Variations in the surface texture of suspended quartz - INFO-SED

Sedimentology (1987) 34,495-5 10
Variations in the surface texture of suspended quartz grains in the Loire River:
an SEM study
S . M A N I C K A M * and L . B A R B A R O U X t
Laboratoire de Gkologie Marine, Universite de Nantes, 2, rue de la Houssiniere, 44072 Nantes cedex, France
ABSTRACT
Statistical size distribution and scanning electron microscopic studies of suspended sand grains in the Loire
River at Montjean, France were carried out over a period of a year (hydrological cycle) to discern seasonal
variations. The sand fraction in suspension is better sorted during winter (average mean=0.69 mm,
median = 0 6 5 0 . 9 5 mm, sorting value, u = 1.1-1.35) and is dominated by quartzo-feldspathic minerals.
During summer, on the contrary, this fraction is rich in mica minerals and is poorly sorted (average
mean = 1.21 mm, median = 0.33-0.95 mm, sorting value, u = 1.4-2.0). The grain size of the coarser fraction
shows a tendency to increase with river discharge up to an optimum discharge of about
1000 m3 s - and thereafter decreases.
Scanning electron photomicroscopy of quartz grains from the suspended sand population indicates that
both mechanical and chemical features occur. The former (conchoidal fractures, mechanical fractures and
breakage) dominate in the samples collected near the water surface during winter floods and the latter
(solution pits, vermicular features, silica flowers, neogene silica and diatoms) in the samples from the
bottom during low summer flows. During summer, chemical action takes place on sediments prior to or
upon their deposition. Sediments that are resuspended during winter floods undergo mainly physical
processes (attrition/abrasion). Mixed surface features are, therefore, observed during average and low river
discharge. Inheritance of these surface features from the source area is, however, not completely excluded.
Thus, the history of quartz grains in suspension can be reconstructed from SEM exoscopic studies:
therefore, it can be proposed that the fluvial quartz grain surface textures result from a combination of
alternating chemical and physical processes.
’
RESUME
Cet article portera sur les variations mensuelles pour un an de la granulometrie, de la mineralogie et de
l’etat de surface (par MEB) des grains de quartz dans les fractions grossitres en suspension de la Loire a
Montjean, France. Les suspensions grossieres montrent le meilleur classement (moyenne = 0,69 mm,
mediane=0,65 a 0,95 mm, deviation standard, u = 1,1 a 1,35) lors de la periode hivernale ou elles sont a
dominante quartzo-feldspathiques. Elles ont, par contre, le classement le plus mavais (moyenne = 1,21 mm,
mediane = 0,33 a 0,95 mm, deviation standard, u = 1,4 a 2) en phiode estivale avec une richesse accrue en
micas. En outre, on observe une corr6lation positive de la valeur des medianes en fonction de l’augmentation
de debit, jusqu’a une valeur critique d’environ 1000 m3 s-’ au dela de laquelle cette relation disparait.
L’etude des surfaces des quartz au microscope Clectronique a balayage, revele des variations saisonnieres
Present addresses: *Ocean Data Centre, C. W.R., College
of Engineering, Anna University, Madras 600 025, India.
TUniversite de Provence, Laboratoire de Stratigraphie et de
Paleoecologie, Centre de Recherche sur l’evolution des
systemes biosedimentaires, J.E. CNRS No. 334 and CNRS
GRECO I C.O. No. 52, 13331 Marseille cedex 3, France.
495
496
Surface texture ofsuspended quartz
nettes. Les traces les plus rtcentes etant seules prises en compte, pour tliminer les effets d’htritage de traces
anciennes likes au contexte geologique et pedologique, on note que les traces de chocs et d’abrasion
mecanique dominent en ptriode hivernale, en crue. Les traces chimiques de faGonnement s’instaurent en
periode estivale, aux faibles debits d’etiage. Un faGonnement mixte s’exprime lors des saisons de transition
(automne, printemps). Une zonation verticale est de surcroit visible; ainsi, dans la tranche d’eau proche de
la surface, lors des premieres crues les traces mecaniques fraiches sont plus frequentes qu’en profondeur.
La reponse des sediments en suspension par rapport aux divers changements du milieu de transport est
donc acquise tres rapidement dans la nature; ceci est en bon accord avec les exptriences de laboratoire
recensees dans la litterature rtcente. L’ttude permet de preciser qu’il s’etablit tres vite un tquilibre
saisonnier d’ete et d’hiver, rompu lors des saisons de transition. Notre ttude a ete delicate, et ses rtsultats
ni simples ni univoques n’ont pu Ctre interprttts qu’en raison de travaux anttrieurs et fond& sur une
connaissance prtalable suffisante du contexte gtologique qui alimente le systeme fluvio-estuarien.
INTRODUCTION
Studies of detrital minerals, especially quartz grains,
with the scanning electron microscope (SEM) called
‘exoscopy’ (Le Ribault, 1975) are commonly applied
to the interpretation of depositional settings. Diverse
physical and chemical processes which attack quartz
grains are identified by examining the surface features
of these grains. These features have been analysed
and classified with respect to environmental and
hydrodynamic parameters by Barbaroux et al. (1972),
Krinsley & Doornkamp (1973), Le Ribault (1975) and
Prone (1980). By observing these surface textures,
many workers have tried to reconstruct ancient
sedimentary environments.
