Fluvial systems and tectonics

Base level in fluvial systems

● Deposition above sea-level

● Base level= longitudinal graded profile

● Greatly influenced by sediment flux and tectonics

Graded profile

Quirk (1996)

Evolution of graded profiles

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 470

100

200

300

400

500

600

Depostion is a function of transport capacity loss = downstream reduction in slope.

Initial steeper profile

Paola & Martin

Graded profiles and grain-size

Downstream reduction in grain size controlled by deposition:At a reference point determined by a fixed fraction of the total sediment mass extracted (deposited) upstream, the grain-size and proportion of channel vs. Floodplains is constant.

Changes in fluvial graded profiles

Quirk (1996)

Sedimentary input: climate and tectonics● Sedimentary yield of source areas (kg km-2 .y-1) and area of eroding sources

determine the sediment input to the system.

● Sedimentary yield is controlled by slope, erodibility and climate.

For example: Ludwig & Probst (1996): SY= 0.02*(R*S*VP)

SY= sediment yield (t/km²/year)

R= specific runnof (mm/year)

S=average slope at source area

VP=variability of precipitation= P² monthes/ P year (mm/year)

● Tectonics controls slope (often in pulses of uplift)

● Uplift control precipitation (orographic rainfall)

● Climate change imposes high frequency cycles (tens of ky)

Orographic precipitation

Poulsen et al. 2010. Science, Vol. 328 no. 5977 pp. 490-493

Tectonic environments and sediment yield

Hovius (1998)

SY as a function of stable average slope at sources

Effect of climate change on SY

Effects of climate change on SY

Long-lasting changes in precipitation cause initial spike of SY and subsequent stabilization at the former level (with different height and slope)

Augmented spike due to previous arid period

Longer recovering time during dryer period

Variable uplift and sediment yield

Changes in uplift rates cause durable change in SY – for each uplift rates there is one fixed SY (if all other variables are kept constant)

Effect of SY on the graded profile

1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031323334353637383940414243444546470

100

200

300

400

500

600

1 2 3 4 5 6 7 8 9 10111213141516171819202122232425262728293031323334353637383940414243444546470

100

200

300

400

500

600Low SY High SY

Larger sediment volume

Flatter final profile

Lower proportion of sediment stored in proximal setting:

Advance of proximal facies basinward

Smaller sediment volume

Steeper final profile

Higher proportion of sediment stored in proximal settings:

Contraction of facies belts

Effect of subsidence on the graded profile

Subsidence pulses act instantaneously in generating accommodation space, while uplift has a retarded effect on the sediment input.Blair & Bilodeau

Whittaker et al.

Effect of tectonic pulses

Q. Clevis et al. / Sedimentary Geology 163 (2003) 85–110

Retarded clastic advance

Effect of subsidence on graded profile

Diminished sediment flux (extraction through depostion)

Paola & Martin

Effect of subsidence on graded profile

Change in the form of the profile

Stratigraphic Respose

Paola et al. (1992)

Advance andretreat of clastic wedges

Depositional Sequences and systems tracts

Connectivity of channel bodies

Connectivity of channel bodies – physical modelling

High and Low Accommodation Tracts

Catuneanu & Elango (2001)

Proportion of Channel Bodies and Floodplains

Catuneanu (2006)

Channel styles

Channel styles

Slope is a major control on channel style:The evolution of the graded profile controls changes in local channel styles

Almeida et al. unpublished

Pilcomayo river near the Andes

Pilcomayo river a few tens of km downstream

Accommodation space and avulsion rates Kosi River

Accommodation space and avulsion rates

SinhaSinha

Accommodation space: Distributive Fluvial Systems

Effects of lateral tectonic tilting in meandering river

Asymmetrical preservation of abandoned meanders due to tectonic tilting Senguerr River, Argentina.

Intrabasinal faulting and river response

Magnavita 1994

Fluvial deposition tends to outpace the displacement of minor intrabasinal faults

Graded profile evolution over and active intrabasinal fault

Growth strata

Increasing dispacement

UndeformedDepositionalSurface

Fluvial deposition tends to outpace the displaciment of minor intrabasinal faults

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

-200

-100

0

100

200

300

400

500

600

Tectonic deformation of previous deposits

Additional space affects profile form

No displacement of the depositional surface

Local effects of local tectonics

When displacement is too large: Intrabasinal High

Increased SY due to erosion of loose sediment

Intrabasinal high development with nostarved phase in the basin.

Marconato et al. umpublished

Summary

Tectonics effects on fluvial systems:

- Changes in sedimentary yield (retarded after tectonic pulse)

- Changes in precipitation – orographic rainfall

- Changes in local river slopes (instantaneous)

Changes in channel styles

- Sediment capture through subsidence (instantaneous):

Adjustments of graded profile

Shifts in facies belts

River response to higher accommodation space

Avulsion

Distributary paterns