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Sedimentary Rocks. Sedimentary Rocks. Products of mechanical and chemical weathering Account for about 5% of Earth’s crust Contain evidence of past environments Texture Fossils. Sedimentary Rocks. Texture and composition - the keys to classification. Texture: Clastic or detrital - PowerPoint PPT Presentation
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Sedimentary Rocks Sedimentary Rocks
Sedimentary Rocks Sedimentary Rocks Products of mechanical and chemical weathering Account for about 5% of Earth’s crust Contain evidence of past environments
TextureFossils
Sedimentary Rocks Sedimentary Rocks TextureTexture and and compositioncomposition - the keys to classification. - the keys to classification. Texture:Texture:
ClasticClastic or or detritaldetritalNon-clasticNon-clastic
ChemicalChemical (or crystalline) (or crystalline)BiochemicalBiochemical
Sedimentary Rocks Sedimentary Rocks Clastic or detritalClastic or detrital rocks are composed of particles of pre- rocks are composed of particles of pre-existing rocks which have been weathered, eroded, existing rocks which have been weathered, eroded, transported, deposited, and cemented together.transported, deposited, and cemented together.
Grain sizeGrain size (energy) (energy)RoundingRounding - energy and length of transport - energy and length of transportSortingSorting - uniformity of grain size - uniformity of grain size
Sedimentary Rocks Sedimentary Rocks
ChemicalChemical sedimentary rocks: precipitated from solution. sedimentary rocks: precipitated from solution. Texture also referred to as Texture also referred to as crystallinecrystalline- readily - readily recognized in moderately coarse-grained examples. recognized in moderately coarse-grained examples. Very fine-grained chemical rocks appear Very fine-grained chemical rocks appear massivemassive. .
Some limestone, halite, sulfates, etc. Some limestone, halite, sulfates, etc. EvaporitesEvaporites are a common source. are a common source. Also caves, hot springs.Also caves, hot springs.
Sedimentary Rocks Sedimentary Rocks BiochemicalBiochemical rocks: formed by the processes of organisms rocks: formed by the processes of organisms
CalciteCalcite or or silicasilica shells or skeletons. shells or skeletons. Form directlyForm directly (coral reefs) or (coral reefs) or Cemented togetherCemented together after organisms die & accumulate after organisms die & accumulate
Energetic wave action may break up shells and produce Energetic wave action may break up shells and produce clastic texturesclastic textures
= clastic or biochemical??= clastic or biochemical??We'll consider it biochemical because the fragments are We'll consider it biochemical because the fragments are of biochemical originof biochemical originIf shell fragments are clearly recognizable, the texture is If shell fragments are clearly recognizable, the texture is called called skeletalskeletal
Sedimentary Rocks Sedimentary Rocks
Shale-Shale- fine grained (mud, silt, clay) fine grained (mud, silt, clay)FissileFissile (splits in layers) (splits in layers)
Shale with leaf fossilsShale with leaf fossils
Sedimentary Rocks Sedimentary Rocks Clastic/Detrital RocksClastic/Detrital Rocks
Fissile ShaleFissile Shale
Low-energy environment:Low-energy environment:Offshore shallow marineOffshore shallow marineLakeLake
Siltsone/mudstone-Siltsone/mudstone- fine grained (mud, silt, clay) fine grained (mud, silt, clay)Massive- breaks in clumpsMassive- breaks in clumps
Shale with leaf fossilsShale with leaf fossils
Sedimentary Rocks Sedimentary Rocks Clastic/Detrital RocksClastic/Detrital Rocks
Fissile ShaleFissile Shale
Low-energy environment:Low-energy environment:Offshore shallow marineOffshore shallow marineLakeLake
Sandstone-Sandstone- Composed of sand-sized particlesWell-sorted: water or windForms in a variety of environments: beach, floodplain…Quartz is the predominant mineral
Sedimentary Rocks Sedimentary Rocks Clastic/Detrital RocksClastic/Detrital Rocks
Thin-section of sandstone under the petrographic microscope
Sedimentary Rocks Sedimentary Rocks Clastic/Detrital RocksClastic/Detrital Rocks
GraywackeGraywacke “Immature” sandstone
Contains lots of easily-weathered material:Mafic minerals, volcanic glass/ash
Typically occurs in subsiding basin Typically occurs in subsiding basin near an active volcanic arc near an active volcanic arc
(uplift/erosion and burial > chemical (uplift/erosion and burial > chemical weathering)weathering)
