Basin Analysis

„ Introduction Basin Analysis „ Mechanisms of Basin Formation

„ Basin Classification

„ Basins and Sequence Stratigraphy

„ Summary

Introduction Introduction

„ Basin analysis - Study of sedimentary rocks „ What is a basin? to determine: „ Repository for sediment „ Subsidence history „ Formed by crustal subsidence relative to „ Stratigraphic architecture surrounding areas „ Paleogeographic evolution „ Surrounding areas sometimes uplifted „ Tools: „ Many different shapes, sizes and „ Geology (outcrops, wireline logs, core) mechanisms of formation „ Geophysics (seismic, gravity, aeromag)

„ Computers (modeling, data analysis)

Introduction Introduction

„ Zonation of the Earth – Composition „ Zonation of the Upper Earth –

„ Crust Rheology

„ Mantle „ Lithosphere

„ Core „ Rigid outer shell „ Crust and upper mantle

„ Asthenosphere

„ Weaker than lithosphere

„ Flows (plastic deformation)

1 Introduction Introduction

„ Zonation of the Upper Earth – „ Plate motions

Rheology „ Plate-plate interactions can generate

„ Vertical motions (subsidence, uplift) in vertical crustal movements

sedimentary basins are primarily in „ We will examine basins according to their response to deformation of lithosphere positions with respect to plate and asthenosphere boundaries and plate-plate interactions

„ “Wilson Cycle” – opening and closing of ocean basins

Mechanisms of Basin Introduction Formation

„ Three types of plate boundaries: „ Major mechanisms for regional „ Divergent – plates moving apart subsidence/uplift: „ Mid-ocean ridges, rifts „ Isostatic – changes in crustal or „ Convergent – plates moving towards lithospheric thickness each other „ Loading – by thrust sheets, volcanic piles, „ Subduction zones sediment „ Conservative – plates move parallel to each other „ Dynamic effects – asthenospheric flow,

„ Strike-slip systems mantle convection, plumes

Mechanisms of Basin Mechanisms of Basin Formation Formation

„ Isostatic Processes: „ Isostatic Processes:

„ Crustal thinning „ Crustal densification

„ Extensional stretching, erosion during uplift, „ Density increase due to changing magmatic withdrawal pressure/temperature conditions and/or emplacement of higher density melts into „ Mantle-Lithosphere Thickening lower density crust „ Cooling of lithosphere, following cessation of stretching or cessation of heating

2 Mechanisms of Basin Mechanisms of Basin Formation Formation

„ Loading: „ Loading:

„ Local isostatic compensation of crust and „ Sedimentary or Volcanic Loading

regional lithospheric flexure „ Tectonic loading

„ Dependent on flexural rigidity of „ During overthrusting and/or underpulling

lithosphere „ Subcrustal loading

„ Lithospheric flexure during underthrusting of dense lithosphere

Mechanisms of Basin Formation Basin Classification

„ Dynamic effects: „ Many different classification systems

„ Asthenospheric flow have been proposed

„ Descent or delamination of subducted „ Principal factors: lithosphere „ Position of the basin in relation to plate „ Mantle convection margins „ Plumes „ Crustal/lithospheric substratum

„ Oceanic, continental crust

„ Type of plate boundary

Basin Classification Basin Classification

„ Ingersoll and Busby (1995): 26 „ Alternate approach (Allen and Allen, different types of basin (see handout) 2005): focus on basin-forming „ Divided into various settings processes

„ Divergent „ What causes subsidence? „ Intraplate

„ Convergent

„ Transform

„ Hybrid

3 Basin Classification

„ This course – hybrid approach:

„ What causes subsidence?

„ What is tectonic setting?

„ We do not have time 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 „ Position with respect to plate boundary with a mid-ocean ridge (b, c) „ Nature of plate boundary

„ “Wilson Cycle” Rift basin evolves into passive margin

Allen and Allen, 2005

Basin Classification Basin Classification

„ Rift Basins „ Rift Basins „ Elongate, valleys „ Seismic studies indicate rifts overlie bounded by normal thinned crust faults

„ Few km -> 10s of km „ Evidence for thermal anomalies at depth: wide „ Negative Bouguer gravity anomalies „ Length – up to 1000s of km „ High heat flow „ Bimodal volcanic activity „ Occur in many plate settings, but most common in divergent settings

4 Basin Classification Passive Rifting – regional extension causes rifting, „ Rift Basins upwelling of hot mantle „ Active rifting: follows. „ Mantle upwelling causes crustal thinning Example: Rio Grande (heating)

„ Thinning leads to uplift

„ Uplift leads to tension and rifting Active Rifting – Upwelling of hot mantle leads to uplift „ Passive rifting: and extension. „ Regional extension causes failure Example: East African Rift „ Hot mantle rocks rise and penetrate lithosphere Allen and Allen, 2005

