Geologic Map and Report of Findings for the Redlair Property, Gastonia, North Carolina
Jason R. Price
Millersville University
2009
Introduction and Background
Bedrock influences topography, water movement, and soil physicochemical properties
including fertility, and therefore asserts a major influence on ecosystems. For south-central North
Carolina a large-scale (1:250,000) bedrock map is available (Goldsmith et al., 1988). However this
map lacks the resolution needed for the Redlair property located in Gastonia, North Carolina. This
report provides findings of bedrock mapping and other field observations at the Redlair property
conducted in June 2009.
Bedrock mapping in the humid, temperate Appalachian Piedmont Physiographic Province is
very challenging. There is typically a paucity of outcroppings as bedrock is covered with a thick
regolith and abundant vegetation. Based on these limitations, the following objectives for field
mapping were established:
(1) Verify location of the Boogertown Shear Zone. Goldsmith et al. (1988) show this shear
zone bisecting the Redlair property and separating two very different lithologic units. Soils
maps (Woody, 1989) provide an approximate location for the shear zone that is very
different from that reported by Goldsmith et al. (1988).
(2) Look for additional shear zones. Larger shear zones are often accompanied by smaller shear
zones which may also juxtapose very different lithologies.
(3) Verify locations of rocks already mapped at 1:250,000 by Goldsmith et al. (1988).
(4) Look for mafic bodies, especially on hilltops and in valleys. Goldsmith et al. (1988)
describe one the primary lithologies underlying Redlair as containing intermediate and mafic
rocks. As mafic rocks typically weather very differently than felsic rocks, they are capable
of influencing topography and regolith, and yielding very distinctive soils typically
recognizable in the field.
Results
The lithologic descriptions of units observed at Redlair are provided in Table 1. These
descriptions are based on the work by Goldsmith et al. (1988), with verification/modification based
on field observations. The geologic map of Redlair is provided in Figure 1.
Discussion
Colluvium and Alluvium. No efforts have been made to map transported regolith as bedrock
mapping has not been impeded by its presence. The only exception is the southwestern extent of
the Boogertown Shear Zone which is discussed below. Certainly alluvium occurs on all floodplains
and is evident on topographic maps by its very low slope and being adjacent to the South Fork of
the Catawba River. Distinctively colluvial material was observed on the southwest corner of the
property in the lobe of land surrounded on three sides by the meander in the South Branch of the
Catawba River. This material is characterized by being above the floodplain and containing
rounded fragments of vein quartz.
Boogertown Shear Zone. No structural or tectonic interpretations have been made based on the
field work completed. However, from field observations the Boogertown Shear Zone appears to be
nearly vertical and no wider than a few tens of meters. It is easily recognizable in the field as it
separates two lithologies with distinctively different regolith and geomorphic expression (Figure 1;
Table 1). The southwest extent of the shear zone was not directly observable and its approximate
location is dashed in Figure 1. The location of the Boogertown Shear Zone shown in Figure 1
differs from its locations reported by Goldsmith et al. (1988), and its location determined from soil
maps compiled by Woody (1989).
Table 1. Lithologic units observed at Redlair. Descriptions are based on field observations and the
work of Goldsmith et al. (1988).
Symbol
Name
mvf
Felsic
Metavolcanic
Rocks
Mq
Quartzite
Zbs
Quartz-sericite
schist of the
Battleground
Formation (Late
Proterozoic)
Zbkq
High-alumina
quartzite of the
Battleground
Formation (Late
Proterozoic)
Zbvf
Felsic
metavolcanic
rocks of the
Battleground
Formation (Late
Proterozoic)
Kings Mountain Belt
Chalotte Belt
Metamorphic
Belt
Description
Fine- to coarse-grained felsic metatuffs with a very small
percentage of mafic minerals. Ubiquitous vein quartz.
Massive to foliated on scales of millimeters. Possibly
correlative with felsic metavolcanic rocks of the
Battleground Formation (Zbvf) described below.
Frequently form the lower portions of stream valleys and
channel bottoms. Soils developed on this unit are
typically red with abundant angular vein quartz fragments
up to a few tens of centimeters in size.
Dark gray to dark-green metamorphosed sandstone.
Massive and lacks vein quartz. Forms large steep
outcrops on the south side of Redlair adjacent to the South
Fork of the Catawba River. Results in rapids/riffles in the
river. Soils developed on this unit are brown and devoid
of vein quartz. May be the unit mapped as “q” by
Goldsmith et al. (1988) which is described as:
“Commonly containing muscovite, andalusite,
kyanite, or sillimanite, chloritoid, pyrite (less
commonly hematite), accessory rutile, locally minor
gahnite and aluminum phosphates. Mostly
metamorphosed, hydrothermally leached and silicified
rock; some may be metamorphosed sandstone.”
