Scientific registration nº : 1200 Symposium nº : 16 Presentation : poster Genesis of the Red Mediterranean and morphogenesis of the Albernoa area-Portugal Genèse des sols rouges méditerranéens et morphogenèse dans la région de l’Albernoa, Portugal

ABREU Maria Manuela (1), MONTEIRO MARQUES Manuel (2), JOAQUIM Catarina (1), ROBERT Michel (3)

(1) ISA, Dept. Ciências do Ambiente. Tapada da Ajuda 1399 Lisboa Codex, Portugal. (2) Centro Estudos Pedologia.I.I.C.T. Tapada da Ajuda 1399 Lisboa Codex, Portugal. (3) Science du Sol, INRA Versailles. Route de St. Cyr 78000 Versailles, France.

Abstract The aim of this work was to demonstrates that in the Albernoa area the Quaternary climate changes have led to Red Mediterranean Soils (RMS) being out of equilibrium of the present physical environment and consequently subject to new morphogenetic dynamics,which have recently been further enhanced by anthropogenic activities.The soils studied were: one Plinthic Lixisol, five Ferric Lixisols, four Chromic Luvisols and one Haplic Luvisol, developed on flanglomerates covering ferruginous and/or phyllites and turbidites. Our studies suggested the following genetic steps: regional neotectonic led to the erosion of the older relief under wet to semiarid climates; the resulting desaggregated materials covered the remaining laterites and/or phyllites; then, under a stable environment (humid and warm climate), weathering and occurred in the middle Pleistocene; after that, soils were rubified in a relatively wet and warm climate, already considered as mediterranean-type, but wetter than the actual, so, in the late Pleistocene, the genesis of RMS occurred; and in subrecent times the regional base level was lowered, giving rise to gully formation. Two types of RMS were determined: The S1/P2 Lixisol and S1/P2A Luvisol were formed in the Holocene, while P1/95, S1/P1, S2/P3, S2/P2 and B/Vx Lixisols and 1/Vx, 2/Vx, 3/Vx, 4/Vx Luvisols seem to be developed in the late Pleistocene under relative wetter and warmer climatic conditions. Therefore, some of the Red Mediterranean Soils of Albernoa occur in an area where the present day climatic conditions are not compatible with their genesis. So, these soils might be considered as .

Introduction In the earlier systems of the European Classification, the Red Mediterranean Soils have always received a special place due to their distinctive red colours and the genetic implications associated with the site and the climatic conditions in which they occur. However, unequal genesis conditions within the Mediterranean basin have resulted in the formation of a great variety of soils in this area. Teixeira and Pais (1976), Diniz (1985)

1 showed paleontological evidences of climate fluctuations in Portugal since Pliocene- Pleistocene times. Besides, Suc (1984) referred that the north-western parts of the Mediterranean basin were strongly affected by such climatic fluctuations since Pliocene, varying in the rainfall rhythm and temperature. According to Singer (1976) the Quaternary fluctuations of climate have affected, in different degrees, genesis in the areas bording the Mediterranean basin and, in their north-western fringes, Red Mediterranean Soils are often not compatible with the present-day climatic conditions and they have therefore to be considered relict, polygenetic soils or paleosols. The main objective of this work was to demonstrate that climatic fluctuations since late Tertiary have affected, in the Albernoa area, the geomorphological evolution and the genesis of the Red Mediterranean Soils.

Environmental characterization Physical environment of the studied area The area considered, Albernoa (Beja), is included in Baixo Alentejo region. The geology- lithology of the studied area consists mainly of Paleozoic and Quaternary formations: later Devonian phyllites and turbidites and which in some small areas are covered by Pliocene-Pleistocene ferruginous laterites, fanglomerates and recent Quaternary colluvium-alluvium. The fanglomerates covered both phyllites and the laterites (Carta Geológica Portugal,1992). Baixo Alentejo region has been submitted to a temperate climate with a hot and dry summer (according to Köppen classification, Csa) or to a sub- humid dry, mesothermic climate with moderate to great excess of water in winter (according to Thornthwaite classification). The mean annual temperature is around 16º C (the mean temperature of the warmest month is approximately 24º C) and the total precipitation is between 550 to 600 mm, occurring mainly in winter. In geomorphic terms, the region is part of the Alentejo pediplain formed by the coalescence of a number of Cenozoic pediments (middle Terciary). In this applanation two surface levels are observed: one with 200-300 m of altitude and the other with 100-200 m of altitude. Some residual hills are in evidence in the first surface level. The correspondig pediments, cutted by incipient streams, became isolated and originated small plateaus. The area of Albernoa is located in the second surface drained by Sado and Guadiana rivers by means of the tributary stream right borders. The base-level fall of Guadiana river (Pleistocene- Holocene?) promotes the downcutting of all tributary streams near its confluence.