Early Mesozoic Evaporites Basin Classification

„ Rift Basins „ Evaporites accumulated in „ Rift fill commonly consists of shallow basins “continental” deposits „ as Pangaea „ Fluvial, lacustrine, alluvial fans broke apart during the „ Evaporites may form if rift valley/basin is Early Mesozoic located in a hot, dry area „ Water from „ Invasion of the sea the Tethys Sea „ Closed drainage basins flowed into the Central „ Volcanic rocks, and associated intrusions, Atlantic Ocean may be present

Basin Classification Basin Classification

„ Continued rifting can lead to „ Passive Margins formation of oceanic crust – opening of ocean basin

„ E.g., Red Sea „ “Rift-Drift” transition „ Rift-drift transition may be marked by a “breakup unconformity” Continental Oceanic Crust Transitional Crust Crust „ If rift associated with subaerial relief at onset of drifting

5 Scotian Shelf Basin Classification

„ Passive Margins

„ Strongly attenuated continental crust

„ Stretched over distances of 50-500 km

„ Overlain by seaward-thickening sediment prisms

„ Typically shallow-marine deposits

„ Sometimes referred to as “Atlantic-type margins” or “continental rises and Beaumont et al. 1992 – cited in Allen and Allen 2005 terraces” (Boggs)

Basin Classification Basin Classification

„ Passive Margins „ Passive Margins

„ Various subsidence mechanisms: „ Subsidence variable in space and time

„ Cooling (thermal contraction) following „ Subsidence rate increases in offshore lithospheric thinning direction

„ Main mechanism „ Subsidence rate decreases with time for all „ Phase changes in lower crust/mantle (gabbro parts of the profile to eclogite)

„ Not known if this process can be widespread enough

„ Sediment loading

„ Adds to other effects

Subsidence as a Function of Time

Time ->

Total Subsidence A

B

Subsidence C

A B C

6 Basin Classification Basin Classification

„ Passive Margins „ Passive Margins

„ Morphology characterized by shelf, slope „ Slope/rise – material shed from and continental rise continental shelf during lowstands

„ Shelf margin builds out with time (clastic systems)

„ Shelf sediments can be clastic or „ Aprons/fans deposited along slope/rise carbonate „ Also pelagic sediments, contourites, etc.

„ Water depth stays relatively constant on shelf

„ Abundant sediment supply

Basin Classification

„ Gravity-driven deformation common in drift-phase sediments

„ Listric growth faults, salt tectonics, mud diapirs, etc.

7 Basin Classification Convergent Plate „ Aulacogens Aulacogen Boundaries

„ “Failed rifts”

„ Occur at high angle Subduction of oceanic plate to continental (d) may lead to closing of margin ocean basin (e) and ultimately to continental „ Fill: non-marine to collision (f) deep marine

„ Example: Reelfoot Rift (Mississippi

valley) Allen and Allen, 2005

Convergent Plate Boundaries Basin Classification

Age of oceanic crust affects „ Arc-related basins angle at which it is subducted Edge of Continent Volcanic Island Arc Forearc Basin Young crust (top) – shallow Backarc Basin angle subduction, Deep-sea Trench compression behind arc Old crust (bottom) – steep angle subduction, “roll- Spreading back”, extension behind arc Center Accretionary complex

Basin Classification Basin Classification

„ Arc-related basins „ Foreland basins

„ Forearc and backarc basins dominated by Thrust belt

sediment derived from arc Foreland basin

„ Immature clastics

„ Backarc basin may also have component derived from continent

„ Deep-sea trench has sediments derived from arc and sediments scraped off subducting oceanic crust

„ “Melange”

8 Basin Classification Subsidence Uplift „ Foreland basins

„ Crustal loading of thrust sheets causes subsidence

„ May face towards or away from continental interior g din loa „ Ocean-continent or continent-continent st hru collision T Peripheral bulge „ Rate of subsidence greatest adjacent to thrust loading

Peripheral (pro) Retro Foreland Basin Foreland Basin

Himalayan peripheral foreland basin

Depth to basement (km; outcrop=0)

Decelles and Giles, 1996

Retro foreland basins

Turcotte and Schubert, 1982

9 Late Cretaceous

Basin Classification

„ Foreland basins

„ Generally clastic – high sediment input from adjacent uplifts

„ “Clastic wedges”

„ Date thrusting

„ Carbonates in some settings

„ Marine or non-marine fill

„ Turbidites, pelagic, deltaic, shoreface/shelf, fluvial

Basin Classification

„ Foreland basins

„ Basin fill adjacent to thrusting typically gets caught up in deformation

Cretaceous Clastics, Alberta

10 Basin Classification Basin Classification

„ Intracratonic Basins „ Intracratonic Basins

„ “Interior Basins”

„ Semi-circular to ovate downwarps

„ Within continental interiors

„ Otherwise stable cratonic areas

„ Away from plate boundaries

Basin Classification

„ Intracratonic Basins Subsidence Uplift „ Causes of subsidence?

