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Differential alteration of phyllosilicate minerals under hydromorphic conditions
Applied Clay Science, 1 (1985) 57--64
57
Elsevier S c i e n c e Publishers B.V., Amsterdam -- Printed in T h e N e t h e r l a n d s
DIFFERENTIAL ALTERATION OF PHYLLOSILICATE MINERALS UNDER HYDROMORPHIC CONDITIONS
M I C H E L C A I L L I E R I, B E R N A R D G U I L L E T 2 and M I C H E L G U R Y 2 IDdparternent des Sols, Universitd Laval, Quebec, P.Q. G I K 7P4 (Canada) 2 Centre de P$dologie, Biologique du C.N.R.S., B.P. 5, 54500, Vandoeuvre-les-Nancy (France) (Accepted for publication March 11, 1985)
ABSTRACT Caillier, M., Guillet, B. and Gury, M., 1985. Differential alteration of phyllosilicate minerals under hydromorphic conditions. Appl. Clay Sci., 1: 57--64. Differential alteration processes of clay minerals are well expressed in the albic tongues of soils with glossic features. The explanation of these processes can be found in the reducing and acidic conditions created by the presence of a temporary perched water table. The observed phases are: the chlorite microdivision of the silty fraction, the formation of interstratified (14C--14V) chlorite--vermiculite clay which by magnesium release is further transformed into a vermiculite, and the alteration and partial removal of hydroxyaluminum interlayers of a chloritized smectite present in the clay fraction.
INTRODUCTION
Soils with giossic features generally present a well~iifferentiated characteristic morphology. The A2 horizon, having less clay and being more or less completely whitened, penetrates deeply into the Bt horizon in the form of narrow vertical channels which are widened at the top. These channels or albic tongues, which are silty at the top and more clayed at the bottom, may cross the complete solum (Jamagne, 1973). Examples of glossification in progress are seldom observed. However, the alluvial terraces of the Moselle Valley (Vosges department, France) which are covered with silt, allow this process to be followed. A pattern of albic tongues, developed from the upper part of the Bt horizon, can be observed below the A2g horizon in a "sol brun lessiv6" (Caillier, 1977). Macrofissures, filled with dark reddish gray (SYR 4/2) clay material extend from these albic tongues into a paleosol (II Bt). This filling of clay material slows down the vertical drainage and is responsible for the perched water table the bottom of which in winter is located at the wide-mouthed level of the albic tongues. By mineralogical and chemical analyses of samples obtained at every level of albic tongue, macrofissure, and corresponding matrix systems, it is possible to follow the different stages of
0169-1317]85/$03.30
© 1 9 8 5 Elsevier S c i e n c e Publishers B.V.
58 clay mineral transformation and weathering, associated with the various phases of the glossification process. METHODOLOGY The sampled profile is located in "le Rang du X a y " (sheet 1GN 1:25,000, Epinal 3--4; 6°26'12"E 48°12'47"N) on the left bank of the Moselle at 3 2 5 m of altitude on a 15--20m high terrace level (Caillier et al., 1984). Samples were taken from each horizon and from all levels of the albic tongue--macrofissure system. After drying and sieving at 2 mm, particle-size fractionation was done according to