Sequence stratigraphy

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Angdredd
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261258
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Sequence stratigraphy
Updated:
2014-02-17 13:54:02
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Four
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Test 1
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Stratigraphic surfaces
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  1. Truncation
    termination of strata against an overlying erosional surface. Toplap may develop into truncation, but truncation is more extreme than toplab and implies either the development of erosional relief or the development of an angular unconformity.
  2. Toplap
    termination of inclined strata (clinoforms) against overlying lower angle surface, mainly as a result of nondeposition (sediment bypass),  minor erosion. Strata lap out in a landward direction at the top of the unit, but the successive terminations lie progressively seaward.  The toplap surface represents the proximal depositional limit of the sedimetary unit, in seismic stratigraphy, the topset of a deltaic system (delta plain deposits) may be too thin to be "seen" on the seismic profiles as a separate unit (thickness below the seismic resolution).  In this case, the topset may be confused with the toplap (i.e., apparent toplap).
  3. Onlap
    • (Or lapout) termination of low-angle strata against a steeper stratigraphic surface.
    • May develop in marine, coastal, or nonmarine settings.
  4. Marine onlap
    develops on continental slopes during transgressions (slope aprons, or healing phase deposits), when deep water transgressive strata onlap onto the maximum regressive surface.
  5. Coastal onlap
    refers to transgressive coastal to shallow-water strata onlap onto the transgressive (tidal, wave) ravinement surfaces.
  6. Fluvial onlap
    refers to the landward shift of the upstream end of the aggradation area within a fluvial system during base-level rise (normal regressions and transgression), when fluvial strata onlap onto the subaerial unconformity.
  7. Downlap
    Termination of inclined strata against a lower-angle surface. Downlap may also be referred to as baselap, and marks the base of a sedimentary unit at its depositional limit. Downlap is commonly seen at the base of prograding clinoforms, either in shallow-marine or deep-marine environments. It is uncommon to generate downlap in nonmarine settings, excepting for lacustrine environments. Downlap therefore represents a change from marine (or lacustrine) slope deposition to marine (or lacustrine) condensation or nondeposition.
  8. Offlap
    (Forced regression) the progressive offshore shift of the updip terminations of the sedimentary units within a comfortable sequence of rocks in which each successively younger unit leaves exposed a portion of the older unit on which it lies. Offlap is the product of base-level fall, so it is diagnostic for forced regressions.
  9. truncation, fluvial (stratal termination)
    forced regression, base level fall
  10. Truncation, marine (stratal termination)
    forced regression or transgression, baselevel fall or rise respectively.
  11. Toplap (stratal termination)
    regression, base level stillstand
  12. Apparent toplap (stratal termination)
    normal regression or forced regression, base level rise or fall respectively.
  13. Offlap (stratal termination)
    forced regression, base level fall.
  14. onlap, fluvial (stratal termination)
    normal regression or transgression, base level rise in both cases
  15. Onlap, coastal (stratal termination)
    Transgression, base level rise
  16. Onlap, marine (stratal termination)
    transgression, base level rise
  17. Downlap (stratal termination)
    normal regression or forced regression, base level rise or fall respectively.