Methodology The characteristics of the bulk samples (<2 mm) were determined as follows: clay content by the pipette method; pH in water in a 1:2.5 soil/water suspensions using a glass electrode; organic matter content in a Ströhlein apparatus and using the factor 1.724; cation exchange capacity (CEC) by ammonium acetate at pH 7.0 and at pH 8.3 according to Mehlich (1953); free iron oxihydroxides (Fed) and free aluminuim hydroxides (Ald) by the Mehra and Jackson (1960) method; non-crystalline iron oxihydroxides (Feo) by the Tamm method (Schwertmwnn,1964). Atomic absorption spectromety was used for Al and Fe measurements in the extracts. Mineralogy of the fraction was determined by X-ray diffraction using both a Philips and a Siemens D 5000 diffractometers with Cu ka radiation. Soil and vegetation characteristics The soils are classified according to FAO (1989) as Ferric Lixisols – profiles S1/P1, S1/P2, S2/P2; S2/P3, B/Vx; Plinthic Lixisol – profile P1/95; Chromic Luvisols – profiles 1/Vx, 2/Vx, 3/Vx, 4/Vx; Haplic Luvisol– profile S1/P2A. The Plinthic Lixisols and Ferric Lixisols (S1/P1, S2/P2 and S2/P3) were developed on flanglomerates covering ferruginous laterites, soil profiles S1/P2 and S1/P2A were developed on flanglomerates and latter laying on phyllites and the other soil profiles were developed on phyllites. Most of the soils contain large amounts of coarse fragments (>2 mm) of schist and/or vein quartz in their Ap horizons (Ricardo et al., 1972; Abreu, 1986). These fragments represent a disperse coverage formation of recent (Holocene) fanglomerates. The soil profiles S/P belong to two toposequences, with slopes ranging from 0.5 to 1.5%, limiting a close depression. These toposequences are S1 with profiles P1, P2, P2A located for this order from the top to the middle of the sequence, and S2 with profiles P3 and P2 located in the top positions of the sequence. Some characteristics of the bulk samples (<2 mm) and the mineralogy of the clay fraction (<2 mm) are given in Table 1. Comparing Lixisols with Luvisols, a trend towards the lowest values of clay content was observed in B horizons of Lixisols, except in the soil profile B/Vx. The clay content of the latter is similar to that of the Chromic Luvisols and all of them, including B/Vx, were developed on phyllites, with values ranging from 463 to 655 g kg-1. On the contrary, the Haplic Luvisol contains the lowest clay content (278 g kg-1); this soil might be considered as a reorganized profile related to its topographic position. The soils were acid to neutral, with pH ranging from 4.4 to 6.9. O.M. content was generally low, which agree with the environmental conditions of the studied area. The CEC values tended to increase in soil profiles developed on phyllites as a result of their clay mineralogy (Table 1). The lowest values of CEC were measured in Lixisols, where kaolinite is the main constituent, whereas CEC values ranging from 9.45 to 19.34 cmol kg-1 were observed in Chromic Luvisols. In the latter, the dominant clay minerals are vermiculite, mica or interstratified vermiculite-smectite minerals with some kaolinite. However, the S1/P2A Haplic Luvisol and both S1/P2 and B/Vx Lixisols contain also smectite as well as kaolinite and mica in different proportions, presenting CEC values which lie between the soils referred above. -1 The Fed of B horizons of the soils ranged from 34.20 to 54.18 g kg in Lixisols and from -1 19.95 to 33.04 g kg in Luvisols, which presented the lowest Fed contents. Again, the S1/P2 and S1/P2A soil profiles showed the lowest levels of Fed in the corresponding soil unit, probably related to the soil profile reorganization, which also agree with their clay mineralogy and position in the toposequence. The Ald content was in general low in all soils, although in Luvisols developed on phyllites Ald was slightly higher. In the soils developed on fanglomerates and in the B/Vx soil, magnetic and non-magnetic ferruginous pisolites were identified. The pisolites were formed by a ferruginous clay plasma where skeletal grains were embedded: the plasm was compose of kaolinite, iron oxides and mica and the skeletal grains revealed a high degree of weathering and were constituted by quartz, K-feldspar and also grains of iron oxides. Hematite and goethite were present in the non-magnetic pisolites, whereas the magnetic pisolites contained maghemite and hematite (Abreu,1990). The past vegetation of the region included dense woods of green-oak (Quercus rotundifolia), cork oak (Quercus suber) and/or olive trees (Olea europaea var. europaea) and brushwood. During last centuary, the woods were partially cut off and the

3 soils have been cultivated (usually wheat) between some scattered green and cork oak and olive trees.

