A FOSSIL WOOD FROM THE IRATI FORMATION (UPPER PERMIAN), PARANÁ BASIN, SÃO PAULO STATE, BRAZIL

The occurrence of well-preserved silicified wood logs in the Upper Permian of the Paraná Basin, particularly in Irati Formation outcrops of São Paulo State, has allowed for detailed systematic, paleoclimatic, paleogeographic and stratigraphic studies to be carried out. A new fossil is described from the Vitti limestone quarry, an outcrop of the Irati Formation near Rio Claro, São Paulo, at km 7.5 of the Rio Claro-Piracicaba highway. The studied specimen was recovered in situ from a carbonate mudstone layer, near the base of the outcrop section, where it was found together with disarticulated vertebrae of mesossaurs. Several diagnostic features observed in this fossil log permit its attribution to the genus Barakaroxylon, including: presence of a solid medulla with 0.7 cm, a heterocellular medulla, primary endarch xylem, a secondary xylem with distinct growth rings, early wood formed by 100-123 tracheid and late wood narrow formed by 6-15 tracheids, uniseriate bordered pits, uniseriate or partially biseriate medullar rays, with 1- 4 -16 cells high in tangential view, scalariform thickenings in radial walls of tracheids and crossing fields with large an isolated punctuations. Detailed analyses of growth rings of this and of other fossil logs recovered from the Irati Formation suggest a climate of “the Mediterranean” type, characterized by hot and dry summers, and winters with the occurrence of storms and cyclones.