Three-dimensional reconstruction of the Aluminé in situ fossil forest from the Upper Oligocene of Rancahué Formation, Neuquén, Argentina

BREA, M; ARTABE, A.E.; FRANZESE, J.R.; ZUCOL, A.F.; SPALLETTI, L.A.; MOREL, E.M.; VEIGA, G.D.; GANUZA, D.G.

PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 418 p. 19 - 42

0031-0182

This research focuses on the three-dimensional reconstruction of in situ Aluminé forest based on a fossil wood assemblages recovered in the Rancahué Formation (late Oligocene), Neuquén, Argentina. Atherospermataceae, Lauraceae, Nothofagaceae, Eucryphiaceae, Cunoniaceae and Myrtaceae are described. The mapping of a forest floor section and their in situ tree diameters allow obtain palaeoecological quantitative data like: tree density, dominance, basal area, biomass, diametric classes, canopy height, and age classes. Palaeoclimatical data were determined from physiognomic anatomical features using multivariate anatomical analyses. These results are compared with other proxies including Carlquist´s index, Coexistence Approach (CA), Nearest Living Relatives (NLRs), and growth-rings analyses. The structural data of Aluminé forest inferred from these analyses are tree density of 463?701 tree/ha, mean height of 15.22 m, dominance of the genus Nothofagoxylon of 89.66 m2/ha, total basal area of 158.20 m2/ha, biomass between 43 and 712 tn/ha and mean age of 223 years old (31?700 years old). These results are comparable to those of mature low to middle altitude extant forest dominated by Nothofagus, and developed under humid temperate conditions. Based on the NLRs method, the Aluminé forest has a floristic composition similar to the Valdivian forest today. The persistence of Nothofagus as dominant element in the temperate rainforests correlates with regimes where large-scale disturbances, such as volcanism and earthquakes are prevalent. The fossil taxa are closely related to extant Laurelia, Persea, Eucryphia, Nothofagus, Weinmannia, Myrceugenia and Luma. The forest contained intermixed deciduous and evergreen elements, shade-intolerance and intermediate tolerance to shade taxa. Also the majority of these taxa require water availability soil. The integrated analysis of multiple sets of proxy data suggests that the late Oligocene forest grew under a temperate and humid climate, and the eco-anatomical features and sedimentary data provide information about the environmental stress conditions of forest development and the violent causes of their burial.