Modern Clastic Depositional Environments, South Carolina: Charleston to Columbia, South Carolina, July 20-25, 1989

88 Pages·8.873 MB·English

by  Miles O. Hayes, Walter J. Sexton(auth.)

Modern Oastic Depositional
Environments, South Carolina
Charleston to Columbia, South Carolina
July 20-25, t 989
Field Trip Guidebook T37t
Leader: Miles O. Hayes
Associate Leader: \\%1lter}. Sexton
American Geophysical Union, Washington, D.C.
COVER Oblique aerial view of the Santee/Pee Dee delta front.
Note North Santee Inlet in middle distance and Winyah Bay
Entrance at the top of the photo, and the numerous beach
ridges behind the beach, which indicate that wave and tidal
processes completely mold the delta front. Photo taken in
October 1979 by Peter J. Reinhart.
Leader: Associate Leader:
Miles O. Hayes, Ph.D., President Walter J. Sexton, Ph.D.
RPI International, Inc. Geologist/President
P.O. Box 328 Athena Technologies Inc.
Columbia, SC 29202 600 South Holly Street
Columbia, SC 29205
Copyright 1989 American Geophysical Union
2000 Florida Ave., N.W., Washington, D.C. 20009
ISBN: 0-87590-572-2
Printed in the United States of America
IGC FIELD TRIP T371:
MODERN CLASTIC DEPOSITIONAL
ENVIRONMENTS, SOUTH CAROLINA
Miles O. Hayes
RPI International, Inc., Columbia, South Carolina
Walter J. Sexton
Athena Technologies, Inc., Columbia, South Carolina
INTRODUCTION tectonic highs, the Cape Fear Arch on the
north and the Ocala Arch on the south, border
The coastal plain of South Carolina is an the basin. This tectonic regime has appar
excellent natural laboratory for studying the ently been in existence since late Paleocene
formation of terrigenous clastic depositional [Colquhoun et al., 1983]. According to
systems. The occurrence of these systems in Colquhoun et al. [1983], the coastal plain
a trailing-edge setting alloys one to focus sediment package (Cretaceous-Holocene) is on
on the depositional processes, free of com ly 300 m thick at the North Carolina/South
plex tectonic overprints. The scale of the Carolina border, but it thickens to 1,000 m
region is compressed; it is only 160 km from at the South Carolina/Georgia border. Evi
the Fall Line to the ocean, which allows dence published by Winker and Howard [1977]
ready access to a broad range of depositional indicates that the ±100,OOO BP Pleistocene
settings during a 5-day trip. Numerous na shoreline sequence, which they call the
ture preserves and wildlife refuges exist in Chatham Sequence, has been raised 5 m in
the area, some containing virgin floral as North Carolina relative to the center of the
semblages, which provides a rare opportunity Georgia Basin. Thus, we can assume that this
to see the natural process unmodified by man. tectonic element, however mild, remains ac
The trip begins at the Fall Line in Colum tive even to this day.
bia (see Fig. 1)• We spend the first day The coastal plain deposits of South Caro
inspecting the alluvial deposits of the Con lina are basically an offlap sequence of sed
garee River valley, the most notable of which imentary units ranging from Cretaceous to
is a series of coarse-grained point bars. Holocene in age. Colquhoun [1969] divided
Visits to two virgin forests, a hardwood bot the coastal plain into three morphological
tomland (floodplain) and cypress-tupelo units:
swamp, will give the visiting geologists a
clearer image of what such environments were 1) Upper Coastal Plain - Area of moderately
like in prehistoric times. The second day is rugged relief underlain by Cretaceous to
an intensive inspection of the upper and low middle Eocene sedimentary rocks.
er delta plain of the Santee-Pee Dee delta, 2) Middle Coastal Plain - Area ~f relatively
the largest delta complex on the east coast low relief with mostly Tertiary rocks
of the USA. The third and fourth days will cropping out at the surface.
