THOUGHTS ON THE EVOLUTION OF THE UPPER ARKANSAS RIVER DRAINAGE, COLORADO: DRAINAGE REARRANGEMENT AND INCISION - PowerPoint PPT Presentation

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THOUGHTS ON THE EVOLUTION OF THE UPPER ARKANSAS RIVER DRAINAGE, COLORADO: DRAINAGE REARRANGEMENT AND INCISION

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Title: THOUGHTS ON THE EVOLUTION OF THE UPPER ARKANSAS RIVER DRAINAGE, COLORADO: DRAINAGE REARRANGEMENT AND INCISION


1
THOUGHTS ON THE EVOLUTION OF THE UPPER ARKANSAS
RIVER DRAINAGE, COLORADO DRAINAGE REARRANGEMENT
AND INCISION
  • Eric Leonard, Colorado College

2
Collaborators
  • Peter Sak, Dickinson College
  • Adrian Biscontini, Dickinson College
  • Emily Jemison, Colorado College
  • Scott Miller, Pennsylvania State University

3
Talk Outline
  • Overview of Cenozoic drainage evolution
  • Timing, magnitudes, rates of late Cenozoic
    incision
  • Whats driving all of this?

4
COLORADO
Arkansas River
5
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6
RIO GRANDE RIFT -- UPPER ARKANSAS VALLEY
7
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8
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9
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10
RIO GRANDE RIFT -- UPPER ARKANSAS VALLEY
UPPER CANYON
SALIDA
11
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12
RIO GRANDE RIFT -- UPPER ARKANSAS VALLEY
UPPER CANYON
SALIDA
OFF-AXIS GRABEN -- PLEASANT VALLEY
13
RIO GRANDE RIFT -- UPPER ARKANSAS VALLEY
UPPER CANYON
SALIDA
OFF-AXIS GRABEN -- PLEASANT VALLEY
LOWER CANYONS
14
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15
RIO GRANDE RIFT -- UPPER ARKANSAS VALLEY
UPPER CANYON
SALIDA

CANON CITY
OFF-AXIS GRABEN -- PLEASANT VALLEY
LOWER CANYONS
PIEDMONT
16
  • Ages of tuffs in latest Eocene and Oligocene
    paleovalleys
  • Epis et al., 1976, 1980
  • McIntosh and Chapin, 2004

36.1-37.5ma
33.8ma
27.4-27.8ma
17
  • Proposed Miocene drainage
  • pattern
  • Epis et al., 1976, 1980

UAV
Local-source depocenter
SLV
SdC
18
Top-down Forcing
  • Tectonic blockage of southward drainage of the
    upper Arkansas valley was critical in
    Plio-Pleistocene drainage evolution.
  • Spillover from the upper valley played a major
    role in drainage integration.
  • Spillover led to a large increase in downvalley
    stream power, facilitating canyon cutting.

19
Bottom-up Forcing
  • Range-front base-level drop, due to faulting or
    differential erosion, was critical in
    Plio-Pleistocene drainage evolution.
  • Base-level lowering led to knickpoint formation
    and migration, and thus to canyon formation.
  • Drainage integration occurred as a result of
    successive upvalley basin-capture events.

20
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21
Timing of Inception of Neogene Incision
Post 3.6 ma, pre ca 1 ma
?
Post 9 ma, possibly accelerated after 3.6 ma
22
Magnitude of Neogene Incision
gt100 - 120 m
Browns Canyon
700 - 800 m
gt250 - 300 m
1100 - 1200 m
23
Rate of Neogene Incision
0.6 m/ka 0.9 m/ka
Browns Canyon
2.1 m/ka
1.8 m/ka
1.2 m/ka (9 my)
24
Lower Bighorn Sheep Canyon
25
Ca 400m of incision prior to integration
Ca 290m of incision with uncertain
relationship to integration
Ca 45m of incision clearly postdates integration
26
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28
Magnitude of Arkansas River Incision (m) (Leonard
2002, this study)
700-800
100-300
1160
460
1200
770
40
29
Southern Rocky Mountains and Western Great Plains
30
Components of West-to-East Tilt of the Miocene
Ogallala Group on the High Plains(Leonard, 2002
McMillan , Heller, and Angevine, 2002)
  • Original depositional slope
  • Tilting due to erosionally driven isostasy
  • Tilting due to tectonics -- is this necessary?

31
Erosion and Warping of the Basal Ogallala Surface
Along North-South Transects
32
Results of Flexural Modeling
33
Components of West-to-East Tilt of the Basal
Ogallala Surface (Leonard 2002)
3.5 m/km
4.8 m/km
6.4 m/km
34
Magnitudes (m) of late Cenozoic
Tectonic/Isostatic Rock Uplift Along the Arkansas
River (Leonard 2002, 2003)
600/540
250/180
670/470
290/140
410/330
0/-10
460/290
0/-30
Assuming a flexural rigidity of 1023 Nm.
Assuming a flexural rigidity of 1024 Nm.
35
Rock uplift and erosion on the Piedmont, and
base-level drop for mountain streams (Leonard,
2002, 2003)
  • Post-Ogallala tectonic rock uplift raised the
    western margin of the Colorado High Plains, by
    200-600m, with magnitude of uplift increasing
    southward.
  • Erosion of Piedmont sediments by the Arkansas
    River was a response to this uplift, taking the
    form of long wavelength erosion of the plains
    (200-250 km width of the Arkansas Valley on the
    western Piedmont), resulting in significant
    flexural isostatic compensation.
  • Strong feedback developed between rock uplift and
    erosion that nearly doubled the magnitude of the
    initial tectonic tilting. This feedback was best
    developed on the western Piedmont and resulted in
    a km-scale erosion of the Piedmont and relative
    base-level fall at the mountain front.

36
One Further Suggestion
  • A fairly strong erosion/isostatic rock uplift
    feedback had developed on the Colorado Piedmont
    amplifying initial tectonic rock uplift.
  • Late Cenozoic incision into the crystalline rocks
    of the mountains has been limited to very short
    wavelength (narrow) canyons. As a result,
    flexural response is probably minimal and there
    has probably been little or no feedback between
    rock uplift and river incision.
  • With no feedback, total rock uplift in the
    mountains may have been less than rock uplift of
    the Piedmont near the mountain front, even if
    initial tectonic forcing was greater in the
    mountains.?

37
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38
Thank You!
39
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40
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41
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42
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43
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44
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45
Glacier limit
Knickpoint
Mountain Front
Crystalline Rock
Sedimentary Rock
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