|
Ferron
Stratigraphy Descriptions
Part 2
The type area of (Kf-2-Iv-c) is the
mouth of Ivie Creek Canyon. This unit undoubtedly warrants designation
as a parasequence inasmuch as the associated transgressive surface
is clearly recognizable both in Ivie Creek Canyon and to the south
in the I-70 roadcut. The pinch-out of (Kf-2-Iv-c) trends just slightly
west of north. The shoreline sandstone unit displays some interesting
and unusual changes at the mouth of Ivie Creek Canyon, changing
over about 100 yards from a strongly wave-modified shoreface unit
to a much lower wave energy unit that contains mud interbeds and
finer sand, and that has a silvery-gray color on outcrop. This change
suggests a change from a coast directly facing the sea to one that
was sheltered from wave energy. In some respects, this resembles
the change from (Kf-1-IC-c) to (Kf-1-IC-d). The relationships between
(Kf-2-Iv-c) and (Kf-2-Mi-a,b) are presently unknown. It can be speculated,
however, that (Kf-1-Mi-a) represents the western margin of a major
delta that provided the sheltering from wave energy (see below).
Suggested type section: Ivie Creek Canyon, NW1/4SE1/4 section 17,
T. 23 S., R. 6 E., Salt Lake Base Line. Seaward limit: not determined.
Facies content of shoreline unit: wave-modified coast, probably
shoreface in the proximal part, transforming to low-wave-energy
coast, possibly ay shoreline.
The type area of Kf-2-Miller Canyon-a
is the mouth of Miller Canyon. The boundary between this unit
and overlying Kf-2-Mi-b is difficult to recognize in many places,
but is very apparent where rotated slump blocks, which are generally
restricted to (Kf-2-Mi-a) in this area, are present. The transgressive
surface is perfectly apparent where it has bevelled the tops of
the rotated blocks, which are common enough to facilitate tracing
the contact throughout the "Tri-Canyon" area. The landward limit
of (Kf-2-Mi-a) has not been determined. Its seaward feather-edge
can be approximately located in Miller Canyon and in the lower
part of Muddy Creek Canyon, near the "Upper Gooseneck." It has
a general northeast trend, suggesting that this parasequence built
northwestward, probably as a deltaic lobe. The deltaic complex
from which this lobe built may have provided the sheltering from
wave energy noted for (Kf-2-Iv-c). Rotated blocks are present
in (Kf-2-Mi-a) in the Coal Cliffs south of Miller Canyon, in the
lower part of Muddy Creek Canyon, and are particularly well exposed
in "Grassy Canyon." A few are present on the east side of "Dino
Head Point" on the western margin of the "Molen Amphitheatre."
Failure of the rotated blocks is consistently toward the northwest,
the direction that the delta lobe appears to have prograded. The
abundance of rotated blocks, which are relatively rare entities
elsewhere in the Ferron, in the particular area may once again
be related to a zone of flexure. Tilting toward the west may have
encouraged failure of the delta-front. Type section: near mouth
of Miller Canyon, south side, NE1/4NE1/4 section 36, T. 22 S.,
R. 6 E., Salt Lake Base Line. Landward limit: not determined.
Seaward limit: Miller Canyon, NE1/4SW1/4 section 26, T. 22 S.,
R. 6 E., Salt Lake Base Line; Muddy Creek Canyon, CNW1/4 section
24, T. 22 S., R. 6 E., Salt Lake Base Line. Facies content of
shoreline unit: river-dominated delta.
Kf-2-Mi-b includes the shoreline
sandstone that forms the massive cliffs in the lower parts of
Miller and Muddy Creek Canyons. It appears to be a very strongly
wave-modified unit. The landward pinch-out of (Kf-2-Mi-b) has
not yet been located. It thins toward the northwest into "Grassy
Canyon" and the "Molen Amphitheatre", finally disappearing into
marine shale in the southern part of Molen Reef along with overlying
(Kf-2-MC-a). In Muddy Creek Canyon (but not yet elsewhere), it
is possible to subdivide (Kf-2-Mi-b) into two subunits bounded
by a distinctive surface. The southern subunit is wave modified,
the northern one very strongly wave modified. The surface that
separates these subunits could be a transgressive surface, but
the overlying transgressive surface beneath (Kf-2-MC-a) has removed
any direct evidence. In the absence of compelling evidence to
the contrary, it is assumed the surface marks some change of autocyclic
origin. Type section: same as (Kf-2-Mi-a), near the mouth of Miller
Canyon, south side, NE1/4NE1/4 section 36, T. 22 S., R. 6 E.,
Salt Lake Base Line. Landward limit: not determined. Seaward limit:
Molen Reef, CSE1/4 section 29, T. 22 S., R. 7 E., Salt Lake Base
Line. Facies content of shoreline unit: wave-modified, probably
strand plain in proximal part; may include deltaic deposits in
medial and distal parts.
