Geosciences 528Sedimentary Basin Analysis

Spring, 2011

G528 – Sedimentary Basins

• Prof. M.S. Hendrix– Office SC359– Office Phone: 243-5278– Cell Phone: 544-0780– marc.hendrix@umontana.edu

• Textbook = Principles of Sedimentary Basin Analysis - Andrew Miall

• Lab 320• Syllabus

Introduction to sedimentary basin analysis

What is a sedimentary basin?• thick accumulation (>2-3 km) of sediment• physical setting allowing for sed accumulatione.g. Mississippi Delta up to 18 km of sediment

accumulated• significant element of vertical tectonics which

cause formation of sed basins, uplift of sed source areas, and reorganization of sediment dispersal systems

• Study of history of sedimentary basins and processes that influence nature of basin fill

Vertical tectonics caused primarily by:

• plate tectonic setting and proximity of basin to plate margin

• type of nearest plate boundary(s• nature of basement rock• nature of sedimentary rock

Requires working or expert knowledge on wide variety of geologic subdisciplines

• sedimentology (basis of interpretation of depositional systems• depositional systems analysis• paleocurrent analysis• provenance analysis• floral/ faunal analysis• geochronology• crustal scale tectonic processes, geophysical methods• thermochronology (Ar/Ar, apatite F-T, etc.)• special techniques

- organic geochemical analysis- paleosol analysis- tree ring analysis

• involves both surface and subsurface data• involves large changes in scale and may involve long temporal histories

Location/ exposure quality

Stratigraphic measurements,sedimentology, paleoflow data

Clast Composition Analysis

Paleogeographic/paleoenvironmental

interpretation

Regionaltectonicpicture

Basin models:

1) a norm, for purposes of comparison2) a framework and guide for future observation3) a predictor4) an integrated basis for interpretation of the class of basins it

represents

Francis Bacon: ‘Truth emerges more readily from error than from confusion.’

S.J. Gould: ‘Classifications are theories about the basis of natural order, not dull catalogues compiled only to avoid chaos.’

Vertical crustal controls on sed basins (Subsidence mechanisms)• Crustal thinning: extensional stretching, erosion during uplift, magmatic

withdrawal• Mantle-lithospheric thickening: cooling of mantle following cessation of stretching

or heating due to asthenospheric melts• Sedimentary or Volcanic loading• Tectonic loading• Subcrustal loading (underthrusting of dense lithosphere)• Asthenospheric flow, for example due to descent of subducted lithosphere;

emplacement of high density melts into lower density crust• difference in thickness and density between oceanic and continental crust

(isostacy)• thermal history of continental & oceanic crust• combinations of above

More specific details of sedimentary basin fill patterns governed by:• geometric shape and size of basin and evolution of floor and flanks of basin• nature of stratigraphic fill• structures that develop within basin during its evolution (e.g. growth faults, salt

diapirs

Dickinson, 1976

Basin Analysis and Classification

• Basins should be classified according to their tectonic setting at the time of deposition of given stratigraphic interval; basins may change their teconic seting rapidly and often.

• A complete basin analysis must incorporate all phases of development of a basin and must consider both proximal and distal tectonic influences.

• Sedimentary successions (basin fill) may accumulate due to subsidence of a shallow substrate (‘sinking substratum’) OR from filling of a space below base level (usually sea level; ‘filling hole’). Most basins are hybrid.

• Preservation potential of a basin is an important factor in basin analysis.e.g. trench-slope basins have low preservation potential, whereas intracratonic basins are likely to be preserved

• Fundamental difference between preservability of a sedimentary basin vs. tectonostratigraphic assemblages that make up the basin fill (e.g. Bay of Bengal vs. Bengal Fan turbidites).

Convergent margin settings, cont.

Brief Survey of Basin ModelsI. Extensional basins

• Most modern passive continental margins resulted from breakup of supercontinent Pangea. Likewise, many Paleozoic plate margins (e.g. Cordillera, Appalachians) originated from breakup of Rodinian supercontinent.

