Follow the Energy

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Basin Analysis
Follow the Energy
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Controls on the Stratigraphic Record
Alluvial Fan
Braided
Meandering
Beach
L-Bar/ T-Bar
Shelf
Point Bar
Laminated Sands
Hummocky
Submarine Fan
Bouma
Basin
Laminated black Shale
Energy dissipation changes systematically from
proximal to distal.
This is obvious because sequences of sedimentary
structures, which represent differences in how
energy is dissipated, change systematically from
proximal to distal.
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Regressive Sequences
Alluvial Fan
Braided
Meandering
Beach
L-Bar/ T-Bar
Shelf
Point Bar
Laminated Sands
Hummocky
Submarine Fan
Bouma
Basin
Laminated Shale
But, this observation is only a snapshot in time
which happens to be the present, this moment in
time.
Geologically, we have to ask, What happens if we
observe how environments change with time
relative to each other.
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Regressive Sequences
Regressive Sequence
Prograding Regression
Beach sandstone
Time Transgressive Rock Unit
Beach sandstone
Near Shelf shale
Near Shelf shale
Far Shelf limestone
Far Shelf limestone
Beach moves closer
Water gets shallower
Sediment gets coarser
After all, we already know that environments
shift with time.
During a regression more proximal environments
build out and on top of more distal environments
near shelf on far shelf, and beach on near shelf.
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Regressive Sequences
Alluvial Fan
Braided
Meandering
Beach
Shelf
Submarine Fan
Basin
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Vertically Stacked Regressive Sequences
Proximal
Disorganized Gravels
Alluvial Fan
L-Bar/T-Bar Sequence
Braided
Point Bar Sequence
Meandering
Beach
Laminated Sands
Depositional Sequences
Shallowing
Shelf
Hummocky Sequences
Submarine Fan
Bouma Sequences
Basin
Laminated Shale
Distal
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Walthers Law
Sediments or environments distributed
horizontally across a series of depositional
environments (beach, near shelf, far shelf) will
become stacked vertically during a transgression
or regression
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Basin Analysis
A Theoretical Framework
The Tectonic Creed
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Controls on the Stratigraphic Record
Tectonic
Wilson Cycle
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How many different kinds of basins exist on
earth, And how are they similar or different?
Basin Analysis
Ocean Basins
Divergent Margins
Convergent Margins
Transform Boundaries
Cratons
Wilson Cycle
Rift Basins
Fore arcs
Pull Apart Basins
Ophiolite Suite
Aulacogens
Back arcs
Divergent Margins
Hinterlands
Forelands
These are tectonic regimes
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Tectonic Theory of Basin Analysis
Each tectonic regime develops specific kinds of
basins.
basin
Each
develops characteristic depositional
environments.
environment
Each
has particular depositional sequences.
depositional sequence
Each
has particular facies elements
Grain size, . . . Sedimentary structures, . . .
Compositions, . . . Colors, etc.
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Or, conversely
Each facies element,
in each sequence,
in each environment,
in each basin,
in each tectonic regime
is the way it is because of the way energy is
dissipated in the tectonic regime.
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Basin Analysis
A Theoretical Framework
Accommodation
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Accommodation
Creating Space For Sediment to Fill
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Controls on the Stratigraphic Record
Accommodation
The space available for sediment to fill
1. Eustatic control
2. Tectonic control
3. Sediment Control
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Controls on the Stratigraphic Record
Eustasy
World Wide Sea Level Changes
High Stand
Falling sea level
Falling sea level
Rising sea level
Decreasing Accommodation
Increasing Accommodation
Low Stand
Accommodation is proportional to the area under
the curve
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Here 2nd order curve has little effect on
accommodation while the 3rd and 4th order curves
have the greatest effect. Many smaller
fluctuations are prominent.
Accommodation here controlled principally by 2
order curve (because slope of curve is steep and
water is getting deep fast) with minor
fluctuations caused by 3rd and 4th order curves
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Controls on the Stratigraphic Record
Accommodation
The space available for sediment to fill
1. Eustatic control
2. Tectonic control
Tectonics affects accommodation through
subsidence (sinking of a basin creating space)
and uplift (decreasing space).
