Sedimentation and Stratigraphy Geology 5142 Dr' Thieme

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Sedimentation and StratigraphyGeology 5142Dr.
Thieme

• Lecture 4 Saprolite, Sediment, and Sedimentary
  Rocks

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Goldich's stability series is the inverse of
Bowen's reaction series. The most stable mineral,
quartz, is also the last to crystalllize in an
igneous magma as it cools.
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• REGOLITH fragmentary and unconsolidated
  materials beneath the Earth's surface and above
  solid rock.
• SAPROLITE soft, earthy, clay-rich, thoroughly
  decomposed rock formed in place by chemical
  weathering of igneous or metamorphic rocks.
• SOIL a natural body, occurring at the Earth's
  surface, consisting of layers or horizons of
  mineral and organic materials, capable of
  supporting plants out-of-doors.

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Soil formed on upper deposit
Regolith of weathered Quaternary sediment
near Phenix City, Alabama
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Schist saprolite in the Blue Ridge, northeastern
Georgia
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Saprolite of amphibolite gneiss from the Promised
Land formation on SR 124 near Stone
Mountain, Georgia
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Saprolite at the top of granite in the quarry at
Sparta, Georgia
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Sediment

• solid material settling out of a fluid
• weathered rock detritus
• matter deposited by
• water (alluvial)
• wind (aeolian)
• gravity (colluvial)
• Clasts are particles in sediment or sedimentary
  rock which derive from preexisting rock

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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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USDA
USCS
State Highways
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Unified Soil Classification System (USCS)

• Basis for USCS
• Percentage of gravels, sands and fines
• Shape of the grain size distribution curve
• Plasticity
• Three Categories
• Coarse-grained (G for gravel S for sand)
• Fine-grained (M for silt C for clay
• Highly organic (O for organic P for peat)

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SP (Poorly-graded sand)
(Well "graded" sediment is actually poorly
sorted.)
ML (low plasticity clayey silt)
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Types of sedimentary rocks

• Sediment originates from physical or chemical
  weathering
• Rock types are based on the source of the
  material
• Clastic (Detrital) rocks sediment transported
  as solid particles
• Chemical rocks sediment that was once in
  solution

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Detrital sedimentary rocks

• The chief constituents of detrital rocks include
• Clay minerals
• Quartz
• Feldspars
• Micas
• Particle size is used to distinguish among the
  various types of detrital rocks

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Detrital Sedimentary Rocks
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Clastic Sediment transport

• Sediment transport varies in energy and
  persistence over time and space.
• The strength of currents that transport a
  sediment can be inferred from particle sizes and
  sorting
• How far the sediment traveled is indicated by the
  degree of particle rounding

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Particle Size

• Particle size indicates the energy conditions
  during transport and deposition
• High-energy processes such as swift-flowing
  streams and waves are needed to transport gravel
• Conglomerate must have been deposited in areas
  where these processes prevail
• Sand transport also requires vigorous currents
• Low-energy conditions such as in lakes and
  lagoons create environments that trap silt and
  clay

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Sorting

• refers to the variation in size of particles
  making up sediment or sedimentary rocks
• results from processes that selectively transport
  and deposit sediments of particular sizes

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Sorting

• Well sorted sediment if the size range is not
  very great
• Wind has a limited ability to transport sediment,
  so dune sand tends to be well sorted
• Poorly sorted sediment has a wide range of sizes
• Glaciers can carry any sized particles, because
  of their transport power, so glacial tills are
  poorly sorted

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Sorting
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Rounding

• Rounding is the degree to which detrital
  particles have their sharp corners and edges warn
  away by abrasion
• Gravel in transport is rounded very quickly as
  the particles collide with one another
• Sand becomes rounded with considerably more
  transport

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Rounding and Sorting

• A deposit
• of well rounded
• and well sorted gravel

• Angular, poorly sorted gravel

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Conglomerate
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Breccia
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Clastic sedimentary rocks

• Sandstone
• Composed of sand-sized particles
• 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 75 of clasts are quartz
• may be cemented with iron oxide, calcite, chert,
  clay minerals

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Idealized geologic conditions under which a
quartz arenite would be deposited. There is
little tectonic movement in this environment.
Water depth is shallow, and the basin subsides
very slowly.
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Arkose

• more than 50 of clasts are
• feldspar
• also typically contains quartz, mica, and iron
  oxides

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Geologic environment in which an arkose would be
deposited.
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Graywacke (Litharenite)

• more than 50 of clasts
• are rock fragments

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Tectonic setting in which graywacke is deposited.
Frequently graywackes are transported by masses
of water highly charged with suspended sediment.
Because of the suspended matter, the mass is
denser than surrounding water and moves along
the sloping sea floor or down submarine canyons
as a turbidity current. Graywacke sediment
characteristically accumulates in deep-sea fans
at the base of the continental slope.
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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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Clastic sedimentary rocks

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

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Humid
Arid
Humid
Arid
Arid or Temperate
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Humid
Passive
Arid
Active
Humid
Passive
Arid
Active
Arid or Temperate
Active
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Humid
Passive
High and consistent
Arid
Active
Inconsistent
Humid
Passive
Inconsistent
Arid
Active
High and consistent
Arid or Temperate
Active
Inconsistent
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Humid
Passive
High and consistent
Long
Humid
Arid
Active
Inconsistent
Short
Arid
Humid
Passive
Humid
Inconsistent
Short
Arid
Active
High and consistent
Long
Arid
Arid or Temperate
Active
Arid or Temperate
Inconsistent
Short