Sedimentary Rocks

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Sedimentary Rocks
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What is a sedimentary rock?

• Sedimentary rocks are products of mechanical and
  chemical weathering
• They account for about 5 percent (by volume) of
  Earths outer 10 kilometers
• Contain evidence of past environments
• Provide information about sediment transport
• Often contain fossils

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What is a sedimentary rock?

• Sedimentary rocks are important for economic
  considerations because they may contain
• Coal
• Petroleum and natural gas
• Sources of iron, aluminum, and manganese

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Gravel Beach
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Talus Cones
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delta
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Owens River
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Meandering River
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Alluvial fans
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Sand Dunes
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Death Valley salt pan
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Playas
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Deep Springs Lake
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fringing reef
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Sandy Beach
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Spits
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Swamps
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Successive stages in coal formation
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coal
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Sedimentary Rocks
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Fossil Fish - 50 Million Year Old Lakes in
southern Wyoming
These fish tell us the Wyoming climate 50 million
years ago.
Sedimentary Rock made of fine-grained mudstone.
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Sedimentary Rocks

• Sedimentary form in water
• Generally formed by the deposition, burial,
  compaction, and cementation of sediments (pieces
  of other rocks)
• 3 Types
• Clastic
• Chemical (crystalline)
• Organic (Bioclastic)

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3 Types of Sedimentary Rocks

• Clastic (also called Detrial)made of broken
  pieces of other rocks

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3 Types of Sedimentary Rocks

• Organicremains of plants and animals are
  deposited in thick layers
• Examples
• Fossil rich limestone is made from the shells of
  ocean animals used to make chalk

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3 Types of Sedimentary Rocks

• Chemicalminerals dissolved in lakes, seas, or
  underground water

Mineral crystals are made as the shallow water
that has flooded the bottom of Death Valley
evaporates. Click on image for full size (66K
JPG)Courtesy of Martin Miller, University of
Oregon
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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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Classification of sedimentary rocks

• Two major textures are used in the classification
  of sedimentary rocks
• Clastic
• Discrete fragments and particles
• All detrital rocks have a clastic texture
• Nonclastic
• Pattern of interlocking crystals
• May resemble an igneous rock

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Detrital sedimentary rocks
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Detrital sedimentary rocks

• Common detrital sedimentary rocks (in order of
  increasing particle size)
• Shale
• Mud-sized particles in thin layers that are
  commonly referred to as laminea
• Most common sedimentary rock

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Lake Bed Deposits
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Shale containing plant remains
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Detrital 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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• B. Descriptions of individual clastic rocks
• Arkose
• Graywacke
• Quartz Sandstone

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Worlds Biggest Rock

• The Ayers Rock is made up of arkose, a
  course-grained sandstone rich in feldspar at
  least 2.5 km thick. Uplifting and folding between
  400-300 mya turned the sedimentary layers nearly
  90 degrees to their present position. The surface
  has then been eroded.

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Graywacke
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Detrital sedimentary rocks

• Alternating sequences of shale and sandstone
  exposed in the Grand Canyon. Shale cannot
  support steep cliffs or form erosion

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Detrital sedimentary rocks

• Conglomerate and breccia
• Both are composed of particles greater than 2mm
  in diameter
• Conglomerate consists largely of rounded gravels
• Breccia is composed mainly of large angular
  particles

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• B. Descriptions of individual clastic rocks
• Breccia
• Conglomerate

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Conglomerate
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Conglomerate
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Breccia
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breccia1
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Characteristics of sedimentary rocks

• Sorting the distribution of grain sizes in a
  rock

Sorting depends on properties of the depositing
agent
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Graded Beds
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Sorting
Glacier deposit poorly sorted
Sand dune well sorted
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3 Types of Sedimentary Rock

• Clastic
• Formed from the deposition, burial, compaction,
  and cementation of sediments (fragments of other
  rock)

Examples
Grain Size
Composition
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3 Types of Sedimentary Rock

• Chemical (crystalline)
• Precipitates minerals fall out of solution when
  the water chemistry changes
• Evaporates minerals left behind when water
  evaporates

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Chemical sedimentary rocks

• Consist of precipitated material that was once in
  solution
• Precipitation of material occurs in two ways
• Inorganic processes
• Organic processes (biochemical origin)