Rouiller et al. (1972). Clays were completely fractionated in three particle-size classes (0--0.1 pm; 0.1--0.5 tim; 0.5--2gm) by ultracentrifugation of continuous flow (Brethes, 1971). The mineralogical analysis was done by X-ray diffractometry on oriented clay saturated with Mg ~+ or K ÷. The swelling tests of the 2/1 clay minerals were done using ethylene glycol and those of kaolinite with hydrazine. Heating tests were done at 330°C and 550°C to determine the thermal stability of the h y d r o x y a l u m i n u m interlayers and the presence of chlorites. The total chemical analysis was conducted on 500 mg of each clay fraction that had been pre-treated with dithionite-bicarbonate-citrate (Mehra and Jackson, 1960). The washed and dried residue was decomposed with strontium metaborate (Jeanroy, 1972) and the elements were determined by atomic absorption. RESULTS
Fine clays: 0--0.1 gm Mineralogical analysis. This clay fraction is composed of three mineral groups. Chlorite and interstratified (101--14V) illite--vermiculite are the two minor components. The most important group is composed of a complex population consisting of a chloritized smectite. The incomplete closure at 10A when K ÷ saturated suggests the presence of h y d r o x y a l u m i n a in the smectite interlayers. Geochemical analysis. The molecular ratios SIO2/A1203 (Table I) varies from 2.64 to 2.91 in the different horizons as well as in the macrofissure and TABLE I Molecular SiO2/AI2 03 ratio of the fine clay fraction (0--0.1 pm)
Matrix Albic tongue Macrofissure
A2
A2 Bt
Btg
IIBt
2.76
2.91 3.29
2.80 2.83
2.64 2.77
59
A2Bt
Ao
u.I O
Z
O 0 n.1 <
Vlz
if) x er }-
0 U < =Z
3,57
5
7,25
10 14 16,6A °'-
3,57
5
7,25 10
14 16,6A ~
Fig. 1. X - r a y d i f f r a c t i o n p a t t e r n s f o r t h e f i n e c l a y f r a c t i o n ( 0 - - 0 . 1 / . t i n ) ; a = M g 2+ t r e a t e d ; b = e t h y l e n e - - - g l y c o l s o l v a t e d ; c -- M g 2+ t r e a t e d , h e a t e d at 3 3 0 ° C f o r 2 h ; d = M g 2+ treated, heated at 550°C for I h; e = K + treated.
60
MATRIX
~
i "'~
~
J ~I
]]Bt ~ \ y.
s
715
lo
14
A°
5
715
10
14 Av
Fig. 2. X - r a y d i f f r a c t i o n p a t t e r n s f o r t h e m e d i u m c l a y f r a c t i o n ( 0 . 1 - - 0 . 5 p r o ) ; + 2+ o treated; b = K treated; c = Mg t r e a t e d , h e a t e d at 5 5 0 C f o r 1 h.
a : M g 2+
61
in the matrices. In the albic tongue, the ratio varies from 2.91 to 3.29 in the matrix.
Medium (0.1--0.5 I~m) and coarse (0.5--2 #m) clays Mineralogical analysis. Illite and interstratified (101--14V) illite-vermiculite are present in all the horizons and they represent about 25%. The well crystallized kaolinite, with sharp peaks between 7.13 and 7.17A moving to 10.45A when hydrazine-treated, is estimated to be 15% in each of the two clay-fractions. The remaining amount {60%) is made up of 14A minerals (Fig. 2). Ethylene glycolation shows that swelling minerals are absent. This group is composed of chlorite, vermiculite sensu stricto (collapse to 10A when K+-saturated) and of a population of aluminous intergrades (VA1) and/ or interstratified (14C--14V) chlorite--vermiculite. When K÷-saturated, these intergrades and/or interstratified minerals remain at 13.8A or partially collapse to around 10A (Fig. 2). At 550°C there is some collapse to 10A but this peak is