Very fine- to medium-grained muscovite-quartz schist
and phyllite. Very light gray, light-bluish-gray, lightbrown, or yellowish-gray. Composed largely of quartz
(typically >50%) and sericite white mica (muscovite and
paragonite). Accessory minerals may include chloritoid,
biotite, pyrite, hematite, kyanite, andalusite, sillimanite,
staurolite, garnet, oligoclase or albite, chlorite,
tourmaline, zircon, and graphite. Very fissile with
weathering occurring preferentially along foliation. Does
not sustain slopes, and does not outcrop. Very rarely
occurs as float or within the root wods of overturned
trees. Soils are commonly beige to brown.
Light- to medium-gray kyanite quartzite. Quartz is fine
grained and equigranular. Kyanite typically occurs as
aggregates or blades up to 1 cm long, mostly parallel to
foliation but locally across it. Occurs mostly as float
boulders.
This unit was not directly observed in the field and its
location and description are from Goldsmith et al. (1988).
White to medium-gray, fine- to medium-grained,
metamorphosed dacitic to rhyolitic flows and tuffs.
Contains minor intermediate and mafic metavolcanic
rocks. Probably correlative, at least in part, with felsic
metavolcanic rocks (mvf) in the Charlotte belt.
Figure 1. Geologic map of the Redlair property, Gastonia, North Carolina. Portion of Boogertown
Shear Zone that is dashed with question marks is an approximate location.
The Boogertown Shear Zone is not only important for separating different lithologies, but it
is also a boundary for different metamorphic facies (Goldsmith et al., 1988). The shear zone
separates the Kings Mountain belt to the west, from the Charlotte belt to the east. The former is
characterized by metasedimentary and metavolcanic rocks, and relatively low metamorphic grades.
In contrast, the Charlotte belt is characterized by plutonic rocks and metavolcanic rocks, and a
paucity of metasedimentary rocks.
The Boogertown Shear Zone is located approximately 11 m above the West Stone Farm
Creek (Figure 1). In addition, the channel of the South Fork of the Catawba River cuts across
lithologic and tectonostructural boundaries. The lack of coincidence between fluvial and bedrock
features permits the interpretation that the current stream locations were established prior to
exhumation of the current bedrock.
Geomorphology and Hydrology. The highest surface elevations (>250 m amsl) in Redlair are
located on the north and east sides of the property at the greatest distance from the South Branch of
the Catawba River. These high elevation areas are the oldest geomorphic surfaces on the property
and approximately form a “peneplain.” The term peneplain is used herein as a general term to
denote an imaginary surface that approximately connects accordant summits and not in the sense of
Davisian Cyclicity. Beneath these high elevation surfaces the regolith is thickest. The southern and
western portions of the property near and adjacent to the South Fork of the Catawba River are
highly dissected and reflect truncation of a weathering profile originally at the elevation of the
peneplain. The floors of the stream channels in this portion of property reflect the youngest
geomorphic surfaces and occur at ~200 m amsl. Therefore, based on the peneplain elevation from
the north and east sides of the property, the regolith thickness in the southern and western portions
of the property prior to stream incision was >50 m. A typical regolith thickness in this part of the
property is currently ~25 m. Regolith thickness also correlates qualitatively with hillslope gradient.
The relatively lower slopes in the north and east portion of the property reflect thicker regolith and
lack of bedrock exposure. The relatively higher slopes in the south and west reflect thinner regolith
with bedrock occasionally outcropping in stream valleys and channel floors and yielding the highest
slopes. Based on this discussion the Redlair topography east of the Boogertown Shear Zone is
dictated by geomorphic processes and not lithologic or bedrock structures.
Water in Redlair streams may disappear and reappear along the channel length. This
appears in the field to be related to the composition of the stream channel floor. When the channel
floor is bedrock, water will likely be present. However, when the channel floor is composed of
regolith, the water may drop below the channel floor, presumably to continue flow through the
regolith and over the bedrock at the weathering front. The implication of this observation is that
there is no regional aquifer at Redlair. Rather, precipitation that infiltrates the regolith percolates to
the weathering front where it is thwarted horizontally to the stream channel. Therefore, continuous
baseflow to perennial streams is resulting from water draining from unsaturated zone pore space
(e.g., Hewlett 1961, Hewlett and Hibbert 1963). These authors term this phenomenon “cistern”
storage.
Suggestions for Future Research
Based on the results and discussion outlined above, numerous future directions for research
are being proposed. The list below is not all inclusive, but simply reflects ideas conceived by the
author following bedrock mapping. Many of the suggestions below may be modified to include
data useable to multiple researchers from different disciplines. It is hoped that this list will
stimulate thinking for future projects and grant proposals, including those that may be collaborative
and/or interdisciplinary.
(1) Because the climate at Redlair does vary appreciably across the property, the site is well
suited for studies where climate needs to be held constant. The only exception is with
regards to aspect which may introduce intraRedlair variations in thermal regime.