be spent investigating mesotidal (tidal range 3) Lower Coastal Plain - Very flat area with
= 2-4 m) barrier islands and tidal inlets of mostly Pleistocene sediments cropping out
the South Carolina coast. Both field days at the surface.
will be spent within the confines of federal
and state wildlife preserves. In the after We will traverse the Upper and Middle Coastal
noon of day 4, we will conduct an overflight Plain on day 1, but the remainder of the trip
of the area to be visited on days 2-5. Day 5 will be confined to the Lower Coastal Plain.
is spent in the pristine, tide-dominated St. The climate of the area borders between
Helena Sound, where we will see a spectrum of subtropical and temperate. Annual rainfall
environments ranging from peat swamps to averages around 122 em, and temperatures av
tidal sand ridges. erage 60°F. During July, the time this trip
is scheduled, it is common for afternoon tem
Regional Setting peratures to reach the mid- to high 90s, with
accompanying high humidity. Thunderstorms
The study site is located on the north are common that time of year.
eastern flank of a subsiding basin, the
Southeast Georgia Embayment. NW-SE oriented
T371: 1
PIEDMONT ~
RIVER - It;ill
COASTAL
PLAIN
RIVER- •
o
50 100
·~A.
FLA.----:
) KM
FIGURE 1 Location of area to be visited on this field trip. Numbers indicate days we will
visit each area. Also shown are the two major types of rivers that occur in the area: (1)
Piedmont rivers - those whose drainage basins include the Piedmont and Appalachian Moun
tains regions; and (2) coastal plain rivers - those whose drainage basins are completely
contained within the coastal plain region. Also shown are the different Pleistocene high
stand shoreline deposits [after Winker and Howard, 1977]. All workers do not agree with
the correlations of highstand shorelines depicted here [D.J. Colquhoun, pers. comm.].
The Georgia Bight occur at Cape Hatteras, North Carolina, yet
waves rarely exceed 1 m at the head of the
One of the more significant aspects of the embayment (Fig. 1)• Even within the area
study area is its position along the shore visited on this trip, one can see a marked
line of what mariners refer to as the Georgia difference in these parameters•. For example,
Bight. We use the term to define the major the shorelines at the Santee-Pee Dee Delta
bend in the coastline that extends from Cape (Day 2) and Cape Romain (Day 3) are what we
Hatteras, North Carolina, to Cape Canaveral, refer to as mixed-energy coasts (have signif
Florida (Figs. 2 and 3). Although the shore icant effects of both waves and tides). How
line bends, the shelf-slope break is rela ever, at St. Helena Sound (Day 5), which is
tively straight. Consequently, the conti located closer to the apex of the embayment,
nental shelf is quite wide and shallow at the tides are the dominant process.
apex of the embayment. This physiography has The coastal morphology changes around the
a marked influence on tidal and wave condi perimeter of the Georgia Bight in response to
tions in the area. Tides are microtidal changes in tidal and wave regimes. For exam
(less than 2 m) at the extremities of the em- ple, as shown in Figure 3, transgressive,
bayment but range up to mesotidal, close to 3 wave-dominated barrier islands are the preva
m, at the head of the embayment. Some of the lent barrier type at the extremities of the
largest waves on the east coast of the USA embayment. Regressive, mixed-energy barrier
T371: 2
.
SPRING TIDAL RANGE IMetersl
islands are present elsewhere in the embay
.9 1.5 2.1 2.9
ment. Tidal inlets are much more common to
ward the head of the embayment (Fig. 3).
-~----~\
Sea-Level Changes NORTHCAROLINA ,I,f'')
After basic tectonic framework controls,
probably the most striking effects on the de
positional systems of the study area have
been brought about by changes in sea level.
Two examples to be stressed on this trip are:
a) Base-level changes causing erosion and
fill of alluvial valleys.
b) Alternation of transgressive/regressive
coastal sequences as a result of minor
FLORIDA
sea-level fluctuations.