skewed towards lower angles. This indicates the presence of aluminous vermiculites and interstratified (14C--14V) chlorite--vermiculite. A small amount of quartz, which increases in the coarse clay fraction (0.5--2 #m), is also present. Geochemical analysis. The SiO2/A12 03 ratios are not meaningful because of the presence of quartz in these two fractions. The F e 2 0 3 / K 2 0 ratio of the medium clay fraction (Table II) shows lower values in the albic tongue (0.89) as compared to those of the macrofissure (1.23) and matrices (1.03--1.54). This ratio varies similarly in the coarse clay fraction. The evolution of the MgO/K2 O ratio is identical in the medium clay fraction (Table III); it is lowest in the albic tongue (1.65--1.68), and increases in the macrofissure (2.23) and the matrices (1.83--2.36). The situation is the same for the coarse clay fraction with 1.21 in the albic tongue, 1.51 in the macrofissure and 1.36 to 1.54 in the matrices. TABLE II Molecular Fe203/K2 O ratio of the medium (0.1--0.5/lm) and coarse (0.5--2gm) clay fractions
Matrix Albic tongue
A2
A2 Bt
Btg
IIBt
1.06 .1 (0.73)
1.03 (0.72)
1.03 (0.72)
1.54 (0.87)
0.89 (0.62)
0.88 (0.62)
Macrofissure
• 1 1.06: medium clay fraction (0.1--0.5//m) (0.73): coarse clay fraction (0.5--2pm)
1.23 (0.67)
62 TABLE III Molecular MgO/K20 ratio of the medium (0.1--0.5pm) and coarse ( 0 . 5 - - 2 p r o ) c l a y fractions
Matrix
A2
A2 Bt
Btg
IIBt
1.96 .1 (1.40)
1.83 (1.36)
1.96 (1.37)
2.36 (1.54)
1.68 (1.21)
1.65 (1.21)
Albic tongue Macrofissure
2.23 (1.51)
• 11.96: medium clay fraction 0.1--0.5/lm (1.40): coarse clay fraction 0.5--2pm
The silt (2--20 pm) This fraction is composed of quartz, feldspar and chlorite. Based on the relative peak intensities ( 0 0 2 = 004 > 001 >> 003), the chlorites can be associated with the iron-octahedral and Mg-brucitic chlorite group (Pochon, 1974). DISCUSSION
Fine clay fraction evolution (0--0.1 pm) The increase of the SiO2/A12 03 ratio in the albic tongue clearly indicates decrease in the aluminum content of the minerals. This may be explained by the reducing environment created by the temporarily hydromorphic conditions. The loss of aluminum may be explained by the solubility of hydroxyaluminum contained in the smectite interlayers. The following evidence supports the loss of hydroxyaluminum interlayers. In X-ray diffraction, we observe a better swelling with ethylene glycol at 17A (Fig. 1)and the appearance of a distinct peak at 9.6A when heated at 550 °C. We also observe a definite increase in the cation exchange capacity (C.E.C.) (Table IV) which implies a larger number of exchange sites. Finally, these TABLE IV Cation exchange capacity (meq./100 g) of the fine clay fraction (0--0.1 pm)
Matrix Albic tongue Macrofissure
A2
A2 Bt
Btg
IIBt
61.4
61.7 70.3
61.9 62.5
62.3 62.5
63 TABLE V CaO content of the fine clay fraction (0--0.1/.tm)
Matrix Albic tongue Macrofissure
A2
A2 Bt
Btg
IIBt
0.4
0.4 6.1
0.3 0.5
0.6 0.2
clays have a high CaO content (Table V). This calcium was not dissolved with the chemical treatments used to isolate this fraction. Thus, the mineralogical and geochemical analyses of phyUosilicate minerals of the finest clay fraction (0--0.1 #m) clearly show an active leaching process of A1 from the hydroxyaluminum interlayers of smectites under hydromorphic conditions.
