Prepared by Iggy Isiorho for

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Chapter 6

• Prepared by Iggy Isiorho for
• Dr. Isiorho
• Sediments and
• Sedimentary Rocks
• Index ?

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On pg. 121

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Sediment

• Sediment Loose, solid particles that can
  originate by (1) weathering and erosion of
  preexisting rocks, (2) chemical precipitation
  from solution, usually in water, and (3)
  secretion by organisms.
• Fig. 6.1
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Size Matters

• Gravel Rounded particles coarser than 2 mm in
  diameter.
• Sand Sediment composed of particles with a
  diameter.
• Silt Sediment composed of particles with a
  diameter of 1/256 to 1/16 mm.
• Clay Sediment composed of particles with
  diameter less than 1/256 mm. (Table 6.1)
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Transportation

• Rounding The grinding away of sharp edges and
  corners of rock fragments during transportation.
• Sorting Process of selection and separation of
  sediment grains according to their grain size for
  grain shape or specific gravity.
• Fig. 6.2
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Deposition

• Deposition The settling or coming to rest of
  transported material.
• Fig. 6.3 Fig. 6.4
• One of the most important jobs of geologists
  studying sedimentary rocks is to try to determine
  the ancient environment of deposition of the
  sediment that formed the rock.
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Lithification

• Lithification is the general term for a group of
  processes that convert loose sediment into
  sedimentary rock. Most sedimentary rocks are
  lithified by a combination of compaction, which
  packs loose sediment grains tightly together, and
  cementation, in which the precipitation of cement
  around sediment grains binds them into a firm,
  coherent rock. Crystallization of minerals from
  solution, without passing through the
  loose-sediment stage, is another way that rocks
  may be lithified.
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Fig. 6.6

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Crystallization

• Crystallization Crystal development and
  growth.
• Crystalline texture An arrangement of
  interlocking crystals.
• Fig. 6.7
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Types of Sedimentary Rocks

• Clastic sedimentary rocks
• Chemical sedimentary rocks
• Organic sedimentary rocks
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Clastic Rocks

• Sedimentary Breccia A coarse-grained
  sedimentary rock (grains coarser than 2 mm)
  formed by the cementation of angular rubble.
  (Fig. 6.8)
• Conglomerate A coarse-grained sedimentary rock
  (grains coarser than 2 mm) formed by the
  cementation of rounded gravel. (Fig. 6.9)
• Sandstone A medium-grained sedimentary rock
  (grains between 1/16 and 2 mm) formed by the
  cementation of sand grains. (Fig. 6.10)
• Matrix Fine-grained material found in the pore
  space between larger sediment grains. (Fig.
  6.12)
• Turbidity currents A flowing mass of sediment
  laden water that is heavier than clear water and
  therefore flows downslope along the bottom of the
  sea or a lake. (Fig. 6.13)
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Fig. 6.8

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Fig. 6.9

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Fig. 6.10

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Fig. 6.12

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Fig. 6.13

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Clastic Rock II

• Rocks consisting of fine-grained silt and clay
  are called shale, siltstone, claystone, and
  mudstone.
• Shale is a fine-grained sedimentary rock notable
  for its splitting capability (called fissility).
  (Fig. 6.14)
• Fine-grained rocks such as shale typically
  undergo pronounced compaction as they lithify.
  (Fig. 6.15)
• A rock consisting mostly of silt grains is called
  siltstone. Somewhat coarser-grained than most
  shales siltstones lack the fissility and
  laminations of shale. Claystone is a rock
  composed predominately of clay-sized particles,
  but lacking the fissility of shale. Mudstone
  contains both silt and clay, having the same
  grain size and smooth feel of shale but lacking
  shales laminations and fissility.
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Fig. 6.14

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Fig. 6.15

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Chemical Sedimentary Rocks

• Chemical sedimentary rocks have been precipitated
  from an aqueous environment. Chemical sedimentary
  rocks are either precipitated directly by
  inorganic processes or by the actions of
  organisms.
• Limestone is a sedimentary rock composed mostly
  of calcite. Limestones are either precipitated by
  the actions of organisms or are precipitated
  directly as the result of inorganic processes.
  The two major types of limestone can be
  classified as either biochemical or inorganic
  limestone.
• Fig. 6.18 Fig. 6.20 Fig. 6.22 Table 6.2 6.1
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Fig. 6.18

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Fig. 6.20

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Fig. 6.22

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Table 6.2

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6.1

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Organic Sedimentary Rocks

• Coal A sedimentary rock formed from the
  consolidation of plant material. It is rich in
  carbon, usually black, and burns readily.
• Fig. 6.25
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Fig. 6.25

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Sedimentary Structures

• Sedimentary Structures A feature found within
  sedimentary rocks, usually formed during or
  shortly after deposition of the sediment and
  before lithification.
• Bedding An arrangement of layers or beds of
  rocks.
• Original horizontality The deposition of most
  water-laid sediment in horizontal or near
  horizontal layers that are essentially parallel
  to the earths surface. (Fig. 6.26)
• Bedding plane A nearly flat surface separating
  two beds of sedimentary rock.
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Sedimentary Structures II

• Cross-bedding An arrangement of relatively thin
  layers of rock inclined at an angle to the more
  nearly horizontal bedding planes of the larger
  rock unit. (Fig. 6.27 Fig. 6.28)
• Graded bed A single bed with coarse grains at
  the bottom of the bed and progressively finer
  grains toward the top of the bed. (Fig. 6.29)
• Mud cracks Polygonal crack formed in a very
  fine-grained sediment as it dries. (Fig. 6.31)
• Ripple marks Any of the small ridges formed on
  sediment surfaces exposed to moving wind or
  water. The ridges form perpendicularly to the
  motion. (Fig. 6.32)
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Fossils

• Fossils Traces of plants or animals preserved
  in rock.
• Fig. 6.33 Fig. 6.34
• A contact is the boundary surface between two
  different rock types or ages of rocks. In
  sedimentary rock formations, the contacts are
  usually bedding planes.
• Fig. 6.35
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Source Area

• The source area of a sediment is the locality
  that eroded and provided the sediment. The most
  important things to determine about a source area
  are the type of rocks that were exposed in it and
  its location and distance from the site of
  eventual deposition. (Fig. 6.36)
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Environment of Deposition

• Fig. 6.38 shows the common environments in which
  sediments are deposited. Geologists study modern
  environments in great detail so that they can
  interpret ancient rocks.
• Continental environments include alluvial fans
  (Fig. 6.39), river channels (Fig 6.40), flood
  plains, lakes, and dunes.
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Table 6.1

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Fig. 6.1

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Fig. 6.2

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Fig. 6.3

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Fig. 6.4

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Fig. 6.7

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Fig. 6.26

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Fig. 6.27

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Fig. 6.28

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Fig. 6.29

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Fig. 6.31

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Fig. 6.32

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Fig. 6.33

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Fig. 6.34

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Fig. 6.35

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Fig. 6.36

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Fig. 6.38

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Fig. 6.39

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Fig. 6.40

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