Silvia N. Césari

Palynostratigraphy of upper Paleozoic sequences in central‐western Argentina

Lower Carboniferous to Permian palynological zones are described from sections in central–western Argentina. In ascending stratigraphic order these zones are: (1) the Cordylosporites– Verrucosisporites (CV) Assemblage Biozone (spanning the Maliman and Cortaderas formations); (2) the Raistrickia densa– Convolutispora muriornata (DM) Assemblage Biozone (which is subdivided into: Sub-biozone A in the Guandacol and equivalent formations, Sub-biozone B in the Tupe Formation and equivalents, and Sub-biozone C in the upper part of the Santa Maxima and El Imperial formations); (3) the Fusacolpites fusus–Vittatina subsaccata (FS) Interval Biozone in the Bajo de Veliz and Tasa Cuna formations and equivalents, and (4) the Lueckisporites– Weylandites (LW) Assemblage Biozone in the De La Cuesta and Yacimiento Los Reyunos formations. The oldest biozone (CV) is assigned to the Early Carboniferous and the overlying DM Biozone to the Late Carboniferous. The uppermost FS and LW biozones are Permian in age. Palynological records show the impact of the Early-to-Late Carboniferous glacial event, which caused significant changes in the composition of the assemblages from this interval. Further studies are necessary to calibrate a regional geological time scale in Gondwana, which is essential for precise correlation.

Paleoclimatic significance of the lacustrine Carboniferous deposits in Northwest Argentina

Abstract The origin and probable paleoclimatic significance of Carboniferous lacustrine deposits in northwest Argentina are discussed. These rocks are developed extensively throughout northwestern Argentina, but are described in the present paper only from the region of the Sistema del Famatina. Five lithofacies have been identified: (A) laminated siltstones and claystones; (B) thinly interbedded mudstones and sandstones; (C) interlayered mudstones and sandstones with sole structures (flute marks and tool marks); (D) conglomerates and fine sandstones; (E) sandstones and diamictites. These lithofacies are interpreted as lacustrine deposits formed during the final episode of the Carboniferous glaciation. Lithofacies A originated as a suspension-load deposit in the central and intermediate parts of the lake; the presence of dropstones in this lithofacies suggests coeval ice-rafting processes. Underflow currents probably formed lithofacies B, and lacustrine turbidites lithofacies C. Lithofacies D and E were deposited in marginal environments and represent in some cases shoreline bars and small deltas. The age of the lacustrine episode is deduced from paleobotanical information. Both palynological and megafloristic data suggest that these deposits were formed during the middle Carboniferous. A palynological assemblage dominated by Cristatisporites-like spores characterizes these sediments.

An Early Carboniferous flora from Argentina. Biostratigraphic implications

Abstract A Lower Carboniferous flora from the Del Raton Formation, exposed near Calingasta, San Juan province of Argentina, is described and illustrated and its biostratigraphic significance is evaluated. The megafossils include Lepidodendropsis eximius (Frenguelli) Sessarego et Cesari, Archaeosigillaria conferta (Frenguelli) Menendez, Diplothmema bodenbenderi (Kurtz) Cesari, Eusphenopteris devonica (Frenguelli) nov. comb., “ Hyenia” argentina , “ Rhodea ” sp. and Telangiopsis sp. The associated microflora, described for the first time, includes Verrucosisporites congestus Playford, Anapiculatisporites amplus Playford et Powis, Dictyotriletes submarginatus Playford, cf. Densosporites spinosus Dybova et Jachowicz, Retusotriletes avonensis Playford, Dibolisporites cf. D. distinctus (Clayton) Playford and Grandispora debilis Playford. The megafossil species are referable to the Archaeosigillaria Lepidodendropsis biozone, which combines the Archaeosigillaria Zone and Lepidodendropsis Flora of Archangelsky and Azcuy (1985) and Archangelsky et al. (1986). The plant megafossils and associated microflora suggest a Visean age for this biozone. The presence of an associated marine fauna in the stratigraphically equivalent Maliman Formation, having Protocanites scalabrinii Antelo, corroborates a Lower Carboniferous age for our biozone. By comparison with others in the world this is the oldest Carboniferous taphoflora in Argentina and probably in the whole of South America. The evolutionary significance of the Lepidodendrossis flora is analysed.

