1Earth Materials: Sedimentary Rocks• What we can learn from sedimentary rocks• Types of sediment• Classification of sedimentary rocks1• Sedimentary processes• Depositional environments & sedimentary structuresSediments and Sedimentary rocksWhy study sediments and sedimentary rocks?• Most of the earth’s surface is covered with sediments.• They record past environmental conditions and much of thehistory of the earth.• They contain fossil evidence of past life.2• Some natural resources are of sedimentary origin or are foundprimarily in sedimentary rocks: i.e. coal, oil, natural gas, etc.Three main categories of sediments and sedimentary rocks:• Clastic (also called detrital)• Chemical• BiochemicalRock composed of clastic sedimentRock composed of chemical sediment3Chapter 7 Understanding EarthRock containing biochemical sedimentSediments and Sedimentary rocksClassification of clastic sedimentary rocks:TextureMaximum grain size: fine, medium, coarseStilltd ltd4Sorting: well-sorted, poorly-sortedGrain shape: rounded, angularCompositionwhat the grains are composed of: i.e. quartz, feldspar, clay, rock fragments, etc.Well-sorted, angular, quartz sand (magnified) Fig 7.2 Understanding EarthPoorly sorted sediment (mixture of sand and gravel) with rounded fragmentsGeology - Chernicoff5Sediments and Sedimentary rocksClassification of clastic sedimentary rocks by texture:Texture Rock Typecoarse roundedConglomerate6coarse, roundedConglomeratecoarse, angular Brecciamedium Sandstonefine Siltstone, Mudstone,Claystone, or Shale2The four major types of sandstones:an example of classification by grain composition7Fig 7.16 Understanding EarthClassification of chemical and biochemical sedimentary rocks by compositionComposition Rock Typecalcite (may also contain some mud) limestone (several types)8plant remains coal or peatsilica cherthalite rock saltgypsum rock gypsumThree examples of limestoneChalk - a type of fossil-bearing limestoneFossiliferous limestoneFig 7.19 Understanding Earth 9Geology - ChernicoffRock salt (halite) - a chemical sedimentary rock formed by evaporation of waterRock gypsum -a chemical sedimentary rock formed by evaporation of waterChert - a sedimentary rock formed from silica sediment. Chert may be chemical or biochemical in originFig 7.19 Understanding Earth10Fig 7.19 Understanding EarthFig 7.19 Understanding Earth11Relative abundance of major sedimentary rock typesFig 7.14 Understanding EarthSediments and Sedimentary rocksSedimentary processes:WeatheringErosion and Transportation12DepositionBurial and compactionDiagenesis and lithification3Processes involved in the formation of sedimentary rocks:Weathering, Erosion, Transportation, Deposition, Burial, and DiagenesisFig 7.1 Understanding EarthGrain shape related to the duration of transport of clastic sedimentAngular grainsRounded grainsFig 7.3 Understanding EarthSediments and Sedimentary rocksFrom sediment to rock, changes after deposition:- dissolution- re-crystallization- compaction- formation of new minerals- cementation16Fig 7.13 Understanding EarthSediments and Sedimentary rocksDepositional environments:-where17- what / howSome common sedimentary environments18Fig 7.5 Understanding Earth4Sediments and Sedimentary rocksSome sedimentary structures:- sedimentary layering19- ripples- cross-bedding- mud cracks- burrows and tracks (bioturbation, trace fossils)20Sedimentary layersCh 7 Understanding EarthModern ripples on a beach (below) and ancient ripples preserved in sandstone (left)Understanding Earth21Cross-bedding in sandstoneThese sediments were deposited in desert dunes.Understanding Earth22Mud cracks: modern (left) and ancient (right)Understanding
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