GEOL 462: Principles of Sedimentology and Stratigraphy

Lecture 17: Tuesday, March 24, 2009

Topics
1. Occurrences of reefs and mounds
2. Reef and Mounds: Environments, Rock Types and Controls
3. Carbonate Slope Environments: Processes, Facies, and Examples

Occurrences of reefs and mounds
1. Platform margins: Barrier reefs
2. Shelf lagoons: patchy reefs and mounds
3. Carbonate banks: barrier reefs and patchy reefs
4. Reefs in ramps and eperic seas
5. Microbial (stromatolitic) shoal complexes

Reef and Mounds: Environments, Rock Types and Controls
1. Types of reefs: Coral reefs, Stromatoporiod reefs (S-D), and Microbial (alage, stromatolite,etc.) reefs;
2. Types of mounds: Skeletal mounds, mud mounds, microbial mounds;
3. Reef facies: Reef cores, Flanks, forereefs, backreefs;
4. Common types of reef rocks: Bafflestone, Bindstone, Framestone, Float stone, Rudstone; See page 28 of your textbook for the definition of these rock types;
5. Processes in reef environments:
a. Frame-making: framestones;
b. Encrusting: Cements, internal sediments;
c. Wave and Tidal activities: cross lamination, broken of reef-making organisms, winning of carbonate mud;
d. Gravity: Talus and debris flows in fore reef to slope
6. Reef development and sea level changes: Keep up, catch up and give up;
7. Carbonate Mounds:
a. Mostly from rock record; modern analogies are few;
b. Mostly occur in: downslope on gently dipping platform margins, deep basins, and in tranquil backreef lagoons or shelf areas;
c. Microbial mounds (cyanobacteria, true algae, diatoms, and authophs), Skeletal mounds (bryozoans, branching corals and stromatoporoids, akeletal algae, sponges, etc.); Mud mounds (relief of lime mud, containing variable fauna/flora);
d. Mounds can develop alone and never grow to a reasonable reef;
e. Mounds can grow into reefs, forming the base or core of the reefs in the first one or two stages, indicating the diversification of organisms (environmental control)

Carbonate Slope Environments: Processes, Facies, and Examples
1. Carbonate debris flows (Talus or Olistostrome blocks from platform margin)
2. Turbidites (normal graded bedding, Bouma sequences);
3. Pelagic or suspension deposits (carbonate mud, ooze, or shale);
4. Slumping structures and deformation;
5. Progradation sequences: from laminated, normally-gradded carbonate mud to turbidites, debris flow deposits, slump blocks, etc, to carbonate margin deposits (reefs rocks or sand shoal deposits);