PALEOBOTANICAL RECORD FROM THE DESCANSO-YAURI BASIN, PERU: INSIGHTS INTO THE NEOGENE ELEVATION HISTORY OF THE CENTRAL ANDEAN PLATEAU

With an average elevation of 4000 m and up to 500 km wide, the Central Andes exerts a large influence in the climate and biogeography of tropical South America. What role played the orogen in the climate and life evolution of the modern Neotropics? Here we study the paleoflora of the Descanso-Yauri Basin, an intermontane basin located in the northern part of the Central Andean Plateau. The basin has an extensive Neogene sedimentary record of the Central Andes. Fossil wood, leaves and pollen from Miocene and Pliocene localities from this basin were morphologically and anatomically described. We used stratigraphic field observations and U/Pb radiometric dating in zircons to assess their age and stratigraphic position.

Ten permineralized wood specimens were found in the late Miocene localities, together with one palm leaf morphotype, and abundant Podocarpaceae pollen. Wood anatomical characters suggest a tropical lowland canopy tree assemblage. Three wood specimens belong to the legume family (Fabaceae). Tree-height estimations for one of legume specimens suggest more than 35 m.

Abundant leaf material in the Pliocene localities was studied including Equisetum, Polystichum, Berberis, Polylepis, Ribes and tentatively Baccharis, The palynological record was mostly dominated by grasses and herbs.

The paleobotanical record suggests that by the late Miocene the Descanso-Yauri basin was dominated by a low to mid elevation tropical forest, and the basin elevation could not be higher than 2500 m. In contrast the paleobotanical record of the early Pliocene (~5 Ma) suggest highland conditions with a vegetation similar to today’s ecosystem. Our results supports the hypothesis of a rapid regional surface uplift of the northern Central Andean Plateau between ca. 10 and 6 Ma.