Origin of the Bessarabian limestones with Nubecularia novorossica of Northeastern Bulgaria

The Central and Eastern Paratethys Basins were connected and the joint Sarmatian Sea (Paratethys) appeared after the end of the Badenian. It was separated from the Mediterranean and Indopacific Ocean. As a result, the seawater salinity dropped and mass production of a few euryhaline groups (mainly benthic foraminifera, molluscs, and ostracods) with increasing endemisms developed at the beginning of the Sarmatian (s.l. and s.s.). The fauna and paleoenvironments (facies) were similar throughout the Paratethys. The Bessarabian limestones (referred to the Odartsi Formation) are composed almost entirely of the endemic foraminifera Nubecularia novorossica Karrer & Sinzow, 1877 and exposed on the territory of Northeastern Bulgaria are described in the present article. Six sections were examined, and it was found that the limestones were predominantly stratified and only in the upper parts of some sections were dome-shaped. Two varieties Nubecularia novorossica solitaria and Nubecularia novorossica nodula were defined and they are the predominant rock-forming constituent. The most appropriate environmental conditions for the occurrence, blooming and accumulation in the initial sediments of the Nubecularia novorossica tests were identified. Comparison with the findings of this nubeculariid from other Sarmatian sections reveals that the stratified limestones studied are rigid mainly due to the presence of cement, whereas abundant encrusting and microbial organisms in the dome-shaped bodies contributed to the formation of their rigid framework.