Carbonatation in palaeosols formed on terraces of the Tormes river basin (Salamanca, Spain)

Geoderma 118 (2004) 261 – 276 www.elsevier.com/locate/geoderma

Carbonatation in palaeosols formed on terraces of the Tormes river basin (Salamanca, Spain) P. Alonso a, C. Dorronsoro b,*, J.A. Egido a b

a Departamento de Edafologı´a, Universidad de Salamanca, Salamanca, Spain Departamento de Edafologı´a y Quı´mica Agrı´cola, Universidad de Granada, Faculdad de Ciencias, Fuentenueva s/n, Granada 18002, Spain

Received 22 October 2002; accepted 7 May 2003

Abstract A macro- and micromorphological study was made of the carbonate accumulations in a total of 21 relict (unburied) palaeosols (Haploxeralfs and Palexeralfs), of ages corresponding to the Late, Middle and Early Pleistocene, formed on fluvial terraces in the Tormes river basin (Salamanca, Spain) under a present-day subhumid continental Mediterranean climate. The fluvial deposits were predominantly gravels and sands derived from the erosion of granite, slate, sandstone and quartzite, with a notable absence of calcareous materials. Secondary carbonates commonly filled cracks, forming laminae in preferentially horizontal disposition (though also tipped and vertical), giving rise to distinctive patterns that have long attracted scientific attention. In the youngest soils of the lower terraces (Late Pleistocene, < 50,000 years), the carbonate morphologies are almost exclusively micrite, whereas sparry calcite was abundant in the oldest soils of the middle and upper terraces (Middle and Early Pleistocene, >300,000 years), especially in the upper levels within the calcic horizon. In rare cases, the pseudomycelia and the coatings were comprised of fine needle-fibre calcite. The carbonates in these soils are recrystallized, even in the some of the youngest soils of these terraces ( z 40,000 years). The older soils of the middle terraces, and particularly in the upper terraces ( z 300,000 years) reflected an intense process of replacement of silicates by carbonates; in addition, the clays in the micromass and illuvial coatings, as well as the detrital grains, such as feldspars and quartz, were progressively replaced by carbonates. The carbonate accumulations, as well as the subsequent recrystallization and replacement, tended to increase with the age of the soils. In addition, the secondary carbonatation and dissolution of carbonate observed indicate the genetic complexity of these soils. The form of the carbonates present (at the micro- as well as macroscopic level), their distribution (within the soil profiles and throughout the region), as well as the relationship with other processes (subsequent to clay illuviation and associated with hydromorphy) imply that vadose water, at certain geological stages, must have been responsible for the carbonate accumulation in these soils. The carbonates were deposited during the coldest periods of the isotope substages 6.2, 7.4, 10.2, 12.2, 13.2 and 16.2. The presence of dissolution in the soils corresponding to the isotope substages 7.4 and 13.2 appears to indicate the development of two wetter periods towards 200,000 and 500,000 years B.P. The absence of carbonates in the soils of the youngest surfaces (plains flood and the lowest terraces; Holocene and Late Pleistocene, < 30,000 years) indicates that this process is not currently occurring in these chronosequences. Therefore, simply the presence of carbonate accumulations in these soils suffices to characterize such palaeosols. This criterion is applicable not only to the soils of the Tormes river basin, but also to a great number of soils throughout the region. D 2003 Elsevier B.V. All rights reserved. Keywords: Pedogenic carbonates; Palaeosols; Micromorphology; Chronosequences; Terraces

* Corresponding author. Fax: +34-958-244160. E-mail address: [email protected] (C. Dorronsoro). 0016-7061/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0016-7061(03)00211-8

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1. Introduction Accumulations of secondary carbonates are common in palaeosols formed in the fluvial terraces of the Tormes river basin (Salamanca, central-western Spain). These soils formed fundamentally from deposits of eroded granites, sandstones, slates and quartzites, but notably lack carbonate materials. Secondary carbonates commonly fill cracks, forming laminae in preferentially horizontal disposition (though also tipped and vertical), and give rise to distinctive patterns that have long attracted scientific attention (Huguet del Villar, 1937; Glinka, 1963; Roquero and Ontan˜on, 1966). In the present study, we characterize the palaeosols of the Tormes river basin in relation to the presence of carbonate accumulations in these soils. To do so, we identify the origin and trace the genesis of the carbonates of these soils, describe the micromorphological characteristics of the accumulations, determine the processes of formation and transformation affecting the soils, and finally establish relationships between carbonatation and soil age and palaeoclimatic conditions.

2. Area description, materials and methods A total of 21 soils were studied in fluvial terraces of the Tormes river basin (Table 1). Over geological time, this river has left a typical steeped relief, with abundant horizontal surfaces between abrupt scarps, which according to Vreeken (1975) are post-incisive sequences. The river terraces analysed are located near the villages of Macotera (UTM coordinates: TL 03014/45212 and 03125/45240 of National Grid Map 479), Fresno Alha´ndiga (TL 02817/45111 and 02932/ 45060 of National Grid Map 503), Calvarrasa de Abajo (TL 02594/45511 and 02605/4548 of National Grid Map 451) and San Pedro del Valle (UL 03084/ 45270 and 03124/45232 of National Grid Map 479). In general, the terraces are well preserved, occupying a few km2 of surface area, sometimes dissected by water courses of surface runoff. These terraces are formed by non-consolidated deposits some 1.5 to 5 m thick of coarse and very coarse materials (2 –200 mm in diameter) embedded in a fundamentally sandy matrix. In the rock fragments, quartz and quartzite

predominate, with subangular forms and without showing alteration, accompanied by granite (very rounded and strongly altered), and, in lesser proportions, cobbles of slate, phyllites, flattened angular, moderately altered schists (sometimes encrusted with Mn compounds), and sandstone fragments. The granite gravels are more abundant in the younger terraces and in their superficial horizons, disappearing almost completely in the soils of the high terraces. The sands have a mineralogical composition of quartz, feldspars (potassium and plagioclases of albite), and micas (moscovite and biotite); the clays were composed of smectite, illite and kaolinite (Dorronsoro, 1994; Dorronsoro and Alonso, 1994; Alonso et al., 1994). The descriptions of the morphological properties of the soils were made by conventional methods (Soil Survey Staff, 1999). All of the samples were air-dried and screened to 2 mm, and the percentages of gravels (>2 mm) and fine earth ( < 2 mm) were determined. The laboratory analyses were made with the fine-earth fraction. Particle-size distribution was measured by the pipette method after eliminating organic matter with H2O2 and dispersion with sodium hexametaphosphate (Loveland and Whalley, 1991). The pH was measured potentiometrically in a 1:2.5 soil – water suspension, in a CRISON Digit 501 instrument. The CaCO3 equivalent was determined manometrically via the Barahona (1984) method. Total carbon was measured by dry combustion with a LECO mod. SC144DR instrument. Organic carbon was calculated as the difference between total carbon and inorganic carbon from CaCO3. The cation-exchange capacity (CEC) was determined with 1 N Na acetate at pH 8.2 (Rhoades, 1982), measuring the sodium in a METEOR NAK-II flame-photometer. For the micromorphological study, the polymerized samples, previously embedded in polyester resin (chronolite 1108, with an activating and catalysing solvent) were cut and polished to a thin layer, using a Logitech PM2A instrument. The local climate is classified as subhumid (mean annual rainfall, 412 mm) and mesic (mean annual T, 11 jC), within the continental Mediterranean type. The soils lie on a supramediterranean bioclimatic base with an alkaline substratum. The climax vegetation is composed of oaks (Genisto-Histricis-Quercetum rotundifoliae sigmetum association). In certain areas, this vegetation has been altered by cultivation.

