Fluvial systems and tectonics
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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
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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
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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
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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
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