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The infra-red determination of total carbonate in marine carbonate sediments
Chemical Geology - Elsevier Publishing Company, Amsterdam Printed in The Netherlands
THE INFRA-RED DETERMINATION OF TOTAL CARBONATE IN MARINE CARBONATE SEDIMENTS
R. CHESTER and H. ELDERFIELD Department of Oceanography, University of Liverpool, Liverpool (Great Britain} (Received July 4, 1966)
SUMMARY An i n f r a - r e d method is described for the determination of total carbonate in m a r i n e sediments. The method is calibrated with samples of known composition and may be used to determine total carbonate to ca. + 2% of the chemical values. It can also be used to give semi-quantitative estimates of A1203 and SiO 2.
INTRODUCTION Calcium carbonate is a quantitatively important component of many marine sediments, and about 50% of the deep ocean floor is covered by sediments containing m o r e than 30% organically derived calcium carbonate (El Wakeel and Riley, 1961). Recent geochemical studies have attempted to define the origin of t r a c e elements in m a r i n e sediments in relation to the methods by which they have been incorporated into the sedimentary phases (see Goldberg and Arrhenius, 1958; Chester and Hughes, 1966). This kind of approach will lead ultimately to a partial distinction between those t r a c e elements derived f r o m sea water, and those t r a n s p o r t e d in p r e - e x i s t i n g mineral lattices (such as the clay minerals). The two most important quantitative components derived from sea water are f e r r o m a n g a n e s e nodules (hydrogenous origin), and calcium carbonate (biogenous origin). A knowledge of the distribution of calcium carbonate in marine sediments is t h e r e f o r e important in studies aimed at establishing the distribution and origin of the m a j o r mineral components, and also the t r a c e element geochemistry. The i n f r a - r e d identification of carbonate m i n e r a l s has been established by s e v e r a l w o r k e r s , e.g., Adler et al. (1950), Keller et al. (1952), and has been s u m m a r i z e d by Chester and Elderfield (in preparation). Quantitative aspects of carbonate mineralogy, such as the determination of c a l c i t e dolomite ratios and calcite-aragonite ratios, have been examined by Hunt and T u r n e r (1953), Adler and K e r r (1962) and C h e s t e r and Elderfield (in preparation). The present paper outlines a quantitative i n f r a - r e d method of determining total carbonate, i.e., calcium and magnesium carbonates in sediments, based on the c a r b o n a t e - c l a y ratio in the samples, which is both rapid and accurate. Chem. Geol., 1 (1966) 277-290
277
TABLE I Wavelengths of the i n f r a - r e d a b s o r p t i o n bands of the i m p o r t a n t m a r i n e c a r b o n a t e s 1 (After C h e s t e r and E l d e r f i e l d , in p r e p a r a t i o n ) Carbonate mineral
Wavelength (p)
Calcite
7.00(s,b)
Aragonite
6.78(re,b)
Magnesite
6.90(s,b)
Dolomite
6.94(s,b)
v3
v1
9.23(m,sh)
v2
v4
11.41(s,sh) 11.76(w) 11.67(s,sh) 11.90 (w) ll.30(s,sh) 11.73(w,sh) ll.38(s,sh) 11.73(w)
14.08(s,sh) I 14.08(s,sh) [ 14.39 (s, sh) 13.40(s,sh) 13.76(s,sh)
1Key: s = strong; m = medium; w = weak; sh = sharp; b = b r o a d ; ~ = doublet. TABLE II Wavelengths of the i n f r a - r e d a b s o r p t i o n bands of the i m p o r t a n t m a r i n e clay m i n e r a l s in the 8-12~ range 1 Clay m i n e r a l
Wavelength r a n g e (p)
s~
9~
10p
] 1~
Chlorite Illite Kaolinite
9.30(sd) 9.75(sd) 10.10(s) 10.46(sd) 8.65(sd) 9.17(sd) 9.75(s) 8.99(sd) 9.09(s) ~9.71(s) 10.68(sd) t9.90(s) Montmorillonite 9.13(sd) 9.80(s)
11.49(m) 10.95(w) 10.95(s) 10.95(w) l l . 4 0 ( s d ) l l . 9 0 ( s d )
1Key: s = strong; m = medium; w = weak; sd = s h o u l d e r ; f = doublet.
WAVELENGTH 6.5
7.0
I
7.5
I
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I
I
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(~,)
9.O
I
9.5
I
I
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11,O
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12.0
13.O 140
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15.O
f
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CANIONATE
20
Vj CLAy
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WAVE N U M B E R
MINERAl. (.~"~,~M1rl)
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i
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800
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(crn-')
Fig.1. I n f r a - r e d s p e c t r u m of a typical d e e p - s e a carbonate sediment. 278
Chem. Geol., 1 (1966) 277-290
7.5
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WAVELENGTH(MICRONS) Fig.2. I n f r a - r e d s p e c t r a of clay m i n e r a l s . A. C h l o r i t e . B. I l l i t e . C. Kaolinite. D. M o n t m o r i l l o n i t e .
SELECTION O F ABSORPTION BANDS Calcite, aragonite and minor amounts of magnesite and dolomite are the main c a r b o n a t e m i n e r a l s in m a r i n e s e d i m e n t s . The a b s o r p t i o n s p e c t r a of t h e s e m i n e r a l s a r e given in T a b l e I, and a g e n e r a l i z e d i n f r a - r e d s p e c t r u m of a Chem. Geol., 1 (1966) 277-290
Z79
d e e p - s e a c a r b o n a t e s e d i m e n t i s i l l u s t r a t e d in F i g . 1 . In T a b l e I the a b s o r p t i o n b a n d s a r e c l a s s i f i e d a c c o r d i n g to t h e s c h e m e g i v e n by H e r z b e r g (1945), into Vl, v2, v3 and v 4 f u n d a m e n t a l a b s o r p t i o n b a n d s e a c h of which c o r r e s p o n d s to a p a r t i c u l a r d e f o r m a t i o n a l m o d e of t h e CO32- ion. F r o m T a b l e I it can b e s e e n that the v 2 and v4 b a n d s will r e s o l v e into a s e r i e s of p e a k s if a m i x t u r e of t h e c a r b o n a t e s i s p r e s e n t . On the o t h e r hand, t h e v 3 band h a s i t s b a n d h e a d in the r e g i o n 6 . 7 8 - 7 . 0 0 p f o r a l l t h e c a r b o n a t e s . T h i s i s a b r o a d b a n d and t h e a d d i t i o n of one of t h e c a r b o n a t e s to a n o t h e r in a s a m p l e i n c r e a s e s the b a n d i n t e n s i t y without m a t e r i a l l y a l t e r i n g t h e p o s i t i o n of t h e b a n d h e a d . F o r t h i s r e a s o n the v3 b a n d w a s s e l e c t e d f o r total carbonate determination. The c l a y m i n e r a l s p r e s e n t in m a r i n e s e d i m e n t s a r e m a i n l y i l l i t e , c h l o r i t e , k a o l i n i t e and m o n t m o r i l l o n i t e . The i n f r a - r e d s p e c t r a of a l l t h e s e m i n e r a l s i n c l u d e a S i - O bond p e a k at ca. 8 . 0 - 1 1 . 0 ~ . T h e s e a r e l i s t e d in T a b l e II, a l o n g with o t h e r a b s o r p t i o n b a n d s in t h i s r e g i o n , and the i n f r a - r e d s p e c t r a of t h e s e m i n e r a l s a r e i l l u s t r a t e d in F i g . 2 .
SPECTROPHOTOMETER
DISCS
S a m p l e s w e r e i n t r o d u c e d into t h e s p e c t r o p h o t o m e t e r in t h e f o r m of p o t a s s i u m b r o m i d e d i s c s . The p a r t i c l e s i z e of t h e m a t e r i a l in t h e d i s c s m u s t be l e s s than t h e m i n i m u m i n f r a - r e d w a v e l e n g t h u s e d , h e r e 2 . 5 - 1 5 g . To e n s u r e t h i s , t h e s a m p l e s and K B r w e r e g r o u n d m e c h a n i c a l l y in a s t e e l b a l l m i l l f o r 15 min. C h e c k s r e v e a l e d t h a t g r i n d i n g f o r t h i s t i m e r e d u c e d ca. 90% of the s a m p l e s to a g r a i n s i z e ~ 2 g . The t r a n s m i s s i o n r a n g e o v e r w h i c h m e a s u r e m e n t s can be m a d e i s p a r t i c u l a r l y i m p o r t a n t in q u a n t i t a t i v e i n f r a - r e d m e a s u r e m e n t s . S m i t h (1965) h a s r e p o r t e d t h a t o p t i m u m r e a d i n g s can be o b t a i n e d in the r e g i o n 20-60% t r a n s m i s s i o n , and in t h e p r e s e n t w o r k the weight of s a m p l e in e a c h d i s c w a s a d j u s t e d to g i v e r e a d i n g s in t h i s r e g i o n .
