Palaeoenvironmental reconstruction of the Puerto Madryn Formation (Middle to Late Miocene), northeast of Patagonia: palynology, nannofossils and stratigraphy

FUENTES SABRINA; CUITIÑO, J.I.; MARTZ; PÉREZ PANERA, J.P.; GULER, M.V.; PALAZZESI, L; BARREDA, V.D.; SCASSO, R. A.

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2019 vol. 56 p. 28 - 52

0002-7014

Abstract. A 20 m-thick interval of the Puerto Madryn Formation was the subject of a multiproxy study, including sedimentological and stratigraphicalobservations as well as marine-derived amorphous organic matter, phytoclast, palynomorphs and calcareous nannofossilsassessments. Three palynofacies were defined based on qualitative and quantitative analysis of the palynological organic matter that contributedto the palaeoenvironment inferences. Based on their sedimentology, palynology and calcareous nannofossils, the section was dividedinto four intervals: Interval 1 accumulated in relatively stable, warm water conditions, without salinity fluctuations, in an inner shelf; Intervals2 and 3 show a marked upward fining trend and a progressive change towards a phytoclast-dominated palynofacies; Interval 4, which representsa reinstauration of normal marine conditions with a regressive trend. The accumulation of the finest-grained deposits on the shelfcorresponds to the most continental signature of the succession which seems to contradict the classic grain-size stratigraphic trends for shallowmarine sedimentary successions. We interpret this deposit as the result of the progressive increase of fluvial, mud-laden freshwater input intothe depositional system produced by switching of deltaic channels processes. The dinocyst assemblages reflect overall warm-water conditions.Nevertheless, the presence of cool-water indicator species in some levels suggests the influence of Antarctic cold-waters. The diagnosticdinocyst and nannofossil taxa support the age of the studied interval as Serravalian?Tortonian.