Medium (0.1--0.5 #m) and coarse (0.5--2 I~m) clay fraction evolution It is well known that, in acidic soils, the alteration and break-down of trioctahedral chlorites result in accumulation of interstratified chlorite-vermiculite (Lelong and Souchier, 1972) and vermiculites (Schwertmann, 1976) that axe susceptible to destruction. The comparison of phyllosilicate minerals present in the wide part of the albic tongue, in the macrofissure, and the matrices shows these mineralogical transformations starting from the iron and magnesium chlorites contained in the silty and coarse clay fractions. The decrease of interstratified chlorite--vermiculite in the albic tongue can be explained by the selective dissolution of brucitic layers of chlorite which axe unstable under the acidic and reducing conditions created by the temporary water table. The weathering of the interstratified chlorite--vermiculite results in formation and accumulation of vermiculite and release of magnesium. As observed by Gury (1976), we also see that this magnesium mobilization is accompanied by an increase of exchangeable magnesium (Table VI). TABLE VI Variation of Ca 2+ and M g 2+ content on the exchange complex
Matrix Albic tongue
A2
A2 Bt
Btg
IIBt
2.93 .1 (0.40)
2.01 (1.06)
1.36 (1.71)
0.76 (1.19)
1.06 (0.72)
1.91 (2.76)
Macrofissure
*~ 2 . 9 3 : Ca 2÷ m e q . / l O 0 g (0.40): Mgz÷ meq./lO0 g
1.66 (2.74)
64 CONCLUSION
T h e mineralogical a n d g e o c h e m i c a l analyses o f t h e albic t o n g u e - - m a c r o fissure m a t r i x s y s t e m o f soil w i t h glossic f e a t u r e s i n d i c a t e d t h e t r a n s f o r m a t i o n s o c c u r r i n g in t h e albic t o n g u e u n d e r h y d r o m o r p h i c c o n d i t i o n s . T w o m a j o r p h e n o m e n a were o b s e r v e d : t h e selective loss o f a l u m i n u m f r o m h y d r o x y a l u m i n u m i n t e r l a y e r s , w h i c h is p a r t i c u l a r l y e v i d e n t in the fine clay fraction, and the degradation of interstratified (14C--14V) chlorite-v e r m i c u l i t e o f m e d i u m a n d coarse clay f r a c t i o n s , w h i c h can be c o r r e l a t e d w i t h t h e d o m i n a n c e o f e x c h a n g e a b l e m a g n e s i u m . We also o b s e r v e d a m i c r o division o f p r i m a r y m a g n e s i u m chlorites of t h e silty f r a c t i o n and t h e a p p a r e n t stability o f kaolinite. ACKNOWLEDGEMENTS T h e a u t h o r s wish t o t h a n k Mr. B l a c k b u r n o f Soil Science D e p a r t m e n t o f Laval U n i v e r s i t y a n d G.J. Ross of t h e C h e m i s t r y a n d Biology R e s e a r c h I n s t i t u t e o f A g r i c u l t u r e C a n a d a f o r reviewing t h e m a n u s c r i p t . REFERENCES Brethes, A., 1971. Etude d'une m~thode de fractionnement des particules inf6rieures fi 2 microns. D.E.A. de P~dologie, Nancy, 37 pp. Caillier, M., 1977. Etude chronos~quentielle des sols sur terrasses alluviales de la Moselle. Gen~se et ~volution des sols lessiv6sglossiques. Th~se de Sp6cialit6, Universit6 Nancy I, 87 pp. Caillier, M., Gury, M. and Guillet, B. 1984. Dissolution d'oxyhydroxydes de fer et alteration diff~rentielle de min~raux phylliteux en milieu hydromorphe. P~dologie, XXXIV-1:43---66. Gury, M., 1976. Evolution des sols en milieu acide et hydromorphe sur terrasses alluviales de la Meurthe. Th~se de SpecialitY, Universit~ de Nancy I, 100 pp. Jamagne, M., 1973. Contribution ~ l'dtude pddog~n~tique des formations loessiques du Nord de la France. Th~se, Facult~ des Sciences Agronomiques de l'Etat, Gembloux,
445 pp. Jeanroy, E., 1972. Analyses totales des silicates naturels par spectrophotom~trie d' adsorption atomique. Applications au sol et ~ ses constituants. Chim. Anal., 54 (3). Lelong, F. and Souchier, B., 1972. Nature et g~n~se des argiles dans |es profils vosgiens de la s~quence sols bruns acides-podzols sur granite. Science de la Terre, 17(4):353--379. Mehra, O.P. and Jackson, M.L., 1960. Iron-oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. Clays Clay Miner., 7: 317--327. Pochon, M., 1974. Origine et ~volution des sols du Haut-Jura suisse. Ph~nom~ne d' alteration des roches calcaires sous climat temp~r~ humide. Th~se, Facult~ des Sciences, Neufchhtel, 322 pp. Rouiller, J., Burtin, G. and Souchier, B., 1972. La dispersion des sols dans l'analyse granulom~trique. M~thode utilisant les rdsines ~changeuses d'ions. Bull. E.N.S.A.I.A., Nancy, 14(2):193--205. Schwertmann, U., 1976. Verwitterung mafischer Chlorite. Z. Pflanzenernaehr. Bodenkd., 1:27--36.
