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Lecture 1 Reef Types and Formation PowerPoint Presentation
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Lecture 1 Reef Types and Formation

Lecture 1 Reef Types and Formation

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Lecture 1 Reef Types and Formation

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  1. Lecture 1 Reef Types and Formation

  2. Bonaire. N.A.

  3. Scope of the course Prevailing winds “Wild Side” Reef Mangrove

  4. Reef - any upthrusting substrate in the ocean (generally rock or coral)

  5. Carbonate Reefs -reefs comprised principally of CaCO3 (have been defined as “aquatic biosedimentary structures”) Formed by some creature Grow to form a reef Attacked by a number of physical and biological factors Change structure of original reef Fills in original reef and becomes cemented Generates sediment Disperse away from original reef Hydromechanical build-up

  6. Carbonate Reefs -reefs comprised principally of CaCO3 (have been defined as “aquatic biosedimentary structures”) Primary Framework Reefs Mud mounds

  7. Problems in Classification of Carbonate “Reefs” Matrix Cavity + cement In-place skeletons

  8. Problems in Classification of Carbonate “Reefs” Ecological abilities of organisms to build reefs Differences in rate and nature of construction and destruction of a reef Changes in sedimentation, temperature & salinity Wave energy Sea level changes Development of different reef types

  9. Classification of Carbonate Reefs Points of agreement • carbonate reefs owe their origin to biological secretion of CaCO3 • rigid structures that stand above the ocean floor • exert some control on local oceanographic processes • historically, reef-builders are in several different taxonomic groups

  10. Classification of Carbonate Reefs Points of Disagreement • centred on the ‘framework’ of a reef • a ‘true’ reef  in-place and organized interlocking meshwork of skeletons providing rigidity

  11. Problems in Classification of Carbonate “Reefs” Sea level 2 Sea level 1 -high rates of sediment accumulation, infilling -sediment flushing, less infilling 10’s of kms.

  12. Classification of Carbonate Reefs Points of Disagreement • centred on the ‘framework’ of a reef Ancient Reefs Carbonate mass - recognizable organisms but loosely packed and in detrital matrix

  13. Coral Reef - compacted and cemented assemblage of skeletons and skeletal sediment of sedentary organisms living in warm marine water with strong illumination

  14. 100% Displaced Framework 2º Framework Reef Baffling Increasing Secondary Encrusters and Cement Sedimentary Buildup Reefs Mud mounds, stromatolites 1º Framework Reef Sand bars,Spits Hydromechanical Build-Up 100% In-place Framework % Sediment

  15. Types of Coral Reefs Atolls - ring or horseshoe shaped

  16. Types of Coral Reefs Atolls -

  17. Types of Coral Reefs 2. Fringing Reefs - built on margins of land

  18. Types of Coral Reefs 2. Barrier Reefs - Separated from land

  19. Comparison of the three types of reefs -form at the edge of land mass -form around volcanoes • stand offshore separated from land by lagoon -outer edge is upturned

  20. Patch Reef -isolated coral community - often in lagoon

  21. Submerged Shelf Edge Reef

  22. Summary - Major Reef Types

  23. Comparison of the types of reefs Type Shape Location Emergent? Lagoon Fringing Linear Near shore yes < 500 m wide < 5 m deep Barrier Linear Dictated by yes > 500 m wide oceanography > 5 m deep Atoll Circular Platform margin yes central: deep Patch Reef ≈ Equant Lagoon can be N/A Shelf Edge Linear At shelf edge no N/A

  24. How are reefs formed? Atolls as an example

  25. Lyell - 1832 - Principles of Geology -Formation of Atolls -corals grew on submerged volcanoes

  26. R.A. Daly- 1910 - Glacial Control Theory

  27. Darwin - 1840’s Theory of Volcanic Subsidence

  28. Growth of an Atoll

  29. Drilling at Enewetok Atoll

  30. Drilling at Eniwetok Atoll Why????

  31. Drilling at Enewetok Atoll Drill core Coral skeleton matrix (CaCO3) Igneous (volcanic) rock Ca. 1400 m

  32. Atoll Structure limestone & dolomite (CaCO3) volcanic rock

  33. In the process of atoll formation, the three kinds of reefs grade into one another