STANDARD
CURVE
A d l e r and K e r r (1962) and C h e s t e r and E l d e r f i e l d (in p r e p a r a t i o n ) h a v e shown t h a t t h e s h a p e s of i n f r a - r e d s t a n d a r d c u r v e s a r e d e p e n d e n t on the m i n e r a l s u s e d in t h e i r c o n s t r u c t i o n , and c u r v e s c o n s t r u c t e d f r o m i n o r g a n i c a l l y p r e c i p i t a t e d c a l c i t e d i f f e r f r o m t h o s e of o r g a n i c c a l c i t e . F o r t h i s r e a s o n a s e r i e s of c a l i b r a t i o n c u r v e s w a s p r e p a r e d in an a t t e m p t to s i m u l a t e t h e m i n e r a l c o m p o s i t i o n of m a r i n e c a r b o n a t e s e d i m e n t s . T h e s e w e r e a s f o l l o w s : (1) I n o r g a n i c c a l c i t e and i l l i t e ( i l l i t e w a s s e l e c t e d a s b e i n g r e p r e s e n t a t i v e of m a r i n e c l a y m i n e r a l s ) . (2) O r g a n i c s h e l l c a l c i t e (Balanus balanoides) and t h e a c i d i n s o l u b l e r e s i d u e of a d e e p - s e a r e d c l a y ( s a m p l e no.9, E1 W a k e e l and R i l e y , 1961). (3) D e e p - s e a c a r b o n a t e s e d i m e n t s , t h e c o m p o s i t i o n s of which had b e e n d e t e r m i n e d c h e m i c a l l y . T h e c o m p o s i t i o n s a r e l i s t e d in T a b l e III. F o r e a c h of t h e s e m i x t u r e s s t a n d a r d c u r v e s w e r e c o n s t r u c t e d s h o w i n g the r e l a t i o n s h i p b e t w e e n t h e t o t a l c a r b o n a t e and " c l a y " c o m p o n e n t s ( u t i l i s i n g the r a t i o of t h e b a n d i n t e n s i t i e s at c a . 7 ~ and 9 - 1 1 ~ r e s p e c t i v e l y b y a m e t h o d g i v e n l a t e r ) , and t h e c h e m i c a l l y d e t e r m i n e d t o t a l c a r b o n a t e content. T h e 280
Chem. Geol., 1 (1966) 277-290
TABLE HI Samples used in the construction of standard curve 1" Sample no. (El Wakeel and Riley, 1961)
Analyst 1
3
-
Percentage total carbonate 0
Position
Type and colour
35°55TN 17°29'E
Globigerina ooze-buff (2N HC1 washed} deep-sea clay volcanic muddy sand, 2-19 cm of core deep-sea calcareous clay Globigerina ooze-buff calcareous ooze; light brown-red calcareous manganiferous; chocolate calcareous ooze; white Globigerina ooze; white calcitic shell
2 1
3.00 11.98
northwest Atlantic 19°46'N 154°58'W
9 1
2 1 1
24.00 54.54 61.30
northwest Atlantic 35°55'N 17°29'E 24°20'N 24°28'W
15
1
72.82
22°07'S I I 5 ° I 0 ' W
6
2 1 3
90.00 92.62 i00.00
29°02'N 25°27'W 26°08'S 14°36'W Plymouth
-
30 -
-
-
(Balanus balanoides) *See Fig.4. 1Chemical analyses by: (1} E1 Wakeel and Riley {1961}; (2) Wilson (in preparation}; (3) the authors. TABLE
IV
Comparison of the results of total carbonate determined chemically with those obtained from the three standard curves on application of the i n f r a- r ed technique Sample I 61 A 44
Chemical method 32.0 59.0 87.5
Infra-red method using standard curves curve 1
curve 2
curve 3
45.0 63.0 90.5
25.1 57.0 97.0
31.5 59.0 88.4
1See Table V. t h r e e s t a n d a r d c u r v e s d i f f e r e d s i g n i f i c a n t l y , and e a c h w a s t e s t e d e m p i r i c a l l y t o d e t e r m i n e t h e t o t a l c a r b o n a t e in a s e r i e s of m a r i n e s e d i m e n t s w h i ch had been previously analyzed. T h e r e s u l t s a r e g i v e n in T a b l e IV, and t h e s t a n d a r d c u r v e s a r e i l l u s t r a t e d in F i g . 3 and 4. T h e r e a s o n s f o r t h e v a r i a t i o n s in t h e s t a n d a r d c u r v e s a r e not known, but it m a y be t h a t m e c h a n i c a l m i x i n g cannot a p p r o x i m a t e to t h e i n t i m a t e m i n e r a l a d m i x t u r e found in n a t u r a l m a r i n e s e d i m e n t s . A n o t h e r p o s s i b i l i t y i s t h a t t h e o r g a n i c m a t e r i a l u s e d t o c o n s t r u c t c u r v e 2 did not r e p r o d u c e the n a t u r a l c o n d i t i o n s s u f f i c i e n t l y w e l l. T h e c u r v e c o n s t r u c t e d f r o m n a t u r a l s e d i m e n t s t a n d a r d s a p p e a r e d t o be t h e m o s t p r o m i s i n g , and w a s c h o s e n as b e s t r e p r e s e n t i n g the natural conditions.
Chem. Geol., 1 {1966} 277-290
281
ioo
I
F
[
~
B
I00
,P
8o
1
80
w Z
o m ,< U
6o i
60
40
40
20
io
.i U w a.
0 0
0.2
0.4
0.6
0,8
INTENSITY
0.2
1.0
RATIO
0.4
0.6
0.8
I.O
CARBONATE CA R ~ N A T E +~CLAY '
Fig.3. S t a n d a r d c u r v e s f o r the d e t e r m i n a t i o n of total c a r b o n a t e u s i n g : A. I n o r g a n i c c a l c i t e and i l l i t e . B. O r g a n i c c a l c i t e (Balanus balanoides s h e l l ) and a c a r b o n a t e - f r e e d e e p - s e a s e d i m e n t ( s a m p l e 9, E1 W a k e e l and R i l e y , 1961). Ioo
8o
6o w
g < u4o IZ w U n,.
2O
o
...-"'"7'~1 0
I 0,2
I
INTENSITY
I 0.4
I
I 0.6
I
I 0.8
RATIO
CARBONATE CARBONATE + 'CLAY'
I
l 1.0
Fig.4. Standard curve for the determination of total carbonate using chemically analysed samples (see Table ]I1). 282
Chem. Geol., i (1966) 277-290
EXPERIMENTAL CONDITIONS
Apparatus A H i l g e r and Watts H900 " I n f r a s c a n " d o u b l e - b e a m r e c o r d i n g s p e c t r o p h o t o m e t e r , i n c o r p o r a t i n g a g r a t i n g m o n o c h r o m a t o r and s o d i u m - c h l o r i d e optics was u s e d to obtain the s p e c t r o g r a m s . The r a t e of scanning e m p l o y e d was 16 rain f o r the range 3,880-650 cm-1. To offset any m i n o r i m p u r i t i e s in the K B r , and to m i n i m i s e the effects of a b s o r b e d w a t e r , a K B r d i s c ( p r e p a r e d using the s a m e weight of KBr as the s a m p l e disc) was p l a c e d in the r e f e r e n c e b e a m of the i n s t r u m e n t . This tends to i n c r e a s e the b a s e l i n e t r a n s m i s s i o n and as this is i m p o r t a n t the t r a n s m i s s i o n was modified by attenuating the s a m p l e b e a m to give a t r a n s m i s s i o n in the r a n g e 20-60%.
Preparation of samples The s e d i m e n t s a m p l e s (and s t a n d a r d s ) and K B r ( " a n a l a r " g r a d e ) a r e ground s e p a r a t e l y to p a s s a 240 m e s h s i e v e (B.S.S.), and a r e s t o r e d in an oven at 90°C until r e q u i r e d .
Preparation of KBr discs T r a n s f e r an amount of the d r i e d s a m p l e (ca. 0.25 g) to a s t e e l b a l l m i l l , add 10 d r o p s alcohol and grind m e c h a n i c a l l y f o r 15 min to reduce the p a r t i c l e s i z e to < 2~. (Since s t r u c t u r e s of the clay m i n e r a l s can be b r o k e n down by d r y grinding, 10 d r o p s (ca. 0.5 ml) of alcohol w e r e added to the s e d i m e n t s and s t a n d a r d s p r i o r to m e c h a n i c a l grinding. This is c o m p l e t e l y e v a p o r a t e d d u r i n g s t o r a g e at 90°C.) Weigh out ca. 1.5 mg of this s m a l l s i z e f r a c t i o n and t r a n s f e r to a clean b a l l mill. Add 600 mg KBr and mix m e c h a n i c a l l y f o r 15 min. E x t r a c t the powder, weigh out ca. 0.175 g and t r a n s f e r to a s t e e l die. E v a c u a t e f o r 5 min and p r e s s u n d e r vacuum at 15 tons p r e s s u r e f o r 2 min.
Preparation of spectrograms Using t w e e z e r s p l a c e the d i s c in the s a m p l e b e a m h o l d e r of the s p e c t r o p h o t o m e t e r , p l a c e a p u r e K B r d i s c in the r e f e r e n c e b e a m h o l d e r and attenuate the s a m p l e b e a m to give a b a s e l i n e t r a n s m i s s i o n of ca. 60%.
Preparation of standard curve K B r d i s c s w e r e p r e p a r e d ( a s d e s c r i b e d above) f r o m a s e r i e s of m a r i n e s e d i m e n t s of known c h e m i c a l c o m p o s i t i o n (see Table HI). A s t a n d a r d curve was c o n s t r u c t e d showing the r e l a t i o n s h i p between the total c a r b o n a t e and " c l a y " a b s o r p t i o n bands of the s e d i m e n t s (at ca. 7/x and 9-11/x r e s p e c t i v e l y ) , and the c h e m i c a l l y d e t e r m i n e d total c a r b o n a t e content. The r a t i o u s e d was: (1) c a r b o n a t e / ( / ) c a r b o n a t e + ( 1 ) " c l a y " . (1 = i n t e n s i t y . ) The band i n t e n s i t i e s w e r e m e a s u r e d by the " b a s e l i n e " method ( s e e Chem. Geol., 1 (1966) 277-290
283
WAVELENGTH 6.0
6.5
"0-
7.0
" ~.~, ..............
