Middle Palaeogene dinoflagellate cysts from Tierra del Fuego, Argentina: biostratigraphy and palaeoenvironments

GUERSTEIN, G.RAQUEL; GULER, M. VERONICA; FENSOME, R; WILLIAMS, G.; CHIESA, J.O.

JOURNAL OF MICROPALEONTOLOGY

GEOLOGICAL SOC PUBL HOUSE

Lugar: Londres; Año: 2008 vol. 27 p. 75 - 94

0262-821X

Palynological data from four surface sections in northern Tierra del Fuego, southernArgentina, provide a biostratigraphical and palaeoenvironmental framework for the lower member of theLa Despedida Formation and the Cabo Peña Formation in their type areas. Selected dinoflagellate cyst(dinocyst) events indicate that the age of the lower member of the La Despedida Formation is MiddleEocene and that of the Cabo Peña Formation is Late Eocene?earliest Oligocene. The age assigned to theLa Despedida Formation agrees with determinations based on calcareous microfossils, but there is apotential discrepancy regarding the Cabo Peña. According to recent stratigraphic studies, the CaboDomingo Group, which includes the Cabo Peña Formation, is late Eocene?Miocene in age. Thepalynomorph assemblages from the lower member of the La Despedida Formation contain the endemic?Transantarctic Flora?, which reflects marginal marine conditions. The maximum abundance of Enneadocystaspp. reflects more open-sea conditions and a warming event during the late Middle Eocene. Thelower part of the Cabo Peña Formation has a high ratio of dinocysts to sporomorphs and an abundanceof Nematosphaeropsis lemniscata, Reticulatosphaera actinocoronata and Impagidinium spp., suggesting anoceanic to outer neritic environment. Abundant Gelatia inflata and protoperidiniacean cysts indicate coolsurface waters rich in dissolved nutrients. These cold-water markers may reflect the development of theAntarctic Circumpolar Current, an important event in the transition from a greenhouse to an icehouseclimate mode. Toward the top of the sections, the lower ratios of dinocysts to sporomorphs, as well as thecomposition of the dinocyst assemblages, reflect a neritic rather than an oceanic setting. This palynologicalchange may be due to eustatic sea-level lowering caused by cooling during the latest Eocene?earliestOligocene. A new species, Spiniferites scalenus, is described and the new combination Lingulodiniumechinatum proposed; an emendation for the latter species is also proposed