Estratigrafía y evolución geológica de la Cuenca de Cañadón Asfalto, Provincia del Chubut, Argentina

La Cuenca de Cañadón Asfalto, ubicada entre el Macizo Nordpatagónico y la Cuenca del Golfo San Jorge, presenta una importante columna de sedimentos jurásicos y cretácicos acumulados en hemigrábenes pertenecientes a un sistema de rift formado durante la fragmentación de Gondwana. La Cuenca de Cañadón Asfalto incluye varios depocentros sedimentarios denominados Gastre, Gan Gan, Fossatti, Valle de General Racedo, Gorro Frigio y Paso de Indios, limitados por bloques basamentales en zonas de transferencia. La columna sedimentaria jurásica y cretácica puede dividirse en tres megasecuencias principales (J 1, J 2 y K) separadas entre sí por discordancias de significado regional que se apoyan sobre un basamento de metamorfitas y granitoides del Paleozoico. La Megasecuencia J 1 está constituida por la Formación Las Leoneras, la Formación Lonco Trapial y la Formación Cañadón Asfalto, y su edad se extiende entre el HettangianoSinemuriano?/Pliensbachiano y el Bajociano tardío. Se acumuló en ambientes fluvial, lacustre y volcánico durante los estadíos incipiente a juvenil del rift. La Megasecuencia J 2 incluye sedimentos aluviales y lacustres continentales correspondientes a la Formación Cañadón Calcáreo, de edad oxfordiana-kimmeridgiana, que se depositaron en depocentros parcialmente coincidentes con los anteriores durante una reactivación tectónica multiepisódica del rift. Durante el Tithoniano tardío – Hauteriviano existe un importante hiato estratigráfico. Durante este lapso se generaron esfuerzos transpresivos-transtensivos con rotación de bloques a escala regional, que originaron levantamientos de grandes áreas de la cuenca y la subsecuente erosión de zonas extensas, aunque el entorno tectónico y su correspondiente campo de esfuerzos se encuentran aún en discusión. El posterior colapso de estas áreas elevadas, con un control tafrogénico inicial y una posterior subsidencia termal, permitió el desarrollo del espacio disponible para la acumulación de la Megasecuencia K, formada por los niveles continentales del Grupo Chubut del Barremiano-Campaniano, al cual le siguieron los depósitos marinos y litorales de las formaciones Paso del Sapo y Lefipán del CampanianoDaniano, representativos de la primera transgresión atlántica en la cuenca. Como consecuencia de los procesos detallados más arriba, una marcada discordancia angular separa a la base de la Megasecuencia K de todos los depósitos más antiguos de la cuenca. Posteriormente, durante el Paleoceno tardío-Eoceno, se produjo un episodio tectónico compresivo en el margen occidental de la cuenca, seguido por la acumulación del Complejo Volcánico y Piroclástico del Río Chubut Medio en ambientes de calderas asociadas a un vulcanismo de retro-arco. En el Oligoceno?- Mioceno a Reciente se produjo el levantamiento y la inversión tectónica de la mayor parte de la Cuenca de Cañadón Asfalto, representado por fallamiento generalizado y por plegamiento localizado de intensidad y estilo variables. En este momento se desarrollaron pequeñas cuencas intermontanas limitadas por fallas

Insect herbivore and fungal communities on Agathis (Araucariaceae) from the latest Cretaceous to Recent

Agathis (Araucariaceae) is a genus of broadleaved conifers that today inhabits lowland to upper montane rainforests of Australasia and Southeast Asia. A previous report showed that the earliest known fossils of the genus, from the early Paleogene and possibly latest Cretaceous of Patagonian Argentina, host diverse assemblages of insect and fungal associations, including distinctive leaf mines. Here, we provide complete documentation of the fossilized Agathis herbivore communities from Cretaceous to Recent, describing and comparing insect and fungal damage on Agathis across four latest Cretaceous to early Paleogene time slices in Patagonia with that on 15 extant species. Notable fossil associations include various types of external foliage feeding, leaf mines, galls, and a rust fungus. In addition, enigmatic structures, possibly armored scale insect (Diaspididae) covers or galls, occur on Agathis over a 16-million-year period in the early Paleogene. The extant Agathis species, throughout the range of the genus, are associated with a diverse array of mostly undescribed damage similar to the fossils, demonstrating the importance of Agathis as a host of diverse insect herbivores and pathogens and their little-known evolutionary history

A new cupressaceous wood from the Lower Cretaceous of central Patagonia reveals possible clonal growth habit

