GE0-3112%20Sedimentary%20processes%20and%20products

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GE0-3112 Sedimentary processes and products

• Lecture 13. Sequence stratigraphy

• Literature
• - Leeder 1999. Ch. 14. Changing sea level and
  sedimentary sequences.
• - Reading Levell 1996. Ch. 2. Controls on the
  sedimentary rock record.

Geoff Corner Department of Geology University of
Tromsø 2006
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Contents

• Stratigraphy
• Why sequence stratigraphy?
• Parasequences
• Systems tracts
• Bounding surfaces

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Stratigraphy the subdivision of rocks in time
and space

• Lithostratigraphy
• Biostratigraphy
• Chronostratigraphy
• Magnetostratigraphy
• Chemostratigraphy
• Morphostratigraphy
• Climatostratigraphy
• Kinetostratigraphy
• Tectonostratigraphy
• Allostratigraphy
• Sequence stratigraphy

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What is sequence stratigraphy?

• Packages of strata deposited during a cycle of
  relative sea-level change and/or changing
  sediment supply.
• Genetic/interpretative approach
• packages related to relative sea-level and/or
  sediment supply.
• packages bounded by chronostratigraphic surfaces.

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Walker 1992
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Why use sequence stratigraphy?

• To correlate and predict facies and
  unconformities division of the sedimentary
  record into time-related genetic units.
• To understand the distribution of sedimentary
  facies and unconformities in time and space.
• To determine the amplitudes and rates of change
  of past relative sea-level and, in turn,
  understand the cyclic and non-cyclic nature of
  tectonics and climate change (durations of 10 ka
  - gt50 Ma).

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What criteria do we use?

• Stacking patterns - indicate relative sea-level
  change and or sediment supply.
• Bounding surfaces

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Components of a sequence

• Bounding surfaces
• Sequence boundary
• Transgressive surface
• Maximum flooding surface
• Systems tracts
• LST
• TST
• HST/RST
• Parasequences

Prothero Schwab 1996
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Parasequences

• Parasequences the small-scale building blocks of
  systems tracts and sequences.
• A parasequence represents a proximal to distal
  change in facies accumulated during a minor cycle
  in the balance between sediment supply and
  accomodation.
• Each parasequence is bounded above by a flooding
  surface.

Prothero Schwab 1996
Flooding surfaces
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Stacking pattern of parasequences

• Progradational
• Retrogradational
• Aggradational

Prothero Schwab 1996
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Sequences

• A sequence is composed of a succession of
  parasequence sets.
• Each sequence represents one major cycle of
  change in the balance between accomodation space
  and sediment.
• A sequence is subdivided into 3 or 4 systems
  tracts, each representing a specific part of the
  cycle.

Prothero Schwab 1996
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Systems tracts

• Exxon
• LST, TST, HST (incl. RST)
• Alternative
• LST, TST, HST, RST (forced RST)

Walker 1992
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Lowstand ST

• Formed immediately following s.l. lowstand.
• Fluvial incision ceases progradational to
  aggradational marine parasequences deposited.
• Active submarine fans below the shelf break.

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Transgressive ST

• Formed during s.l. rise.
• Accomodation space gt sediment supply ?
  retrogradational parasequences.
• Base of TST is the transgressive surface
  (ravinement erosional surface of shoreface).
• Top of TST is the maximum flooding surface.

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Highstand ST

• Formed during rising and high s.l.
• Accomodation sediment supply ? aggradational to
  progradational parasequences.

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Falling stage ST

• Formed during a s.l. fall (forced regression).
• (Included in late HST in Exxon system).
• May be associated with erosion.

Walker 1992
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Bounding discontinuites

• Sequence boundary (SB) - surface of subaerial
  erosion and its correlative marine surface formed
  during sea-level fall. Corresponds to base of
  incised valley in proximal areas.
• Transgressive (ravinement) surface (TS) -
  transgressive surface of marine (shoreface)
  erosion.
• Marine flooding surface - surface across which
  there is evidence of an abrupt increase in water
  depth (may be used to separate parasequewnces).
• Maximum flooding surface (MFS) - surface marking
  regional transition from trangression to
  regression and most landward extent of the
  shoreline - commonly marked by a condensed
  section (horizon).
• Regressive surface of erosion.
  (NB. may be removed by
  subaerial
  erosion or
  transgressive surface).

Prothero Schwab 1996
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Wheeler (time-distance) diagrams
Prothero Schwab 1996
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Sequence stratigraphy and global sea-level cycles

• Various orders of global sea-level change
  distinguisged
• 1st order (200-400 m.y.), e.g. lowstand during
  Permian Pangea. Controlled by major tectonic
  cycles.
• 2nd order (10-100 m.y.), e.g. Mid-Cretaceous
  highstand. Controlled by changes in ocean-ridge
  spreading rate.
• Global correlation of sequences related to
  eustatic sea-level curves is difficult or
  impossible due to local variations in tectonics
  and sediment supply. Sequence development is
  dependent on 1) sea level, 2) tectonics, 3)
  sediment supply.

Walker 1992
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An example of sequence stratigraphic subdivision
applied to fjord-valley fills
Corner, in press
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• Deglacial-postglacial transgressive-regressive
  fill

Corner, in press
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• TST
• HST
• RST

Highstand systems tract
Transgressive systems tract
Forced-regressive systems tract
Corner, in press
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Corner, in press
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Further reading

• Coe (ed.) 2003. The Sedimentary Record of
  Sea-Level Change.
• Well illustrated, modern treatment of sequence
  stratigraphy and depositional successions.
• Emery Myers 1996. Sequence stratigraphy.
• Similar to above but more dated. Gives background
  to nomenclature.
• E-learning journal. Sequence stratigraphy.
• Walker 1992, in Walker James (Ch. 1, 'Facies,
  Facies Models and Modern Stratigraphic
  Concepts').
• Corner, G.D. (in press, 2006). A
  transgressive-regressive model of fjord-valley
  fill stratigraphy, facies and depositional
  controls. In Dalrymple, R.W., Leckie, D. and
  Tillman, R.W. (eds.) Incised-Valley Systems in
  Time and Space', SEPM Special Publication.