Factors favouring carbonate growth

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Factors favouring carbonate growth

• 1. No clastic input
• 2. Warm water
• 3. High biologic productivity
• 4. Shallow water (photic zone)
• 5. Low latitude, shallow water
• Platform and ramps

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Walthers law

• In a prograding (building towards the sea) system
  (like our carbonate factory in Bar al-Hikman) we
  find in a vertical sequence reef-facies placed
  on top of upper slope facies, upper slope facies
  placed on top of lower slope facies etc. In
  nature we find that reefs are situated next to
  the upper slope and the upper slope is situated
  next to the lower slope. This is what Walther
  formulated as a law. (He assumed continious
  deposits, i.e, no erosion).

If this is a prograding system (see text) you
would in a vertical succession see B on top of C
and A on top of B
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Example of carbonate factory
Shelf margin
Upper slope
Lower slope
Basin
Shore zone
Sabkha
Lagoon
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Basin

• Does not belong to the carbonate factory per ce,
  but the basin is filled with products created by
  the factory.(i.e gets its input from the factory)
  as well as from microorganisms living in the
  ocean. (These m.o secrets carbonate).
• Below storm wave base (SWB)? There is no flow
  regime in the basin? small particles like
  carbonate mud (who would elsewhere be kept in
  suspension) settles on the basin floor.
• Both siliciclastics and carbonate turbidites
  associated with basin floor fans occur, but is
  very fine-grained.

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Lower slope

• Is above the storm weather base
• Mud layers deposited because of low energy
  regime
• Turbidite deposits mostly fine sediment fraction
  and low channel relief because the turbidites are
  dying out towards the basin (far from the basin ?
  only fine particles still suspended). Some extra
  large turbidites may take coarse material further
  out than usual giving this fraction in some of
  the turbidite deposits.
• The coarse fraction comes from storms which
  swash coarser material far from its usual
  habitat, which is further up the slope.
• Rocks that form from this geomorphic environment
  could be packstones, wackestones and mudstones.

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Upper slope

• The upper slope is located right below the reef
  (or the shelf margin), and gets its input from
  wave break-off and/or erosion of the reef/shelf
  margin.
• The products of the erosion is transported to the
  upper slope by mega breccia debris flows and
  coarse grained siliciclastic and carbonate
  turbidites.
• We also find algal mounds (lumps created by/with
  algae)in the upper slope along with pack- wacke-
  and mudstones.

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Shelf margin

• High energy flow regime (subjected to waves and
  tidal currents) ? reef deposistion of coarse
  sediment fraction
• Reef
• waveresistant framework (formed by carbonate
  secreting organisms)
• Components
• Framework organisms
• Internal sediments
• Bio eroders
• Cement
• Rocks formed from this geomorphic environment can
  be grainstone, bindstone and packstone

Typical carbonate reef
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8
Lagoon

• Protected by reefs or barrier islands.
• Influenced by tidal- and storm regimes.
• A lot of biologic activity in form of
  brachiopodes (small crabs),algae
  mats,sulfate-bacterias etc.
• Could be a very good source for H.C, but is
  seldom preserved.

Lagoon, BarAl Hikman, Oman
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Shore zone

• Influenced by both wind and waves (high flow
  regime) ? mostly homogenous material (beach sand
  and other fragments from the carbonate factory
  eolian dunes)
• Storm deposits high up on the beach (from waves
  throwing material higher up than usual)
• The shore zone forms a crest (natural high) and
  we often have a sabkha or a lagoon behind it.
• This geomorphic environment often gives
  grainstones (contains no mud)

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Sabkha

• Sabkha means salt flat.
• We find sabkhas in areas where the evaporation
  far exceeds the average rainfall pr year.
• We separate between coastal and continental
  sabkhas, where coastal sabkhas are influenced by
  marine waters and continental is influenced by
  freshwater aquifers.
• When water evaporates in a dry climate, salt is
  precipitated. As the space diminish, the salt
  crack in hexagonal shapes and grows towards
  eachother.

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11
Dunhams classification
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