Mineralogy of iron oxides in two soil chronosequences of Central Spain

CATENA

vol. 16, p. 291-299

Cremlingen 1989 ]

MINERALOGY OF IRON OXIDES IN T W O SOIL C H R O N O S E Q U E N C E S O F C E N T R A L SPAIN M.C. Diaz, Madrid J. Torrent, Cfrdoba Summary

1

Introduction

Changes in the mineralogy of iron oxides The iron oxide mineralogy of soils of in soil chronosequences have been used two river terrace sequences of the rivers as indicators of paleoclimatic changes Jarama and Henares, Central Spain, and relative ages of geomorphic surwhich are in close proximity, was studfaces. River terrace sequences, in paried. The degree of weathering increases ticular, have yielded interesting results with age, as shown by several mineralog( A L E X A N D E R 1974, T O R R E N T et al. ical and geochemical indicators, such as 1980, A R D U I N O et al. 1984, 1986, Mcthe increase in the ratio dithionite exF A D D E N & H E N D R I C K S 1985, AJtractable (free) Fe / total Fe. Low valM O N E M A R S A N et al. 1988). These ues for oxalate extractable Fe indicate authors studied the changes with age of that the Fe oxides are essentially crysone or several of the following forms of talline. In the Jarama sequence goethite Fe or their ratios: is the dominant pedogenic Fe oxide. In the Henares sequence both goethite 1. total free iron oxides, as given by and hematite are present in significant dithionite-extractable Fe (Fea); amounts. The difference is attributed to pedoenvironmental differences, such as 2. poorly crystalline Fe oxides, as given the lower pH and the moister pedocliby oxalate-extractable Fe (Fed); mate of the Jarama sequence soils. The sensitivity of the goethite-hematite sys3. the Fea/Fet ratio where Fet is the tem to pedoenvironmental factors shows total soil Fe; the limited value of iron oxides for the 4. the Feo/Fea ratio, and estimation of paleoclimatic conditions or relative age in chronosequences, even in 5. the goethite/hematite ratio. relatively small geographical areas.

ISSN 0341-8162 (~)1989 by CATENA VERLAG, D-3302 Cremlingen-Destedt,W. Germany 0341-8162/89/5011851/US$ 2.00 + 0.25

Color is another property that has been used to compare individual soils within chronosequences in warm temperate and Mediterranean regions because it is markedly influenced by Fe oxides

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Diaz & Torrent

Jarama

# MADRID ~~/~Yi~-\R"~i~rest,bkm R. Henares

Fig. 1: Map of the study areas. (SCHWERTMANN 1988). In particular, when pedogenic hematite forms in those soils, a process referred to as rubification (BUOL et al. 1980, SCHWERTMANN et al. 1982), the amount of hematite can be estimated from its known quantitative relationship to reddening (TORRENT et al. 1980, TORRENT & CABEDO 1986). When both goethite and hematite are formed during pedogenesis the hematite/goethite ratio depends on several factors such as temperature, activity of water, pH, soil organic matter, AI in the system and rate of Fe release during weathering (SCHWERTMANN 1985). Some of these factors may vary, sometimes markedly, with topographic position, depth and pedoclimate. This means that the hematite/goethite ratio is not always a reliable indicator of general paleoclimatic conditions or relative

ages. PElqA & TORRENT (1984), for instance, found that in the terraces of the river Guadalquivir in southern Spain contiguous soils had strongly different colors (and hematite contents) because of differences in moisture regime. In this paper we show how slight differences in the pedoenvironment give contrasting iron oxide mineralogies in the soils of two geographically close river terrace sequences of central Spain.

