Sedimentary Rocks Chemical Sedimentary Rocks Limestone Limestone Chert – Silica Chert – Silica...
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Transcript of Sedimentary Rocks Chemical Sedimentary Rocks Limestone Limestone Chert – Silica Chert – Silica...
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 SnailsCorals 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
EvaporationEvaporationH2O
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+ 10,556
Mg2+ 1,272
K+ 380
Ca2+ 400
Cations
parts per million
Ions: 34,387 ppmH2O: 965,613 ppm
35 o/oo normal marine salinity
Total
NaCl
Common Mineral Salts
KMgCl3•6H2O - CarnaliteMgCO3 - MagnesiteCaMg(CO3) - DolomiteCaSO4 - Anhydrite
Other Mineral Salts
Na Cl
- Halite
CaSO4•H2O
K
Cl
KCl - Sylvite
Ca
SO4
H2O
- Gypsum
Basin of Seawater
15 ft
Gypsum - CaSO40.5 ft.
Sylvite (KCl) and Mg-salts
Halite - NaCl11.8 ft.
1000 ft
EvaporationEvaporationH2O
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