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STRATIGRAPHIC FRAMEWORK AND HEAVY
MINERAL RESOURCE POTENTIAL OF THE INNER
CONTINENTAL SHELF, CAPE FEAR AREA, NORTH
CAROLINA: FIRST INTERIM PROGRESS REPORT
NORTH CAROLINA GEOLOGICAL SURVEY
OPEN-FILE REPORT 91-3
DIVISION OF LAND RESOURCES
DEPARTMENT OF ENVIRONMENT, HEALTH,AND NATURAL RESOURCES
STRATIGRAPHIC FRAMEWORK AND HEAVY
MINERAL RESOURCE POTENTIAL OF THE INNER
CONTINENTAL SHELE CAPE FEAR AREA, NORTH
CAROLINA: FIRST INTERIM PROGRESS REPORT
by
Charles W . Hoffman, Patricia E. Gallagher, and Larry Zarra
DIVISION OF LAND RESOURCES
Charles H. Gardner, State Geologist
NORTH CAROLINA GEOLOGICAL SURVEY
OPEN-FILE REPORT 91-3
1991
srATE OF NORTH CAROLINA
JAMES G. MAKI'IN, GOVERNOR
DEPAKfMENT OF ENVIRONMENtHEALTH, AND NATURAL RESOURCES
WILLIAM W •COBE~ JR., SECRETARY
CONTENTS
Abstract 1Introduction 1Previous Work . 4Methodology.................. 5Results..................................................................................................................................... 6
General.... 6Lithologic Descriptions and Stratigraphic Correlations 6Heavy Minerals 13
Summary 17Acknowledgements 17References Cited 17
FIGURES
1 Regional location map 22 Detailed location map 33 Heavy-mineral distributions by location and water depth 144 Heavy-mineral distributions by lithology and age of sediment 155 Heavy-mineral distributions by combined age and lithology of sediment 16
TABLES
1 Lithologic and stratigraphic data for vibracore samples 72 Sample length, water depth, bulk weight, weight percent plus 10 mesh, and
weight percent heavy minerals for vibracore samples 10
APPENDIX
Grain size distribution of spiral light subsample for non-carbonatevibracore samples 19
Stratigraphic Framework and Heavy-Mineral Resource Potentialof the Inner Continental Shelf, Cape Fear Area, North Carolina:
First Interim Progress Report
by
Charles W. Hoffman, Patricia E. Gallagher, and Larry Zarra
ABSTRACT
This report presents results from the first phase of a multi-year study to definethe geologic framework and assess the potential for heavy-mineral resources of theinner continental shelf off southeastern North Carolina. Examination anddetermination of weight percent heavy minerals (S.G >2.96) has been completed for68 samples from 19 vibracores. Upper Cretaceous through Holocene age sedimentswere recovered in the vibracores. Lithologies include carbonates, muddy quartzsands, and clean quartz sands typical of continental shelf depositional settings. Theaverage weight percent heavy minerals for all samples (as a percent of the totalsample) was 0.57 percent with a range from 0.00 percent to 3.69 percent and astandard deviation of 0.59 percent. Although these numbers are not encouraging interms of the heavy-mineral resource potential, more work is needed before makinga definitive assessment.
INTRODUCTION
This report presents an interim review of progress for the initial phase of amulti-year research project planned to develop an integrated geologic frameworkand assess the potential for heavy-mineral resources of the inner continental shelfoff southeastern North Carolina (Figures 1 and 2). The overall effort is a jointproject by the North Carolina Geological Survey (NCGS), the U. S. GeologicalSurvey (USGS), and North Carolina State University. Partial funding for the workis provided through a cooperative agreement between the U. S. Department of theInterior, Minerals Management Service (MMS) and the Continental MarginsCommittee of the Association of American State Geologists (AASG). The NorthCarolina Department of Environment, Health, and Natural Resources is aparticipant in the program by virtue of a subagreement administered andcoordinated for MMS by the University of Texas - Bureau of Economic Geology. Theremaining support is being provided by the participating research organizations.The MMS-AASG cooperative agreement covering work reported herein is number14-12-0001-30432; the subagreement number is 30432-NC.
This report presents lithologic, biostratigraphic, and heavy-mineral dataderived from study of a set of vibracores (Figures 1 and 2) and compares the results
1
o 10 20 30
Kilometers
...•:.
/./dl((Y ,;;1;
,../"/ @2002
Onslow Bay
~ AREA OF FIGURE 2
710
3:Nautical ~i:~>//'/....:•........;"
Figure 1. Map showing location and USGS core number for two vibracores innorthern Onslow Bay that were used in this study.
2
~
~~ ~
Wilmington
......................................................···························1·························· .
4~/34°20'N
b"~/:::/>... 1
r-.~ ~.\" l
/ dlS~f \!I:
. '/r'C!liS9!34.10'N ..
)/ 1149 ~~
A~46@@ eli-:"':~ :.0 ~
················································1····· , ························1··· J~i····ff~~···································.··· 34·00·N .
. . .:~·05
•.••••
••••.•.••.••.•••••.••••.•••.•w •••w •., .•+.:.:.~..A ·/··· I Om ::: : '1' , : :. ~.{.... 792
~ / ... ,..... ~ i @ \~. : G>:go 1 j @ ~......: 732\!1 : 755 ';,,: ..': :
·"'!:···················i:~~;:;····u u............~,··'''';{,:~~C~~~EA"R··u u u'u33.S0.Nu74~ 1 <... ~ @@ : : .:.~ '.
738@ I 177 i'@~ t~
...u.....u......u.,uu...u.uuu·lu.....ulu .. ·t:~~!;t~~.si;···········"UU33.40.N.u10 Nautical Miles 1 . !
I I' !
Figure 2. Map showing location and USGS core number for vibracores in the CapeFear area that were used in this study.