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Table 1 Soils, geomorphic surfaces and ages Profile (code)

Stratigraphic Elevationa Geologic age position (meters)

Ageb Substagec Classification (approx. d18O soil taxonomy years B.P.)

Soil horizons

Macotera chronosequence AM14a 6th terrace 14 AM14b 6th terrace 14 AM18a 5th terrace 18 AM18b 5th terrace 18 AM25 4th terrace 25 AM36 3rd terrace 36 AM47 2nd terrace 47

Late Pleistocene Late Pleistocene Late Pleistocene Late Pleistocene Middle Pleistocene Middle Pleistocene Middle Pleistocene

50,000 3.3 50,000 3.3 100,000 6.2c 100,000 6.2c 200,000 7.4c 300,000 9.3w 500,000 13.2c

Typic Typic Typic Typic Typic Typic Typic

AM64

Middle Pleistocene

600,000 16.2c

Typic Palexeralf

Ap-2Bt1-2Bt2-3CBt-3Ck1-3Ck2 Ap-Bt-Btg-2Btk-2CBtk1-2CBtk2 Ap-2Bt1-3Bt2-3BCt-3Ck1-4Ck2 Ap-Bt-2Btg-2BCtk-2CBt Ap-2Bt1-2Bt2-2CBtk-2Ck1-2Ck2 Ap-Bt1-Bt2-CBtk1-CBtk2-CBtk3-2Ck Ap-Bt1-Bt2-CBtk1-2CBtk2-3CBtk34CBtk4 Ap-2Bt1-2Bt2-2Btk-2BCtk1-2BCtk2

Calvarrasa de Abajo chronosequence TC12 2nd terrace 12 Late Pleistocene TC45 1st terrace 45 Middle Pleistocene

40,000 3.3 430,000 12.2c

Typic Haploxeralf Calcic Palexeralf

Ap-Bt-Ck-2C Ap-Bt1-2Bt2-2CBk

Alha´ndiga chronosequence 4th terrace 13 Late Pleistocene 3rd terrace 23 Late Pleistocene 2nd terrace 63 Middle Pleistocene

40,000 3.3 200,000 7.4c 600,000 16.2c

Apuultic Haploxeralf Calcic Haploxeralf Tapto-Alfic Typic Rhodoxeralf Ultic Haploxeralf Typic Palexeralf

Ap-BA-Btg-CBtg1-2CBtg2-2Ckg Ap-2Bt-2Btg-3BCtk-3CBtk Ap-Bt-2Btb-2Btb/2Ckb-2CBtkb12CBtkb2 Ap-2Bt1-3Bt2-3Bt3-3Btk-4CBtk Ap-AB-Bt1-Bt2-2BCt-3CBt1-4CBtk4CBt2-5CBtk2-6CBt3 Ap-Bt-Btg-2Btk1-2Btk2-

Fresno TF13 TF23 TF63a TF63b TF63c

1st terrace

2nd terrace 2nd terrace

TF115a 1st terrace

64

63 63 115

Middle Pleistocene Middle Pleistocene Early Pleistocene

600,000 16.2c 600,000 16.2c 1,200,000

San Pedro del Valle chronosequence TP38a 3rd terrace 38 Middle Pleistocene

350,000 10.2c

TP38c TP42

3rd terrace 2nd terrace

38 42

Middle Pleistocene Middle Pleistocene

350,000 10.2c 400,000 12.2c

TP50a TP50b

1st terrace 1st terrace

50 50

Middle Pleistocene Middle Pleistocene

500,000 13.2c 500,000 13.2c

Haploxeralf Haploxeralf Haploxeralf Haploxeralf Haploxeralf Palexeralf Palexeralf

Calcic Palexeralf

Thapto-Alfic Typic Haploxeralf Typic Haploxeralf Calcic Palexeralf Typic Palexeralf Thapto-Alfic Calcic Palexeralf

Ap-Bt1-Bt2-2Btb1-2Btb2-2Ck Ap-BA-Bt-2BTg-2BCtk-3CBt Ap-2Bt1-2Bt2-2CBtk1-2CBtk23CBtk3-4C Ap-Bt-2Btg1-2Btg2-2Btk-3BCtk-4Ck Ap-Bt1-Bt2-2BCtk/2Btb-2CBtkb12CBtkb2

a

Above the present-day riverbed. The soil surfaces have been dated by Santonja and Querol (1976), Santonja and Perez Gonzalez (1984), Santonja et al. (1982) and by the Instituto Geolo´gico y Minero de Espan˜a (1982) by archaeological and stratigraphic methods. c After Bassinot et al. (1994). ‘‘c’’ signifies very cold periods and ‘‘w’’ very warm ones. b

The soil surfaces have been dated by Santonja and Querol (1976), Santonja and Perez Gonzalez (1984), Santonja et al. (1982) and by the Instituto Geolo´gico y Minero de Espan˜a (1982), mainly by archaeological and stratigraphic methods. Dorronsoro and Alonso (1994) reported very good results on correlating the age and the evolution of the soils of the chronosequence of Macotera, providing comparisons with other chronosequences having similar soil-forming factors and dated with radiometric methods.

3. Results 3.1. The soils In all cases, the soils were Xeralfs (Soil Survey Staff, 1999), the youngest being Haploxeralfs and the oldest, Palexeralfs. Of the latter, the subgroup Calcic corresponded to the oldest soils of each series. Table 2 summarizes the characteristics of the three types of most representative soils. These were 21 relict palae-

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Table 2 Macromorphological, physical and chemical properties of the selected soils Profile code

Horizon

AM14a

Ap 2Bt1 2Bt2

0 – 23 23 – 45 45 – 53

3CBt 3Ck1

53 – 95 95 – 175

TP42

TF63a

3Ck2 Ap 2Bt1 2Bt2 2CBtk1 2Btk 3BCtk 4C Ap Bt Btg 2Ck/Btb 2CBtkb1 2CBtkb2 2CBtkb3 2CBtb1 3CBtb2 3CBtb3 3CBtb4

Depth [cm]

175 – 250 0 – 18 18 – 45 45 – 95 95 – 112 112 – 130 130 – 170 170 – 280 0 – 22 22 – 85 85 – 135 135 – 153 153 – 183 183 – 205 205 – 238 238 – 250 250 – 310 310 – 350 350 – 393

Moist color (mottles)

Structure

Gravel [%]

Sand [%]

Silt [%]

Clay [%]

CaC03 [%]

OC [%]

pH (paste)

CEC [cmolc kg

10YR4/3 10YR3/3 7.5YR4/3 (5YR4/6) 10YR5/3 2.5Y6/4 (white) 2.5Y7/4 5YR4/4 2.5YR46 2.5YR3/6 (white) 7.5YR5/2 7.5YR5/6 5YR4/8 7.5YR4/6 2.5YR3/6 5YR4/8 7.5YR6/8 7.5YR5/4 7.5YR5/8 7.5YR5/8 7.5YR5/8 7.5YR5/8 7.5YR5/8 7.5YR5/8

cr, m, 2 sbk, m, 2 sbk, c, 3

12.0 60.7 35.9

61.8 48.1 38.7

27.2 21.3 11.8

11.0 30.7 49.5

0.0 0.0 0.0

0.93 0.90 0.88

4.9 5.1 5.8

4.1* 12.1* 22.4*

100 100 100

pr, c, 3 0

6.3 0.3

25.9 30.0

22.1 51.6

52.0 17.9

0.0 6.6

0.72 0.44

6.3 7.4

27.6* 36.9N

100 100

0 sbk, c, 2 sbk, c, 3 pr, c, 3 0 0 0 0 sbk, f, 2 abk, f, 2 pr, c, 3 0 0 0 0 0 0 0 0