  18. Sequence stratigraphic surfaces
    • defined relative to 2 curves
    • 1. base-level changes at the shoreline (naturally not a sine form)
    • 2. T-R curves associated shoreline shifts
  19. Four main events associated with depositional trends during base level shift cycles
    • 1. onset of forced regression
    • 2. end of forced regression
    • 3. end of regression
    • 4. end of transgression
    • thses control formation of ALL seq strat surfaces
  20. Onset of forehead regression
    onset of base-level fall at shoreline
  21. End of forced regression
    end of base-level fall at shoreline
  22. End of (normal) regression
    During base level rise at shoreline
  23. End of transgression
    During base level rise at shoreline
  24. BSFR
    Basal surface of forced regression
  25. MFS
    • Maximum flooding surface
    • between retrograding and prograding geometries
    • figure 4.48
  26. R
    ravinement surface
  27. MRS
    Maximum regressive surface
  28. c.c. SU
    • Correlative conformity
    • subaerial unconformity
  29. RSME
    • Regressive surface of marine erosion
    • strat surface of falling stage in wave dominated shallow marine setting
  30. Surfaces of sequence stratigraphy
    • Base level fall
    • 1., 2. Subaerial unconformity, and it's correlative conformity
    • 3. Basal surface of forced regression
    • 4. regressive surface of marine erosion
    • Base level rise
    • 5. maximum regressive surface
    • 6. maximum flooding surface
    • 7. ravinement surfaces (transgressive)
    • Sequence stratigraphic surfaces may be used, at least in part, as systems tract boundaries or sequence boundaries.  This is their fundamental attribute that separates them from any other type of mappable surface.
  31. Within trend facies contacts
    • Regression
    • 1. Within-trend NR surface
    • 2. Within-trend FR surface
    • transgression
    • 3. Flooding surfaces (other than MRS, MFS, or RS)
    • within-trend facies contacts are lithological discontinuities within systems tracts.  Such surfaces may have a strong physical expression in outcrop or subsurface, but are more suitable for lithostratigraphic or allostratigraphic analysis.
  32. Key features of main stratigraphic surfaces
    • 7 surfaces of sequence stratigraphy
    • 3 within trend facies contacts
  33. 1. Subaerial unconformity figure 4.10
  34. nature of contact: scoured or bypasses
    • facies, below and above: variable (where marine, c-u); nonmarine
    • depositional thrends below and above: NR, FR; NR, T
    • substrate-controlled ichnofacies: N/A
    • stratal terminations: above: fluvial onlap, surface: offlap; below: truncation, toplap
    • temporal attributes: variable hiatus
  35. 7. transgressive wave ravinement surface figure 4.14
    • nature of contact:  scoured
    • facies, below and above: variable (where marine, c-u); marine f-u
    • depositional thrends below and above: NR, T; T
    • substrate-controlled ichnofacies: Glossifugites, Trypanites, Teredolites
    • stratal terminations: above: coastal onlap, surface: N/A, below: truncation
    • temporal attributes: high diachroneity
  36. 2. Correlative conformity figure 4.17
    • nature of contact:  conformable
    • facies, below and above: marine, c-u; marine (c-u on shelf)
    • depositional thrends below and above: FR; NR
    • substrate-controlled ichnofacies: N/A
    • stratal terminations: above: downlap, surface: downlap, below: N/A
    • temporal attributes: low diachroneity
  37. 3. Basal surface of forced regression
    • nature of contact:  conformable
    • facies, below and above: marine (c-u on shelf); marine, c-u
    • depositional thrends below and above: NR; FR
    • substrate-controlled ichnofacies: Glossifungites, where reworked by the RWR
    • stratal terminations: above: downlap, surface: downlap, below: N/A, truncation
    • temporal attributes: low diachroneity
  38. 4. regressive wave revinement
    • nature of contact: scoured
    • facies, below and above: shelf, c-u; shoreface, c-u
    • depositional thrends below and above: NR, FR; FR, NR
    • substrate-controlled ichnofacies: Glossifungites
    • stratal terminations: above: downlap, surface: N/A, below: truncation
    • temporal attributes: high diachroneity
  39. 5. maximum regressive surface
    • nature of contact: conformable
    • facies, below and above: variable; variable (where marine, f-u)
    • depositional thrends below and above: NR; T
    • substrate-controlled ichnofacies: N/A