• Supercontinent cycle 350-400 Ma. Several different hypotheses to explain breakup of supercontinent

• 1) random motions of continents around earth• 2) Supercontinent acts as a thermal blanket,

inducing thermal upwelling of mantle to initiate rifting and eventual breakup.

• 3) Subduction principally of old, cold crust during times of supercontinent formation.Slab roll-back (i.e. density driven ‘slab pull’) = important phenomena that may induce supercontinent breakup.

Formation of ‘passive continental margins’

• Pre-Rift phase includes sedimentary and tectonic setting prior to initiation of rifting. Depends on pre-rift setting. Commonly continental sedimentation on craton.

• Rift phase is tectonically active, with normal faulting, crustal thinning, volcanism, high heat flow and locally high rates of subsidence and sediment accumulation.

• Drift phase (post-rift) = dominated by lithospheric cooling, thermal subsidence, and development of broad flexural basins dominated by sediment loading (e.g. continental embankments).

Simple model for evolution of passive

continental margins

Dickinson, 1976

“Active” vs. “Passive” Rifting:

• Active: Kinsman (1975): early, domal uplift preceeded crustal stretching; surficial and tectonic erosion of thermal dome thins upper crust and produces major subsidence once margin rafted away from heat source.

– Test: Predicts >15 km subaerial erosion = amount cont. crust has been thinned by rifting. Also predicts centrifugal drainage patterns and sediment starvation (unless significant volcanism). Basaltic volcanism predominates in early rift stages.

• Passive: early thermal doming in response to crustal thinning. Doming is caused by mantle upwelling.

Active vs. Passive Rifting Models

www.mantleplumes.org/WebDocuments/InfolioEngIvanov.pdf

Baikal Rift regional tectonic setting

www.mantleplumes.org/WebDocuments/InfolioEngIvanov.pdf

Baikal Rift Lithospheric structure

www.mantleplumes.org/WebDocuments/InfolioEngIvanov.pdf

Rift Geometries

• simple shear (no mechanism for bringing mid-crustal rocks to shallow levels)

• delamination between upper and lower crust

• low angle detachment faults: either as through-going (cut entire lithosphere) or intracrustal

RiftGeometries

cont.

Crustal Detachment Rift Model

• Asymmetry of rift systems by presence of major detachments will produce ‘upper plate’ and ‘lower plate’ margins

– Upper plate: originate in hanging walls of detachments; thick continental crust with narrow continental shelves and thin sedimentary cover; structurally simple with only weakly rotated normal faults

– Lower plate margins: originate in footwalls of detachments; thin continental crust with broad shelves, thick sedimentary cover, and exhumed middle to lower crustal rocks and remnants of upper plate in strongly tilted blocks.

Crustal scale detachment rift model, cont.

Busby and Ingersoll, 1991

Detachment model, cont.

Asymmetry of rift systems involving major detachments produces ‘upper plate’ and ‘lower plate’ margins

Upper plate: originate in hanging walls of detachments; thick continental crust with narrow continental shelves and thin sedimentary cover; structurally simple with only weakly rotated normal faults.

Lower plate margins: originate in footwalls of detachments; thin continental crust with broad shelves, thick sedimentary cover, and exhumed middle to lower crustal rocks and remnants of upper plate in strongly tilted blocks. Busby and Ingersoll, 1991

Crustal scale detachmentrift model, cont.

polarity reversals exertMajor control on passivemargin geometry

Busby and Ingersoll, 1991

Rift basins

Characteristics of Rift basins• very early stages of rift development• high heat flow• extensional• interstratified lavas and redbed sediments; evaporites

common due to screening of rivers by rift shoulders- e.g. Red Sea, Rio Grande Rift

Red Sea is only true proto-oceanic basin on earth, so our understanding of these basins is strongly weighted towards examination of that basin.