In the Loire River of France, Barbaroux et al. (1972)
noted three types of population. First, a small
population of unabraded quartz grains with regular
pits, fissures, cracks and slices of silica, which
originated from volcanic rocks (Upper Loire). Secondly, a population of grains with neogenic silica on
one side and solution pits on the other came from
pedogenic soils, and a third group with ‘v’ marks of
marine origin were derived from Mesozoic and
Cenozoic rocks (Middle Loire). Barbaroux (1980,
1982) and Brossk (1982) determined the pattern of
quartz sand surface features through Loire River
including its estuarine section by undertaking SEM
studies on bed-load sand deposits.
The purpose of the present study is to investigate
the seasonal variations in surface features present on
quartz grains in suspension.
STUDY LOCALITY A N D METHODS
This study was carried out in the Loire River at
MontjeanILoire, France where thelast gauging station
is situated at the point where the river enters a 90 km-
long estuary. Montjean/Loire is situated 972 km
downstream from the river’s source, and 140 km from
the Atlantic Ocean. At the sampling station the flow
is unidirectional and saline intrusion does not occur.
The small study area was chosen after consideration
of previous work on the Loire River (Barbaroux, 1980;
Brosse, 1982) because it is a transition zone between
the estuary and the river.
Bulk water sampling
Every month, nearly 10001 of water was collected
from 0.5 m above the river bed and 0.5 m below the
water surface of the river using a teflon pump. The
water was transported in 120 1 barrels to the laboratory
and decanted or centrifuged immediately for turbid
sediment extraction. During each sampling, velocity
and water level in the river were measured with a
current meter and a permanent level mark in the
channel respectively. The sampling period (May 1981May 1982) spanned a complete hydrological cycle
which included three major floods.
Separation of sand fractions
Turbid sediment or total suspended matter (TSM)
recovered from 1000 1 of water was wet sieved through
a 45 pm sieve (mesh). Only the coarser fraction (CF >
45 pm) is considered here. The finer fraction (FF<
45 pm) is described elsewhere (Manickam 1982a,
1983; Manickam, Barbaroux & Ottmann, 1985;
Barbaroux, Manickam & Yvon, 1983). The coarser
fraction (CF) was first dried and then treated with
dilute H 2 0 2to remove organic and inorganic matter.
Recovered sand grains were slowly attacked with
dilute HCl to remove coatings. These treatments left
merely a few grains of sand in the sample studied.
Only by measuring and counting individual grains
could the mean of median size of the sands in
497
S . Manickam and L. Barbaroux
winter is narrow [median > 06-0.95 mm, sorting
index (a)= 1.1-1.35, So= 1-25, variance (aZ)=0.20.61, whereas the curve for summer is broad [median = 0.33 to 0.95 mm; sorting index (a)= 1.4-2.0,
So=1.6, variance (a2)= 0.2-0.61. These results can
be explained in the following way. The winter floods
have coarser sand in suspension because of their
SEM analysis
substantial carrying capacity and because soil erosion
is more active in contributing coarser material.
The method followed here is outlined by Barbaroux et
However, during summer, the carrying capacity of the
al. (1972). Acid-treated quartz grains were classified
river is less and also becomes more variable. Sources
both morphologically and by size (Cailleux & Tricart,
also vary with local inputs and produce, by way of
1959), coated with gold by cathode pulverisation
aggregation of particles broader and more segmented
method (Selcier & Barreau, 1977) and scanned with a
curves with major breaks at 0.5 and 0.3 mm. As Leroy
JEOL scanning electron microscope at various mag(1981) has pointed out, line segments in cumulative
nifications.
curves may be mathematical artifacts, but here, where
the same procedure was applied for all samples, only
the summer group shows such segmentation; thereRESULTS
fore, we suggest that the breaks in the cumulative
curves reflect some contribution from local subGranulometry of sand grains in suspension
populations (Manickam, 1982b). General granuloDue to the meagre quantity of sand obtained in each
metric results are given in Table 1 and in Fig. 2. The
sample, size analyses (granulometry) by measuring
coarsest grain transported in suspension in the Loire
and counting-as described by Berthois (1954) &
River at Montjean was 5 6 m m in diameter. The
Barbaroux (1970)-were performed on the coarser
median size shows a slight tendency to increase with
fraction. In this method, grain size is measured with a
river discharge (Fig. 2) i.e., the maximum occurs
binocular microscope and grains are counted individduring the winter and the minimum during the
ually by size and classified into various size fractions.
summer. Statistical investigations (Table 2, Fig. 3)
These size fractions are then converted into cumulashow that for a whole population (including maximum
tive frequency curves and subsequently regrouped
size variations) the summer mean (8=0.69 mm) and
into two enclosed (enveloped) curves (Fig. 1) reprevariance (a2= 0.6) are about half of the winter values
senting summer and winter. The enclosed curve for
1.21 mm; a2= 1.54); whereas for the central
population (excluding the extreme variations) the
difference between the summer and winter means
declines and variance is far less pronounced (8
summer =0 5 6 mm;
winter =0.8 1 mm ; cr2 sum?m
mer=0.5; a2 winter=0.4). This difference can be
understood by examining the frequency curves in Fig.