Table 1- Some selected soil characteristics

Profile Horizon Depth pH Clay O.M. CEC Fed Feo Ald Clay minerals* -1 -1 -1 cm H2O g kg cmol kg g kg K M S I V P1/95 Ap 0-15 5.5 333 11.0 6.38 26.80 1.33 2.76 4 1 - - - B1 15-30 5.2 304 10.0 5.75 26.60 1.33 2.47 4 1 - - - B2 30-60 5.9 473 6.0 8.42 34.20 1.33 3.29 4 1 - - - C 60-80 5.0 588 4.0 7.74 39.60 1.19 4.38 4 1 - - - S1/P1 Ap 0-10 5.4 244 16.0 5.41 24.60 1.33 2.09 3 1 - - - B 10-41 4.8 429 6.0 5.87 36.60 1.05 2.93 3 1 - - - C >40 4.4 486 4.0 5.22 38.20 0.84 3.73 3 1 - - - S1/P2 Ap 0-20 5.7 285 17.0 7.55 23.70 2.59 2.12 2 1 3 - - B 20-45 5.1 334 6.0 6.57 21.30 2.38 1.74 3 1 2 - - C >45 5.3 592 6.0 14.00 12.80 1.82 1.09 3 1 2 - - S1/P2A Ap 0-10 4.9 246 16.0 8.98 10.70 3.01 1.13 2 1 3 - - B >10 5.4 278 16.0 7.94 10.60 3.01 1.11 2 1 3 - - S2/P2 Ap 0-10 5.4 363 19.0 7.91 39.70 1.54 3.45 4 1 - - - B >10 5.4 353 13.0 6.79 38.40 1.54 2.74 4 1 - - - S2/P3 Ap 0-15 5.5 297 21.0 6.37 29.30 2.03 2.70 4 1 - - - B >15 5.6 335 14.0 7.58 35.70 2.17 2.74 4 1 - - - B/Vx Ap 0-22 5.8 193 13.0 8.10 28.80 3.43 1.96 4 2 - - - A3 22-42 6.7 235 9.6 8.10 30.31 3.29 1.75 4 2 - - - B2t 42-71 6.9 431 4.4 9.40 41.37 3.15 2.49 4 1 1 - - B3t 71-85 6.2 517 3.9 12.10 54.18 2.94 3.23 4 1 1 - - C 85-115 - 300 3.0 10.30 42.63 3.78 2.92 4 2 1 - - 1/Vx Ap 0-24 5.7 202 16.5 9.96 18.90 - 2.99 3 3 - - 3 B2t 24-69 5.5 481 4.0 13.89 19.95 - 3.79 2 3 - - 3 C 69-86 5.7 488 2.0 17.06 20.30 - 4.45 2 3 - 3 - 2/Vx Ap 0-15 5.4 186 13.0 9.45 20.72 - 2.54 2 3 - 3 - B2t 15-33 5.2 510 6.0 14.58 27.79 - 3.82 3 3 - 3 - B3t 33-49 4.7 655 6.0 17.03 33.04 - 4.66 3 3 - - 3 C 49-60 4.5 545 0.4 19.34 29.05 - 5.14 2 3 - - 3 3/Vx Ap 0-22 5.4 205 16.0 9.83 28.63 - 2.39 3 3 - - 2 A3 22-40 6.0 242 13.0 10.25 31.50 - 2.70 3 3 - - 2 B2t 40-70 6.7 463 4.0 11.01 24.01 - 2.70 3 3 - - 3 B3t 70-85 5.3 492 4.0 11.32 29.05 - 3.13 3 3 - - 2 C 85-110 4.5 413 2.0 12.31 24.22 - 2.33 3 3 - 3 - 4/Vx Ap 0-27 6.2 243 12.5 11.30 20.06 - 2.94 2 3 - - 2 B2t 27-54 6.3 526 3.0 12.80 27.16 - 4.03 3 3 - - 3 C 54-90 6.0 506 3.0 15.36 28.91 - 4.56 3 3 - - 3 *K- Kaolinite; M- Mica; S- Smectite; I- V-S Interstratified minerals; V- Vermiculite. (1) <10%; (2) 10-20%; (3) 20-40%; (4) 40-60% Discussion Climatic and geomorphological evolution Regional climatic variations affected rates of geomorphological processes by changing rates of chemical weathering and erodibility. As a result of the field observations, the studied soil characteristics and the information from various authors, an hypothesis of climatic and geomorphic evolution may be advanced for the studied area. The Alentejo region during the middle Tertiary have been submitted to a relief degradation, possibly under a semiarid to arid climate (?), which gave rise to a polygenetic surface (Feio, 1952) formed by the coalescence of a number of pediments and residual hills (Marques and Abreu,1995). In the middle to late Tertiary, the improvement of the climate conditions in terms of humidity induced the denudation of the drainage basin surface, putting in evidence the former residual relief. Local and gradual climate fluctuations from wet to semiarid, during the late Tertiary, led to pediment genesis. This was caused by the coalescence of the flood plains of intermitent rivers as the result of both lateral applanation and sheet flood transportation (Marques, 1977). These processes originated the fanglomerates, which covered the Devonian lithology. The Pliocene-Pleistocene transition was time of change to much wetter and warmer climate than that prevailing in the middle to late Tertiary (Suc,1984; Diniz, 1985; Abreu, 1986). These climatic conditions promoted a rapid and intense chemical weathering, corresponding to a stable landscape (Marques, 1977). This dynamic gave rise to the genesis of soft laterites of absolute accumulation. Due to a climatic change to arid or semiarid which appears to have characterized the early Pleistocene, the soft laterites were submitted to drying producing hard ferruginous laterites (ferricretes). In this period, the neotectonic events (Cabral, 1995) led to the deformation of the pediplain, which in turn conduced to a new morphogenesis phase under a wetter climate. Consequently, an important organized stream system, the Guadiana river, was established which excavated the laterites and, at the same time, gave rise to erosional and depositional processes forming a second generation of fanglomerates. Then, these materials can contain some ferruginous pisolites as the result of desaggregation. The second generation fanglomerates covered, not only the pediment phyllite rocks, but also the remaining laterites. The gully formation (first generation) was also the result of the stream system cited above, which was buried by later colluvium-alluvium deposits. During the middle Pleistocene in the Mediterranean region (Bull, 1991) and again under a wet climate with periods of occasional semiarid conditions, the rainfall was effective for the weathering of the stable parts of the studied landscape, where the pedogenesis rate was not exceeded by that of morphogenesis, and thus soil profiles were developed.