57
Elsevier S c i e n c e Publishers B.V., Amsterdam -- Printed in T h e N e t h e r l a n d s
DIFFERENTIAL ALTERATION OF PHYLLOSILICATE MINERALS UNDER HYDROMORPHIC CONDITIONS
M I C H E L C A I L L I E R I, B E R N A R D G U I L L E T 2 and M I C H E L G U R Y 2 IDdparternent des Sols, Universitd Laval, Quebec, P.Q. G I K 7P4 (Canada) 2 Centre de P$dologie, Biologique du C.N.R.S., B.P. 5, 54500, Vandoeuvre-les-Nancy (France) (Accepted for publication March 11, 1985)
ABSTRACT Caillier, M., Guillet, B. and Gury, M., 1985. Differential alteration of phyllosilicate minerals under hydromorphic conditions. Appl. Clay Sci., 1: 57--64. Differential alteration processes of clay minerals are well expressed in the albic tongues of soils with glossic features. The explanation of these processes can be found in the reducing and acidic conditions created by the presence of a temporary perched water table. The observed phases are: the chlorite microdivision of the silty fraction, the formation of interstratified (14C--14V) chlorite--vermiculite clay which by magnesium release is further transformed into a vermiculite, and the alteration and partial removal of hydroxyaluminum interlayers of a chloritized smectite present in the clay fraction.
INTRODUCTION
Soils with giossic features generally present a well~iifferentiated characteristic morphology. The A2 horizon, having less clay and being more or less completely whitened, penetrates deeply into the Bt horizon in the form of narrow vertical channels which are widened at the top. These channels or albic tongues, which are silty at the top and more clayed at the bottom, may cross the complete solum (Jamagne, 1973). Examples of glossification in progress are seldom observed. However, the alluvial terraces of the Moselle Valley (Vosges department, France) which are covered with silt, allow this process to be followed. A pattern of albic tongues, developed from the upper part of the Bt horizon, can be observed below the A2g horizon in a "sol brun lessiv6" (Caillier, 1977). Macrofissures, filled with dark reddish gray (SYR 4/2) clay material extend from these albic tongues into a paleosol (II Bt). This filling of clay material slows down the vertical drainage and is responsible for the perched water table the bottom of which in winter is located at the wide-mouthed level of the albic tongues. By mineralogical and chemical analyses of samples obtained at every level of albic tongue, macrofissure, and corresponding matrix systems, it is possible to follow the different stages of
0169-1317]85/$03.30
© 1 9 8 5 Elsevier S c i e n c e Publishers B.V.
58 clay mineral transformation and weathering, associated with the various phases of the glossification process. METHODOLOGY The sampled profile is located in "le Rang du X a y " (sheet 1GN 1:25,000, Epinal 3--4; 6°26'12"E 48°12'47"N) on the left bank of the Moselle at 3 2 5 m of altitude on a 15--20m high terrace level (Caillier et al., 1984). Samples were taken from each horizon and from all levels of the albic tongue--macrofissure system. After drying and sieving at 2 mm, particle-size fractionation was done according to Rouiller et al. (1972). Clays were completely fractionated in three particle-size classes (0--0.1 pm; 0.1--0.5 tim; 0.5--2gm) by ultracentrifugation of continuous flow (Brethes, 1971). The mineralogical analysis was done by X-ray diffractometry on oriented clay saturated with Mg ~+ or K ÷. The swelling tests of the 2/1 clay minerals were done using ethylene glycol and those of kaolinite with hydrazine. Heating tests were done at 330°C and 550°C to determine the thermal stability of the h y d r o x y a l u m i n u m interlayers and the presence of chlorites. The total chemical analysis was conducted on 500 mg of each clay fraction that had been pre-treated with dithionite-bicarbonate-citrate (Mehra and Jackson, 1960). The washed and dried residue was decomposed with strontium metaborate (Jeanroy, 1972) and the elements were determined by atomic absorption. RESULTS
