Reconstrucción de paleocomunidades arbóreas mediante análisis fitolíticos en sedimentos del paleoceno superior-eoceno? (Formación Las Flores), Chubut, Argentina

Abstract

En la cuenca del Golfo San Jo rge (Chubut, Patagonia central, Argentina) durante el Paleoceno superior-Eoceno, se desarrolla un importante ciclo fluvial cuyos sedimentos han sido denominados como Grupo Río Chico (conformado por tres formaciones: Peñas Coloradas, Las Flores y Koluél Kaike). Las muestras provienen de la Gran Barranca del lago Colhué Huapi (45° 43’ 26’’ LS y 68° 37’ 14’’ LO), cercano a la localidad de Sarmiento, provincia del Chubut. Se reconocieron dos zonas fitolíticas en sedimentos del Paleoceno superiorEoceno? con asociaciones fitolíticas caracterizadas por la abundancia de fitolitos de angiospermas y palmeras, asociados a fitolitos de Poaceae, Cyperaceae y Podostemaceae. También han sido encontradas en esta asociación espículas de esponjas, quistes de Chrysostomataceae y diatomeas. Se reconocieron nueve familias y un Orden: Arecaceae, Chrysobalanaceae, Mimosaceae, Magnoliaceae, Annonaceae, Burseraceae, Zingiberales, Poaceae, Cyperaceae y Podostemaceae. La paleovegetación habría conformado bosques tropicales a subtropicales húmedos, uno dominado por angiospermas leñosas y el otro por palmeras. Estos bosques se habrían desarrollado bajo condiciones climáticas cálidas y húmedas. La existencia de estas condiciones climáticas para el Paleoceno superior-Eoceno está avalada también por los registros paleoxilológicos y las características sedimentológicas de estos depósitos.

In the Golfo San Jorge basin (Chubut, central Patagonia, Argentina), during the Upper Paleocene-Eocene, an important fluvial cycle is developed whose sediments have been called the Rio Chico Group. This Group is conformed by three formations: Peñas Coloradas, Las Flores and Koluél Kaike. The studied sedimentary samples come from the Gran Barranca profile, in the Gran Barranca locality from the Lake Colhué Huapi (45° 43’ 26’’ S and 68° 37’ 14’’ W), Sarmiento, Chubut province. Two phytolith zones were recovered from Upper Paleocene-Eocene sediments, with phytolith assemblages characterized by the abundance of dicotyledons phytoliths and palm phytoliths, associated with Poaceae, Cyperaceae and Podostemaceae phytoliths. Siliceous sponge spicules, Chrysostomataceae stomatocycts and diatoms have been found also in these assemblages. Nine Families and one Order were recognized: Arecaceae, Chrysobalanaceae, Mimosaceae, Magnoliaceae, Annonaceae, Burseraceae, Zingiberales, Poaceae, Cyperaceae y Podostemaceae. The palaeovegetations would have conformed humid tropical and subtropical forests, one dominate by woody dicotyledoneous and the other by palms. These forests were developed under warm and humid climatic conditions. The paleoxylologic records as well as the climatic inferences obtained through the sedimentological characteristics of these deposits support the existence of these climatic conditions for the Upper Paleocene-Eocene? in this region.from the Lake Colhué Huapi (45° 43’ 26’’ S and 68° 37’ 14’’ W), Sarmiento, Chubut province. Two phytolith zones were recovered from Upper Paleocene-Eocene? sediments, with phytolith assemblages characterized by the abundance of dicotyledons phytoliths and palm phytoliths, associated with Poaceae, Cyperaceae and Podostemaceae phytoliths. Siliceous sponge spicules, Chrysostomataceae stomatocycts and diatoms have been found also in these assemblages. Nine Families and one Order were recognized: Arecaceae, Chrysobalanaceae, Mimosaceae, Magnoliaceae, Annonaceae, Burseraceae, Zingiberales, Poaceae, Cyperaceae y Podostemaceae. The palaeovegetations would have conformed humid tropical and subtropical forests, one dominate by woody dicotyledoneous and the other by palms. These forests were developed under warm and humid climatic conditions. The paleoxylologic records as well as the climatic inferences obtained through the sedimentological characteristics of these deposits support the existence of these climatic conditions for the Upper Paleocene-Eocene? in this region.