Basins

basins on continental crust

basins on continental crust

last longer

Three ways to make a sedimentary basin

RIFTING

THERMAL SUBSIDENCE

FLEXURE

RIFTING

1. extensional thinning of the lithosphere

2. followed by isostatic adjustment

3. timescale of adjustment ≈ 105 years

THERMAL SUBSIDENCE

1. following rifting, cooling of the lithosphere and the asthenosphere, and subsequent isostatic adjustment

2. timescale of subsidence ≈ 50 x 106 yrs

FLEXURE

1. elastic bending of lithosphere under load

2. not permanent - if load is removed, some recovery on timescales of 1-100 x 106 years

3. encountered in convergent margins

Archimede’s Principle

the boyant force in = to the displaced water

Isostasy

isostasy: state of gravitational equilibrium provided by buoyant force from a fluid that supports a floating solid

compensation depth

line of equal pressure form above and below

non-Newtonian fluid

viscosity changes with strain rate

deforms like solid under high strain rates (earthquakes!) deforms like a fluid under low strain rates (plate tectonics)

Rifting and isostatic adjustment

lithosphere block will sink bc it has been thinned

created rift basin and a depression to collect water air and sediment

most important factors of sediments thickness

B=how much thinning=orig thick/new thickness (cursta nd lisophere)

B^=ys^

ps= density of filling

ps^=ys^

Rift basins

beta can show up as stretching

beta is always greater than 1

syn-rift sediments thicken

towards faults and are rotated more with increasing age

where will you find courses sediments in rift lake

footwalls form aluvial fans and steep systems

Rift basins - marine

rift sediments are fault bounded and more rotated with increasing age

marine vs lake

reefs form at foot wall bc of the nutrients and shallowness

after rifting

asthenosphere rises adds heat

cools to reach EQ and then sinks bc of density

thermal substance

cooling crust

as sea floor ages the dense lithospheric mantle thickens an the sea-flour gets deeper

older thicker lithosphere sinks deeper

Rift and Drift

rift: confined to the grabens the layers thicken towards fault plane

drift: gentle draping

Garben and horst

gar

reFlex

1. elastic bending of lithosphere under load

2. not permanent - if load is removed, some recovery on timescales of 1-100 x 106 years

3. encountered in convergent margins

flexural rigidity

larger D = more rigid = less flexure

Fore arc basins

back arc

develop on overriding plate undergoing extension

mantle flow pulls

Foreland basins

develop on continental crust of underridina/subducting plate

basin move landwards as oreogenic wedge grows with time

sed rate increases with time as the wedge gets larger and mroe heavy

thermal subtinence sedimentation

Decreases with time