GEOL 340 Sedimentology and Stratigraphy
Lecture 11
1. Carbonates: Composition
2. Carbonates: Classification
3. Diagenesis and Dolomitization
Carbonates: Composition
Geochemistry = Ca, Mg, C, O, Sr, Mn, Fe, B, Cu, Co. Cl
Mineralogy (Table 6.1, p. 172)
a. calcite = CaCO3 (rhombohedral) = more stable
b. aragonite = CaCO3 (orthohombic) = metastable polymorph
c. dolomite = CaMg(CO3)2 = most stable
Textures
grain = skeletal and nonskeletal
matrix (mud = micrite)
cement
porosity
Definitions
a. most carbonates are BORN or PRECIPITATED, not eroded and transported
b. allochthonous = transported into depositional site
c. autochthonous = formed and bound in place
Grain Types
a. lithoclasts
extraclasts
intraclasts
b. skeletal
foraminifera bivalves (pelecypods)
sponge spicules corals
bryozoans echinoderms
brachiopods algae
c. ooids
oolites
coated grains
d. peloids
silt to fine sand size micrite grains
e. aggregate grains
grapestones
Micrite (microcrystalline calcite)
matrix
cement
micrite envelopes (margins of grains)
Carbonates: Classification
Dunham Classification (Table 6.3, p. 185)
mudstone = matrix-supported and < 10% grains
wackestone = matrix-supported and > 10% grains
packstone = grain-supported and still contains matrix
grainstone = grain-supported with no matrix
boundstone = original components bound together in place
crystalline carbonate = extensive diagenesis recrystallized fabrics
Diagenesis and Dolomitization
Environments of Diagenesis (Fig. 6.14, p. 202)
Dolomitization and the Dolomite Problem (Fig. 6.11, p. 197)