Basin Analysis
Basin Analysis
Introduction
Mechanisms of Basin Formation Basin Classification
Basins and Sequence Stratigraphy Summary
Introduction
Basin analysis -Study of dimentary rocks to determine:
Subsidence history
Stratigraphic architecture
Paleogeographic evolution
Tools:
Geology (outcrops, wireline logs, core)
Geophysics (ismic, gravity, aeromag)
Computers (modeling, data analysis)
Introduction
What is a basin?
Repository for diment
Formed by crustal subsidence relative to surrounding areas
Surrounding areas sometimes uplifted Many different shapes, sizes and
mechanisms of formation
Introduction
Zonation of the Earth –Composition Crust
Mantle
Core
Introduction
Zonation of the Upper Earth –Rheology
Lithosphere
Rigid outer shell
Crust and upper mantle
Asthenosphere
Weaker than lithosphere
Flows (plastic deformation)
Introduction
Zonation of the Upper Earth –Rheology
Vertical motions (subsidence, uplift) in dimentary basins are primarily in
respon to deformation of lithosphere and asthenosphere
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
Introduction
Three types of plate boundaries: Divergent –plates moving apart
Mid-ocean ridges, rifts
Convergent –plates moving towards
each other
英文字体设计Subduction zones
Conrvative –plates move parallel to each other
Strike-slip systems
Mechanisms of Basin Formation
Major mechanisms for regional subsidence/uplift:
Isostatic–changes in crustal or
6p营销理论lithospheric thickness
Loading –by thrust sheets, volcanic piles, diment
Dynamic effects –asthenospheric flow,
mantle convection, plumes
Mechanisms of Basin Formation
Isostatic Process:
Crustal thinning
Extensional stretching, erosion during uplift,
magmatic withdrawal
Mantle-Lithosphere Thickening
Cooling of lithosphere, following cessation of
stretching or cessation of heating
Mechanisms of Basin Formation
Isostatic Process:
Crustal densification
Density increa due to changing
pressure/temperature conditions and/or
emplacement of higher density melts into
lower density crust
Mechanisms of Basin Formation
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
den lithosphere
Mechanisms of Basin Formation
Dynamic effects:
Asthenospheric flow
Descent or delamination of subducted
lithosphere
Mantle convection
Plumes
Basin Classification
Many different classification systems have been propod
Principal factors:
Position of the basin in relation to plate
margins
Crustal/lithospheric substratum
Oceanic, continental crust
Type of plate boundary
Basin Classification
Ingersoll and Busby (1995): 26 different types of basin (e handout)
Divided into various ttings
Divergent
Intraplate
Convergent
Transform
Hybrid
Basin Classification
Alternate approach (Allen and Allen, 2005): focus on basin-forming process
What caus subsidence?
Allen and Allen (2005)
Basin Classification
This cour –hybrid approach:
What caus subsidence?
What is tectonic tting?
We do not have time to cover all types of basins
Focus on lected basin types
Basin Classification
Basins can be related to tectonic
tting
Position with respect to plate boundary
Nature of plate boundary
“Wilson Cycle”
Allen and Allen, 2005Divergent Plate Boundaries
Continental rifting (a) may lead to opening of an ocean with a mid-ocean ridge (b, c)
Rift basin evolves into passive margin
石头的秘密Basin Classification Rift Basins
Elongate, valleys
bounded by normal
faults
Few km -> 10s of km
wide
Length –up to 1000s of
吉林农科院km
Occur in many plate
ttings, but most
common in divergent
ttings
Basin Classification
Rift Basins
Seismic studies indicate rifts overlie
thinned crust
Evidence for thermal anomalies at depth: Negative Bouguer gravity anomalies
High heat flow
Bimodal volcanic activity
Basin Classification
Rift Basins
Active rifting:
Mantle upwelling caus crustal thinning
(heating)
Thinning leads to uplift
Uplift leads to tension and rifting Passive rifting:
Regional extension caus failure
Hot mantle rocks ri and penetrate营运能力分析
lithosphere
Passive Rifting –regional
extension caus rifting,
upwelling of hot mantle
follows.
Example: Rio Grande
Active Rifting –Upwelling of
hot mantle leads to uplift
and extension.
Example: East African Rift Allen and Allen, 2005
驾考科目一Basin Classification
Rift Basins
Rift fill commonly consists of
“continental” deposits
Fluvial, lacustrine, alluvial fans
Evaporites may form if rift valley/basin is located in a hot, dry area
Invasion of the a
Clod drainage basins
Volcanic rocks, and associated intrusions, may be prent Evaporites
accumulated in
shallow basins
as Pangaea
broke apart
during the
Early Mesozoic
Water from
the Tethys Sea
flowed into the
Central
Atlantic Ocean
Early Mesozoic Evaporites
Basin Classification
Continued rifting can lead to formation of oceanic crust –opening of ocean basin
<, Red Sea
“Rift-Drift” transition
Rift-drift transition may be marked by a “breakup unconformity”
If rift associated with subaerial relief at
ont of drifting
Basin Classification Passive Margins
Continental
Crust
Oceanic
Crust
Transitional
Crust
Basin Classification
Passive Margins
Strongly attenuated continental crust Stretched over distances of 50-500 km
Overlain by award-thickening diment prisms
Typically shallow-marine deposits
Sometimes referred to as “Atlantic-type margins” or “continental ris and terraces” (Boggs)
Beaumont et al. 1992 –cited in Allen and Allen 2005
Scotian Shelf
Basin Classification
Passive Margins
Various subsidence mechanisms:
Cooling (thermal contraction) following lithospheric thinning
Main mechanism
Pha changes in lower crust/mantle (gabbro to eclogite)鼻子构造
Not known if this process can be widespread enough
Sediment loading
品牌分析Adds to other effects
Basin Classification
Passive Margins
Subsidence variable in space and time
Subsidence rate increas in offshore direction
Subsidence rate decreas with time for all parts of the profile
Total Subsidence
Subsidence as a Function of Time
S u b s i d e n c e
Time ->
A B C
A B C