0.1 21.8 7.3 5.9 11.5 41.9 15.7 67.9 24.8 47.1 0.5 7.5 0.3 0.8 1.3 3.1 14.2 11.2 13.4

39.7 55.4 28.4 15.8 50.1 61.7 78.0 73.8 42.3 18.1 10.3 40.9 23.5 61.6 68.9 75.5 71.4 72.8 75.2

49.1 36.4 28.1 20.1 22.1 14.9 7.3 3.6 34.6 16.8 5.5 17.6 52.7 20.6 9.3 5.7 3.8 5.3 5.0

11.3 8.2 43.5 64.1 27.8 23.4 14.8 22.9 23.1 65.1 84.2 41.5 23.8 17.8 21.5 19.4 24.7 21.9 19.9

5.8 0.0 0.0 0.0 16.5 8.3 4.5 0.0 0.0 0.0 0.0 36.0 11.0 4.2 0.8 0.0 0.0 0.0 0.0

0.34 0.51 0.56 0.41 0.28 0.11 0.09 0.09 1.41 0.77 0.45 0.39 0.30 0.15 0.09 0.13 0.08 0.07 0.07

7.3 4.8 5.2 6.7 7.7 7.8 7.8 7.6 4.9 5.1 6.7 7.6 7.7 7.7 7.7 7.7 7.5 7.5 7.4

38.2N 2.6* 11.0* 23.3* 33.5N 28.2N 22.4N 3.9* 10.2* 25.0* 37.5* 22.6N 26.0N 18.9N 16.3N 16.9* 15.7* 14.3* 12.9*

100 100 100 100 100 100 100 100 32 43 168 100 100 100 100 96 98 100 100

1

]

BS [%]

OC, organic carbon; CEC, cation-exchange capacity; *: CEC by AcNH4; BS, base saturation; cr, crumb; sbk, subangular blocky; abk, angular blocky; pr, prismatic; vf, very fine; f, fine; m, medium; c, coarse. 0: structureless; 1: weak; 2: moderate; 3: strong.

osols that, on three occasions buried fossil soils, according to Reuter (2000). Following the classification of Nettleton et al. (2000), these are Truncated, Oxidized, Unleached, Enduric Palaeoevolvisol, residual, extensive and, in the case of the three buried soils, Truncated, Oxidized, Unleached, Kryptic Palaeoevolvisol, residual, extensive. The soils were characterized by substantial thickness, high gravel contents, differing textures, an argillic horizon of a clayey texture, acidic pH, low soluble-salt contents and high degree of base saturation. 3.2. The carbonates in the soil profile Pedogenic carbonates were widely distributed in these palaeosols, although their contents were generally not extraordinarily high (mean content: 11%, maximum: 51%; Table 3).

3.2.1. Forms The carbonates appeared in varied forms, both macro- and microscopic, and were either isolated or massive. When examined individually, they appeared as pseudomycelia, coatings, hypo-coatings, nodules and laminae (Table 3). The pseudomycelia (Fig. 1a) were generally comprised of small needle-fibre calcite—that is, elongated, highly developed crystals forming fine fibres of some 2 Am in diameter and 30 Am in length, creating a fine interlacing partially filling in pores, (which were invariably intrapedal and in discrete cavities, channels and chambers). The needle-fibre calcite and micro-rod forms are well known in terms of morphology and crystallography; they are thought to originate from fungal biomineralization (Callot et al., 1985; Verrecchia and Verrecchia, 1994; Verrecchia and Dumont, 1996; Bezce-Deak et al., 1997; Loisy et al., 1999) and are also considered

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Table 3 Characteristics of the carbonate accumulations and associated hydromorphic features Soil code

Horizon Depth [cm]

AM14a AM14a AM14b AM14b AM18a AM18a AM18b AM25 AM25 AM36

CaCO3

Mn/Fe

%

Crystal type

Pedofeatures

3Ck1 95 – 175 3Ck2 175 – 250 2Btk 83 – 105/140 2CBtk1 105/140 – 200 3Ck1 114 – 150 4Ck2 150 – 260 2BCtk 103 – 190 2CBtk 85/97 – 135 2Ck1 135 – 240 CBtk1 110/120 – 170

6.6 5.8 7.1 3.8 5.6 18.8 18.7 41.6 26.6 1.5

H(++) C(+) I(+) C(++) H(+) I(+) I(+++) H(+) H(++) C(+) I(+++) N(++) I(+) I(+++) I(+++) C(+) Fm(+++) N(+++) L(+++) C(+)

AM36 AM47 AM47 AM64 AM64 AM64

CBtk2 CBtk1 CBtk2 2Btk 2BCtk1 2BCtk2

4.7 17.4 6.7 6.1 9.1 25.1

M(+++) M(+++) M(+++) M(+++) M(+++) M(+++) M(+++) M(+++) M(+++) M(+++) Nf(+) M(+++) M(+++) M(+++) M(+++) M(+++) M(+++)

TC12 TC45 TC45

Ck 2CBk 2Ck

TF13 TF23 TF63a TF63a

2Ckg 3BCtk 2Ck/Btb 2CBtk1

132 – 160 120 – 175 135 – 153 153 – 183

6.5 14.2 36.0 11.1

M(+++) S(+) M(+++) M(+++) S(+) M(++) S(+++)

TF63a TF63b TF63c TF115

2CBtk2 5CBtk2 3Btk 2Btk1

183 – 205 212 – 260 140 – 200 125 – 180

4.2 6.5 3.2 24.0

M(+++) S(+) M(++) S(++) M(++) S(+++) M(+) S(+++)

TF115

2Btk2

180 – 260

2.7 M(+++) S(+)

TP38a TP38c

2Ck 2BCtk

157 – 270 100 – 225

10.7 M(+++) S(+) 3.1 M(++) S(+++)

TP42

2CBtk1

95 – 112

16.5 M(+++) S(++)

TP42

2CBtk3

130 – 170

TP50a TP50a TP50a TP50b

2Btk 3BCtk 4Ck 2BCtk

105 – 158 158 – 232 232 – 280 100 – 150

4.5 M(+++) S(+) Nf(+) 4.6 M(++) S(++) 1.4 S(+++) 8.9 M(+++) 1.1 M(+) S(+++)

TP50b TP50b

2CBtk1 2CBtk2

150 – 200 200 – 270

170 – 205 106 – 180 180 – 215 100 – 110 110 – 140 140 – 200 51 – 100 83/91 – 121 121 – 196

S(+) Nf(+) S(+) S(+) S(+) S(+) S(+) S(+) S(+) S(+)

L(+++) L(+++) I(++) I(+++) H(+) I(++) N(++) I(++) N(++) Fm(+++)

13.8 M(+++) H(+++) 51.4 M(+++) S(+) Fm(+++) 16.7 M(+++) Nf(++) Fm(+++) S(+)

8.3 M(+++) 18.0 M(+++)

N(++) H(+) C(+) H(+++) L(+++) N(++) I(++)

Processes

Accumulations Depletions N(+) H(+) H(++) N(+) N(+) H(+) H(++) N(+) H(+) N(+)

cRp(+) cRp(+) dRp(+) Rc(+) cRp(+) cRp(++) dRp(+) Ds(+) Rb(+) N(+) H(+) H(+++) N(+) cRp(++) Rb(+) Rc(+) Rc(+) Ds(+)

H(+++)

cRp(+)

N(+)

Mo(+) Fm(+++) Mo(+) Mo(++) Fm(+++)

