A reef system of Hauterivian age that is situated on the south side of Bolshoy Balkhan (Turkoman Republic) has been investigated. Research on a number of sections has allowed the reconstruction of the palaeogeography of the underwater slope as developed along the isochronous surface. On the basis of the lithological composition of, and fossil communities in, the deposits, 10 facies distributed within three zones of the palaeobasin have been identified. There was a favourable environment for the establishment of numerous reef-builders, mainly scleractinian corals. New data concerning their dispersal, systematics, morphological types and epibiont fauna have been obtained. Twenty-six forms of scleractinians belonging to 16 genera from this region have been identified. A study of the reef deposits allowed the reconstruction of the conditions of their formation and revealed regular links between species and growth forms of scleractinians and facies of certain types. The majority of the corals occur in the Urgonian of many other parts of the Tethyan region. Bolshoy Balkhan is another area where the Urgonian biosedimentary system began before the Barremian.