This is my presentation on the tectonic control of sediments. It includes the effects of tectonics either direct or indirect on sediments and sedimentation. Sedimentation along various plate boundaries. Few examples as evidence from Pakistan (the Siwalik Group) and Argentina (Fiambala Basin)

1. Tectonic Control of
Sediments
Prepared
By
ARSHAD AYUB
UNIVERSITY OF MALAKAND
SESSION 2014-2018

2. Introduction
• Sedimentation is controlled by three extrinsic variables: Tectonics, Climate and
Sea level.
• Climate and sea level depends upon each other and they both depends upon
tectonics.
• Tectonics affects sedimentation in two different but often related ways:
1) Uplift of the land
2) Subsidence of the crust

3. Introduction
• Subsidence may be formed by vertical upset of fault.
• Uplifting expose various rocks to weathering and erosion and is then transported.
• Subsidence provides the accommodation space for the accumulation and burial
of these sediments to be deposited in the sedimentary basin.
• Although sediments may be deposited in tectonically in-active and
topographically low areas of the crust.

4. Introduction
• Among these variables, which effect sedimentation, Tectonics has the most
important control on sedimentation.
• The important effect of tectonics on sedimentation, wither direct or indirect
include:
1. Nature of sediments
2. Rate of sediment supply
3. Rate of deposition

5. Introduction
4. Depositional environments
5. Nature of source rock
6. Nature of vertical succession
• Sedimentation also affect tectonics, although to a much lesser extent,
mainly by increasing lithospheric load on the basin.

6. Why to study Sediments and Tectonics?
• We study sediments and sedimentary rocks in order to know the effect of
extrinsic and intrinsic processes on the depositional history of a sedimentary
basin.
• Sedimentary record in sedimentary basin tell us about paleotectonics in the best
way.
• The deposition of sediment types, sediment thickness and paleocurrent in a basin
gives us evidence of the existence and location of elevated areas of the crust
created by tectonics.

7. Example
• Siwaliks of Pakistan:
• Study of the Siwaliks of Pakistan show us that they are formed from the
sediments weathered and eroded from Himalayas.
• These Himalayas were uplifted by Tectonics since Miocene.

8. Tectonics and Erosion
• There are three processes that can increase rate of erosion at high elevation and
provides abundant sediments to be deposited:
1) Active faulting that exposes fresh unweathered rocks
2) High altitude mechanical weathering due to steep slope, lack of vegetation and
glacial weathering
3) Orographic rainfall on windward slope of mountain ranges

9. Tectonics and Erosion

10. Tectonics and Erosion

11. Tectonics and Sedimentation
• As sedimentation depends upon Tectonics, so first we must know about
Tectonics.
• Tectonics is the study of origin and arrangement of the structural features of the
earth`s surface, including mountain belts, continents and earthquake belts.
• The concept of Plate Tectonics was born in the late 1960s by combining two pre-
existing ideas; 1) Continental Drift and 2) Sea Floor Spreading.
• Basically Tectonics means that the earth surface is divided into few large and
many small plates that move slowly and change in size.

12. Tectonics and Sedimentation
• Plate is a large mobile slab of a rock that is part of the earth`s surface.
• These plates move along plate boundaries and intense geologic activity occurs at
these boundaries.
• These plates either move away from each others (Divergent Boundary), past one
another (Transform Boundary) or towards one another (Convergent Boundary).
• More tectonic activities will lead to more sedimentation on the earth`s surface
mostly along basins.

13. Divergent Margins
• If two plates are separating, they form a divergent margin.
• It is characterized by extensional features like seafloor spreading, normal faulting
etc.
• In the first stage continental crust begin to rift apart and hot mantle plumes move
upward.
• This upward movement produces domed uplifts that shed coarse, immature
alluvial and fluvial deposits onto their flanks.

14. Divergent Margins
• In the second stage, uplift and extension breaks apart the crust, and a crustal block drops
down to form a fault graben called a rift valley.
• This stage is occurring today in the East Africa Rift Valley.
• These rift valley form basins for the sediment that erodes from the up-thrown areas.
• Most of the sediments are coarse, immature alluvial debris and lesser fluvial deposits.
• In the center of the basin, small lakes may form lacustrine shales or limestone
and even evaporates.

