Sedimentary Rocks

Chemical Sedimentary Rocks Limestone Chert – Silica Evaporites Organic Rocks

Coal Oil and natural gas

Clastic Sedimentary RocksFormed from clasts (bits and pieces of pre-existing rocks) transported, deposited,and lithified

Chemical Sedimentary RocksFormed from precipitation of minerals within the depositional basin. Includes

biominerals, evaporites, coal, chert, etc.

Chemical Sedimentary Rocks

http://csmres.jmu.edu/geollab/Fichter/SedRx/chembiokey.html

Evaporites 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

CarbonatesVariety of limestones composed of calcite, aragonite, and dolomite precipitated either organically or inorganically

Corals and Snails

Common Minerals:Calcite CaCO3

Aragonite CaCO3

Dolomite (CaMg)CO3

Carbonates - Limestone Biochemical (corals)

Bioclastic (chalk, coquina) Inorganic – chemical precipitate

travertine tufa oolitic limestone

Limestone

Unlike other chemical sedimentary rocks, limestone is usually formed from loose sediment similar to clastic sediment. These kind of limestone are sometimes called bioclastic.

It is therefore relatively easy to mistake limestone for a clastic rock unless you perform an acid test. Carbonates will react with acid; clastic sediments will not.

Calcite and aragonite react energetically with rather weak acid. Dolomite will react sluggishly, and usually needs to be ground up to see a reaction with weak acid.

Snails

Some algae precipitate aragonite flakes and needles as skeletons. When they die, the skeletal bits become sand-

and mud-sized carbonate sediment.

http://www.turtles.org/

http://seis.natsci.csulb.edu/bperry/Sedimentary%20Rocks%20Tour/biochemical_sedimentary_rocks.htm

Lime mudstone - limestone with mud-sized carbonate grains. Comes in many different colors, and frequently contains fossils.

http://www.geo.mtu.edu/FIELD_TRIPS/florida/

http://www.ndc.edu/stones/newpage16.htm

Fig. 06.22a

Underwater dunes formed from carbonate sediment

Stony corals precipitate sometimes massive aragonite skeletons, which break up to form boulder- to mud-sized carbonate sediment.

Fringing coral reef around a island. As the volcanic island sinks, the coral growth keeps up, eventually forming a coral atoll.

http://earthobservatory.nasa.gov/Library/Coccolithophores/

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

Shell CoquinaShells cemented together with little or no matrix

http://www.dep.state.fl.us/geology/geologictopics/rocks/anastasia.htm

Inorganic CarbonatesLimestone precipitated from dissolved ions in water, including:

Seawater

Hot springs

Groundwater

Evaporating basins

Pore water

http://www.thermopolis.com/

Dissolved Solids in Thermopolis Hot Spring

Total Dissolved Solids 2373 Nitrate (NO3) 10Hydrogen Sulfide (H2S) 4.5 Strontium 20“Hardness” (CaCO3) 1274 Lithium 2Thorium less than 0.6 Barium 2Bicarbonate (HCO3) 755 Aluminum 1Silica (SiO2) 82 Chromium traceIron (Fe) 03 Calcium (Ca)Lead 0.004 Boron 0.56Magnesium (Mg) 76 Manganese 0.02Sodium (Na) 262 Titanium 60Potassium (K) 49 Zinc 2Sulfate (SO4) 760 Tungsten 0.01Chloride (Cl) 328 Vanadium 0.1 Fluoride (F) 3.7 Copper trace

http://www.diskworks.com/octoberopals/opal1.html

Siliceous Sedimentary RocksMicrocrystalline 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.

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

Fig. 06.23a

Chert nodules

common occurrence of chert in other sedimentary rocks (this is limestone)

Bedded Chert Another common mode of occurrence in sedimentary deposits.

Evaporites

Minerals (halite, gypsum, sylvite etc.) precipitated from dissolved ions in basins from which water is evaporating.

Evaporite Production

1000 ft

EvaporationH2O

H2O H2O

Example: Minerals formed from dissolved ions as seawater evaporates

Ionic Composition of Seawater

Cl- 18,980(SO4)2- 2,649

(HCO3)- 140

Anions

Na+ 10,556Mg2+ 1,272K+ 380Ca2+ 400

Cations

parts per million

Ions: 34,387 ppmH2O: 965,613 ppm

35 o/oo normal marine salinity

Total

NaCl

Common Mineral SaltsKMgCl3•6H2O - CarnaliteMgCO3 - MagnesiteCaMg(CO3) - DolomiteCaSO4 - Anhydrite

Other Mineral Salts

Na Cl

- Halite

CaSO4•H2O

K

Cl

KCl - Sylvite

Ca

SO4H2O

- Gypsum

Basin of Seawater

15 ft

Gypsum - CaSO40.5 ft.

Sylvite (KCl) and Mg-salts

Halite - NaCl11.8 ft.

1000 ft

EvaporationH2O

H2O H2O

2.6 ft.

As the water evaporates, the ions become more concentrated, and different minerals precipitate.

http://speclab.cr.usgs.gov/PAPERS.calibration.tutorial/

Shores of the Great Salt Lake, Utah

http://geoinfo.nmt.edu/education/litegeology/images/coal.gif

CoalSedimentary rock formed from the remains of plant material

Coal comes in various grades, depending on the amount of post-depositional alteration:

Peat

Lignite

Bituminous coal

Anthracite (a metamorphic rock)

http://www.fmnh.org/

Coal is formed from swamp deposits

It is derived from woody plants

The buried material is compressed and heated in the Earth, driving off the water, increasing the carbon content.

Higher carbon content = higher grade fuel

Coal almost always contains pollution-causing impurities.

coal bed

Oil and Natural Gas

Formed when microscopic organisms die and accumulate in an area of low oxygen, preserving organic matter.

When sediments are compacted and heated, organic matter is transformed into hydrocarbons, producing oil and natural gas.

http://www.sohoblues.com/GulfWarWeb/previewpages/previewpage5.htm