Turbiosphaera archangelskyi sp. nov. and a morphological complex from the late Middle to Late Eocene of southern high latitudes: Biostratigraphic, palaeoenvironmental and palaeoceanographic implications

Abstract

We record a morphological complex of species of the dinoflagellate-cyst genus Turbiosphaera from the uppermost Río Turbio Formation, considered to be of late Priabonian age, and from equivalent units of the Austral-Magallanes Basin, southern Argentina and southern Chile. Previously, specimens now assigned to Turbiosphaera archangelskyi sp. nov and Turbiosphaera sarrisii were assigned to the cosmopolitan latest Maastrichtian to Middle Eocene species Turbiosphaera filosa. We now identify three species in our Turbiosphaera archangelskyi species complex, which excludes Turbiosphaera filosa. At one end of the complex is Turbiosphaera sarrisii with incipient processes, and at the other end, with well-developed individual processes, is Turbiosphaera sagena. The new species, Turbiosphaera archangelskyi, represents the intermediate stage and is the most abundant form. These three species have only been recorded together in the Austral-Magallanes Basin; their earliest occurrences are slightly asynchronous: Turbiosphaera sarrisii and Turbiosphaera archangelskyi have earliest occurrences in the late Bartonian, but that of Turbiosphaera sarrisii is slightly older. The earliest occurrence of Turbiosphaera sagena is recorded in the middle Priabonian. Our results highlight the biostratigraphic value of these species and their limited palaeogeographical distribution. The morphological variability exhibited by the Turbiosphaera archangelskyi species complex in the latest Eocene may be environmentally influenced, perhaps reflecting the deepening of the Drake Passage and the consequent influx of low-salinity water from the shelf and nearshore regions of the southeastern Pacific onto the Patagonian Shelf.