3. The curves for summer are smooth and platykurtic
without dominant modes, whereas for winter they are
leptokurtic with dominant primary modes. Another
main difference is also observed for the whole winter
population, i.e.a bimodal curve in which the secondary
mode is related to the coarser fractions of the peak
E, 20
flood of January 1982.
u
During the spring-summer period, the sand fraction
is more micaceous (Table 3) and if the total suspended
0
30 2.0
1.0
0-5
0-2
0-1 coarser fraction is plotted against mica content an
inverse relationship is seen (Fig. 4a). On the contrary
Diameter d sand grairr (mm)
a
positive correlation exists between the quartzoFig. 1. Enclosed (enveloped) granulometric curves (25) of
feldspathic content and the total coarser fraction (Fig.
sands in suspension in the Loire River at Montjean (by
measuring and counting the grains).
4b). Thus, the mica and quartzo-feldspathic fractions
suspension be determined (it was impossible to find
out mean grain size for all samples, therefore median
is reported). However, as pointed out by Krinsley &
McCoy (1977), a very small number of sand grains are
sufficient to obtain representative surface textures.
(x=
t
8 r
t
x
1150
670
338
235
770
810
2320
3354
1360
1300
940
440
June 1981
July 1981
Aug. 1981
Sept. 1981
Autumn Winter
Oct. 1981
Nov. 1981
Dec. 1981
Jan. 1982
Feb. 1982
Mar. 1982
Spring
April 1982
May 1982
1.9
9.9
48
9.2
11.9
11.1
11.9
14.4
13.1
51
53
23
49
33
56
60
11.1
4.8
42
39
6.6
10.9
54
46
11.0
11.0
Dissolved
silica
(mg1-l)
63
51
TSM
(mg I-')
S = Surface, B = bottom, 8=average.
*Mainly micaceous sand.
B
+
1550
Average monthly
river discharge
(m3 s-')
Spring Summer
May 1981
+
Date
10
13
8
17
9
12
14
10
18
Coarse
Fraction
(%)
28
10.5
24
2s
37
25
28
39
22
38
41
32
40
41
(%)
Micas
17
8.5
8
6
4
21
22
17
33
20
18
23
24
22
Feldspars
(%)
24
-
(7%
Carbonate
49
57
68
69
42
71
so
44
45
(%I
Quartz
1.0
1.0
1.0
2.9
5.6
2.4
4.0
1.0
1.0
1.0
1.0
S 1.0
B 1.0
S 0.9
B 0.8
B
S
S
B
S
B
S
B
S
B
S
S
B
S
B
S
B
S
B
S
B
S
S
B
S
B
0.62
0.60
0.50
0.48
0.98
0.90
0.80
0.68
0.85
0.78
0.78
0.88
0.83
0.94
0.68
0.697
0.490
0.610
0.810
0.855
0.830
0.780
0.740
0.938
Maximum Median size Average
size
(mm)
ofMedians
(mm)
(mm)
* 1.210
Mean
size
(mm)
Table 1. Average monthly river discharge, TSM, Dissolved silica content Composition and Size measurements of sands in the Loire River at Montjean, France (Mainly
after Manickam, 1982a)
B;;
R
%
3
S . Manickam and L. Barbaroux
I
1
1982
1
1982
I
I
I
I
499
discharges which gives a lower sand content whereas
curve 2 is related to increasing stream flow which
gives more coarser material. Both curves 1 and 2 have
similar shapes with their respective maximum sand
supply in suspension (62% and 78%) near the mean
discharge of about 1000 m3 s - I . From the crest to
1500 m3 s-' a dilution effect is seen on the coarser
fraction and below 750 m3 s-' the river competence
is not enough to carry coarser sediments in suspension
despite the fact that there is a well-known trend
towards increasing total suspended material concentration. It seems that the supply of more quartzofeldspathic sand during winter becomes mainly
micaceous during summer due to small discharge. The
average median value of sand in suspension is 0.7 mm,
contrasting with previous studies (Berthois, 1971)
which found a negligible percentage of suspended
sand grains in the Loire River greater than 0.5 mm.
This may be an indication of a new cycle of erosion
which might have started since last decade.
In conclusion, quartzo-feldspathic grains with maximum diameters of approximately 1 mm (although
sometimes reaching 6 mm) could be transported in
suspension during large floods in the Loire River at
Montjean. The daily average velocity maximum of
1.74 m s - ' (January 13,1982-peakof flood) provides
sufficient competence.
$
1
Exoscopy of quartz grains with the scanning electron
microscope
0
0
1
Median grain size (mm)
Fig. 2. (a) Plot of the median grain size of suspended sand
and dissolved silica content with respect to river discharge
in the Loire River at Montjean; (b) Tentative correlation
between river discharge and granulometry of suspended
coarser fraction with respect to seasonal mineralogical
changes.
are inversely related. A closer look at the dischargemineralogy curve (Fig. 4c) shows that the river
discharges affect the suspended coarser-fraction variations, especially the quartzo-feldspathic supply.
Curve 1 is related to a group of decreasing river
Since only a few grains were present in each sample,
only two classes, large and small, were examined. The
number of grains studied varied with each season and
environment (Fig. 5). In total 520grains were scanned.
