Lecture 1 Reef Types and Formation

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

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

16. 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

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

18. Types of Coral Reefs Atolls -

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

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

21. 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

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

23. Submerged Shelf Edge Reef

24. Summary - Major Reef Types

25. 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

26. How are reefs formed? Atolls as an example

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

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

29. Darwin - 1840’s Theory of Volcanic Subsidence

30. Growth of an Atoll

31. Drilling at Enewetok Atoll

32. Drilling at Eniwetok Atoll Why????

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

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

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