Basin Analysis

Basin Analysis
Basin Analysis

Introduction
Basin analysis - Study of sedimentary rocks
to determine:
Subsidence history
Stratigraphic architecture
Paleogeographic evolution

Tools:
Geology (outcrops, wireline logs, core)
Geophysics (seismic, gravity, aeromag)
Computers (modeling, data analysis)

Introduction
Zonation of the Earth – Composition
Crust
Mantle
Core

IntroductionMechanisms of Basin Formation
Basin Classification
Basins and Sequence Stratigraphy
Summary

Introduction
What is a basin?
Repository for sediment
Formed by crustal subsidence relative to
surrounding areas
Surrounding areas sometimes uplifted

Many different shapes, sizes and
mechanisms of formation

Introduction
Zonation of the Upper Earth –
Rheology
Lithosphere
Rigid outershell
Crust and upper mantle

Asthenosphere
Weaker than lithosphere
Flows (plastic deformation)

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Introduction
Zonation of the Upper Earth –
Rheology
Vertical motions (subsidence, uplift) in
sedimentary basins are primarily in
response to deformation of lithosphere
and asthenosphere

Introduction
Three types of plate boundaries:
Divergent – plates moving apart
Mid-oceanridges, rifts

Convergent – plates moving towards
each other
Subduction zones

Conservative – plates move parallel to
each other
Strike-slip systems

Mechanisms of Basin
Formation
Isostatic Processes:
Crustal thinning
Extensional stretching, erosion during uplift,
magmatic withdrawal

Mantle-Lithosphere Thickening
Cooling of lithosphere, following cessation of
stretching or cessationof heating

Introduction
Plate motions
Plate-plate interactions can generate
vertical crustal movements
We will examine basins according to their
positions with respect to plate
boundaries and plate-plate interactions
“Wilson Cycle” – opening and closing of
ocean basins

Mechanisms of Basin
Formation
Major mechanisms for regional
subsidence/uplift:
Isostatic – changes in crustalor
lithospheric thickness
Loading – by thrust sheets, volcanic piles,
sediment
Dynamic effects – asthenospheric flow,
mantle convection, plumes

Mechanisms of Basin
Formation
Isostatic Processes:
Crustal densification
Density increase due to changing
pressure/temperature conditions and/or
emplacement of higher density melts into
lower density crust

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Mechanisms of BasinFormation
Loading:
Local isostatic compensation of crust and
regional lithospheric flexure
Dependent on flexural rigidity of
lithosphere

Mechanisms of Basin
Formation
Loading:
Sedimentary or Volcanic Loading
Tectonic loading
During overthrusting and/or underpulling

Subcrustal loading
Lithospheric flexure during underthrusting of
dense lithosphere

Mechanisms of Basin
FormationDynamic effects:
Asthenospheric flow
Descent or delamination of subducted
lithosphere

Mantle convection
Plumes

Basin Classification
Many different classification systems
have been proposed
Principal factors:
Position of the basin in relation to plate
margins
Crustal/lithospheric substratum
Oceanic, continental crust

Type of plate boundary

Basin Classification
Ingersoll andBusby (1995): 26
different types of basin (see handout)
Divided into various settings
Divergent
Intraplate
Convergent
Transform
Hybrid

Basin Classification
Alternate approach (Allen and Allen,
2005): focus on basin-forming
processes
What causes subsidence?

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Basin Classification
This course – hybrid approach:
What causes subsidence?
What is tectonic setting?

We do not havetime to cover all types
of basins
Focus on selected basin types
Allen and Allen (2005)

Basin Classification

Divergent Plate Boundaries

Basins can be related to tectonic
setting

Continental rifting (a) may
lead to opening of an ocean
with a mid-ocean ridge (b, c)

Position with respect to plate boundary
Nature of plate boundary

“Wilson Cycle”

Rift basin evolves into...