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Shallow/deep marine environments. Stratigraphic principles. Sequence stratigraphy ... major source of sediment for the deep sea, and is a setting where slumps ... – PowerPoint PPT presentation

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Title: Contents


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Contents
  • Introduction
  • Unconsolidated clastic sediments
  • Sedimentary rocks
  • Diagenesis
  • Sediment transport and deposition
  • Sedimentary structures
  • Facies and depositional environments
  • Glacial/eolian/lacustrine environments
  • Fluvial/deltaic/coastal environments
  • Shallow/deep marine environments
  • Stratigraphic principles
  • Sequence stratigraphy
  • Sedimentary basins
  • Models in sedimentary geology
  • Applied sedimentary geology
  • Reflection

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Shallow/deep marine environments
  • Shallow marine environments
  • Shallow seas can be subdivided into clastic and
    carbonate-dominated systems, depending mainly on
    sediment supply and climatic setting
  • Idealized models predict a general decrease of
    grain size with water depth (i.e., away from the
    shoreline) however, this simple picture is
    complicated by a large number of factors (e.g.,
    shelf bathymetry)

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Shallow/deep marine environments
  • Shallow marine environments
  • Storm-dominated clastic shelves ideally exhibit a
    transition from predominantly wave-rippled sands
    in the upper shoreface, to alternating sands and
    muds (tempestites with hummocky cross
    stratification) in the lower shoreface, to muddy
    facies below storm wave base
  • Tide-dominated clastic shelves may exhibit
    erosional features, sand ribbons, and sand waves
    with decreasing flow velocities, commonly
    associated with mud-draped subaqueous dunes
    tidal sand ridges (tens of m high, many km
    across) are characteristic of shelves with a high
    supply of sand
  • Bioturbation can obliterate many primary
    sedimentary structures in shelf environments

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Shallow/deep marine environments
  • Shallow marine environments
  • Shallow seas within the photic zone are the
    premier carbonate factories
  • Carbonate platforms can cover continental shelves
    or epicontinental seas, when the conditions for
    carbonate production (temperature, salinity,
    light conditions) are favorable
  • Isolated platforms (atolls) are found in shallow
    seas surrounded by deep water, like extinct
    volcanoes

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Shallow/deep marine environments
  • Shallow marine environments
  • Carbonate ramps exhibit processes and
    characteristics comparable to clastic shelves,
    with carbonate sands and muds ultimately
    producing a seaward transition from grainstone to
    mudstone, commonly with similar sedimentary
    structures
  • Rimmed carbonate shelves consist of a coral reef
    or carbonate sand barrier at some distance from
    the mainland the shelf lagoon can be up to many
    tens of kilometers wide
  • Boundstones dominate the reef facies
  • Shelf lagoon facies are mostly fine-grained and
    ultimately lead to the formation of mudstones and
    wackestones

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Shallow/deep marine environments
  • Deep marine environments
  • The continental slope is a major source of
    sediment for the deep sea, and is a setting where
    slumps can occur
  • Debris flows and turbidity currents are the main
    mechanisms of transport from the continental
    slope into the deep sea these processes can be
    triggered by external forcing (e.g., an
    earthquake) or by the slope reaching a critical
    state as a result of ongoing deposition
  • Debris-flow deposits and turbidites are often
    genetically related
  • Turbidites can be both clastic (commonly leading
    to the formation of wackes) or calcareous

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Shallow/deep marine environments
  • Deep marine environments
  • Submarine canyons at the shelf edge (commonly
    related to deltas) are connected to submarine
    fans on the ocean floor
  • Contrary to debris flows, turbidites exhibit a
    distinct proximal to distal fining
  • Submarine fans share several characteristics with
    deltas they consist of a feeder channel that
    divides into numerous distributary channels
    bordered by natural levees and are subject to
    avulsions
  • Proximal fan (trunk channel)
  • Medial fan (lobes)
  • Distal fan

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Shallow/deep marine environments
  • Deep marine environments
  • Basal Bouma-divisions have the highest
    preservation potential updip upper
    Bouma-divisions are more common downdip
  • Turbidite lobes characterize the medial fan and
    may exhibit the most complete Bouma sequences
  • The Bouma-model is increasingly challenged,
    because many turbidites do not conform to it
    (e.g., high-concentration turbidites)
  • Contourites are formed by ocean currents and
    commonly represent reworked turbidites

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Shallow/deep marine environments
  • Deep marine environments
  • Pelagic sediments primarily have a biogenic
    origin
  • Calcareous ooze (e.g., foraminifera) forms above
    the calcite compensation depth (CCD) at 4000 m
    depth
  • Siliceous ooze (e.g., radiolarians, diatoms)
    forms between the CCD and 6000 m depth where
    silica dissolves it lithifies into cherts
  • Hemipelagic sediments consist of fine-grained
    (muddy) terrigenous material that is deposited
    from suspension
  • Eolian dust is an important component (50) of
    hemipelagic (and pelagic) facies
  • Black shales have a 1-15 organic-matter content
    and form in anoxic bottom waters
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