Definition, Formation, Classification Sedimentary Rocks Definition, Formation, Classification

Sedimentary Rocks: Outline Definition of a Sedimentary Rock How sedimentary rocks “fit in” the Rock Cycle Formation of a Sedimentary Rock Sediments and How They’re Made Lithification Classification of a Sedimentary Rock Three main types (and some subtypes)

Revisit the Rock Cycle http://www.washington.edu/uwired/outreach/teched/projects/web/rockteam/WebSite/rcycle.gif

Sedimentary Rocks: Definition Sedimentary rocks usually come from SEDIMENTS E.g., mud, sand, pebbles broken from previous rocks Sediments are pressed into layers “strata” (singular “stratum”) http://en.wikipedia.org/wiki/File:Geology_of_Cyprus-Chalk.jpg

Sedimentary Rocks: Formation Sediment usu. comes from two processes teaming up: Weathering Erosion Weathering weakens a rock chemically or physically Erosion tears away at a rock, starting to move sediment http://en.wikipedia.org/wiki/File:Toroweap_Sunrise_%2810727086534%29.jpg

Sedimentary Rocks: Weathering vs. Erosion http://en.wikipedia.org/wiki/File:Weathering_Limestone_State_College_PA.jpg http://en.wikipedia.org/wiki/File:Torre_Sant%27Andrea.jpg

Sedimentary Rocks: Weathering vs. Erosion ANOTHER JOEL BARTON ORIGINAL http://en.wikipedia.org/wiki/File:USA_10654_Bryce_Canyon_Luca_Galuzzi_2007.jpg

Sedimentary Rocks: Formation Ctd. Once sediments are settled, lithification (making a rock) begins Can involve two main processes: Compaction: sediments are pressed together by weight, and water is forced out Cementation: minerals deposit out of water and “cement” together sediments (Pictured in next slide)

Sedimentary Rocks: Formation Ctd. http://astro.wsu.edu/worthey/earth/html/im-geology/grain-compaction.gif

Types of Sedimentary Rocks: Clastic Clastic rocks from broken pieces of other rock (as was just described) Further classified according to their pieces (“clasts”) http://en.wikipedia.org/wiki/File:Conglomerate_Death_Valley_NP.jpg

Clastic Rocks ctd. Conglomerates have large, round, pieces (see previous slide) Poorly sorted Breccias have large, angular pieces Clastic rocks from smaller pieces can be sandstones, mudrocks, and more Usu. well sorted http://en.wikipedia.org/wiki/File:UpperTriassicYorkCountyPA.jpg http://en.wikipedia.org/wiki/File:Lower_antelope_2_md.jpg

Organic Rocks Form directly or indirectly from living material Despite our definition of minerals Example: limestone is calcium carbonate from the shells of dead sea organisms (clams, etc.) http://en.wikipedia.org/wiki/File:OrdOutcropTN.JPG

Chemical Rocks Form by chemical processes (not regular compaction) “Evaporites” form when water evaporates, leaving just minerals Ex: gypsum, halite, and even some limestone are from evaporating water http://en.wikipedia.org/wiki/File:Cristales_cueva_de_Naica.JPG

Check yourself What are some features of a rock that might indicate it is a sedimentary rock? In a clastic rock, why are some poorly sorted and others well sorted? (Just think on this.) What are two ways that limestone can form? How are chemical rocks different from other sedimentary rocks?