Fine clays: 0--0.1 gm Mineralogical analysis. This clay fraction is composed of three mineral groups. Chlorite and interstratified (101--14V) illite--vermiculite are the two minor components. The most important group is composed of a complex population consisting of a chloritized smectite. The incomplete closure at 10A when K ÷ saturated suggests the presence of h y d r o x y a l u m i n a in the smectite interlayers. Geochemical analysis. The molecular ratios SIO2/A1203 (Table I) varies from 2.64 to 2.91 in the different horizons as well as in the macrofissure and TABLE I Molecular SiO2/AI2 03 ratio of the fine clay fraction (0--0.1 pm)
Matrix Albic tongue Macrofissure
A2
A2 Bt
Btg
IIBt
2.76
2.91 3.29
2.80 2.83
2.64 2.77
59
A2Bt
Ao
u.I O
Z
O 0 n.1 <
Vlz
if) x er }-
0 U < =Z
3,57
5
7,25
10 14 16,6A °'-
3,57
5
7,25 10
14 16,6A ~
Fig. 1. X - r a y d i f f r a c t i o n p a t t e r n s f o r t h e f i n e c l a y f r a c t i o n ( 0 - - 0 . 1 / . t i n ) ; a = M g 2+ t r e a t e d ; b = e t h y l e n e - - - g l y c o l s o l v a t e d ; c -- M g 2+ t r e a t e d , h e a t e d at 3 3 0 ° C f o r 2 h ; d = M g 2+ treated, heated at 550°C for I h; e = K + treated.
60
MATRIX
~
i "'~
~
J ~I
]]Bt ~ \ y.
s
715
lo
14
A°
5
715
10
14 Av
Fig. 2. X - r a y d i f f r a c t i o n p a t t e r n s f o r t h e m e d i u m c l a y f r a c t i o n ( 0 . 1 - - 0 . 5 p r o ) ; + 2+ o treated; b = K treated; c = Mg t r e a t e d , h e a t e d at 5 5 0 C f o r 1 h.
a : M g 2+
61
in the matrices. In the albic tongue, the ratio varies from 2.91 to 3.29 in the matrix.
Medium (0.1--0.5 I~m) and coarse (0.5--2 #m) clays Mineralogical analysis. Illite and interstratified (101--14V) illite-vermiculite are present in all the horizons and they represent about 25%. The well crystallized kaolinite, with sharp peaks between 7.13 and 7.17A moving to 10.45A when hydrazine-treated, is estimated to be 15% in each of the two clay-fractions. The remaining amount {60%) is made up of 14A minerals (Fig. 2). Ethylene glycolation shows that swelling minerals are absent. This group is composed of chlorite, vermiculite sensu stricto (collapse to 10A when K+-saturated) and of a population of aluminous intergrades (VA1) and/ or interstratified (14C--14V) chlorite--vermiculite. When K÷-saturated, these intergrades and/or interstratified minerals remain at 13.8A or partially collapse to around 10A (Fig. 2). At 550°C there is some collapse to 10A but this peak is skewed towards lower angles. This indicates the presence of aluminous vermiculites and interstratified (14C--14V) chlorite--vermiculite. A small amount of quartz, which increases in the coarse clay fraction (0.5--2 #m), is also present. Geochemical analysis. The SiO2/A12 03 ratios are not meaningful because of the presence of quartz in these two fractions. The F e 2 0 3 / K 2 0 ratio of the medium clay fraction (Table II) shows lower values in the albic tongue (0.89) as compared to those of the macrofissure (1.23) and matrices (1.03--1.54). This ratio varies similarly in the coarse clay fraction. The evolution of the MgO/K2 O ratio is identical in the medium clay fraction (Table III); it is lowest in the albic tongue (1.65--1.68), and increases in the macrofissure (2.23) and the matrices (1.83--2.36). The situation is the same for the coarse clay fraction with 1.21 in the albic tongue, 1.51 in the macrofissure and 1.36 to 1.54 in the matrices. TABLE II Molecular Fe203/K2 O ratio of the medium (0.1--0.5/lm) and coarse (0.5--2gm) clay fractions