Morphologically, grains were categorized as wellrounded, rounded, sub-angular and angular (Cailleux
&Tricart, 1956).Only major characteristicsare shown,
synthesized and discussed here.
Principal grain-surface characters are summarized
in Fig. 6 and three main types of action are inferred :
physical, chemical and combined (or mixed) (Barbaroux et al., 1972; Le Ribault, 1975).
Dominant physical action
During winter floods (December-February) the TSM
concentration (121 mg 1- I ) attains its maximum value
(Manickam, 1982a; Manickam et al., 1985). The
turbulent currents (1.74 m s- ')occurring in this period
could fragment the suspended grains (see Moss,
500
Surface texture of suspended quartz
Table 2a. Statistics upon whole population
xfx
xf
General statistical parameters used = X
Class
limits
7.93-3.17
3.17-2.00
2.00-1.41
1.41-1.00
1.004.71
0.7 1-0.50
0.504.35
0.35-0.25
0.25-0.177
= -;
Mean class
Frequencies
A
5.55
2.59
1.70
1.20
0.86
0.60
0.42
0.30
0.21
30.8
6.68
2.90
1,452
0.73
0.366
0.180
0.090
0.044
c
AX,
Cf;m2
AX2
Summer
Winter
Summer
Winter
Summer
f;X~IW,
Ax,2(,, A X 2 ( W ,
-
2
2
-
11.1
5.17
0
10.845
16.245
3.025
0.850
-
-
0
9
19
5
1
10
9
4
1
-
2
-
25
39
1.205
8.55
5.445
1.70
0.30
-
-
17.2
47.2
-
-
1.452
7.30
3.29
0.72
0.09
Winter
61.6
13.4
0
13.1
13.9
1.8
0.36
-
-
12.85
Summer
Winter
V;XJ2l.,
v;XJZ1W)
-
123.2
26.7
0
117.7
263.9
9.15
0.72
-
1.45
73.10
29.64
2.89
0.09
-
-
104.2
107.2
541.37
Winter
Summer
A K 2 ( W ,
V ; ~ J Z l S )
Summer: Mean x~,,,,,,,=O~688; Variance uz (,,,,,,,=0~597.
1.54.
Winter: Mean W(wlnter)=1.210; Variance u2
Table 2b. Statistics upon central population
Class
Limits
Mean class
Frequence
Summer
Xm
1-41 1.OO
1'00-0.71
0.71-0.50
0.5C0.35
0.35-0.25
0.25-0.17
-
XI
x,
1.205
0.855
0.605
0.425
0.30
0.2135
1-452
0,730
0.366
0.180
0.090
0.044
Winter
Summer
A(,,
0
3
8
5
2
0
AX,
AX,
J;
0
9
2
0
-
Winter
Summer
Axl(s) Ax,(w, Lx,2,s,
(f;XJ'
Winter
Cf;XJ2w
-
-
-
-
-
-
2.57
4.84
2.125
0.60
-
7.7
1.21
6.6
0.73
6.6
23.4
4.5
0.36
59.3
1.46
-
2.2
2.93
0.9
0.18
-
-
-
8.9
6.21
7.33
-
-
~
-
-
~
c
18
11
10
34.86
60.76
Summer: Mean su summer) = 0.56;
Variance
= 0.50.
Variance u2(W,nte,)
Winter: Mean
= 0.81 ;
=0.42.
Same general statistical parameters as table 2a.
z(,tnter,
Walker & Hutka, 1973). Thus, more angular grains
are observed with conchoidal fractures (Fig. 7A)
mechanical fractures (Fig. 7D & F) and single
mechanical breakage (Fig. 8A). Inheritance of these
surface features from the source of the winter floods,
however, is not excluded (Barbaroux et a{., 1972).
Chemical destabilisation (dissolution - pH >> 8.3)
= Solution pits (Fig. 7B and E ; Fig. 8C), surface
solution features (Fig. 7C; Fig. 8B and D), and
vermicular features (Fig. 8D).
Dominant chemical action
Chemical growth (precipitation - pH < 8)
= silica flowers (Fig. 8E), neogene silica coatings
(Fig. 7F; Fig. 8A), and trapped diatoms (Fig. 8A
and F).
In the case of grains sampled during the summer,
many chemical features are observed which can be
attributed to two dominant subclasses, dissolution and
precipitation.
The monthly abundance of the above features is
shown in Fig. 6. The warm conditions (maximum
temperature of water measured in the Loire River on
July 6, 1982 was 26°C-see Manickam, 1982a) linked
501
S. Manickam and L. Barbaroux
A
fi
,
Summer
I
I
I
I
*.
