Presentation on theme: "Sedimentary Rocks Sedimentary rocks form when weathered sediment is deposited and is lithified. –Review. What is: Sediment Weathering Deposition Lithification."— Presentation transcript:
Sedimentary Rocks Sedimentary rocks form when weathered sediment is deposited and is lithified. –Review. What is: Sediment Weathering Deposition Lithification
Formation of Sedimentary Rocks Lithification? –The process of cementing and/or compacting sediment together. In the lab we did the other day (sand and food), which one represented compaction and which one represented cementation and why? What is an evaporite? –Rocks that form after water has evaporated
Subclasses of Sedimentary Rocks What’s a subclass? Sedimentary rocks are sub-classified by the processes by which the rocks form and by the composition of the rocks. The three main sub-classes of sedimentary rocks are: –Clastic –Chemical –Organic
Clastic Sedimentary Rock Clastic is Latin for “broken.” Clastic sedimentary rocks form when fragments of preexisting rocks are compacted or cemented together Clastic sedimentary rocks are classified by the size and shape of the sediments they contain.
Sediment Size Sediment Shape Rock Name LargeRoundedConglomerate Small – LargeAngularBreccia SmallRoundedSandstone Very Small (clay or Mud Sized) Rounded and/or Angular Shale Classification of Clastic Sedimentary Rocks
Characteristics of Clastic Sediments The physical characteristics of sediments are determined by the how much weathering took place before lithification. –Lots of weathering = smaller and rounded sediment –Little weathering = larger and more angular sediment
Characteristics of Clastic Sediments The tendency for currents of air or water to separate sediments according to size is called sorting. –Happens during weathering and erosion –Well-sorted sediments, all of the grains are roughly the same size and shape. –Poorly sorted sediment consists of grains that are many different sizes.
Chemical Sedimentary Rocks chemical sedimentary rocks form when minerals precipitate (solid out of liquid) when water evaporates. When water evaporates, the minerals that were dissolved in the water are left behind. –What lab was this like? Rocks that form through evaporation are called evaporites. Rock gypsum and rock salt are common evaporites.
Organic Sedimentary Rocks organic sedimentary rocks form from the remains of plants or animals Coal and some limestones are examples of organic rocks (shell limestone, coquina, and chemical limestone). Organisms such as clams and coral make their shells from minerals. When the organism dies, their shells settle to the bottom of the ocean, accumulate, and are compacted and/or cemented to form limestone.
Organic Sedimentary Rocks The diagram below shows the formation of organic limestone.
Sedimentary Rock Summary Parent Material RockMineralsClass Round pebblesConglomerateAnyClastic Angular sedimentBrecciaAnyClastic SandSandstoneMostly quartzClastic ClayShaleMostly feldsparclastic Dissolved saltRock saltHaliteChemical Dissolved gypsumRock gypsumGypsumChemical Dead plants loosely compactedPeatOrganic Dead plants tightly compactedBituminous CoalOrganic Cemented shellsShell limestoneCalciteOrganic Compacted shellsCoquinaCalciteOrganic Dissolved shellsChemical limestoneCalcitechemical