Kf-2-Muddy Canyon-a forms ledges
and lesser cliffs above the grander cliffs formed by (Kf-2-Mi-b)
throughout most of the lower part of Muddy Creek Canyon and into
the southern Coal Cliffs to the south. Most of the thickness of
(Kf-2-MC-a) has been cut out by meanderbelt deposits. Although
very sandy in some areas, much of the meanderbelt deposit consists
of "inclined heterolithics." Two distinct meanderbelt units are
distinguished on the basis of paleocurrent directions, the southern
one being the younger of the two. At one locality on the west
side of Muddy Creek Canyon north of the "Lower Gooseneck", the
fluvial erosional surface rises to reveal a river-dominated delta-front
sequence. On the east side of "Dino Head", near the southern mouth
of "Pinion Jay Valley", the meanderbelt deposit ends and the delta-front
unit, only about 20 feet in thickness, appears. It grades from
marine mudstone at the base to predominantly sandstone in the
upper part and can be traced continuously through the "Molen Amphitheatre"
to a point where it disappears into marine shale in the southern
part of Molen Reef. Although a landward pinch-out of (Kf-2-MC-a)
cannot be located because of the fluvial erosion, there can be
no question that the surface that separates (Kf-2-MC-a) from the
underlying (Kf-2-Mi-b) is a transgressive surface: it places offshore
marine shale directly upon upper shoreface sandstone and, locally,
has planed off small channels within the top of (Kf-2-Mi-b). Type
section: southern part of Muddy Creek Canyon, NW1/4SW1/4 section
24, T. 22 S., R. 6 E., Salt Lake Base Line. Landward limit: cannot
be determined owing to erosion by fluvial facies. Facies content
of shoreline unit: river-dominated delta; probably represents
a low-wave-energy delta that prograded into a protected bay.
Kf-2-Muddy Canyon-b is defined on
the basis of a shoreline sandstone unit that has a distinctive
white color. The landward pinch-out of (Kf-2-MC-b) is present
in the southern Coal Cliffs just north of "Bear Gulch", at the
mouth of Miller Canyon, and is almost reached in the bend opposite
the "Lower Gooseneck" in Muddy Creek Canyon. Near the pinch-out,
the unit is characterized by large-scale, inclined surfaces that
dip to the north, essentially parallel to the trend of the pinch-out
(strike of inclined surfaces perpendicular to shoreline trend).
The surfaces are interpreted to represent a series of tidal inlets
that were driven northward by longshore drift. Equivalent flood
tidal delta and lagoonal deposits have been tentatively identified
in Miller Canyon and "Bear Gulch." (Kf-2-MC-b) thickens rapidly
eastward, attaining thicknesses in excess of 75 feet in "Grassy
Canyon." It extends eastward into Molen Reef, where it is a major
cliff former, and northward to Dry Wash. Its seaward limit has
not been precisely identified. The areal distribution of this
unit is very large compared to most Ferron parasequences, and
it is possible that it can be divided. Type section: southern
part of Muddy Creek Canyon, NW1/4SW1/4 section 24, T. 22 S., R.
6 E., Salt Lake Base Line. Landward limit: southern Coal Cliffs
north of "Bear Gulch", CSE1/4 section 35, T. 22 S., R. 6 E, Salt
Lake Base Line; mouth of Miller Canyon, NE1/4NE1/4 section 35,
T. 22 S., R. 6 E. and SE1/4SE1/4 section 26, T. 22 S., R. 6 E.,
Salt Lake Base Line; Muddy Creek Canyon, SW1/4SE1/4 section 23,
T. 22 S., R. 6 E., Salt Lake Base Line. Seaward limit: near Dry
Wash, approximately NE1/4SW1/4 section 2, T. 22 S., R. 7 E., Salt
Lake Base Line, if (Kf-2-MR) is determined to constitute a parasequence
(see below). Facies content of shoreline unit: wave-modified coast
in proximal part, probably strand plain; may include deltaic deposits
in distal part.
