Inheritance of 2:1 Phyllosilicates in Costa Rican Andisols

Autor: A.M. Jaunet, F. van Oort, J.D.J. van Doesburg, Peter Buurman, A.G. Jongmans, A. Nieuwenhuyse
Přispěvatelé: Unité de Recherche AgroPédoClimatique de la zone caraïbe (APC), Institut National de la Recherche Agronomique (INRA), Unité de recherche Science du Sol (USS), ProdInra, Migration
Rok vydání: 1994
Předmět:
Zdroj: Soil Science Society of America Journal
Soil Science Society of America Journal, Soil Science Society of America, 1994, 58 (2), pp.494-502
Soil Science Society of America Journal 58 (1994)
Soil Science Society of America Journal, 58, 494-501
ISSN: 0361-5995
1435-0661
DOI: 10.2136/sssaj1994.03615995005800020035x
Popis: The occurrence of 2:1 phyllosilicates in Andisols is variously ascribed to in situ pedogenic origin, aeolian addition, or the presence of hydrothermally altered rock fragments. We studied the origin of 2:1 phyllosilicates that occur in Holocene Hapludands on andesitic, sandy beach ridges in Costa Rica by micromorphological, mineralogical, and submicroscopical techniques. The 2:1 phyllosilicates also occur as pseudomorphs after primary minerals in fresh rock of the inland volcanoes, from which the parent material of the beach ridges was mainly derived. Hydrothermal processes are most likely responsible for the formation of such pseudomorphs. Rock weathering produces sand-sized rock fragments with clay pseudomorphs and also liberates individual pseudomorphs. Subsequent erosion and alluvial transport affect their shape, but not their internal fabric. In the beach ridges, clay pseudomorphs appear as individual, sand-sized clay bodies, and inside sand-sized andesitic rock fragments. Submicroscopical analyses A.G. Jongmans, A. Nieuwenhuyse, P. Buurman, and J.D.J. van Doesburg, Dep. of Soil Science and Geology, Agricultural Univ. P.O. Box 37, 6700 AA Wageningen, the Netherlands; F. van Oort, INRA, Station Agropedoclimatique, Guadeloupe, France; A.M. Jaunet, INRA, Station de Science du Sol, Versailles, France. Received 31 Aug. 1992. *Corresponding author. Published in Soil Sci. Soc. Am. J. 58:494-501 (1994). of these individual clay bodies and andesitic rock fragments with clay pseudomorphs indicate a predominance of 2:1 phyllosilicates. This implies that they are inherited from the parent material and are not due to postdepositional soil formation in the beach ridges. Weathering and biological activity affect the clay bodies and rock fragments with clay pseudomorphs, leading to the formation of clay-sized particles consisting of 2:1 phyllosilicates. Toward the soil surface, these particles are incorporated into the allophanic groundmass resulting from actual soil formation. The geographically extensive occurrence of 2:1 phyllosilicates in Andisols suggests that the genetic processes described here may have more than regional validity. A and 1:1 phyllosilicates are the most common secondary minerals in soils formed in pyroclastic deposits in humid tropical areas without a distinct dry season (Mizota and van Reewijk, 1989; Parfitt and Kimble, 1989; Quantin et al., 1990). The occurrence of 2:1 phyllosilicates has often been reported in such soils Abbreviations: EDS, electron diffraction spectometer; EG, ethylene glycol; SSXRD, step-scan x-ray diffraction; TEM, transmission electron microscope; XRD, x-ray diffraction. JONGMANS ET AL.: INHERITANCE OF 2:1 PHYLLOSILICATES 495 (Wada, 1980; Pevear et al., 1982; Shoji et al., 1985, 1987; van Oort, 1988), but there are different concepts concerning their genesis (Lowe, 1986). Shoji and Yamada (1981) and Shoji et al. (1982) favored an in situ pedogenic origin, and suggested that 2:1 phyllosilicates are formed by weathering of volcanic glass. Other workers such as Mokma et al. (1972) and Mizota and Takahashi (1982) attributed the presence of 2:1 phyllosilicates in soils on tephra deposits to later aeolian additions. Dudas and Harward (1975), Pevear et al. (1982), and Ping et al. (1988) ascribed the occurrence of 2:l-type phylJosilicates in air fall tephra deposits to hydrothermally altered rock fragments that were ejected during eruptions. Hydrothermal alteration in volcanic rocks transforms primary minerals such as olivine, pyroxenes, and plagioclase into clay pseudomorphs (Kristmannsdottir, 1979; Fan, 1979). Dudas and Harward (1975) demonstrated that 2:1 phyllosilicates in some volcanic ash horizons could be relicts of an underlying montmorillonitecontaining paleosol. Micromorphology and related in situ submicroscopy were not carried out in the cited studies, except for Pevear et al. (1982). Consequently, the properties of the individual soil constituents in terms of size, shape, arrangement, and composition were not studied. Among other factors, these properties influence the occurrence of clay minerals in soils formed on volcanic deposits (Nahon, 1991; Jongmans et al., 1994), so they need to be examined in studies concerning mineral weathering and neoformation. In a chronosequence of Andisols and younger Tropopsamments on Holocene andesitic beach ridges of Costa Rica, Nieuwenhuyse etal. (1994) reported the occurrence of 2:1 phyllosilicates. These soils were formed under humid tropical conditions where soil weathering (supergene alteration, Delvigne, 1990) has led to formation of short-range order material. The goal of our study was to determine the origin and genesis of the observed 2:1 phyllosilicates in the Andisols of the Costa Rican beach ridge sequence by means of micromorphological, mineralogical, and in situ submicroscopical techniques of undisturbed samples. MATERIALS AND METHODS Five Andisols (2000-5000 yr old) and three Tropopsamments ( 150 cm) of Hapludand AT7 were studied by XRD. The fractions were prepared after removal of organic matter by buffered (pH 5.5) H2O2 treatment, repeated washing with distilled water (5-10 times) and addition of 0.005 M NaCl solution. The XRD was performed after grinding of the separated particle size fractions. In order to improve the quality of the XRD diagrams, part of the ground material was ultrasonically dispersed and sequentially extracted in darkness with ammonium oxalate at pH 3.3 (Tamm, 1922; Robert and Tessier, 1974), then with sodium citrate at pH 7.3 (Tamura, 1957). The XRD patterns were obtained from Mg-saturated, oriented pastes before and after EG solvation and from K-saturated, oriented pastes after heating. Finally, fresh rock collected on the Irazu volcano was ground and ultrasonically dispersed. The XRD was performed on the clay fraction after Mg and K saturation. The allophane content was calculated by the method proposed by Parfitt and Wilson (1985). From four Hapludands, microquantities of sand-sized, anisotropic, clay bodies from uncovered thin sections were isolated with a microscope-mounted drill (Verschure, 1978). The material was transferred to glass or Al slides according to the method of Beauford et al. (1983). The XRD analyses of the microquantities were obtained by SSXRD, (Meunier and Velde, 1982) with steps of 0.05° 26 and counting times of 80 s per step. Two sand-sized, anisotropic clay bodies from Hapludand AT7 were selected optically and removed from uncovered thin sections without disturbing them according to the method proposed in van Oort et al. (1990). After reimpregnation of these clay bodies, undisturbed sections of 50-nm thickness Table 1. Selected properties and classification of five Andisols from Costa Rica. Particle-size distribution Chemical and physical properties B horizon C horizon A horizon B horizon Profile Classification A horizon Clay Sand Clay Sand Clay Sand Organic matter pH (H2O) Bulk density Allophanet
Databáze: OpenAIRE
Externí odkaz: