Structural Geology Geol 305 Semester 071

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Structural Geology(Geol 305)Semester (071)

• Dr. Mustafa M. Hariri

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Non-Tectonic Structures
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Objectives

• By the end of this unit you will be able to know
• The Fundamental Concepts in Geology and their
  importance
• What is the Non-Tectonic Structures and how they
  formed?
• The difference between Tectonic and Non-Tectonic
  Structures
• The different types of Non-Tectonic Structures

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FUNDAMENTAL CONCEPTS

• These concepts are very important to study
  structural geology and they help in solving the
  structural problems
• Doctrine of uniformitarianism
• The present is the key to the past (Processes are
  taking place today within the earth are similar
  to the ones took place in the past and to that
  will take place in the future) example sand bars
  and beaches
• Can't be applied to Iron to iron formation in
  lake superior (different atmospheric composition)
• Contrast in nature of Archean and proterozoic
  crusts (differences in processes)
• 2) Law of superposition
• Within layered sequence oldest rocks occur at the
  base of sequence and younger rocks toward top
  unless the sequence is inverted
• 3) Law of original horizontally
• Sediments and Sedimentary rocks form in
  horizontal to nearly horizontal orientation at
  the time of deposition.

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FUNDAMENTAL CONCEPTS

• 4) Law of crosscutting relationships (structural
  relationships)
• An igneous body or any structure (fold or fault)
  must be younger than the rocks it cuts ( the
  rocks contain the igneous body or structure must
  have been there before the structures or the
  igneous body)
• 5) Law of faunal succession
• The fossil organisms should be systematically
  changed, possibly more advanced toward the top
  of the sequence (Permits determination of whether
  the sequences is upright or overturned)
• 6) Multiple working hypotheses
• Consider more than one assumptions and test them
  until you are sure from one of them.

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FUNDAMENTAL CONCEPTS

• 7) Outrageous hypothesis
• Consider the data to reach to solution and
  illuminate other hypothesis
• 8)Pumpellys rule
• Small structures are a key to and mimic the
  styles and orientation of larger structures of
  the same generation within a particular area.

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NONTECTONIC STRUCTURES

• Those structures include the primary sedimentary
  and volcanic structures. They are useful in
  determining the facing direction in a sequence of
  rocks
• Examples of these structures are
• Bedding features
• mud cracks
• ripples marks
• sole marks
• vesicles

Bedding Planes
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Nontectonic Structures can be distinguished from
Tectonic Structures by the following

• 1)Nontectonic structures usually older than the
  tectonic structures
• 2)Tectonic structures usually show a parallel
  orientation over wide area compare to the
  nontectonic ones.
• 3) Small structures in tectonic mimic large size
  ones.

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Non-Tectonic StructuresPrimary Sedimentary
StructuresBEDDING

• Bedding planes represents mechanical zones of
  weakness and they form when there is a
  compositional or textural difference is exist
  between two beds.
• Examples are
• Different grain sizes
• Different compaction
• Discontinuity of deposition
• .
• Graded bedding contain a range of particle sizes
  from large at the base to small at the top.
  (boulder to.clay)
• Graded bedding is important in determining the
  facing direction
• They are useful in determining the facing
  direction.

Bedding Planes
Graded Bedding
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Non-Tectonic StructuresPrimary Sedimentary
Structures BEDDING

• Cross bedding forms in sediments transported by
  water or wind
• Types
• tangential
• planar
• trough
• festoon
• For finer sediments and small scale
• ripple
• Hummocky
• Mud cracks form by extensional cracks due to
  drying of fine grain sediments deposited by
  water.

Cross Bedding
Mud Cracks
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Non-Tectonic StructuresPrimary Sedimentary
StructuresBEDDING

• Ripple Marks form where sediments is moved by a
  current. They are very common along beaches and
  streams as well as deeper water, where bottom
  currents or surface waves interact with bottom
  sediments.
• Types
• 1) current they are asymmetric, their steep sides
  face downstream in the direction of transport.
  They are not useful in determining the facing
  direction
• 2) oscillatory they are symmetrical and consist
  of high and low crests
• They form by back and forth motion of water (such
  as lake)
• They are useful in determining the facing
  direction as the crests have sharp peaks
  separated by rounded trough.

Ripple Marks
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Non-Tectonic StructuresPrimary Sedimentary
StructuresBEDDING

• Rain Imprints form where rain falls on fine
  sediment and preserved in sedimentary record by
  another layer of sediment. They are used also to
  determine facing direction.
• Tracks and Trails left by organisms, used also
  in determining the facing direction of beds.
• Sole Marks, Scour Marks, Flute Casts Marks
  formed as an object moves across a bedding
  surface or as currents scour a bedding surface.
  Flute molds consist of scoop-shaped structures
  formed when the currents scour and erode a
  surface. Flute casts form when these molds filled
  with sediment.
• All these features are used to determine the top
  of the bed.

