BaseLevel Buffers and Buttresses

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Base-Level Buffers and Buttresses A MODEL FOR
FLUVIAL PRESERVATION
John Holbrook University of Texas at
Arlington Robert Scott Precision Stratigraphy
Associates/University of Tulsa Franca
Oboh-Ikuenobe University of Missouri, Rolla
Supported by the National Science Foundation and
the Petroleum Research Fund
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River-to-Basin Processes
(Van Wagoner, et al., 1991)
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Models for Downstream (Eustatic) Control on
Base-level and Resultant Channel Stacking
Patterns
?
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Base Level Buffers and Buttresses
Instantaneous Profile
Buttress (Sea Level, Cataract, Lake Level, etc.)
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Principles The Static-Buttress Model
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Assumption Base level, and the related
longitudinal profile, is the primary control on
aggradation in both upstream and downstream
settings.Downstream vs. Upstream Base Level
Controls

• Downstream Controls

• Upstream Controls

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Assumption Base level, and the related
longitudinal profile, is the primary control on
aggradation in both upstream and downstream
settings.Downstream vs. Upstream Base Level
Controls

• Downstream Controls
• Eustatic (sea level/lake level), morphologic
  (e.g., tributary junctures), tectonic (e.g.,
  faults)

• Upstream Controls
• Climate (e.g., sediment supply, discharge),
  tectonic (e.g., uplift rate)

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Assumption Base level, and the related
longitudinal profile, is the primary control on
aggradation in both upstream and downstream
settings.Downstream vs. Upstream Base Level
Controls

• Downstream Controls
• Eustatic (sea level/lake level), morphologic
  (e.g., tributary junctures), tectonic (e.g.,
  faults)
• Local effects to lower reaches causing
  adjustments that propagate and dampen upstream

• Upstream Controls
• Climate (e.g., sediment supply, discharge),
  tectonic (e.g., uplift rate)
• Broad effects in upstream reaches causing
  adjustments that propagate and dampen downstream

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Assumption Base level, and the related
longitudinal profile, is the primary control on
aggradation in both upstream and downstream
settings.Downstream vs. Upstream Base Level
Controls

• Downstream Controls
• Eustatic (sea level/lake level), morphologic
  (e.g., tributary junctures), tectonic (e.g.,
  faults)
• Local effects to lower reaches causing
  adjustments that propagate and dampen upstream
• Generally causes adjustments on the scale of 101
  to 102 meters and 104 to 107 years

• Upstream Controls
• Climate (e.g., sediment supply, discharge),
  tectonic (e.g., uplift rate)
• Broad effects in upstream reaches causing
  adjustments that propagate and dampen downstream
• Generally causes adjustments on the scale of 100
  to 101 meters and 101 to 104 years

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The Graded Longitudinal Profile
Profile variable because of non-constant upstream
controls Water Discharge (Qw) Sediment Flux
(Qs) Substrate Erodability Uplift Rate Local
Tectonics Etc.
?!
River Profile
Anchor point Downstream base-level control (e.g.,
sea level)
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Base Level Buffers and Buttresses
Instantaneous Profile
Buttress (Sea Level, Cataract, Lake Level, etc.)
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Applications The Mobile-Buttress Model
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Some Effects of Buttress Shift
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Lower Mesa Rica
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Upper Mesa Rica
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Romeroville Ss
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Profiles and Thickness, Lower Cretaceous
Sandstones
300km
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Model Predictions 1) Continuous Layer 2) Thickens
up dip 3) Stable Buffers
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Romeroville Sandstone Architecture
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Model Predictions 1) Continuous Lower Layer
Capped by Aggradation 2) Continuous Layers where
buffers become stable 3) Layers Thicken up dip 4)
Stable layers merge up dip
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Model Predictions 1) Continuous Layer 2) Thickens
up dip 3) Stable Buffers
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Mesa Rica Sandstone Architecture
ChannelBed10m
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Mesa Rica
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Lateral Geometry (i.e., Sheet vs. Lens) Buffer
Stability
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Romeroville (1 regression) Buffers Stable .78 -
2.69ma
Mesa Rica (2 regressions) Buffers Stable .62
2.15ma
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Romeroville (1 regression) Buffers Stable .78 -
2.69ma
Mesa Rica (2 regressions) Buffers Stable .62
2.15ma
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Model Predictions 1) Erosion of Earlier Layers 2)
Deep Valley Incision 3) Layers where Buffers
Stable
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Model Predictions 1) Erosion of Earlier Layers 2)
Deep Valley Incision 3) Layers where Buffers
Stable
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Model Predictions 1) Erosion of Earlier Layers 2)
Deep Valley Incision 3) Layers where Buffers
Stable
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Conclusion The Buffers and Buttresses model
incorporates both upstream and downstream
controls into predictions of geometry and
architecture for fluvial units deposited during
T/R cycles, and applies farther up dip than prior
models. (Example Prediction Regressive
sandstone sheets should merge and become more
complex and thicker up dip where up dip tectonic
effects are minimal (Example Prediction Sheet
geometry reflects lateral storage and reworking
under conditions of stable buffers whereas,
lenses reflect more mobile buffers