(.MICRONS)
7. 5
i.
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WAVE NUMBER
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1200
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I100
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I000
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900
(CM'I)
Fig.5. Method of b a s e l i n e m e a s u r e m e n t . I = i n t e n s i t y of the t r a n s m i t t e d r a d i a t i o n ; Io = i n t e n s i t y of the incident r a d i a t i o n . P o t t s , 1963). A b a s e l i n e was obtained by extending the h o r i z o n t a l p o r t i o n of the s p e c t r u m at ca. 6.25~ l a t e r a l l y a c r o s s both a n a l y s i s bands m e e t i n g the s p e c t r u m at ca. 8~ (the t r a n s m i s s i o n m a x i m u m between the two bands) and at ca. 11.2/.£ (the low wavelength s h o u l d e r of the v2 c a r b o n a t e band). The i n t e n s i t i e s w e r e then obtained by r e a d i n g the d i f f e r e n c e of the t r a n s m i s s i o n v a l u e s at the r e l e v a n t band head ( r e a d f r o m the s p e c t r u m chart), f r o m that where the b a s e l i n e i n t e r s e c t s a p e r p e n d i c u l a r line equal to the wavelength of the a b s o r p t i o n m a x i m a of the band ( s e e Fig.5). The r a t i o of the i n t e n s i t y of one peak to a n o t h e r was obtained f r o m t h e s e r e a d i n g s . The s t a n d a r d curve is r e p r o d u c e d in Fig.4.
RESULTS The total c a r b o n a t e content of t h i r t e e n m a r i n e c a r b o n a t e s e d i m e n t s was d e t e r m i n e d using the method outlined above. In addition, the c a r b o n a t e content of seven t e r r e s t r i a l s e d i m e n t a r y c a r b o n a t e r o c k s was a l s o d e t e r m i n e d in o r d e r to i l l u s t r a t e the wide a p p l i c a b i l i t y of the method. The r e s u l t s a r e l i s t e d in T a b l e V, and a r e c o m p a r e d to the c h e m i c a l d e t e r m i n a t i o n of t o t a l carbonate. The c o r r e l a t i o n coefficient between the total c a r b o n a t e content d e t e r mined c h e m i c a l l y and by the i n f r a - r e d method is r = 0.999. The s t a n d a r d e r r o r of e s t i m a t e in the i n f r a - r e d v a l u e s i s 0.443%, which m e a n s that 95% of the r e s u l t s a r e within 0.89% of the e s t i m a t e d value, and 99% within 1.33% of the e s t i m a t e d value. Of the total n u m b e r of r e s u l t s , including those in the s t a n d a r d c u r v e , 95% l i e within ± 2.0% of the c h e m i c a l d e t e r m i n a t i o n s . The method cannot be u s e d f o r s e d i m e n t s containing l e s s than ca. 5% total c a r bonate m i n e r a l s . The s e d i m e n t s and s e d i m e n t a r y r o c k s a n a l y s e d w e r e chosen to include a wide v a r i e t y of component m i n e r a l s . T h e s e include v a r i e t i e s of all m a r i n e 284
Chem. Geol.. 1 (1966) 277-290
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285
TABLE VI Single disc r e p r o d u c i b i l i t y Run no.
P e r c e n t a g e of total c a r b o n a t e grey c a l c a r e o u s turbidite
s a m p l e 21
s a m p l e 44
58.0 57.4 58.0 58.2 58.1
48.5 48.4 48.3 48.6 48.0
89.0 89.6 88.3 89.1 89.7
1 2 3 4 5 coeff, of variation
0.31
0.23
0.38
TABLE VII Multi-disc reproducibility Run no.
1 2 3 4 5 eoeff, of variation
P e r c e n t a g e of total c a r b o n a t e grey c a l c a r e o u s turbidite
s a m p l e 21
s a m p l e 44
57.4 59.6 60.4 59.7 57.9
48.5 49.4 47.4 50.3 48.0
89.1 90.4 88.6 90.4 88.2
1.28
1.10
1.02
TABLE VIII The effect of variation in p e r c e n t a g e t r a n s m i s s i o n on single disc r e p r o d u c i b i l i t y Run no.
1 2 3 4 5 coeff, of variation
P e r c e n t a g e of total c a r b o n a t e 5 s c a n s on s a m e disc
s c a n s on 5 separate discs
57.3 58.1 57.6 56.0 59.5
52.1 52,1 49.8 58.6 57.3
1.27
3.77
c l a y m i n e r a l s a n d c a l c i t e , d o l o m i t e , m a g n e s i t e a n d q u a r t z . In a d d i t i o n t o t h e s e m i n e r a l s , two s p e c i a l s a m p l e s w e r e i n c l u d e d in t h o s e m a k i n g u p the standard curve. These were no.30, a deep-sea volcanic carbonate sediment, a n d n o . 1 5 , a c a l c a r e o u s m a n g a n i f e r o u s o o z e . It w o u l d a p p e a r t h e r e f o r e t h a t t h e i n f r a - r e d m e t h o d d o e s n o t s u f f e r f r o m i n t e r f e r e n c e f r o m a n y of t h e m i n e r a l s n o r m a l l y p r e s e n t in m a r i n e s e d i m e n t s . In o r d e r t o t e s t t h e r e p r o d u c i b i l i t y o f t h e i n f r a - r e d m e t h o d f i v e s e p a r a t e r u n s w e r e m a d e on o n e K B r d i s c f r o m e a c h of t h r e e s a m p l e s . R e s u l t s a r e l i s t e d in T a b l e VI. 286
Chem. Geol., I (1966) 277-290
F i v e s e p a r a t e K B r d i s c s w e r e a l s o m a d e f r o m e a c h of t h e t h r e e s a m p l e s . R e s u l t s a r e g i v e n in T a b l e VII. It w a s s t a t e d e a r l i e r t h a t t r a n s m i s s i o n r e a d i n g s s h o u l d be in t h e r a n g e 20-60%, a n d t h a t t h e p e r c e n t a g e t r a n s m i s s i o n i s d e p e n d e n t on t h e a m o u n t of s a m p l e in a K B r d i s c . To i l l u s t r a t e t h i s , r e p r o d u c i b i l i t y t e s t s w e r e c a r r i e d out on one s a m p l e u s i n g a s a m p l e w e i g h t g i v i n g a t r a n s m i s s i o n at t h e v 3 c a r b o n a t e a b s o r p t i o n m a x i m u m of 7.5%. T h e r e s u l t s a r e l i s t e d in T a b l e VIII. It i s c l e a r f r o m t h e s e f i g u r e s t h a t t h e r e i s a d e c r e a s e in r e p r o d u c i b i l i t y with d e c r e a s e in b a n d h e a d t r a n s m i s s i o n . T h e S i - O b a n d in t h e r e g i o n 8 - 1 1 ~ d e r i v e s f r o m S i - O b a n d s in the c l a y m i n e r a l s , q u a r t z and o p a l (if p r e s e n t ) . E x a m i n a t i o n of t h e i n t e r r e l a t i o n s h i p s b e t w e e n t h e i n t e n s i t y of t h i s b a n d and t h e c o n t e n t s of A120 3 and SiO 2 in t h e s e d i m e n t s r e v e a l e d t h a t t h e i n f r a - r e d s p e c t r o g r a m s can b e u s e d to o b t a i n a s e m i - q u a n t i t a t i v e e s t i m a t i o n of A1203 and SiO 2. A1203 in m a r i n e s e d i m e n t s i s c o n f i n e d a l m o s t e x c l u s i v e l y to t h e c l a y m i n e r a l s , and the S i - O b a n d p e a k , o r t h e r a t i o of t h i s to a n o t h e r p e a k , s h o u l d g i v e a q u a n t i t a t i v e e s t i m a t e of t h e A1203 content. In o r d e r to s t u d y t h i s r e l a t i o n s h i p a s t a n d a r d c u r v e , u t i l i s i n g t h e r a t i o (I) " c l a y " / ( / ) " c l a y " + (I) c a r b o n a t e w a s d r a w n f r o m t h e s a m e s p e c t r a l c h a r t s u s e d to p r e p a r e the t o t a l c a r b o n a t e s t a n d a r d c u r v e . T h e A1203 c u r v e i s i l l u s t r a t e d in F i g . 6 A . T h e c u r v e w a s u s e d t o d e t e r m i n e t h e A1203 c o n t e n t of e l e v e n m a r i n e c a r b o n a t e s e d i m e n t s and s i x t e r r e s t r i a l c a r b o n a t e r o c k s . T h e r e s u l t s a r e l i s t e d in °/o ALUMINA
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"CLAY" "C LAY*'t'CARBONATE F i g . 6 . S t a n d a r d c u r v e s f o r t h e s e m i - q u a n t i t a t i v e d e t e r m i n a t i o n . A. A l u m i n a . B. S i l i c a .
