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

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

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

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

http://www.glossary.oilfield.slb.com/ 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

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

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.

Deposition

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.

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. http://www.flmnh.ufl.edu/alligatorfund/potm-nov04.html http://www.ufz.de/index.php?de=5366

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

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.

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

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

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

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

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

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

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