1
I
I
,
TI
Winter
I
I
I
1
I
I
I 1
I
Jan.-March 1982(3354- 1300m3/s
k
0-6
0.3
B
fi
15
°
0.3
0.6
I
I
2.6 5.5 Xi
1 *2
Winter
I
I
I
I
I
i
7
1.2 1.7 Xi
Fig. 3. (a) Frequency curves for whole population; (b) Frequency curves for central population.
this dominant chemical action with algal bloom
conditions (phytoplankton), high organic content and
catastrophic eutrophic events in the downstream
reaches during the summer. In addition to this,
precipitation of silica in the form of diatoms (Fig. 8A
& F) and silica flowers (Fig. 8E) takes place in the
Loire River when the pH is below 8 and this is often
followed by calcite precipitation when the pH increases beyond 8.3 (Manickam, 1983; Manickam et
a/., 1985). This is also suggested by a deficit budget in
dissolved silica (upstream to downstream for a
distance of about 50 km, the deficit in dissolved silica
is - 6.5%) during the same periods (Barbaroux, 1980;
Manickam, 1982a; Manickam et a/., 1985). These
chemical textures have been reported in the Loire
estuary by Barbaroux et al. (1972), Barbaroux (1982)
and in the upper Loire by BrossC (1982) on the
deposited grains. Hence, it is concluded that the
chemical processes take place either on deposited
sediments and or just prior to their deposition.
Combined action
During the periods of low and average river discharge,
all of these features were observed, but in low
abundance (Figs 6-8), which means that these
processes complement each other due to their (seasonal) weakness. These features can also occur via
reworking effects on previous deposits (Barbaroux et
al., 1972).
In general, more mechanically derived features
(Figs 7D, 8A, 9A, B & C) are observed on grains
obtained from near the water surface and more
chemical features (Figs 7E, 8B, 9D, E & F) on grains
from the bottom of the river. Moreover, more rounded
grains (Fig. 9D & E) are observed near the bottom of
the river than near the surface (Figs 8A & 9A).
Table 3. Mineralogical variations in the suspended coarser fractions with respect to seasons in
the Loire River, France. (Values are given in percentage)
Mineral
Quartz
Feldspar
Micas
Spring-Summer 1981
36-45 (R= 40)
18-24 ( 8 ~ 2 1 )
32-41 ( 8 = 3 8 )
Winter 1981-82
42-71 (R= 54)
4-33 (8=
17)
22-39 (R=29)
Total coarser fraction
Surnmer=7; Winter= 13.3
Surface texture of suspended quartz
502
2
20
40
30
50
18
f
-
I
I
I
I
1
1
1
1
1
quartz Ro1at increasing discharge
I
I
I
-
c$~artzP/d at decreasing
ischarge
Winter mean valutot
quartz +feldspar
Winter mean value ot
quartz
I
I
v
c
I
quartz +feldspar('/.)
'4-
0
I
50
70
80
Quartz + feldspar content (*Io)
Mica corrtent (%)
I
Small discharge
0 - A'
r
A '
30 10-
1
L
+
In
Summer mean value
of quartz t teMspar
l
Summer mean value
of quartz
L
-
01
L
2
1
5
70
90
30
40
50
60
Feldspar + quartz content (%)
80
Fig. 4. (a) Relationship between the coarser fraction and mica content in the TSM; (b) Relationship between the coarser
fraction and quartz+ feldspar content in the TSM; (c) Effect of discharge on quartzo-feldspathic supply in coarser fraction.
S . Manickam and L. Barbaroux
'
1
I
h
1
A
B
Fig. 5. Approximate distribution of grains studied with the
SEM with respect to (a) seasons, and (b) inferred processes.
Therefore, there is a selective action in the river with
respect to season and depth, correlated with granulometric and mineralogic data (Tables 1-3).
DISCUSSION AND GENERAL
CHEMICAL PROCESSES
It is necessary to consider in more detail the chemical
processes involved in previous sections. At 25°C the
503
solubility level of quartz in natural waters ranges from
0.03-30 mg 1- S O 2 , and some geochemical investigations seem to preclude either dissolution or precipitation of quartz in fresh surface water (pH < 9) because
of kinetic constraints (Berner, 1971). But, as summarized by Yariv & Cross (1979), in natural suspension
as well as in experiments, different results can be
obtained. Henderson, Syers & Jackson (1970) show
that mechanical grinding increases quartz surface's
reactivity (solubility?); thus, the well-known observations about quartz stability of Krauskopf (1957) are
not valid. Kamiya, Ozaki & Imahashi (1974) confirm
these results by getting the highest solubility of quartz
near pH 7 in the presence of organic matter. On the
other hand, Mackenzie & Gees (1971) crystallized
quartz directly from sea water at 20°C. Kastner,
Keene Gieskes (1977) insist upon the importance
Of quartz neoformations at Ordinary pressure and
temperature from an opal CT. Our observations are
in good
agreement
not only with the above-mentioned
results showing a silica mobility but also with those of
Jones & Uehara (1973) for coating quartz evolution,
Henderson et af. (1970) for quartz-surface modifications, Hall (1974) and Moriyama (1976) for the role of
organic polyelectrolyte in protecting colloidal silica
* , n i x e d action
Fig. 6. Relative abundance of the principal characters of surface features of suspended quartz grains.
Fig. 7.SEM photomicrographs of quartz grains collected during floods: Scale bar on A, B, D, E & F is 10 pm; on C it is 1 pm.
A-Winter flood. Angular grain with conchoidal fractures which could have been transported locally and recently. Dominant
mechanical action population; B-Winter flood. Subangular grain with solution pits which shows neogenic residues at the
bottom. This could have been transported from a long distance and/or reworked. Dominant chemical action population; CWinter flood. Well-rounded, large grain which shows numerous ‘v’ marks with solution features. Mixed mechanical and
chemical action populations; D-Winter flood. Sample from the river surface, angular small grain showing fractures.
