Sedimentary Rocks

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


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


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


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


Thin-section of sandstone under the petrographic microscope


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)


Conglomerate-Conglomerate- Pebbles/cobbles

Well-rounded: long transportHigh-energy environments:

Beach, River


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


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


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


Coal Coal is organic: buried and un-oxidized plant is organic: buried and un-oxidized plant remainsremains


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


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



Graded beds- offshore turbiditesGraded beds- offshore turbidites



Mud-cracks and raindrop imprintsMud-cracks and raindrop imprints

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Sedimentary Rocks