127 БЪЛГАРСКО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, Национална конференция с международно участие „ГЕОНАУКИ 2016“ BULGARIAN GEOLOGICAL SOCIETY, National Conference with international participation “GEOSCIENCES 2016” Triassic nannofossils from borehole R-1 Golitsa, East Balkan, Bulgaria Триаски нанофосили от сондаж Р-1 Голица, Източен Балкан, България Dimitar Sinnyovsky Димитър Синьовски University of Mining and Geology “St. Ivan Rilski”, 1700 Sofia; Е-mail: sinsky@mgu.bg Keywords: Triassic, East Balkan, calcareous nannofossils. Triassic calcareous nannofossils are rarely encoun- tered due to their poor preservation and low diver- sity. Well preserved Late Triassic nannofossils have been described in limestone-marl alternations from alpine sections in Northern and Southern Alpes, and from borehols in NW Australian continental shelf. First biostratigraphic consideration of Late Triassic nannofossils belongs to Prins (1969), who described Crucirhabdulus primulus from nonspecified local- ity and defined a taxon range zone Crucirhabdulus (Rethian–Chetangian). Unfortunately his new taxa re- mained invalid because their description did not meet the requirements of the code of ISBN. Thus the new species Crucirhabdulus primulus was introduced by Rood et al. (1973) based on TEM microphotographs. Jafar (1983) confirmed the presence of this species in Upper Triassic carbonate rocks in NE Alps on the territory of Germany and Austria. He described new genera and new species calcareous nannofossils – Euconosphaera tollmannia and Prinsiosphaera trias- sica with several subspecies based on SEM investiga- tion. Brallower et al. (1991, 1992) believed that dif- ference between these subspecies is a result of etching and overgrowth of the outer wall and this gives rise to the diversity of forms described by Jafar (1983). They referred the hollow forms of Prinsiosphaera geomet- rica Jafar to the genus Thoracosphaera Kamptner (T. geometrica). The authors defined a taxon range zone Prinsiosphaera triassica (Carnian–Rhaetian) with two subzones based on the first appearance of Euco- nosphaera zlambachensis (Moshkovitz) in the Upper Norian: Thoracosphaera geometrica (Lower Carnian– Upper Norian) and Euconosphaera zlambachensis (Upper Norian–Rhaetian). In the present study calcareous nannofossils from borehole R-1 Golitsa in East Balkan are described, re- covered from the interval between 3488 and 3740 m composed of motley clayey and micritic limestones with marl intercalations, assigned to the Omurtag/Tvarditsa Formations (Carnian–Norian). They contain poor nanno- fossil assemblages with characteristic Late Triassic forms. The nannofossil association in the investigated in- terval is of low diversity. It consists of several forms belonging to the genera Prinsiosphaera Jafar and Obliquipithonella Keupp. Similar to the previously descrbed Upper Triassic nannofossil associations, Prinsiosphaera triassica Jafar is the dominating form in the investigated samples. Very rare are the repre- sentatives of the hemispherical calcareous dinocists, originally described by Brallower et al. (1991) as Thoracosphaera wombatensis. In the present study these forms are referred to the Triassic members of the genus Obliquipithonella Keupp. The other forms are considered to be new species, accompanied by brief diagnosis. Sistematic paleontology Genus Prinsiosphaera Jafar, 1983 Prinsiosphaera triassica Jafar, 1983 (Pl. I, a, b) Remarks: These nannofossils indicate a large diver- sity of forms. According to Brallower et al. (1991, 1992) the species includes only specimens of solid structure while the hollow forms belong to the genus Thoracosphaera Kamptner. In the present study sev- eral broken specimens were observed with entirely destroyed outer cycle. This is the dominating form in the poorly preserved associations observed in the in- vestigated stratigraphic interval. Genus Obliquipithonella Keupp, 1984 Obliquipithonella wombatensis (Bralower et al., 1991) new comb. (Pl. I, c) Remarks: According to Brallower et al. (1991) this species has a very different shape and texture from Thoracosphaera geometrica (Jafar, 1983) Brallower et al., 1991. It consists of bowl- or hat-shaped hemi- spherical specimens with coarser textute than typical Thoracosphaera, between 5 and 13 μm in diameter,open at the wide end. Brallower et al. (1991, 1992) noted that they may be valves of a bivalved structure as is the case in Schizosphaerella (Moshkovitz, Erlich, 1976). Age: Late Triassic.