KARST CONNECTION MODEL FOR THE GRAND CANYON

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KARST CONNECTION MODEL FOR THE GRAND CANYON
ARIZONA, USA
By Carol A. Hill, Noel Eberz, and Bob Buecher
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GRAND CANYON PROJECT

• Age of the Grand Canyon. Dating of cave deposits
  to determine
• water-table position over time and space. Victor
  Polyak, Carol Hill, Yemone
• Asmeron. Dating project supported by the National
  Science Foundation and
• University of New Mexico Radiogenic Isotope
  Laboratory.

(2) Ancestral Colorado River. Where did the
ancestral Colorado River flow before it went
through the Grand Canyon? Carol Hill, Wayne
Ranney, Bob Scarborough, and Doug Powell. Field
support from- BLM Grand Staircase-Escalante
National Monument.
(3) Karst Connection Model. Addresses 4 major
geomorphic mysteries about the Grand Canyon from
a karst perspective. Carol Hill, Noel Eberz,
and Bob Buecher. Grants from National Park
Service, Grand Canyon Association, and National
Speleological Society.
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5 MAJOR MYSTERIES GEOMORPHIC EVOLUTION OF
EASTERN GRAND CANYON
?
(1) Where did Ancestral Colorado River flow
before its integration through the Grand Canyon
6 Ma?
Sub-project 2
(2) Why do the young narrow Little Colorado and
Marble Canyons meet at the Confluence C,
whereas the Grand Canyon opens up below the
Confluence?
Marble Canyon
Kaibab arch
Colorado R.
(3) Why does the young narrow Marble Canyon cut
its course less than a mile from the Chuar Basin?
This karst connection sub-project 3
C
Chuar basin
(4) Why does the Colorado River make a sudden
bend from south to west?
Colorado R.
Little Colorado R.
(5) How did the Colorado River cross the Kaibab
arch high? That is, how did the eastern Grand
Canyon connect with the western Grand Canyon?
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PRESENT-DAY HYDROLOGY OF THE EASTERN GRAND CANYON
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A
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F
KAaxis
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C
B
H

• Map showing groundwater divides (dashed lines)
  between hydrologic basins. Blue Springs (B) is
  the discharge point for the Black Mesa
• basin today. For each of these modern basins,
  water follows structure (synclines, faults) along
  the steepest hydraulic gradient to spring
• outlets in the Redwall Limestone.
• Solid arrows shows probable route Redwall water
  takes today from the 3 pits (Ah Hol Sah A,
  Indian, Black Abyss) to Fence Springs (F).
• From Huntoon (2000).
  
  

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A AH HOL SAH SINKHOLE
Ah Hol Sah sinkhole, near Tanner Wash, is 150 m
across and 40 m deep. The sinkhole is
actively collapsing into the Redwall karst
aquifer, which is probably discharging at Fence
Springs. A small wash (foreground) now drains
(arrow) directly into the sinkhole i.e.,
drainage to Tanner Wash has been pirated down the
sinkhole to karst channels (caves) below.
The Karst Connection Model proposes that this
same process happened at the Confluence 6 Ma.
Water flowing along the ancestral Little
Colorado River was pirated down into a Confluence
sinkhole in the same manner as it is today at Ah
Hol Sah.
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THE PRESENT IS THE KEY TO THE PAST
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A
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F
KAaxis
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C
B
H
Essentially, we are projecting what is happening
today in the Kaiparowits basin (where the Redwall
aquifer is still intact), back in time and
spacially southward. At6 Ma, before canyon
dissection, the Redwall aquifer was still intact
in the area of the Confluence (C). Note that the
proposed karst connection goes under the Kaibab
arch.
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PROPOSED KARST CONNECTION ROUTE PRE-6Ma
To Utah (Glen Lake)
Water flows east down East Kaibab monocline,
vertically down collapse features, and west
along ancestral Black Mesa basin. It converges
on Blue Springs fault, descends to the Redwall
aquifer, and then moves northward, in
the direction of the hydraulic gradient.

• Pre- 6 Ma
• No Marble Canyon
• No Little Colorado
• River Canyon
• No eastern Grand
• Canyon
• No Blue Springs
• (erosion had not cut
• down to Redwall
• level yet)

Ancestral Little Colorado River flows north to
Utah prior to connection at 6 Ma
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11145'
Cedar Ridge anticline
Marble Canyon
3615'
3615'
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Subsurface
Surface
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C
Surface
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Cedar Ridge anticline
Breccia pipe
Collapse feature
Redwall karst aquifer flow
Water flowed north in the Redwall aquifer until
it encountered the Cedar Ridge anticline then it
was diverted southwest to the Confluence (C),
creating a zone of collapse features - the
Confluence sinkhole being one of this zone.
Little Colorado River water was pirated down this
collapsing sinkhole (blue arrow). The Cedar Ridge
anticline caused water to divert toward the
Confluence (green arrow), thus allowing headward
erosion of Marble Canyon to proceed against dip.
Confluence surface subsurface water. Collapse
features and base map from Sutphin (1986)
breccia pipes from Sutphin and Wenrich (1989) and
Huntoon et al. (1996).
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PROPOSED KARST CONNECTION ROUTE 6 Ma
C Collapsing sinkhole at Confluence
Reversal of drainage
Where does water go?

