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A Miocene macroflora recovered from Ñirihuau Formation sediments exposed at Quebrada Vera site in northwesterern Patagonia, Argentina, is recorded and described for the first time. The assemblage is composed exclusively of free-sporing plants, mainly by Equisetum remains with subordinate occurrences of four fern morphotypes (represented by bi-, tri- and pinnate fronds). Equisetum imprints and molds include distinctive jointed stems with whorls of linear and basally fused leaves, numerous scars of lateral branches arranged in a radially symmetrical pattern situated at the nodes, and nodal diaphragms of up to 4 cm in diameter. The large size and regular branching of the stems link the fossils to the South American giant members of the genus and they probably represent a new fossil species. This is the first conclusive fossil record of a giant Equisetum worldwide, and consequently, it is biogeographically and evolutionarily relevant. The new findings attest that members of the giant horsetail clade were components of the Patagonian vegetation in the Miocene, implying that the age of the clade must predate that estimated from morphological and/or molecular data. The plant fossil assemblage represents part of a wetland community probably growing close to a riverside or lakeshore in coincidence with previous sedimentological estimates.

El análisis palinofacial permitió caracterizar las secuencias deposicionales JC4.1 (Toarciense superior alto - Bajociense inferior bajo), JC4.2, JC4.3 y JC4.4 (Bajociense inferior medio), JC4.5 (Bajociense inferior medio - Bajociense inferior alto) y JC5 (Bajociense inferior alto - Bajociense superior alto), reconocidas por Zavala (1993) para las formaciones Los Molles y Lajas, en el perfil Lohan Mahuida del sector suroccidental de la Cuenca Neuquina, Argentina. En cada secuencia se reconocieron cortejos sedimentarios de alto nivel (HST), transgresivos (TST) y de bajo nivel (LST). La palinoflora estudiada corresponde a la Zona de Callialasporites dampieri (Toarciense tardfo - Oxfordiense), Subzona de Callialasporites turbatus (Toarciense tardío - Bajociense temprano) y Subzona de lschyosporites marburgensis (Bajociense temprano alto - Bajociense tardío), definidas por Quattrocchio et al. (1996a). Los HST se caracterizan por presentar elevados porcentajes de Cheirolepidiaceae, Araucariaceae y esporas. El paleomicroplancton marino muestra la mayor diversidad. Los fitoclastos predominan sabre la materia orgánica amorfa. En los TST !as Cheirolepidiaceae estan asociadas con granos de polen sacado de Podocarpaceae y Caytoniaceae. Las frecuencias relativas del paleomicroplancton marino son menores que en los HST. La materia orgánica amorfa se presenta en elevadas proporciones. Los LST se caracterizan por presentar Cheirolepidiaceae, Araucariaceae y esporas; altos valores de diversidad y frecuencias relativas de acritarcos y dominancia de fitoclastos translucidos.