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PAUL G. NYSTROM, JR.
DRILL HOLE DESCRIPTIONS AND INTERPRE-
TATIONS
Hole GMP-3
Description
This hole (figure 2) was drilled on the south-side of
Tyler Bridge Road 3400 ft west of the bridge over Upper
Three Runs. The collar elevation was 198 ft (estimated from
1:24,000 topographic map) and the hole was drilled to a
depth of 60 ft. The Qal at the site is 40 ft thick. The interval
from 0 to 25 ft is mainly poorly, sorted medium to very
coarse grained sand with some granules. Sample GMP-3 was
collected from a layer of wet, black, organic, gooey sand in
the 25 to 30 ft interval of the hole. The base of the organic
rich bed is about 10 ft above the base of the Qal, which is
mainly a section of coarse to very coarse grained sand with
minor granules dispersed throughout. The lower four ft is a
prominent pebbly grit. The organic rich bed was not intersected
in hole GMP-4 located 1600 ft to the east. In that hole
the sediment in the elevation range corresponding to the
organic rich bed is poorly sorted, medium to very coarse
grained sand with granules like that in the 0 to 25 ft interval
of hole GMP-3.
Interpretation
Where Tyler Bridge Road crosses Upper Three Runs
valley the 1:24,000 scale topographic map of New Ellenton
SW Quadrangle shows an alluvial fan extending onto the
Upper Three Runs floodplain. The alluvial fan is located at
the mouth of a tributary entering the floodplain from the
west. The 0 to 25 ft interval in hole GMP-3 is entirely or
mainly alluvial fan sediment. The organic rich layer in the 25
to 30 ft interval was deposited as floodplain sediment at the
top of a fining upward sequence now buried by the alluvial
fan. As the top of the organic rich bed is slightly higher than
the active floodplain the fining upward sequence is an old
terrace rather than part of the active floodplain.
The radiocarbon date of 33,900+370 yr. B.P. (see Table
1) should be the age of the fining upward sequence at the
base of the alluvial section, and may approximate the age of
the youngest terrace sediments adjacent to the active floodplain
of Upper three Runs. The active floodplain, then, is
younger than that date. Furthermore, before deposition of the
dated peat deposit, incision along this part of Upper Three
Runs had reached a level approximately 240 ft below the
present inter-fluves. Therefore, in this area Upper Three
Runs valley was cut almost to the present base of floodplain
alluvium prior to 33,900 yr. B.P.
GMP-12
Description
This hole (figure 3) was drilled on the northeast side of
Hickson Mill Road on the lower north bank of Tinker Creek
approximately 1.6 miles west of Kennedy’s Pond. The collar
elevation was 220 ft (estimated from 1:24,000 topo map).
Twenty-three ft of alluvial sediments including three separate
peat beds were intersected. From 0 to 9 ft the sediment is
poorly sorted, fine to very coarse grained sand with a noticeable
amount of heavy minerals. From 9 to 11 feet there is a
bed of brown peat which is somewhat sandy from 10 to 11 ft.
Sample GMP-12-1 ft. was taken from the 9 to 10 ft. interval.
The 11 to 15 interval is very poorly sorted, medium to very
coarse grained sand with granules, and noticeable medium to
coarse grained heavy minerals. From 15 to 18 ft there is
black sand with much organic material including some
brown wood fragments. Sample GMP-12-2 was collected
from this interval. The 18 to 20 ft intervals is fine to coarse
grained sand. Another layer of brown peat occurs in the 20 to
22 ft interval, and sample GMP-12-3 was collected from this
bed. Poorly sorted pebbly sand with noticeable dark heavy
minerals comprises the basal ft (22 to 23) of the alluvial section.
Interpretation
The site for this drill hole is not in the active floodplain
of Tinker Creek, but is located on the north bank of a fluvial
terrace. The lithologic log for the hole indicates four fluvial
sequences were intersected in the 23 ft alluvial section. The
uppermost part of the section is a sequence from 0 to 9 ft
with no recognizable surficial floodplain sediments. Below
the upper 9 ft of section are three fluvial sequences, each
capped by peat deposits. Thus the alluvial terrace section in
this drill hole indicates repeated events of channel deposition
followed by floodplain stabilization.
The youngest radiocarbon date of 37,950+620 yr. B.P.
for the middle peat bed bracketed by older dates of greater
than 45,000 yr. B.P. for the peat bed above, and greater than
46,800 yr. B.P. for the peat bed below, causes some concern
about how to interpret these dates. Stone and Brown (1981)
discussed the need for critical interpretation of radiocarbon
dates in the range of 30,000 to 40,000 y. B.P. which is near
the limit for the technique. They pointed out that due to contamination
by small amounts of more recent carbon, it can be
difficult to discriminate between sediments actually deposited
35,000 yr. B.P. and those deposited during a much earlier
time. The date of 37,950+620 yr. B.P. should be a
minimum age for the beds from which samples GMP-12-2
was collected must be somewhat younger than the middle
peat bed, and could be much younger. The radiocarbon date
of greater than 45,000 yr. B.P., however, suggests that it may
not be much younger than the 37,950+620 yr. B.P. date for
the middle peat bed. The date for the middle peat bed is close
to the 33,900+370 yr. B.P. date for the buried terrace intersected
in hole GMP-3.
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