Recurvoides infernus sp. nov., one of the oldest representatives of the superfamily Recurvoidacea (Foraminifera), is described from a thin black claystone overlying the manganese deposits of the Krížna Unit in the Western Tatra Mountains (Poland). These manganese carbonates/silicates were laid down around a shallow−water exhalative submarine hydrothermal vent that was active in the early Toarcian. The microfossils are possibly the first described Jurassic foraminifera associated with hydrothermal vents. The assemblage is characterized by a high abundance and dominance of this new species. The primary lamination of the black claystone, the lack of any macrofauna, and an elevated TOC content point to oxygen−deficient conditions during sedimentation of these deposits. Furthermore, the nearly exclusive occurrence of agglutinated foraminifers suggests a low pH level. It is likely that the foraminifers colonized vent−related bacterial mats which acted as a rich and stable food source. Modern shallow− and deep−water hydrothermal vents may represent similar habitats.

Key words: Foraminifera, Ammosphaeroidinidae, agglutinated foraminifera, hydrothermal vent, black claystone, suboxia, the Carpathians, Tethys, Jurassic.

Jarosław Tyszka [ndtyszka@cyf-kr.edu.pl], Institute of Geological Sciences, Polish Academy of Sciences, Cracow Research Centre, Senacka 1, PL31-002 Kraków, Poland; Renata Jach [renata.jach@uj.edu.pl], Institute of Geological Sciences, Jagiellonian University, Oleandry 2a, PL30-063 Kraków, Poland; Miroslav Bubík [miroslav.bubik@geology.cz], Czech Geological Survey, Leitnerova 22, 658 69 Brno, Czech Republic.