3. Sediment Control
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How many different kinds of basins exist on
earth, And how are they similar or different?
Basin Analysis
Ocean Basins
Divergent Margins
Convergent Margins
Transform Boundaries
Cratons
Wilson Cycle
Rift Basins
Fore arcs
Pull Apart Basins
Ophiolite Suite
Aulacogens
Back arcs
Divergent Margins
Hinterlands
Forelands
These are tectonic regimes
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Examples Of Rift to Drift Basin Accommodation
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Proto-Atlantic Rift to Drift
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Proto-Atlantic Rift to Drift
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Proto-Atlantic Rift to Drift
An exponential decay
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Atlantic Rift to Drift
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Atlantic Rift to Drift
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Atlantic Rift to Drift
An exponential decay
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Foreland Basin Development
Taconic Orogeny
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Foreland Basin Development
Acadian Orogeny
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Foreland Basin Development
Acadian Orogeny
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Foreland Basin Development
Acadian Orogeny
How fast does this accommodation increase?
Slow and steady?
Slow then fast?
Fast then slow?
Rapid initial subsidence followed by exponential
decay
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An Example Of Foreland Basin Subsidence
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Foreland Basin Subsidence And Accommodation
Tectonic stability
Very slow basin subsidence
Small Accommodation
Carbonates and quartz sandstones
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Foreland Basin Subsidence And Accommodation
Tectonic activity begins
Rapid basin subsidence
Accommodation increases rapidly
Deep water black shales
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Foreland Basin Subsidence And Accommodation
Tectonic activity at peak
Basin subsidence slowing
Accommodation large with deep water
Bouma sequences prograde and begin filling process
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Foreland Basin Subsidence And Accommodation
Tectonic activity slowing
Basin subsidence close to stopped
Accommodation decreasing with filling
Shelf hummocky sequences prograde
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Foreland Basin Subsidence And Accommodation
Tectonic activity over
Basin largely filled with sediment
Accommodation decreasing with filling
Shoreline environments followed by point bar
sequences prograde
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Foreland Basin Subsidence And Accommodation
Tectonic activity over
Basin filled with sediment
Accommodation little changing
Carbonate or quartz sand deposition returns
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Initial rapid subsidence to deep water, followed
by long, slow shallowing-upward filling sequence.
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An Example Of a Single Foreland Basin Filling
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Black basin shales
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Submarine Fan
Black basin shales
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Bouma Sequences
Hundreds or thousands of Bouma sequences stacked
vertically
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Shelf
Submarine Fan
Black basin shales
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Hummocky Sequences
Hundreds of hummocky sequences stacked vertically
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Shoreline
Shelf
Submarine Fan
Black basin shales
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Meandering
Shoreline
Shelf
Submarine Fan
Black basin shales
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Hundreds of point bar sequences stacked
vertically
Meandering River
Point Bar Sequences
Shoreline
Shelf
Submarine Fan
Basin
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Meandering River
Shoreline
We will symbolize a tectonic basin filling
sequence with this bar, containing all the
numerous sequences in each environment.
Shelf
Submarine Fan
Basin
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Finally, the periods of tectonic calm will be
symbolized by the blue bar.
Carbonates/ Qtz sandstone
Point Bar
Shoreline
Hummocky sequences
Bouma sequences
Black basin shales
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An Example From Virginia Geologic History
Zooming Out
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A Zooming Out Example From Virginia Geologic
History
Rodinia Rifting
Accumulating stratigraphic record
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A Zooming Out Example From Virginia Geologic
History
Proto-Atlantic DCM
Accumulating stratigraphic record
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A Zooming Out Example From Virginia Geologic
History
Taconic Orogeny
Accumulating stratigraphic record
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A Zooming Out Example From Virginia Geologic
History
Inter-Orogenic Calm
Accumulating stratigraphic record
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A Zooming Out Example From Virginia Geologic
History
Acadian Orogeny
Accumulating stratigraphic record
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A Zooming Out Example From Virginia Geologic
History
Inter-Orogenic Calm
Accumulating stratigraphic record
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A Zooming Out Example From Virginia Geologic
History
Inter-Orogenic Calm
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A Zooming Out Example From Virginia Geologic
History
Tectonic Activity
Lo
Hi
Interorogenic Calm
Pulse of Tectonic Activity
Acadian orogeny
Each pulse of tectonic energy, of course, changes
the sedimentary energy.
