Middle Triassic dipterid ferns from west-central Argentina and their relationship to palaeoclimatic changes

Dipterid ferns possess robust fossil record from Mesozoic times on, and they are considered to be a reliable indicator of warm to subtropical humid or seasonal paleoclimatic conditions. In this contribution, we revised and described new samples of fossil Dipteridaceae, from the Barreal and Cortaderita formations (Sorocayense Group), Middle Triassic (Anisian–Ladinian), central-western Argentina. We found out that three species of Dictyophyllum, one of Hausmannia, and one of Thaumatopteris are present in the Sorocayense Group. We erected a new species Dictyophyllum menendezi sp. nov., which is characterized by petiolate fan-shaped fronds, rachis dividing into two arms, each one bearing 5 or 6 oblanceolate pinnae, basal lamina of adjacent pinnae fused forming a wide web, pinnae margin entire to undulate, primary veins catadromous to isodromous, secondary veins subopposite, tertiary veins subopposite to alternate, falcate or with a zig-zag pattern, dichotomizing four times to form a fine reticulate mesh of polygonal irregular areoles. Temporal changes in the diversity of Dipteridaceae were identified in Sorocayense Group. The first record and the maximum species richness occur at the top of the Barreal Formation (late Anisian) with three species. The lower member of the Cortaderita Formation (early Ladinian) presents two species. Dipteridaceae fossils are not registered in the upper member of the Cortaderita Formation (late Ladinian). An important diversification pulse of the family is registered during the late Norian–Rhaetian in other areas of Argentina (Paso Flores, Malargüe, and Atuel depocenters). The flourishing of Dipteridaceae during the late Anisian–early Ladinian and the late Norian–Rhaetian could be related to the increasing humidity episodes of the subtropical seasonal climate that prevailed during the Triassic. Furthermore, Dipteridaceae appear important in the establishment of plant communities, being part of early stages of floristic succession.Facultad de Ciencias Naturales y Muse

Middle Triassic dipterid ferns from west-central Argentina and their relationship to palaeoclimatic changes

Dipterid ferns possess robust fossil record from Mesozoic times on, and they are considered to be a reliable indicator of warm to subtropical humid or seasonal paleoclimatic conditions. In this contribution, we revised and described new samples of fossil Dipteridaceae, from the Barreal and Cortaderita formations (Sorocayense Group), Middle Triassic (Anisian–Ladinian), central-western Argentina. We found out that three species of Dictyophyllum, one of Hausmannia, and one of Thaumatopteris are present in the Sorocayense Group. We erected a new species Dictyophyllum menendezi sp. nov., which is characterized by petiolate fan-shaped fronds, rachis dividing into two arms, each one bearing 5 or 6 oblanceolate pinnae, basal lamina of adjacent pinnae fused forming a wide web, pinnae margin entire to undulate, primary veins catadromous to isodromous, secondary veins subopposite, tertiary veins subopposite to alternate, falcate or with a zig-zag pattern, dichotomizing four times to form a fine reticulate mesh of polygonal irregular areoles. Temporal changes in the diversity of Dipteridaceae were identified in Sorocayense Group. The first record and the maximum species richness occur at the top of the Barreal Formation (late Anisian) with three species. The lower member of the Cortaderita Formation (early Ladinian) presents two species. Dipteridaceae fossils are not registered in the upper member of the Cortaderita Formation (late Ladinian). An important diversification pulse of the family is registered during the late Norian–Rhaetian in other areas of Argentina (Paso Flores, Malargüe, and Atuel depocenters). The flourishing of Dipteridaceae during the late Anisian–early Ladinian and the late Norian–Rhaetian could be related to the increasing humidity episodes of the subtropical seasonal climate that prevailed during the Triassic. Furthermore, Dipteridaceae appear important in the establishment of plant communities, being part of early stages of floristic succession.Facultad de Ciencias Naturales y Muse

Revisión de la paleoflora de la Formación Nestares (Jurásico temprano), provincia del Neuquén y Río Negro, Argentina

