Palynology of a Danian warm climatic wetland in Central Northern Patagonia, Argentina

VOLKHEIMER, W., SCAFATI, L., MELENDI, D.L.

REVISTA ESPANOLA DE MICROPALEONTOLOGIA

Instituto Geológico y Minero de España

Lugar: Madrid; Año: 2007 vol. 39 p. 117 - 134

0556-655X

The study area is located north of the Chubut River, near Las Plumas locality (Chubut province, Argentina). The Danian age of the microfossiliferous Cerro Bororó Formation here studied was established  elsewhere. The objective of this contribution is to explain the paleoenvironmental and paleoclimatic significance of the palynologic assemblage of extremely high specific diversity found in a single bed of 15 cm thickness, of an organic rich carbonaceous mudstone. The characteristics of the diversity of this microbiota of excellent preservation and specially the investigation of the scarcely studied group of aquatic species, which have been unknown up to the moment for this Formation, made necessary an intensive and exhaustive use of scanning electron microscopy, in order to achieve an exact taxonomic analysis of the material, composed of 36 form-species of angiosperm pollen, 10 species of gymnosperms (bi- and trisaccate pollen), four forms of Botryococcus, massulae of Azollopsis spp., four species of zygnematacean algae, prasinophyceans and unfrequent dinoflagellates. -The sampling point was a freshwater paleoenvironment (swamp) with abundant hydrophile forms (Chlorococcales, Salviniaceae, Sphagnaceae) and Zygnematacea, surrounded by  a hygrophile community of Filicales, Bryophyta,  Lycopodiaceae and Selaginellaceae, separated from the sea  by brackish swamps with a subtropical community of prevailing Arecaceae (palms): Proxapertites, Longapertites, Spinizonocolpites. The presence of monospecific agglomerates of pollen grains indicates, together with the state of preservation of the palynomorphs, a strong predominance of local (parautochthonous) material.- Proteacean pollen (11 species) is a mayor element of the palynoflora. Proteaceans may have been the most conspicuous floral elements of the subhumid  to semiarid lowlands located between the near-coast wetlands and the Podocarpacean forests of the hinterland. Gymnospermous pollen (10.5% of the total spectrum) is represented mainly  by podocarpacean pollen, reflecting the existence of a nearby “Conifer-Forest” . The megafloral register of a similar Conifer Forest from this Formation is known from earlier studies published elsewhere.