Scarciglia,F., Saporito,N., La Russa,M.F., Le Pera, E., Macchione,M., Puntillo,D., Crisci,G.M. and Pezzino,A.(2012): Role of lichens in weathering of granodiorite in the Sila uplands (Calabria, southern Italy). Sedimentary Geology, 280, 119-134.

『シラ台地(南部イタリアのカラブリア州)の花崗閃緑岩の風化におけるコケの役割』


Abstract
 This paper explores the role of five recurrent epilithic lichen species (Aspicilia internutans (Nylk) Arnold, Xanthoparmelia pulla (Ach) O. Blanco, A. Crespo, Elix, D. Hawlsw. & Lumdsch, Rhizocarpon lecanorinum Anders, Tephromela atra (Huds.) Hafellner and Lecanora bolcana (Pollini) Poelt), which encrust granodiorite spheroidal boulders exposed in the Sila uplands (Calabria, southern Italy), in weathering of plutonic rocks in a typical mountainous Mediterranean environment. A detailed investigation was carried out on the lichen-rock interface if each species, by comparing them mutually and with lichen-free granodiorite samples. For this purpose, the lichen species were sampled together with the encrusted rock surface for detailed mineral-petrographic analyses performed in thin and ultra-thin sections. Optical and scanning electron microscopy of these sections and of bulk samples permitted us to highlight the peculiar modes of physical and chemical attacks of lichen thalli and hyphae on and into the substratum for each species. Crack systems often parallel to the outer rock surface appear often intruded by hyphae, which cause rupture of primary minerals, with detachment and progressive incorporation of their fragments into the thallus. In particular, the species L. bolcana and T. atra revealed an unexpected, partly endolithic behavior, presumably enhanced by the presence of rock fractures earlier generated by other physical breakage processes already affecting the spheroidal boulders in the Sila mountains. Dissolution features often affect primary minerals (even quartz), that may show very peculiar patterns which are suggestive of a biologically-induced control. Various phyllosilicate clay minerals were identified using SEM-EDS microprobe analyses and FT-IR spectroscopy, which also enabled the identification of possible amorphous silica (or quartz micrograins), rhizocarpic acid and carotenoid at the encrusted granodiorite interface. In contrast, neither oxalic acids nor oxalates were detected.

Keywords: Lichens; Granodiorite; Lichen-rock interface; Biomechanical weathering; Biochemical weathering』

1. Introduction
2. Geological/geomorphological and climate setting
3. Materials and methods
4. Results
 4.1. The five lichens studied
 4.2. Petrographic analyses
  4.2.1. Lichen-free granodiorite
  4.2.2. Weathering features at the lichen-rock interface
   4.2.2.1. A. intermutans
   4.2.2.2. X. pulla
   4.2.2.3. R. lecanorinum
   4.2.2.4. T. atra
   4.2.2.5. L. bolcana
 4.3. FT-IR spectroscopy and SEM-EDS microprobe analysis
5. Discussion
 5.1. Biophysical and biochemical weathering
 5.2. Bioweathering products and organic acids
6. Conclusions
Acknowledgments
References


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