Abstract
Five new morphospecies of calcareous dinoflagellate cysts belonging to the genus Stomiosphaera Wanner, are described from the Tithonian–Berriasian Vaca Muerta Formation, in the Neuquén Basin, Western Argentina: Stomiosphaera triangulata sp. nov., Stomiosphaera quadrata sp. nov., Stomiosphaera subechinata sp. nov., Stomiosphaera subspinosa sp. nov., and Stomiosphaera gracilis sp. nov. Their stratigraphic distribution is discussed, particularly that of Stomiosphaera subechinata sp. nov. (Tithonian – lower Berriasian), which was previously assigned to Stomiosphaera echinata Nowak, a species that in the Tethys domain appears for the first time in the upper Valanginian. Likewise, possible assignments to the genera defined from three-dimensional observations are proposed, and eutrophic neritic conditions are interpreted for the time in which these species appear in the Neuquén Basin.
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