Chem. Geol., 1 (1966) 277-290
287
TABLE IX The s e m i - q u a n t i t a t i v e d e t e r m i n a t i o n of alumina and s i l i c a of a s e r i e s of m a r i n e c a r b o n a t e s e d i m e n t s and t e r r e s t r i a l s e d i m e n t a r y r o c k s Sample No. 1
Analyst 2
P e r c e n t alumina
Percent silica
chemical
infra-red
chemical
infra-red
1 5 13 21 4 9 44 61 18 35 37 11
1 1 1 1 1 1 2 2 2 2 2 2
6.87 7.24 15.09 9.63 8.79 8.73 1.71 13.09 15.16 9.52 5.64 8.23
6.7 7.2 16.0 9.6 14.1 8,0 1,8 13,3 15,2 9.0 6.2 8.3
21.82 24.57 50.30 29.48 47.23 25.10 5.85 55.91 64.08 42.31 25.85 42.18
21.8 23.5 67.0 35.0 60.0 27.0 5.8 55.0 67.5 32.5 20.0 32.0
-
3 3 3
13.12 9.53 10.17
12.6 7.1 9.0
47.61 26.00 30.10
51.0 23.5 33.5
-
3
3.13
2.5
6.91
7.0
-
3
3.61
3.1
8.68
8.5
1See a p p r o p r i a t e publication: 2Chemical a n a l y s e s byi (1) E1 Wakeel and Riley (1961); (2) C h e s t e r (1965); (3) Wilson (in p r e p a r a t i o n ) :
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Fig.7. C o m p a r i s o n of r e s u l t s determined chemically and by the u s e of standard c u r v e s ( s e e Fig.6). A. Alumina. B. Silica. 288
Chem. Geol., 1 {1966) 277-290
T a b l e IX, w h e r e t h e y a r e c o m p a r e d to t h e c h e m i c a l d e t e r m i n a t i o n of A1203 , and a r e i l l u s t r a t e d in F i g . 7 A . T h e c o r r e l a t i o n c o e f f i c i e n t b e t w e e n t h e A1203 c o n t e n t s d e t e r m i n e d c h e m i c a l l y and by t h e i n f r a - r e d m e t h o d i s r = 0.940. I n f r a - r e d d e t e r m i n a t i o n s of c h e m i c a l c o m p o n e n t s a r e i n d i r e c t , i . e . , the c h e m i c a l c o m p o n e n t i s e s t i m a t e d f r o m a g r o s s a b s o r p t i o n band. F o r t h i s r e a s o n s u c h d e t e r m i n a t i o n s w i l l be m o r e a c c u r a t e f o r t h o s e e l e m e n t s w h i c h a r e l o c a l i s e d in one s e d i m e n t a r y c o m p o n e n t , s u c h a s A1203 in the c l a y m i n e r a l s . H o w e v e r , t o t a l s i l i c a d e t e r m i n e d a s p a r t of a r o u t i n e s i l i c a t e a n a l y s i s w i l l i n c l u d e s i l i c a f r o m a v a r i e t y of l o c a t i o n s in t h e s e d i m e n t s , s u c h a s q u a r t z , opal and the clay minerals. These minerals have different infra-red chara c t e r i s t i c s and w i l l c o m p l i c a t e the i n f r a - r e d e s t i m a t i o n of t o t a l SiO 2. T h e r e l a t i o n s h i p b e t w e e n t h e i n t e n s i t y of t h e S i - O b a n d at ca. 9 - - l l g and c h e m i c a l l y d e t e r m i n e d t o t a l SiO 2 w a s e x a m i n e d in s o m e of t h e s e d i m e n t s l i s t e d in T a b l e HI. A s t a n d a r d c u r v e w a s d r a w n u t i l i s i n g t h e r e l a t i o n s h i p (I) " c l a y " / ( / ) " c l a y " + (1) c a r b o n a t e v % SiO 2. M e a s u r e m e n t s w e r e m a d e f r o m t h e s p e c t r a l c h a r t s u s e d to d r a w t h e t o t a l c a r b o n a t e c a l i b r a t i o n c u r v e . T h e SiO2 c u r v e i s i l l u s t r a t e d in F i g . 6 B . T h e c u r v e w a s u s e d to d e t e r m i n e the t o t a l SiO2 c o n t e n t of e l e v e n m a r i n e c a r b o n a t e s e d i m e n t s and f o u r t e r r e s t r i a l c a r b o n a t e r o c k s . The r e s u l t s a r e l i s t e d in T a b l e IX, w h e r e t h e y a r e c o m p a r e d to t h e c h e m i c a l d e t e r m i n a t i o n s , and a r e i l l u s t r a t e d in F i g . 7 B . T h e c o r r e l a t i o n c o e f f i c i e n t b e t w e e n the t o t a l SiO2 c o n t e n t s d e t e r m i n e d c h e m i c a l l y and the i n f r a - r e d m e t h o d i s r = 0.914. F r o m the p r e s e n t s t u d y it i s e v i d e n t t h a t i n f r a - r e d a n a l y s i s can b e u s e d f o r t h e r a p i d , a c c u r a t e , d e t e r m i n a t i o n of t o t a l c a r b o n a t e . T h e d e t e r m i n a t i o n s of A12O 3 and SiO2 a r e l e s s a c c u r a t e , but a r e n e v e r t h e l e s s u s e f u l if t h e n u m b e r of s a m p l e s i s t o o g r e a t to p e r m i t a full c h e m i c a l a n a l y s i s to b e m a d e on e a c h one. The c o r r e l a t i o n b e t w e e n i n f r a - r e d and c h e m i c a l l y d e t e r m i n e d A120 3 and SiO2 a r e r = 0.940 and r = 0.914 r e s p e c t i v e l y . T h e s e m a y b e c o m p a r e d with c o r r e l a t i o n c o e f f i c i e n t s b e t w e e n c h e m i c a l l y and s p e c t r o g r a p h i c a l l y d e t e r m i n e d A1203 and SiO2 o b t a i n e d f r o m G o l d b e r g and A r r h e n i u s (1958). T h e i n d i v i d u a l d e t e r m i n a t i o n s w e r e r e a d f r o m F i g . 2 ( G o l d b e r g and A r r h e n i u s , 1958), and g a v e the f o l l o w i n g r e s u l t s f o r A1203 and SiO2: r = ca. 0.830 and r = ca. 0.811, r e s p e c t i v e l y .
ACKNOWLEDGEMENT T h e a u t h o r s e x p r e s s t h e i r t h a n k s to D r . J . P . R i l e y , D e p a r t m e n t of O c e a n o g raphy, The University, Liverpool, England, for kindly making available a s e r i e s of d e e p - s e a c a r b o n a t e s e d i m e n t s , and f o r a l l o w i n g t h e a u t h o r s to m a k e u s e of a n a l y s e s f i r s t p u b l i s h e d b y E1 W a k e e l and R i l e y (1961).
REFERENCES Adler, H.H., Bray, E.E., Stevens, N.P., Hunt, J.M., Keller, W.D., Pickett, E.E. and K e r r , P.F., 1950. I n f r a - r e d spectra of reference clay minerals. Am. Petrol. Inst. Proj., Prelim. Rept. 8, 49: 7-146. Adler, H.H. and Kerr, P.F., 1962. I n f r a - r e d study of aragonite and calcite. Am. Mineralogist, 47: 700-717.
Chem. Geol., 1 {1966} 277~290
289
C h e s t e r , R., 1965. G e o c h e m i c a l c r i t e r i a for d i f f e r e n t i a t i n g r e e f f r o m n o n - r e e f f a c i e s in c a r b o n a t e r o c k s . Bull. Am. Assoc. P e t r o l . G e o l o g i s t s , 49: 258-276. C h e s t e r , R. and E l d e r f i e l d , H., in p r e p a r a t i o n . The a p p l i c a t i o n of i n f r a - r e d a b s o r p t i o n s p e c t r o s c o p y to c a r b o n a t e m i n e r a l o g y . C h e s t e r , R. and Hughes, M.J., 1966. The d i s t r i b u t i o n of m a n g a n e s e , iron and nickel in a N o r t h P a c i f i c d e e p - s e a clay c o r e . D e e p - S e a R e s . , in p r e s s . E1 Wakeel, S.K. and Riley, J . P . , 1961. C h e m i c a l and m i n e r a l o g i c a l s t u d i e s of d e e p - s e a s e d i m e n t s . Geochim. C o s m o c h i m . Acta, 25: 110-146. Goldberg, E.D. and A r r h e n i u s , G.O.S., 1958. C h e m i s t r y of Pacific pelagic s e d i m e n t s . Geochim. C o s m o c h i m . Acta, 13: 153-212. H e r z b e r g , G., 1945. M o l e c u l a r S p e c t r a and M o l e c u l a r S t r u c t u r e . 2. I n f r a - r e d a n d R a m a n S p e c t r a of P o l y a t o m i c Molecules. Van N o s t r a n d , New York, N.Y., 658 pp. Hunt, J.M. and T u r n e r , S.T., 1953. D e t e r m i n a t i o n of m i n e r a l c o n s t i t u e n t s of r o c k s by i n f r a r e d s p e c t r o s c o p y . Anal. Chem., 25(8): 1169-1174. K e l l e r , W.D., Spott, J.H. and Biggs, D.L., 1952. I n f r a - r e d s p e c t r a of some r o c k - f o r m i n g m i n e r a l s . Am. J. Sci., 250: 453--471. P o t t s , W.J., 1963. C h e m i c a l I n f r a - r e d S p e c t r o s c o p y . 1. T e c h n i q u e s . Wiley, New York, N.Y., 322 pp. Smith, L.A., 1965. I n f r a - r e d s p e c t r o s c o p y . In: I.M. Kolthoff, P.J.. Elving and E.B. Sandell (Editors), T r e a t i s e on Analytical C h e m i s t r y . Wiley, New York, N.Y., 6: 3535-3743. Wilson, F., in p r e p a r a t i o n . Some A s p e c t s of the G e o c h e m i s t r y of S e d i m e n t s and SeaW a t e r . Ph.D. T h e s i s , Univ. Liverpool.
