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Allostratigraphy/Sequence Stratigraphy

Allostratigraphy/Sequence Stratigraphy. Subdivision of the stratigraphic record otbo bounding discontinuities Bounding discontinuities define Depositional Sequences relatively conformable successions of genetically related strata bounded by unconformity or correlative conformities.

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Allostratigraphy/Sequence Stratigraphy

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  1. Allostratigraphy/Sequence Stratigraphy • Subdivision of the stratigraphic record otbo bounding discontinuities • Bounding discontinuitiesdefine Depositional Sequences • relatively conformable successions of genetically related strata bounded by unconformity or correlative conformities

  2. Utility of Depositional Sequences • If bounding discontinuities are produced by isochronous events (at least basin-wide) then these material (or non-material) features can be used for correlation since they are isochronous. • How are sequence bounding unconformities recognized and correlated in different places?

  3. Aggradation, Progradation, and Retrogradation • Stacking patterns of sedimentary basin fill due to relative sea level and sediment input influence on accommodation • Aggradation • Progradation • Retrogradation

  4. also progradational

  5. Effects of Changing Accommodation on the Stratigraphic Record • Transgression/Regression • Water depth/shoreline changes interpreted from vertical changes in grain size (CUS/FUS) or sedimentary facies in local sections • Onlap/Offlap • Landward/basinward shift in shoreline due to relative sea level change • The fundamental geometric aspect of the sedimentary record upon which relative sea level change is interpreted

  6. Wheeler DiagramsTime/Space relationships of Unconformity • Space/Space Stratigraphic Cross Section • Time/Space Chronostratigraphic Chart

  7. Cycles of Relative Sea Level Change Fichter and Poche, 2001 Nichols, 1999

  8. In Fichter and Poche, 2001 After Mitchum and Van Wagoner, 1990

  9. Relatively Conformable Genetically Related (abide by Walther's Law) Bounded by Unconformity or Correlative Conformity isochronous with respect to unconformity Depositional Sequences are Chronostratigraphic Units the defining Sequence Boundary defines older (below) and younger (above) strata Chronostratigraphic Units geological time significant Depositional Sequences

  10. Major Sequence Stratigraphic and Chronostratigraphic Surfaces Kendall, USC Sequence Stratigraphy www site

  11. That’s all Folks!

  12. Use of Depositional Sequence concepts to predict stratal geometry Three dimensional assemblage of sedimentary facies genetically linked by their origin in related depositional environments Basically Waltherian World Depositional Systems Tracts

  13. Low Stand Systems Tract • Forced Regression • Subaerial exposure and formation of a Sequence Boundary • Offlap • Basinward shift in facies belts

  14. Transgressive Systems Tract • Retrogradation • Flooding of the shelf and onlap • Landward shift in facies belts

  15. Maximum Flooding SurfaceCondensed Section • Between TST and HST (highstand systems tract) • Represented by a change from retrogradation to aggradation/progradation • The surface or thin succession characterized by evidence for slow rates of sedimentation

  16. Highstand Systems Tract • Progradation (accommodation < sediment input) • Regressive successions • Onlap and offlap/down-lap

  17. Short Term Cycles Long Term Cycles Stratigraphic Expression of Relative Sea Level Cycles • The Sequence Model • A tool for predicting stratigraphic architecture • Methodology for basin wide correlation • May be used for interregional correlation through recognition of Eustatic Cycles

  18. Allostratigraphy and Lithostratigraphy • Lithostratigraphy maps sedimentary rocks solely on the basis of their lithology and does not necessarily consider that these rocks may have accumulated over different periods of time (diachronous lithostratigraphic units) • “Lithostratigraphy” often ignores significant breaks in the sedimentary section, including those caused by unconformities, omission surfaces, ravinement surfaces, and flooding surfaces Dunbar and Rodger, 1957; copied directly from Prothero and Schwab, 1996

  19. Allostratigraphy and Lithostratigraphy • Allostratigraphy maps rock units on the basis of the timing of their accumulation • Allostratigraphy (sequence stratigraphy) uses a framework based on surfaces of erosion and non-deposition (sequence boundaries), and flooding (transgressive surfaces and/or maximum flooding surfaces [mfs]) that can be recognized in 2-D and 3-D seismic, well log data, and outcrops Dunbar and Rodger, 1957; copied directly from Prothero and Schwab, 1996

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