Fm(+++) Fm(+++) Fm(+++) Fm(+++) Mo(++) Fm(+++)

Rb(+)

cRp(+++) dRp(+) Rc(+)

Rc(+) cRp(+)

Rc(++) cRp(++) dRp(++) Rc(++) cRp(++) dRp(++) Rb(++) L(+++) Rc(+) cRp(+) dRp(+) H(++) I(+) Rc(++) I(+++) L(++) Rc(+++) cRp(++) dRp(++) I(+++) N(++) H(+) Rc(+++) cRp(++) dRp(+) Rb(+) I(++) N(+) H(+) Rc(+) cRp(+) dRp(+) Rb(+) L(+++) I(+) Ll(+++)

N(+) N(+) H(+) N(+) H(+)

Fm(+++)

H(+) N(+) H(++) N(++) H(+) H(+) N(+)

Fm(+++) Fm(+++) Mo(+) Mo(++)

H(+) N(+) H(+++) N(+) H(+) H(+) N(+)

Mo(++) Mo(+) Mo(+) Mo(+)

N(+)

cRp(+++) dRp(+) Rc(+) Rc(+++) cRp(++) dRp(+) Ds(+) Ll(+++) I(++) H(+) Rc(+++) cRp(++) dRp(++) Rb(+) L(+++) I(++) N(+) Rc(+) cRp(+) dRp(+) Rb(+)

H(+++) N(++) H(+)

Mo(++)

N(+) H(+)

Mo(+)

H(+) N(+)

Mo(++)

I(++) N(++) N(+++) L(++) I(++) L(+++)

H(+) N(+) H(+) N(+) H(++) H(++)

Mo(++) Mo(++) Fm(+++) Fm(+++)

H(+) H(+)

Fm(+++) Fm(+++)

L(+++) I(+++) H(+)

Rc(+++) cRp(++) dRp(++) Rc(+++) cRp(++) dRp(++) Rc(+++) cRp(++) dRp(++) Ds(+)

M, micrite; S, esparite; Nf, needle-fiber; C, coatings; H, hypo-coatings; I, infillings; N, nodules; L, laminaes, Ll, laminaes with laminar microstructure; Fm, fine mass; Rc, recrystallization; cRp, clay replacement; dRp, detrital grains of quartz, mica and feldspar replacement; Ds, dissolution; Rb, secondary carbonate precipitation; Mo, mottles. (+++), very abundant; (++), moderately abundant; (+) present in low quantities.

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Fig. 1. (a) Random mesh of needle-fibre calcite, profile TC45, horizon 2Ck, crossed polarized light (XPL). (b) Abundant carbonate coatings on the walls of pores, with rare fusing of the coatings of neighbouring pores, profile AM14a, horizon 3Ck2, XPL. (c) Coatings formed by needlefibre calcite crystals oriented parallel to each other and to the walls of the pores, which were in turn intercalated between illuvial-clay coatings, profile TP42, horizon 2CBtk3, XPL. (d) The recrystallization process is evident due to the presence of highly variable sizes of the crystals, grouped in domains, with transition zones between micritic and sparry domains, profile TF63a, horizon 2CBtk1, XPL. (e) The presence of central masses of microsparite formed by radiating sparry crystals is also a distinctive feature of recrystallization, profile TF63a, horizon 2Ck/ Btb, XPL. (f) Contact surfaces of the sparry calcite crystals that are rounded also distinguish the process of recrystallization, profile TF63a, horizon 2Ck/Btb, XPL.

to be purely physico-chemical features (Riche et al., 1982; Verges et al., 1982; Verrecchia and Verrecchia, 1994).

The coatings and hypo-coatings covered the surfaces of the aggregates, gravels and the walls of the pores. Macroscopically, these appeared with some

P. Alonso et al. / Geoderma 118 (2004) 261–276

frequency, covering the undersides of the gravel pebbles and reaching great thicknesses (up to 1 cm), with thicker coatings appearing at the bottom of larger clasts (Treadwell-Steitz and McFadden, 2000). Microscopically, the coatings and hypo-coatings were abundant on the walls of the pores, the former type more common than the latter. Both types of coatings appearing within any type of void (most commonly within channels, cavities and cracks) were irregularly distributed, with some coated pores occurring next to others completely lacking any calcareous accumulation. In rare cases, the coatings of neighbouring pores fused (Fig. 1b) and filled in the entire pore (infillings). The size of the crystals varied markedly with, micrites being more abundant than sparry calcite. At times, the coatings were formed by needle-fibre calcite crystals precipitated parallel to each other and to the walls of the pores, which were in turn covered with illuvial-clay coatings. (Fig. 1c). The nodules varied considerably in size and shape, and exhibited a certain rounded tendency. In profile, these were distinctively white, at times with a sharp

267

border, but generally indistinct. Some of these were soft and crumbly, whereas others were hard, the latter commonly showing signs of having undergone surface dissolution. Microscopically, these were far less abundant than the coatings, had a micritic composition (in some cases sparry), and generally had distinct borders. Some nodules fused, giving rise to broad carbonaterich zones with a typical crystalline texture. Horizontal laminae were common in the carbonates of these soils, although tipped and vertical laminae are also present. In some cases, the intersection of various directions of lamination caused distinctive interlacing (Fig. 2), but this occurred only in the C horizon, in sandy materials without gravel. Generally, the laminae were thin ( < 1 cm). Microscopically, these were micritic and massive in distribution, although in some cases, laminar fragments intruded from the Bt horizon immediately above. The laminae exhibited moderate porosity in the form of cracks, channels and cavities. As in previous cases, the borders were generally clearly distinguishable. Finally, in the horizons with the highest carbonate content, the CaCO3 distribution was massive.

Fig. 2. (a) Distinctive networks of horizontal lamination of carbonates in the C horizon of profile TP38a. (b) Detail of the intersection of various directions of lamination in carbonates causing distinctive interlacing in the C horizon of profile AM64.

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3.2.2. Distribution of the carbonates in the profile The pedogenic carbonates in these soils followed a classical distribution, with several leached surface horizons to 100 cm in depth overlying horizons containing carbonate accumulations, and these, in turn, overlying deeper leached horizons. Generally, the uppermost part of the calcic horizon abruptly registered the highest values, then declined gradually with depth until reaching the leached zone. 3.3. Carbonates and parent material The fluvial materials that comprise the terraces was derived from the erosion of siliceous rocks, primarily granite and sandstone, together with minor proportions of slates and quartzites. It is important to emphasize that in no case was any carbonate detrital grain found, either in the parent material of the terrace soils, or in any of the fluvial deposits that formed the present-day riverbeds and floodplains of this hydrographic basin. 3.4. The carbonates and underlying material No carbonate minerals were found in the substratum of the series of terraces at Fresno Alha´ndiga, Calvarrasa de Abajo and San Pedro del Valle, in which the parent materials were Tertiary sands and sandstone, as well as Palaeozoic slates. In the case of the terrace series of Macotera, the fluvial surfaces were deposited over feldspathic (potassium and plagioclases of albite), muddy sands of Tertiary age, in which carbonate levels appeared with a certain frequency.