The Kf-2 cliffs in the Molen Reef
outcrops south of Dry Wash include two distinct upward-coarsening
units. They appear to constitute distinct parasequences, the lower
being (Kf-2-MC-b), and the upper (Kf-2-MR), but no clear evidence
has yet been found to demonstrate that the boundary between them
is a transgressive surface. The name is listed here in anticipation
that it will be assigned parasequence status. Type section: Molen
Reef south of Dry Wash, NW1/4 section 11, T. 22 S., R. 7 E., Salt
Lake Base Line. Landward limit: not determined, but approximately
NE1/4 section 15, T. 22 S., R. 7 E.,, Salt Lake Base Line. Seaward
limit: not determined; somewhere north of Dry Wash. Facies content
of shoreline unit: probably deltaic.
Kf-2-Dry Wash is defined on the basis
of a shoreline sandstone unit whose landward pinch-out crosses
the northern edge of the cliffs of the Molen Reef south of Dry
Wash and intercepts the cliffs on the north side of the wash,
defining a northwest shoreline trend. The pinch-out is less distinct
than most others, possibly because of development of a flood tidal
delta in this area. A large lagoon/bay complex lies landward of
the pinch-out and can be traced for several miles southward in
the Molen Reef outcrops and westward to the limit of Kf-2 outcrops
in Dry Wash. The lagoon/bay unit is bracketed by splits of the
lower C coal that under- and overlie it. The seaward limit of
(Kf-2-DW) has not been determined. It is, at present, the youngest
known parasequence of Kf-2. Numerous channel deposits, including
three large, lenticular channel bodies in Dry Wash and several
in the Molen Reef cliffs appear to belong to (Kf-2-DW). Type section:
cliffs north of Dry Wash, SW1/4 section 35, T. 21 S., R. 7 E.,
Salt Lake Base Line. Landward limit: Dry Wash, SW1/4 section 2,
T. 22 S., R. 7 E. and SW1/4SW1/4 section 35, T. 21 S., R. 7 E.,
Salt Lake Base Line. Seaward limit: not determined. Facies content
of shoreline unit: wave-modified, probably strand plain in proximal
part; distal part not yet studied.
Shoreline sandstones of Kf-3 extend
from the "Molen Amphitheatre" northward beyond Dry Wash. At present,
only two parasequences are distinguished. It is likely that one
or more additional parasequences will eventually be defined in
the northern part of the area of distribution of Kf-3. Much of
the thickness of the C-coal bed, previously considered as belonging
to Kf-3, has now been reassigned to Kf-2. The uppermost approximately
one foot of coal of the C-coal zone, including the thick tonstein
bed, extends over the top of (Kf-3-MR-a) near the mouth of "Gnat
Canyon" in the "Molen Amphitheatre." Details of coal correlations
farther north have not been worked out. With reassignment of most
of the coal of the C-coal zone to Kf-2, Kf-3 becomes one of the
leanest parasequence sets in the Ferron with respect to its coal
content.
The type area for (Kf-3-Mr-a) is
the large "Molen Amphitheatre." The landward pinch-out of (Kf-3-Mr-a)
is very well exposed on the cliffs just to the west of the mouth
of "Gnat Canyon." The pinch-out takes place into the C-coal zone,
with about 1 foot of coal passing above, and the remaining 6 to
7 feet passing below. Only 100 feet to the south, there is no
trace of the unit within the C-coal zone, which carries its full
compliment of tonsteins. This is a remarkable situation. In the
majority of cases, transgression of the sea across the Ferron
coastal/delta plain led to formation of bays or lagoons that are
preserved landward of the pinch-outs of the subsequently deposited
shoreline sandstones. In the case of (Kf-3-Mr-a), the transgressing
shoreface cut into and partially eroded a mass of peat. The top
of the peat must have lay far enough above sea level to preclude
inundation southwest of the shoreline. Peat accumulation was only
briefly interrupted, if at all, before progradation of the shoreline
occurred. Several well-exposed, lenticular channel deposits filled
with "inclined heterolithics" complicate the stratigraphy of (Kf-3-MR-a)
in the vicinity of its landward pinch-out. Type section: at mouth
of "Gnat Canyon" NE1/4SW1/4 section 30, T. 22 S., R. 7 E., Salt
Lake Base Line. Landward limit: just W of mouth of "Gnat Canyon":
CSW1/4 section 30, T. 22 S., R. 7 E., Salt Lake Base Line. Seaward
limit: not determined. Facies content of shoreline unit: wave-modified,
probably strand plain in proximal part; distal part may include
deltaics.
Kf-3-Molen Reef-b lies above (Kf-3-MR-a)
in the "Molen Amphitheatre", being separated from it by a thin
zone of carbonaceous mudstone. The landward pinch-out of (Kf-3-MR-b)
occurs on the floor of "Gnat Canyon" and so is not exposed, although
its position can be determined to within one to two hundred feet.
