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Download 6.3 Sedimentary Rocks PPT
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Sedimentary Rx pages 548-557 http://www.fi.edu/fellows/payton/rocks/create/sediment.htm For thousands, even millions of years, little pieces of our earth have been eroded-broken down and worn away by wind and water. These little bits of our earth are washed downstream where they settle to the bottom of the rivers, lakes, and oceans. Layer after layer of eroded earth is deposited on top of each. These layers are pressed down more and more through time, until the bottom layers slowly turn into rock. Sedimentary rock is Most common rock at Earth's surface Thin blanket over 2/3 of the surface covering igneous and metamorphic rocks Fossils are often found in sedimentary rock. Ammonite Fossil fish Sedimentation Volcanism builds new rocks Weathering breaks them down into sediments Two types of weathering: Mechanical and Chemical Mechanical weathering breaks rock into smaller pieces Three ways Frost wedging Root wedging Gravity Mechanical weathering increases the surface area of the rock exposed to chemical weathering 2. Chemical Weathering Chemical Reactions with water dissolve rock H2O + CO2 H2CO3 Water and carbon dioxide yields carbonic acid This is what dissolves limestone and makes caves Erosion Erosion--movement of seds What can move it? (Agents of erosion) Wind Water Ice The larger the sediment the harder it is to move Deposition— seds are deposited When deposited sediment accumulates, it begins to transform into sedimentary rock Two types of sedimentary rocks Clastic Made of bits and pieces of recycled rock Chemical Form by precipitation or evaporization Called Precipitates and evaporites Transformation occurs in two ways: Compaction seds are pressed together – grains interconnect Cementation Seds are cemented together like glue – Calcite, – silica, and – iron oxide are the most common cements. of Clastic rocks Clastic sediments bits and pieces of old rock/plants/animals Clastic sedimentary rocks are classified by their sediment size and shape Most common is shale--very fine particles Sandstone—sand sized particles Siltstone—silt size Rounder seds mean longer transport And by shape of seds Conglomeraterounded seds Breccia—angular seds Egyptian statue made from breccia Chemical Sediments Chemical sediments precipitate from water Two types – Carbonates – Evaporites Carbonates Made of mostly calcite CaCO3or CaMgCO3 Limestone is CaCO3 Very common here Dolomite is CaMgCO3 Some of the carbonate is replaced by magnesium Evaporites Evaporites evaporate from water when a basin dries up . Gypsum CaSO4 H2O Halite (Rock Salt) NaCl Halite--—a salt playa Sedimentary Rock Lab Name the rocks you find in your sample bag. Choices Sandstone Coal Conglomerate Coquina Gypsum Rock salt Oolitic limestone Sed rock review A sed rock quiz Sedimentary environments Sedimentary rocks provide information about events that occurred on Earth's surface Their color, grain size, and composition give us information about what was happening when they formed S e d i m e n t a r y r o c k e n v i r Crossbedding and Ripple Marks Crossbedding gives us an indication of wind or water direction Ripple marks may be Symmetrical-oscillating Asymmetrical- current ripple marks Caves form in sedimentary rock Depositional Environments Delta-a fan-shaped body formed when water flows from a stream into a standing body of water Example the Mississippi River Delta The Nile River Delta Environments River—Alluvial Desert--aeolian Delta Shoreline Alluvial--River Channel Unconsolidated gravels, sand, and clay Alluvial Fan Forms when sediment flows from a steep incline onto a flat floored valley and looses velocity rapidly Seds are laid down the largest first, followed by progressively smaller and smaller as the velocity slows Oxbow lake formation An oxbow lake occurs between here and Oxford Conglomeraterounded seds Rounded seds indicate a longer distance of transport Evaporites---Gypsum Ca SO4. H2O Halite (Rock Salt) NaCl Gypsum Sandstone would indicate a beach or desert was once there Limestone Sedimentary environment What ancient environment would produce the following: A REEF a. A linear outcrop of fossiliferous limestone, massive bedding, many corals and algal structures SAND DUNES b: cross-bedded, well-sorted sandstone, with frosted quartz grains GLACIAL c: Unsorted, unstratified, the angular boulders have scratches A Glacial Moraine ALLUVIAL FAN d. Unsorted, unstratified, the the angular boulders don't have scratches. Name this structure e: poorly sorted, but somewhat stratified sandstone and conglomerate with cut and fill structures. RIVER f: very fine parallel bedding, diatoms, red clay, some thin graded bedding. DEEP OCEAN RESTRICTED CONTINENTAL SEAS g. Thick deposits rock salt and gypsum. Jurassic Seawayexample of a continental sea h. Fine-grained sand (made of shell fragments) with ripple marks and worm burrows. LAGOON BEHIND REEF
