes 3. Hydrogenous Sources: Precipitation of minerals from solution Material: Carbonates, Metal Oxides and Sulfides 4. Cosmogenous Sources: Extraterrestrial dust and meteorites Material: Tektite particles, Glassy spheres, Silicate dust

45 Type and Locality of Marine Sediments

46 Marine Sediment Sampling Methods Bucket-Scooping Piston Coring Submersible Drilling

47 Marine Sediment Sampling Tools Camel Grab Drill Core Box Core Piston Core

48 Core Sample Processing and Analysis

49 Marine Sediment Sampling Locations

50 Terrigenous Sediments Sources: Erosion of land; volcanic eruptions; wind-blown dust; icebergs Material Comp: Quartz, Feldspar, Mica, Amphibole, Fe Oxide, & Clays Material Size: Cobbles, Gravels, Sands, Silts, and Clays Ash from volcanic eruptions Sediment from rivers Wind-blown material Sediment-filled glacial ice flows

51 Biogenous Sediments Sources: Carbonate reefs; Benthic shelled-animals; Plankton Material Comp: Calcium carbonate and Silica Material Size: Gravel, Sand, Silt, and Clay Coral and Sponge Reefs Benthic shelled-animals Microscopic Plankton

52 Type and Locality of Marine Sediments

53 Continental Margins of the World Seafloor that includes shoreline, continental shelf and slope Submerged continental margins are shown in pale orange color

54 Continental Margin Settings Seafloor that includes shoreline, continental shelf and slope

Organic carbonate and silica materials of marine life skeletons from reefs and sea bottom habitats Carbonate, silica and phosphate seawater

55 Shallow Marine Sediments Key Points 1) Shallow marine sediments that deposit along shorelines and offshore shelf are termed littoral and neritic 2) Coast and shelf sediments are of two types: Land-derived inorganic rock and mineral fragments of gravel, sand, silt, and clay Organic carbonate and silica materials of marine life skeletons 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 turbidity currents moving down submarine canyons

56 Deep Ocean Basins of the World Deep seafloor excluding the continental shelf and slope From continental rise to mid-ocean ridge

57 Key Points Deep Marine Sediments 1) Deep ocean sediments are termed pelagic 2) Pelagic sediments are predominately very fine-grained 3) Two types of pelagic sediments Inorganic clays from land Biogenic oozes from plankton 4) Two types of biogenic oozes Calcareous Siliceous 5) Abundant benthic organisms crawl over and burrow through the sediment = Bioturbation

58 Calcareous 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) foraminifera cocolithophores

shallow, low- to mid-latitude regions of deep

59 Distribution of Calcareous Ooze Sediments 1) Calcareous oozes principally deposit in relatively shallow, low- to mid-latitude regions of deep ocean 2) Concentrated on tops and flanks of mid ocean ridges

60 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

61 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

62 Comparing Silica and Carbonate Oozes

63 Types of Hydrogenous Sediment Sources: Precipitation of minerals from solution Material: Carbonates, Metal Oxides and Sulfides Black Smoker Chimneys Manganese Nodules

64 Types of Cosmogenous Sediment Sources: Extraterrestrial rock, dust,and debris Material: Silicates, glass, and metals Microtektites Tektite Strewn Fields

65 Type and Distribution of Marine Sediments

66 Percentage Distribution of Pelagic Sediments 1) Calcareous Oozes = covers 48% of deep seafloor 2) Abyssal Clays = covers 38% of deep seafloor 3) Siliceous Oozes = covers 15% of deep seafloor

67 Rates of Deposition of Marine Sediments

68 Total Sediment Thickness in Ocean

69 MARINE SEDIMENTS Discussion

Marine Sediments. Introductory Oceanography. Ray Rector: Instructor

Marine Sediments. Introductory Oceanography. Ray Rector: Instructor Marine Sediments Introductory Oceanography Ray Rector: Instructor Ocean Basins are Vast Sinks for Huge Amounts of Sediment from Numerous Different Sources Four Major Types of Seafloor Sediments 1. Lithogenous