4. Discussion 4.1. Carbonate precipitation and leaching processes The presence, morphology and distribution of carbonates in the soil profile are governed by complex conditions of solubility. 4.1.1. Crystallization The most common size of the carbonates of these soils was micritic, indicating rapid crystallization (Bathurst, 1971; Folk, 1974; Bal, 1975). In this sense, the nucleation effect exerted by clays in the soil has been recognized by numerous authors (Wieder and Yaalon, 1974, 1978; Elbersen, 1982). Because clay particles hamper the formation of large crystals, close relationships have generally been found between the soil texture and the crystal size of the carbonates formed. Nevertheless, in these soils, we did not find this correlation, either in the microscopic or in the analytical studies, presumably because in most cases the carbonates in the soils studied underwent later transformation processes. Needle-fibre calcite was common in certain settings, invariably within discrete pores (channels and cavities), and forming pseudomycelia of more or less loose interlaced fine crystals inside the pores. Needlefibre calcites formed preferentially in the upper levels of the calcic horizons and represent a strongly diagnostic indicator of crystallization of soil carbonates. Needle-fibre calcite constitutes the first stage in the precipitation of the carbonates in the soil, which many researchers have attributed to oversaturated solutions (Buckley, 1951; James, 1972; Folk, 1974; Elbersen, 1982; Magaldi, 1983).

3.5. The carbonates in the hydrographic basin Acidic rocks occupied great expanses in the field area, and were comprised of adamellitic granites, slates, sandstones, quartzites, graywackes, schists, mica schists, phiyllites and conglomerates. There were only small outcrops of more or less calcareous composition (Palaeo- or Neogene Tertiary sediments, such as marls, calcarenites and limestones). The small sizes, together with the higher weatherability of these materials, explains their complete absence in the fluvial deposits comprising the terraces.

4.1.2. Recrystallization Recrystallization was substantially developed in these soils. In one step of the recrystallization, needle-fibre calcite interlaced to form micritic masses, and in another step, these masses recrystallized to sparry calcite crystals (Loisy et al., 1999) by a mechanism of neomorphic aggradation (Bathurst, 1971). The distinctive features of carbonate recrystallization in these soils, in accordance with Bathurst (1971), were: (i) Highly variable sizes of the crystals, grouped in domains; with micrite, microsparite aggregates

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(f = 4 –10 Am), pseudosparite (f = 10– 50 Am) and sparitic. There were transition zones between micritic and sparry calcite domains (Ringrose et al., 2002) (Fig. 1d). (ii) Central masses of microsparite or pseudosparite formed by radiating spar crystals (Fig. 1e). (iii) Contact surfaces of the spar crystals being rounded or undulated (Fig. 1f). (iv) Coatings of elongated spar crystals, parallel, with radiating fibrous shapes and frequently with undulating edges. In addition, it is noteworthy that in the youngest soils from the Late Pleistocene, (lower terraces, < 50,000 years) the carbonates appeared almost exclusively in the form of micrite, whereas the sparry calcite was more abundant in the oldest soils from the Middle and Early Pleistocene (>300,000 years, medium and high terraces), especially in the upper levels of the calcic horizon. Recrystallization rarely occurred in the youngest soils from the Late Pleistocene ( < 40,000 years), but was more common in the Middle Pleistocene soils (medium terraces, 350,000 years), and increased in development with the age of the soil (Table 3). 4.1.3. Replacement The replacement of silicate material by carbonates has been discussed by numerous authors (e.g., Degens and Rutte, 1960; Gile et al., 1966; Multer and Hoffmeister, 1968; Reeves, 1970; Millot et al., 1977; Ruellan et al., 1978; Millot, 1979; Bech et al., 1980; Ruellan, 1980; Watts, 1980; Paquet and Ruellan, 1997), and is referred to as epigenesis by Nahon and Ruellan (1975). In these soils, this process is quite generalized, because replacement affects not only the coatings of illuvial clay and other clay masses, but also detrital quartz grains, feldspars and micas. The illuvial-clay coatings underwent intense replacement that began in the soils of the low terraces (Late Pleistocene) and reached extraordinary development in the medium terraces (Middle Pleistocene). The process was represented in all its phases from the initial stage of disorganization of the coatings to complete replacement by the carbonates, with the only trace of the clay being the yellowish and reddish colorations of the carbonates impregnated by iron compounds from the clay. Typically, this transforma-

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tion appears in the intermediate stages, in which halfreplaced illuvial-clay coatings are extremely common. Quartz sands, feldspars and micas were more stable, and are replaced only in Middle Pleistocene and older soils. The mica grains were progressively replaced by carbonates. In the first phase, the mica lamellae/cleavages planes were separated by the crystallization of the carbonates and were finally completely replaced, with only some residual traces remaining. Feldspars and quartz underwent an equally progressive replacement (Fig. 3a and b). A highly characteristic result of the replacement process was the brecciation of the grains (Ruellan et al., 1978; Paquet and Ruellan, 1997). The sands and gravels of the detrital minerals were broken into a number of fragments that remained separated but retained the orientation of the original crystal (Fig. 3a and c). The replacement generally led to the formation of colourless sparry calcite crystals, some of which showed secondary coatings of distinctive interference colours (Fig. 3c) (Ruellan et al., 1978; Paquet and Ruellan, 1997). In some cases, the original shapes of the replaced detrital grains were recognizable (Fig. 3c). In comparison with the preceding cases, the replacement of clayey masses by carbonates produced yellowish-brown calcite of thick fibrous crystals, which grew radially, forming aggregates in fan-shaped clusters. According to several authors (Swineford et al., 1958; Multer and Hoffmeister, 1968; Nagtegaal, 1969; Reeves, 1970; Millot et al., 1977; Reheis, 1988; Paquet and Ruellan, 1997), the replacement of silicate grains is indicated by the presence of floating grains of quartz and feldspar (quartz and feldspar grains separated from the carbonate matrix by a porous spaces. This fabric was common in these soils, and is attributed to the dissolution of the quartz and of the feldspars in an arid palaeoclimates; this interpretation is reasonable because, in a calcic horizon, the pH can be locally quite high and spatially variable (Callot et al., 1978). Under such high pH conditions, the solubility of the silica and the alumina increases, easily reaching oversaturation for the carbonates. The complex microstructures described previously are highly characteristic features of replacement and recrystallization. In some cases, the roots of plants were replaced by elongated carbonate crystals in parallel arrangements, following the vegetal morphology, commonly forming tubes with a hollow central part (Jaillard, 1992; Bezce-Deak et al., 1997) (Fig. 3d).

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Fig. 3. (a) Quartz crystal partially replaced by carbonates, profile TF63a, horizon 2Ck/Btb, XPL. (b) Plagioclase feldspar crystal partially replaced by carbonate, profile TF63a, horizon 2Ck/Btb, XPL. (c) The replacement generally led to the formation of colourless sparry calcite crystals, in some cases with secondary coatings exhibiting distinctive interference colours, whereas in other cases, as in this K-feldspars crystal, the original shapes of the replaced detrital grains were recognizable, profile TF63a, horizon 2CBtk1, XPL. (d) Roots of plants replaced by elongated carbonate crystals in parallel arrangements, following the vegetal morphology, profile AM25, horizon 2CBtk, XPL.

In general, all these types of replacements were visible beginning with the Middle Pleistocene soils, and developing with steadily greater intensity with the age of the soil; they are prominent in the soils older than 300,000 years (Table 3). 4.1.4. Displacement Displacement was not found to be a major process in the formation of calcic horizons in the soils studied, perhaps because, in general, the carbonate content of these soils was not high and thus some carbonate zones still maintained appreciable porosity. 4.1.5. Dissolution Some soils revealed signs of dissolution and mixing of the previously accumulated carbonates (Srivastava, 2001). Commonly, the grains were rounded

(usually ellipsoidal, but sometimes spherical), and widely separated in most cases (Fig. 4b). However, the most distinctive feature of this process was the presence of crystals with pronounced serration as a result of dissolution (Fig. 4a). In some places, unexpected aggregates of clay coatings with sponge-like porosity appeared without carbonate crystals. In thin section, these took the form of well-defined networks of highly uniform holes corresponding to fine grains of sand (Fig. 4c and d). An analysis of other zones of the same horizon revealed that the same clay coatings of similar characteristics covered sparry equidimensional calcite grains (Fig. 4e). Thus, the formation of the networks of empty clay coatings can be attributed to the dissolution of formerly coated carbonate crystals.