It is generally conceded that sea-level .3 .6 .9 1.2 1.5
dropped more than 100 m during the Wisconsin MEAN WAVE HEIGHT IMetersl
glaciation [Milliman and Emery, 1968]. Be-
ginning around 17,000 [Laville and Renault- FIGURE 2 Variation of tidal and wave regime
Miskovsky, 1977], sea level probably rose along the shoreline of the Georgia Bight.
rapidly to near its present level around
WAVE-DOMINATED ~ TRANSGRESSIVE
BARRIER ISLANDS t REGRESSIVE
o 100 200
FIGURE 3 Distribution of wave-dominated barrier islands and t'idal inlets along the shore
line of the Georgia Bight. Generally speaking, the outer areas are wave-dominated, the
head tends toward tide dominance, and the flanks are significantly affected by both pro
cesses (mixed energy).
T371: 3
6,000 yr BP. The sea-level curve since that Because this is a field trip to a natural en
time has been greatly refined by excellent vironment, we will retain the originally
collaborative efforts by archeologists and proposed nomenclature.
geologists [see DePratter and Howard, 1980; Two important studies of bedforms in mac
and Colquhoun et al., 1981; 1986]. The sea rotidal (greater than 4 m tidal range) areas,
level curve that has been derived for this that of Dalrymple et al. [1978] in the Bay of
time period in the Georgia Bight is shown in Fundy and Elliot and Gardiner [1981] in the
Figure 4. LoughorEstuary in the United Kingdom, gener
ally ~gree' with our assertion_that there are
THOUSANDS OF YEARS B.P. three discrete bedform types in estuaries.
o However, they define two megaripple classes:
7 6 5 4 3 2 ~
m
-t
1!B Type 1 Low-amplitude, long-span,
fn two-dimensional forms devoid of
2m scour pits.
m
Type 2 -- Higher-amplitude, shorter
30
span, three-dimensional forms with
~
4:::1: scour pits.
si5
,:::.I: They do not have specific wavelength bound
6~ aries as we do; thus, they rely more ongeom
71 etry to define bedform type, and there may be
:::I: some overlap in size. More research is
needed on this topic in a variety of geo
SEA~LEVEL CURVE - SC COAST
graphic settings before a definitive classi
FIGURE 4 Changes in sea level on the South fication can be determined.
Carolina coast over the past 6,000 years,
based on detailed, combined archeological and Acknowledgments
stratigraphical research [modified after
Colquhoun et al., 1981; 1986]. The bulk of the original research upon
which this guidebook is based was carried out
Bedform Nomenclature by graduate students in the Coastal Research
Division of the Department of Geology at the
The nomenclature" used for lower-flow re University of South Carolina (USC). Between
gime, asymmetric bedforms in this guidebook, 1973 and 1986, a total of 32 M.S. and Ph.D.
which is based on bedform wavelengths, or theses were carried out under Hayest super
spacing, was first proposed for New England vision in the area of study covered by this
estuaries by Hayes and his associates [Hayes, trip. The specific studies are cited under
1969; Boothroyd and Hubbard, 1974]. It fol each trip description. The management of
lows: this research program was assisted greatly by
a succession of several able postdoctoral as
Bedform Spacing sociates, namely, Pulak Ray, Dag Nummedal,
Larry Ward, and Gary Zarillo.
ripple o - 60 cm The Geology Department at USC and RPI In
megaripple 60 cm - 6 m ternational, Inc., are gratefully acknowl
sand wave > 6 m edged for supporting our research program
over the years. Financial assistance was
These boundaries were proposed based on sam provided by a number of additional sources,
pling of three distinct populations of bed including (1) Coastal Engineering Research
forms in New England estuaries. It is gen Center, U.S. Army Corps or Engineers (several
erally conceded by most workers that the contracts for studies in New England and
distinction between ripple and megaripple is South Carolina); (2) U.S. Army Research Of
based on a natural break between the two. fice (Contract No. DAAG-29-76-G-Oll1, Price
However, there are some workers who disagree Inlet, S.C.); and (3) NOAA's Sea Grant Pro
that our megaripples and sand waves should be gram, State of South Carolina (Contract No.
