Changes in Ocean Geometry Over the Past Billion Years

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Changes in Ocean GeometryOver the Past Billion
Years
Ben Black. EPS 131 2004. Professor Tziperman.
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What Im talking about

• Through the machinery of plate tectonics,
  continents and oceanic plates move around the
  surface of the globe.
• The geometry of the oceans has changed vastly and
  repeatedly over time, as the plates move.

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A Brief Explanation of the Mechanisms of Change

• Plate movement driven by subduction and
  spreadingmainly oceanic plates.
• Continental plates are too light to subduct.
• Continents as scum floating on a pond.

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Changing Ocean Geometry Explains a Lot.

• Perhaps one of the most famous examples of
  changing ocean geometry is the growth of the
  Atlantic ocean. The Atlantic began to form about
  150 Ma, in the Mesozoic.

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Wegener and Plate Tectonics

• Wegener used similarities between South America
  and Africa to postulate continental drift.
• Combined with theories of subduction and
  sea-floor spreading, this became modern plate
  tectonics.

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And Now, the Meat Ocean Geometry Over the Past
Billion Years

• As we said before, continental material doesnt
  subduct. Thus it has been accreting for billions
  of years. The first continents would have
  accreted from volcanic islands rising out of a
  global ocean.

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Precambrian Collisions 1 Ba to 544 Ma

• There were many major supercontinents that formed
  and broke apart.
• About a Billion years ago, the supercontinent
  Rodinia began to fragment, forming the Pacific
  Ocean to the West of Laurentia (future North
  America) around 800 Ma, and also forming what
  would become Gondwanaland.

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Gondwanaland 500 Ma to 300 Ma

• The Gondwanaland and Laurentia formation was
  fairly stable and lasted about 200 My. But in the
  meantime, Gondwanaland drifted over the South
  Pole.

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The Significance of High Latitude Continents

• The formation of massive glaciers on top of
  Gondwanaland lowered sea level by at least 165
  feet.
• A tremendous marine mass extinction
• Shifts in currents and locations of deep water
  formationlittle known.

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Pangea255 Ma to 180 Ma

• Pangea was a true supercontinent, formed from the
  collision of Laurasia and Gondwanaland. There was
  even a massive inland sea, the Paleo-Tethys
  Ocean. It was not until after the breakup of
  Pangea in the middle Jurassic that the Atlantic
  began to form.

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The Breakup of Pangea and the creation of the
Modern Globe
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750 Ma to the Present
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Research Paper Paleogeographic reconstructions
and basins development of the Arctic

• By Golonka, Bocharova, Ford, Edrich, Bednarczyk,
  Wildharber
• Published 2003, in Volume 20 of the journal
  Marine and Petroleum Geology
• Major reconstruction project including 31 maps.
  Data from geology, stratigraphy fed into a plate
  tectonic model of about 300 plates to model
  evolution of Arctic Basin
• Verified by independent regional analysis

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Research Paper Paleogeographic Reconstructions
of the Arctic

• A Plate tectonic model tracing the evolution of
  the Arctic Ocean from 500 Ma to present
• A major Oceanthe Iapetusexisted roughly where
  the Arctic is now relative to other plates from
  482-438 Ma.
• Up to 200 Ma, the ocean then closed
  upreappearing around the same time as the
  Atlantic (163 Ma) at the north pole.
• Rifting of Arctic caused by Anui-Anvil Ocean
  subduction zonesnow gone, but around present-day
  Iceland.
• A very active region tectonically, with lots of
  volcanoes
• Several oceanic plates disappear (Izanagi) and
  appear (Kula) here.
• Until 133 Ma, still restricted circulation
  resulting in organic-rich shale depositsbut
  there is also strong upwelling, helping biologic
  activity. Thus some thermohaline circulation also
  possible in Barents?
• By 58 Ma, present form of Arctic easily
  recognizable, as encircling North America,
  Greenland, and Eurasia break apart. It officially
  becomes the Arctic around 55 Ma. It was only in
  the Eocene (55-34 Ma) that sea-floor spreading
  shifts from the West to the East of Greenland.

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