3
to an earlier reconnaissance study in which the vibracores were collected.Subsequent phases of our research will integrate this initial data and additionalvibracore data with a shallow high-resolution seismic stratigraphic model toprovide a three-dimensional geologic framework of the region. Within such aframework, we expect to be able to provide a relatively definitive assessment of thepotential for heavy-mineral resources.
The initial work reported here suffered setbacks due to staff turnover in midproject (requiring additional training of new staff) and to the discovery ofcontamination in several heavy-mineral concentrates during microscopic andgeochemical analyses. To compensate for this processing error by a subcontractor,vibracore material reserved for archiving was used to generate new heavy-mineralconcentrates for determination of weight percent heavy minerals. The weightpercent gravel (plus 10 mesh) determined for this second set of samples is reportedherein. Core photographs and lithologic descriptions of the vibracores, made priorto any processing, were not affected by this error. Grain size distribution datagenerated from the spiral reject or "spiral light" fraction on the original samples wasjudged not to be affected by the sample handling error.
PREVIOUS WORK
The cores examined in this initial phase of study are part of a group of 114 corestaken in the Cape Fear region by the U. S. Army Corps of Engineers CoastalEngineering Research Center (CERC) as part of their Inner Continental ShelfSediment and Structure (ICON) program. The ICON cores ultimately came into thecustody of the USGS which, in turn, provided them to the NCGS for this research.The ICON program investigated sand aggregate resources of the eastern U. S.continental shelf. Two reports, Meisburger (1977) and Meisburger (1979), wereproduced as a result of the North Carolina portion of the ICON study. The first ofthese two reports assessed aggregate resource potential and identified severalpotential borrow areas for beach nourishment sand. The second report presented areconnaissance description of the geology of the inner continental shelf within thesurvey area based on shallow high-resolution seismic data, and subsamples fromthe vibracores. Lithologic descriptions, textural classification, and limitedbiostratigraphic data were generated from the vibracore subsamples. Meisburgercompiled the data set and presented the distributions of sediment textures andchronostratigraphic and seismic stratigraphic units on a series of small-scale maps(approximately 1:420,000 scale).
From Meisburger (1979), Hine and Snyder (1985), and Snyder (1982) we knowthat the geology of the study area is relatively complex. Numerous UpperCretaceous through Quaternary geologic units outcrop on the inner shelf of OnslowBay, Long Bay, and the intervening Frying Pan Shoals. These units are comprised ofdominantly carbonate, mixed carbonate-siliciclastic, and purely siliciclastic
4
sediments. Most of the units that occur on the inner shelf have updip extensionsthat either crop out or are known within the shallow subsurface of the emergedCoastal Plain adjacent to the study area (Zarra, 1991). During relative lowstands ofsea level in the Quaternary, numerous paleofluvial channels were incised into theTertiary and Cretaceous sediments. These channels were filled by bioclastic andsiliciclastic sediment.
Grosz and others (1990) analyzed a broad sampling of surficial sediments fromthe continental shelf off North Carolina including the region under study here.They found that samples from the southern North Carolina inner shelf region(water depth less than 20 meters (65 feet» averaged 1.2 weight percent heavyminerals as a part of the total sample with a range of 0.1 percent to 3.3 percent.. Noattempt was made to relate these samples to known geologic units.
MEfHODOLOGY
The vibracores analyzed for this report were opened, photographed, anddescribed by NCGS staff. Procedures for handling the cores, numbering samples,and processing them for sedimentological and mineralogical data generally followthose set forth in Grosz, Berquist, and Fischler (1990). Core photos, lab notebooks,paleontologic slides, archive samples and other basic data from the project arecurrently stored at the Coastal Plain Office and Sample Repository facility of theNCGS in Raleigh. Permanent storage is expected to be under the purview of theUSGS. Parties interested in these materials may contact the lead author foradditional information.
A total of 20 vibracores comprising 72 samples were examined, processed, andanalyzed for this portion of the study. One core, number 732R, contained numerousartifacts in the upper half and was determined not to be representative of thegeology of the site; therefore it was eliminated from the study. This core was areplicate sample of core number 732 which contained a markedly different lithologyfrom number 732R. Vibracores ranged from about 4 meters to 6 meters (13 to 20 feet)long. Cores were subdivided into two, three, or four samples about 1 to 2 meters (3to 6 feet) long. The average sample length was 1.5 meters (5 feet). Vibracore samplesare designated by the core number (for example, 725 or 1124), followed by 11.1", 11.2",and so on to indicate the uppermost and subsequently lower sections, respectively.
The vibracores were cut lengthwise on a static blade cutter, then werephotographed, described, and subsampled. Subsamples provided a 300- to SOD-gramarchive sample and a sample to process for micropaleontologic analysis. Theremaining vibracore material was weighed and:
• wet sieved through a U. S. Standard 10-mesh screen (2 mIn, -1 Phi)• the pius 10-mesh fraction was dried, weighed, and described.
5
• the minus 10-mesh fraction was passed through a 3-turn Humphreys spiral toprovide an initial concentration of the heavy-mineral fraction.
• a representative subsample taken from the IIspiral light" fraction was dried,weighed, and a sink/float test was performed in acetylene tetrabromide <s.g.2.96} - the weight percent heavy minerals in the aliquot was extrapolated todetermine the amount of heavy minerals that were rejected by the spiral.
• grain size distribution analysis was performed on the spiral light fraction• a sink/float test was performed on the "spiral heavy" fraction (also in acetylene
tetrabromide) to recover the main component of the heavy-mineral fraction.
Magnetic fractionation and mineralogic analysis of the heavy-mineralconcentrates obtained by heavy liquid separations will be part of the next phase ofthis study.
RESULTS
General
Tables 1 and 2 present the primary data developed during this phase of thestudy. Derivative data and summaries of the Appendix data are provided in thefigures and the appendix referenced below. The lithologies and stratigraphic unitsidentified from the vibracores are consistent with what was anticipated from theprevious work of Meisburger (1979). Differences can largely be attributed to the factthat the previous study of lithologies, microfauna, and seismic data was of a purelyreconnaissance nature. This study is more comprehensive and involves detailedexamination and processing of complete vibracore sections.