    • stratal terminations: above: marine onlap; surface: onlap, downlap; below: N/A
    • temporal attributes: low diachroneity
  40. 6. Maximum flooding surface
    • nature of contact: conformable or scoured
    • facies, below and above:variable (where marine, f-u); variable (where marine, c-u)
    • depositional thrends below and above: T; NR
    • substrate-controlled ichnofacies:Glossifungites, Trypanites, Teredolites
    • stratal terminations: above: downlap; surface: onlap, downlap; below: N/A, truncation
    • temporal attributes: low diachroneity
  41. 8. Transgressive tidal ravinement
    • nature of contact: scoured
    • facies, below and above: variable (where marine, c-u); estuary mouth complex
    • depositional thrends below and above: BR, T; T
    • substrate-controlled ichnofacies: Glossifungites, Trypanites, Teredolites
    • stratal terminations: above: coastal onlap; surface: N/A; below: truncation
    • temporal attributes: high diachroneity
  42. 9. within-trend NR surface
    • nature of contact: conformable
    • facies, below and above: delta front or beach; delta plain or fluvial
    • depositional thrends below and above: NR; NR
    • substrate-controlled ichnofacies: N/A
    • stratal terminations: N/A
    • temporal attributes:high diachroneity
  43. 10. within-trend FR surface
    • nature of contact: conformable
    • facies, below and above: prodelta; delta front
    • depositional thrends below and above: FR; FR
    • substrate-controlled ichnofacies: N/A
    • stratal terminations: above: downlap; surface: N/A; below: N/A
    • temporal attributes: high diachroneity
  44. 11. Flooding surface
    • nature of contact: conformable or scoured
    • facies, below and above: variable; marine f-u or c-u
    • depositional thrends below and above: T, NR; T, NR
    • substrate-controlled ichnofacies: Glossifungites, Trypanites, Teredolites
    • stratal terminations: above: onlap, downlap; surface: onlap, downlap; below: truncation
    • temporal attributes: low to high diachroneity
  45. Shallow marine deposits of FSST river dominated deltaic setting
    Clinoforms steeper than wave equilibrium profile->no wave scouring and BSFR preserved and FR surface package has gradational base
  46. BSFR at base of submarine fan complexes
    But be wary of lobe switching->younger but similar facies dislocations
  47. Regressive surface of marine erosion (RSME)
    Shoreface above outer shelf
  48. Gutter casts
    • Where the off shore flowing currents have enough energy to cut into the fine grained marine muds
    • filled in with sands and may have hummocky texture.
  49. Figure 4.38
    wave dominated estuary
  50. Figure 4.38
    Tide dominated estuary
  51. Seismic expression of MFS in cost-shallow marine setting
    On TST shelf
  52. MFS on top of TST strata
    • Figure 4.41
    • May have two wedges
    • shelf(coastal onlap)
    • deep marine (marine onlap)
  53. MFS may rework older MRSs and scour
    TST facies missing
  54. Fluvial-shallow marine succession with MFS and R
    • Figure 4.45
    • MFS seen as:
    • onshore - change in fluvial architecture (meander up to braided) 
    • nearshore - estuarine topped by fluvial
    • offshore is the youngest part of the RS with transgressive lag
  55. In a wave dominated setting
    • Tidal (TRS) and wave (WRS) ravinement surfaces during transgression and facies retrogradation
    • same in a tide dominated setting
    • get tidal flat as opposed to delta plain
  56. TRS
    Tidal ravinement surface
  57. WRS
    • Wave ravinement surface
    • always at base of shoreface facies onlap
    • figure 4.48
  58. Figure 4.52
    Model of incised valley (IV) fill with all facies of base level rise phase represented with corresponding surfaces
  59. Within trend surfaces
    • Surfaces within STs expressed by facies contacts
    • caused by shift in depositional environments with changes in environmental energy and sediment

    • often used to define parasequences
    • figure 4.55
  60. Within trend forced regressive surfaces
    • At conformable contacts between prodelta and deltafromt - base of prograding delta
    • forms only in river dominated deltaic settings
    • highly diachronius
  61. Within trend flooding surfaces
    • Defined by an abrupt increase in water depth
    • could have minor submarine erosion of non-deposition
  62. Figure 4.61
    WT-FS between transgressive shoreface strata below and transgressive outer shelf shales above

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