Estudio bioestratigráfico y paleoambiental de la Formación Río Turbio (Eoceno Medio a Superior) en el sudoeste de Patagonia (Argentina) basado en quistes de dinoflagelados

Abstract

BIOSTRATIGRAPHIC AND PALEOENVIRONMENTAL STUDY OF RÍO TURBIO FORMATION (MIDDLE-UPPER EOCENE) IN SOUTHWEST OF PATAGONIA (ARGENTINA) BASED ON DINOFLAGELLATE CYSTS. During the middle and late Eocene the Austral Basin, in southern Patagonia (Argentina), was fl ooded by an AtlanticOcean transgression, which was responsible for the deposition of the upper member of the Río Turbio Formation. We have analyzed the dinofl agellate cyst assemblages from this stratigraphic section in order to provide a biostratigraphic framework and reconstruct the paleogeographic and paleoceanographic conditions in this area. Dinofl agellate cyst events recorded were compared and interpreted based taking into account other records recognized for the South Pacifi c Ocean. The comparison allowed us to suggest an age between 45.5 Ma (mid-Lutetian) and 33.5 Ma (Priabonian) for the upper member of the Rio Turbio Formation. We recognized three zones of dinofl agellate cysts. Zone I presents an alternating dominance between Enneadocysta dictyostila, Defl andrea antarctica and Vozzhennikovia apertura indicating two sea level rises. Zone II is dominated by V. apertura suggesting high trophic levels and cool waters in a shallow-marine coastal environment. The lower part of the Zone III shows a high abundance of Turbiosphaera fi losa with different morphotypes, which may correspond to physicochemical changes in the water column. The uppermost part of the Zone III is characterized by Protoperidinaceae and typical forms of T. fi losa suggesting an oceanic environment infl uenced by upwelling processes. Zones I and II are defi ned by the dominance of middle Eocene endemic-Antarctic assemblage, while Zone III shows a signifi cant replacement of these taxa by cosmopolitan species. This turnover seems to be forced by the deepening of the Southern Atlantic Ocean gateways and the changes in the ocean circulation patterns.

Correlation of Middle to Upper Eocene Units from High Latitude Southwestern Atlantic Sites

“…Although both AD and AV-S groups comprise Antarctic peridiniacean taxa, we keep them separated into two groups because of their different paleoecological requirements. While Deflandrea antarctica (AD group) proliferate in inner neritic environment associated with high trophic levels (Röhl et al , 2004; Sluijs et al , 2005, 2009), influenced by freshwater discharge that increased nutrient inputs (González Estebenet et al , 2014, 2015), monospecific assemblages of Vozzhennikovia (AVS group) are characteristic of inner neritic environment subjected to freshwater discharges that generate environmental stress (Sluijs et al , 2005, 2009; González Estebenet et al , 2014, 2015). The Turbiosphaera complex group encompasses T. sagena , T. sarrisii and interspecific morphological types that differ in overall shape, structure and degree of development of process unions (Archangelsky, 1968; González Estebenet et al , 2015).…”

Dinoflagellate cyst zonation for the middle to upper Eocene in the Austral Basin, southwestern Atlantic Ocean: implications for regional and global correlation

“…The bars at the right show the percentages of dinoflagellate cysts over total of palynomorphs. Modified from González Estebenet, Guerstein & Alperin (2014), Guerstein et al (2014 a ) and González Estebenet et al (2015). …”

“…The first studies on dinoflagellate cysts of the Río Turbio Formation were carried out by Archangelsky (1968, 1969) and Archangesky & Fasola (1971) in samples recovered from Yacimientos Carboníferos Fiscales (YCF) Cores. Recently, Guerstein et al (2014 a ), González Estebenet, Guerstein & Rodríguez Raising (2014) and González Estebenet, Guerstein & Casadío (2015) studied the dinoflagellate cyst assemblages from sections cropping out near the type area of the Río Turbio Formation.…”

“…The stratigraphic framework for the composed Cancha Carrera section is based on Rodríguez Raising (2010), and the dinoflagelate cysts assemblages were studied by González Estebenet, Guerstein & Casadío (2015).…”

“…In Zone RTF 4, the endemic middle Eocene dinoflagellate cyst taxa are largely replaced by cosmopolitan species. There are species of Turbiosphaera filosa characterized by well-developed processes, suggesting normal marine conditions (González Estebenet, Guerstein & Casadío, 2015; Table 3). This zone also shows higher proportions of protoperidiniaceans associated with nutrient-rich surface waters (Pross & Brinkhuis, 2005; Zonneveld, Susek & Fischer, 2010; Zonneveld et al 2013), and the number of endemic peridinoids is considerably reduced.…”