Aspect influence on the weathering micro-rates of limestones exposed under semiarid coastal Mediterranean climate

A novel methodology is presented for measuring weathering microrates after one-year of direct exposure of rocks to environment. The study focuses on building materials used in the cultural heritage exposed to semiarid coastal Mediterranean climate (SE Spain). Three different carbonate rocks, with significant differences in porosity and texture, were studied in two different exposition orientations (north and south). Results are interpreted according to local microenvironmental conditions and petrologic aspects (porosity, pore size distribution and mineralogy). South-facing rock blocks show the highest weathering microrates (9130 mm/ky and 18750 mm/ky for fine and coarse-grained porous limestones, respectively). They are 1.55 and 1.92 times higher than rates obtained in north-facing rock samples. Physical and chemical decay mechanisms overlap in the weathering process. On the one hand, physical processes are more evident in porous limestones, being predominant in south exposure samples. On the other hand, chemical corrosion is the main weathering mechanism in massive limestones as well as in porous limestones with unstable components. Dissolution prevails in northern exposure. Obtained weathering rates are two to three magnitude orders higher than the erosion rates measured in the same rocks, highlighting the conceptual differences between both parameters.