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

2007; Volume: 39; Issue: 1 Linguagem: Espanhol

0556-655X

Wolkheimer Volkheimer, Laura Scafati,

Geology and Paleoclimatology Research

espanolEn Chubut extraandina, Patagonia, Argentina, aflora la Formacion Cerro Bororo, cuya edad daniana esta controlada por estudios micropaleontologicos previos. El objetivo de este estudio es demostrar el significado paleoambiental y paleoclimatico de una asociacion palinologica muy diversa, excelentemente preservada, hallada en una fangolita carbonosa de la parte inferior de esta Formacion. Se realizo un estudio intensivo y exhaustivo del material al microscopio electronico de barrido, con especial consideracion de las especies acuaticas hasta ahora no ilustradas para esta Formacion. Se distinguieron 36 morfoespecies de polen de angiospermas, 12 de gimnospermas, 4 formas de Botryococcus, masulas de Azollopsis, 4 especies de zygnemataceas, prasinoficeas y escasos dinoflagelados. El lugar de muestreo fue un pantano dulceacuicola daniano con palinomorfos correspondientes a una paleocomunidad hidrofila (Botryococcaceae, Zygnemataceae, Salviniaceae, Sphagnaceae), rodeada por una comunidad higrofila ecotonal, reflejada por esporas de Filicales (22 especies), Lycopodiaceae, Selaginellaceae y Hepaticae. Entre estos humedales y el mar abierto se intercalaron pantanos salobres con una paleocomunidad de palmeras (indicada por la gran frecuencia del grupo de Proxapertites, Longapertites y Spinizonocolpites). El polen de Proteaceae (11 especies) es un elemento mayoritario en la palinoflora. La flora de proteaceas puede haber constituido los elementos mas conspicuos de los llanos subhumedos a semiaridos ubicados entre los humedales cercanos a la costa y los bosques de podocarpaceas de las areas mas elevadas y mas humedas tierra adentro. La presencia de aglomerados monoespecificos de granos de polen, junto con el excelente estado de preservacion de los palinomorfos, indican el gran predominio del material local (parautoctono). EnglishThe study area is located north of the Chubut River, near Las Plumas locality (Chubut province, Argentina). The Danian age of the microfossiliferous Cerro Bororo 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.