Matrix Albic tongue
A2
A2 Bt
Btg
IIBt
1.06 .1 (0.73)
1.03 (0.72)
1.03 (0.72)
1.54 (0.87)
0.89 (0.62)
0.88 (0.62)
Macrofissure
• 1 1.06: medium clay fraction (0.1--0.5//m) (0.73): coarse clay fraction (0.5--2pm)
1.23 (0.67)
62 TABLE III Molecular MgO/K20 ratio of the medium (0.1--0.5pm) and coarse ( 0 . 5 - - 2 p r o ) c l a y fractions
Matrix
A2
A2 Bt
Btg
IIBt
1.96 .1 (1.40)
1.83 (1.36)
1.96 (1.37)
2.36 (1.54)
1.68 (1.21)
1.65 (1.21)
Albic tongue Macrofissure
2.23 (1.51)
• 11.96: medium clay fraction 0.1--0.5/lm (1.40): coarse clay fraction 0.5--2pm
The silt (2--20 pm) This fraction is composed of quartz, feldspar and chlorite. Based on the relative peak intensities ( 0 0 2 = 004 > 001 >> 003), the chlorites can be associated with the iron-octahedral and Mg-brucitic chlorite group (Pochon, 1974). DISCUSSION
Fine clay fraction evolution (0--0.1 pm) The increase of the SiO2/A12 03 ratio in the albic tongue clearly indicates decrease in the aluminum content of the minerals. This may be explained by the reducing environment created by the temporarily hydromorphic conditions. The loss of aluminum may be explained by the solubility of hydroxyaluminum contained in the smectite interlayers. The following evidence supports the loss of hydroxyaluminum interlayers. In X-ray diffraction, we observe a better swelling with ethylene glycol at 17A (Fig. 1)and the appearance of a distinct peak at 9.6A when heated at 550 °C. We also observe a definite increase in the cation exchange capacity (C.E.C.) (Table IV) which implies a larger number of exchange sites. Finally, these TABLE IV Cation exchange capacity (meq./100 g) of the fine clay fraction (0--0.1 pm)
Matrix Albic tongue Macrofissure
A2
A2 Bt
Btg
IIBt
61.4
61.7 70.3
61.9 62.5
62.3 62.5
63 TABLE V CaO content of the fine clay fraction (0--0.1/.tm)
Matrix Albic tongue Macrofissure
A2
A2 Bt
Btg
IIBt
0.4
0.4 6.1
0.3 0.5
0.6 0.2
clays have a high CaO content (Table V). This calcium was not dissolved with the chemical treatments used to isolate this fraction. Thus, the mineralogical and geochemical analyses of phyUosilicate minerals of the finest clay fraction (0--0.1 #m) clearly show an active leaching process of A1 from the hydroxyaluminum interlayers of smectites under hydromorphic conditions.
Medium (0.1--0.5 #m) and coarse (0.5--2 I~m) clay fraction evolution It is well known that, in acidic soils, the alteration and break-down of trioctahedral chlorites result in accumulation of interstratified chlorite-vermiculite (Lelong and Souchier, 1972) and vermiculites (Schwertmann, 1976) that axe susceptible to destruction. The comparison of phyllosilicate minerals present in the wide part of the albic tongue, in the macrofissure, and the matrices shows these mineralogical transformations starting from the iron and magnesium chlorites contained in the silty and coarse clay fractions. The decrease of interstratified chlorite--vermiculite in the albic tongue can be explained by the selective dissolution of brucitic layers of chlorite which axe unstable under the acidic and reducing conditions created by the temporary water table. The weathering of the interstratified chlorite--vermiculite results in formation and accumulation of vermiculite and release of magnesium. As observed by Gury (1976), we also see that this magnesium mobilization is accompanied by an increase of exchangeable magnesium (Table VI). TABLE VI Variation of Ca 2+ and M g 2+ content on the exchange complex