290
Chem. Geol., 1 (1966) 277-290
THE INFRA-RED DETERMINATION OF TOTAL CARBONATE IN MARINE CARBONATE SEDIMENTS
R. CHESTER and H. ELDERFIELD Department of Oceanography, University of Liverpool, Liverpool (Great Britain} (Received July 4, 1966)
SUMMARY An i n f r a - r e d method is described for the determination of total carbonate in m a r i n e sediments. The method is calibrated with samples of known composition and may be used to determine total carbonate to ca. + 2% of the chemical values. It can also be used to give semi-quantitative estimates of A1203 and SiO 2.
INTRODUCTION Calcium carbonate is a quantitatively important component of many marine sediments, and about 50% of the deep ocean floor is covered by sediments containing m o r e than 30% organically derived calcium carbonate (El Wakeel and Riley, 1961). Recent geochemical studies have attempted to define the origin of t r a c e elements in m a r i n e sediments in relation to the methods by which they have been incorporated into the sedimentary phases (see Goldberg and Arrhenius, 1958; Chester and Hughes, 1966). This kind of approach will lead ultimately to a partial distinction between those t r a c e elements derived f r o m sea water, and those t r a n s p o r t e d in p r e - e x i s t i n g mineral lattices (such as the clay minerals). The two most important quantitative components derived from sea water are f e r r o m a n g a n e s e nodules (hydrogenous origin), and calcium carbonate (biogenous origin). A knowledge of the distribution of calcium carbonate in marine sediments is t h e r e f o r e important in studies aimed at establishing the distribution and origin of the m a j o r mineral components, and also the t r a c e element geochemistry. The i n f r a - r e d identification of carbonate m i n e r a l s has been established by s e v e r a l w o r k e r s , e.g., Adler et al. (1950), Keller et al. (1952), and has been s u m m a r i z e d by Chester and Elderfield (in preparation). Quantitative aspects of carbonate mineralogy, such as the determination of c a l c i t e dolomite ratios and calcite-aragonite ratios, have been examined by Hunt and T u r n e r (1953), Adler and K e r r (1962) and C h e s t e r and Elderfield (in preparation). The present paper outlines a quantitative i n f r a - r e d method of determining total carbonate, i.e., calcium and magnesium carbonates in sediments, based on the c a r b o n a t e - c l a y ratio in the samples, which is both rapid and accurate. Chem. Geol., 1 (1966) 277-290
277
TABLE I Wavelengths of the i n f r a - r e d a b s o r p t i o n bands of the i m p o r t a n t m a r i n e c a r b o n a t e s 1 (After C h e s t e r and E l d e r f i e l d , in p r e p a r a t i o n ) Carbonate mineral
Wavelength (p)
Calcite
7.00(s,b)
Aragonite
6.78(re,b)
Magnesite
6.90(s,b)
Dolomite
6.94(s,b)
v3
v1
9.23(m,sh)
v2
v4
11.41(s,sh) 11.76(w) 11.67(s,sh) 11.90 (w) ll.30(s,sh) 11.73(w,sh) ll.38(s,sh) 11.73(w)
14.08(s,sh) I 14.08(s,sh) [ 14.39 (s, sh) 13.40(s,sh) 13.76(s,sh)
1Key: s = strong; m = medium; w = weak; sh = sharp; b = b r o a d ; ~ = doublet. TABLE II Wavelengths of the i n f r a - r e d a b s o r p t i o n bands of the i m p o r t a n t m a r i n e clay m i n e r a l s in the 8-12~ range 1 Clay m i n e r a l
Wavelength r a n g e (p)
s~
9~
10p
] 1~
Chlorite Illite Kaolinite
9.30(sd) 9.75(sd) 10.10(s) 10.46(sd) 8.65(sd) 9.17(sd) 9.75(s) 8.99(sd) 9.09(s) ~9.71(s) 10.68(sd) t9.90(s) Montmorillonite 9.13(sd) 9.80(s)
11.49(m) 10.95(w) 10.95(s) 10.95(w) l l . 4 0 ( s d ) l l . 9 0 ( s d )
1Key: s = strong; m = medium; w = weak; sd = s h o u l d e r ; f = doublet.
WAVELENGTH 6.5
7.0
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7.5
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9.5
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MINERAl. (.~"~,~M1rl)
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(crn-')
Fig.1. I n f r a - r e d s p e c t r u m of a typical d e e p - s e a carbonate sediment. 278
Chem. Geol., 1 (1966) 277-290
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WAVELENGTH(MICRONS) Fig.2. I n f r a - r e d s p e c t r a of clay m i n e r a l s . A. C h l o r i t e . B. I l l i t e . C. Kaolinite. D. M o n t m o r i l l o n i t e .
SELECTION O F ABSORPTION BANDS Calcite, aragonite and minor amounts of magnesite and dolomite are the main c a r b o n a t e m i n e r a l s in m a r i n e s e d i m e n t s . The a b s o r p t i o n s p e c t r a of t h e s e m i n e r a l s a r e given in T a b l e I, and a g e n e r a l i z e d i n f r a - r e d s p e c t r u m of a Chem. Geol., 1 (1966) 277-290
Z79
d e e p - s e a c a r b o n a t e s e d i m e n t i s i l l u s t r a t e d in F i g . 1 . In T a b l e I the a b s o r p t i o n b a n d s a r e c l a s s i f i e d a c c o r d i n g to t h e s c h e m e g i v e n by H e r z b e r g (1945), into Vl, v2, v3 and v 4 f u n d a m e n t a l a b s o r p t i o n b a n d s e a c h of which c o r r e s p o n d s to a p a r t i c u l a r d e f o r m a t i o n a l m o d e of t h e CO32- ion. F r o m T a b l e I it can b e s e e n that the v 2 and v4 b a n d s will r e s o l v e into a s e r i e s of p e a k s if a m i x t u r e of t h e c a r b o n a t e s i s p r e s e n t . On the o t h e r hand, t h e v 3 band h a s i t s b a n d h e a d in the r e g i o n 6 . 7 8 - 7 . 0 0 p f o r a l l t h e c a r b o n a t e s . T h i s i s a b r o a d b a n d and t h e a d d i t i o n of one of t h e c a r b o n a t e s to a n o t h e r in a s a m p l e i n c r e a s e s the b a n d i n t e n s i t y without m a t e r i a l l y a l t e r i n g t h e p o s i t i o n of t h e b a n d h e a d . F o r t h i s r e a s o n the v3 b a n d w a s s e l e c t e d f o r total carbonate determination. The c l a y m i n e r a l s p r e s e n t in m a r i n e s e d i m e n t s a r e m a i n l y i l l i t e , c h l o r i t e , k a o l i n i t e and m o n t m o r i l l o n i t e . The i n f r a - r e d s p e c t r a of a l l t h e s e m i n e r a l s i n c l u d e a S i - O bond p e a k at ca. 8 . 0 - 1 1 . 0 ~ . T h e s e a r e l i s t e d in T a b l e II, a l o n g with o t h e r a b s o r p t i o n b a n d s in t h i s r e g i o n , and the i n f r a - r e d s p e c t r a of t h e s e m i n e r a l s a r e i l l u s t r a t e d in F i g . 2 .
SPECTROPHOTOMETER
DISCS
S a m p l e s w e r e i n t r o d u c e d into t h e s p e c t r o p h o t o m e t e r in t h e f o r m of p o t a s s i u m b r o m i d e d i s c s . The p a r t i c l e s i z e of t h e m a t e r i a l in t h e d i s c s m u s t be l e s s than t h e m i n i m u m i n f r a - r e d w a v e l e n g t h u s e d , h e r e 2 . 5 - 1 5 g . To e n s u r e t h i s , t h e s a m p l e s and K B r w e r e g r o u n d m e c h a n i c a l l y in a s t e e l b a l l m i l l f o r 15 min. C h e c k s r e v e a l e d t h a t g r i n d i n g f o r t h i s t i m e r e d u c e d ca. 90% of the s a m p l e s to a g r a i n s i z e ~ 2 g . The t r a n s m i s s i o n r a n g e o v e r w h i c h m e a s u r e m e n t s can be m a d e i s p a r t i c u l a r l y i m p o r t a n t in q u a n t i t a t i v e i n f r a - r e d m e a s u r e m e n t s . S m i t h (1965) h a s r e p o r t e d t h a t o p t i m u m r e a d i n g s can be o b t a i n e d in the r e g i o n 20-60% t r a n s m i s s i o n , and in t h e p r e s e n t w o r k the weight of s a m p l e in e a c h d i s c w a s a d j u s t e d to g i v e r e a d i n g s in t h i s r e g i o n .
