Lichenic alteration and mineralization in calcareous monuments of northeastern Spain

Biodeterioration processes on three Spanish calcareous monuments (Scipio's Tower, Olerdola Wall, and the Naveta d'Es Tudons) were investigated. Scipio's Tower and Olerdola Wall, both located in Catalonia, were built with blocks of bioclastic packstones (foraminifera, bivalves, gastropods, red algae, echinoderms) of the Langhian (Middle Miocene) Age. The Naveta d'Es Tudons, located on the island of Menorca, was constructed with blocks made up of bioclastic packstones, partially dolomitized and dedolomitized, and is of Miocene Age. The main organisms that inhabited these three monuments were lichens [mainly Dirina massiliensis Durieu et Mont, Verrucaria nigrescens Pers., Caloplaca aurantia (Pers.) Hellb., Caloplaca velana (Massal.) Du Rietz, Caloplaca erythrocarpa (Pers.) Zw., Petractis thelotremalla (Bagl.) Vezda, and Strigula calearea Bricaud et Roux], which caused the main alteration of the rock. The distributions of these lichens were determined and their actions on the stone were studied by different techniques. From the samples studied, a general and complete alteration profile was proposed and described. In this profile from the external area of the stone to tire unaltered substratum, five zones were distinguished: lichen thallus, microcorrosion surface, altered zone, transition zone, and finally the unaltered zone or substratum. A model of evolution of these zones was also developed. Some structures found in tire different zones of these profiles were morphologically described and filaments and spheres were identified. In the fame way, some diagenetic products found in these zones were described and related to tire processes that originated them. An interpretation of these structures and products and their relation to organisms and microorganisms was attempted.