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Chapter 9: Subsidence and Thermal History

Chapter 9: Subsidence and Thermal History This presentation contains illustrations from Allen and Allen (2005). Geohistory Analysis. Quantitative analysis that produces subsidence of various geological boundaries and rates of sediment accumulation through time. Coined by Van Hinte (1973).

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Chapter 9: Subsidence and Thermal History

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  1. Chapter 9: Subsidence and Thermal History This presentation contains illustrations from Allen and Allen (2005)

  2. Geohistory Analysis • Quantitative analysis that produces subsidence of various geological boundaries and rates of sediment accumulation through time. • Coined by Van Hinte (1973). • Backstripping involves additional incorporation of isostatic (local, flexural, 1-D, 2-Dor 3-D) effects of sediment unloading.

  3. Subsidence History and Thermal History time present past Layer 3 Layer 2 “Tectonic” subsidence” Layer 1 depth basement

  4. Backstripping • (Watts and Ryan, 1976) • Tectonic subsidence is what remains after the effects of sea-level and sediments are removed. • …. It is the background subsidence caused by stretching and thermal cooling of the lithosphere.

  5. Backstripping

  6. For original matlab program from Allen’s book: see the following link to a matlab program Backstripping

  7. Subsidence History and Thermal History time present past Layer 3 Layer 2 “Tectonic” subsidence” Layer 1 depth Thermal window

  8. Subsidence in the forward sense Sea-level

  9. Subsidence in the forward sense Sea-level

  10. Subsidence in the forward sense Sea-level

  11. Subsidence in the forward sense

  12. Subsidence in the forward sense

  13. Subsidence in the forward sense

  14. Subsidence in the forward sense • We need to know: • Sea-level (assumed constant in the example) • Original sediment thickness and hence water-depth (known at all times) • Type of isostatic behavior does the crust exhibit when loaded (flexural, or local/Airy)

  15. Subsidence in the reverse sense • Sea-level (never constant in the past) • Original sediment thickness ( we don’t know??) • We DO know current sediment thickness • Water-depths ( never constant)

  16. Subsidence in the reverse sense

  17. Subsidence in the reverse sense Porosity: The “new”decompacted thickness must conform to a pre-defined porosity-depth relation. This calculation is achieved by trial and error.

  18. Subsidence in the reverse sense Paleo-water depth: From biostratigraphic assemblages Sea-level estimations: Long-term changes are accepted. Flexural Model: Various Te values can be used.

  19. Flexural backstripping

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