Sedimentation and Stratigraphy Geology 5142 Dr' Thieme

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Sedimentation and StratigraphyGeology 5142Dr.
Thieme

• Lecture 5 Sediment Texture (Sorting, Skewness,
  Kurtosis), Provenance, Sandstones

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Udden-Wentworth Scale
Phi - log D in millimeters
Gravel is coarser than 2 mm
Geometric reduction 1/2, 1/4, 1/16,...
Sand is 1/16 - 2 mm, visible to naked eye.
Silt is too small to see but can be felt.
Clay as particle size (lt 4 microns) but
also mineral group (phyllosilicates)
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Phi Size Classes (Mean, Median, Mode)
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Mean on the Answer Sheet
Sort on the Answer Sheet
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Sorting
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Skew on the Answer Sheet
Kurtosis on the Answer Sheet
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UNKNOWN 1 Honey Hole Gravel Pit, Glacial
Outwash, Nescopeck, PA
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UNKNOWN 2 "Georgia Coast"
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UNKNOWN 4 Aeolian Sand Dune, Albany, GA
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Maturity

• Four stage model of Folk (1951, 1966) based upon
• amount of mud (particles lt30 microns)
• sorting of sand fraction
• rounding of sand fraction
• Immature if gt5 mud
• abundant feldspars or
• abundant lithic clasts

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Mudrock

• Shale
• Mud-sized particles in thin layers that are
  commonly referred to as laminae
• Most common sedimentary rock

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Sandstone ("Arenite")

• particles are sand sized (1/16 - 2 mm diameter)
• forms in a variety of environments
• Sorting, shape, and composition of the grains can
  be used to interpret the rocks history
• Quartz is the predominant mineral

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Quartz Arenite

• more than 90 of clasts are quartz
• may be cemented with iron oxide, calcite, chert,
  clay minerals

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Quartz-dominated beach sand from Florida
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Tybee Island beach sand with heavy minerals (lt5?)
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Idealized geologic conditions under which a
quartz arenite would be deposited. There is
little tectonic movement ("passive margin" of
divergent plate boundary). Water depth is
shallow, and the basin subsides very slowly.
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Arkose

• more than 25 of clasts are feldspar
• must also have more feldspar than lithic frags)

• also typically contains quartz, mica, and iron
  oxides

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Arkosic sand from Australia
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Geologic environment in which an arkose would be
deposited. The area is being actively uplifted
either by subduction zone volcanism or
continent-continent collision (convergent plate
boundary). Arid climate is also implied by
abundance of feldspar in sand.
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Graywacke (Litharenite)

• more than 50 of clasts
• are rock fragments

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Beach Sand rich in volcanic lithic clasts from
the Big Island of Hawaii
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Beach Sand rich in lithic clasts from the Virgin
Islands
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Tectonic setting in which graywacke is deposited
- Deep-sea fans at the base of the continental
slope in an island arc or subduction zone
convergent plate boundary setting.
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Beach Sand rich in quartz with shell fragments
from Sapelo Island
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Beach Sand dominated by shell fragments from the
Bahamas
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Oolite sands with some quartz from Utah
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Four categories of sandstone as seen in thin
section under the microscope. Diameter of field
of view is about 4 mm.
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Quartz arenite under cross-polarized light
Arkose under cross-polarized light
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Litharenite under cross-polarized light
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Chert under cross-polarized light
Conglomerate under cross-polarized light
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