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Weathering of sandstone lotus petals at the Angkor site: a 1,000-year stone durability trial |
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| Authors: | Marie-Françoise André Bruno Phalip Olivier Voldoire Franck Vautier Yves Géraud Mhammed Benbakkar Christophe Constantin Fabienne Huber Gilles Morvan |
| Institution: | 1. Laboratoire de Géographie physique et environnementale (GEOLAB), UMR 6042 CNRS-Université Blaise Pascal, MSH 4 rue Ledru, 63057, Clermont-Ferrand Cedex 1, France 2. Centre d’Histoire “Espaces et Cultures” (CHEC)-EA 1000, Université Blaise Pascal, MSH 4 rue Ledru, 63057, Clermont-Ferrand Cedex 1, France 3. Institut de Physique du Globe (IPG), UMR 7516 CNRS-Université de Strasbourg/EOST, 5 rue René Descartes, 67084, Strasbourg Cedex, France 4. Laboratoire Magmas et Volcans (LMV), UMR 6524, OPGC-Université Blaise Pascal-CNRS-IRD, 5 rue Kessler, 63038, Clermont-Ferrand Cedex, France 5. Laboratoire d’Hydrologie et de Géochimie de Strasbourg (LHyGeS), UMR 7517 Université de Strasbourg/EOST, CNRS, 1 rue Blessig, 67084, Strasbourg Cedex, France |
| Abstract: | This article is based on field investigations carried out at Ta Keo and Banteay Srei temples (Angkor, Cambodia), which have similar environmental histories and display the same recurrent decorative pattern (lotus petal) in three different sandstone lithotypes. Based on two original scales of mechanical and chemical weathering, the degree of deterioration of c.2000 sandstone petals was visually assessed, resulting in the proposal of a durability scale. An explanatory scheme was provided, based on laboratory analyses of stone materials (ICP-AES, XRD, SEM-EDS, polarizing microscopy and mercury injection). The key drivers of sandstone durability are both mineralogical and petrophysical. The remarkable preservation of the pink sandstone is due to the quartzose nature of its clasts, the non-swelling clay content of its abundant matrix (kaolinite) and its porosity structure (large connected pores and probable non-connected porosity). The overall good preservation of the green sandstone is due to its extremely low porosity and specific surface area, associated with its strong cementation. The severe deterioration of the grey sandstone is due to its laminated structure (oriented biotites), the susceptibility to hygric swelling and solution of its binding agents (chlorite/smectite and calcite) and its porosity structure, which evolves during a two-stage weathering sequence. The first stage is characterized by a bimodal porosity due to the partial clogging of macropores by swelling clays, and the second stage by a substantial increase in porosity and the penetration of salts (barite and anhydrite). Conversely, oxidation phenomena associated with weathering can lead to a drastic reduction of porosity. |
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