Dominant mechanical action population; E-Winter flood. Sample from the river bottom, abraded large grain with solution
pits. Dominant chemical action population; F-Flood resulted from snow melt. Mechanical, conchoidal fractures representing
a relict surface carved by numerous small ‘v’ pits. Remains of neogene deposits (silica and diatoms) were dissolved on the
trough of the grain. This grain was probably resuspended.
S. Manickam and L. Barbaroux
505
Fig. 8. SEM photomicrographs of quartz grains collected during summer and at times of average river discharge: Scale bar is
10 pm. A-Spring. Sample from the river surface; angular grain with fixed diatom showing neogenesis in one side and fresh
fractures on the other sides. Indication of reworked sediment; B-Spring. Sample from the river bottom, rounded grain with
solution features and without diatoms; C-Summer. Small grain with more solution pits. Dominant chemical action
population ; D-Summer. Well-rounded, large grain displaying the vermicular texture. Sampled during an algal bloom
(maximum chemical activity); E-Autumn. Abraded subangular grain with dendritic silica overgrowths. Probably a
resuspended grain originally deposited at the end of summer; F-Autumn. Reworked sediment; subangular abraded grain
with abundant debris and diatoms (in trough) attacked during summer.
506
Surface texture of suspended quartz
Fig. 9. SEM photomicrographs of quartz grains sampled from surface to bottom of the river channel: Scale bar on A, D & E is
100 pm; on B, C & F it is 10 pm. A-Spring 1981. Sample from the river surface angular grain with numerous mechanical
features; B & C. Details of previous photo with abundant nail impressions, crescent shaped features (chattermarks) and
traction marks (glacial origin?). D-Autumn 1981. Sample from the bottom of the river; well rounded abraded grain with
dominant chemical features; E-Spring 1982. Sample from the bottom of the river; well rounded abraded grain; F-Detail of
previous photo reveals dominant chemical solution processes.
507
S . Manickam and L. Barbaroux
followed before entering the studied area. The pH and
temperature ranges (7.5-8.0 and 20-28"C, respectively) are also smaller than those given by Kennedy
(1971) and many others in such a medium.
A conceptual model which, in trying to explain the
observed variations in textural features in the Loire
River suspended-sediments, emphasizes seasonal
change is shown in Fig. 11. In addition to this study,
more investigations are needed to confirm and enhance
these statements.
deposits on quartz grains, Kranck (1973,1975) for the
role of particulate aggregation in these processes, and
Snoeyink & Weber (1972) for the speed of quartz
surface mobilization (a few hours to some months).
In estuarine environments not only the work of
Barbaroux (1980) but also of Edwards & Liss (1973)
and Burton & Liss (1 973) affirms the suspended quartz
reactivity for buffering of silica (Friedman & Sanders,
1978).Kennedy's (1971)seasonal silica concentrationdischarge results from the Mattole River, North
Carolina are in good accord with this study (Table 1,
Fig. 2a).
Consideration of studies such as those mentioned
suggests that it is reasonable to assume that the
chemical stability of quartz grain surfaces can be
rapidly modified in natural waters by grinding and
coating during their transportation. The SEM results
obtained during the present study provide direct
evidence of these changes. Comparisons with the
quartz surface textures of deposited sediments (Fig.
10) reveal many seasonal variations integrated by
sedimentation, where the latest features (by hierarchy)
are the mirror image of the last environmental impact.
The features are in good agreement with the possible
origin of quartz and with the evolutionary steps
CONCLUSIONS
Sand grains in suspension in the Loire River at
Montjean, analysed statistically and studied with
scanning electron microscope, during a complete
hydrological cycle, seem to show the following
seasonal variations.
The sand fraction (CF >45 pm) in suspension is
better sorted (average mean = 0.69 mm, median =
0.65-0.95 mm sorting index, u = 1.1-1.35) with unimodal homogeneous (quartzo-feldspar) transport in
suspension during winter and polymodal heterogeneous (micaceous sand) transport during summer
ations,
I conchoidal
s t ti
LOWER LO!
-*-0
y
l
f e a Utes
fractures
1
/
UPPER LOIRE
v
ti ssures,
OC
/"
0J
-'
\
./
i'stLary
outer estuary
v PttS,
L
rhombohedra1 m a r k s I
Fig. 10. Evolution of quartz grains with various textures sampled along a continent-ocean transect (modified from Barbaroux,
1982, fig. 9, page 65). Approximate distances: Upper Loire-Middle Loire, 510 km; Middle Loire-Lower Loire, 240 km; Lower
Loire-Inner estuary, 160 km; Inner estuary-Outer estuary, 70 km (upper limit of tidal effect); Outer estuary-delta, 20 km.
Surface texture of suspended quartz
508
(a)
INNER ESTUARINE INTERFACE
OCEAN
I
more loial input
CONTINENT
less long distance
fluvial input
I
!
average iocal input
- Rveraae lona
I
Octobe; to February
-.
