Subsidence and analysis of subsidencein sedimentary basins

March 2, 2011

Vertical crustal controls on sedimentary basins

• Difference in density and thickness between oceanic and continental crust

• Thermal history of continental and oceanic crust• Flexure• Combinations of these

Subsidence dominated bythermal contractive cooling:- Intracratonic basins- Aulacogens (failed rift arms)- Protoceanic rifts- Miogeoclinal prisms- Continental Embankments- Young ocean basins- Pull-apart basins- Inter- and intra arc basins

Subsidence controlled largelyby lithospheric flexure:- oceanic trenches- slope basins- forearc basins- broken foreland basins- downwarped basins along

transpressional faults- remnant ocean basins

Subsidence Analysis: determination of vertical crustal behavior of basement through time, independent of load and isostatic adjustment

How is subsidence determined?process of “backstripping” a stratigraphic section

1) decompact each stratigraphic layer, beginning with youngest2) remove layer from section3) calculate amount of isostatic adjustment of basement by

removal of sedimentary layer4) ‘hang’ new vertical position of basement on paleobathymetry curve

Data needed to conduct subsidence analysis:1) stratigraphic section, including:

a) lithology of stratigraphic unitsb) thickness of stratigraphic unitsc) age of stratigraphic unitsd) paleobathymetry of stratigraphic units

2) some way to decompact sediment to estimate original thicknesses3) estimates on crustal densities of mantle, crustal section, and water column4) estimates on sea level changes, since this affects bathymetry

Paleobathymetric zonesAssigning paleobathymetry to strata in a well

decompaction