Carbonate Marine Facies Models
Types of carbonate shelves and platforms (Fig. 13.2, p. 464)
a. rimmed shelf - pronounced shelf break with reef growth
b. unrimmed shelf - pronounced shelf break with little to no
reef growth
c. ramp - no pronounced shelf break
d. isolated platform - steep pronounced shelf break with or without
reef growth
General Facies Model (Fig. 13.3, p. 465)
a. inner shelf
b. middle shelf
c. outer shelf (clinoforms)
d. basin
Carbonate production factory (Fig. 13.4, p. 466)
General Governing Principles
a. carbonates are born, not made
diversity and abundance of organisms with time
abundance (Fig. 13.5, p. 467)
composition (James diagram, Fig. 13.18, p. 485)
sediment composition (Tab. 13.1, p. 469)
b. dependence on sunlight (photic zone)
depth versus growth rate
maximum growth in the upper 10 to 20 m
c. adequately warm water, but upper temperature threshold
latitudinal control +/- 32o (Fig. 13.1, p. 462)
tropical and temperate carbonates (Australian and Ordovician)
foramol = temperate
chlorozoan = tropical
d. adequate nutrient supply, but upper concentration threshold
clear tropical waters are actually submarine deserts
e. during sea level rise, platform depositional patterns shift
abruptly; either:
backstepping (illustrate with profiles)
drowning
f. "bucket anatomy construction" (seafloor diagenesis)
wave-resistant margins
slump-resistant slopes
Modern Examples (follow handout)
a. isolated platform = Bahamas Banks
~700 x 300 km (comparable in size to ancient platforms)
geomorphology names (GBB, LBB, TOTO)
5000 m of Jurassic through modern carbonates
platform top < 7 m WD, surrounding basins = 5 km
sediment transport only significant at margins
lithofacies
beaches/rocky - high energy shorelines
tidal flats - intertidal/suprtidal
coralgal - moderate to high wave energy < 50 m WD
oolite - high wave energy < 3 m WD
oolite/grainstone - moderate wave energy winnows muds <10
m
muds/pellets - low wave energy < 4 m WD
grain flows and talus - poorly sorted 50 to > 3000 m WD
hemipelagic ooze and turbidites - > 3000 m
b. rimmed shelf = Florida Bay and the Florida Keys
c. ramp = Trucial Coast, Arabia
Ancient Examples
a. Sella Platform, Alpine Dolomites
b. Vercors Platform, French Alps
Vertical Sequences
a. upward-shallowing with tidal flat cap (Fig. 13.10, p. 474)
b. upward-shallowing with beach cap (Fig. 13.11, p. 475)
c. types of forereef-periplatform slope-basin transitions (handout)
depositional margins
bypass margins