(2) Using cosmogenic nuclides, age date peneplain surfaces and stream channel bottoms. From
this data incision rates for the Redlair streams may be calculated.
(3) Drill approximately 60 m below surface grade (bsg) at one of the highest surfaces in the
north and east portions of the property. Samples of regolith and unweathered bedrock
should be collected as frequently as is reasonable and appropriate (perhaps every ~0.5 to 1
m) for physicochemical analyses (e.g., bulk density, bulk chemistry, petrography, major and
trace element analyses of primary and secondary minerals) and characterization of chemical
weathering reactions. The boring should be finished as a well for future studies that include
solute data, and ideally to permit sampling at discrete depths. Wells could be drilled in three
locations:
a. Into the felsic metavolcanic rocks (mvf; Table 1, Figure 1)
b. Into the Boogertown Shear Zone (Figure 1)
c. Into the quartz-sericite schist (Zbs; Table 1, Figure 1).
Such a drilling program can be easily accomplished using access road #1.
(4) If drilling is not possible or feasible, then characterization of chemical weathering could be
completed using available exposures of bedrock and regolith along stream channels.
(5) Establish a climate station with datalogging capabilities.
(6) Establish gaging stations and measure discharge for streams appropriate to a given
experimental design.
(7) Sample water from the gaged streams weekly for analyses of:
a. Base cations
b. Silica
c. Bicarbonate
d. Suspended sediment
e. Nitrate, sulfate, phosphate, and other anionic nutrients
f. Chloride
Base cations and silica would allow for calculation of present-day chemical denudation
rates at the watershed-scale. Bicarbonate would allow for calculations of
soil/atmospheric CO2 consumption due to chemical weathering and stream CO2
degassing, also at the watershed-scale. Suspended sediment would allow for calculation
of present-day physical erosion rates. Anionic nutrients and base cations would allow
for analyses of ecosystem processes. Chloride would allow for calculation of
evapotranspiration and water storage in the regolith.
(8) Sample surface materials and possibly stream sedimen) from gaged watersheds for
cosmogenic nuclide and bulk chemical analyses. Such data will permit calculation of longterm (geologic timescale) average physical and chemical denudation rates.
(9) Data determined in (6) and (7) above may be used to compare weathering and mass loss
from watersheds that differ by characteristics such as:
a. Type of vegetation cover (e.g., deciduous, conifer, pasture)
b. Amount of vegetation cover (e.g., watersheds that vary solely by percentage of
deciduous forest cover),
c. Regolith thickness (a proxy for tectonics since steeper slopes have thinner regolith)
d. Land-use (e.g., row crops, residential, pasture)
Such studies would be even better if they included more than two [paired] watersheds.
Watershed-scale studies provide an excellent means to explore controls on and
quantification of physical and chemical weathering, which have implications for global
biogeochemical cycles, including the carbon cycle. Such studies are even strengthened
when physical and chemical denudation rates are combined, whether long-term (i.e., (8)
above) or present-day (i.e., (7) above). Redlair is an ideal location for watershed-scale
studies because it lacks a regional aquifer and is underlain by crystalline silicate
bedrock. Furthermore, it has never been glaciated and no evidence was found for
significant periglacial activity.
(10)
Sampling of unweathered bedrock through drilling ((3) above) would allow for
petrologic studies with implications for continental-scale tectonic processes and events.
Bulk chemical analyses of bedrock, and major and trace element analyses of individual
minerals would be data of value to both petrologists and low-temperature regolith
geochemists.
(11)
Geophysical surveys to constrain the locations of lithologic and structural features.
(12)
Digging of trenches to bedrock permitting installation of lysimeters for collection of
pore waters at discrete depths. At the same time the lysimeters are installed, the regolith and
bedrock can be sampled at the same locations for comparison of present-day (from solute
data) and long-term average (from the solid-phase data) hydrobiogeochemical changes in the
regolith.
References
Goldsmith, R., Milton, D.J., and Horton, Jr., J.W., 1988. Geologic Map of the Charlotte 1° x 2°
Quadrangle, North Carolina and South Carolina (Map I-1251-E). United States
Geological Survey, Miscellaneous Investigations Series.
Hewlett, J.D., 1961, Soil moisture as a source of base flow from steep mountain
watersheds: Southeastern Forest Experiment Station Paper no. 132, U.S.
Department of Agriculture–Forest Service, Asheville, North Carolina, 11 p.
Hewlett, J.D., and Hibbert, A.R., 1963, Moisture and energy conditions within a sloping
soil mass during drainage: Journal of Geophysical Research, v. 68, p. 1081-1087.
Woody, W.E., 1989. Soil Survey of Gaston County, North Carolina. U.S. Department of
Agriculture, Soil Conservation Service, 127 pp. (available online).