gb 1978.book - Carolina Geological Society

DONALD T. SECOR, JR., AND ARTHUR W. SNOKE
In the Red Hill quadrangle, Pirkle (1977) mapped a
sequence involving Terrane III and parts of Terranes II and
IV as a homoclinal sequence. He suggested correlating the
older volcanic and volcaniclastic rocks of Terrane II with the
Persimmon Fork Formation of central South Carolina, and
also suggested that the younger volcanic and volcaniclastic
rocks of Terrane IV might correlate with the Cid Formation
in central North Carolina.
Daniels (1974) mapped a synclinal axis trending
through the middle of Terrane III. By his interpretation, Terranes
II and IV are correlative and older than Terrane III. The
epiclastic rocks in Terrane I are beneath the volcanic and
volcaniclastic rocks in Terranes II and IV.
In the Lincolnton, Georgia and McCormick, South
Carolina area, Carpenter (1976) and Carpenter and others (in
press) have proposed that the volcanic and volcaniclastic
rocks in Terrane IV are older than the epiclastic rocks in Terrane
III. As previously mentioned, the stratigraphic sequence
proposed by Carpenter and others (in press) resembles the
sequences in central South Carolina (Conley and Bain, 1965;
Stromquist and Sundelius, 1969). The radiometric ages
reported by Carpenter and others (1978, in press) for the Lincolnton
metadacite (Rb-Sr whole rock- 562 +-20; U-Pb zircon-
568) suggest that Terrane IV is more nearly correlative
with the Uwharrie Formation in North Carolina than with the
younger volcanic units in the Cid Formation, as proposed by
Pirkle (1977).
In our reconnaissance work in South Carolina we have
adopted a simple stratigraphic model in which an older volcanic
sequence is overlain by a younger epiclastic
sequence(Terrane 1 = Terrane III = Richtex Formation). The
evidence for the equivalence of Terranes II and IV is that
identical quartz crystal lapilli tuffs are found in Terrane IV in
the Lincolnton-McCormick area, in Terrane II in the Batesburg-Emory
area, and in the Persimmon Fork Formation
near Columbia, South Carolina. Terranes I and III are
equated with each other and with the Richtex Formation
because of lithologic similarity. We interpret the Richtex
Formation of Terrane I to be conformable with the Persimmon
Fork Formation of Terrane II because of the gradational
nature of the contact between them. The data that suggest
that the Richtex Formation is younger than the Persimmon
Fork Formation are top criteria derived from sedimentary
structures and the structural position of the Richtex Formation
in the core of a major upright F1 syncline in the area
between Batesburg and Lake Murray (Plate II).
Persimmon Fork Formation
The Persimmon Fork Formation forms part of a northeast-trending
band crossing the central and northeastern part
of the Emory quadrangle and extends to the western end of
Lake Murray (Plate II). This unit is predominantly coarsegrained
intermediate to felsic lapilli and crystal-lapilli tuffs
with some fine-grained vitric tuff. These rocks are interlayered
with lesser amounts of epiclastic rocks and are intruded
by small masses of mafic to felsic hypabyssal rocks. The
coarse-grained tuffs are very poorly sorted, and intermediate
and felsic lithologies are intimately interbedded so that
meaningful subdivision has not been accomplished. The typical
metamorphic mineral assemblage in the felsic rocks is
quartz-albite-epidote-white mica-chlorite-opaque oxidesapatite.
Potash feldspar is not present and there is no textural
evidence for its former existence; therefore the felsic rocks
are probably keratophyres or quartz keratophyres. The intermediate
rocks containing less quartz and more epidote and
chlorite are probably andesitic in composition. The epiclastic
rocks, predominantly volcanic siltstones and wackes, contain
the same metamorphic mineral assemblage as the metavolcanic
rocks, however they are better sorted, and relic sedimentary
structures suggest aqueous transportation and
deposition. The mafic to felsic hypabyssal rocks have also
undergone greenschist facies metamorphism. These bodies
appear to be similar to the shallow level intrusions that are
commonly found in thick volcanic accumulations.
The boundary between the Persimmon Fork Formation
and the overlying Richtex Formation is gradational with volcanic
rocks interlayered with epiclastic rocks through an
interval of a hundred meters or more. Although the bottom
of the Persimmon Fork Formation has not been identified in
the Batesburg-Emory area, its thickness probably exceeds 2
km.
Richtex Formation
The Richtex Formation is a heterogeneous sequence of
epiclastic rocks locally interbedded with felsic to intermediate
fragmental volcanic rocks. It underlies extensive areas in
the Batesburg and Emory quadrangles, is well-exposed along
the southwestern shores of Lake Murray (e.g. Shull Island
peninsula) and is widespread in the Columbia area (Plate II).
Although the top of the Richtex Formation has not been
identified by mapping in the slate belt of South Carolina, at
least 5 km of strata are present in the Batesburg-Emory area.
The lower and middle parts of the Richtex Formation
contain lenses and layers, up to 1500 m thick, of a distinctive
quartz-rich siltstone. In most places this siltstone contains
bifurcated wavy flaser bedding (Reineck and Wunderlich,
1968), in which lenticular, quart-rich layers (sometimes
cross-stratified), 0.3 - 30 mm thick and 5 -30 cm long, are
separated by very thin pelitic seams (Fig. 2 and STOP 5). In
a few places planar bedding and lenticular bedding with connected
lenses have been observed in this unit. These sedimentary
structures are similar to those found in modern
environments where sedimentary transport and deposition
are dominated by tidal currents (Reineck, 1972; Reineck and
Singh, 1975). The quartz-rich siltstone grades laterally and
vertically into evenly laminated mudstone, graywacke, inter-
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