differentiated. To quote Allen [1983, p. 04-6-148-44096). Of special importance was a
22]: grant from the Division of Earth Sciences,
National Science Foundation (Contract No. EAR
"The evidence seems to me unconvincing, 78-13662), which supported our coring studies
particularly as most of the claims of coastal sand bodies.
originate from studies of natural en This trip has been conducted several times
vironments." a year since 1976 by RPI International, Inc.,
T371: 4
FIGURE 5 Location of field stops during day 1.
under sponsorship by the American Association Schumm [1977] proposed an idealized
of Petroleum Geologists. Industrial groups fluvial system consisting of 3 zones (Fig.
who have sponsored the same trip include 7), which are described below (with some mod
Schlumberger, Tenneco, and Standard Oil. Re ifications by us):
search in support of these industrial train
ing courses has added considerably to our un Zone 1 - Production
derstanding of the Holocene stratigraphy of THE DRAINAGE BASIN
the area. The area from which sediment and water
John H. Barwis and Donald J. Colquhoun are are derived. Its characteristics are
acknowledged for their thoughtful reviews of controlled by climate, diastrophism,
this field guide, which have helped us make and human land usage.
several improvements of the earlier draft. Zone 2 - Transfer
THE ALLUVIAL VALLEY
This is the zone through which sedi
DAY 1: THE ERODED VALLEY, POINT BARS, ments are transferred from the drain
AND FLOOD PLAIN OF THE CONGAREE RIVER; age basin to the receiving basin. It
CYPRESS/TUPELO SWAMP is affected greatly by changes in base
level.
Introduction Zone 3 - Deposition
DELTA or ALLUVIAL FAN
This day will be devoted mostly to the ex Primarily a zone of deposition. Its
amination of depositional environments of the characteristics are controlled by
Congaree River system, with a brief visit to changes in base level, the magnitude
a cypress/tupelo swamp in the Edisto River of the sediment load of the stream,
drainage basin. The trip will begin in and hydrographic energy of the receiv
Columbia, which is located on the Fall Line ing basin.
just below the confluence of the Broad and
Saluda Rivers, where the Congaree River be Although zone 1 is of considerable interest
gins (Figs. 1, 5, and 6). The Congaree joins to hydrologists and geomorphologists, it will
the Wateree River 80 km southeast of Columbia not be visited on this trip. The alluvial
to form the Santee River. The drainage basin valleys and their deposits of zone 2 are com
for the Congaree, which covers 22,000 km2 of monly preserved'in the rock record, with many
the Piedmont and Blue Ridge geological prov containing important economic deposits. This
inces of South and North Carolina [Levey, is the region we will focus on during this
1978], is illustrated in Figure 6. day's trip. The delta region of zone 3 is
T371: 5
SANTEERIVER BASIN ---V-IRG-INIA-~--
I
~~~f,~/\/ *
;~;./ RALEIGH
NORTH CAROLINA
,
t
LOCATION MAP
FIGURE 6 Drainage basin of the Congaree, Wateree, and Santee Rivers. The Congaree's source
streams, a combination of the drainages of the Saluda and Broad Rivers, flow across Paleo
zoic and pre-Cambrian metamorphic and igneous rocks with a wide range of composition. The
region is mantled with lateritic soils and saprolites [from USDA, 1973].
the topic for day 2. This field trip is or graphic models in use today in the explora
ganized so that the first day begins at the tion for hydrocarbons is the aggraded allu
fall line and the last day ends in an estu vial valley model [R. J. Weimer, pers comm.,
arine system located far from the outlet of 1983; numerous RPI regional stratigraphic
any primary Piedmont stream. studies]. A key to applying this model suc
cessfully is understanding how these valleys
Evolution of Alluvial Valleys, evolve.