Post-rift basinsPost-rift basins (as opposed to syn-rift) are formed mainly

from subsidence resulting from thermal relaxation

Miogeoclinal Prisms• require one-sided open ocean setting• transition of sedimentary facies

- nonmarine to shallow marine deltaic- shelf and paralic sediments of continental terrace- marine turbidites of slope and rise

• may be characterized by salt diaparism and growthfaulting

• Heavily influenced by fluctuations in sea level

Continental Embankments• advancement of shelf break to point over oceanic crust

-Mississippi embankment is 1000 km wide from OK coastal plain to edge of Sigsbee escarpment

• series of lensoidal sedimentary packages• immense sediment accumulation (16-18 km) which loads continental and

oceanic margins• unstable: results in growth folding, gravitational failure, salt diaparism, etc.

Sigsbee salt nappe is one of largest single structural features of the North American continent

• usually result from drainage of large continents toward mouths of failed rifts and away from ‘normal rifted continental margins (e.g. Mississippi delta, Nile delta)

• Rapid subsidence (10-100m/Ma) results from-sedimentary load which induces lithospheric flexure-listric normal faulting (growth faulting)-salt withdrawal during diapirism-compaction of unconsolidated sediments.

• Progradation of rise-slope-shelf triad results in predictable sedimentary sequence: deep sea fan, slope mud with diapirs, shelf and shoreline, continental (primarily fluvial).

Continental Embankments

Dickinson, 1976

Active Ocean basins

• largely a function of cooling and contraction of oceanic lithosphere

• development of thicker strata on older, colder (and more subsided) oceanic crust

• sediment largely pelagic and hemipelagic; influenced by position of CCD and presence of local bathymetric features like seamounts.

Dormant ocean basins

• underlain by oceanic crust• plate margin rearrangement results in cessation of

actively spreading centers or subducting margins• dominant mode of subsidence is sediment loading• classic ‘filling hole’ basin (e.g., Arctic Ocean)• weakest part of basin would be along residual

continental margins related to extinct rifting or subduction; subsequent orogeny might create intermontane basins corresponding to ancient dormant ocean basins (e.g., Junggar basin, China)

Intracratonic basins

•overlie fossil rift, underpinned by transitional crust?•probably high heat flow early on•doming, normal faulting followed by thermal subsidence•sedimentary fill usually shallow marine, mature sediment; occasional basin starvation

- e.g. Michigan basin, Illinois basin•Changes in stress regime appears to change the viscosity of crust beneath the basement, resulting in accelerated subsidence during times of orogeny in nearby mobile belts.

Marginal Aulacogens

• failed rift arm, underpinned by oceanic or transitional crust

• early high heat flow• rifting, normal faulting followed by thermal

subsidence• sedimentary fill usually thick accumulations of

shallow marine sediment• subsequent closure of associated oceanic basin

"inverts" aulacogen, changes dispersal patterns and provenance trends

• e.g. Oklahoma Aulocogen; Benue Trough

Arc-trench systems

• Can be extensional, neutral, or compressional

• Extensional: trench rollback is faster than trenchward migration of overriding plate; characterized by low relief, thin sediments, and deep trenches.

• Compressional: overriding plate advances trenchwrd faster than trench rollback; characterized by high relief, abundant sediments, and shallow trenches.

• Neutral: trench rollback is about equal to trenchward advance of overriding plate.

Kanamori (1986) concluded that a relationship existed between convergence rates, plate age, and seismicity. Backarc opening generally associated with subduction zones of low seismicity.

Jarrard, 1986 suggested that major factors that affect tendency for arc-trench system to be extensional, compressional or neutral include:

- convergence rate- slab age- slab dip

Plot of slab descent angle (trajectory) against dip angle (architecture) demonstrates that:

1) most slabs do not descend at angles parallel to their dip angle

2) most slabs descend at angles steeper than their descent angle (slab roll-back)

3) a few slabs descend at angles shallower than their descent angle

4) a few slabs descend at angles greater than 90 degrees

5) no tendency for old slabs to descend steeply and young slabs to descend more shallowly

6) probably greater slab age does not result in swinging of slab descent towards vertical.

