BIOGENIC WEATHERING OF MARBLE MONUMENTS IN DIDIM, TURKEY AND IN TRAJAN COLUMN, ROME

The Temple of Apollo in Didim, Turkey, was built in 560-550 B.C. with marble. Mean annual rainfall there is 656 mm. Much of the marble surface is covered by a black crust of microorganisms. Weathering patterns, associated mainly with cyanobacteria, observed there were: 1. Exfoliation with pleurocapsalean cyanobacteria in fissures. 2. Gradual removal, by splashing rain drops, of marble crystals. the coherence of which is reduced as a result of microbial activity. 3. Pits formed by cyanobacteria living in circular patches. The mechanism described in No. 2. leads there to the creation of depressions where the lithobionts are situated. Trajan's column was erected in Rome 112 C.E. Mean annual rainfall there is ca. 700 mm. The column is almost devoid of microbial life at present, but until 1942 had many patches of microbial black crusts. From 1942 to 1948 it was covered by brick walls and sand as a way of protection against war hazards. The light-demanding microorganisms that populated the monument for hundreds of years disappeared after being covered for 6 years and have not returned yet. Pits resembling those in Didim damaged much of the artistic relief on parts of Trajan's column. The most affected parts are those facing south and southeast. These are the directions of the most common incident rainfall in Rome which bring water at high energy to the marble monument.