Fil: Morel, Eduardo Manuel. División Paleobotánica. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La PlataFil: Ganuza, Daniel Gustavo. División Paleobotánica. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Artabe, Analía Emilia Eva. División Paleobotánica. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La PlataFil: Spalletti, Luis Antonio. Centro de Investigaciones Geológicas (CIG). Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

Voltziales y pinales (= coniferales) de la formación Cortaderita (Triásico medio), Argentina, y su implicancia en la reconstrucción de las coníferas triásicas

Fil: Bodnar, Josefina. División Paleobotánica. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgentinaFil: Ruiz, Daniela Paula. División Paleobotánica. Museo Argentino de Ciencias Naturales Bernardino Rivadavia. Buenos Aires; ArgentinaFil: Artabe, Analía Emilia Eva. División Paleobotánica. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La PlataFil: Morel, Eduardo Manuel. División Paleobotánica. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; ArgenrinaFil: Ganuza, Daniel Gustavo. División Paleobotánica. Facultad de Ciencias Naturales y Museo. Universidad Nacional de La Plata; Argentin

New species of osmundaceous fertile leaves from the upper Triassic of Argentina

A new species of Osmundopsis Harris is described based on several impression-compression fossils from the upper section of the Potrerillos Formation (Uspallata Group) at Cerro Cacheuta Hill, Mendoza Province, Argentina. Osmundopsis zunigai sp. Nov. is characterized by having fertile pinnae with a slender striate rachis, bearing widely separate, opposite to subopposite short falcate pinnules with an entire margin, rounded apex, and a partially reduced lamina. The pinnules bear sporangia loosely disposed in clusters of four or five on the abaxial side. The sporangia are wedge-to heart-shaped, shortly stalked, with cells of the apical region thickened, and have a vertical dehiscence slit. The spores are trilete and laevigate. This is the first record of Osmundopsis in the Triassic of Argentina. The mutual occurrence or co-preservation of Osmundopsis zunigai sp. Nov. with sterile fronds of Cladophlebis kurtzi suggests the possibility that these species formed part of a dimorphic bipinnate frond. The diversity and geographic extent of fertile leaves of the Osmunda lineage in the early Late Triassic, with records in South Africa and Antarctica and now with this new taxon, support the idea of a moist mesothermal climatic belt in southern Gondwana.Facultad de Ciencias Naturales y Muse

New species of osmundaceous fertile leaves from the upper Triassic of Argentina

A new species of Osmundopsis Harris is described based on several impression-compression fossils from the upper section of the Potrerillos Formation (Uspallata Group) at Cerro Cacheuta Hill, Mendoza Province, Argentina. Osmundopsis zunigai sp. Nov. is characterized by having fertile pinnae with a slender striate rachis, bearing widely separate, opposite to subopposite short falcate pinnules with an entire margin, rounded apex, and a partially reduced lamina. The pinnules bear sporangia loosely disposed in clusters of four or five on the abaxial side. The sporangia are wedge-to heart-shaped, shortly stalked, with cells of the apical region thickened, and have a vertical dehiscence slit. The spores are trilete and laevigate. This is the first record of Osmundopsis in the Triassic of Argentina. The mutual occurrence or co-preservation of Osmundopsis zunigai sp. Nov. with sterile fronds of Cladophlebis kurtzi suggests the possibility that these species formed part of a dimorphic bipinnate frond. The diversity and geographic extent of fertile leaves of the Osmunda lineage in the early Late Triassic, with records in South Africa and Antarctica and now with this new taxon, support the idea of a moist mesothermal climatic belt in southern Gondwana.Facultad de Ciencias Naturales y Muse

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 Río Seco de los Castaños 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 Río Seco de los Castaños 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.Facultad de Ciencias Naturales y Muse

Sedimentología de la Formación Carrizal (Triásico) en el depocentro Marayes - El Carrizal, Provincia de San Juan, República Argentina

