FOSSIL WOOD FROM THE SERRA ALTA FORMATION (UPPER PERMIAN), PARANÁ BASIN, SOUTHERN BRAZIL

The Paraná Basin consists of an extensive South American basin filled with sedimentary deposits spanning in age from the Paleozoic to the Cenozoic, and spreading over most of southern Brazil, eastern Paraguay, Argentina and northern Uruguay. The Serra Alta Formation is composed by dark-grey massive siltstones, with rhythmic stratification at the base, and locally interbedded sandstones. The occurrence of silicified wood logs in the Upper Permian of the Paraná Basin, particularly in Serra Alta Formation outcrops of Rio Grande do Sul State, has made it possible to carry out detailed systematic, paleoclimatic, paleogeographic and stratigraphic studies based on well-preserved specimens. Several diagnostic features observed in the fossil log analyzed herein permit its attribution to the genus Barakaroxylon, including: a heterocellular medulla, primary endarch xylem, a secondary xylem with distinct growth rings, uniseriate bordered pits, uniseriate or partially biseriate medullar rays, with 14–15 cells high in tangential view, and crossing fields with large punctuations, isolated or in groups of 2 to 5. Detailed analyses of growth rings in fossil logs recovered from the Serra Alta Formation suggest a climate subject to cyclic variations from rainy tropical to humid temperate. Paleoxylological data recorded for the studied sequence points out to the dominance of morphogenera with canals in the medulla, related to Barakaroxylon and Polysolenoxylon. These morphogenera are reported from the Barakar stage (Damuda Series) of India, and the Whitehill interval of South Africa.