1. Carbonates & Carbonate
Carbonates Platforms
Carbonate production
Carbonate Platforms
Carbonate Buildups
Sequences
Carbonate Production Carbonate Production
“Carbonate Factory”: Climate
Shallow, illuminated seafloor Evaporation, precipitation
Particles of all sizes: skeletons, mud Clastic sediment supply
(direct or biologically mediated Fauna: cool water: Foramol assemblage
precipitation) warm water: Chlorozoan assemblage
Much sediment accumulates “in place”, Oceanography
but some transported landward (peritidal Light penetration
flats/shoreline) or basinward (slope and
Water temperature, circulation
basin margin)
Oxygenation
Removed from siliciclastic sedimentation
Salinity
Carbonate Production Carbonate Platforms
Tectonics Ramp, Shelf, Bank, Epeiric
Rate and style of subsidence Rimmed or unrimmed
Terrigenous sediment supply Sediment texture a function of energy
level and carbonate production
Many different facies models (energy
level, temperature, platform
morphology, platform energy,
siliciclastic input, etc.)

2. Terms: Terms:
Ramp Basin Bank Basin Shelf Ramp Basin Bank Basin Shelf
Platform Platform
Platform: Platform:
• a large edifice formed by the accumulation of sediment • Shelf: Platform linked to an adjacent landmass, and
in an area of subsidence “distally steepened”
• Generally flat topped, with steep sides, many 100s of • Ramp: Shelf that dips gently (<1 deg. basinward)
km2 in extent without a break in slope
• Bank: Isolated platform cut off from terrigenous clastics
• Epeiric platform: flooded cratonic areas
Carbonate Platforms Vertical Successions
Rimmed platforms Unrimmed platforms
Barrier reefs/shoals – high energy zones Wave energy dissipated over entire
Grainstones, bafflestones, framestones
platform
Back-barrier areas – variable energy
Gradational facies boundaries
Skeletal/ooid grainstone shoals
Packstones, wackestones Outer shelf – low energy (mudstones)
Evaporites? (restricted circulation) “Inner shelf” (shoreface) – high energy
Patch reefs (framestones, boundstones) (grainstones)
Shoreline – low energy
Boundstones, rudstones, evaporites

3. Shoaling-upward succession:
High-energy carbonate shelf
Vertical Successions
Vertical succession depends on:
Platform/shelf morphology
Energy level (waves)
Rimmed versus unrimmed Regression
Climate (temperature, precipitation)
Sea-level change (sequence stratigraphy)
Shoaling-upward successions
common
Transgression
Like siliciclastic shelf/shoreline systems
Shoaling-upward succession:
Low-energy carbonate shelf
Regression
Transgression

4. Paradox Group
Pennsylvanian “glacioeustatic” sea level changes
?~100 m over ~105 years
Paradox Basin
• “Ancestral
Rocky Mtns”
to NE
• Deposition
close to
Equator
• (Semi)
restricted
basin
Carbonate Buildups
Reef (Boggs):
“Any biologically influenced buildup of
carbonate sediment which affected
deposition in adjacent areas (and thus
differed to some degree from surrounding
sediments), and stood topographically
higher than surrounding sediments during
deposition” (Longman, 1981)
Ordovician Platform Carbonates – Montreal Area
Buildups Through the Ages Carbonate Buildups
Mounds: “Biogenic mounds”
Modern reefs:
• Microbial*
Barrier reefs – platform margins • Stromatolites/thrombolites, calcimicrobes,
Fringe reefs – adjacent to shoreline mud
Atolls – around tops of seamounts • Skeletal*
Patch reefs, pinnacle reefs, table reefs – • Organisms control trapping
shelf margins or middle shelf • Small “reef builders”, calcareous algae,
bryozoa, spiculate sponges, brachiopods,
rudist bivalves
• Mud
• Inorganic accumulation with some fossils

5. Carbonate Buildups
Bioherm:
Lens-shaped reef or mound
Biostrome:
Tabular body
Carbonate buildup
No compositional, size or shape
connotation
“Stratigraphic
Facies/Processes
reef”: stacked
mounds, never Core facies
had much relief Massive, unbedded carbonate, with or
without skeletons
Flank/forereef facies
“Ecologic reef”: Bedded carbonate sand and conglomerate
Was a of in situ or derived material
topographic Dips and thins away from core
feature
Interreef/open platform facies
Subtidal deposits (carbonate/clastic)
unrelated to reef growth

6. Narrow rimmed shelf - Bahamas Barrier Reef – corals - Bahamas
Barrier reefs
Shoreline
Reef
Back
Patch reefs
~ 400 m
Reef front – Red Sea Reef front – Red Sea
Reef crest – Red Sea Back Reef – Red Sea

7. Grass-stabilized open shelf sediment – back reef Patch reef – water depth < 1m – back reef
Dunes of oolitically coated peloids Cross-bedded Pleistocene grainstones
Leduc Formation
Upper Devonian
Sabkha

8. Permian Reef Complex – West Texas
Marine cement
Sponge
Encrusting algae

9. Buildups Through the Ages
Cenozoic
Reef-building organisms have changed
through time
Sedimentological roles of reef-building
organisms haven’t changed
Siluro-Devonian
Early Proterozoic
Sequence Stratigraphy Sequence Stratigraphy
Carbonate systems are similar to Carbonate systems are similar to
clastic systems, but: clastic systems, but:
1. Carbonate production is commonly 2. Carbonate platforms accumulate at/near
greater than rate of creation of sea level, therefore they are excellent
accommodation (relative sea level rise). indicators for interpreting changes in
During highstands carbonate produced on relative sea level.
platform tops can be shed into adjacent
deep water “highstand shedding”
Sequence Stratigraphy Sequence Stratigraphy
Carbonate systems are similar to Carbonate systems are similar to
clastic systems, but: clastic systems, but:
3. Aggradational margins more common in 4. “Drowning unconformity” can be
carbonate systems: keep-up response to produced by (rapid) increase in water
depth – shuts down carbonate factory.
relative sea level rise. Clastics tend to Surface may be onlapped and
backstep. downlapped by other sediments (e.g.,
deepwater clastics). Recognizable in
outcrop/core (“abrupt deepening”) and
seismic data (resembles a sequence
boundary)

10. Sequence Stratigraphy
Carbonate systems are similar to
clastic systems, but:
5. Platforms exposed during lowstand, but
chemically eroded carbonates do not
generate much carbonate debris for
resedimentation as submarine fans on
basin floor
Summary Summary
Carbonates represent in situ Different types of carbonate platforms
generation of sediment Shelves, banks, ramps
Climate Rimmed or unrimmed
Oceanography Platform morphology affects wave
Tectonics energy dissipation/facies distribution
Sediment Supply Vertical successions commonly show
Organism Biology shoaling upward trends
“Carbonate factory” – shallow, Some like clastic shelf/shoreline systems
illuminated seafloor, low (no) Not always “coarsening upward”
siliciclastic supply Many types of successions possible

11. Summary Summary
Various types of “carbonate buildups” Nature of reef-building organisms has
Reefs changed through time
Mounds Stromatoporids, corals, sponges, bivalves,
Bioherms etc.
Biostromes Sedimentological role of reef-building
3 different sub-environments: organisms has not changed
Reef core
Reef flank
Inter-reef
Summary
Sequence stratigraphic character of
carbonate systems has
similarities/differences with clastic
systems