15. Convergent Margins
• If two plates are moving towards each other, they form a convergent margin.
• Such margins are characterized by folding and thrusting.
• Due to plate convergence several types of mountain belts can be produced.
• Convergence of the two plates may be:
i. Continent-Continent convergence
ii. Ocean-Continent convergence
iii. Ocean-Ocean convergence

16. Continent-Continent Convergence
• In this case non of the plate subducts beneath the other, so they become uplifted
and deformed and finally suture along the line of collision.
• The suture belt itself is an area of erosion.
• It sheds coarse clastic debris and fluvial deposits off its flank into adjoining
plains.
• Himalayas is one of such sutures.
• The molasse sequence of the Siwalik hills of Pakistan and India are the product
of the Himalaya uplift since the Miocene.

17. Himalayas
• Himalayas have been formed by the collision of Indian and Eurasian Plate.
• This collision began 50 million years ago and still continue today.
• The Himalayas are still rising by a rate of 1 cm per year as India continue to
move Northwards into Asia.
• But at the same time weathering and erosion are lowering the Himalayas at about
the same rate.
• Himalayas contain sedimentary rocks of marine origin that were originally
deposited below sea.

18. Himalayas

19. Ocean-Continent Convergence
• In this type of convergence the oceanic plate subducts beneath the continental
plate.
• Due to this type of convergence continental-margin arc forms.
• As this region is epicontinental and sub-aerial, so the sediments filling the basin
are mostly immature alluvial and fluvial sandstones and shales.
• Most of the pelagic sediments of the oceanic plate is scraped onto the continental
plate and accommodate along the arc to form accretionary wedge.

20. Sedimentation along Subduction Zone

21. Transform Margins
• If two plates are sliding past each others, neither separating nor converging they
form a Transform margin.
• They are characterized by horizontal shear and strike-slip faulting.
• No such basins are associated with transform margins.
• Because of the irregularities in the sliding, local compression and extension
occurs, forming two types of fault bounding troughs.
1) Transtensional or pull-apart basin
2) Transpressional basin

22. Transform Margins
1) Transtensional or pull-apart basin is formed by extensional gap. Salton
Trough along the Southern Sand Andreas Fault is its common example.
2) Transpressional basin is formed by the compressional down warping. Mio-
Pliocene Ridge Basin of California
• They accumulate thick pile of sediments.
• Thick, narrow and immature accumulation of sediments can only occurs in
basins on transform margin.

23. Transform Margins
• Because of rapid rate of deposition and burial of organic materials, fault bounded
basin are good places to explore for petroleum.
• Many of the petroleum occurrences in California are related to basins that are
formed as a result of the Sand Andreas transform fault.

24. San Andreas Transform Fault

25. Tectonics and Type of sediments
• The windward side of a mountain receive more rainfall than the Lee side.
• Due to more rainfall on the windward side most of the sediments will lack
feldspar because of its alteration to other minerals.
• So, in such case the rocks formed will have no or very less feldspar.
• Less rainfall leads to increased aridity on the Lee side.
• The sediments and sedimentary rocks so formed will have more feldspar.

26. Clues and Evidences
• There are various clues to show that sedimentation is strongly controlled by
Tectonics.
• Siwaliks
• Fiambala Basin, Which includes:
i. Punaschotter Formation
ii. Tamberia Formation
iii. Guanchin Formation

27. Siwaliks
• Sediments study of the Siwalik group show that the detritus or sediments
deposited here, came from the weathering and erosion of the Himalayas.

28. Fiambala Basin
• Fiambala basin bounding ranges have been uplifted by the late Miocene (~7-6
Ma).
• The Punaschotter Formation, Tamberia Formation and Guanchin Formation of
the Fiambala Basin record exhumation and erosion of the surrounding ranges.
• Regional tectonics were the most probable cause of deposition of these
sediments/conglomerates.
• These conglomerates may record global climate changes, tectonic activity or
both, and can serve as a proxy for tectonic activity worldwide.

29. Fiambala Basin

30. The End
Thanks for giving me your precious time