Genesis of Red Mediterranean Soils The soil characteristics taken into account were mainly those described in Table 1 and also the presence of an argillic horizon, the presence of quartz grains strongly weathered and the replacement of some quartz and mica sand grains by iron oxides (Abreu, 1986; Abreu, et al., 1988). Based on the past and recent geomorphological characteristics of the soils selected for this study, some of them with a well developed profile, and also supported by the results obtained in studies carried out in Spain (Mollina and Perez-González, 1989; Martin Serrano and Mollina,1989), a new approach for Red Mediterranean Soils genesis is outlined. The soil profiles not yet rubified might be formed in the middle Pleistocene to ante- Holocene, when the prevailing climatic conditions ended with the approach of full glacial times (tardi-Würm). However, in the late Pleistocene, the relatively wet and warm

5 climate (Mediterranean-type), characterized by greater fluctuations in moisture than in temperature and wetter than the actual (Suc, 1984), created the conditions for soil rubification. These conditions were mainly related to temperature, water activity, iron concentration, solid phases influence, iron oxidation rates (Abreu, 1990) and the geomorphological caracteristics of the region. In the Holocene, in an intergrade environment (pedogenesis/morphogenesis), the lowering of the regional base level promoted river captures by retrogressive erosion (Marques, 1977). Hence, the formation of the lowest stream terraces and gullies of second generation, which have recently been accelerated by anthropogenic activities. These stream terraces are not rubified (Zbyszewski, 1958). In an environment with morphogenesis tendency, colluvium deposits are formed. Some of these deposits may represent an heritage of earlier formed Red Mediterranean Soils but with a reorganized profile ("Sols Remaniés" in the French terminology). These reorganized recent soil profiles, located nearby or in closed depressions, may have partially lost their red colours by the fluctuation of ground-water level. This is the case of S1/P2 and S1/P2A soil profiles where the smectite presence is also a mineralogical evidence of this fact. The other studied soils are developed in situ: on fanglomerates of second generation corresponding to more evoluted P1/95, S1/P1, S2/P3 and S2/P2 Lixisols; and, on plyllites or turbidites corresponding to 1/Vx, 2/Vx, 3/Vx, 4/Vx Luvisols, with an intermediate evolution, and to B/Vx Lixisol, playing the bed rock also a role in this soil mineralogy. All Red Mediterranean Soils are actually covered by ephemeral thin mantles of colluvial materials, mainly quartz.