2

The study areas

The fluvial terraces considered are those of the rivers Jarama and Henares, in the vicinity of Madrid, central Spain (fig.l). Two areas, showing the most complete sequence of levels, were chosen for a detailed study. The terraces have a climatic origin. No precise ages are available; tentative ages (tab.l) have been given

CATENA An Interdisciplinary Journal of SOIL SCIENCE H Y D R O L O G Y ~ E O M O R P H O L O G Y

Mineralogy of Iron Oxides, Two Soil Chronosequences to both systems by comparison to the well-dated Manzanares and Tajo systems in Central Spain ( P E R E Z - G O N Z A L E Z personal communication). Six and twelve terrace levels have been recognized, respectively, in the Jarama and Henares systems. In the present study we selected subsets of five and eight levels, respectively, after excluding those levels showing marked erosion or deposition from nearby areas. Mean altitudes were 750 m in the Jarama area and 700 m in the Henares area. Upstream of the study area the basin of the river Jarama consists mainly of granites, gneisses, slates, phyllites and quartzites. Some small areas of Tertiary clays and Cretaceous limestones are also present. The basin of the river Henares is more complex and has conglomerates (Buntsandstein), dolomitic limestones (Muschelkalk), gypsiferous marls (Keuper), augen-gneisses, slates and phyllites similar to those of the Jarama basin, Pliocene clays and gravels and Tertiary clays and limestones. As a result of these lithological differences the alluvium is noncalcareous in the Jarama and moderately calcareous (5-10% calcium carbonate equivalent) in the Henares. The study areas have a typical Mediterranean climate. Mean annual precipitation is 510 and 450 mm for the Jarama and Henares areas respectively. Summer (June-September) precipitation is 105 mm for both areas. Mean annual temperatures are 12.5°C and 13°C for the Jarama and Henares areas, respectively. Thus the climate of the Jarama area is slightly moister and cooler. The areas have been cultivated for a long time (usually under wheat and barley) but the original vegetation was a green oak (Quercus rotundifolia) forest.

3

293

Field and laboratory methods

After a detailed field examination, three soil profiles were chosen in each terrace level excluding areas showing erosion or deposition, slopes higher than 1° and depressions were excluded. The soils were described and sampled. For the recent alluvial soils with only Ap and C horizons samples were taken at depths of 10, 30 and 70 cm; in the Alfisols of the terraces samples were taken for the Ap, AB (when present), Bt and Btk (when present) horizons down to a depth of 120 cm. The Bt horizons were subdivided into several subhorizons on the basis of morphological properties (color, structure, etc). This gave a total of 3-5 samples per soil and 9-11 samples per terrace level, which were subsequently dried and ground (<2 mm) for analysis. Particle size distribution, organic matter content, pH, calcium carbonate equivalent, mineralogy of the clay fraction, total Fe (Fet), A1 and Mg, dithionite extractable Fe (Fea), oxalate extractable Fe (Feo) and hematite (Hm) amd goethite (Gt) in the clay fraction were analyzed by the methods reported by T O R R E N T & CABEDO (1986). Color (dry) was measured in the <2 mm fraction with a Hunterlab model D25 A-2, diffuse reflectance colorimeter (Hunter Associates Laboratory Inc., Reston, Virginia). The X, Y, Z tristimulus values were converted to Munsell colors according to the procedures given by W Y S Z E C K I & STYLES (1967). The 0.2q3.05 mm sand fraction was treated with Na-dithionite to eliminate Fe oxides, peroxydized to eliminate organic matter, and the heavy fraction (d = 2.96) separated and counted. Unless otherwise stated, results refer to mean and standard deviation of the results of analyses of all the horizons in

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Diaz & Torrent

294 2.5

JARAMA

E 2.0 o +

HENARESI I

e

•"=- 1.5 o

= o

+

0.5

o.o

Relative t e r r a c e

level

Relative t e r r a c e

level

Fig. 2: Average ( +a ) values of the (tourmaline -t- zircon)/(staurolite -t- garnet) ratio

in the 0.2--0.05 mm heavy fractions. Terrace level 0 is present alluvium. 0.5

II

0.4

0.3 o

tttl t

~0.2 -s -6 ~0.I

JARAMA

HENARES

0.0 Relative t e r r a c e

Relatlve~ t e r r a c e

level

level

Fig. 3: Average (+_a) values of the total Mg/total Al ratio for the clay fractions. all three profiles together for each terrace level.