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Fig. 4. Dissolution process, profile TP50b, horizon 2BCtk. (a) The most distinctive feature of this process was the presence of crystals with pronounced serration as a result of dissolution, XPL. (b) Rounded carbonate grains embedded in a mass of illuvial clay, XPL. (c) Unexpected aggregates of clay coatings with sponge-like porosity appearing without carbonate crystals in plane polarized light (PPL). (d) The same microscopic field as c), with XPL. (e) In the centre of the image, clay coatings with characteristics similar to those of the preceding image but covered now by sparry, equidimensional calcite grains; on the left, calcite grains appear without clay coatings (having not undergone dissolution, the coatings did not form hollows and the clay was not illuviated), XPL.

These networks would have formed in three stages: (i) partial dissolution of the carbonate grains, forming intergranular pores; (ii) clay illuviation filling the pores; (iii) dissolution of carbonate grains and consequent formation of clay-coating networks. These three

stages correspond to climatic shifts towards consistently wetter conditions. Evidence of carbonate dissolution was also apparent at the macroscopic level of the soil profile based on in the presence of hard calcareous nodules with clean

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surfaces, as well as with clear borders, and commonly with elongated forms vertically arrayed in the profile. This dissolution was active only in the oldest Middle Pleistocene soils ( z 200,000 years), in the Late Pleistocene soils, and in the upper levels of the calcic horizons. 4.1.6. Recarbonatation The late development of secondary carbonate was evident in carbonate coatings that covered the illuvialclay coatings (Fig. 5a and b) (Bronger et al., 1998), at times cross-cutting through the previously formed clay coatings. These horizons are called compound soil horizons with mixed calcic and argillic properties (Kleber, 2000). Occasionally, there were coatings composed of various alternating layers of carbonates and illuvial

clay, which are unequivocal evidence of various phases of successive secondary carbonate precipitation (Fig. 5c). These multiple processes took place only in the oldest soils, beginning with the Middle Pleistocene soils ( z 200,000 years), and represent additional proof of the various climatic changes that these soils had undergone. 4.2. Origin of the carbonates The origin of carbonates in soil forming over non-calcareous parent material, as in the present case, constitutes a controversial issue. The possibility of a geological origin for our carbonates can be dismissed on the basis of the observations analysed above: carbonate coatings in the lower part of the gravel; highly irregular and heterogeneous distribu-

Fig. 5. (a) The precipitation of secondary carbonate was evident in carbonate coatings that covered the illuvial-clay coatings, profile TF63a, horizon 2CBtk1, PPL. (b) Carbonate coatings covering illuvial clay coatings, profile TF115, horizon 2Btk2, XPL. (c) Coatings composed of various alternating layers of carbonates and illuvial clay, unequivocal evidence of various phases of successive secondary carbonate precipitation, profile TF115, horizon 2Btk2, XPL. (d) Many carbonate accumulations, are accompanied by Mn accumulations, profile AM 25, horizon 2Ck1, PPL.

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tion of carbonate accumulations; and carbonate coatings over illuvial-clay coatings. Thus, it appears evident that pedological processes caused the distribution and morphology of the carbonate accumulations in these soils. These pedological carbonates can be autochthonous or allochthonous. 4.2.1. Autochthonous origin The carbonates may have come from parent material either directly (being present within that material) or indirectly (forming from components of the parent material). The possibility of inheritance (direct origin) can be discarded on the basis of a lack of carbonates in the present alluvial deposits, as well as the lack of parent material in any terrace. If mineral alteration (indirect origin) of the parent material were responsible, the mineral would have to be feldspar, but feldspars of these soils are albite and oligoclase-sodium-rich silicate minerals that are calcium-poor. These minerals present diverse degrees of alteration, invariably becoming clay phyllosilicates (illite and kaolinite) and gibbsite. In addition, we found no relationship between the intensity of the alteration of the feldspars (expressed by the quartz/feldspar ratio of the sand fraction) and the carbonate content of the soils. Finally, if this process were responsible for the pedogenic carbonate accumulations in these soils, we might expect to find pedogenic carbonate accumulations in the broad and diverse neighbouring granite regions (the origin of the fluvial materials of these terraces), but no such accumulations were found. 4.2.2. Allochthonous origin The carbonates in question must be of external origin, derived either from the air or from water. No features indicate aeolian transport (for example, substantial increases in the silt or fine-sand fraction in the surface horizons, soils containing abundant fine and translocated dust in the matrix have continuous coatings; Treadwell-Steitz and McFadden, 2000). The derivation of carbonates from surface runoff does not appear probable either, as there are no calcareous zones near the terraces. As indicated above, at times carbonates appear in preferentially horizontal laminae which crisscrossed with more or less vertical grains, creating

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distinctive patterns with the following characteristics: (i) The interlacing is not limited to the soils of these terraces but appears also in numerous surfaces throughout the region and is occurs preferentially in high-altitude surfaces composed of sand, sandstone and clay. (ii) In some cases, these patterns appear immediately beneath an argillic horizon, but in other cases, appearing at subsoil depths, they are difficult to relate to soils (3 –5 m; Fig. 2a). (iii) In rare cases, these patterns appear in Tertiary sands, forming thick (10 cm), well-defined laminae and with a slope that does not correspond to the present topographical surface. (iv) In some soils, the upper levels of the calcic horizon show a clear horizontal lamination consisting of carbonate laminae alternating with layers of leached material. This lamination could be attributed to the fluctuations of the water table. (vi) In some soils, the distribution of the carbonates with depth is irregular and leached horizons appear among carbonate horizons. This fact may also indicate oscillations in a water table, at the time the carbonates were deposited in the soils. (vii) In nearly all cases, carbonate accumulation is associated with distinctive hydromorphic processes (Table 3), generally involving hypocoatings, coatings and black nodules of Mn compounds (Fig. 5d). In light of all these observations, we interpret that these patterns of carbonate distribution have a vadose origin. The laminae must have been the result of the temporal shifts of the water table, which periodically provided carbonates during certain geological stages. Given the great tectonic stability of the zone during the Pleistocene, the formation of the sequence of terraces studied should be attributed to climatic changes (Instituto Geolo´gico y Minero de Espan˜a, 1982). Thus, during cold and wet periods (episodes of resystaxia) the fluvial courses of the Tormes basin were eroded progressively until reaching a new equilibrium at a lower level. The low temperatures of these episodes led to a greater bicarbonate concentration in the vadose waters (Arkley, 1963), which in wet

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periods would increase the carbonate content in the soils of the fluvial deposits, primarily as a consequence of suction and evaporation processes. This scenario appears to be corroborated by the fact that the soils high in carbonate content formed in colder periods of the isotope stages described by Bassinot et al. (1994); specifically, the carbonates could have accumulated during substages 6.2, 7.4, 10.2, 12.2, 13.2 and 16.2 (Tables 1 and 3). In warmer periods (episodes of biostaxia), which alternated with the colder ones, the fluvial deposits (terraces) that would have been left exposed after the waters receded underwent pedological processes such as weathering, leaching, carbonates precipitation and clay illuviation. The presence of carbonate dissolutions in the soils AM25 and AM47 appear to indicate the development of the two wettest periods in the isotope substages 7.4 and 13.2, occurring around 200,000 to 500,000 years B.P. The complexity of the climatic changes that these soils have undergone, especially the oldest ones, could be manifested by the recrytallization, replacement, dissolution and secondary carbonate precipitation found in the carbonates in these soils (Table 3), as well as the alternation of several phases of clay illuviation with episodes of carbonate accumulation. In each chronosequence, and in the overall composition of the soils, there was a trend of the carbonate contents to diminish the younger the soils (Table 3), apparently indicating that the climate of this geographical region has been changing in the last 1,200,000 years, towards warmer and presumably drier periods (Vidal, 1979; Gutierrez, 1986; Simo´n et al., 2000; Ortiz et al., 2002).

