Chemical sedimentary rocks
Evaporites: Rock salt, rock gypsum
Limestone: most common chemical sed rock
made of calcite
90% biochemical (from organisms)
10% of limestone inorganically precipitated.
Chert: from organisms that have silica shells, and inorganic precipitation
Coal: chemical sedimentary rock formed from land plants
Oil and gas –Formed from marine organic matter,
- both buried and heated (concentrates H and C)
Detrital Sedimentary Rocks
Sediments are eroded, transported, and deposited by:
wind,glaciers,mass movement, water
Clues about history:
1. Grain size: tells about energy of erosion, transport.
Deposition occurs when energy drops.
2. Rounding: tells about type and distance of transport
3. Sorting: tells about type and distance of transport
4. Fossils (remains or traces of organisms): tell about deposition
and age
5. sedimentary structures
a. bedding
b. crossbeds
c. mudcracks
d. ripple marks
Lithification: sediment becomes
rock
Compaction: fluid squeezed out
Cementation: new minerals precipitated between particles
Names of detrital sedimentary rocks
Clay and silt (flour sized) form Mudstone/shale
Sand (size of pinhead) forms Sandstone
Gravel (rounded) forms Conglomerate
Angular gravel forms Breccia