Geology unit 2 - Carbonate deposits : Limestones

These revison cards were created to make understanding limestones easier, i Do Not take credit for these revison cards. All credit goes to my geology teachers and OCR specification notes.

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  • Created by: Rock
  • Created on: 10-04-12 11:03

Oolitic Limestone

  • Form in shallow seas, when grains of sand or shell fragments are rolled around by currents and accumulate a layer of calcium carbonate around the centre.
  • Due to the above, they are formed by Chemical Processes.
  • Only formed in strong currents, and only forms in hot climates in which, calcium carbonate is precipitated.

From hhtp://www.angelstarcreations.com (http://www.angelstarcreations.com/writings/rocks_minerals/rocks_files/image058.jpg)

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Fossiliferous Bioclastic or Shelly Limestone

  • Potentially 75% of the rock may be composed of invertebrate skeletons from crinoids, brachiopods or mixtures of fossils. (Gonna have to look those things up).
  • Rest of rock is calcite mud and ordinary detrial mud.
  • The rock has a grey colour and has easilly visable fossils.
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Reef limestone

  • Rich in corals and algea which build up the framework.
  • Form in warm, shallow tropical waters.
  • Are unbedded as they grow upwards.
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Chalk

  • Purest of the limestones, containing only a tiny amount of mud or sand.
  • White, hard, often massive and well jointed.
  • Mostly formed by the remains of a microscopic algae called a coccolith.
  • Formed in medium depth water (200m), note that landmasses contribute very little to the formation of chalk.
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Micrite

  • Fine, hard crystaline limestone, that shows no features.
  • Formed by purely calcite mud which has undergone diagenisis.
  • No fossils visable.
  • Formed in low energy, shallow water environments e.g. lagoons.
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