Geologic Setting of The Ocean

• Pangea


  Supercontinent that existed less than 100 million years ago, derived from the Greek pangaia meaning "all the Earth had existed"
• Formation of ocean basins


  1. Tectonic forces and processes cause the supercontinent Pangea to break apart

  2. Volcanic rock is released from fissures at mid-ocean ridges

  3. Oceanic lithosphere is forced to move under the mantle through subduction process and high gravitational energy

  4. Over years, four major ocean subdivisions are formed

  
• Major ocean subdivisions


  • North Pacific
  • South Pacific
  • North Atlantic
  • South Atlantic
  • Indian
  • Arctic

  
• Pacific Ocean basin

  • Largest, deepest, and oldest existing ocean basin
  • More trenches and more frequent tsunamis happen here
  • Shaped by plate tectonics

  
• Atlantic Ocean basin


  • Second largest ocean basin
• Indian Ocean basin


  • Third largest ocean basin
• Southern Ocean basin


  • Fourth largest ocean basin
• Arctic Ocean basin


  • Smallest of the earth's ocean basins, covered by ice
• Features and structures formed through ocean basin formation


  • Continental shelf
  • Continental slope
  • Continental rise
  • Abyssal plain
  • Island
  • Seamount
  • Trench
  • Mid-oceanic ridge

  
• Continental shelf


  Partly shallow extension of the continent underwater

  
• Continental slope


  Transition zone of continental shelf and deep ocean floor, starts from oceanic crust to continental crust

  
• Continental rise


  Where the ocean begins, all basaltic and oceanic rocks are found here, place where sediments from land are washed, continental margin starts from continental shelf up to continental rise

  
• Abyssal plain


  The flattest part of the ocean, 50% of the earth's surface is covered by this plain
• Island


  Part of the ocean basin that extends up from the ocean floor, not just a piece of land floating in the middle of the sea

  
• Seamount


  Undersea mountain, erosion caused by waves destroyed the top which caused it to be flattened
• Trench


  The deepest part of the ocean
• Mid-oceanic ridge


  Seafloor mountain system situated in the middle of the ocean basin, where upwelling of magma happens which causes the seafloor to spread

  
• The Earth's oldest rocks - around 3850 Ma old - include both water-lain sediments and evidence of ancient oceanic crust, indicating oceans have been forming since the beginning of the geological record, and probably before that

  
• No oceanic crust older than about 180 Ma is known from the present oceans

  
• As one ocean basin expands, another must have contracted, just as the Atlantic and Pacific are doing today

  
• Continents and ocean basins are continually changing their shapes and relative positions at rates that are geologically very rapid and are not slow even on human time-scales

  
• The speed of sea-floor spreading has been compared with that of growing fingernails
• Since the compilation of the first maps to cover any appreciable area of ocean, around five centuries ago, the Atlantic coasts have drawn apart from each other by about 10-20 m

  
• Spreading rates in parts of the Pacific are several times greater than in the Atlantic
• Wilson Cycle


  1. Explains the process of the opening (beginning) and the closing (end) of an ocean which is driven by Plate Tectonics

  2. Divided into 6 stages: Embryonic Ocean Basin, Juvenile Ocean Basin, Mature Ocean Basin, Declining Ocean Basin, Terminal Ocean Basin, Suturing

  
• Embryonic Ocean Basin (Stage A)


  Stable Continental Craton with a hot spot underneath, causes craton to swell upwards and continental crust to get thinner and crack, forming a small ocean in the middle

  
• Juvenile Ocean Basin (Stage B)


  Spreading of earth plates starts, a small ocean has formed between the newly broken up continents, continental edges cool down and sink below the newly formed sea

  
• Mature Ocean Basin (Stage C)


  A large ocean has formed between two continental margins, spreading still occurs, a well developed mid ocean ridge has formed along the divergent boundary

  
• Declining Ocean Basin (Stage D)


  A subduction zone has formed and the ocean begins to close up, one tectonic plate is subdued below another tectonic plate at a convergent boundary, eventually the ocean will disappear and all that is left is a remnant ocean basin

  
• Terminal Ocean Basin (Stage E)


  Continents are almost colliding, formation of magma happens deep in the subduction zone and small mountains are building up, metamorphism, folding and faulting occurs, the sea is narrow and irregular

  
• Suturing (Stage F)


  The two continents moving towards each other will collide and a mountain chain forms, eventually the mountains will erode down to a peneplain
• Panthalassa was the huge ocean that dominated one hemisphere, Pangea was the supercontinent in the other hemisphere, of which Eurasia and Gondwanaland were two components

  
• Ancient coastlines did not coincide with present-day coastlines
• Birth of a new ocean basin


  1. During crustal extension, the ductile lower part of the crust is stretched but the brittle upper part is rifted, blocks of crust slide down fault planes and sediments accumulate in the lakes and valleys

  2. When separation occurs, basaltic magma rises to fill the gap between the two continental blocks, the resulting new oceanic crust is both thinner and denser than continental crust so it lies below sea level

  3. The remainder of the lithosphere subsides by thermal contraction

  
• Panthalassa


  The huge ocean that dominated one hemisphere

  
• Pangea


  The supercontinent in the other hemisphere, of which Eurasia and Gondwanaland were two components
• The maps show present-day coastlines for ease of reference. Ancient coastlines did not coincide with these.

  
• Development of a new ocean basin


  1. Crustal extension

  2. Rifting of brittle upper crust

  3. Blocks of crust slide down fault planes

  4. Sediments accumulate in lakes and valleys

  5. Basaltic magma rises to fill gap between continental blocks

  6. New oceanic crust is thinner and denser than continental crust

  
• Evaporites


  Salt deposits that accumulate when seawater becomes wholly or partly evaporated
• Normal marine sedimentation


  Deposition of muds, sands and limestones, depending on local conditions