Refinement of Meisburger's stratigraphic interpretations are primarily withinsediments he reported as being Pliocene to Holocene age. Several cores thatMeisburger assigned to his Holo/Pleistocene unit, specifically numbers 738 (CERC29), 740 (CERC 13), 771 (CERC 46), 773 (CERC 63), and 783 (CERC 53), are hereinassigned either Pliocene or Pliocene/Pleistocene ages. In cores 1140 (CERC 79) and1154 (CERC 106) we differentiate a Pliocene unit within the upper part of the corewhereas Meisburger's reported the entire core to contain Oligocene strata.
Lithologic Descriptions and Stratigraphic Correlations
In several cores we can establish correlation to onshore lithostratigraphic unitsby lithologic criteria backed up with foraminiferal paleontologic data. The lowertwo samples from core 724 contained phosphorite sand of the Pungo RiverFormation (lower to middle Miocene). Core 732 contained fine to medium-grainedcalcareous silty sand of the Peedee Formation (Upper Cretaceous). Core 755 wascomprised of bryozoan biomicrudite of the Comfort Member of the Castle HayneFormation (middle Eocene), and core 2002 was comprised of sandy, molluscan-mold
6
Tab
le1.
Lit
holo
gic
and
stra
tigr
aphi
cda
tafo
rvi
brac
ore
sam
ples
.
SA
MP
.C
ER
eS
HO
RT
LIT
HO
LO
GIC
DE
SC
RIP
TIO
NS
TR
AT
IGR
AP
HIC
NO
.N
O.
UN
IT
724.
195
mud
dytsa
ndy
shel
lhas
hPl
ioce
ne
724.
2m
uddy
,slig
htly
shel
ly,p
oorl
yso
rted
,med
ium
-gra
ined
phos
phat
icsa
ndM
ioce
ne(P
ungo
Riv
erFm
.)
724.
3m
uddy
,slig
htly
shel
ly,p
oorl
yso
rted
,med
ium
-gra
ined
phos
phat
icsa
ndM
ioce
ne(p
ungo
Riv
erFm
.)
732.
14
2m
uddy
,poo
rly
sort
ed,m
ediu
msa
ndw
ithsh
elly
and
part
ially
indu
rate
dzo
nes
Cre
tace
ous
(Pee
dee
Fm
.)
732.
2m
uddy
,mod
erat
ely
sort
ed,m
ediu
msa
ndC
reta
ceou
s(p
eede
eFm
.)
732.
3m
uddy
,mod
erat
ely
wel
lsor
ted,
fme
sand
Cre
tace
ous
(pee
dee
Fm
.)
738.
129
shel
ly,s
ilty,
med
ium
sand
Plio
/Ple
isto
cene
738.
2sl
ight
lysh
elly
,silt
y,fm
esa
ndPl
ioJP
leis
toee
ne
738.
3si
ltyfm
esa
ndPl
io/p
leis
toce
ne
~73
8.4
silty
fine
sand
Plio
/ple
isto
eene
740.
113
mud
dy,m
oder
atel
yw
ells
orte
d,sh
elly
med
ium
sand
Plio
cene
740.
2bi
omic
rudi
tePl
ioce
ne
740.
3bi
omic
rudi
tePl
ioce
ne75
5.1
19br
yozo
anbi
omic
rudi
teM
.Eoc
ene
(Cas
tleH
ayne
Fm.)
755.
2br
yozo
anbi
omic
rudi
teM
.Eoc
ene
(Cas
tleH
ayne
Fm.)
771.
146
slig
htly
shel
ly,w
ells
orte
d,fi
nesa
ndPl
io/p
leis
toee
ne
771.
2sl
ight
lysh
elly
,wel
lsor
ted,
fme
sand
Plio
/Ple
isto
eene
771.
3sl
ight
lysh
elly
,wel
lsor
ted,
fine
tom
ediu
msa
ndw
ithcl
ayle
nses
Plio
/Ple
isto
cene
771.
4sl
ight
lysh
elly
,wel
lsor
ted,
med
ium
sand
with
clay
lens
esPl
iolP
leis
toce
ne77
3.1
63sl
ight
lysh
elly
tw
ells
orte
d,fi
nesa
ndPl
ioce
ne
773.
2sh
elly
,wel
lsor
ted,
med
ium
sand
;4-c
m-t
hick
cla
yle
nsat
248-
252
emP
lioc
ene
773.
3m
uddy
,slig
htly
shel
ly,m
oder
atel
yw
ells
orte
d,fi
nesa
ndPl
ioce
ne
777.
158
shel
ly,w
ells
oned
,med
ium
sand
Hol
o/Pl
eist
oeen
e77
7.2
shel
lytw
ells
orte
d,m
ediu
msa
ndH
olo/
plei
stoc
ene
777.
3sh
elly
,wel
lsor
ted,
med
ium
sand
Hol
o/Pl
eist
ocen
e77
7.4
shel
ly,w
ells
orte
d,m
ediu
msa
ndH
olo/
plei
stoe
ene
Tab
le1.
Lith
olog
ican
dst
rati
grap
hic
data
for
vibr
acor
esa
mpl
es(c
onti
nued
).
SAM
P.C
ERe
SHO
RT
LIT
HO
LO
GIC
DE
SCR
IPT
ION
STR
AT
IGR
APH
ICN
O.
NO
.U
NIT
779.
162
shel
lytw
ells
orte
d,m
ediu
mto
coar
sesa
ndH
olo/
plei
stoe
ene
779.
2sh
elly
tw
ells
orte
d,m
ediu
mto
coar
sesa
ndH
olo/
Plei
stoe
ene
779.