STANDARD
CURVE
A d l e r and K e r r (1962) and C h e s t e r and E l d e r f i e l d (in p r e p a r a t i o n ) h a v e shown t h a t t h e s h a p e s of i n f r a - r e d s t a n d a r d c u r v e s a r e d e p e n d e n t on the m i n e r a l s u s e d in t h e i r c o n s t r u c t i o n , and c u r v e s c o n s t r u c t e d f r o m i n o r g a n i c a l l y p r e c i p i t a t e d c a l c i t e d i f f e r f r o m t h o s e of o r g a n i c c a l c i t e . F o r t h i s r e a s o n a s e r i e s of c a l i b r a t i o n c u r v e s w a s p r e p a r e d in an a t t e m p t to s i m u l a t e t h e m i n e r a l c o m p o s i t i o n of m a r i n e c a r b o n a t e s e d i m e n t s . T h e s e w e r e a s f o l l o w s : (1) I n o r g a n i c c a l c i t e and i l l i t e ( i l l i t e w a s s e l e c t e d a s b e i n g r e p r e s e n t a t i v e of m a r i n e c l a y m i n e r a l s ) . (2) O r g a n i c s h e l l c a l c i t e (Balanus balanoides) and t h e a c i d i n s o l u b l e r e s i d u e of a d e e p - s e a r e d c l a y ( s a m p l e no.9, E1 W a k e e l and R i l e y , 1961). (3) D e e p - s e a c a r b o n a t e s e d i m e n t s , t h e c o m p o s i t i o n s of which had b e e n d e t e r m i n e d c h e m i c a l l y . T h e c o m p o s i t i o n s a r e l i s t e d in T a b l e III. F o r e a c h of t h e s e m i x t u r e s s t a n d a r d c u r v e s w e r e c o n s t r u c t e d s h o w i n g the r e l a t i o n s h i p b e t w e e n t h e t o t a l c a r b o n a t e and " c l a y " c o m p o n e n t s ( u t i l i s i n g the r a t i o of t h e b a n d i n t e n s i t i e s at c a . 7 ~ and 9 - 1 1 ~ r e s p e c t i v e l y b y a m e t h o d g i v e n l a t e r ) , and t h e c h e m i c a l l y d e t e r m i n e d t o t a l c a r b o n a t e content. T h e 280
Chem. Geol., 1 (1966) 277-290
TABLE HI Samples used in the construction of standard curve 1" Sample no. (El Wakeel and Riley, 1961)
Analyst 1
3
-
Percentage total carbonate 0
Position
Type and colour
35°55TN 17°29'E
Globigerina ooze-buff (2N HC1 washed} deep-sea clay volcanic muddy sand, 2-19 cm of core deep-sea calcareous clay Globigerina ooze-buff calcareous ooze; light brown-red calcareous manganiferous; chocolate calcareous ooze; white Globigerina ooze; white calcitic shell
2 1
3.00 11.98
northwest Atlantic 19°46'N 154°58'W
9 1
2 1 1
24.00 54.54 61.30
northwest Atlantic 35°55'N 17°29'E 24°20'N 24°28'W
15
1
72.82
22°07'S I I 5 ° I 0 ' W
6
2 1 3
90.00 92.62 i00.00
29°02'N 25°27'W 26°08'S 14°36'W Plymouth
-
30 -
-
-
(Balanus balanoides) *See Fig.4. 1Chemical analyses by: (1} E1 Wakeel and Riley {1961}; (2) Wilson (in preparation}; (3) the authors. TABLE
IV
Comparison of the results of total carbonate determined chemically with those obtained from the three standard curves on application of the i n f r a- r ed technique Sample I 61 A 44
Chemical method 32.0 59.0 87.5
Infra-red method using standard curves curve 1
curve 2
curve 3
45.0 63.0 90.5
25.1 57.0 97.0
31.5 59.0 88.4
1See Table V. t h r e e s t a n d a r d c u r v e s d i f f e r e d s i g n i f i c a n t l y , and e a c h w a s t e s t e d e m p i r i c a l l y t o d e t e r m i n e t h e t o t a l c a r b o n a t e in a s e r i e s of m a r i n e s e d i m e n t s w h i ch had been previously analyzed. T h e r e s u l t s a r e g i v e n in T a b l e IV, and t h e s t a n d a r d c u r v e s a r e i l l u s t r a t e d in F i g . 3 and 4. T h e r e a s o n s f o r t h e v a r i a t i o n s in t h e s t a n d a r d c u r v e s a r e not known, but it m a y be t h a t m e c h a n i c a l m i x i n g cannot a p p r o x i m a t e to t h e i n t i m a t e m i n e r a l a d m i x t u r e found in n a t u r a l m a r i n e s e d i m e n t s . A n o t h e r p o s s i b i l i t y i s t h a t t h e o r g a n i c m a t e r i a l u s e d t o c o n s t r u c t c u r v e 2 did not r e p r o d u c e the n a t u r a l c o n d i t i o n s s u f f i c i e n t l y w e l l. T h e c u r v e c o n s t r u c t e d f r o m n a t u r a l s e d i m e n t s t a n d a r d s a p p e a r e d t o be t h e m o s t p r o m i s i n g , and w a s c h o s e n as b e s t r e p r e s e n t i n g the natural conditions.
Chem. Geol., 1 {1966} 277-290
281
ioo
I
F
[
~
B
I00
,P
8o
1
80
w Z
o m ,< U
6o i
60
40
40
20
io
.i U w a.
0 0
0.2
0.4
0.6
0,8
INTENSITY
0.2
1.0
RATIO
0.4
0.6
0.8
I.O
CARBONATE CA R ~ N A T E +~CLAY '
Fig.3. S t a n d a r d c u r v e s f o r the d e t e r m i n a t i o n of total c a r b o n a t e u s i n g : A. I n o r g a n i c c a l c i t e and i l l i t e . B. O r g a n i c c a l c i t e (Balanus balanoides s h e l l ) and a c a r b o n a t e - f r e e d e e p - s e a s e d i m e n t ( s a m p l e 9, E1 W a k e e l and R i l e y , 1961). Ioo
8o
6o w
g < u4o IZ w U n,.
2O
o
...-"'"7'~1 0
I 0,2
I
INTENSITY
I 0.4
I
I 0.6
I
I 0.8
RATIO
CARBONATE CARBONATE + 'CLAY'
I
l 1.0
Fig.4. Standard curve for the determination of total carbonate using chemically analysed samples (see Table ]I1). 282
Chem. Geol., i (1966) 277-290
EXPERIMENTAL CONDITIONS
Apparatus A H i l g e r and Watts H900 " I n f r a s c a n " d o u b l e - b e a m r e c o r d i n g s p e c t r o p h o t o m e t e r , i n c o r p o r a t i n g a g r a t i n g m o n o c h r o m a t o r and s o d i u m - c h l o r i d e optics was u s e d to obtain the s p e c t r o g r a m s . The r a t e of scanning e m p l o y e d was 16 rain f o r the range 3,880-650 cm-1. To offset any m i n o r i m p u r i t i e s in the K B r , and to m i n i m i s e the effects of a b s o r b e d w a t e r , a K B r d i s c ( p r e p a r e d using the s a m e weight of KBr as the s a m p l e disc) was p l a c e d in the r e f e r e n c e b e a m of the i n s t r u m e n t . This tends to i n c r e a s e the b a s e l i n e t r a n s m i s s i o n and as this is i m p o r t a n t the t r a n s m i s s i o n was modified by attenuating the s a m p l e b e a m to give a t r a n s m i s s i o n in the r a n g e 20-60%.
Preparation of samples The s e d i m e n t s a m p l e s (and s t a n d a r d s ) and K B r ( " a n a l a r " g r a d e ) a r e ground s e p a r a t e l y to p a s s a 240 m e s h s i e v e (B.S.S.), and a r e s t o r e d in an oven at 90°C until r e q u i r e d .
Preparation of KBr discs T r a n s f e r an amount of the d r i e d s a m p l e (ca. 0.25 g) to a s t e e l b a l l m i l l , add 10 d r o p s alcohol and grind m e c h a n i c a l l y f o r 15 min to reduce the p a r t i c l e s i z e to < 2~. (Since s t r u c t u r e s of the clay m i n e r a l s can be b r o k e n down by d r y grinding, 10 d r o p s (ca. 0.5 ml) of alcohol w e r e added to the s e d i m e n t s and s t a n d a r d s p r i o r to m e c h a n i c a l grinding. This is c o m p l e t e l y e v a p o r a t e d d u r i n g s t o r a g e at 90°C.) Weigh out ca. 1.5 mg of this s m a l l s i z e f r a c t i o n and t r a n s f e r to a clean b a l l mill. Add 600 mg KBr and mix m e c h a n i c a l l y f o r 15 min. E x t r a c t the powder, weigh out ca. 0.175 g and t r a n s f e r to a s t e e l die. E v a c u a t e f o r 5 min and p r e s s u n d e r vacuum at 15 tons p r e s s u r e f o r 2 min.
Preparation of spectrograms Using t w e e z e r s p l a c e the d i s c in the s a m p l e b e a m h o l d e r of the s p e c t r o p h o t o m e t e r , p l a c e a p u r e K B r d i s c in the r e f e r e n c e b e a m h o l d e r and attenuate the s a m p l e b e a m to give a b a s e l i n e t r a n s m i s s i o n of ca. 60%.
