evolution of sedimentary basins

7/30/2019 Evolution of Sedimentary Basins

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Evolution of Sedimentary Basins

Sedimentation and Tectonics:


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Evolution of sedimentary basins is spatially relatedto continental evolutionand global tectonicprocesses.

Several studies show a close relationship betweensedimentary pattern and larger structuralelements of the Earth

Continents are formed bydifferent tectonicprocessess and related magmatism.

On the other hand these continents are destroyed

by continuous physical and chemicalweathering/erosion processes.

These sediments have been shifted through masstransport by water, wind and ice to nearest

depression(Basins).


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In order to understand evolution of sedimentary

basins following aspects/factors are considered :

1) Distribution of sediments(Large Scale).

2) Kinds of Sedimentary basins existing during

geological history.

3) Nature and organisation of sedimentary fill.

4) Relationship between sediments and theirsource land(Provenance)


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1) Distribution of Sediments

Sediments are known to occur throughout thegeological history from 4200 m.y to present day.

They are extremly useful and provide crucial

information on the evolution of upper

continental crust, global surface environments,

redox conditions and biological evolution


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During the Achaean era(4200-2500m.y)

sediments spatially associated with volcanism

and chemical alteration processes weredominant over physical breakdown. These

sediments were involved in sedimentation and

metamorphism of varying degrees.

During Proterozoic stable environments

prevailed so sediments was quite extensive and

extensive flat sequences of conglomerates,

sandstone, shales and limestone weredeposited and these sediments were not

affected by deformation and metamorphism.


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During Phanerozoic, sediments were dominated

by volcanoclastic sequences in differentenvironments(shallow to deep waters). These

sedimentary associations contain abundant

biogenic materials such as plant and animal

fossils.


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2) Kinds of sedimentary basins existing

during Geological history

Achaean sedimentary basins are extremelydifficult to characterize in regard of its nature

and geometry as these basins were affected by

several episodes of deformation andmetamorphism and their original geometry and

other characteristics have been erased.

Intracratonic and back arc basins were commonduring middle to late archaean(3200-2600)


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During Proterozoic, globally stable environment

prevailed as continental crust lost huge amountof heat producing elements during late archaean

techtanothermal events.

Most of the Proterozoic sedimentary basins arestable, continental platforms, where detrital

sediments derived from large cratons were filled.


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During Phanerozoic large sedimentary basins

developed along plate margins(back arc andisland arc basins) and also in collisional

environments(Sedimentary fill between two

continents e.g Tethys sea between India andAsian plate).

The sedimentary basins were huge and spatially

associated with orogenic cycle.


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4) Nature and organisation of

sedimentary fill

The Nature and organisation of sedimentary

sequences provide information on sedimentary

environments

It is not easy to characterise the nature and

organisation of sedimentary fill up in the

Archaean sedimentary sequence as they are

affected by deformaton and matamorphism andtheir original and depositional characteristics have

been disrupted.


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The Proterozoic sedimentary sequences globally

comprise abundant flat sequences of

conglomerate-sandstone-shale and carbonateassociationswhich are unmetamorphosed

The Phanerozoic sediments are fossiliferous and

comprise thick associations of conglomerate,sandstone, greywacke-argillite, shale, carbonate

and iron stones. These sediments were deposited

in diverse environments including shallow to

deep marine environments and were derived

from old continental crust as well as young

volcanic arc.


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4) Relationship between sediments

and their source land (Provenance)

In recent years numerous studies focussed on

sedimentologgy particularly to characterise

sediment source(provenance) by using sediment

characteristics, dating of heavy minerals(zircon,

monazite, garnet)and isotope tracers.

These studies show that sediments derived from

mixed sources with contrasting histories.

Combined sedimentological and geochronological

studies of clastic sediments useful to reconstruct

geometry of the source land


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Isotope tracers (Nd, Sr and Pb) provide

information on history of source areas of someclastic and chemical sediments.

O and C isotopes are particularly useful tocharacterize sedimentary environments and

digenetic processes including residence time of

non-clastic sediments in water.


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In summary sedimentary basins known to occur

throughout the earths history and provide

information on the evolution of continents.

They are known to occur in diverse

environments including Intracratonic, passive

margin, backarc, island arc, rift and continental

collisional environments.

Thus Evolution of sedimentary basins is spatially

associated with magmatism and tectonic

processes


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Sediment Supply and climate

The process of transporting/deposition ofsediments from the source area to the

depositional area or basin is known as sediment

supply

Normally sediments are derived through physical

or chemical breakdowns while the Achaean

sediments presents a different scenario as

sediments were derived through volcanism and

chemical alteration processes.


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Climate

Climate play a very crucial and important rule insedimentary formations

The very basic building block i.e sediments were

derived as a result of climatic factors acting ondifferent rocks or materials

Without the influence of climate a lot of

sedimentary formations would not be available.

evolution of sedimentary basins

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