As is true for (Kf-3-MR-a), channels are numerous in the landward
part of (Kf-3-MR-b). (Kf-3-MR-a) and (Kf-3-MR-b) merge to form
the Kf-3 cliff along the Molen Reef, but the parasequences have
not yet been distinguished there. Thus, the seaward extent of
these two parasequences are not known. (Kf-3-MR-b) is strongly
wave modified in its landward part. Suggested type section: east
side of "Gnat Canyon" where it merges into the cliffs of the "Molen
Amphitheatre." Type section: "Molen Amphitheatre", east of "Gnat
Canyon", NE1/4 section 31, T. 22 S., R. 7 E., Salt Lake Base Line.
Landward limit: at mouth of "Gnat Canyon", NE1/4SW1/4 section
30, T. 22 S., R. 7 E., Salt Lake Base Line. Seaward limit: not
determined. Facies content of shoreline unit: wave-modified coastline,
probably stand plain, in proximal part; distal part may include
deltaics.
Compared to the parasequence sets that preceded
it, Kf-4 thickens very rapidly seaward, indicating a high
rate of relative sea level rise during its deposition. Two parasequences
are recognizable, although a third may prove to be distinguishable
in the "Fracture Canyon" area. The associated G-coal zone only
locally contains more than a few feet of coal, probably because
peat accumulation could not keep up with the rapid relative rise
of sea level that characterized this unit. Carbonaceous mudstones
of the G-zone have been mined to produce a soil conditioner, locally
referred to by the trade name "Live Earth", for about 20 years
in Miller Canyon, although that mine appears to now be inactive.
The type area of (Kf-4-Mi) is the
mouth of Miller Canyon, where its shoreline sandstone body forms
high cliffs. The landward pinch-out of (Kf-4-Mi) occurs just south
of "Bear Gulch", but is somewhat obscured because the upper part
of the unit is replaced by a meanderbelt deposit. The meanderbelt
deposit is very widespread, being recognized throughout the "Tri-Canyon"
area and eastward into the "Molen Amphitheatre." It is also relatively
coarse-grained, being made up of medium- to coarse-grained sandstone
that locally includes granules and, rarely, pebbles. The landwardmost
part of (Kf-4-Mi) is strongly wave modified and this is probably
true of the unit as a whole, although it is difficult to tell
with the upper part of the unit removed. Type section: southern
Coal Cliffs at the mouth of Miller Canyon, SE1/4SE1/4 section
26, T. 22 S., R. 6 E., Salt Lake Base Line. Landward limit: in
Coal Cliffs south of "Bear Gulch", SW1/4NE1/4 section 2, T. 23
S., R. 6 E., Salt Lake Base Line. Seaward limit: not determined,
probably in southern part of Molen Reef. Basic facies content:
wave-modified shoreline--strand plain in proximal part to wave-modified
delta in distal part.
(Kf-4-MR) is defined on the basis
of a shoreline sandstone unit that forms a striking, white wall
throughout the "Molen Amphitheatre" area. The landward pinch-out
of (Kf-4-MR) is well exposed just west of the mouth of " Gnat
Canyon", almost directly above the landward pinch-out of (Kf-3-MR-a).
Pronounced landward thinning toward the pinch-out is also evident
in "Pinion Jay Valley" and in the area north of "Molen Point."
(Kf-4-MR) is extremely wave modified in its landward part. The
more distal part, however, may include some lower-wave-energy
shoreline deposits, some of which may represent river-dominated
deltas. It may be that the latter constitute one or more additional,
as yet undefined parasequences. Type section: Molen Reef, SE1/4SW1/4
section 29, T. 22 S., R. 7 E. or along white, south-facing wall
in "Molen Amphitheater", SE1/4SE1/4 section 30, T. 22 S., R. 7
E., Salt Lake Base Line. Landward limit: mouth of "Gnat Canyon",
NE1/4SW1/4 section 30, T. 22 S., R. 7 E., Salt Lake Base Line.
Seaward limit: not determined. Probably extends most of the way
up Molen Reef toward Dry Wash, where a younger parasequence may
be present. Basic facies content: wave-modified shoreline--strand
plain in proximal part to wave-modified delta in distal part.
Kf-5 thickens rapidly seaward from
its landward limit in Muddy Creek Canyon. Its seaward feather
edge lies in "Fracture Canyon" just south of Dry Wash. Kf-5 has,
to date, defied division into parasequences. Almost everywhere,
the upper part of the shoreline sandstone of Kf-5 has been cut
out and replaced by meanderbelt deposits (among them the channel
deposits so extensively studied by the Texas Bureau of Economic
Geology in Muddy Creek Canyon, Grassy Valley, and "Cedar Canyon").