3sh
elly
,wel
lsor
ted,
med
ium
toco
arse
sand
Hol
o/pl
eist
oeen
e
783.
153
slig
htly
shel
ly,m
uddy
,peb
bly,
poor
lyso
rted
,fin
esa
ndPl
ioce
ne
783.
2sl
ight
lysh
elly
,mud
dy,p
ebbl
y,po
orly
sort
ed,f
ine
sand
Plio
cene
783.
3m
uddy
,she
lly,p
oorl
yso
rted,
fme
tom
ediu
msa
nd;t
hin
inte
rbed
so
fcla
y&
coar
sesa
ndPl
ioce
ne78
3.4
mud
dy,s
andy
,poo
rly
sort
ed,s
hell
hash
Plio
cene
792.
177
bios
paru
dite
Plio
/ple
isto
eene
792.
2bi
orud
itePl
io/P
leis
toee
neC
D79
2..3
bios
paru
dite
Plio
/ple
isto
eene
792.
4bi
orud
itePl
io/P
leis
toee
ne80
5.1
70bi
orud
itePl
io/p
leis
toee
ne
805.
2bi
ospa
rudi
tePl
io/P
leis
toee
ne80
5.3
bios
paru
dite
Plio
/Ple
isto
eene
805.
4bi
ospa
rudi
tePl
io/P
leis
toce
ne11
40.1
79sh
elly
,wel
lsor
ted,
fme
tom
ediu
msa
ndPl
ioce
ne11
40.2
wel
lsor
ted,
carb
onat
e-ce
men
ted,
very
fine
tofin
esa
ndO
ligoc
ene
1140
..3w
ells
orte
d,ca
rbon
ate-
cem
ente
d,ve
ryfm
eto
fme
sand
Olig
ocen
e11
46.1
80si
lty,s
helly~
wel
lsoR
ed,f
ine
tom
ediu
msa
ndO
ligoc
ene
1146
.2si
lty,
shel
ly,w
ells
orte
d,fi
neto
med
ium
sand
Oli
goce
ne
1146
.3si
lty,s
helly
,wel
lsor
ted,
fine
tom
ediu
msa
ndO
ligoc
ene
1146
.4si
lty,s
helly
,wel
lsor
ted,
fine
sand
Oli
goce
ne
1149
.192
shel
ly,m
oder
atel
yw
ell
sort
ed,m
ediu
mto
coar
sesa
ndPl
eist
ocen
e11
49.2
shel
ly,s
ilty,
wel
lsor
ted,
med
ium
sand
with
carb
onat
ece
men
ted
stri
nger
sO
ligo
cene
1149
.3sh
elly
,silt
y,w
ells
orte
d,fi
neto
med
ium
sand
with
carb
onat
ece
men
ted
strin
gers
Olig
ocen
e11
49.4
shel
ly,s
ilty
,wel
lso
rted
,fin
eto
med
ium
sand
wit
hca
rbon
ate
cem
ente
dst
ring
ers
Oli
goce
ne
Tab
le1.
Lit
holo
gic
and
stra
tigr
aphi
cda
tafo
rvi
brac
ore
sam
ples
(con
tinu
ed).
SAM
P.C
ERe
SHO
RT
LIT
HO
LO
GIC
DE
SCR
IPT
ION
STR
AT
IGR
APH
ICN
O.
NO
.U
NIT
1154
.110
6sh
elly
,wel
lsor
ted,
fme
sand
Plio
cene
1154
.2sh
elly
,peb
blyt
poor
lyso
rted
,fin
eto
med
ium
sand
Plio
cene
1154
.3sh
elly
,slig
htly
mud
dy,p
oorl
yso
ned,
fine
tom
ediu
msa
ndO
ligoc
ene
1154
.4sh
elly
,mud
dy,p
oorl
yso
rted
,fm
eto
med
ium
sand
Olig
ocen
e11
59.1
84sl
ight
lysh
elly
,silt
yw
ells
orte
d,fi
nesa
ndO
ligoc
ene
1159
.2sl
ight
lysh
elly
,silt
yw
ells
orte
d,fin
esa
ndO
ligoc
ene
1159
.3sl
ight
lysh
elly
,silt
yw
ells
orte
d,fi
nesa
ndO
ligoc
ene
1159
.4sl
ight
lysh
elly
,silt
yw
ells
orte
d,fi
nesa
ndO
ligoc
ene
2001
R.l
73m
uddy
,por
lyso
rted
,she
lly,f
me
tom
ediu
msa
nd;w
hole
shel
lsPl
io/p
leis
toce
ne
co20
01R
.2bi
ospa
rudi
tePl
iolP
leis
toee
ne20
01R
.3bi
ospa
rudi
tePl
io/p
leis
toee
ne20
01R
.4bi
ospa
rite
Plio
/ple
isto
eene
2002
.110
2sa
ndy,
mol
lusc
an-m
old
bios
paru
dite
Olig
ocen
e20
02.2
sand
y,m
ollu
scan
-mol
dbi
ospa
rudi
teO
ligoc
ene
2002
.3sa
ndy,
mol
lusc
an-m
old
bios
paru
dite
Olig
ocen
e20
02.4
sand
y,m
ollu
scan
-mol
dbi
ospa
rudi
teO
ligoc
ene
Table 2. Sample length, water depth, bulk weight, weight percent plus 10 mesh, andweight percent heavy minerals for vibracore samples.