'\
7
out immediately-/
more long distance
I
March to April
B B o t t o m sediments
=Suspended
sediments
(b)
Surface
more
angular
1more
rounded
Bottom
abundant solution
pits
more mechanical
features
dominant chemical
corrosion
fewer mechanical
features
abundant solution
pits
Surface
more neogene silica
and diatoms
selection of
small angular
grains
pt3iMEF
less neogene silica
and diatoms
selection of bic
rounded grains
Bottom
Fig. 11. Model depicting seasonal changes of quartz grain surface features in river suspension as determined by scanning
electron microscopic observations. a From continent to ocean. b General trends between surface and bottom at the inner
estuarine interface.
509
S . Manickam and L. Barbaroux
(average mean= 1.21 mm, median=0.33-0.95 mm,
sorting index, u = 1.4-2.0).
The median size of the sand fraction in suspension
shows a broad tendency to increase with river
discharge, and a seasonal variation in mineralogy
from quartz during winter to mica during summer.
An intensive SEM photomicrographic study on the
quartz grains reveals that two principal actions take
place in the Loire River which vary seasonally;
mechanical processes are dominant during the winter
floods and chemical processes dominate during the
summer and whenever small river discharges occur.
However, combined action takes place at times of
average river discharge possibly with reworking of
sediments from previous winter and summer seasons.
More mechanical features are observed on grains
sampled near the surface of the water, whereas more
chemical characteristics are found on grains obtained
near the bottom of the water body. During summer,
chemical processes apparently take place on suspended materials immediately prior to their deposition
and continue thereafter : these could be correlated
with the catastrophic eutrophication (after-spring
algal bloom) and the deficit silica budget.
These deposited sediments are reworked during
winter floods and, hence, suffer physical processes
resulting in the dominance of mixed features during
average river discharge or during post-floods.
This work clearly shows that fluvial sands do not
have unequivocal characteristics and during fluvial
transport, quite different features can co-exist. The
overall distribution of fluvial quartz grain surface
features is a combination of alternating chemical and
physical processes.
ACKNOWLEDGMENTS
The authors wish to acknowledge, with thanks, the
assistance rendered by Mr Alain Barreau in taking
SEM photomicrographs and also the service provided
during field trips by the Fluvial Navigation of Angers
in bulk water sampling. Many thanks are due to
Professor FranGois Ottmann of Nantes University for
his valuable suggestions and help during the thesis
works of the authors. Professor R. M. Garrels of the
South Florida University is also thanked for his
comments on the thesis of L.B. Professor Michel
Colchen of Poitiers University is warmly acknowledged for his kind coordination with the Centre
International des Etudiants et des Stagiaires (CIES)
and the Ministry of External Relations of France who
financed S.M’s research activities in Europe. Partial
financial support by the Comiti: Scientifique de
]’Environment et de 1’Estuaire de la Loire (CSEEL)
and the French CNRS is also acknowledged.
This article was prepared while S.M. was in
Shizuoka University, Japan as a Post-DoctoralFellow.
Suggestions and comments by Professor Hakuyu
Okada (Shizuoka University) and David Krinsley
(Arizona State University) were appreciated ;Doctors
K. 0. Stanley (EXXON Production Research Company, Houstan), R. H. Blodgett (Ohio State University), E. Merino (Indiana University), J. H. Tellam
(Birmingham University), D. Crerar (Princeton), M.
M. Smith (South Carolina) and P. H. Bridges (Derby)
greatly helped in improving the standard of the
manuscript.
REFERENCES
BARBAROUX,
L. (1970) Essai de granulometrie par computeur
analyseur d’image. Comparaison avec la methode pondtrale. Bull. Inst. geol Bassin Aquitain, 9, 157-166.
BARBAROUX,
L. (1980) Evolution des propriitts physiques et
chimiques des stdiments dans le passage Continent-Ocban.
L’Effet estuarian. DSc thesis, Nantes University, 433 pp.
BARBAROUX,
L. (1982) Un exemple subactuel d’echange
sedimentaires Continent-Ocean en region temperee,
l’estuaire de la Loire (France). Texture et structure
stdimentaires. Mem. Soc. geol. Fr., 144,53-75.
BARBAROUX,
L., BOUQUET,B., BROSSE,R., DA NOBREGA
COUTINHO,
P. & JOVIC,P. (1972) Examen au microscope
tlectronique a balayage de grains de quartz de diverses
origines. Essai de typologie, signification environmentale.
Bull. Bur. Rech. Geol. Min., 4,3-31.
L., MANICKAM,
S. & YVON,B. (1983) MicroBARBAROUX,
structures evolution of suspended matter and sediments
through fresh-saline environment transition. Proc. 4th
IAS European meeting, Splitz, Yugoslavia, p. 19.
R. A. (1971) Principles of Chemical Sedimentology.
BERNER,
McGraw-Hill, New York, 240 pp.
L. (1954) Etude critique de la mtthode d’analyse
BERTHOIS,
granulometrique baske sur la frequence numerique. Bull.
Soc. Sci. Bretagne, 29, 105-1 10.
L. (1971) Les transports sedimentaires et l’erosion
BERTHOIS,
dans le bassin de la Loire. Etude ligerienne, No. 11,Colloque
sur le lit de la Loire et ses iles. Nov. 20-21,1971.
BROSSE,R. (1982) Les processus sidimentaires dans le Jeuve
Loire. DSc thesis, Angers University, 530 pp.