Conclusion: strain regime is probably a complex function of slab age, slab dip, and convergence rate

Oceanic trenches and slope basins:

•formed by flexure of downgoing slab•dominated by accretion tectonics•sediment fill dominated by gravity flow

deposits, rafted oceanic sediments

•local variations in bathymetry of subduction complex may result in slope basins

•subduction complex highly deformed by imbricate thrusting and gravitational spreading

•contacts between sediment fill and accreted material may be either depositional or tectonic

•very low geothermal gradient

Forearc basins• occur within the arc-trench gap• not as highly deformed as oceanic trench and slope basins• very low geothermal gradient• variety of types

Factors affecting forearc geometry include• sediment thickness on subducting plate• rate of sediment supply to trench• rate of sediment supply to forearc• rate and orientation of subduction• time since initiation of subduction• Arc-trench gaps tend to widen with time due to accretion of

sediments; thus general tendency for forearcs is to enlarge with time (e.g. Great Valley forearc basin, California)

Intra-arc basins:

• basins within an arc system • usually filled with volcanic material resulting from:

- magmatic explosions due to exsolution of volatiles- hydroclastic fragmentation (magma-water interactions)- autoclastic lava fragmentation- weathering products from emergent arc

• form in several possible settings- low regions between volcanoes and their flanks- when axis of volcanism shifts to new position on an oceanic arc platform- fault-bounded basins within arc itself (relief created by tectonic structure, not constructional volcanic features

• poorly understood basin type due to thermal and metamorphic overprinting and susceptibility of volcanic seds to diagenesis

Intra-arc basins

Intra-arc basins

Back-Arc Basins:

• Oceanic basins behind intraoceanic magmatic arcs• Continental basins behind continental-margin arcs that

lack foreland foldthrust belts.• Most are extensional, forming by rifting and sea-floor

spreading• May result in remnant arc behind BAB (if subduction does

not jump)• Probably have relatively low preservation potential due to

eventual closing of BAB by subduction• Many ophiolites of geologic record may have originated

from BAB’s floored by oceanic crust.• Evolutionary model for BAB’s includes periods of major

extension, minor extension, and major compression

Remnant Ocean Basins• form during intense deformation

associated with attempted subduction of nonsubductable, buoyant continental crust during terminal ocean closure.

• irregularity of continental margins tends to create great variability of timing, structural deformation, and preservability occurs along strike

• most sed from orogenic highlands pours longitudinally through deltaic complexes into remnant ocean basins as turbidites that are subsequently deformed and incorporated into orogenic belts as collisional sutures lengthen

Remnant Ocean Basins

Foreland-style basins

• formed by flexure of continental crust by tectonic and sedimentary loads

• may be formed either in retro-arc or peripheral positions• strongly asymmetric transverse profile• orogenic flanks of basin undergo deformation during life of

basin• cratonal flanks of basin merge with platform sequences• composite foreland basins may reflect net effects of successive

orogenic episodes (e.g. Appalachian basin)• usually dominated by nonmarine or shallow marine strata• recycled orogen provenance (sandstones dominated by

recycled sedimentary or metasedimentary detritus)

Foreland-style basins

Distinction between ancient retroarc and ancient peripheral foreland basins:- polarity of magmatic arc- oceanic subduction complex assoc with early phase of peripheral dev.- greater water depths in peripheral stage- protracted development of retroarc (e.g. Appalachians) vs. discrete development of

peripheral foreland (terminal ocean closure)- possible volcanic input to retroarc forelands, minimal to peripherals

Transpressional and transtensional basins in strike-slip fault systems•en echelon or curved strike-slip fault at constraining or releasing bends•occur in wide variety of settings•characterized by rapid, complex facies changes