4 4.1

Results and discussion General soil characteristics

Tab.1 summarizes some of the characteristic properties of the soils under dis-

cussion. Except for the youngest surfaces aU soils are Alfisols. With increasing age the soils of the Jarama sequence show increasing textural contrast between the Ap and the Bt horizons and go from Haploxralfs to Palexeralfs. In the Henares sequence the Haploxeralfs give way, with age, to Rhodoxeralfs. The soils of the two sequences differ markedly

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Mineralogy of Iron Oxides, Two Soil Chronosequences

295

0.8

',~ 0.6 o F--

..Q 0

~0.2 ."2--

g

HENARES

JARAMA 0.0 Relative terrace

level

Relative terrace

level

Fig. 4: Average (+a) values of the ged/fet ratio for soils. in color, except for the recent alluvial soils. The color of the Jarama soils is brown or yellowish brown without discernible trends with age. In contrast the Henares soils have redder colors; their degree of redness, according to the redness rating (RR) of TORRENT et al. (1980), increases with age up to level 4 and then decreases slightly. The Henares soils have usually more clay than the Jarama soils of similar age and become increasingly clayey with age. In the Jarama soils pH is acid and decreases with age to values around 5 in the highest terrace. The Henares soils show usually a horizon of calcium carbonate accumulation; pH values below 6.5 are infrequent probably because, even when the upper horizons of the soils have been decarbonated during pedogenesis, some contamination from nearby calcareous soils has taken place. Owing to cultivation the organic matter contents of the Ap horizons are low in both areas.

4.2

Mineralogical changes with soil age

Soils become progressively weathered with age as indicated, for instance, by the general increase in the (tourmaline + zircon)/(garnet + staurolite) ratio for the 0.2-0.05 mm heavy fractions (fig.2) and the decrease of the Mg/A1 ratio for the clay fractions (fig.3). The Fed/Fer ratio increases as soils become older (fig.4), in agreement with the progressive degree of weathering mentioned before. Poorly crystalline Fe oxides (estimated by Fee) appear only in very small amounts (tab.l). In both sequences the Feo/Fea ratio decreases with age, from about 0.15 in the present alluvium to 0.04 in the oldest terraces (detailed values not shown). Thus iron oxides are predominantly crystalline, goethite and hematite being the minerals identified by X-ray diffraction. The pedogenic formation of goethite and hematite can be visualized by plot-

CATENA--An Interdisciplinary Journal of SOIL SCIENCE--HYDROLOGY 4 3 E O M O R P H O L O G Y

Diaz & Torrent

296 O.6

t

,~ 0.5 "6

_0.4

" , 0.3

0.2

iIIiI

o',0.1 .E

I

o.o

Relative t e r r a c e

Relative terrace level

level

0.8 0.7

HENARES

JARAMA 0.6

0.5

0.5

'~0.4 -6

0.4

o o.3

: yo. 0.3

®

0.2 O

E .~o.1 ._.q

~ o.o

T

i

0

1

Relative

T

T 2 terrace

3

4

I

I o.o 5

Relative terrace level

level

Fig. 5: Average (-t-o) values of the Fegt/Fe t and Fehra/Fe t ratios for soils.

ting the Fegt/Fet and Fehm/Fet ratios against terrace levels (fig.5), in which Fegt and Feh., represent Fe in the form of goethite and hematite, respectively. In the Jarama sequence the Fegt/Fet ratio shows an increasing trend with age, indicating progressive goethite formation. The Fehm/Fet ratio is very low and changes little with age; consequently the pedoenvironmental conditions in this sequence have favored goethite over hematite. In the Henares sequence the Fegt/Fet ratio ranges from 0.16 to 0.44 and does not show clear trends with age. The Feh,./Fet ratio ranges from 0.07 to 0.46; it increases CATENA

with age up to level 5 and then decreases. The H m / G t ratio (as deduced from fig.5) shows the same trend. The redness rating of the soils is highly correlated with the hematite content determined by Xray diffraction (RR = 2.7Hm + 0.9; r = 0.86"" ; n = 114). 4.3

Discussion

In spite of their geographical proximity, and the similar regional climates and biotic factors during the Pleistocene, the two sequences show contrasting Fe oxides mineralogies. One or several of the following factors may be respon-

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5.3/3.9 5.0/3.8 4.2/4.7 4.8/5.2 4.0/5.4 4.4/5.5 4.3/5.5 4.5/6.0 4.7/5.9

5.13.3 5.5/3.1 5.5/4.1 5.4/3.7 5.4/3.9 5.2/4.5

1.2 1.5 3.9 4.6 7.8 6.9 7.2 7.1 5.5

0.5 0.0 1.0 1.1 0.7 1.6

Redness rating

7 10 20 28 34 45 37 42 44

12 25 21 20 18 25

(%)

Clay content

Properties of soils.