Fossil woods (Coniferales) from the Baqueró Group (Aptian), Santa Cruz Province, Argentina

Two new conifer morphospecies represented by a secondary xylem are reported for the Lower Cretaceous Baqueró Group (Santa Cruz Province, Argentina). Agathoxylon sp. is characterized by poorly defined growth rings, predominantly uniseriate pitting in the radial wall of the tracheids, cross fields with 1-6 pits and uniseriate rays. These features are shared with the leafy branches described for the unit as Araucaria grandifolia Feruglio emend. Del Fueyo and Archangelsky. The second taxon, Brachyoxylon sp. cf. B. boureaui, possesses poorly defined growth rings, mixed wood with predominantly uniseriate radial pitting, cross fields with 8-26 pits and uniseriate rays. These taxa represent the first fossil woods described for Baqueroan strata.

An anatomically preserved stem from the Carboniferous of Gondwana: Phyllocladopitys petriellae Brea and Césari, sp. nov.

Phyllocladopitys petriellae Brea and Cesari, sp. nov. occurs in the early Late Carboniferous Jejenes Formation, Argentina. The description of the taxon is based on one anatomically preserved stem, a few centimeters in diameter. The primary xylem is mesarch. The secondary xylem shows only inconspicuous growth rings. Pitting on the walls of the tracheids is bordered. Rays are low, uni- or biseriate. Two to four simple pits are present in the cross fields. Comparisons are made with early gymnosperms and Cordaitales and palecolimatic evidence is analyzed.

Anatomy of a new probable pteridosperm stem from the Late Carboniferous of Argentina

A new genus and species, Amosioxylon australis, based on an anatomically preserved stem from the Late Carboniferous Jejenes Formation, Argentina, is described. The specimen is six cm in diameter and has some features usually found in pteridosperms, including the presence of several vascular segments surrounded by secondary xylem. The pycnoxylic wood resembles progymnosperms and the tissue between the vascular strands, with reticulate thickenings and pits, is similar to the transfusion tissue found in extant conifers and cycads. According to the available evidences a relationship with primitive pteridosperms is suggested.

La Biozona Pakhapites fusus-Vittatina subsaccata en la Formación Patquía (Pérmico), Precordillera de La Rioja, Argentina

Fil: Cesari, Silvia Nelida. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina

BUMBUDENDRON VERSIFORME. A NEW LYCOPHYTE SPECIES FROM THE LATE PALEOZOIC OF ARGENTINA

Abstract Bumbudendron versiforme sp. nov. is described on the basis of imprints from the Agua Colorada Formation, Sierra de Famatina, Argentina. It is characterized by fusiform leaf cushions with a variable length-width ratio in a single stem. Megaspores are found associated with the lycopod remains. Comparisons with other species having infrafoliar bladders are made. The associated microflora suggests a Late Carboniferous age for this lycophyte species.

PALINOFLORAS CISURALIANAS EN EL SUBSUELO DEL NORESTE DE LA PROVINCIA DE LA PAMPA

Muestras de testigos de la perforacion Arata-1 en la provincia de La Pampa (Argentina) han brindado resultados palinologicos. La seccion de la perforacion palinologicamente productiva corresponde a la Formacion Arata y es asignable a la Biozona Pakhapites fusus/Vittatina subsaccata , indicando asi una edad cisuraliana (Permico temprano) para la seccion y permitiendo su correlacion con palinofloras de las cuencas Paganzo y Claromeco. Este primer registro de asociaciones palinologicas neopaleozoicas en la provincia permite tambien su correlacion con la flora de Glossopteris reconocida en la cuenca Carapacha.

Systematic study of Early Carboniferous palynological assemblages from the Llanos Orientales Basin, Colombia∗

This paper concerns the description of palynomorphs recovered from subsurface Early Carboniferous strata of the SM-4 well located in the Llanos Orientales Basin, Colombia. Thirty-two species of spores are recognized within the palynoflora. A new species is proposed: Spelaeotriletes colombianus Duenas and Cesari sp. nov. The assemblages were referred to the Tournaisian-Visean by the presence of distinctive spore species with previous records in the Visean and Tournaisian of Western Europe and Western Gondwana.