A new genus and species, Austrocupressinoxylon barcinense, based on remains of cupressaceous wood is described for the Lower Cretaceous of central Patagonia, Argentina. The studied specimens are silicified fragments of picnoxylic and homoxylic wood that exhibit a combination of characters not previously reported, therefore a new genus is erected. The characters are: 1- growth ring boundaries distinct, 2- transition from earlywood to latewood gradual, 3- axial parenchyma diffuse,4- radial tracheid pitting predominantly abietinean,5- cross-field pitting cupressoid, arranged in both cupressoid and araucarioid patterns, 6- rays uniseriate heterocellular, 7- end and horizontal walls of ray parenchyma cells smooth or slightly nodular, and 8- ray tracheids with smooth walls. The cross-field pitting patterns and the presence of ray tracheids are two traits of particular interest in the context of systematic affinities. The fragments were collected from two stumps found in life position attached to each other by a main root, consequently, the disposition of the stumps suggests a case of clonal growth by root suckering. This is the second report of such mechanisms in the fossil records worldwide and the first one for South America.Facultad de Ciencias Naturales y Muse

Oldest Known Eucalyptus Macrofossils Are from South America

The evolutionary history of Eucalyptus and the eucalypts, the larger clade of seven genera including Eucalyptus that today have a natural distribution almost exclusively in Australasia, is poorly documented from the fossil record. Little physical evidence exists bearing on the ancient geographical distributions or morphologies of plants within the clade. Herein, we introduce fossil material of Eucalyptus from the early Eocene (ca. 51.9 Ma) Laguna del Hunco paleoflora of Chubut Province, Argentina; specimens include multiple leaves, infructescences, and dispersed capsules, several flower buds, and a single flower. Morphological similarities that relate the fossils to extant eucalypts include leaf shape, venation, and epidermal oil glands; infructescence structure; valvate capsulate fruits; and operculate flower buds. The presence of a staminophore scar on the fruits links them to Eucalyptus, and the presence of a transverse scar on the flower buds indicates a relationship to Eucalyptus subgenus Symphyomyrtus. Phylogenetic analyses of morphological data alone and combined with aligned sequence data from a prior study including 16 extant eucalypts, one outgroup, and a terminal representing the fossils indicate that the fossils are nested within Eucalyptus. These are the only illustrated Eucalyptus fossils that are definitively Eocene in age, and the only conclusively identified extant or fossil eucalypts naturally occurring outside of Australasia and adjacent Mindanao. Thus, these fossils indicate that the evolution of the eucalypt group is not constrained to a single region. Moreover, they strengthen the taxonomic connections between the Laguna del Hunco paleoflora and extant subtropical and tropical Australasia, one of the three major ecologic-geographic elements of the Laguna del Hunco paleoflora. The age and affinities of the fossils also indicate that Eucalyptus subgenus Symphyomyrtus is older than previously supposed. Paleoecological data indicate that the Patagonian Eucalyptus dominated volcanically disturbed areas adjacent to standing rainforest surrounding an Eocene caldera lake

Late cretaceous aquatic plant world in Patagonia, Argentina.

In this contribution, we describe latest Cretaceous aquatic plant communities from the La Colonia Formation, Patagonia, Argentina, based on their taxonomic components and paleoecological attributes. The La Colonia Formation is a geological unit deposited during a Maastrichtian-Danian transgressive episode of the South Atlantic Ocean. This event resulted in the deposition of a series of fine-grained sediments associated with lagoon systems occurring along irregular coastal plains in northern Patagonia. These deposits preserved a diverse biota, including aquatic and terrestrial plants and animals. The aquatic macrophytes can be broadly divided into two groups: free-floating and rooted, the latter with emergent or floating leaves. Free-floating macrophytes include ferns in Salviniaceae (Azolla and Paleoazolla) and a monocot (Araceae). Floating microphytes include green algae (Botryoccocus, Pediastrum and Zygnemataceae). Among the rooted components, marsileaceous water ferns (including Regnellidium and an extinct form) and the eudicot angiosperm Nelumbo (Nelumbonaceae) are the dominant groups. Terrestrial plants occurring in the vegetation surrounding the lagoons include monocots (palms and Typhaceae), ferns with affinities to Dicksoniaceae, conifers, and dicots. A reconstruction of the aquatic plant paleocommuniy is provided based on the distribution of the fossils along a freshwater horizon within the La Colonia Formation. This contribution constitutes the first reconstruction of a Cretaceous aquatic habitat for southern South America

Reconstructing the early evolution of the cupressaceae: A whole-plant description of a new austrohamia species from the cañadón asfalto formation (early Jurassic), Argentina