Matrix Albic tongue
A2
A2 Bt
Btg
IIBt
2.93 .1 (0.40)
2.01 (1.06)
1.36 (1.71)
0.76 (1.19)
1.06 (0.72)
1.91 (2.76)
Macrofissure
*~ 2 . 9 3 : Ca 2÷ m e q . / l O 0 g (0.40): Mgz÷ meq./lO0 g
1.66 (2.74)
64 CONCLUSION
T h e mineralogical a n d g e o c h e m i c a l analyses o f t h e albic t o n g u e - - m a c r o fissure m a t r i x s y s t e m o f soil w i t h glossic f e a t u r e s i n d i c a t e d t h e t r a n s f o r m a t i o n s o c c u r r i n g in t h e albic t o n g u e u n d e r h y d r o m o r p h i c c o n d i t i o n s . T w o m a j o r p h e n o m e n a were o b s e r v e d : t h e selective loss o f a l u m i n u m f r o m h y d r o x y a l u m i n u m i n t e r l a y e r s , w h i c h is p a r t i c u l a r l y e v i d e n t in the fine clay fraction, and the degradation of interstratified (14C--14V) chlorite-v e r m i c u l i t e o f m e d i u m a n d coarse clay f r a c t i o n s , w h i c h can be c o r r e l a t e d w i t h t h e d o m i n a n c e o f e x c h a n g e a b l e m a g n e s i u m . We also o b s e r v e d a m i c r o division o f p r i m a r y m a g n e s i u m chlorites of t h e silty f r a c t i o n and t h e a p p a r e n t stability o f kaolinite. ACKNOWLEDGEMENTS T h e a u t h o r s wish t o t h a n k Mr. B l a c k b u r n o f Soil Science D e p a r t m e n t o f Laval U n i v e r s i t y a n d G.J. Ross of t h e C h e m i s t r y a n d Biology R e s e a r c h I n s t i t u t e o f A g r i c u l t u r e C a n a d a f o r reviewing t h e m a n u s c r i p t . REFERENCES Brethes, A., 1971. Etude d'une m~thode de fractionnement des particules inf6rieures fi 2 microns. D.E.A. de P~dologie, Nancy, 37 pp. Caillier, M., 1977. Etude chronos~quentielle des sols sur terrasses alluviales de la Moselle. Gen~se et ~volution des sols lessiv6sglossiques. Th~se de Sp6cialit6, Universit6 Nancy I, 87 pp. Caillier, M., Gury, M. and Guillet, B. 1984. Dissolution d'oxyhydroxydes de fer et alteration diff~rentielle de min~raux phylliteux en milieu hydromorphe. P~dologie, XXXIV-1:43---66. Gury, M., 1976. Evolution des sols en milieu acide et hydromorphe sur terrasses alluviales de la Meurthe. Th~se de SpecialitY, Universit~ de Nancy I, 100 pp. Jamagne, M., 1973. Contribution ~ l'dtude pddog~n~tique des formations loessiques du Nord de la France. Th~se, Facult~ des Sciences Agronomiques de l'Etat, Gembloux,
445 pp. Jeanroy, E., 1972. Analyses totales des silicates naturels par spectrophotom~trie d' adsorption atomique. Applications au sol et ~ ses constituants. Chim. Anal., 54 (3). Lelong, F. and Souchier, B., 1972. Nature et g~n~se des argiles dans |es profils vosgiens de la s~quence sols bruns acides-podzols sur granite. Science de la Terre, 17(4):353--379. Mehra, O.P. and Jackson, M.L., 1960. Iron-oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate. Clays Clay Miner., 7: 317--327. Pochon, M., 1974. Origine et ~volution des sols du Haut-Jura suisse. Ph~nom~ne d' alteration des roches calcaires sous climat temp~r~ humide. Th~se, Facult~ des Sciences, Neufchhtel, 322 pp. Rouiller, J., Burtin, G. and Souchier, B., 1972. La dispersion des sols dans l'analyse granulom~trique. M~thode utilisant les rdsines ~changeuses d'ions. Bull. E.N.S.A.I.A., Nancy, 14(2):193--205. Schwertmann, U., 1976. Verwitterung mafischer Chlorite. Z. Pflanzenernaehr. Bodenkd., 1:27--36.