Eocene Varna Reefs in NE Bulgaria

Abstract

The Varna microbial carbonate reefs, known as the ‘upright stones’, аrе limestone columns of natural origin, formed in the Eocene sands near the town of Varna, NE Bulgaria. These unique geological formations are among the most impressive natural phenomena in Bulgaria and lie in a protected area of 253.3 hectares which includes 18 geosites of aesthetic and scientific value. Some of these features forme part of the ‘Golden Sands’ Natural Park. The upright stones are bacterial-algal reefs formed within non-carbonate Ypresian sands and silts of the Dikilitash Formation. They are of geomorphological, sedimentological and paleontological interest. Human interest in the columns is a result of their unique morphology, due to which they were originally considered to be the remains of ancient temples and castles. According to various theories, these are weathering or infiltration formations, concretions, coral reefs, petrified forests, etc. At the end of the twentieth century, their genesis was studied in the context of a phytogenetic origin, and it was concluded that they are bacterial-algal bioherms similar to recent atolls and miniatols in modern oceans and seas. In support of this hypothesis is the presence of microbial stromatolite laminations and structures, tubular bodies and algal remains in the columns that are not found in the sediments outside of the columns. The Varna reefs are an attractive tourist destination for visitors of the Bulgarian Black Sea coast. These are included in the UNESCO Programme for the protection of geological heritage of scientific value. The future of these unique geological formations depends on their protection at a national and a European level.