“…Such a type of Carboniferous succession exists in the Donets Basin and in the Cantabrian Zone, in which the marine and terrestrial fossils have been studied for a long time (for the Donets, see Aisenverg et al, 1979;Fissunenko & Laveine, 1984;Izart et al, 1996Izart et al, , 1998Ueno & Nemyrovska, 2008;Khodjanyazova & Davydov, 2013;Khodjanyazova et al, 2014; and for the Cantabrian Zone, see van Ginkel, 1965van Ginkel, , 1971van Ginkel, , 1973van Ginkel, , 1987van Ginkel & Villa, 1996;Villa, 1995;Villa et al, 2015;Villa & Merino-Tomé, 2016;Wagner & Winkler Prins, 1985a, 1985bWagner et al, 2002;Wagner & Álvarez-Vázquez, 2010). However, the correlation of the marine and terrestrial biostratigraphic units from both areas is a problematic issue.…”