Carbonate platforms Flashcards
Give three chemical controls on carbonate deposition
Nutrient supply, salinity, oxygen
Give four physical controls on carbonate deposition
Light, turbulence, temperature, nature of substrate (hard/soft)
What is carbonate depostion primarily dominated by?
Biological acitivity
What are the three primary energy sources for carbonate precipitation?
Carbonate supersaturation, light, organic matter
Describe the transport of carbonate grains
Usually not transported any great distance
What is produced by carbonate supersaturation?
Non-skeletal grains, muds, microbes (ooids, stromatolites)
What is carbonate supersaturation controlled by?
High temperatures, high salinity, oceanic restriction
Describe whitings
Precipitation of aragonite in regions of elevated salinity
What factors control light availability?
Temperature, depth, transparency
What carbonate producers are allowed by light?
Photozoan (corals, green algae), symbiotic foraminifera, and red algae
What is the main controlling parameter of organic matter?
Food supply
What carbonate producer is energised by organic matter
Heterozoans
Give three examples of in situ carbonate build up by growth of skeletons of autotrophic organisms
Corals, algae, stromatoporoids
Give three sources of in situ carbon growth by heterotrophic organisms
Bryozoa, crinoids, bivalves
What leaves to high volumes of carbonate mud?
Growth of benthic algae
Where does 80% of modern carbonate depostion come from?
Deposited as carbonate ooze, derived from coccoliths and planktonic forams
Driven by photosynthesis by autotrophic organisms
Describe the role of benthic organisms in carbonate production
Deposit carbonates in shallow to deep marine environments
Dominated by heterotrophic organisms
How do platforms form?
In situ deposition of carbon
What are the three modes of production of carbonate platforms?
Tropical topmost water, cool-water-controlled precipitates, mud mound micrite
What are the four classification of carbonate platform?
Ramp, rimmed, epeieric, isolated
Where are the main settings for carbonate production?
Shallowest areas with waves and currents and the most photic energy
Describe a rimmed shelf
Shelf margin break, defined by reef growth or carbonate sandbodies
Zone of high organic productivity
e.g. Bahamas platform
Describe the shelf margin of a rimmed shelf
Ocean-facing, high energy, and turbulent
Why do carbonate sheleves have steep angles at the edge?
Competitive growth of coral
Describe a carbonate ramp
Shallow-dipping carbonate platforms
Subdivided on the basis of the influence of waves/storms on sedimentation
Describe the inner section of a carbonate ramp
This area is high energy and wave agitated, sand shoals can develop, offering landward protection from wave/storm energy
Describe the mid and outer ramp of a carbonate ramp
Sedimentation is frequently storm influenced in the mid ramp and infrequently storm-reworked in the outer ramp
Describe the basin of a carbonate ramp
Very low energy with negligible storm influence
Describe epeiric carbonate platforms
Deposited in epi-continental seas, no analogue today
Dominated by shallow water, storm-influenced, shallow subtidal-intertidal sedimentation
What conditions favour carbonate production?
Warm water, elevated salinity, protection from terrigenous influx
Describe high-energy platform margins
Reef growth (in situ carbonate build up)
Reworking by storms, currents (producing rubble)
Export to basin by gravity processes
Describe where oolite carbonate sand shoals are found
High energy locations
Depositional processes include in situ precipitation of ooids and reworking by tidal currents/storms/waves
Describe the back interior/lagoon
Low-energy
Depositional processes include accumulation of faecal pellets (worms/gastropods), chemical precipitation (e.g. whitings), disintegration of algae (mud)
Describe tidal flats
Land-attached areas
Depositional processes include reworking by tidal currents and waves and the movement of subtidal sediement onto tidal flat/into lagoon by storms