Rain-imprint
Fossils Track
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Non-Tectonic StructuresPrimary Sedimentary
StructuresBEDDING

• Dewatering Structures (Load Cast) form after
  deposition and dewatering of sediments as a
  result of gravitational instability at the
  interface between a layer of water saturated sand
  and underlying mud. The weight of the newly
  deposited overlying sediment forces out the
  interstitial water.
• They can also be used in determining the facing
  direction by using the broadly convex bottom side
  of the cast that face the toward the bottom.
• Fossils they are useful in determining the
  relative age and facing direction by studying the
  relative position in sequence.
• They are also useful strain indicators.
• Reduction Spots are sedimentary structures
  produced by a small grain or fragment that is
  chemically different from the surrounding.
• They are useful as strain indicators.

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Non-Tectonic StructuresPrimary Sedimentary
Structures Sedimentary Facies

• Sedimentary Facies
• The vertical and lateral variation in sedimentary
  rocks due to the paleoenvirnoments change. Each
  sediment (rock) type is called a facies or
  lithesome. One facies is separated from others by
  particular characteristics (composition, texture,
  sorting, physical and biogenic sedimentary
  structures)

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Non-Tectonic StructuresPrimary Sedimentary
Structures Unconformities
Disconformity

• Unconformities
• A break in the sedimentary record, where part of
  a stratigraphic succession and history is
  missing. Unconformities are produced by erosion
  or non-depostion (or both).
• Types of unconformities
• Disconformity
• Is produced by deposition of a sequences followed
  by erosion without tilting or deformation, then
  comes subsidence and renewed deposition. Beds
  above and below unconformity remain parallel.
  Topographic relief along the unconformity may be
  present.
• Paraconformity is in places where there is little
  relief on an unconformity.

Angular
Non-conformity
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Non-Tectonic StructuresPrimary Sedimentary
Structures Unconformities

• Angular unconformity
• Is produced where a sequence has been tilted as a
  result of slumming or tectonic processes, and
  followed by deposition of new sedimentary strata.
• Nonconformity
• Is an unconformity in which igneous or
  metamorphic rocks (or both) occur below the
  erosion surface, and sedimentary rocks occur
  above. It indicates that a long time interval
  passed between formation of the igneous and
  metamorphic rocks at great depths in the Earth
  and deposition of sediment.
• The three types of unconformities may be present
  in one area.

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Non-conformity and Angular Unconformity
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Non-Tectonic StructuresPrimary Igneous Structures
Foliation and Lineation

• Foliation,
• Pillow structures
• Phenocrysts,
• Cross-cutting,

Cross-cutting
Pillow Lava
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Non-Tectonic StructuresPrimary Igneous Structures

• -Xenoliths,
• - Pyroclastic rock structures
• -Compositional banding
• - Contact metamorphic zones
• -Vesicles.
• Some of these structures are useful in
  determining the facing direction and top position

Breccia
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Non-Tectonic StructuresGravity Related Features

• Landslide and Submarine Flows
• They form above and below sea level and triggered
  by
• earthquakes (tectonic)
• overloading of slopes
• high precipitation
• oversteeping of slopes
• human activities

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Non-Tectonic StructuresGravity Related Features

• Turbidities are deposits by rapid flow of
  sediments driven by turbidity current down a
  slope onto sea floor or lake floor. They consist
  of unsorted mass of sediments called
• BOUMA SEQUENCE

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Non-Tectonic StructuresGravity Related Features

• BOUMA SEQUENCE OF TURBIDITES
• Shale (pelite)
• Silt (pelite)
• Rippled or cross-bedded sandstone
• Laminated sandstone (well sorted)
• Graded bedding of poorly sorted sandstone
• These are useful in determining the facing
  direction and the top of the sedimentary sequence.

Bouma Sequence
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Non-Tectonic StructuresGravity Related Features

• SALT STRUCTURES
• Evaporite deposits occur in sedimentary sequences
  at shallow crustal levels. Rock salt deposits
  formed by evaporation of sea water and composed
  mostly of halite. These rocks flow more readily
  than does any other rock type.

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Non-Tectonic Structures Gravity Related Features

• Salt flows at surface conditions by the force of
  gravity. The salt density contrasts with the
  greater density and strength of the sediments
  surrounding them. This produces a variety of
  structures ranging form glacier on the surface to
  salt pillow and stocks and domes at depth. The
  internal structure of these salt features
  indicates a plastic flow with folds, foliation,
  and other structures similar to the ones form
  under high pressure and temperature in
  metamorphic rocks.

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Non-Tectonic StructuresGravity Related Features

• SALT STRUCTURES
• Diapirs are salt or other material that move
  upward and gravitationally intrude the above
  sediments. They serve in many places of the world
  as hydrocarbon traps.
• Locations of diapirs and geometry of the
  structures produced within the sediments are
  controlled by
• extensional process in cover sediments related to
  the flow of the salt by gravity underneath.

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Non-Tectonic StructuresGravity Related Features

• IMPACT STRUCTURES
• These structures are formed by meteoritic impact
  and are usually have a circular or elliptical
  outlines. They are characterized by shatter cones
  structures (cone shape fractures with epics at
  the point of force and the base is away from it)
  

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