It has been recognized for a long time
One of the most often applied strati- that water running downhill under the influ-
T371: 6
grade, a condition defined by Leopold and
Maddock [1953, p. 51; in paraphrasing Mackin,
1948] as follows:
ZONE 1 - (production) "The graded stream is a system in equi
DRAINAGE BASIN librium; its diagnostic characteristics
is that any change in any of the con
trolling factors will cause a displace
ment of the equilibrium in a direction
that will tend to absorb the effect of
the change."
ZONE 2 - (transf.r) It is important to realize that grade devel
ALLUVIAL VALLEY ops first near the mouth of a river and
gradually extends headward [Bloom, 1978, p.
224]. The typical longitudinal profile of a
graded stream is asymmetrically concave up
ward, with the flattest part of the curve be
ing at the ocean and the steepest part at the
head of the stream.
According to Leopold and Maddock [1953], a
stream in grade must adjust to changes in (1)
discharge, (2) sediment load, or (3) ultimate
[LAKE; BAY; OCEAN] base level. On the other hand, the stream
can "self regulate" such factors as channel
FIGURE 7 The idealized fluvial system [mod width, channel depth, and grain size of the
ified after Schumm, 1977]. Day 1 of this sediment load to maintain grade. According
trip is devoted to zone 2, and day 2 to zone to Bloom [1978, p. 221], slope is usually the
3. final adjustment the stream makes in becoming
graded. He states further that:
ence of gravity is the principal agent re
sponsible for the formation of alluvial val "The critical factor in the achievement
leys. This observation was stated eloquently of the graded condition is that the
by Playfair [1802, p. 102], in what is now stream must flow on 'adjustable' mate
known as Playfair's Law: rials, so that changes of one variable
can produce appropriate changes in oth
"Every river appears to consist of a ers. Alluvium is the ideal bed for a
main trunk, fed from a variety of river, and the establishment of an
branches, each running in a valley pro alluvium-lined channel on a continuous
portioned to its size, and all of them flood plain signals the achievement of
together forming a system of valleys, grade in that part of the river."
communicating with one another, and
having such a nice adjustment of their Following these criteria, we can assume
declivities, that none of them join the that the Congaree River system is at or near
principal valley, either on too high or grade seaward of the fall line, the ultimate
too low a level; a circumstance which base level of erosion (i.e., mean sea level)
would be infinitely improbable, if each having been relatively constant for the past
of these valleys were not the work of 4,000-6,000 years. Before that time, and
the stream that flows in it." possibly beyond, the valley of the river
aggraded on an average of 20 m in the study
Of course, other processes, such as mass area in response to the Holocene rise in sea
flows [e.g., Sharpe, 1938; Voight, 1978], level. Brooks et ale [1986] indicate that a
contribute by making sediments available to "wave" of grade extended from the coast to
the stream for further downslope transport. the Fall Line of the Savannah River, starting
The depth to which the river cuts a valley at the coast at 6,000 yr BP and reaching the
is controlled by the ultimate base level of Fall Line at 2,500 yr BP, based on dated
stream erosion [Bloom, 1978]. For major riv archeological sites. This process of valley
ers like the Santee, this level is where the erosion during the Wisconsin glaciation and
river enters the sea (i.e., where the gravity valley aggradation during the Holocene rise
potential of the falling water equals zero). in sea level has been clearly demonstrated
If base level stays constant for a signifi earlier by Fisk's [1947] classic work on the
cant amount of time, the stream may achieve Mississippi River Valley.
