1. Every stone a story, like a rosary. ---Joan Osborne
Sedimentary Rocks
Every stone a story, like a rosary.
---Joan Osborne

2. Weathering Mechanical & Chemical Weathering
The sediments that make up sedimentary rocks are produced by:
Mechanical & Chemical Weathering

3. Sedimentary Rocks and Processes
Clastic
Non-Clastic
Sediments are derived from fragments of pre-existing rocks (clasts).
All sedimentary rocks not composed of clasts
Categorized primarily by clast size
Categorized primarily by composition

4. e.g., conglomerate, breccia, sandstone, siltstone, shale
Clastic Rocks
Formed from clasts (bits and pieces of pre-existing rocks). The major processes in clastic rock formation are:
Weathering of clasts from pre-existing rock
Transport of clasts
Deposition of clasts
Lithification of clasts
clast size
Weathering processes continue to alter the clasts until deposition. In general, both physical and chemical weathering tend to make clasts smaller and rounder.
Sorting of clasts by size occurs mostly during transportation.
e.g., conglomerate, breccia, sandstone, siltstone, shale

5.
Wentworth Scale
Boulders
Cobbles
Gravel (pebbles)
Sand
Silt
Clay
Sedimentary clasts are classified by grain size (the size of the individual clasts) using the Wentworth Scale:
Larger clasts require more energy to transport
Smaller clasts require less energy to transport

6. Clast Sorting
The farther the clasts have traveled from the source, the more well sorted they tend to be.

7. Clast Rounding
As clasts are rolled around during transportation, sharp corners tend to be knocked off, and the clasts become more rounded the farther they are transported.
Angular grains are usually found only near the source rock.

8. Deposition

9. Proximal Depositional Environments
Near the source rock, the clasts have not experienced much physical or chemical weathering.
These areas contain poorly rounded and poorly sorted clasts.
Clasts composed of chemically unstable minerals (e.g., feldspar) are most common close to the source rock.

10. Distal Depositional Environments
Clasts experience both chemical and physical weathering as they are transported. Thus, the further they have traveled from the source the more altered the clasts are.
Distal areas contain well rounded and well sorted clasts. Large clasts (e.g., boulders) are rare (they have either been left upstream, or have weathered into smaller clasts).
Clasts composed of chemically unstable minerals (e.g., feldspar) are very rare in distal settings. Clay minerals derived from feldspars are common.

11. Clast size indicates ancient relative current velocity
weak
moderate
>=1.8 km/hr (strong currents)

16. Chemical Sedimentary Rocks
Clastic Sedimentary Rocks
Formed from clasts (bits and pieces of pre-existing rocks) transported, deposited,and lithified
Chemical Sedimentary Rocks
Formed from precipitation of minerals within the depositional basin. Includes biominerals, evaporites, coal, chert, etc.

17. Evaporites Siliceous Rocks Coal and Peat Carbonates
minerals precipitated from evaporating water
Siliceous Rocks
Silica and opalline silica precipitate either organically or inorganically
Coal and Peat
Carbon-rich deposits formed from build-up of plant material in swamps
Carbonates
Variety of limestones composed of calcite, aragonite, and dolomite precipitated either organically or inorganically

18. Carbonates - Limestone
Common Minerals:
Calcite CaCO3
Aragonite CaCO3
Dolomite (CaMg)CO3
Carbonates - Limestone
Biochemical (corals)
Bioclastic (chalk, coquina)
Inorganic – chemical precipitate
travertine
tufa
oolitic limestone
Corals and Snails

19. Chalk
Limestone formed from the microscopic calcite skeletons of tiny animals.

20. Siliceous Sedimentary Rocks
Microcrystalline quartz and opal precipitated from dissolved ions in sedimentary environments. Can be precipitated organically or inorganically.
Microcrystalline quartz can also precipitate in pore spaces to form cement.

21. Scanning Electron Micrograph (SEM) of tiny, siliceous skeletons of radiolarians, which are a source silica chert

23. normal marine salinity
Ionic Composition of Seawater
Na+ 10,556
Mg2+ 1,272
K+ 380
Ca2+ 400
Cations
parts per million
Cl- 18,980
(SO4)2- 2,649
(HCO3)- 140
Anions
Ions: 34,387 ppm
H2O: 965,613 ppm
35 o/oo
normal marine salinity
Total
Common Mineral Salts
KMgCl3•6H2O - Carnalite
MgCO3 - Magnesite
CaMg(CO3) - Dolomite
CaSO4 - Anhydrite
Other Mineral Salts
NaCl
- Halite
KCl
- Sylvite
CaSO4•H2O
- Gypsum

25. Fossil example of the past activity of organisms mixing sediment --- an example of fossil BIOTURBATION