Se efectúa el análisis sedimentológico de la Formación Carrizal (Triásico) del Depocentro de Marayes - El Carrizal, ubicado en el sector oriental de la provincia de San Juan. Sobre la base de muy contrastantes características faciales y arquitecturales, la Formación Carrizal es dividida en dos miembros: Arroyo Seco y Rickard. El Miembro Arroyo Seco se caracteriza por el predominio de conglomerados, a los que se asocian areniscas, areniscas conglomerádicas y escasas intercalaciones pelíticas. Estos depósitos se asignan a un sistema fluvial desarrollado en áreas de marcado gradiente y caracterizado por cambios en la disponibilidad de agua y de materiales detríticos, los que fueron esencialmente transportados como carga de lecho. El Miembro Rickard consiste en una sucesión en la que predominan las areniscas y pelitas en litosomas que poseen marcada continuidad lateral, las que aparecen bruscamente cortadas por cuerpos lenticulares de conglomerados medianos. Estas facies permiten definir un sistema fluvial de carga mixta con buen desarrollo de depósitos de planicie de inundación y rellenos de canales compuestos esencialmente por sedimentitas psefíticas. El importante cambio en la arquitectura fluvial que se produce entre los miembros de la Formación Carrizal se relaciona con una marcada variación en la acomodación sedimentaria. El Miembro Arroyo Seco constituye un cortejo de baja acomodación, mientras que el Miembro Rickard se define como un cortejo de alta acomodación. La superficie de retrogradación que limita a ambos miembros señala un cambio importante en el perfil gradado del sistema fluvial, tiene dimensión regional y puede ser considerada como un horizonte de valor cronoestratigráfico

Middle Triassic dipterid ferns from west-central Argentina and their relationship to palaeoclimatic changes

Dipterid ferns possess robust fossil record from Mesozoic times on, and they are considered to be a reliable indicator of warm to subtropical humid or seasonal paleoclimatic conditions. In this contribution, we revised and described new samples of fossil Dipteridaceae, from the Barreal and Cortaderita formations (Sorocayense Group), Middle Triassic (Anisian–Ladinian), central-western Argentina. We found out that three species of Dictyophyllum, one of Hausmannia, and one of Thaumatopteris are present in the Sorocayense Group. We erected a new species Dictyophyllum menendezi sp. nov., which is characterized by petiolate fan-shaped fronds, rachis dividing into two arms, each one bearing 5 or 6 oblanceolate pinnae, basal lamina of adjacent pinnae fused forming a wide web, pinnae margin entire to undulate, primary veins catadromous to isodromous, secondary veins subopposite, tertiary veins subopposite to alternate, falcate or with a zig-zag pattern, dichotomizing four times to form a fine reticulate mesh of polygonal irregular areoles. Temporal changes in the diversity of Dipteridaceae were identified in Sorocayense Group. The first record and the maximum species richness occur at the top of the Barreal Formation (late Anisian) with three species. The lower member of the Cortaderita Formation (early Ladinian) presents two species. Dipteridaceae fossils are not registered in the upper member of the Cortaderita Formation (late Ladinian). An important diversification pulse of the family is registered during the late Norian–Rhaetian in other areas of Argentina (Paso Flores, Malargüe, and Atuel depocenters). The flourishing of Dipteridaceae during the late Anisian–early Ladinian and the late Norian–Rhaetian could be related to the increasing humidity episodes of the subtropical seasonal climate that prevailed during the Triassic. Furthermore, Dipteridaceae appear important in the establishment of plant communities, being part of early stages of floristic succession

Las plantas fósiles triásicas en pelitas lacustres del Cañadón de Pancho (Formación Paso Flores) provincia del Neuquén

The Paso Flores Formation exposed in the Pancho creek is mainly composed of fine-grained sediments. The pelitic rocks have been deposited from aqueous suspensions in deep lacustrine settings. Some upward fining sequences from shale to sandstone represent shallower lacustrine (wave formed) bars. To the top of the PFF. clast-supported conglomerates and cross-bedded sandstones show the progradation of a braided fluvial system upon the lacustrine succession. The paleo- floristic association, composed of Corystosperms, Cycadals, Ginkgoals and Conifers, is characteristic for lacustrine deposits formed during the late Triassic.Facultad de Ciencias Naturales y Muse