THRUST FAULTS: ASSOCIATED STRUCTURES AND IMPLICATIONS IN HYDROCARBONS TRAPS

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THRUST FAULTS ASSOCIATED STRUCTURES AND
IMPLICATIONS IN HYDROCARBONS TRAPS
STRUCTURE AND HYDROCARBON PROSPECTIVITY OF BASINS
James Moore Alex Nyombi Christian
Hidalgo Adekunle Odutola
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Aims Objectives

• A brief introduction to Thrust Faults
• Define Tectonics Settings involving Thrust Faults
  formation
• Review structures associated with Thrust Faults
• Highlight two examples of Hydrocarbon Traps
  associated with Thrust Faults
• Summarise

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Why Study Thrust Faults ?

• The are very damaging. Host of the largest and
  potentially most destructive earthquakes
• Associated with mountain building and
  collisional tectonics
• Influence positions of ore deposits and
  hydrocarbons

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What Are Thrust Faults ?

• They are reverse faults with low dip that form in
  layered sequences where horizontal stress is
  greater than vertical stress.
• They are formed by compressive stresses
• Thrust faults are dip-slip faults
• They have dip less than 45

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What Are Thrust Faults ?
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Major Types of Thrust Faults

1. Thin-Skinned Thrusts

• Thin skinned thrusts developed within sedimentary
  basins
• Basement may act as a basal detachment
• Basement is not involved
• Typical of leading edges of compressive orogens

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Major Types of Thrust Faults
2. Thick-Skinned Thrusts

• Thick skinned thrusts cut upward through the
  basement and propagate through the sediment
• Thick skinned thrusts usually steepen upwards and
  are covered by drape folds

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Rules For Thrust Development

• Thrust always cut up-section in the direction of
  transport
• Thrust always place older over younger rocks
• Higher thrust develop first
• Thrusting proceeds from higher to lower and from
  hinterland towards foreland

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Dynamics of Thrust Motion

• Conditions for thrust movement include
  overcoming
• Frictional resistance to sliding on the basal
  fault surface
• Gravitational forces resulting from the mass of
  the sheet

• Hypothesis supporting thrust movement include
• Gravity sliding hypothesis
• Fluid pressure hypothesis

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Mechanisms of Thrusting

• They are formed by compressive tectonic stresses
  and occur at convergent plate boundaries.
• ?1 is horizontal and ?3 is vertical.
• The two sets of thrust faults intersect along the
  horizontal ?2 axis with dip less that 45.
• Horizontal contraction parallel to ?1 and
  vertical extension parallel to ?3

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Components of a Thrust System

• Foreland is the area in front of the thrust belt
• Hinterland is the area behind the thrust belt
• Imbricate fan Individual thrust sheets overlap
  like roofing tiles
• Duplex system of imbricate thrusts that branch
  off from a single fault below and merge with a
  thrust fault above. The rock body bounded by
  faults above and below is called a horse
• Ramps Flats Faults consist of flats parallel
  to bedding (surface of weakness) and ramps where
  the fault cuts across the bedding

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Components Of Thrust Faults
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Tectonic Setting of Thrust Fault

• Thrust faults accommodate shortening of the
  earth's crust
• Most big mountain ranges are fold-and-thrust
  belts
• Consists of a set of folds and thrust faults that
  extend for 10s to 100s of kilometres along strike
• Usually shortening takes place near the plate
  boundary in convergent margins (Himalayas, Alps,
  Appalachians, Urals)

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Formation of Duplex Structure
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Formation of Thrust Duplex
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Structures Associated with Thrust Faults

• Foreland thrust and fold belts
• Belts of deformed sedimentary rock in which the
  layers are folded and duplicated by thrust faults
  are common at the edges of orogens
• Folds and thrust faults are the dominant
  structures
• Results in the formation of foreland basin and
  piggy- back basin
• Classic examples occur in the Main Ranges,
  Valley and Ridge province of the Appalachians,
  and the Jura Mountains in the Alps

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Foreland Thrust And Fold Belt
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Folds Associated with Thrust Faults

• Fault bend folds
• Detachment folds
• Fault propagation fold

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Thrust Faults as Hydrocarbon Traps Hypothetical
Example

• Thrust Faults
• This example shows sediment deposited by a
  glacier 10,000 years ago.

• When the glacier moved back over the sediments,
  faulting occurred. A glacial readvance.

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Thrust Faults as Hydrocarbon Traps Hypothetical
Example

• Hypothetical situation set up below.

• Sandstone source rock, Shale seal rock.

• Rock sequence is thrusted creates a possible
  hydrocarbon trap.

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Thrust Faults as Hydrocarbon Traps Nepal
Location of Nepal
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Thrust Faults as Hydrocarbon Traps Nepal

• Traps can be seen in the Siwalk Fold Belt.
• A blind thrust is also seen. This can also act
  as a trapping mechanism.

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Thrust Faults as Hydrocarbon Traps Moose
Mountain, Canada
McConnell Thrust
Moose Mountain
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Thrust Faults as Hydrocarbon Traps Moose
Mountain, Canada

• Moose Mountain
• thrust sheet is defined
• as the uppermost thrust
• sheet which strata are
• exposed at the surface.
• This thrust essentially
• placed a single repetition of the entire Cambrian
  through Cretaceous sequence in the hanging wall,
  over the footwall.
• Strata in the footwall of the Moose Mountain
  thrust range from Paleozoic to the Lower
  Cretaceous.

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Summary

• They are found in compressional settings like
  orogenic belts, salt domes and diapiric
  structures in general
• Repeat stratigraphy, puts older rocks on top of
  younger rocks and contracts layering
• They closely associated with folds and thrust
  belts
• 2 major types of Thrust faults Thin-Skinned
  Thrusts and Thick-Skinned Thrusts.

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Summary

• Components of a Thrust System Foreland,
  Hinterland, Imbricate fans, Duplexes, Ramps
  Flats
• When rock sequence is trusted creates a possible
  hydrocarbon trap
• Two examples of thrust faults forming a
  structural trap for hydrocarbons Nepal, Moose
  Mountains

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Questions ?
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References

• Park, R.G. Foundations of Structural Geology,
  Chapman Hall. pp 95 96, 1997.
• Twiss, R. J. and E. M. Moores, Structural
  Geology, W. H. Freeman Co., New York, 256p,
  1992.
• http//vle.leeds.ac.uk/site/nbodington/earthscienc
  e/fifth/msc_struc/
• http//ic.ucsc.edu/casey/eart150/Lectures/4Thrust
  Flts/4thrustfaults.htm
• http//courses.eas.ualberta.ca/eas421/lecturepages
  /thrust.html
• http//earth.leeds.ac.uk/faults/thrust/tipline/fbf
  old.htm
• http//www.colorado.edu/geolsci/courses/GEOL3120/3
  120lect_13.pdf
• (Taken from http//www.cseg.ca/conferences/2000/20
  00abstracts/505.PDF)