GEOL 340 Sedimentology and Stratigraphy
Lecture 12
1. Evaporites
2. Travertines and Tufas
3. Cherts
4. Ironstones
5. Phosphorites
Evaporites (Tab. 7.1, p. 211)
= mineral deposits precipitated from saline solutions concentrated
by evaporation
handout on sequence of precipitation from evaporating seawater
Marine Evaporites
chlorides
halite
potash salts
sulfates
anhydrite
gypsum
potash salts
carbonates
calcite
dolomite
Examples:
shallow-water models = sabhkas and salinas
deep-water models = Messinian crissis in the silled Mediteranean
Nonmarine Evaporites
hydrated Na, Ca and Mg sulfates with little Cl
Examples = Great Salt Lake and Mono Lake
Travertines and Tufas
Composition
carbonate (aragonite and calcite)
siliceous
Types
Travertines (sinters) = subaerial eruption of spring waters
Mammoth Hot Springs, Yellowstone National Park
Tufas = subaqeous eruption of spring waters
Mono Lake, California
Organic versus Inorganic Controls
example of shrub fabrics
Cherts
Chemistry
more soluble at high temperature and high pH
Types
Primary - from dissolving skeletal material
sponges, radiolarians, diatoms, silicoflagellates
Diagenetic - from dissolved silica in groundwater or seawater
Ironstones
Composition
a. Fe-Oxides
b. Silicates
c. Carbonates
d. Sulfides
Types
ironstone - non-banded, non-cherty, Fe-rich
iron-formation - banded, cherty, Fe-rich
Phosphorites (>15 to 20% P2O5)
Composition
appatite - [Ca10CO3(PO4)]6
Types
a. bedded - Permian Phosphoria, Russian Craton
b. bioclastic - fish bones, shark teeth, coprolites
Origin
a. upwelling of deep ocean waters - cements and replacement
b. biologic utilization in soft body tissue