Renata Jach

A new vent−related foraminifer from the lower Toarcian black claystone of the Tatra Mountains, Poland

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.