Sequence stratigraphy

Card Set Information

Sequence stratigraphy
2014-02-17 13:54:21
Test 1
Accommodation and shoreline shifts
Show Answers:

  1. Sequence stratigraphy astratigraphy a
    Sequence stratigraphy is based on the premise that sed successions can be divided into unconformity-bounded units (sequences) that form during a single major cycle of sea-level change.
  2. Identify autogenic and allogenic controls on sedimentation
    Figure 3.1
  3. Tectonic and orbital controls on eustasy
    • First order, 200-400my, formation and break up of supercontinents
    • second order, 10-100my, volume changes
    • third order (most sequences), 1-10my, regional plate kinematics
    • fourth and fifth order, 0.01-1my,
    • figure 3.2
  4. Systems tracts
    Linkage of contemporaneous depositional systemssystems
  5. Depositional systems
    3D assemblage of lithofacies genetically linked by active (modern) or inferred (ancient) processes and environments
  6. Parasequences
    • Small-scale pro-, ag-, retro-gradational units that stack together to make depositional systems themselves made up of bed-sets
    • 10-100m thick (latter normally parasequence sets)
  7. Signatures of eustatic control on sedimentation
    • Tabular geometry-uniform accommodation
    • synchronicity of depositional and erosion all events
    • lack of evidence of source area rejuvenation-no coarse at rim
  8. Signatures of tectonic control on sedimentation
    • Wedge-shaped geometry - differential subsidence
    • coarse facies along rim - source rejuvenation
    • variation in max burial depth - diagenesis
    • changes in syndepositional slope gradients - fluvial style
    • changes in direction of topographic tilt - paleocurrents
  9. Signatures of paleoclimatic controls on sedimentation
    • Petrography of detrital sandstones
    • early diagenesis mineralogy
    • isotope geochem of early diagenesis cements
    • foraminiferal delta 18O
  10. Relative importance of allogenic controls
    • Tectonic subsidence most important control on seq strat
    • figure 3.3
  11. Processes influencing accommodation
    Figure 3.4
  12. Sediment supply and energy flux
    • A fundamental variable, dependent on climate + tectonics
    • sed supply vs environmental energy flux
    • flow energy > sed supply = erosion
  13. Incised valley figure 3.7
  14. Figure 3.8 top
    Sed supply = environmental energy
  15. Figure 3.8 middle
    Sed supply > wave energy
  16. Figure 3.8 bottom
    Sed supply < wave energy
  17. Accommodation
    Amount of space available for sediments to fill = distance between base level (sea level) and depositional surface (sea floor)
  18. Base level
    • More or less the sea level, although usually below it due to the action of waves and currents. The extension of this surface into the subsurface of continents defines the ultimate level of continental denudation. On the continents, processes of aggradation vs incision are regulated via the concept of Graded (equilibrium) fluvial profile. Graded fluvial profiles meet the base level at the shoreline.
    • Defined as the lowest level of continental denudation (at or near the shoreline)
  19. Eustacy
    Where sea level is relative to the center of the earth (common concept of sea level by most people but not that simple)
  20. Relative sea level
    What we can normally see. Based on a predetermined point
  21. Water depth
    Distance between sea floor and sea surface
  22. Datum
    (base level) can be changed by tectonics or sediment loading which can change sea level.
  23. Relative rise
    • Subsidence + eustatic rise
    • subsidence - eustatic fall (subsidence>eustatic fall)
    • eustatic rise (no subsidence)
    • subsidence (no eustatic change)
    • eustatic rise - uplift (eustatic rise>tectonic uplift)
  24. Relative fall
    • Uplift + eustatic fall
    • uplift - eustatic rise (tectonic uplift > eustatic rise)
    • eustatic fall (no subsidence)
    • tectonic uplift (no eustatic change)
    • eustatic fall - subsidence (eustatic fall>subsidence)
  25. Transgression
    Landward migration of shoreline
  26. Regression
    Seaward migration of shoreline
  27. Retrogradation
    Backward (landward) movement or retreat of a shoreline or coastline by wave erosion
  28. Progradation
    Building seaward of shoreline or coastline by nearshore deposition
  29. Normal regression
    Driven by shoreline sedimentation rates
  30. Forced regression
    Driven by base level fall
  31. Maximum flooding surface
    Sometimes used as the sequence boundary (because it is preserved)
  32. Transgressions
    Factor of base level rise vs sedimentation rates
  33. Wave ravinement surface
    Scour surface cut by waves during shoreline transgression
  34. Healing phase deposits
    On lap ravinement surface by aggrading and retrograding lower shoreface and shelf deposits
  35. Sedimentation during transgression
    • Sed carried landward in backstepping beaches or estuaries.
    • coarse regressive lag on wave ravinement surface.
    • healing-phase deposits onlap max regressive surface offshore.
  36. Forced regressions
    Occur during base level fall when shoreline forced to regress irrespective of sed supply(stair step pattern)
  37. Staley and hummocky cross stratification
    Strong wave action broad troughs (Swaley) and broad domes (hummock)
  38. Forced regressive river dominated delta succesion
    Gradational base no wave scouring
  39. shoreline trajectory in normal regression
    • Combined progradation and aggradation
    • rates of base level rise out paced by sed supply
    • figure 3.35