Sedimentary Rocks Sedimentary Rocks Clastic/Detrital RocksClastic/Detrital Rocks
Conglomerate-Conglomerate- Pebbles/cobbles
Well-rounded: long transportHigh-energy environments:
Beach, River
Sedimentary Rocks Sedimentary Rocks Clastic/Detrital RocksClastic/Detrital Rocks
Breccia-Breccia- Pebbles/cobbles
Poorly-rounded: short transportHigh-energy environments:
Beach, River, Fault zone
BrecciaBreccia
Sedimentary Rocks Sedimentary Rocks Chemical RocksChemical Rocks Some Limestone Some Limestone is precipitated is precipitated
directly from water directly from water
Also true for some Also true for some dolostonedolostone (Ca-Mg-carbonate) and (Ca-Mg-carbonate) and chertchert (SiO(SiO22))
Sedimentary Rocks Sedimentary Rocks Chemical RocksChemical Rocks Some Limestone Some Limestone is precipitated is precipitated
directly from water directly from water
Oolitic limestoneOolitic limestone contains small contains small spherical spherical ooidsooids
TravertineTravertine is typically precipitated from is typically precipitated from groundwater and is seen in cavesgroundwater and is seen in caves
Sedimentary Rocks Sedimentary Rocks Chemical RocksChemical Rocks Evaporites Evaporites are precipitated directly are precipitated directly
from seawater when a large from seawater when a large quantity evaporatesquantity evaporates
Rock salt Rock GypsumRock Gypsum
Sedimentary Rocks Sedimentary Rocks Biochemical RocksBiochemical Rocks
Most Limestone Most Limestone is organic: is organic: precipitated as shells, reefs, precipitated as shells, reefs, and even as tiny shells from and even as tiny shells from planktonic lifeplanktonic life
Fossiliferous LimestonesFossiliferous Limestones
Sedimentary Rocks Sedimentary Rocks Biochemical RocksBiochemical Rocks Most Limestone Most Limestone is organic: is organic:
precipitated as shells, reefs, and even precipitated as shells, reefs, and even as tiny shells from planktonic lifeas tiny shells from planktonic life
Chalk CliffsChalk CliffsLimestone ReefLimestone Reef
Chalk fossils Chalk fossils under electron under electron microscopemicroscope
Sedimentary Rocks Sedimentary Rocks Biochemical RocksBiochemical Rocks
CoquinaCoquina is composed of broken-up is composed of broken-up shell fragments due to marine wave shell fragments due to marine wave
action in the near-tidal zoneaction in the near-tidal zoneIt also qualifies as a detrital rockIt also qualifies as a detrital rock
Sedimentary Rocks Sedimentary Rocks Biochemical RocksBiochemical Rocks
ChertChert, like chalk, is composed of tiny shells , like chalk, is composed of tiny shells from planktonic life, but the organisms involved from planktonic life, but the organisms involved secrete SiOsecrete SiO22 shells. shells.
Diatoms and radiolaria Diatoms and radiolaria have microscopic SiOhave microscopic SiO22
shellsshells
Sedimentary Rocks Sedimentary Rocks Biochemical RocksBiochemical Rocks
Coal Coal is organic: buried and un-oxidized plant is organic: buried and un-oxidized plant remainsremains
Sedimentary Rocks Sedimentary Rocks Biochemical RocksBiochemical Rocks
Coal Coal is organic: buried and un-oxidized plant is organic: buried and un-oxidized plant remainsremains
Sedimentary Rocks Sedimentary Rocks Sedimentary EnvironmentsSedimentary Environments
Using sedimentary rocks to interpret Earth historyUsing sedimentary rocks to interpret Earth history
Sedimentary Rocks Sedimentary Rocks Sedimentary StructuresSedimentary Structures
Using sedimentary rocks to interpret Earth historyUsing sedimentary rocks to interpret Earth history
Large-scale cross-beds: wind-blown Large-scale cross-beds: wind-blown sands in an arid environmentsands in an arid environment
Ripple-marks: running water- beach or riverRipple-marks: running water- beach or river
Many sedimentary structures may be Many sedimentary structures may be used to determine original upward used to determine original upward
direction in vertical or overturned stratadirection in vertical or overturned strata
Sedimentary Rocks Sedimentary Rocks Sedimentary StructuresSedimentary Structures
Using sedimentary rocks to interpret Earth historyUsing sedimentary rocks to interpret Earth history
Graded beds- offshore turbiditesGraded beds- offshore turbidites
Sedimentary Rocks Sedimentary Rocks Sedimentary StructuresSedimentary Structures
Using sedimentary rocks to interpret Earth historyUsing sedimentary rocks to interpret Earth history
Mud-cracks and raindrop imprintsMud-cracks and raindrop imprints
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