SAMPLE SAMPLE WATER BULK +10 TOTALHMNUMBER LENGTH DEPTH WT. MESH (WT%OF
(em) (fl) (g) (WT%) BULK SAMPLE)724.1 206 51 4,422 30.5% 0.44%724.2 177 2,596 3.9% 0.64%724.3 157 2,155 0.8% 1.00%732.1 154 40 4,025 48.0% 0.23%732.2 154 2,871 5.8% 0.21%732.3 126 1,982 17.3% 0.16%738.1 220 58 3,933 15.3% 0.58%738.2 105 2,309 2.5% 0.67%738.3 156 3,099 0.0% 0.83%738.4 130 2,523 0.0% 0.62%740.1 141 53 3,007 3.7% 0.87%740.2 183 3,140 62.9% 0.03%740.3 202 5,049 58.7% 0.02%755.1 176 46 4,634 0.4% 0.09%755.2 185 3,821 43.7% 0.05%771.1 140 32 2,553 0.5% 1.28%771.2 161 3,490 0.2% 0.47%771.3 152 3,157 0.7% 0.65%771.4 170 3,798 3.1% 0.37%773.1 222 41 3,477 0.5% 0.44%773.2 99 1,297 5.3% 0.35%773.3 123 2,165 1.2% 1.09%777.1 153 36 2,712 0.8% 0.41%777.2 155 2,829 1.9% 0.53%777.3 133 1,445 0.8% 0.42%777.4 128 2,096 1.0% 0.36%779.1 109 23 1,549 1.0% 0.38%779.2 112 1,943 1.3% 0.31%779.3 142 2,292 0.6% 0.26%783.1 162 37 3,181 5.5% 0.62%783.2 156 2,447 3.4% 0.65%783.3 144 2,010 6.4% 0.77%783.4 152 2,863 23.6% 0.34%792.1 149 57 3,573 3.6% 0.04%792.2 100 1,763 18.0% 0.00%792.3 145 2,936 64.9% 0.01%792.4 136 2,730 9.2% 0.03%
10
Table 2. Sample length, water depth, bulk weight, weight percent plus 10 mesh, andweight percent heavy minerals for vibracore samples (continued).
SAMPLE SAMPLE WATER BULK +10 TOTALHMNUMBER LENGTH DEPTH WT. MESH (WT%OF
(em) (ft) (g) (WT%) BULK SAMPLE)805.1 131 43 1,949 38.6% 0.05%805.2 130 2,216 5.1% 0.01%805.3 163 3,095 52.5% 0.02%805.4 135 2,479 88.0% 0.01%
1140.1 190 44 4,135 1.3% 0.65%1140.2 122 2,361 9.1% 0.44%1140.3 148 2,570 10.2% 0.54%1146.1 151 59 2,600 3.3% 0.74%1146.2 148 2,554 5.1% 0.50%1146.3 163 3,322 0.6% 0.77%1146.4 152 4,065 0.0% 0.81%1149.1 104 44 856 6.5% 0.32%1149.2 162 3,827 8.4% 0.29%1149.3 153 3,514 0.2% 0.32%1149.4 156 3,803 0.0% 0.26%1154.1 127 46 2,346 2.5% 0.38%1154.2 140 2,738 5.5% 0.43%1154.3 185 1,447 4.1% 2.45%1154.4 156 2,662 0.1% 1.40%1159.1 151 55 1,363 0.3% 3.69%1159.2 159 3,218 0.0% 1.52%1159.3 152 3,203 0.2% 1.52%1159.4 93 2,065 0.1% 0.87%
2001R.l 203 40 1,586 33.9% 1.12%2001R.2 149 3,001 58.4% 0.02%2001R.3 145 2,695 63.7% 0.03%2001R.4 93 1,759 83.7% 0.01%
2002.1 152 42 3,063 26.3% 0.38%2002.2 155 3,010 13.4% 0.41%2002.3 152 3,377 36.2% 0.39%2002.4 146 3,956 26.0% 0.47%
AVERAGE 15.16% 0.54%MINIMUM 00.03% 0.00%
MAXIMUM 87.98% 3.69%STANDARD DEVIATION 22.44% 0.59%
11
biosparudite of the River Bend Formation (Oligocene).
Cores 1146 and 1159 and the lower parts of cores 1140, 1149, and 1154 contain adistinctive lithologic unit comprised of typically clayey, fine- to very finegrained,well to very well sorted quartz sand of Oligocene age. Locally, the sand islithified by carbonate cement and contains sparse, very fine-grained dolomiterhombohedrons. Based on planktic foraminifera present in core 1146, the unit isbiostratigraphically correlative with the River Bend Formation. However, nosimilar onshore lithofacies has been recognized.
Cores 792, 805, and the lower parts of 740 and 2001R contain Pliocene orPliocene/Pleistocene bioclastic calcareous sediments. Correlation of these units withestablished lithostratigraphic units onshore is not possible with the available data.Onshore, the lower to middle Pliocene Duplin Formation, the late Pliocene BearBluff Formation, and the lowermost Pleistocene Waccamaw Formation all havecarbonate facies. We expect to be able to differentiate these units in future phases ofthe study by conducting more detailed paleontologic analyses and by furtherdeveloping the geologic framework with seismic data and with the examination andanalysis of additional vibracores. Snyder (1982) and Meisburger (1979) haverecognized Pliocene and younger carbonate rocks on the inner to middle shelf ofsouthern Onslow Bay. They report them to occur as "caps" or "highs" on theseafloor with abrupt escarpments on one or more sides or, alternatively, as channelfill sequences. Either or both of these settings are considered likely for the lateTertiary and Quaternary bioclastic sediments obtained from these vibracores.
The Pliocene and Pliocene/Pleistocene is also represented in the vibracores ofthis study by muddy, typically poorly sorted, slightly to very shelly quartz sands andby relatively "clean", well sorted quartz sands. The muddy, quartz sand lithologyoccurs in cores 738, and 783 and the upper parts of cores 724, 740, and 2001R. Thewell sorted quartz sands occur in cores 773 and 771 and the upper part of core 1154.As with the Pliocene to Pleistocene age bioclastic sediments, these siliciclasticsediments are facies likely correlative with the Duplin, Bear Bluff, and WaccamawFormations; but the specific correlations can not be resolved with the available data.Younger units (middle to late Pleistocene age) may also be equivalent to parts ofthese sands. Stratigraphic correlation within this part of the section, however, isquite tenuous due to poor faunal control and a less well-establishedlithostratigraphy onshore.