Conclusions The general pattern of paleoclimatic change from middle Tertiary to Holocene, in Albernoa area, outlines the climatic heritage that caused changes in geomorphological processes and soil genesis. According to their genesis, two types of RMS were studied in this work. The S1/P2 Lixisol and S1/P2A Luvisol were recently formed in the Holocene, while P1/95, S1/P1, S2/P3, S2/P2 and B/Vx Lixisols and 1/Vx, 2/Vx, 3/Vx, 4/Vx Luvisols seem to be developed in the late Pleistocene under relative wetter and warmer climatic conditions than the recent climate of the region. Therefore, some of the Red Mediterranean Soils of Albernoa occur in an area where the present day climatic conditions are not compatible with their genesis. So, these soils might be considered as paleosols.

References – Abreu, M.M., 1986. Aspectos do comportamento do ferro na crusta de meteorização. Alto e Baixo Alentejo. Thesis, Univ. Técnica Lisboa, 250 p. – Abreu, M.M.,Figueiredo, M.O., Waerenborgh, J.C. and Cabral, J.M.P., 1988. Oriented overgrowth of acicular maghemite crystals on quartz. Clay Minerals, 23: 357-365. – Abreu, M.M., 1990. Ferruginous pisolites from south of Portugal. Paleoenvironmental Quaternary relics. Sci. Géol., Bull., Strasbourg, 43 (2-4): 95-102. – Bull, W.B., 1991. Geomophic Responses to Climatic Changes. Oxford University Press, Oxford, 326 p. – Cabral, J., 1995. Neotectónica em Portugal Continental. Mem. Inst. Geol. Min. 31, Lisboa, 265 p. – Carta Geológica de Portugal, Esc. 1:500000. 1992. Carvalho, D. (co-ordinator). Serviços Geológicos de Portugal (Ed.). – Diniz, F., 1985. A bacia de Rio Maior. I Reun. Quater. Ibérico. - Glaciação da Serra da Estrela. Aspectos do Quaternário da Orla Atlântica: 16-33. – FAO-UNESCO, 1989. Carte Mondiale des Sols, Légende Révisée, 125p. – Feio, M., 1952. A Evolução do Relevo do Baixo Alentejo e Algarve. IAC. Centro Estudos Geog., Lisboa, 178 p. – Marques, M. Monteiro, 1977. Contribuição geomorfológica para o estudo da génese, evolução e conservação dos solos em Portugal.1. Primeiras observações sobre a superfície de Santiago do Escoural. An. Inst. Sup. Agron., Lisboa, XXXVII: 68-80. – Marques, M. Monteiro, and Abreu, M.M., 1995. Erosion and conservation of Red Mediterranean Soils in the south of Portugal. Third Intern. Meeting on Red Mediterranean Soils., Greece:228-230. – Martin-Serrano, A. and Mollina, E. Montes de Toledo y Extremadura. Mapa Cuaternario España Esc. 1:1000000. Inst. Tecn. GeoMinero España, Madrid:187-200. - Mehlich, A., 1953. Rapid determination of cation and anion exchange properties and pH of soils. J. Assoc. of Agric. Chem. 36: 445-457. – 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 and Clay Minerals, 7: 317-327. – Mollina, E. and Pérez-González, A., 1989. Depresión del Duero. Mapa del Cuaternario de España Escala 1:1000000. Inst. Tecn. GeoMinero España, Madrid:153-161. – Ricardo, R. P., Furtado, A.F.A. Sanches and Marques, M. Monteiro, 1972. Génese dos Solos Mediterrâneos - O caso de Solos Mediterrâneos Vermelhos de xistos paleozóicos. An. Inst. Sup. Agron., Lisboa, XXXIII: 109-123. – Schwertmann, U., 1964. Differenzierung der Eisenoxide des Bodens. Z. Pflanzenernährung, Düngung, Bodenkund, 105(3): 194-202. – Singer, A., 1976. The significance of the term "Mediterranean" in the Nomenclature of Soils in Europe and Israel. Israel J. of Earth Sci., 25: 76-82. – Suc, J.P., 1984. Origin and evolution of the Mediterranean vegetation and climate in Europe. Nature, London, 307: 218-226. – Teixeira, C. and J. Pais, 1976. Introdução à paleobotânica. As grandes fases da evolução dos vegetais.Lisboa, INIC. – Zbyszewski, G., 1958. Le Quaternaire du Portugal. Bol. Soc. Geol. Portugal, Porto, 13 (1-2), 227 p.

Keywords : Morphogenesis, Paleoenvironments, Pedogenesis, Red Mediterranean Soils, Portugal Mots clés : Morphogenèse, Paléoenvironnements, Pédogenèse, sols rouges méditerranéens, Portugal

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