An Early Miocene coastal lagoon plant community from central Patagonia

PANTI, C.; CUITIÑO, J.J.; TAPIA, M.J.; NOETINGER, S.; PUJANA, R.R.; PALAZZESI, L.; BARREDA, V.D.

Simposio; VII Simposio del Mio?Pleistoceno del Centro Norte de Argentina; 2023

The lower Gaiman Fm. (20.5 Ma) cropping out at Isla Escondida (northeast Chubut)represents a land-sea transition depositional setting. Here, we present the plant fossilremains with preserved cuticles and palynomorphs (fungi, spores and pollen grains)recovered from these sediments. The megafossil assemblage includes several ribbon-likelong parallel-veined leaves, with more or less perpendicular connection between the veinsand sheathing base. They were assigned to the Alismatales, tentatively to the familyHydrocharitaceae due to the presence of paracytic stomata. It includes seagrasses withhydrophilous pollination that may have grown in confined or low-energy coastal lagoons.Among palynomorphs, we found several Gondwanan lineages including Nothofagaceae,Podocarpaceae, Araucariaceae, and ferns of the Lophosoriaceae. We also recoveredspecimens assigned to palms (Arecipites otagoensis (Couper) Mildenhall & Pocknall 1989),cesalpinoid (Margocolporites vanwijhei Germeraad et al. 1968), and mimosoid legumes(Margocolporites tenuireticulatus Barreda 1997), and Rubiaceae Gardenia (Canthiumiditesbellus (Stover & Partridge) Mildenhall & Pocknall 1989). The typical coastal elementscommonly found in salt-marshes are also detected such as Amaranthaceae(Chenopodipollis chenopodiaceoides (Martin) Truswell et al. 1985), Poaceae (Graminiditessp.), Asteraceae Nassauvieae (Huanilipollis cabrerae Barreda & Palazzesi 2008), andConvolvulaceae Cressa (Tricolpites trioblatus Mildenhall & Pocknall 1989). The overallassemblage indicates a rich marginal-marine community developed under a frost-freeclimate, in agreement with previous sedimentological and paleontological studies thatinclude mollusca, bryozoa and diatoms.