A final sediment type recovered in the vibracores was unconsolidated, wellsorted, medium to coarse quartz sands of Holo/Pleistocene age. These occur in cores777 and 779 and appear to represent an active facies of Frying Pan Shoals.
",The grain size distribution of the minus 10-mesh fraction of the vibracore
samples is not specifically analyzed or discussed herein. The data for non-carbonate
12
samples are presented in the Appendix as simple histograms of weight percent foreach size class. The histograms, when considered along with the weight percentgravel shown in Table 2, serve to generally characterize sedimentary textures andprovide graphical comparisons of the samples. It should be noted however, that thesieving and spiraling processes do not recover the predominantly clay-sized fractionthat goes into suspension. Formal textural classification of the samples remains anoption for further studies, but will require processing the only remaining archivematerial.
Heavy Minerals
Table 2 shows the weight percent heavy minerals (S.G >2.96) for each sampleexpressed as a percent of the total sample. The average weight percent for allsamples was 0.57 percent with a range from 0.00 percent to 3.69 percent and astandard deviation of 0.59 percent. Although the average weight percent heavyminerals value is not suggestive of a good potential for heavy-mineral resources,conclusive judgment of the potential for resources based on such a small anddiverse sampling over such a large area would be premature. Determination of thequality of the heavy-mineral concentrates (that is the abundance of the variousspecies) is yet to be done. Additionally, many more vibracores from the study area,some representing stratigraphic units or depositional settings not tested by thisinitial set of cores, are yet to be examined.
The weight percent heavy minerals reported for the Cape Fear area in Groszand others (1990) are in line with the values obtained in this initial work. As aresult of that earlier work, one of the chief premises of continued research in thisregion is that unique conditions that are favorable for the development of heavymineral deposits may exist locally and that the potential for heavy-mineralresources in the area can not be dismissed without more thorough testing.
The weight percent heavy minerals data for this first set of vibracores isillustrated versus several parameters in Figures 3, 4, and 5. In most cases, thenumber of members (n) in a given class are not sufficient to permit meaningfulinterpretations regarding the heavy-minerals content of that group. Classes havingless than three members were not considered. These data are displayed simply forthe purpose of organizing the results according to a variety of logical parameters. Asadditional vibracores are opened and data are added to these or similar displays,systematic patterns of heavy-minerals distribution may emerge.
As shown in Figure 3, the distribution of heavy minerals does not seem to besignificantly affected by either the geographic location of or the water depth at thevibracore site. In Figure 4, part A, the distribution of heavy minerals is shownversus lithology. Not surprisingly, the heavy-mineral content of quartz sands ismarkedly higher than that of the carbonates. Figure 4, part B, presents the
13
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ure
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8)
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16
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distribution of heavy minerals according to the age of the sediment. Somedifferentiation is evident by this graph. Namely, Oligocene age material (despitefour carbonate samples weighting the average down) is approximately double anyother category. A combination of both age and lithology is used in Figure 5 tocategorize heavy-mineral content of these samples. A single core, number 1159which contains clean quartz sand of Oligocene age, stands out on the graph.Otherwise, no patterns emerge from this graph that are not evident from thepreceding graphs of these same parameters.
SUMMARY
The 19 vibracores examined as part of this study provide an initial body of datathat will be expanded and refined in ongoing and forthcoming phases of thisresearch program. Although it is an important beginning and will be an integralpart of the ultimate understanding we expect to reach regarding the geologicframework and mineral resource potential of the study area, no definitiveconclusions can be drawn at this early juncture. The general conceptual frameworkand mineral resource models suggested by previous reconnaissance work in theregion have not been appreciably altered or reinforced.
ACKNOWLEDGEMENTS
The cooperation of Andrew Grosz, who provided guidance, use of USGSlaboratory facilities, and comments on the manuscript is gratefully acknowledged.Steve Snyder of N. C. State University also provided assistance and cooperation forparts of this phase of research and commented on the manuscript. Michael Dixon,geologic technician with the NCGS, performed much of the sample processing. JoelHutwelker, N. C. State University Minerals Research Laboratory, provided grain sizedata on the spiral light fraction of the samples.
REFERENCES OTED
Grosz, A. E., Berquist, C. R., Jr., and Fischler, C. T., 1990, A procedure for assessingheavy-mineral resources potential of continental shelf sediments, in Berquist, C.R., Jr., editor, Heavy-mineral studies - Virginia inner continental shelf: VirginiaDivision of Mineral Resources Publication 103, p. 13-30.
Grosz, A E., Hoffman, C. W., Gallagher, P. E., Reid, J. C., and Hathaway, J. C., 1990,Heavy-mineral resource potential of surficial sediments on the AtlanticContinental Shelf offshore of North Carolina: a reconnaissance study: NorthCarolina Geological Survey Open-File Report 90-3, 58 p.
17
Hine, A. C., and Snyder, S. W., 1985, Coastal Lithosome preservation: evidence fromthe shoreface and inner continental shelf off Bogue Banks, North Carolina:Marine Geology, v. 63, p. 307-330.
Meisburger, E. E, 1977, Sand Resources on the inner Continental Shelf of the CapeFear region, North Carolina, U. S. Army Corps of Engineers, Coastal EngineeringResearch Center Technical Paper 77-11,20 p.
Meisburger, E. E, 1979, Reconnaissance geology of the inner Continental Shelf, CapeFear region, North Carolina, U. S. Army Corps of Engineers, Coastal EngineeringResearch Center Technical Paper 79-3, 135 p.
Snyder, S. W., 1982, Seismic stratigraphy within the Miocene Carolina phosphogenicprovince: chronostratigraphy, paleotopographic controls, sea-level cyclicity, GulfStream dynamics, and the resulting depositional framework [M. S. Thesis]:Chapel Hill, North Carolina, University of North Carolina at Chapel Hill, 183 p.
