Daniel G. Ganuza

Estratigrafía, facies y paleoflora de la sucesión triásica de Potrerillos, Mendoza, República Argentina

Nuevas exposiciones en localidades triasicas clasicas como las de los cerros Bayo y Cocodrilo (Potrerillos, noroeste de la Provincia de Mendoza, Argentina) permitieron (1) describir y caracterizar las formaciones Rio Mendoza, Cerro de Las Cabras, Potrerillos y Cacheuta; y (2) mejorar el conocimiento bioestratigrafico de las sucesiones triasicas basandose en el hallazgo de nuevos registros de plantas fosiles. Dos secciones verticales fueron estudiadas en detalle, y el analisis de las litofacies ha sido usado para interpretar los sistemas de deposicion. Facies gruesas de abanico aluvial caracterizan a la Formacion Rio Mendoza y a la seccion inferior de la Formacion Potrerillos. Sistemas fluviales traccionales gravosos y arenosos aparecen hacia el techo de la Formacion Rio Mendoza y en distintos intervalos de la Formacion Potrerillos. En el tramo basal de la Formacion Cerro de Las Cabras y en la mayor parte de la Formacion Potrerillos se identificaron depositos de sistemas fluviales de alta sinuosidad y de planicies de inundacion. Finalmente, algunos intervalos de la Formacion Potrerillos y mas especificamente la Formacion Cacheuta estan dominados por sucesiones de lutitas negras generadas por procesos suspensivos en lagos meromicticos. En asociacion con los depositos mencionados, secuencias progradacionales discretas de areniscas y conglomerados sugieren el desarrollo de barras de desembocadura hipopicnales y de canales distributarios. Se individualizaron 16 niveles fosiliferos con 23 taxones: Equisetites fertilis, Neocalamites carrerei, Cladophlebis mesozoica, C. mendozaensis, Dicroidium argenteum, D. dubium, D. odontopteroides, Johnstonia coriacea, J. stelzneriana, Xylopteris elongata, Zuberia feistmanteli, Feruglioa samaroides, Pachydermophyllum praecordillerae, Kurtziana cacheutensis, Sphenobaiera argentinae, Baiera africana, B. cuyana, Yabeiella mareyesiaca, Y. spathulata, Y. brackebuschiana, Fraxinopsis andium y Gontriglossa sp. y Rochipteris sp. Se describieron 16 tafocenosis que se relacionaron con los respectivos ambientes de sedimentacion. El analisis de las tafocenosis y su vinculacion con las facies y paleoambientes de acumulacion permitio reconocer en la localidad tipo de la Formacion Potrerillos a dos biozonas de asociacion en continuidad estratigrafica (Yabeiella mereyesiaca-Scytophyllum bonettiae-Protophyllocladoxylon cortaderitaensis -MBC- y Yabeiella brackebuschiana-Scytophyllum neuburgianum-Rhexoxylon piatnitzkyi -BNP-). La Formacion Potrerillos en este sector de la cuenca se desarrollo durante el Triasico Medio tardio-Triasico Tardio temprano

A new peltasperm (Gymnospermopsida) from the Middle Triassic of Argentina

A new peltasperm, Scytophyllum bonettiae sp. nov., is described from the Middle Triassic Cortaderita Formation, San Juan, Argentina. The new species is characterised by having medium to small monopinnate, imparipinnate, lanceolate, bicoherent fronds with a free bipinnate pattern of venation, and lumps on the rachis. Recovered specimens display juvenile to adult foliage. The new taxon, together with other species, characteises late Middle Triassic-early Upper Triassic terrestrial flora from western Argentina.

Primitive Vascular Plants and Microfossils from the Río Seco de los Castaños Formation, San Rafael Block, Mendoza Province, Argentina

In this contribution we describe fossil plant remains from Rio Seco de los Castanos Formation, at San Rafael Block , Mendoza Province, Argentina. The fossil plants comprise non-forked and forked axes without or with delicate lateral expansions, which are assigned to Bowerophylloides cf. mendozaensis and Hostinella sp. We refer them to primitive land plants and discuss about their systematic affiliation. Furthermore, we mention the presence of a diverse acritarch assemblage present in the same lithostratigraphic unit. On the basis of the taxonomical information and stratigraphic correlation, we could infer that Rio Seco de los Castanos Formation has an Early Devonian age. The taphonomical conditions of this fossil association would indicate that the plants were transported some distance from their presumed coastal and riverbank habitats. Finally, studying the amount and the percentage of kaolinite within charcoal levels, warm to cool temperate paleoclimatic conditions were deduced.

Revisión De La Paleoflora De La Formación Nestares (Jurásico Temprano), Provincias Del Neuquén y Río Negro, Argentina

Abstract. REVIEW OF THE PALEOFLORA OF THE NESTARES FORMATION (EARLY JURASSIC), NEUQUÉN AND RÍO NEGRO PROVINCES, ARGENTINA. In this contribution the paleoflora of the Nestares Formation, exposed along both banks of the Limay River, close to the Alicurá dam (northwest of the Northpatagonian Massif) was reviewed. A sedimentological profile was measured, four fossil-bearing levels were identified and the systematic study allowed the identification of 18 taxa, 12 of which were previously described for this site= Neocalamites carrerei (Zeiller) Halle, Marattia muensteri (Goeppert) Zeiller, Goeppertella diazii Arrondo and Petriella, Kurtziana brandmayri Frenguelli, K. cacheutensis (Kurtz) Frenguelli, Taeniopteris sp., Otozamites albosaxatilis Herbst, O. ameghinoi Kurtz, O. bechei Brongniart, O. hislopii (Oldham) Feistmantel, Ptilophyllum acutifolium Morris in Grant, Elatocladus confertus (Oldham and Morris) Halle and six that are new for this formation= Equisetites frenguellii Orlando, Archangelskya protoloxsoma (Kurtz) Herbst, Sagenopteris nilssoniana (Brongniart) Ward, Nilssonia taeniopteroides Halle, O. bengalensis Oldham and Morris, and Elatocladus planus (Feistmantel) Seward. These records are added to 6 other previously studied taxa, including Cladophlebis mendozaensis (Geinitz) Frenguelli, C. oblonga Halle, Gleichenites cf. sanmartini Halle emend. Herbst, Scleropteris vincei Herbst, Araucarites phillipsi Carruthers, Podozamites elongatus (Oldham and Morris) Halle, providing an updated list of 24 taxa for this unit. The compositional similarity with other Early Jurassic paleofloras from Argentina indicates a Sinemurian age.