Scalaroxylon menendezi sp. nov., leño homoxílico de la Formación Montaña (Triásico), provincia de Mendoza, Argentina

Abstract

The detailed stratigraphic measurements of the siliciclastic deposits belonging to the Montaña Formation (Triassic) have been raised at Santa Clara area (Mendoza Province, Argentina). During sedimentological logging, five fossiliferous levels were recognized. Based on the sedimentological log, the main facies attributes and succession were characterized; the depositional system was also inferred and assigned to a mixed load stream fluvial system. Three fossiliferous levels have been recognized in the upper section of Montaña Formation, one of them with well preserved fossil woods. The wood specimens were assigned to Scalaroxylon menendezii sp. nov. The new species, characterized by homoxylic and manoxylic secondary xylem and the lack of distinct growth rings, possesses radial tracheid walls with scalariform pits arranged in a single longitudinal row and cross-fields with several simple or bordered (1-6), rounded to flattened araucarioid pits. The morphotaxon has homocellular and heterogeneous rays, which are short uniseriate or biseriate to very long multiseriate (triseriate to incompletely pentaseriate). The identification of Scalaroxylon menendezii sp. nov. in Argentina has a remarkable biogeographic significance as it is the first occurrence of the morphogenus in Gondwana. The Argentinean record also allows us to confirm the exclusively Triassic age of Scalaroxylon. The palaeoenvironment is interpreted as a mixed-load stream fluvial system with well drained flood plains covered in vegetation.