Zarra, Larry, 1991, Subsurface stratigraphic framework for Cenozoic strata inBrunswick and New Hanover Counties, North Carolina: North CarolinaGeological Survey Information Circular 27, 1 sheet.
18
APP
EN
DIX
-G
rain
size
dist
ribu
tion
ofsp
iral
ligh
tsub
sam
ple
forn
on-c
arbo
nate
vibr
acor
esa
mpl
es.
724.
172
4.2
zs.o
30.0
~20
.0~
25.0
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15.0
5:10
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t =c,:
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APP
EN
DIX
-G
rain
size
dist
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tion
ofs
pira
llig
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for
non-
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5
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APP
EN
DIX
-G
rain
size
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tion
ofs
pira
llig
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non-
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(con
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ed).
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3
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=20
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E(0
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(0)
APP
EN
DIX
-G
rain
size
dist
ribu
tion
ofsp
iral
ligh
tsub
sam
ple
for
non-
earb
onat
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brac
ore
sam
ples
(con
tinu
ed).
771.
277
1.3
45.0
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~~
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477
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~ CJ25
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EN
DIX
-G
rain
size
dist
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ofs
pira
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ple
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non-
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brac
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sam
ples
(con
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253.
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25>4
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GR
AIN
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E(0
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RA
INS
IZE
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777.
177
7.2
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50.0
45.0
45.0
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40.0
t335
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35.0
U~
30.0
~30
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.0~
25.0
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.0Eo-
! =20
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sa15
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15.0
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10.0
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0.0
0.0
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50.
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751.
251.
752.
252.
753.
253.
754.
25>4
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GR
AIN
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E(0
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RA
INS
IZE
(0)
APP
EN
DIX
-G
rain
size
dist
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tion
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iral
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60.0
U ~50
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40.0
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30.0
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50.
000.
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251.
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252.
753.
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25>4
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GR
AIN
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777.
3
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10.0 0.0 -1
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50.
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251.
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753.
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GR
AIN
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779.
177
9.2
60.0
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~ U40
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l:'iii
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30.0
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20.0
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.00
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50.
000.
751.
251.
75u
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75
GR
AIN
SIZ
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3.25
3.75
4.25
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2S
50.0
45.0
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35.0
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0I:lo
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II
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0.00
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1.75
2.25
2.75
3.25
3.75
4.25
>4.2
5
GR
AIN
SIZ
E(0
)
APP
EN
DIX
-G
rain
size
dist
ribu
tion
ofs
pira
llig
htsu
bsam
ple
for
non-
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onat
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brac
ore
sam
ples
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tinu
ed).
779.
3
60.0
Eo-
50.0
~ U4
0.0
I:IC ~ =-30
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- r;%
0.0
I-f~ ~
10.0 0.0 -L
OO
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S0.
000.
751.
251.
752.
252.
75
r\)
GR
AIN
SIZ
E(0
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01
783.
1
35.0
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Z ~zs
.oU ~2
0.0
=-- !C15
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5:210
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s.o 0.0
3.25
3.75
4.1S
>4.
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OG
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000.
751.
251.
752.
252.
753.
253.
754.
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GR
AIN
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E(0
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783.
278
3.3
25.0
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UU
20.0
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0=: ~
=-=--
15.0
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friIi
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0~
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5.0
0.0
0.0
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75:u
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4.25
GR
AIN
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E(0
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RA
INS
IZE
(0)
APP
EN
DIX
-G
rain
size
dist
ribu
tion
ofs
pira
llig
htsu
bsam
ple
for
non-
carb
onat
evi
brac
ore
sam
ples
(con
tinu
ed).
783.
411
40.1
5.0
10.0
1.25
1.75
us
2.75
3.25
3.75
4.25
>4.2
5
GR
AIN
SIZ
E(0
)
50.0
45.0
~40
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fj35
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25.0
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0.0
I'":':-:-:-:-:-:-l~~:6~~::t
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0.00
0.75
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1.75
us
2.75
3.25
3.75
4.25
>4.2
5
GR
AIN
SIZ
E(0
)
15.0
25.0 0.0
Ii
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0-0
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0.00
0.75
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1 E ~ ~ ~
ro en
1140
.211
40.3
US
1.75
2.25
2.75
3.25
3.75
4.25
:>4.
25
GR
AIN
SIZ
E(0
)
40.0
e-.35
.0
~30
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U25
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1~
20.0
e-. ::c15
.00 ~
10.0
~5.
0
0.0 -L
OO-0
.25
0.00
0.75
2.2S
2.75
3.25
3.75
4.25
>4.2
5
GR
AIN
SIZ
E(0
)
40.0
35.0
~30
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~25.0
~ ~20
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!C15
.00 ~
10.0
~5.
0
0.0 -1
.00
-0.2
50.
000.
751.
251.
75
APP
EN
DIX
-G
rain
size
dist
ribu
tion
ofs
pira
llig
htsu
bsam
ple
for
non-
carb
onat
evi
brac
ore
sam
ples
(con
tinu
ed).
1146
.111
46.2
35.0
40.0
~30.0
~35
.0
\"iIi
l25.
0'iI
il3
0.0
U~25.0
=20
.0r.J
il~
~21
M
~15
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10.0
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0~
5.0
0.0
II
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0.0
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0.75
1.25
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us
2..7
53.
253.
754.
25>
4.25
-1.0
0-G
.2S
0.00
0.75
L2
51.
752.
2S2.
.75
:US
3.75
4.2S
>4.
25
GR
AIN
SIZ
E(0
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RA
INS
IZE
(0)
I\)
......
1146
.311
46.4
35.0
40.0
Eo-
30.0
Eo-
3s.o
Z~
30.0
~25
.0U
~25.
0=2
0.0
~~
~20
.0
t:15
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- =15
.0~
10.0
0 S310
.0~
5.0
~5.
