Carbonate Rocks - PowerPoint

Document Sample
Carbonate Rocks - PowerPoint Powered By Docstoc
					Carbonate Rocks
• Carbonate rocks - limestones composed of
  calcite (CaCO3) or dolostones composed
  of dolomite (CaMgCO3).
• Form through biological and biochemical
  processes and through inorganic
  precipitation from seawater
• Carbonate rocks widespread and in every
  geological period beginning with Cambrian
Environment
• Most carbonate sediments form in
    warm waters
•   E.g., corals and algae common in
    carbonate rocks, and mostly found
    tropical to subtropical latitudes or
    from about 30o N and S latitudes
•   Most carbonate sediments
    generated in photic zone
•   Unlike sandstones, most
    carbonate grains formed in
    environment in which they are
    deposited
•   Detrital grains in sandstones
    usually derived from outside the
    environment in which they were
    deposited
Environment Continued
• Carbonate sediments
  do not usually occur
  below depths of about
  3500 -4000 meters in
  the oceans
• Below these depths
  carbonate sediments
  will dissolve
• The depths at which
  carbonate sediments
  dissolve in the ocean
  is called the carbonate
  compensation depth
  or CCD
Classification Scheme
• Two principal classification schemes used for limestones.
    – Folk's classification scheme, named after Robert Folk,
        • Dunham's classification scheme, named after Robert Dunham
• Folk's scheme based on presence or absence of
    allochems (carbonate particles or grains), matrix
    (limestone clay called micrite), and type of cement (spar
    is a cement composed of coarse xls)
•   Dunham's scheme based on texture of rock. i.e. whether
    rock contains matrix, whether carbonate grains float in
    matrix or whether they are in contact with each other,
    and whether rock has carbonate grains
Dunham’s Classification
• Based on whether have
    more or less that 10%
    grains
•   Whether rock is mud or
    grain supported.
•   Also if original
    components were bound
    together like coral.
•   Tells about transport
    history.
Folk Classification
• Carbonate rocks consits
    of:
    – Allochems—grains
    – Intersitial material—micrite
      or spar cement
• Micrite is "lime mud", the
    dense, dull-looking
    sediment made of clay
    sized crystals of CaCO3.
•   Spar—clear to translucent
    carbonate cement.
Micrite and Spar
Folk Continued
•   Name is built up by stringing together all the
    allochem names in order from least to most
    abundant, and then adding the interstitial material
    name ("matrix" below for short). For example, a
    rock like this:
    Oolites + Fossils + Spar matrix = Oo bio
    sparite
      The name is written as one word, Oobiosparite.
      Another example (again allochems from least to
    most abundant):
    Pellets + Oolites + Fossils + Micrite matrix =
    pel oo bio micrite
      The name is written as one word,
    Peloobiomicrite.
        But what if there is both micrite and spar
    matrix? The system is the same; just list them from
    least to most abundant.
    Fossils + Spar matrix + Micrite matrix = bio
    spar micrite
Carbonate Grains
• ooids--Ooids are
  spherical grains formed
  by calcite precipitation
  around a nucleus such as
  a shell fragment, a quartz
  grain, etc. They are less
  than 2mm in diameter
  and typically form in
  shallow, warm, agitated,
  and carbonate-saturated
  waters such as those
  near the Bahamas.
• pisolites--Pisolites
    are ooids greater than
    2mm in size
•   Similar environments
    as ooids
• stromatolites--Stromatolites are
   laminated carbonate sediments
   composed of mats of blue-green algae
   and layers of sediment. The algae,
   which forms the mats, is a plant and
   plants require sunlight to survive.
   Therefore, stromatolites generally form
   in warm shallow waters. The algae is
   "sticky" and it grows filaments. This
   sticky and filamentous algae traps
   sediment brought in by the currents.
   Consequently, a layer of algae forms
   then a layer of sediment is deposited
   on top of the algae. Subsequently, the
   algae grows through the sediment to
   form another mat and the cycle begins
   again. Ultimately, a layered rock
   composed of alternating algal mats and
   sediments is produced. Stromatolites
   form in quiet, hypersaline waters with
   little animal life around to destroy the
   mats.
• oncolites--
  Oncolites are
  stromatolites
  rolled in a ball.
• corals--Corals have a
  symbiotic relationship with
  dinoflagellate algae called
  zooanthellae. Algae are
  plants. Therefore, in order
  for corals to survive they
  generally have to be within
  the photic zone (the zone
  of maximum light
  penetration in the ocean).
  Plants require sunlight for
  photosynthesis. In the
  process of photosynthesis,
  plants produce oxygen and
  consume CO2. Corals are
  major reef formers today
  and in the past. However,
  keep in mind that some
  corals do occur in deep
  waters.
• Intraclasts--Semi-
  consolidated
  carbonate material
  ripped-up and
  incorporated in the
  rock.
• dolostone--A
 dolostone is a rock
 compose of 90-        Launch M icrosoft O ffice Outlook.lnk




 100% dolomite.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:155
posted:9/13/2012
language:English
pages:15