• It follows steepest
• hydraulic gradient
• to exit as springs
• where Redwall Ls
• is exposed.

• Headward erosion
• proceeds up Marble
• Canyon and Little
• Colorado River
• Canyon from
• collapsing sinkhole.

Sinkhole

• Redwall karst
• aquifer flow
• goes under
• the Kaibab arch
• to discharge
• in headward
• eroding western
• Grand Canyon
• along synclinal
• axis of Grandview
• monocline.
• Spring discharge
• occurs along
• Redwall horizon
• in the Hance Rapids
• area where the
• Redwall Ls has been
• uplifted and

• Little Colorado River
• water is pirated down
• the sinkhole to the
• Redwall aquifer no
• longer flows north.

• Reversal of drainage
• in Marble Canyon

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KARST AQUIFER FLOW

• Permeability pathways are produced by the fluid
  of the flow system itself rather than
• by some inherited geologic fabric or structure.

• As karst conduits become larger and better
  integrated, the hydrologic flow system
• becomes dominant and conduits develop along the
  steepest hydraulic gradient.

• Thus, flow in karst aquifers can cross faults and
  folds, move opposite to dip, and go under
• or through structures as it pursues a path along
  the steepest hydraulic gradient to discharg.

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6 Ma Time of Karst Connection
8000 ft
Kaibab arch
GV Grand View Point
TOK 7400 ft
Marble Platform
7000 ft
C Confluence
TOK 6100 ft
6000 ft (?)
6000 ft
PS Potentiometric surface
HS Mesa, TOR 5200
H Hance spring
Confluence sinkhole
Butte fault
5000 ft
TOR 4500(?)
Redwall Ls
TOR 4400 ft
PS
Grandview monocline
East Kaibab monocline
4000 ft
TOR 4100 ft
Redwall Ls
300 ft
Extension faults
3000 ft
Schematic cross section of how Redwall karst
aquifer water could have recharged on the
Marble Platform, gone under the Kaibab arch, and
discharged from the-then still-intact Redwall
Limestone in the Hance Rapids area 6 Ma. TOK
Top of the Kaibab TOR Top of the Redwall PS
Potentiometric surface. Vertically exaggerated.
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POST-CONNECTION EVENTS (

• Once the Little Colorado
• River cut down to Redwall
• level at the Confluence and
• then in Little Colorado
• Canyon, the discharge point
• for the Black Mesa basin
• moved from H to C to B
• (Hance Rapids area to
• Confluence to Blue Springs)

• Subsequent collapse
• and canyon incision
• followed along the
• former karst
• connection route.

• The former Redwall karst
• aquifer route past the
• Confluence thus became
• disconnected from the
• Black Mesa hydrologic
• basin by canyon incision.

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EVIDENCE SUPPORTING A KARST CONNECTION MODEL
(1) The model is consistent with the Principles
of Karst Hydrology. Flow in karst aquifers can
cross faults and folds, move opposite to dip, and
go under or through structures as it pursues a
path along the steepest hydraulic gradient to
discharge. So going under the Kaibab arch is no
problem!
(2) The model is consistent with the Principle
the present is the key to the past. The
model extends Huntoons flow in present-day
hydrologic basins backward in time. We have
just moved what is happening today in northern
Marble Canyon, where the Redwall karst aquifer
is still intact, southward to where the Redwall
aquifer was intact 6 million years ago (i.e.,
before canyon erosion truncated the aquifer in
the area of the Confluence).
(3) The model is consistent with todays
differential incision rates for the eastern and
western Grand Canyon. Eastern Grand Canyon
0.2-0.5 mm/yr Western Grand Canyon 0.07
mm/yr. Since the karst connection at 6 Ma, the
eastern Grand Canyon is still trying to catch
up(equilibriate) with the western Grand Canyon,
incision-wise.
(4) The model is supported by the barbed
tributaries in Marble Canyon.
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San Juan River
Glen Lake
Proposed interior lake basin (Glen Lake)
BARBED TRIBUTARIES
Red arrows Proposed direction of flow of
ancestral Little Colorado River before karst
connection at the Confluence (C). Barbed
tributaries reflect the direction of this
ancestral flow tributaries are obtuse to
todays direction of flow. Ancestral flow
was down the northeast dip of beds todays flow
cuts opposite to dip. Black arrows Direction of
flow today
C
Base drawing from Ranney (2005)
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Confluence C KINGPIN to understanding
mysteries of eastern Grand Canyon
(1) Headward erosion proceeded up Marble and
Little Colorado canyons from collapsing sinkhole
at C hence these canyons are young (narrow.
Chuar Basin
(2) Ancient Chuar basin is located less than a
mile from young Marble Canyon because these two
drainage systems developed independently of each
other.
(3) The Colorado River turns from south to west
because it followed the former karst route that
connected with a western proto-Grand
Canyon eroding eastward.
(4) The Colorado River crossed the Kaibab arch by
going under it, along a karst route independent
of structure.
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CONCLUSION

• Karst processes are key to understanding the
  Grand Canyon,
• from its connection to time of incision yet
  these processes
• are rarely invoked in the standard models of
  its evolution.