BURTON,J.D. & LISS, P.S. (1973) Processes of supply and
removal of dissolved silicon in the oceans. Geochim.
Cosmochim. Acto., 31, 1761-1773.
J. (1959) Initiation i I’etude des
CAILLEUX,
A. & TRICART,
sables et galets. C.D. U . SEDES, 1, Paris, 369 pp.
A.M.C. & LISS,P.S. (1973) Evidence for buffering
EDWARDS,
of dissolved silicon in freshwaters. Nature, 243, 341-342.
FRIEDMAN,
G.M. & SANDERS,J.E. (1978) Principles of
Sedimentology. Wiley, New York, 792 pp.
510
Surface texture of suspended quartz
HALL,D.G. (1974)Theroleof bridgingincolloidflocculation.
Colloid Polymer. Sci. 252, 241-243.
HENDERSON,
J.H., SYERS,J.K. & JACKSON,M.L. (1970)
Quartz dissolution as influenced by pH and the presence
of a disturbed surface layer. I.J. Chem. 8,357-372.
JONES,R.C. & UEHARA,G . (1973) Amorphous coatings on
mineral surfaces. Proc. Am. Soc. Soil Sci. 37,792-798.
KAMIYA,
H., OZAKI, A. & IMAHASHI,
M. (1974) Dissolution
rate of powdered quartz in acid solutions. J . Geochem. 8,
21-26.
KASTNER,
M., KEENE,J.B. &GIESKES,
J.M. (1977)Diagenesis
of siliceous oozes-Part I. Geochim. Cosmochim. Acta, 41,
1041-1059.
KENNEDY,
V.C. (1971) Silica variation in stream water with
time and discharge. Non-equilibrium systems in natural
water chemistry. Adv. Chem. Ser., 106,94-130.
KRANCK,
K. (1973) Flocculation of suspended sediments in
the sea. Nature, 246, 348-350.
KRANCK,
K. (1975) Sediment deposition from flocculated
suspensions. Sedimentology, 22, 111-128.
KRAUSKOPF,
K,B. (1957) Dissolution and precipitation of
silica at low temperatures. Geochim. Cosmochim, Acta, 10,
1-26.
KRINSLEY,
D.H. & DOORNKAMP,
J.C. (1973) Atlas ofQuartz
Sand Surface Textures. Cambridge University Press,
London, 91 pp.
KRINSLEY,
D.H. & McCoy, F.W. (1977) Significance and
origin of surface textures on broken sand grains in deepsea sediments. Sedimentology, 24, 857-862.
LE RIBAULT,
L. (1975) L’exoscopie. Methode et application.
Mem. Compagnie Frayais des Petroles, 12 (ed by C.F.P.),
Paris, 232 pp.
LEROY,D.S. (1981) Grain-size and moment measures: A
new look at Karl Pearsons Ideas on distributions. J . sedim.
Petrol. 51, 625-630.
MACKENZIE,
F.T. & GEES,R. (1971) Quartz synthesis at
earth surface conditions. Science, 173,533-534.
MANICKAM,
S. (1982a) Etude hydrologique et sedimentologique
de la zone de transition enlre la Loirepuviale et I’estuaire.
Thesis, Nantes University, November 1982, 281 pp.+
aPP.
MANICKAM,
S. (1982b) Seasonal variation in grain-size
parameters of the recent sediments and their significances:
the Yamuna River drainage basin, India. Proc. 3rd IAS
European Meeting, Copenhagen,Denmark, April 5-7, 1982,
Abstr. pp. 46-48.
MANICKAM,
S. (1983) Sedimentation processes in the Loire
River and its estuary entrance, France : A bio-chemicosedimentological approach. Proc. II Int. Symp. River
sedimentation, Nanjing-China, October 1983, pp. 11-16.
S., BARBAROUX,
L. & OTTMANN,F. (1985)
MANICKAM,
Composition and mineralogy of suspended sediment In
the fluvio-estuarine zone of the Loire River, France.
Sedimentology, 32,721-741.
N . (1976) Stabilities of aqueous inorganic
MORIYAMA,
pigment suspensions. Colloids Polym. Sci., 254,726-735.
Moss, A.J., WALKER,P.H. & HUTKA,J. (1973) Fragmentation of granitic quartz in water. Sedimentology, 20, 489511.
PRONE,A. (1 980) Les quartz de la provence occidentale. Etude
exoscopique et endoscopique. Implications paliogeographiques. DSc thesis, Marseille University, 466 pp + 1
vol. app.
A. (1977) Utilisation d’un nouveau
SELCIER,
R. & BARREAU,
procede de metalisation par pulv&risation cathodique,
pour l’etude au microscope tlectronique par balayage, des
production tegumentaires des insecte. C.R. Acad. Sci.
Paris, 285, Ser. D, 1053-1056.
SNOEYINK,
V.L. & WEBER,W.J. (1972) Surface functional
groups on Carbon and silica. Progr. Surf: Memb. Sci., 5,
63-1 19.
YARIV,S. &CROSS,H. (1979) Geochemistry of colloidssystem.
Springer-Verlag, Berlin, 450 pp.
(Manuscript received 29 May 1986; revision received 31 July 1986)