Preparation of standard curve K B r d i s c s w e r e p r e p a r e d ( a s d e s c r i b e d above) f r o m a s e r i e s of m a r i n e s e d i m e n t s of known c h e m i c a l c o m p o s i t i o n (see Table HI). A s t a n d a r d curve was c o n s t r u c t e d showing the r e l a t i o n s h i p between the total c a r b o n a t e and " c l a y " a b s o r p t i o n bands of the s e d i m e n t s (at ca. 7/x and 9-11/x r e s p e c t i v e l y ) , and the c h e m i c a l l y d e t e r m i n e d total c a r b o n a t e content. The r a t i o u s e d was: (1) c a r b o n a t e / ( / ) c a r b o n a t e + ( 1 ) " c l a y " . (1 = i n t e n s i t y . ) The band i n t e n s i t i e s w e r e m e a s u r e d by the " b a s e l i n e " method ( s e e Chem. Geol., 1 (1966) 277-290
283
WAVELENGTH 6.0
6.5
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7.0
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(.MICRONS)
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(CM'I)
Fig.5. Method of b a s e l i n e m e a s u r e m e n t . I = i n t e n s i t y of the t r a n s m i t t e d r a d i a t i o n ; Io = i n t e n s i t y of the incident r a d i a t i o n . P o t t s , 1963). A b a s e l i n e was obtained by extending the h o r i z o n t a l p o r t i o n of the s p e c t r u m at ca. 6.25~ l a t e r a l l y a c r o s s both a n a l y s i s bands m e e t i n g the s p e c t r u m at ca. 8~ (the t r a n s m i s s i o n m a x i m u m between the two bands) and at ca. 11.2/.£ (the low wavelength s h o u l d e r of the v2 c a r b o n a t e band). The i n t e n s i t i e s w e r e then obtained by r e a d i n g the d i f f e r e n c e of the t r a n s m i s s i o n v a l u e s at the r e l e v a n t band head ( r e a d f r o m the s p e c t r u m chart), f r o m that where the b a s e l i n e i n t e r s e c t s a p e r p e n d i c u l a r line equal to the wavelength of the a b s o r p t i o n m a x i m a of the band ( s e e Fig.5). The r a t i o of the i n t e n s i t y of one peak to a n o t h e r was obtained f r o m t h e s e r e a d i n g s . The s t a n d a r d curve is r e p r o d u c e d in Fig.4.
RESULTS The total c a r b o n a t e content of t h i r t e e n m a r i n e c a r b o n a t e s e d i m e n t s was d e t e r m i n e d using the method outlined above. In addition, the c a r b o n a t e content of seven t e r r e s t r i a l s e d i m e n t a r y c a r b o n a t e r o c k s was a l s o d e t e r m i n e d in o r d e r to i l l u s t r a t e the wide a p p l i c a b i l i t y of the method. The r e s u l t s a r e l i s t e d in T a b l e V, and a r e c o m p a r e d to the c h e m i c a l d e t e r m i n a t i o n of t o t a l carbonate. The c o r r e l a t i o n coefficient between the total c a r b o n a t e content d e t e r mined c h e m i c a l l y and by the i n f r a - r e d method is r = 0.999. The s t a n d a r d e r r o r of e s t i m a t e in the i n f r a - r e d v a l u e s i s 0.443%, which m e a n s that 95% of the r e s u l t s a r e within 0.89% of the e s t i m a t e d value, and 99% within 1.33% of the e s t i m a t e d value. Of the total n u m b e r of r e s u l t s , including those in the s t a n d a r d c u r v e , 95% l i e within ± 2.0% of the c h e m i c a l d e t e r m i n a t i o n s . The method cannot be u s e d f o r s e d i m e n t s containing l e s s than ca. 5% total c a r bonate m i n e r a l s . The s e d i m e n t s and s e d i m e n t a r y r o c k s a n a l y s e d w e r e chosen to include a wide v a r i e t y of component m i n e r a l s . T h e s e include v a r i e t i e s of all m a r i n e 284
Chem. Geol.. 1 (1966) 277-290
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285
TABLE VI Single disc r e p r o d u c i b i l i t y Run no.
P e r c e n t a g e of total c a r b o n a t e grey c a l c a r e o u s turbidite
s a m p l e 21
s a m p l e 44
58.0 57.4 58.0 58.2 58.1
48.5 48.4 48.3 48.6 48.0
89.0 89.6 88.3 89.1 89.7
1 2 3 4 5 coeff, of variation
0.31
0.23
0.38
TABLE VII Multi-disc reproducibility Run no.
1 2 3 4 5 eoeff, of variation
P e r c e n t a g e of total c a r b o n a t e grey c a l c a r e o u s turbidite
s a m p l e 21
s a m p l e 44
57.4 59.6 60.4 59.7 57.9
48.5 49.4 47.4 50.3 48.0
89.1 90.4 88.6 90.4 88.2
1.28
1.10
1.02
TABLE VIII The effect of variation in p e r c e n t a g e t r a n s m i s s i o n on single disc r e p r o d u c i b i l i t y Run no.
1 2 3 4 5 coeff, of variation
P e r c e n t a g e of total c a r b o n a t e 5 s c a n s on s a m e disc
s c a n s on 5 separate discs
57.3 58.1 57.6 56.0 59.5
52.1 52,1 49.8 58.6 57.3
1.27
3.77
c l a y m i n e r a l s a n d c a l c i t e , d o l o m i t e , m a g n e s i t e a n d q u a r t z . In a d d i t i o n t o t h e s e m i n e r a l s , two s p e c i a l s a m p l e s w e r e i n c l u d e d in t h o s e m a k i n g u p the standard curve. These were no.30, a deep-sea volcanic carbonate sediment, a n d n o . 1 5 , a c a l c a r e o u s m a n g a n i f e r o u s o o z e . It w o u l d a p p e a r t h e r e f o r e t h a t t h e i n f r a - r e d m e t h o d d o e s n o t s u f f e r f r o m i n t e r f e r e n c e f r o m a n y of t h e m i n e r a l s n o r m a l l y p r e s e n t in m a r i n e s e d i m e n t s . In o r d e r t o t e s t t h e r e p r o d u c i b i l i t y o f t h e i n f r a - r e d m e t h o d f i v e s e p a r a t e r u n s w e r e m a d e on o n e K B r d i s c f r o m e a c h of t h r e e s a m p l e s . R e s u l t s a r e l i s t e d in T a b l e VI. 286
Chem. Geol., I (1966) 277-290
F i v e s e p a r a t e K B r d i s c s w e r e a l s o m a d e f r o m e a c h of t h e t h r e e s a m p l e s . R e s u l t s a r e g i v e n in T a b l e VII. It w a s s t a t e d e a r l i e r t h a t t r a n s m i s s i o n r e a d i n g s s h o u l d be in t h e r a n g e 20-60%, a n d t h a t t h e p e r c e n t a g e t r a n s m i s s i o n i s d e p e n d e n t on t h e a m o u n t of s a m p l e in a K B r d i s c . To i l l u s t r a t e t h i s , r e p r o d u c i b i l i t y t e s t s w e r e c a r r i e d out on one s a m p l e u s i n g a s a m p l e w e i g h t g i v i n g a t r a n s m i s s i o n at t h e v 3 c a r b o n a t e a b s o r p t i o n m a x i m u m of 7.5%. T h e r e s u l t s a r e l i s t e d in T a b l e VIII. It i s c l e a r f r o m t h e s e f i g u r e s t h a t t h e r e i s a d e c r e a s e in r e p r o d u c i b i l i t y with d e c r e a s e in b a n d h e a d t r a n s m i s s i o n . T h e S i - O b a n d in t h e r e g i o n 8 - 1 1 ~ d e r i v e s f r o m S i - O b a n d s in the c l a y m i n e r a l s , q u a r t z and o p a l (if p r e s e n t ) . E x a m i n a t i o n of t h e i n t e r r e l a t i o n s h i p s b e t w e e n t h e i n t e n s i t y of t h i s b a n d and t h e c o n t e n t s of A120 3 and SiO 2 in t h e s e d i m e n t s r e v e a l e d t h a t t h e i n f r a - r e d s p e c t r o g r a m s can b e u s e d to o b t a i n a s e m i - q u a n t i t a t i v e e s t i m a t i o n of A1203 and SiO 2. A1203 in m a r i n e s e d i m e n t s i s c o n f i n e d a l m o s t e x c l u s i v e l y to t h e c l a y m i n e r a l s , and the S i - O b a n d p e a k , o r t h e r a t i o of t h i s to a n o t h e r p e a k , s h o u l d g i v e a q u a n t i t a t i v e e s t i m a t e of t h e A1203 content. In o r d e r to s t u d y t h i s r e l a t i o n s h i p a s t a n d a r d c u r v e , u t i l i s i n g t h e r a t i o (I) " c l a y " / ( / ) " c l a y " + (I) c a r b o n a t e w a s d r a w n f r o m t h e s a m e s p e c t r a l c h a r t s u s e d to p r e p a r e the t o t a l c a r b o n a t e s t a n d a r d c u r v e . T h e A1203 c u r v e i s i l l u s t r a t e d in F i g . 6 A . T h e c u r v e w a s u s e d t o d e t e r m i n e t h e A1203 c o n t e n t of e l e v e n m a r i n e c a r b o n a t e s e d i m e n t s and s i x t e r r e s t r i a l c a r b o n a t e r o c k s . T h e r e s u l t s a r e l i s t e d in °/o ALUMINA
18
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"CLAY" "C LAY*'t'CARBONATE F i g . 6 . S t a n d a r d c u r v e s f o r t h e s e m i - q u a n t i t a t i v e d e t e r m i n a t i o n . A. A l u m i n a . B. S i l i c a .