T371: 7
Fluvial Channel Morphology and Stratigraphy of the ratio of suspended to bed load in the
stream as a determinant of channel morpholo
Introduction. The relation of fluvial gy. Three types of channels are thus
channel morphology and processes to alluvial defined--bed load channel (>11% bed load),
stratigraphy has been one of the prime topics mixed load channel «11%>3% bed load), and
of sedimentological science since the birth suspended load channel «3% bed load). Two
of the field [see historic review of Miall, of the more publicized suspended-load channel
1978a]. Fisk's [1947] class'ic work on the types are highly sinuous, meandering chan
Mississippi River Valley was followed by nu- nels, such as those of the Mississippi River
merous studies in the 1950s and 1960s by re [Fisk, 1947], and anastomosing channels, such
search laboratories of major energy companies as those of the Columbia and Saskatchewan
on the point bars of the rivers of the Texas Rivers in western Canada [Smith, 1983].
coastal plain, particularly the Brazos [see These 2 channel types are illustrated in Fig
Bernard et al.'s 1970 discussion of Shell's ure 8.
work] • Review articles on fluvial geomor Levey [1978] has shown that the meandering
phology by Leopold et al. [1964] and on channels of the Congaree River in the study
alluvial sedimentation by Allen [1965] and area have a relatively low sinuosity index of
LeBlanc [1972] provided excellent summaries 1.75, using the method of Brice [1964] (chan
on work completed up to that time. Summaries nel length divided by the meander-belt axis
of more recent work can be found in four col length), and all the point bars have super
lections of papers--Miall [ed. , 1978b] , imposed chute channels. No data are avail
Ethridge and Flores [eds., 1981], Collinson able on the ratio of bed load to suspended
and Lewin [eds., 1982] and Ethridge et al. load in the stream; however, the channel mor
[eds., 1987]--as well as the texts of Reading phology would indicate a rather large bed
[ed., 1986] and Galloway and Hobday [1983]. load component.
Variation of channel types. As shown in Meandering streams. As an alluvial valley
studies by Schumm [1981] and Jackson [1978], aggrades, Fisk [1947] has shown that the riv
river channels and their associated sedimen er commonly passes from a braided to a mean
tary deposits in alluvial valleys [zone 2 of dering pattern in response to rising base
Schumm, 1977] show great diversity, depending level, which decreases the slope of the
upon variations in water discharge and sedi stream. As the meandering channel evolves,
ment load, plus character of bedrock over the zone of meandering is confined to within
which stream flows, man's activities, and a zone much narrower than the confines of the
tectonic/eustatic influences. Nonetheless, two bounding valley walls. This zone, known
Schumm [1981; p. 23] asserts that all of the as the meander belt, may stay in a fixed po
alluvial channels on earth can be "placed sition for some time, with the levee and oth
within ••• five general categories." These er overbank deposits building up a platform
categories, which are illustrated in Figure higher in elevation than the rest of the
8, are: flood plain. During a major flood, it is
possible for the stream to break out into the
1) Straight channel with migrating sand lower flood plain and completely abandon the
waves. meander belt, a process known as avulsion
2) Straight channel with alternating lateral [Allen, 1965].
bars. Because the meander belt functions as a
3) Meandering channel. unit in response to a relatively uniform set
3a) Wider at bends than at crossings- of physical controls, it is useful to consid
chute channels across point bars. er the entire unit in a discussion of deposi
3b) Highly sinuous channel of equal width. tional models. Brown et al. [1973] segregat
4) Meandering-braiding transition. ed meander belts into coarse-grained and
5) Braided-stream pattern. fine-grained types, with the coarser-grained
Sa) Bar-braided, channels switch rapidly. belts normally having higher gradients and
5b) Multiple-channeled; anastomosing chan more flashy discharge.
nels stable. Much of the past work on modern point bars
has been in areas classified as fine-grained
Schumm and Khan [1972] demonstrated that all meander belts by Brown et al. [1973] [e.g.,
of these patterns could be produced experi Frazier and Osanik, 1961; Bernard and Major,
mentally in the laboratory by varying the 1963; Harms et al., 1963; Jackson, 1976]. A
gradient, sediment load, stream power, and depositional model for the idealized fine
type of sediment load transported by the grained meander-belt system [after Brown et
channel. al., 1973] is given in Figure 9A. According
Schumm [1981] also stressed the importance to Brown et al. [1973, p. 16], and reported
T371: 8