(ii) The carbonates of these soils represent a highly active phase, undergoing intense transformations, such as the recrystallization, replacement of the silicate grains, dissolution and secondary carbonate precipitation. The recrystallization, replacement and secondary carbonate precipitation occurred from the Late Pleistocene soils and Middle Pleistocene soils (40,000 years for recrystallization, z 300,000 years for z intense replacement and z 200,000 years for secondary carbonate precipitation) and became more intense with the age of the soils. The presence of carbonate dissolutions in the soils corresponding to isotope substages 7.4 and 13.2 appear to indicate the development of two wetter periods towards 200,000 and 500,000 years B.P. (iii) The diversity and complexity of the processes that have affected the carbonates of these soils, together with the fact of several phases of clay illuviation alternating with episodes of carbonate accumulation reflect the complexity of the climatic changes that these soils have undergone, especially in those of the oldest surfaces. (iv) The forms of appearance (at the micro- and macroscopic level), distribution (in the soil profile and region), and association with other processes (clay illuviation and hydromorphy) imply that in certain periods (particularly the coldest) the vadose waters must have brought in dissolved carbonate that facilitated pedogenic carbonates precipitation. (v) In general, the intensity of the accumulations tended to increase with the age of the soils. This indicates that the climate of this geographical region has been changing during the last 1,200,000 years towards warmer, and presumably drier, periods.

References 5. Conclusions (i) The absence of carbonates in the soils of the youngest surfaces, as well as in the riverbeds, floodplains and the lowest terraces indicates that carbonatation is not occurring at present in these chronosequences. Therefore, simply the presence of carbonate accumulations in the soils studied suffices to diagnose their palaeosol character. This diagnosis is applicable not only to the soils of the terraces of the Tormes river basin but, also to a great number of soils of the region.

Alonso, P., Sierra, C., Ortega, E., Dorronsoro, C., 1994. Soil development indices of soils developed on fluvial terraces (Pen˜aranda, Salamanca, Spain). Catena 23, 295 – 308. Arkley, R.J., 1963. Calculation of carbonate and water movement in soil from climatic data. Soil Sci. 96, 239 – 248. Bal, L., 1975. Carbonate in soil: a theoretical consideration on, and proposal for its fabric analysis: 1. Crystic, calcic and fibrous plasma fabric. Neth. J. Agric. Sci. 23, 18 – 35. Barahona, E., 1984. Determinaciones analı´ticas en suelos: carbonatos totales y caliza activa. I Congreso Nacional de la Ciencia del Suelo, Madrid, pp. 53 – 67. Bassinot, F.V., Labeyrie, L.D., Vincent, E., Quidelleur, X., Shackle-

P. Alonso et al. / Geoderma 118 (2004) 261–276 ton, N.J., Lancelot, Y., 1994. The astronomical theory of climate and the age of the Brunhes – Matuyama magnetic reversal. Earth Planet. Sci. Lett. 126, 91 – 108. Bathurst, R.G.C., 1971. Carbonate Sediments and Their Diagenesis. Elsevier, Amsterdam. 620 pp. Bech, J., Nahon, D., Paquet, H., Ruellan, A., Millot, G., 1980. Sur l’extension ge´ographique et climatique des phe´nome´nes d’e´pigenie par la calcite dans les encrouˆtements calcaires. Exemple de la Catalogne. C.R. Acad. Sci. Paris 291 (D), 371 – 376. Bezce-Deak, J., Langohr, R., Verrecchia, E.P., 1997. Small scale secondary CaCO3 accumulation in selected sections of the European loess belt. Morphological forms and potential for paleoenvironmental reconstruction. Geoderma 76, 221 – 252. Bronger, A., Winter, R., Heinkele, T., 1998. Pleistocene climatic history of East and Central Asia based on paleopedological indicators in loess – paleosol sequences. Catena 34, 1 – 17. Buckley, H.E., 1951. Crystal Growth. Wiley, NY. 586 pp. Callot, G., Chamayou, H., Dupuis, M., 1978. Variations du pH de la solution de mate´rieux calcaires en relation avec la dynamique de l’eau. Ele´ments d’analyse d’un syste`me carbonate´. Ann. Agron. 29 (1), 37 – 57. Callot, G., Guyon, A., Mousain, D., 1985. Inter-relations entre aiguilles de calcite et hyphes myce’liens. Agronomie 5, 209 – 216. Degens, E.T., Rutte, E., 1960. Geochemische Untersuchungen eines kalkkrustenprofils von Altkorinth, Griechenland. Neues Jahrb. Geol. Paleontol. S, 263 – 276. Dorronsoro, C., 1994. Micromorphological index for the evaluation of soil evolution in central Spain. Geoderma 61, 237 – 250. Dorronsoro, C., Alonso, P., 1994. Chronosequence in Almar River, fluvial terrace soil. Soil Sci. Soc. Am. J. 58, 910 – 925. Elbersen, G.W.W., 1982. Mechanical Replacement Processes in Mobile Soft Calcic Horizons; Their Role in Soil and Landscape Genesis in an Area Near Me´rida, Spain. Centre for Agricultural Publishing and Documentation, Wageningen. 208 pp. Folk, R.L., 1974. The natural history of crystalline calcium carbonate: effect of magnesium content and salinity. J. Sediment. Petrol. 44 (1), 40 – 53. Gile, L.H., Peterson, F.F., Grossman, R.B., 1966. Morphological and genetic sequences of carbonate accumulations in desert soils. Soil Sci. 101, 347 – 354. Glinka, K.D., 1963. Treatise on Soil Science (Translated from the Russian). Israel Program for Scientific Translation, Jerusalem. Gutierrez, M., 1986. Some remarks on the problem of climatic changes and geomorphological processes in arid zones. Quaternary Climatic in Western Mediterranean. Lopez-Vega. Pub. Univ., Madrid, pp. 127 – 132. Huguet del Villar, E., 1937. In: Murby, T. (Ed.), Los Suelos de la Penı´nsula Luso-Ibe´rica. 1 Mapa 1:500,000. London, 416 pp. Instituto Geolo´gico y Minero de Espan˜a, 1982. Mapa Geolo´gico de Espan˜a. 1:50,000. Hoja no. 479 (Pen˜aranda de Bracamonte). Jaillard, B., 1992. Calcification des cellules corticales des racines en milieu calcaire. Bull. Soc. Bot. Fr. 139, Actual. Bot. 1, 41 – 46. James, N.P., 1972. Eolocene and Pleistocene calcareous crust (caliche) profiles: criteria for subaerial exposure. J. Sediment. Petrol. 42, 817 – 836. Kleber, A., 2000. Compound soil horizons with mixed calcic and