„ Underlying rifts, large-scale fault blocks

„ Cooling after intrusion of dense material

„ Mantle “cold” spots (downwelling)

„ Phase changes

„ Subsidence greatest towards center of basin

Basin Classification

„ Intracratonic Basins

„ Sedimentary fill terrestrial or marine

„ Carbonates, clastics, evaporites

11 Basin Classification

„ Other basins, e.g. basis associated with wrench faulting, not discussed here (time constaints)

„ Some basins have had multiple-phase history

„ Sometimes related to reactivation because of changes in plate tectonic setting

„ E.g., Western Canada Sedimentary Basin

Middle Cambrian Mid-Ordovician -> Lower Devonian

West East

Causes of subsidence in these areas, many 100s of km away from thrust belt are poorly understood

“Dynamic effects”?

12 Eustasy Basins and Sequence + High Subsidence Stratigraphy

„ Patterns and rates of subsidence and sediment supply can be strongly Eustasy influenced by tectonic processes that + Moderate Subsidence are responsible for forming some basins

„ Temporal and spatial changes in these SeaRelative Level -> factors can significantly affect sequence development in those basins Eustasy

Time ->

“Low Subsidence” “High Subsidence” RSL Can Fall RSL Cannot Fall Basins and Sequence Stratigraphy Total Subsidence „ Towards shelf margin – rate of subsidence is always greater than rate of eustatic fall

„ No fall of relative sea level

„ Further landward – rate of subsidence is less than rate of eustatic fall

„ Fall of relative sea level possible

„ Incised valleys can form

„ Area covered by each zone will change with time, basin to basin

Basins and Sequence Stratigraphy

„ When a discrete shelf margin is present, shelf margin sediments may be thick even in the absence of rapid thermal/tectonic subsidence

„ Faulting, compaction, diapirism cause localized subsidence

Fluvial incision is greatest near landward edge of shelf

13 “High Subsidence” “Low Subsidence” RSL Cannot Fall RSL Can Fall

Subsidence Uplift

g din oa st l hru T Peripheral bulge

Basins and Sequence Stratigraphy

„ Towards thrust belt – rate of subsidence is always greater than rate of eustatic fall

„ No fall of relative sea level

„ Favours fluvial accomodation/deposition

towards thrust belt Posamentier and Allen, 1999 „ Further basinward – rate of subsidence is less than rate of eustatic fall

„ Fall of relative sea level possible „ Area covered by each zone will change with Dignes (Miocene) Foreland Basin, SE France time, basin to basin Thickest preserved fluvial (“alluvial”) sediments adjacent to thrust belt

Basins and Sequence Stratigraphy

„ Variations in subsidence along strike in a basin can also cause variations in sequence development

14 Basins and Sequence Stratigraphy

„ Uplift along basin margins can cause variations in sediment supply

„ Uplift due to thrusting and other processes

„ Erosion of highlands

„ Variations in sediment supply can generate “cycles” whose development has little/nothing to do with eustatic changes in

Posamentier and Allen, 1999 sea level

„ Especially in basins dominated by fluvial deposition

Basins and Sequence Basins and Sequence Stratigraphy Stratigraphy

„ Development of a shelf profile most „ Subsidence rates for a given basin common on passive margins may be determined using a variety of techniques „ Allows lowstand clastic deposits (submarine fans) to form „ E.g., “backstripping” „ Subsidence mechanisms/patterns can „ Foreland basins typically have a ramp be derived from examining profile sedimentary record „ Absence of deep-water deposits (i.e., „ Thick sediment accumulations lowstand fans) correspond to rapid subsidence and/or high sediment supply

Isopach: Isopach: 1st white specks to 2nd Paleozoic to Second White white specks Specks 20m ctr int 100m ctr int

15 Summary Summary

„ Sedimentary basins are repositories „ Sedimentary basins are found in many for sediment that are formed by different tectonic settings

crustal subsidence relative to „ “Wilson Cycle” a useful concept for surrounding areas classifying basins

„ Opening and closing of ocean basins „ Several different mechanisms can „ Not all basins fit into this conceptual produce subsidence, but they can be framework grouped into two main categories:

„ Isostacy

„ Loading

Summary Summary

„ Divergent plate boundaries – rift/drift „ Foreland basins – subsidence due to transitions loading by thrust sheets

„ Not all rifts lead to the opening of ocean „ Highest subsidence closest to thrust basins sheets

„ Passive margins have highest subsidence „ Intracratonic basins – away from that increases seawards plate boundaries, causes of „ Subsidence primarily due to cooling subsidence poorly understood

„ Basins can have complex histories

Summary

„ Tectonic and other factors that cause subsidence and influence sediment supply can have a significant impact on sequence development

„ Likely to vary from basin to basin, and over time within any given basin

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