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 composed of 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:Weathering - produces sedimentErosion and Transportation - by water, wind, or ice12Deposition - accumulation of sediment to form new layersBurial and compactionConversion to rock (lithification and diagenesis)3Processes 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 rocksTurning sediment into sedimentary rock:- dissolution of soluble minerals- recrystallization (i.e. aragonite in shells changes to calcite)- compaction (often involves loss of water from betweengrains; dissolution and recrystallization ofquartz also may contribute to compaction)- formation of new minerals from fluids or growth of existing mineral grains- cementation by calcite, quartz, iron oxides or other mineralsMicrophotograph of a sandstone composed of rounded grains of quartz (gray to white) held together by calcite cement (brightly colored). Quartz, iron oxides, and other minerals also may “glue” sediment grains together to form sedimentary rock.16Fig 7.13 Understanding EarthSediments and Sedimentary rocksDepositional environments:- the locations and conditions under whichsediments accumulate17- the type of depositional environment is directlyrelated to the type of sediment deposited- sedimentary depositional environments may be divided into three general categories:continental, shoreline (transitional), and marineSome 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