Chem. Geol., 1 (1966) 277-290
287
TABLE IX The s e m i - q u a n t i t a t i v e d e t e r m i n a t i o n of alumina and s i l i c a of a s e r i e s of m a r i n e c a r b o n a t e s e d i m e n t s and t e r r e s t r i a l s e d i m e n t a r y r o c k s Sample No. 1
Analyst 2
P e r c e n t alumina
Percent silica
chemical
infra-red
chemical
infra-red
1 5 13 21 4 9 44 61 18 35 37 11
1 1 1 1 1 1 2 2 2 2 2 2
6.87 7.24 15.09 9.63 8.79 8.73 1.71 13.09 15.16 9.52 5.64 8.23
6.7 7.2 16.0 9.6 14.1 8,0 1,8 13,3 15,2 9.0 6.2 8.3
21.82 24.57 50.30 29.48 47.23 25.10 5.85 55.91 64.08 42.31 25.85 42.18
21.8 23.5 67.0 35.0 60.0 27.0 5.8 55.0 67.5 32.5 20.0 32.0
-
3 3 3
13.12 9.53 10.17
12.6 7.1 9.0
47.61 26.00 30.10
51.0 23.5 33.5
-
3
3.13
2.5
6.91
7.0
-
3
3.61
3.1
8.68
8.5
1See a p p r o p r i a t e publication: 2Chemical a n a l y s e s byi (1) E1 Wakeel and Riley (1961); (2) C h e s t e r (1965); (3) Wilson (in p r e p a r a t i o n ) :
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Fig.7. C o m p a r i s o n of r e s u l t s determined chemically and by the u s e of standard c u r v e s ( s e e Fig.6). A. Alumina. B. Silica. 288
Chem. Geol., 1 {1966) 277-290
T a b l e IX, w h e r e t h e y a r e c o m p a r e d to t h e c h e m i c a l d e t e r m i n a t i o n of A1203 , and a r e i l l u s t r a t e d in F i g . 7 A . T h e c o r r e l a t i o n c o e f f i c i e n t b e t w e e n t h e A1203 c o n t e n t s d e t e r m i n e d c h e m i c a l l y and by t h e i n f r a - r e d m e t h o d i s r = 0.940. I n f r a - r e d d e t e r m i n a t i o n s of c h e m i c a l c o m p o n e n t s a r e i n d i r e c t , i . e . , the c h e m i c a l c o m p o n e n t i s e s t i m a t e d f r o m a g r o s s a b s o r p t i o n band. F o r t h i s r e a s o n s u c h d e t e r m i n a t i o n s w i l l be m o r e a c c u r a t e f o r t h o s e e l e m e n t s w h i c h a r e l o c a l i s e d in one s e d i m e n t a r y c o m p o n e n t , s u c h a s A1203 in the c l a y m i n e r a l s . H o w e v e r , t o t a l s i l i c a d e t e r m i n e d a s p a r t of a r o u t i n e s i l i c a t e a n a l y s i s w i l l i n c l u d e s i l i c a f r o m a v a r i e t y of l o c a t i o n s in t h e s e d i m e n t s , s u c h a s q u a r t z , opal and the clay minerals. These minerals have different infra-red chara c t e r i s t i c s and w i l l c o m p l i c a t e the i n f r a - r e d e s t i m a t i o n of t o t a l SiO 2. T h e r e l a t i o n s h i p b e t w e e n t h e i n t e n s i t y of t h e S i - O b a n d at ca. 9 - - l l g and c h e m i c a l l y d e t e r m i n e d t o t a l SiO 2 w a s e x a m i n e d in s o m e of t h e s e d i m e n t s l i s t e d in T a b l e HI. A s t a n d a r d c u r v e w a s d r a w n u t i l i s i n g t h e r e l a t i o n s h i p (I) " c l a y " / ( / ) " c l a y " + (1) c a r b o n a t e v % SiO 2. M e a s u r e m e n t s w e r e m a d e f r o m t h e s p e c t r a l c h a r t s u s e d to d r a w t h e t o t a l c a r b o n a t e c a l i b r a t i o n c u r v e . T h e SiO2 c u r v e i s i l l u s t r a t e d in F i g . 6 B . T h e c u r v e w a s u s e d to d e t e r m i n e the t o t a l SiO2 c o n t e n t of e l e v e n m a r i n e c a r b o n a t e s e d i m e n t s and f o u r t e r r e s t r i a l c a r b o n a t e r o c k s . The r e s u l t s a r e l i s t e d in T a b l e IX, w h e r e t h e y a r e c o m p a r e d to t h e c h e m i c a l d e t e r m i n a t i o n s , and a r e i l l u s t r a t e d in F i g . 7 B . T h e c o r r e l a t i o n c o e f f i c i e n t b e t w e e n the t o t a l SiO2 c o n t e n t s d e t e r m i n e d c h e m i c a l l y and the i n f r a - r e d m e t h o d i s r = 0.914. F r o m the p r e s e n t s t u d y it i s e v i d e n t t h a t i n f r a - r e d a n a l y s i s can b e u s e d f o r t h e r a p i d , a c c u r a t e , d e t e r m i n a t i o n of t o t a l c a r b o n a t e . T h e d e t e r m i n a t i o n s of A12O 3 and SiO2 a r e l e s s a c c u r a t e , but a r e n e v e r t h e l e s s u s e f u l if t h e n u m b e r of s a m p l e s i s t o o g r e a t to p e r m i t a full c h e m i c a l a n a l y s i s to b e m a d e on e a c h one. The c o r r e l a t i o n b e t w e e n i n f r a - r e d and c h e m i c a l l y d e t e r m i n e d A120 3 and SiO2 a r e r = 0.940 and r = 0.914 r e s p e c t i v e l y . T h e s e m a y b e c o m p a r e d with c o r r e l a t i o n c o e f f i c i e n t s b e t w e e n c h e m i c a l l y and s p e c t r o g r a p h i c a l l y d e t e r m i n e d A1203 and SiO2 o b t a i n e d f r o m G o l d b e r g and A r r h e n i u s (1958). T h e i n d i v i d u a l d e t e r m i n a t i o n s w e r e r e a d f r o m F i g . 2 ( G o l d b e r g and A r r h e n i u s , 1958), and g a v e the f o l l o w i n g r e s u l t s f o r A1203 and SiO2: r = ca. 0.830 and r = ca. 0.811, r e s p e c t i v e l y .
ACKNOWLEDGEMENT T h e a u t h o r s e x p r e s s t h e i r t h a n k s to D r . J . P . R i l e y , D e p a r t m e n t of O c e a n o g raphy, The University, Liverpool, England, for kindly making available a s e r i e s of d e e p - s e a c a r b o n a t e s e d i m e n t s , and f o r a l l o w i n g t h e a u t h o r s to m a k e u s e of a n a l y s e s f i r s t p u b l i s h e d b y E1 W a k e e l and R i l e y (1961).
REFERENCES Adler, H.H., Bray, E.E., Stevens, N.P., Hunt, J.M., Keller, W.D., Pickett, E.E. and K e r r , P.F., 1950. I n f r a - r e d spectra of reference clay minerals. Am. Petrol. Inst. Proj., Prelim. Rept. 8, 49: 7-146. Adler, H.H. and Kerr, P.F., 1962. I n f r a - r e d study of aragonite and calcite. Am. Mineralogist, 47: 700-717.
Chem. Geol., 1 {1966} 277~290
289
C h e s t e r , R., 1965. G e o c h e m i c a l c r i t e r i a for d i f f e r e n t i a t i n g r e e f f r o m n o n - r e e f f a c i e s in c a r b o n a t e r o c k s . Bull. Am. Assoc. P e t r o l . G e o l o g i s t s , 49: 258-276. C h e s t e r , R. and E l d e r f i e l d , H., in p r e p a r a t i o n . The a p p l i c a t i o n of i n f r a - r e d a b s o r p t i o n s p e c t r o s c o p y to c a r b o n a t e m i n e r a l o g y . C h e s t e r , R. and Hughes, M.J., 1966. The d i s t r i b u t i o n of m a n g a n e s e , iron and nickel in a N o r t h P a c i f i c d e e p - s e a clay c o r e . D e e p - S e a R e s . , in p r e s s . E1 Wakeel, S.K. and Riley, J . P . , 1961. C h e m i c a l and m i n e r a l o g i c a l s t u d i e s of d e e p - s e a s e d i m e n t s . Geochim. C o s m o c h i m . Acta, 25: 110-146. Goldberg, E.D. and A r r h e n i u s , G.O.S., 1958. C h e m i s t r y of Pacific pelagic s e d i m e n t s . Geochim. C o s m o c h i m . Acta, 13: 153-212. H e r z b e r g , G., 1945. M o l e c u l a r S p e c t r a and M o l e c u l a r S t r u c t u r e . 2. I n f r a - r e d a n d R a m a n S p e c t r a of P o l y a t o m i c Molecules. Van N o s t r a n d , New York, N.Y., 658 pp. Hunt, J.M. and T u r n e r , S.T., 1953. D e t e r m i n a t i o n of m i n e r a l c o n s t i t u e n t s of r o c k s by i n f r a r e d s p e c t r o s c o p y . Anal. Chem., 25(8): 1169-1174. K e l l e r , W.D., Spott, J.H. and Biggs, D.L., 1952. I n f r a - r e d s p e c t r a of some r o c k - f o r m i n g m i n e r a l s . Am. J. Sci., 250: 453--471. P o t t s , W.J., 1963. C h e m i c a l I n f r a - r e d S p e c t r o s c o p y . 1. T e c h n i q u e s . Wiley, New York, N.Y., 322 pp. Smith, L.A., 1965. I n f r a - r e d s p e c t r o s c o p y . In: I.M. Kolthoff, P.J.. Elving and E.B. Sandell (Editors), T r e a t i s e on Analytical C h e m i s t r y . Wiley, New York, N.Y., 6: 3535-3743. Wilson, F., in p r e p a r a t i o n . Some A s p e c t s of the G e o c h e m i s t r y of S e d i m e n t s and SeaW a t e r . Ph.D. T h e s i s , Univ. Liverpool.
290
Chem. Geol., 1 (1966) 277-290