Introduction to Basin Analysis
In the long run, eustatic changes in base level are cyclical
Do not produce permanent increases in accommodation for long-term
sediment storage
Base level is also a function of climate (=energy), but it is unlikely that
climate changes will lead to substantial permanent accommodation creation
Yet many sedimentary basins have kilometers (or 10s of km) of sediment fill
over 10s-100s of Myr
How is that much permanent accommodation space created?
Subsidence is required for formation of a sedimentary basin and long-term
sediment accumulation
Physical mechanisms of subsidence:
1. Isostasy
Pratt isostasy
Airy isostasy
Topography is a function
of lithospheric density
Topography is a function
of lithospheric thickness
Physical mechanisms of subsidence:
2. Flexure (also called regional isostasy)
Earth’s rigid lithosphere acts as an elastic plate. When loaded (by a
mountain range, sediment column, other tectonic plate), it flexes.
Most (but not all) sedimentary basins occur in areas of active plate tectonics
2. Basins due to convergence
3. Strike-slip basins
1. Basins due to extension
Basins due to extension
Crustal extension leads to rift
basins and ultimately to passive
margins
Subsidence driven by crustal
thinning and heat flow changes
Primarily isostatic
Rift-drift transition marked by “breakup unconformity” that coincides with
the onset of seafloor spreading (heat flow from magma production)
Transition to a passive margin
Basins due to convergence
Subsidence primarily driven by flexure of underlying plate from weight of
overriding plate
E.g., forearc basins at continental margins above subduction zones
Foreland basins are deepest next to the mountain front
Marine or terrestrial sediment fill reflects balance between sedimentation rate
and subsidence rate (accommodation space)
Strike-slip basins
Pull apart or fault overstep basins associated with strike-slip fault systems
Small size means that heat is lost through walls, leading to rapid faultcontrolled subsidence
Strike-slip basins often have extremely rapid lateral facies variations
May be sediment-starved (marine or lacustrine) in center