Sediments and Sedimentary Rocks

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Sediments and Sedimentary Rocks
L - 6 cd/EM - E
Tom Bean/DRK
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Sedimentary rocks

• 5 by volume of the upper crust
• 75 by area of continental areas
• Often the only record of geologic events
• e.g. The Himalayas will someday be sandstone

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Sedimentary Stages in the Rock Cycle
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2 KINDS OF SEDIMENTARY ROCKS

1. DETRITAL CLASTIC - Rock resulting from the
   consolidation of loose sediment that has been
   derived from previously existing rocks and
   accumulated in layers
2. CHEMICAL - Rock formed by the precipitation of
   minerals from solution by either organic or
   inorganic processes

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Transport and deposition of clastic sediments

• Movement of sediment by wind, ice or water
  (GEOLOGIC AGENTS).
• Mode of transport produces distinctive deposits.
• Deposit as layers - beds/strata

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Transport affects the sediment in several ways -

• Sorting measure of the variation in the
• range of grain sizes in a clastic rock or
• sediment
• Well-sorted sediments indicate that they have
  been subjected to prolonged water or wind action.
• Poorly-sorted sediments are either not
  far-removed from their source or deposited by
  glaciers.

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Sorting
Well-sorted
Poorly-sorted
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Well-sorted Sand
Rex Elliott
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Poorly-sorted Sand
Rex Elliott
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Transport affects the sediment in several ways -
SHAPE

• Roundness measure of how rounded the corners
  are
• Sphericity measure of how much it is like a
  sphere
• Sorting, roundness, and sphericity all
  increase with LENGTH of transport.

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Sorting
Roundness
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Types of detrital rocks

• Largely based on the size of the particles, which
  may be anything.
• Conglomerate (poorly sorted/round)
• Breccia (poorly sort/angular)
• Sandstone (quartzite, arkose, greywacke)
• Mudstone
• Siltstone
• Shale - most common rock on continents

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Conglomerate
Breck Kent
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Sandstone
Breck Kent
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Shale
D. Cavagnaro/Visuals Unlimited
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SEDIMENTARY ROCKS

• CHEMICAL ROCK- Rock formed by the precipitation
  of minerals from solution by either organic or
  inorganic processes

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Types of chemical sedimentary rocks

• Limestone CaCO3
• Chert SiO2
• Salt NaCl, KCl
• Gypsum CaSO4 2H2O
• Coal altered organic debris

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Limestone
Breck Kent
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Halite
Breck Kent
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Chert
Breck Kent
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Fossiliferous Limestone
Peter Kresan
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Chemical environments Evaporites

• Restricted environments such as Mediterranean
  Sea Texas coast
• Minerals precipitate according to
  solubility.
• Gypsum Halite
• CaSO4 2H2O NaCl

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One Model for the Formation of Evaporites
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Chemical environments Carbonates

• Clear water away from big rivers (or volcanoes)
• Warm water subtropical to tropical
• Shallow water -- two reasons
• Organic sunlight only penetrates to
• about 100 m
• Inorganic CCD so carbonates dissolve

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Foraminifer in the Eye of a Needle
Chevron Corporation
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Coral Reef Surrounding Volcanic Island
Jean-Marc Truchet/Tony Stone Worldwide
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Common Sedimentary Environments
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Clues to interpreting sedimentary depositional
environments

• Sedimentary structures
• Sorting, roundness, sphericity
• Sequence kinds of beds

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Sedimentary structures

• Particular structural features can give
  information about the environment of deposition.
• Structures also help determine if a bed is
  right-side-up important in deformed rocks

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Cross-bedded Sandstone
Peter Kresan
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Varves record annual cycles in glacial lakes
Turbidity currents
S. C. Porter
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Modern Rippled Sand
Raymond Seiver
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Ancient Ripple-marked Sandstone
Reg Morrison/Auscape
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Fig. 7.9
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Mudcracks
MODERN
ANCIENT
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Bioturbation Tracks and Tunnels
Chip Clark
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From Peat to Coal
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The end