Fauna, palaeoecology and ecotypes of the Early Cretaceous sediment hosted hydrothermal vent environment of Zengővárkony (Mecsek Mountains, Hungary)

Abstract

The fossil biota of the upper Valanginian–lower Hauterivian sediment hosted vent (SHV) environment of Zengővárkony comprises 39 species, 55 genera and higher taxa representing seven phyla. Thirteen of these taxa are reported from Zengőrvárkony as new species or new subgenera/genera, and this high endemicity is linked to a unique palaeoenvironment. The palaeoenvironment is developed in an outer shelf epicontinental setting on an elevated block or slope, and is linked to a small sedimentary iron-ore body interbedded with pillow lavas being a result of ferriferous exhalations and biogenic processes. Biogeographically, the brachiopods indicate the Sub-Tethyan domain. Serial sectioning of brachiopods revealed a taxon-dependent rich and diverse microfauna (sponges, foraminifers, gastropods) preserved inside the shells. Internally preserved microfauna in brachiopods reveals differentiation among preventive strategies. It implies different preventive efficiencies of alternative defence strategies of higher brachiopod taxa. The unique Zengővárkony SHV environment attracted both nektonic and benthic organisms by creating different ecotopes around the hydrothermally driven bottom environment. This environment belongs to the group of rare, shelfal, hydrothermally influenced palaeoenvironments formed on continental crust. Water depth was most probably between 100 and 150 m. Recent observations from a similar modern volcanic built-up, and its effects on the marine environment located on continental crust around the Aeolian Islands (Tyrrhenian Sea) support the recognition of this fossil SHV environment and helps to understand better its bathymetry, ecological conditions and ore-formation.