Sedimentología y paleoecología del Terciario Inferior en el sur de la Provincia del Chubut, República Argentina

this contribution investigates sedimentological and paleobotanical aspects of szlápelis and ormachea localities (chubut province). a lot of big petrified trunks have been found associated with conglomeradic levels of the salamanca formation (danian). the two fossiliferous localities are located to the southward of the musters and colhué huapi lakes between 69° 04′ - 69° 18′ w and 45° 48′ - 45° 57′ s, at se of sierra de san bernardo (fig. 1). the methodology has consisted of an integrated-detailed profile (scale 1: 100), sampling of sedimentites and measures of diameter, orientation, fragmentation, authoctony grade and quality of preservation of fossil woods. these data were used to estimate diameter, circumference, basal area, cover, estimated biomass and height, in order to reconstruct paleocommunities and paleoecosystems. the sedimentary sequence begins with reddish-brown to greyish pyroclastic sedimentites of the chubut group and passed unconformably overlain by the salamanca formation (lesta y ferello, 1972), in turn followed by the río chico formation of upper paleocene age (feruglio, 1929). sedimentation is represented by shales, tobaceous shales and yellowish to greenish fine to sabulitic sandstone with conglomeradic beds at their upper yielding silicified wood logs. cross-bedded tabular to simple tangential stratification are well developed. all the sedimentation is disposed subhorizontally, massively in structures, with intercalation of sandy massive strata normally graduated. the paleoflora described in this unit includes palynomorphs, fossil wood and leaf impression and compressions of leaves. the wood flora found in szlápelis and ormachea localities is composed of a large number of petrified trunks of parautocthonous gymnosperms and angiosperms, with a preferential orientation between 45°- 55° sw; only few of them have less than 50 cm in diameter and someone represents stumps. generally they are compressed and hollow at the core part; occasionally they s