Tidal Flats and Other Sedimentary Structures

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Tidal Flats and Other Sedimentary Structures
Associated with Tidal Currents
--Tavia Clark and JoDana Jones
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Structures Associated with Tidal Currents

• A) Herringbone cross--stratification the tide
  goes in the tide goes out causing a cross-bedding
  in opposite directions
• B) Reactivation surfaces--asymmetrical dune from
  the settling of suspended mud during slack tide
• C) Tidal Bundlesan ancient record of a whole
  sequence of mud draped sand packets that show the
  clear thickness of variations of spring and neep
  tides.

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As you move further away from the tidal channels
there is a proportions of sand increasing
proportions of Mud thus you have some changes in
structure

• Wavy Bedding
• Flaser Bedding
• Lenticular Bedding
• Mud Cracks and Salt Casts

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Wavy Bedding

• Roughly 50 sand and 50 Mud. Found in areas more
  distant from channels than flaser bedding.

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Flaser Bedding

• Sandy Beds in which mud-drapes often preserve
  part of the bed form. Often whole ripple shapes
  are preserved in cross-section by a bed of
  overlying mud, but more often the mud is eroded
  in the next current thus removing the ripple
  crests. The mud is thus more often preserved in
  the troughs and down current ripple sides.

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Lenticular Bedding

• Bedding sequence in which a layer comprised of
  mostly mud/silt has isolated lenses and ripples
  of sand.

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Mud Cracks

• Produced in a muddy environment when an area is
  periodically saturated. When the area dries out
  the mud cracks. The preservation of these cracks
  occurs when sediment is washed back over the area
  filling the cracks.
• Since the sediments are often different sized the
  cracks are often visible.

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Tidal Flats

• Definition- A broad flat, region of muddy or
  sandy sediment, covered and uncovered in each
  tidal cycle

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Where do we find Tidal Flats?

• They generally occur in gently sloping, marshy,
  and muddy featureless plains dissected by sandy
  tidal channels and creeks exposed during low
  tide.
• Found primarily along mesotidal- macrotidal
  coasts with LOW relief (to allow flooding no
  cliffs) and low wave energy (may be protected by
  dry land) estuaries, bays, back-barriers,
  deltas, and open coasts.

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3 main zones of tidal flats

• Sub tidal below mean low tide.
• a.) If flow is velocities are perfectly
  symmetrical, you may get cross-beds with
  herringbone stratification.
• b.) With Asymmetrical currents you may get x-beds
  are mostly in one direction.

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• 2. Inter tidal zone flooded and exposed once or
  twice a day.
• a.) Small distributary channels containing sand.
• b.) Traction Deposits may also be found
• c.) may see wavy, lenticular and flasier bedding
• d.) May have well sorted sediments

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• 3.) Super tidal zone flooded by spring tides or
  by seasonal storm surges
• a.) Common to see salt marsh vegetation or
  mangrove trees.
• b.) roots destroy bedding but peds often
  presence.

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Vertical Succession

• Tidal are generally preserved only when the area
  progrades.
• you must bury sediments to preserver them
• Criteria For recognition
• 1. Biomodal X bedding
• 2. Reactivation surfaces/tidal. Bundles flaser/
  wavy/ lenticular bedding.
• 3. Alternations between tidal channels sands to
  sandy muddy tidal flat deposits
• 4. Subaerial exposure evidence Mud cracks,
  raindrop imprints, animal tracks, evaporite
  minerals casts