Red Tank West Dike
The hike about Red Tank-west
revealed some new facets to the analysis of the uplift of the Mogollon
Rim, and I returned Feb 18 04 to ferret out all of the information.
First, the Ts section
to the east of the hiway 179 is entirely different from that shown on the west
bank of the Dry Beaver Creek, just 1 km distant. It was already known that
there was at least one small graben which cut under the 179 hiway, and that
there were large NW-SE faults in the eroded rim there. Further, the
N-S linears which we have been following from
It would appear that
there is a depression in the Woods canyon to Red Tank area, in the Ps, and it
has been filled in Oligocene time with thicker Ts (this might be a local
graben). Further, when we found the dike (independently reported to be of 18
my. age) which cuts this conglomerate, it had brought up large clasts of
carbonates derived from the distant west, stuck to some extrusive material, on
its borders. This hints that there was Lg (Laramie gravels) exhumed from a
depth not exposed locally, and that the entire Ts section would have been
thicker than the 300 feet seen in the cliff walls if this extra Lg had been
added. Possibly this is from deeper in the suspected local graben, and the
extra Lg would have been similar to the younger Ts seen on the west side of the
Dry Beaver Creek. If this is older (by virtue of being exhumed from depths
below the arroyo) than the suspected weathered Oligocene sediments, then
it might be of Laramide age. The Ts, if indeed found deeper than Oligocene
finer sediments, could be substantially older than Oligocene (Paleocene to
Cretaceous would fit my Laramide subductive model).
By my model, Oligocene
sediments (25-37 my.) cannot be Laramide in age, since the change from
compressional to extensional stresses didn't occur until 41 m.y., and the rim
(extensional) didn't occur until after the end of the subductive
(compressional) wedging. Since we found Ts-limestones- label these Tl- at the
top of Ts (just under the Miocene basalts, some of which were baked); this
indicates that the rim area was stagnant and not yet lifted significantly
at limestone time.
We will try to answer
the following questions:
1. Is the 18 my. dike
exhuming Lg from a depth below the base of the arroyo- hence indicating
that there is a graben or depression, where the Lg were saved from erosion
before the suspected Oligocene sediments were deposited?
2. Is the graben or
depression just a simple fault expression, where it has been
mechanically dropped, or is the depression the comparative result
of reduced thermal expansion in the area where vulcanism has released
heat which would have been used to expand the sediments at locations where a
shear rim is revealed?
3. Is there a Mogollan rim
portion hidden below the ramping basalts, but less elevated than the portion
exposed about Sedona (and other localities, such as the Tonto and Drake areas)?
If so, the thermal expansion notion would be somewhat confirmed, relating rim
height to heat not released by vulcanism.
4. Since the Hackberry-
Montezuma linear seems to terminate or be diverted from N-S orientation, when
the stark Mogollon Rim occurs, is the young (although continuing for at least 10
my- from the Miocene basalts shown in the Clear Creek double right angle bends)
linear involved in this ramp localization? We have found that the linear
is noticed continually in the Verde ls.and older rocks, whenever the ramp
basalts lie just to the east of the N-S fractures. This linear appears to be
currently active, since there are the Hance spring and the Montezuma Well flows
occurring now.
Return trip Analysis:
At the base of the Ts section, in an arroyo in
Section 9, T17N R6E, a volcanic dike was scanned for conglomerates brought up
with the intrusion. There were carbonates and Paleozoic rocks at the border of
the flow, in the basaltic host rock- which were in cobble and boulder sizes.
Further, above the dike were loose Paleozoic cobbles and boulders containing
fetid odor (Dm), upon fresh breakage. These rocks can only have come from the
far west, and they are mainly observed in the surrounding shallower Ts outcrops,
as loose cobblestones. Hence they have been exhumed from deeper in the section
(below ground surface) by the rising dike flow. The dike has presented
information which could only have been seen with drilling, if it had not
brought up the hidden deeper rocks. How these rocks were present, when they are
not otherwise viewed in the canyon walls (but mainly as loose cobblestones),
occurs because there is a monocline just to the north which has caused the
basement upon which these rocks were deposited to drop, at the location of the
dike. The top of Ts locally is at 4170 feet.
The Ps monocline occurs in S8 & 9, just
north of the basaltic dike which runs N-S; the monocline strikes NW-SE,
similarly to the normal faulting and fractures in the rim area. Ps or Schnebley
Hill redbeds dip 25 degrees to the SW, in siltstone and fine sandstone thin
beds. There is hardly any cross-bedding, but there is a chance that the
sandstone is fossil dunes. This monocline crosses the arroyo for at least 200
meters, but at the next cliff to the north, the beds are flat and almost level.
Hence the monocline is a local occurrence, which may be a dunal monocline,
which provides a low place for the Lg to be “saved” from erosion, compared to
other flat-living Ts nearby.. Rather, the monocline appears to plunge below the
location of the dike. The dike has not caused the monocline to be upthrown- the
reverse occurs, and the Ts must be incorporated and sheared by the dike.
It appears that the local depression or zone
downstream of the Ps monocline formed as the most northerly occurrence of the
Verde graben, and has dropped the Lg (Laramide gravels), so that they were not
later eroded before Tl and Tbb were deposited, as they were in topographically
higher areas nearby- in
Woods and Bias canyons to the north. This probably would be the first
indication of rim formation (in post- Laramide time), since the rim now exists
NW & SE of this location. The age of the rim should therefore be younger
than Lg and older than Tbb containing extrusive clasts (which is younger than
Tl). This sequence also shows that there was a significant time passage
(unconformity) between Lg and Tl, because of this eroded conglomerate-filled
depression. This hints that the Eocene was eroded after Lg was deposited and
that the Tl could be Oligocene. We investigated this monocline a third day, and
found that the hinge point on the north
side exhibited a small wedge-shaped normal fault or graben, indicating that
part of the monocline was due to down-dropping in the neighborhood of the line
of volcanic vents to the south and east. The strike of the faulting was roughly
E-W, accompanied by cossbedding and open fractures.
To the north of these inter-related dunal
monoclines, volcanic vents, and small faults- fractures, the top of Ps is at
4200 feet and top of Ts is about 4350 feet.
To further investigate whether the Hackberry-
Montezuma Well linear is related to this ramp-covered portion of the Mogollon
rim, a butte was climbed to the south 1.5 miles in Section 20, to look at a
mesa top Tv (Verde limestone). Fractures were found on the mesa top oriented
160-170 degrees from north in Tv, but were more subtle than near Montezuma
Well. These were at 4200 feet elevation, which is not as young as the highest
Tv found in
Harold L. Overton