0
0.0
...
0.0
-1.0
0-0
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0.00
0.75
L25
1.75
%.2
52.
.75
:us
3.75
.us
>4.
25-L
OO
-0.2
50.
000.
75L
2S1.
752.
252.
753.
253.
75.u
s>
4.25
GR
AIN
SIZ
E(0
)G
RA
INS
IZE
(0)
APP
EN
DIX
-G
rain
size
dist
ribu
tion
ofs
pira
llig
htsu
bsam
ple
for
non-
earb
onat
evi
brac
ore
sam
ples
(con
tinu
ed).
1149
.111
49.2
5.0
20.0
25.0
15.0
10.0
3s.o
Eo-
30.0
~ U =g,.. 5: o ; ~
0.0
II
iIh
»:.:·:·
»:jm
l-1
.00
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50.
000.
751.
251.
752.
252.
753.
2S3.
754.
25>4
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GR
AIN
SIZ
E(0
)
L25
1.75
us
2.75
3.2S
3.75
4.25
>4.2
S
GR
AIN
SIZ
E(0
)
40.0
~35
.0
riIi1
30.0
U l:lC25
.0riIi
11:
10.2
0.0
Eo- =
15.0
0 -r:r::I10.0
~5.
0
0.0 .L
OG
-0.2
50.
000.
75
I\)
(X)
5.0
25.0
20.0
15.0
10.0
35.0 0.0
II
II
-1.0
0-0
.25
0.00
0.75
1.25
1.75
2.25
2.75
3.25
3.75
4.2S
>U
S
GR
AIN
SIZ
E(0
)
1149
.4
Eo-
30.0
~ U ~ 1:10. ~ o ~ ~
1149
.3
35.0
Eo-
30.0
Z r:r::I
25.0
U =20.0
1:10. !2
15.0
0 ~10
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~5.
0
0.0 -L
OO
-O.1
S0.
000.
75L
251.
752.
252.
753.
2S3.
754.
25>4
.25
GR
AIN
SIZ
E(0
)
APP
EN
DIX
-G
rain
size
disb
ibut
ion
ofs
pira
llig
htsu
bsam
ple
for
non-
earb
onat
evi
brac
ore
sam
ples
(con
tinu
ed).
1154
.111
54.2
10.0
45.0 5.0
0.0
~~~:i:iiiiiii~
-1.0
0-0
.25
0.00
0.75
1.25
1.75
us
2.75
3.25
3.75
4.25
>4.2
5
GR
AIN
SIZ
E(0
)
40.0
~35
.0~ U
30.0
=: Siril
zs.o
Q... E-c
zo.O
=Cl15
.0
&3 ~
us
1.75
us
2.75
3.2S
3.75
4.25
~4.25
GR
AIN
SIZ
E(0
)
4S.O
40.0
~35
.0Sir
il~
30.0
2:25.0
E-c
20.0
a15.
0~ ~
10.0 5.0
0.0 ·1
.00
.0.2
50.
000.
75
r\) co
1154
.311
54.4
-
70.0
80.0
E-t
60.0
E-c
70.0
;Z~
60.0
riIi150
.0U
~50
.0~
40.0
riIi1
Q...
Q...
40.0
~30
.0E-
t =30
.0
~zo.o
Cl ;
zo.o
~10
.0~
10.0
0.0
....
.....
.0.
0-L
OG
-D.2
50.
000.
751.
251.
75Z.
2S2.
753.
253.
754.
25:>
4.2S
-1.0
0-0
.25
0.00
0.75
1.25
1.75
Z.2S
2.75
3.25
3.75
4.25
>4.2
5
GR
AIN
SIZ
E(0
)G
RA
INS
IZE
(0)
APP
EN
DIX
-G
rain
size
dist
ribu
tion
ofsp
iral
ligh
tsub
sam
ple
for
non-
earb
onat
evi
brac
ore
sam
ples
(con
tinu
ed).
1159
.111
59.2
70.0
80.0
~60.0
70.0
i60
.0riI
i1so
.oU
U
E4M
cr::50
.0riIi1 ~40.0
~30.0
Eo- S
30.0
~20.0
1-004~
20.0
~10
.0~
10.0
0.0
0.0
-1.0
0-0
.25
0.00
0.75
1.25
1.75
2.25
2.75
3.25
3.75
4.25
>4.2
5-L
OO
-0.2
50.
000.
751.
251.
752.
252.
753.
253.
75.u
s>4
.25
GR
AIN
SIZ
E(0
)G
RA
INS
IZE
(0)
W a
1159
.311
59.4
70.0
..60
.0
~60
.0Eo
-50
.0Z
riIi150
.0riIi1
U~
40.0
gs4O
.G~
~~
30.0
~30
.0E-c =
5a20
.0Co
:'20
.01-0
04~
riIi1
~10
.0~
10.0
0.0
II
II
IJ
Ir·y..
..·........·
·,~·......
,.........'
Fw
....w··..
....·......
.....·····I
···w.·...
..w.,
0.0
-LO
O-0
.25
0.00
0.75
L25
1.75
2.25
2.75
3.25
3.75
4.25
>4.2
5-1
.00
-0.2
50.
000.
751.
251.
752.
252.
753.
253.
754.
25>4
.25
GR
AIN
SIZ
E(0
)G
RA
INS
IZE
(0)
APP
EN
DIX
-G
rain
size
dist
ribu
tion
ofs
pira
llig
htsu
bsam
ple
for
non-
earb
onat
evi
brac
ore
sam
ples
(con
tinu
ed).
2001
R.l
25.0
p..
Z20
.0~ U =1
5.0
g". p.. ::c
10.0
to' S ~
5.0 o.o~
·1.0
0-G
.2S
0.00
0.75
:L25
L75
2.25
%.7
53.
253.
754.
25>4
.25
GR
AIN
SIZ
E(0
)U
> ........
