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SEDIMENTARY GEOLOGY OVERVIEW. Andrew S. Madof Orals Review - 2007 January 12, 2007. SEDIMENTARY GEOLOGY = Sedimentology (process) + Stratigraphy (response). Sedimentology = study of PROCESSES (i.e. production, composition, transport, and deposition of sediment)

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SEDIMENTARY GEOLOGY OVERVIEW

Andrew S. Madof

Orals Review - 2007

January 12, 2007

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SEDIMENTARY GEOLOGY = Sedimentology (process) + Stratigraphy (response)

Sedimentology = study of PROCESSES (i.e. production, composition, transport, and deposition of sediment)

Stratigraphy = study of RESPONSES (i.e. inferring the controls on the spatial and temporal changes of strata) → exact processes that created the rocks can’t be know because only the rocks are left, not the processes

sedimentation and sedimentary rocks
Sedimentation And Sedimentary Rocks

Sedimentary Rocks:

  • Form 75% of the rocks exposed at the Earth’s Surface
  • Are the reservoirs for fossil fuels, iron and aluminum ores, and groundwater
  • Record of Earth’s history
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Sediment

  • Sediment = loose, solid particles and can be:
    • Terrigenous = fragments from silicates (igneous and/or metamorphics)
    • Biogenic = fossils (carbonate - reefs; silicates - forams)
    • Chemical = precipates (halite, gypsum, anhydrite, etc…) - note: with chemical sedimentary rocks, evaporation > precipitation and/or supersaturation in closed basins (lakes or oceans)
  • Classified by particle size
    • Boulder - >256 mm
    • Cobble - 64 to 256 mm
    • Pebble - 2 to 64 mm
    • Sand - 1/16 to 2 mm
    • Silt - 1/256 to 1/16 mm
    • Clay - <1/256 mm
grain size
Grain size

Grain size (diameter) and grain-shape depend on:

  • Transport media: rivers (pebbles bounce on river bottom, sand moved in traction, and silt/clay suspended in water column); oceans and lakes (near-shore and deep-water systems); glaciers (sediment moved on glacier bottom); wind (sand dunes)
  • Distance from parent rock: the longer the distance traveled, generally the smaller and the more well-rounded the grains (due to higher kinetic energy)
  • Mineral hardness: the harder the parent rock, the longer it will take the sediments to erode (example: silicates are more resistant to weathering and erosion than feldspars, and this is why beaches are often comprised of sand, not feldspar-rich sediments)
  • Consider: sorting (= range of grain sizes) → winds sort well (meaning grain sizes are very similar); glaciers sort poorly (meaning there is a large spread of grain sizes in glacial deposits)
classification of sedimentary rocks
Classification Of Sedimentary Rocks

DETRITAL (TERRIGENOUS) SEDIMENTARY ROCKS:

  • Mudstones
  • Sandstones
  • Conglomerates
  • Breccias

DETRITAL SEDIMENTARY ROCKS:

  • Classification Based On Particle Size

a) All detrital rocks are clastic

b) Sand and silt are predominantly quartz

c) Finer-sized particles of clay minerals

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SANDSTONES:

a) 25% of all sedimentary rocks

b) Sandstone particles (1/16-2 mm in diameter)

c) Practical uses of sandstones: buildings and reservoir for fossil fuels and groundwater

CONGLOMERATES AND BRECCIAS:

a) Grain diameters larger than 2 mm

b) Conglomerates have rounded grains

c) Breccias have angular grains

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MUDSTONES:

a) More than half of all sedimentary rocks

b) Contain the smallest particles (0.004 mm in diameter)

c) Environments of deposition: lakes, lagoons, deep ocean basins, river floodplains

d) Color variety of shale represents mineral composition

e) Practical uses of shale: bricks, ceramics, cement, and oil shale

chemical sedimentary rocks

Chemical Sedimentary Rocks

Inorganic Chemical Sedimentary Rocks

LIMESTONE (inorganic):

I) FORMATION

II) Oolitic Limestone

III) Tufa

IV) Travertine

lithification turning sediment into sedimentary rock
Lithification = Turning Sediment Into Sedimentary Rock
  • Diagenesis = Changes in the sediment due to increased heat, pressure, and circulating groundwater
  • Lithification = Compaction + Cementation
  • Compaction = Diagenetic process by which the weight of overlying materials reduces the volume of sedimentary body (decreases porosity)
cementation recrystallization
Cementation & Recrystallization
  • Cementation: Precipitation of dissolved ions in the pore space

a) calcium carbonate - CaCO3

b) silica - SiO2

c) iron compounds - Fe+2 and Fe+3

  • Texture of Rock: Formed by compaction and cementation of sediment particles
  • Recrystallization: recrystallization of certain unstable minerals into new, more stable minerals (this happens primarily in carbonates, when you start with carbonate mud [a.k.a. micrite] heat it up, then cool it to form larger grains [a.k.a. sparite])
sedimentary structures
Sedimentary Structures
  • Bedding (stratification): arrangement of sediment particles into distinct layers

A) Changes in sediment change bedding

B) Changes in transport energy change bedding

  • Normally graded bedding: sediment layer (formed by a single depositional event) in which particle size varies gradually with the coarsest particles on the bottom (note: inversely graded bed = fines on bottom and coarse grains on top )
cross bedding and mudcracks
Cross-bedding and Mudcracks
  • Cross-bedding: sedimentary layers deposited at an angle to the underlying set of beds
  • Surface sedimentary features

A) Ripple Marks: small surface ridges produced when water or wind flows over sediment after it is deposited

B) Mudcracks: occur on the top of a sediment layer when muddy sediment dries and contracts

asymmetric and symmetric ripples
Asymmetric and Symmetric Ripples

tidal currents (bi-directional)

river or wind currents (uni-directional)

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Landward Migration of Shoreline = Regression(regression can either form due to 1) lower sea level or 2) shoreline building basinward [a.k.a. progradation])

graded bedding vertical decrease of sediment size
Graded Bedding = Vertical Decrease of Sediment Size

Turbidite = RESPONSE

Turbidity Current = PROCESS