The presence of the meanderbelt deposits preclude recognition
of the landward pinch-outs of any parasequences that Kf-5 contains.
Most of the shoreline strata of Kf-5 appear to represent a wave-modified
coast, probably a wave-modified delta front. The I-coal zone accumulated
in a swamp, probably a "raised mire" that existed along the western
margin of the Kf-5 meanderbelt that trends northward to northeastward
across Muddy Creek Canyon. Coal in the I-zone reaches its maximum
thickness in the area at and south of Christiansen Wash, where
it combines with the overlying J-coal to form a 30-foot-thick
seam. Although the A- and C-coal zones probably include more coal
because of their greater areal distributions, the I-coal bed is
the only one that has been mined on a large scale. The lower 20
feet of coal has been extensively mined by conventional, room-and-pillar
techniques at the Emery mine. The upper 10 feet of coal, which
tends to be higher in sulfur, has been left as roof. Consol estimates
that about 100 million tons of combined I-J coal is strippable
in the area south of Emery. Carbonaceous mudstones of the I-zone
are being mined as "Live Earth" south of "Bear Gulch". Type section:
none. Considered to be a parasequence set at present. If Kf-5
is ultimately considered to constitute a single parasequence,
a good type section would be the west side of Muddy Creek Canyon,
NE1/4SW1/4 section 13, T. 22 S., R. 6 E., Salt Lake Base Line.
Landward limit: Muddy Creek Canyon, somewhat obscured because
of overlying meanderbelt, approximately NW1/4 section 24, T. 22
S., R. 6 E., Salt Lake Base Line. Seaward limit: "Fracture Canyon",
SW1/4 section 24, T. 21 S., R. 7 E., Salt Lake Base Line. Facies
content of shoreline unit: river-dominated delta.
Kf-6 extends from the upper part of
Muddy Creek Canyon to Dry Wash. No parasequences are recognized
at this time and it is likely that none will be. Contemporaneous
channels are rare or absent and all of the shoreline strata of
Kf-6 appear to have accumulated along a wave-dominated coast,
probably a strand plain. Kf-6 is difficult to study in detail
owing to the fact that it is generally exposed only on the lower
part of the Molen dip slope and because outcrops are generally
poor between the few significant canyons. Both the landward pinch-out
at the head of Muddy Creek Canyon and the seaward feather edge
at Dry Wash, however, are particularly well displayed. Type section:
uppermost part of Muddy Creek Canyon, SE1/4NW1/4 section 13, T.
22 S., R. 6 E., Salt Lake Base Line. Landward limit: uppermost
part of Muddy Creek Canyon, SE1/4NW1/4 section 13, T. 22 S., R.
6 E., Salt Lake Base Line. Seaward limit: Dry Wash, NE1/4NW1/4
section 34, T. 21 S., R. 7 E., Salt Lake Base Line. Facies content
of shoreline unit: wave-modified coastline, probably strand plain.
The landward limit of Kf-7 lies somewhere
in the vicinity of Christiansen Wash, although it cannot be defined
for lack of good outcrop and the fact that it has been cut out
by a major meanderbelt deposit. It reaches a seaward feather edge
in the northern part of Muddy Creek Canyon. No parasequences are
presently distinguished and, because of outcrop limitation, it
is likely that none will be. All well exposed parts of the shoreline
unit of Kf-7 are of lower and middle shoreface strata. Dominance
of hummocky-swaley cross stratification and planar lamination
coupled with moderate bioturbation point to a wave-modified shoreline.
The presence of the thick, multi-storied, contemporaneous meanderbelt
deposit at Christiansen Wash demonstrates that a large river was
actively feeding sediment to (Kf-7) in the area between Christiansen
Wash and Miller Canyon. Type section : west side of Muddy Creek
Canyon, NW1/4SW1/4 section 24, T. 22 S., R. 6 E., Salt Lake Base
Line. Landward limit: cannot be determined owing to fluvial erosion,
approximately at Christiansen Wash, NW1/4 section 33, T. 22 S.,
R. 6 E., Salt Lake Base Line. Seaward limit: upper part of Muddy
Creek Canyon, SE1/4NW1/4 section 13, T. 22 S., R. 6 E., Salt Lake
Base Line. Facies content of shoreline unit: wave-modified shoreline,
probably strand plain in proximal part and certainly wave-modified
delta in distal part.
|