275

argillic properties—examples from the northern Great Basin, USA. Catena 41, 111 – 131. Loisy, C., Verrecchia, E.P., Dufour, P., 1999. Microbial origin for pedogenic micrite associated with a carbonate paleosol (Champagne, France). Sediment. Geol. 126, 193 – 204. Loveland, P.J., Whalley, W.R., 1991. Particle size analysis. In: Smith, K.A., Mullig, C.E. (Eds.), Soil Analysis: Physical Methods. Marcel Dekker, New York, pp. 271 – 328. Magaldi, D., 1983. Calcareous crust (caliche) genesis in some Mollisols and Alfisols from southern Italy: a micromorphological approach. In: Bullock, P., Murphy, C.P. (Eds.), Soil Micromorphology. Soil Genesis, vol. 2. A.B. Publishers, Berkhamsted, England, pp. 623 – 636. Millot, G., 1979. Les phe´nome`nes d’e´pige´nie calcaire et leur roˆle dans l’alte´ration. Sci. Sol 2/3, 259 – 261. Millot, G., Nahon, D., Paquet, H., Ruellan, A., Tardy, Y., 1977. L’Epige´nie calcaire de roches silicate´es dans les encrouˆtements carbonate´s en pays subaride Antiatlas, Maroc. Sci. Geol. Bull. 30 (3), 129 – 152. Multer, H.G., Hoffmeister, J.E., 1968. Subaerial laminated crusts of the Florida Keys. Geol. Soc. Am. Bull. 79, 183 – 192. Nagtegaal, P.J.C., 1969. Microtextures in recent and fossil caliche. Leidse Geol. Meded. 42, 131 – 142. Nahon, D.H., Ruellan, A., 1975. Les accumulations de calcaire sur les marnes e´ocee`nes de la Falaise de Thie`s (Senegal). Mise en e´vidence de phe´nome`nes d’e´pige´nie. In: Vogt, T. (Ed.), Colloque Types de Crouˆtes Calcaires et leur Re´partition Re´gionale. Univ. Louis Pasteur, Strasbourg, pp. 7 – 12. 150 pp. Nettleton, W.D., Olson, C.G., Wysocki, D.A., 2000. Paleosol classification: problems and solutions. Catena 41, 61 – 92. Ortiz, I., Simo´n, M., Dorronsoro, C., Martı´n, F., Garcı´a, I., 2002. Soil evolution over the Quaternary period in a Mediterranean climate (SE Spain). Catena 48/3, 13 – 148. Paquet, H., Ruellan, A., 1997. Calcareous epigenie replacement (‘‘e´pige´nie’’) in soils and calcreta formation. In: Paquet, H., Clauer, N. (Eds.), Soils and Sediments, Mineralogy and Geochemistry, vol. 2. Springer, pp. 21 – 48. Reeves, C.C., 1970. Origin, classification and geologic history of caliche on the southern high plains, Texas and eastern New Mexico. J. Geol. 78, 352 – 362. Reheis, M.C., 1988. Pedogenic replacement of aluminosilicate grains by CaCO3 in Ustollic Haplargids, south-central Montana, USA. Geoderma 41, 243 – 261. Reuter, G., 2000. A logical system of paleopedological terms. Catena 41, 93 – 109. Rhoades, J.D., 1982. Cation exchange capacity. In: Page, A.L. (Ed.), Methods of Soil Analysis, Part 2. American Society of Agronomy, Madison, WI, pp. 149 – 157. Riche, G., Rambaud, D., Riera, M., 1982. Etude morphologique d’un encrouˆtement calcaire, Region d’Irece, Bahia, Bresil. Cah. - ORSTOM, Ser. Pedol. 19, 257 – 270. Ringrose, S., Kampunzu, A.B., Vink, B.W., Matheson, W., Downey, W.S., 2002. Origin and palaeo-environments of calcareous sediments in the Moshaweng Dry Valley, Southeast Botswana. Earth Surf. Process. Landf. 27, 591 – 611. Roquero, C., Ontan˜on, J.M., 1966. Une forme d’accumulation des carbonates calcique et magnesique en bandes horizontales et

276

P. Alonso et al. / Geoderma 118 (2004) 261–276

‘‘grillages’’ sous climat semiarid mediterraneen. En Conferencia de suelos mediterraneos, Madrid. Ruellan, A., 1980. L’accumulation du calcaire dans le sols. Reunion organise´e par le groupe d’e´tude des systemes carbonate´es. Univ. Bordeaux, Inst. Geodynamique, INSA. Ruellan, A., Nahon, D., Paquet, H., Millot, G., 1978. Figures d’e´pige´nie par la calcite dans les encrouˆtements calcaires. Proc 5th Inter. Working Meeting on Soil Micromorphology, pp. 1051 – 1056. Santonja, M., Perez Gonzalez, A., 1984. Las Industrias Paleolı´ticas ´ mbito Regional. Ministerio de Cultura, de La Maya I en su A Excavaciones Arqueolo´gicas en Espan˜a. 347 pp. Santonja, M., Querol, A., 1976. Estudio de industrias del Paleolı´tico inferior procedentes de una terraza del Tormes (Galisancho, Salamanca). Zephirus XXVI – XXVII, 97 – 109. Santonja, M., Querol, A., Perez Gonzalez, A., 1982. El yacimiento de La Maya I y la secuencia paleolı´tica del valle del Tormes. Actas de la II Reunio´n Regional de Geologı´a del Duero (Salamanca, 1979), 2a parte: 641 – 662. Temas Geolo´gico-Mineros, VI, I.G.M.E. Simo´n, M., Sa´nchez, S., Garcı´a, I., 2000. Soil-landscape evolution on a Mediterranean high mountain. Catena 39, 211 – 231. Soil Survey Staff, 1999. Soil Taxonomy. A Basic System of Soil Classification for Making and Interpreting Soil Surveys. Agriculture Handbook 436. US Dep. Agric., Washington. Srivastava, P., 2001. Paleoclimatic implications of pedogenic carbonates in Holocene soils of the Gangetic Plains, India. Palaeogeogr. Palaeoclimatol. Palaeoecol. 172, 207 – 222.

Swineford, A., Leonard, A.B., Frye, J.C., 1958. Petrology of the Pliocene pisolitic limestone in the Great Plains. Kans. Geol. Surv. Bull. 130, 97 – 116. Treadwell-Steitz, C., McFadden, L.D., 2000. Influence of parent material and grain size on carbonate coatings in gravelly soils, Palo Duro Wash, New Mexico. Geoderma 94, 1 – 22. Verges, V., Madon, M., Bruand, A., Bocquier, G., 1982. Morphologie et cristallogenese de microcristaux, supergenes de calcite en aiguilles. Bull. Mineral. 105, 351 – 356. Verrecchia, E.P., Dumont, J.L., 1996. A biogeochemical model for chalk alteration by fungi in semiarid environments. Biogeochemistry 35, 447 – 470. Verrecchia, E.P., Verrecchia, K.E., 1994. Needle fiber calcite: a critical review and a proposed classification. J. Sediment. Res. A4, 650 – 664. Vidal, J.R., 1979. El periodo cuaternario en Galicia. Gallaecia 3 – 4, 19 – 35. Vreeken, W.J., 1975. Principal kinds of chronosequences and their significance in soil history. J. Soil Sci. 26, 378 – 394. Watts, N.L., 1980. Quaternary pedogenic calcretes from the Kalahari, Southern Africa: mineralogy, genesis and diagenesis. Sedimentology 27, 661 – 686. Wieder, M., Yaalon, D.H., 1974. Effects of matrix composition on carbonate nodule crystallisation. Geoderma 11, 95 – 121. Wieder, M., Yaalon, D.H., 1978. Grain cutans resulting from clay illuviation in calcareous soil material. In: Delgado, M. (Ed.), Micromorfologı´a de Suelos, vol. 2. Universidad de Granada, Espan˜a, pp. 1133 – 1158.