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The weathering of calcareous rocks by lichens

AuthorsAscaso, Carmen CSIC ORCID ; Galván, Jesús; Rodríguez Pascual, C.
KeywordsCalcareous rocks
Issue Date1982
CitationPedobiología 24: 219-229 (1982)
AbstractSYERS & ISKANDAR (1973)report that lidiens are able to produce bioehemical weathering by the following processes: 1 — Production of C()2. a part of which may be dissolved in water. 2 — Production of biochemieal compounds soluble in water. 3 -- Production of oxalic acid. The importance of r02 in chemical weathering is unknown, but according to the above authors. its significance is probably smaller than that of the other two. The weathering capacity of lichenic substances has been demonstrated in receñí works by ASCASO et al. (1976) who showed that rocks and minoráis are altered by lichenic thalli, as well as by lichenic substances (ASCASO & GALVÁX 1976). HALLBAUER & HAHNS (1977) have shown by SEM that quartz may be etched by the action of Dimalaena oreina. GALVÁX et (ti. (1981) report the formation of important amounts of gels in the zone of contact betvveen lidien and metamorphic rock, and have found that a direct relationship exists between the texture of the rock and the extra-tion of minoráis from the rock. They have also observed a ehloritization of rock ¡sones under particular lidien thalli. Thus, the above studies indícate the importance of lichenic substances in weathering processes. but the presence of oxalates in lichen-rock interfaces has not been reported so far. Howover. oxalic acid is of great interest in weathering processes, particularly in the case of lidien species living on limestones (SYERS & ISKAXDAR 1973). JOXES e{ al. (1980) have observed the effoct to Pertusaria corallina on a basalt which was niainly made up of piagiodase (labradorite-bitownite) with dinopiroxene and olivine as ferromagnesian minoráis and magnetite as accesory mineral. They observed that the calcium-rich piagiodase feldspar and the ferromagnesian minoráis were psrticiilarly affected and. in their opinión, the altoration wa? dúo to the oxalic acid generated by the mycobiont. although the action of lidien acids could not be totally disregarded. WILSOX et al. (1981) studiod a substrato of magnesinm silicato minerals (serpentinite) under the thalli of Lecanora atru. observing the formation of the monohydrate and dihydrate forms of calcium oxalate. as well as a largo aniount of crystallinc magnesium oxalate dihydrate. This oxalate (glushinskite) appears as a creamy white layer made up of piramidal crystals interinixed with the hyphae (WiLSOx ct al. 1980).
Description11 pages, figures, and tables statistics.
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