8.4YR 8.0YR 6.5YR 5.8YR 4.1YR 4.5YR 4.4YR 4.7YR 5.6YR

9.3YR 0.1Y 8.6YR 8.3YR 9.1YR 8.2YR

Munsell color (dry)

Tab. 1 :

Typic Xerofluvent Typic Xerorthent Typic Haploxeralf Typic Haploxeralf Typic Rhodoxeralf Typic Rhodoxeralf Petrocalcic Rhodox. Typic Rhodoxeralf Typic Rhodoxeralf

Typic Xerofluvent Typic Haploxeralf Typic Palexeralf Ultic Palexeralf Ultic Palexeralf Ultic Palexeralf

Soil classification of typical profiles

8.0 8.0 7.8 7.6 7.7 7.7 7.1 7.5 7.0

6.5 6.6 5.8 5.3 5.5 4.9

pH (water)

0.2 0.6 1.0 0.7 0.7 1.1 0.7 1.0 1.3

2.5 0.8 0.6 1.0 1.1 1.6

(%)

Organic matter

11 13 9 10 20 11 12 14 27

16 15 24 20 16 30

(%)

63 65 58 54 53 57 50 42 52

51 47 43 63 66 57

(%)

26 22 33 36 27 32 38 44 21

33 38 33 17 18 13

(%)

Clay mineralogy K I S

1.43 1.79 2.63 2.71 3.41 3.35 3.93 4.02 4.64

2.40 2.22 2.39 1.98 2.25 3.00

(%)

0.64 0.86 1.49 1.81 2.07 2.15 2.91 2.79 3.37

0.82 0.81 1.I0 0.88 0.81 1.63

(%)

0.08 0.10 0.08 0.11 0.06 0.05 0.07 0.08 0.08

0.11 0.10 0.08 0.08 0.08 0.06

(%)

Formsofiron Fet Fed Feo

I = illite, S = smectite.

F o r color, c l a y c o n t e n t , c l a y m i n e r a l o g y a n d f o r m s o f i r o n figures a r e a v e r a g e s f o r all h o r i z o n s s a m p l e d ; p H is the a v e r a g e f o r the h o r i z o n s i m m e d i a t e l y b e l o w A p ; o r g a n i c m a t t e r figures a r e a v e r a g e s f o r A p h o r i z o n s ; figures f o r r e d n e s s r a t i n g ( T O R R E N T et al. 1980) a r e a v e r a g e s f o r all h o r i z o n s s a m p l e d . K = k a o l i n i t e ,

-6 35 70 100 125 145 160 185

Henares sequence Floodplain I Holocene 2 Upper Pleistocene 3 Middle Pleistocene 4 Middle Pleistocene 5 Lower Pleistocene 6 Lower Pleistocene 7 Lower Pleistocene 8 Lower Pleistocene

Altitude above present river level (m)

10 40 55 80 145

Age

Jarama sequence Floodplain 1 Upper Pleistocene 2 Middle Pleistocene 3 Middle Pleistocene 4 Lower Pleistocene 5 Lower Pleistocene

Relative terrace level

"....d

?

298

Diaz & Torrent

sible for this contrast. Firstly, the References Jarama soils have more stones and gravel AJMONE MARSAN, F., BARBERIS, E. & ARthan the Henares soils and have, thereDUINO, E. (1988): A soil chronosequence in northwestern Italy: morphological, physical and fore, less water-holding water capacchemical characteristics. Geoderma 42, 51-64. ity. Therefore they become moist earALEXANDER, E.B. (1974): Extractable iron in lier in autumn and during the rainy relation to soil age on terraces along the Truckee winter months remain moister than River, Nevada. Soil Science Society of America the Henares soils. This moister peProceedings 38, 121-124. doclimate of the Jarama soils favors ARDUINO, E., BARBERIS, E., CARRARO, F. & FORNO, M.G. (1984): Estimating relative goethite over hematite (SCHWERTages from iron-oxide/total-iron ratios of soils MANN 1985). Secondly, the pH of in the western Po Valley, Italy. Geoderma 33, the Henares soils (6.8-8.0) coincides with 39-52. the pH of maximum hematite formation ARDUINO, E., BARBERIS, E., AJMONE found, in vitro, for the competitive forMARSAN, F., ZAN1NI, E. & FRANCHINI, mation of goethite and hematite from M. (1986): Iron oxides and clay minerals within profiles as indicators of soil age in northern ferrihydrite (SCHWERTMANN & MUItaly. Geoderma 37, 45-55. RAD 1983). Thirdly, the higher Ca acBUOL, S.W., HOLE, F.D. & McCRACKEN, tivities in the soils of the Henares area R.J. (1980): Soil Genesis and Classification. may favour hematite, as shown in experIowa State University Press, Ames, Iowa. 404 p. iments with synthetic ferrihydrite (TORMcFADDEN, L.D. & HENDRICKS, D.M. RENT & GUZMAN 1982). Moreover (1985): Changes in the content and composition of pedogenic iron oxyhydroxides in a chronoseCa saturation can also affect the type quence of soils in southern California. Quaterand stability of structure therefore influnary Research 23, 189-204. encing moisture regime and, in turn, the PEI~A, F. & TORRENT, J. (1984): RelationFe oxides formed. ships between phosphate sorption and iron oxDifferences in pedoclimate between ides in Alfisols from a river terrace sequence of soils of the Henares sequence might exMediterranean Spain. Geoderma 33, 283-296. plain why the Hm/Gt ratio increases up SCHWERTMANN, U. (1985): The effect of pedogenic environments on iron oxide minerals. to level 5 and then decreases steadily: In: Advances in Soil Science. Springer-Verlag, soils above level 5 are clayey and field obNew York, Inc. 1, 171-180. servations show that they remain moist SCHWERTMANN, U. (1988): Some properties for longer periods than those of the lower of soil and synthetic iron oxides. In: J.W. Stucki, terraces. B.A. Goodman & U. Schwertmann (Eds.), Iron in soils and clay minerals. Reidel Publishing The former considerations show that Co., Dordrecht, 203-250. the relative amounts of goethite and SCHWERTMANN, U. & MURAD, E. (1983): hematite formed in the course of pedoEffect of pH on formation o f goethite and genesis can be related in general terms hematite from ferrihydrite. Clays & Clay Minto pedoenvironmental factors. The comerals 31, 277-284. petitive goethite-hematite formation apSCHWERTMANN, U., MURAD, E. & pears, however, to be highly sensitive to SCHULZE, D.G. (1982): Is there Holocene reddening (hematite formation) in soils of axthese factors. This impairs the ability eric temperate areas? Geoderma 27, 209-223. of crystalline Fe oxides (and soil colors) TORRENT, J. & CABEDO, A. (1986): Sources to be good indicators of general paleoof iron oxides in reddish brown soil profiles from climatic conditions and relative ages of calcarenites in southern Spain. Geoderma 37 , geomorphic surfaces. 57-66. CATENA--An Interdisciplinary Journal of SOIL SCIENCE H Y D R O L O G Y ~ E O M O R P H O L O G Y

Mineralogy of Iron Oxides, Two Soil Chronosequences

TORRENT, J. & GUZMAN, R. (1982): Crystallization of Fe(III)-oxides from fefihydrite in salt solutions: osmotic and specific ion effects. Clay Minerals 17, 463-469. TORRENT, J., SCHWERTMANN, U. & SCHULZE, D.G. (1980): Iron oxide mineralogy of some soils of two river terrace sequences in Spain. Geoderma 23, 191-208. WYSZECKI, G. & STYLES, W.S. (1967): Color science - - Concepts and methods, quantitative data and formulas. Wiley, New York.

Addresses of authors: M.C. Diaz

Departamento de Edafologia Escuela T~cnica Superior de Ingenieros Agrfnomos Ciudad Universitaria 28040 Madrid J. Torrent

Departamento de Ciencias y Recursos Agrlcolas UrLiversidad de C6rdoba Apdo. 3048 14080 C6rdoba, Spain

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