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Chemical sedimentary rocks

• Common chemical sedimentary rocks
• Limestone (calcareous deposits)
• Most abundant chemical rock
• Composed chiefly of the mineral calcite
• Marine biochemical limestones form as coquina
  (broken shells), and chalk

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Coquina
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Fossiliferous limestone
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Chemical sedimentary rocks

• Common chemical sedimentary rocks
• Dolostone (siliceous deposits)
• Typically formed secondarily from limestone
• Chert (siliceous deposits)
• Made of microcrystalline quartz
• Varieties include flint and jasper (banded form
  is called agate)

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Sedimentary Rocks

• Quartz (SiO2)
• flint, chert

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Chert nodules
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Chemical sedimentary rocks

• Common chemical sedimentary rocks
• Evaporites (saline deposits)
• Evaporation triggers deposition of chemical
  precipitates
• Examples include rock salt and rock gypsum

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• Chemical and Biochemical Rocks
• Evaporites (Halite and Gypsum)

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salt flats in western Utah
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Dessication Cracks
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• Chemical and Biochemical Rocks
• Limestones
• Micrite
• Calcarenite

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• Limestones
• Chalk
• Coquina
• Fossiliferous

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• Limestones Oolitic

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Oolites
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• Chemical and Biochemical Rocks
• Limestones
• Dolomites

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Sinkhole a circular depression in a karst area,
commonly funnel-shaped.
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This is what lies below that sink hole! And yes
my feet were standing on air!
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Examples of Sedimentary Features and Landforms


Narracoorte Caves, southeastern SA
The Queens Throne- Utah
Stalactites (of mineral calcite). Biochemical and
inorganic sedimentary limestone rocks.
http//www.uh.edu/jbutler/physical/chapter7.html
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Stalactites hanging (tight) to the ceiling of a
cave.
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This is what a cave typically looks like.
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A speleothem made of the mineral gypsum, common
in dry caves.
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Chemical sedimentary rocks

• Common chemical sedimentary rocks
• Coal (Carbonaceous deposits)
• Different from other rocks because it is composed
  of organic material
• Stages in coal formation (in order)
• 1. Plant material
• 2. Peat
• 3. Lignite
• 4. Bituminous

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coal
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Sedimentary environments

• A geographic setting where sediment is
  accumulating
• Determines the nature of the sediments that
  accumulate (grain size, grain shape, etc.)

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Sedimentary environments

• Types of sedimentary environments
• Continental
• Dominated by erosion and deposition associated
  with streams
• Glacial
• Wind (eolian)
• Marine
• Shallow (to about 200 meters)
• Deep (seaward of continental shelves)

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Sedimentary environments

• Types of sedimentary environments
• Transitional (shoreline)
• Tidal flats
• Lagoons
• Deltas

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Continental (left) and marine (right)
depositional environments
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Sedimentary environments

• Sedimentary facies
• Different sediments often accumulate adjacent to
  one another at the same time
• Each unit (called a facies) possesses a
  distinctive set of characteristics reflecting the
  conditions in a particular environment
• The merging of adjacent facies tends to be a
  gradual transition

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Sedimentary facies
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Characteristics of Sedimentary Rocks

• May stratified because the sediments are laid
  down in horizontal layers called strata. (
  one layer is called stratum)
• May also contain fossil i.e remains, prints or
  other indications of plants animals found
  buried in rocks

Dipping sedimentary layers of rock, Rocky
Mountains, Canada.
http//www.geog.ouc.bc.ca/physgeog/contents/10f.ht
ml
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Sedimentary structures

• Provide information useful in the interpretation
  of Earth history
• Types of sedimentary structures
• Strata, or beds (most characteristic of
  sedimentary rocks)
• Bedding planes that separate strata

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Fossils Evidence of past life

• By definition, fossils are the traces or remains
  of prehistoric life now preserved in rock
• Fossils are generally found in sediment or
  sedimentary rock (rarely in metamorphic and never
  in igneous rock)

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Fossils Evidence of past life

• Geologically fossils are important for several
  reasons
• Aid in interpretation of the geologic past
• Serve as important time indicators
• Allow for correlation of rocks from different
  places

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Features of Sedimentary Rocks

• Stratification (bedding) is when layers of
  sedimentary rocks form stacked on top of each
  other

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Features of Sedimentary Rocks

• Ripple Marks are sand patterns formed by the
  action of winds, streams, waves, or currents

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Features of Sedimentary Rocks

• Mud Cracks develop in clay when it dries out and
  hardens into rock.