Interorogenic Calm
Pulse of Tectonic Activity
20-30,000 feet (4-6 miles) thick
Taconic orogeny
DCM
Pulse of Tectonic Activity
Rift to Drift
Follow the energy
Patterns, within patterns, within patterns
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A Zooming Out Example From Virginia Geologic
History
Tectonic Activity
Lo
Hi
Interorogenic Calm
Pulse of Tectonic Activity
Acadian orogeny
Each pulse of tectonic energy, of course, changes
the sedimentary energy.
Interorogenic Calm
Pulse of Tectonic Activity
20-30,000 feet (4-6 miles) thick
Taconic orogeny
DCM
Pulse of Tectonic Activity
Rift to Drift
Follow the energy
Patterns, within patterns, within patterns
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A Zooming Out Example From Virginia Geologic
History
Now think about the energy. In this 20-30,000
foot section of stacked rock there are only a few
places where both tectonic and environmental
conditions allow . . . .
Bouma Sequences
Bouma sequences can appear only in these places
20-30,000 feet (4-6 miles) thick
Follow the energy
Patterns, within patterns, within patterns
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A Zooming Out Example From Virginia Geologic
History
Now think about the energy. In this 20-30,000
foot section of stacked rock there are only a few
places where both tectonic and environmental
conditions allow . . . .
Point Sequences
Point Bar sequences can appear only in these
places
20-30,000 feet (4-6 miles) thick
Follow the energy
Patterns, within patterns, within patterns
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Or in Reverse
Zooming In
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Accumulated stratigraphic record
River
Calm
Acadian
Shoreline
20-30,000 feet (4-6 miles) thick
Calm
Taconic
Shelf
DCM
Submarine Fan
Rift
Black basin shales
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River
Calm
Acadian
Shoreline
Calm
Taconic
Shelf
DCM
Submarine Fan
Rift
Black basin shales
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Hundreds of Individual Hummocky sequences
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Zooming in to just a few feet of outcrop
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Briery Gap Run Upper Devonian Greenland Gap Gp
Foreknobs Formation
Mixed Zone Above Second Major Sandbar Above Lower
Covered Zone
The work of a field geologist is to read great
events in the rocks that compose the Earths
crust.
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Follow the Energy !
No Rock is Accidental
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Three Complications
1. History doesnt repeat itself, but it rhymes.
"Attributed to Mark Twain."
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Three Complications
1. History doesnt repeat itself, but it rhymes.
"Attributed to Mark Twain."
2. The section you get depends on where you
measure it.
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Foreland Basin
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Foreland Basin
Craton
Foreland Basin
evolving into
Short System
Long System
Slow, shallow subsidence
Rapid, deep subsidence
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Well developed Bouma Sequences
No Bouma Sequences
It does make a difference where you measure the
section.
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Three Complications
1. History doesnt repeat itself, but it rhymes.
"Attributed to Mark Twain."
2. The section you get depends on where you
measure it.
3. The shuffled deck and palinspastic
restorations.
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The Challenges of Being an Earth Scientist
1. We can never forget the Earth is a system
everything is connected with everything else by
positive and negative feedback.
2. The time scales we must deal with are
ungraspable.
3. The space scales we must deal with are
ungraspable.
4. The record is fractal patterns, within
patterns, within patterns.
5. On the outcrop all these conditions exist
simultaneously. We must keep all in mind at the
same time, and we must know exactly where we are
in all these at every moment of observation.
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Foreland Basin Subsidende And Accommodation
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Foreland Basin Subsidende And Accommodation
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Foreland Basin Subsidende And Accommodation
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Foreland Basin Subsidende And Accommodation
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Foreland Basin Subsidende And Accommodation
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Foreland Basin Subsidende And Accommodation
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