Premise of research. A new Early Jurassic species of Cupressaceae is reconstructed from the Cañadón Asfalto Formation in Argentina, based on impressions of foliage and attached and dispersed seed and pollen cones. Methodology. Over 230 specimens were examined using reflected-light microscopy and epifluorescence. Relevant extant taxa were studied for structural comparisons using herbarium specimens and living material from botanical gardens. Relationships of the new conifer were assessed in the context of currently known fossil and living taxa and used to evaluate morphological trends in the early evolution of Cupressaceae. Pivotal results. The new species, Austrohamia asfaltensis D.L. Contreras, I.H. Escapa, R.C. Iribarren, & N.R. Cúneo, has helically arranged, dorsiventrally flattened leaves that are rotated into semiplanar orientation, seed cones consisting of helically arranged coriaceous ovuliferous complexes that each bear two seeds and have a distinct abaxial keel and acuminate apex, and pollen cones that occur in clusters subtended by keeled bracts. Specimens show evidence that normal vegetative shoot growth continues from the pollen cone clusters, a condition that appears to characterize living Cunninghamia and some extinct conifers but not Taiwania. The new species is assignable to the genus Austrohamia, which shares a combination of characteristics consistent with the Cunninhamioideae and Taiwanioideae subfamilies of the Cupressaceae. It is distinct from other Austrohamia species, most notably by having seed cones that are twice as large and with many more ovuliferous complexes. Conclusions. The new species expands the known morphological diversity of Austrohamia, which is the oldest recorded genus of Cupressaceae based on reproductive material, and provides a new early occurrence of the family in the Southern Hemisphere. The development of a whole-plant concept enabled morphological comparisons over a broad range of traits and with taxa known from different combinations of organs, which has provided additional insights into the early evolution of Cupressaceae.Fil: Contreras Condori, Erick. University of California at Berkeley; Estados UnidosFil: Escapa, Ignacio Hernán. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Iribarren, Rocio Cecilia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Botánica Darwinion. Academia Nacional de Ciencias Exactas, Físicas y Naturales. Instituto de Botánica Darwinion; ArgentinaFil: Cúneo, N. Rubén. Museo Paleontológico Egidio Feruglio; Argentin

Additional observations on the enigmatic Permian plant Buriadia and implications on early coniferophyte evolution

An extensive collection of compressed altered remains, including leafy shoots and ovules similar to specimens described as Buriadia, is reported from Lower Permian rocks on Mount Gran, Victoria Land, Antarctica. The specimens, preserved as a thin layer of aluminosilicate film in a fine-grained black shale, show a number of morphological features like those reported from the type species, Buriadia heterophylla. The leaves are highly polymorphic and appear to be helically arranged. The ovules are orthotropous and attached to leafy shoots by a short stalk; they do not appear to be organized into distinct zones along the axis. The ovules are obovate, with a conspicuous bifid apex and prominent chalazal disk. The combination of features in these Antarctic specimens indicates affinities with the putative Permian coniferophyte, B. heterophylla, originally described from India. The discovery of a presumed coniferophyte with erect terminal ovules from the Permian of Antarctica adds support to the hypothesis that there were at least two major groups of conifer-like plants present during the late Paleozoic. Differences in the ovulate parts of these plants suggest a unique evolutionary history for the late Paleozoic coniferophytes from the Southern Hemisphere.Fil: Serbet, Rudolph. University of Kansas; Estados UnidosFil: Escapa, Ignacio Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Kansas; Estados Unidos. Museo Paleontológico Egidio Feruglio; ArgentinaFil: Taylor, Thomas N.. University of Kansas; Estados UnidosFil: Taylor, Edith L.. University of Kansas; Estados UnidosFil: Cúneo, Néstor Rubén. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; Argentin

Origin of Equisetum: Evolution of horsetails (Equisetales) within the major euphyllophyte clade Sphenopsida

© 2018 Botanical Society of America Premise of the Study: Equisetum is the sole living representative of Sphenopsida, a clade with impressive species richness, a long fossil history dating back to the Devonian, and obscure relationships with other living pteridophytes. Based on molecular data, the crown group age of Equisetum is mid-Paleogene, although fossils with possible crown synapomorphies appear in the Triassic. The most widely circulated hypothesis states that the lineage of Equisetum derives from calamitaceans, but no comprehensive phylogenetic studies support the claim. Using a combined approach, we provide a comprehensive phylogenetic analysis of Equisetales, with special emphasis on the origin of genus Equisetum. Methods: We performed parsimony phylogenetic analyses to address relationships of 43 equisetalean species (15 extant, 28 extinct) using a combination of morphological and molecular characters. Key Results: We recovered Equisetaceae + Neocalamites as sister to Calamitaceae + a clade of Angaran and Gondwanan horsetails, with the four groups forming a clade that is sister to Archaeocalamitaceae. The estimated age for the Equisetum crown group is mid-Mesozoic. Conclusions: Modern horsetails are not nested within calamitaceans; instead, both groups have explored independent evolutionary trajectories since the Carboniferous. Diverse fossil taxon sampling helps to shed light on the position and relationships of equisetalean lineages, of which only a tiny remnant is present within the extant flora. Understanding these relationships and early character configurations of ancient plant clades as Equisetales provide useful tests of hypotheses about overall phylogenetic relationships of euphyllophytes and foundations for future tests of molecular dates with paleontological data

Free-floating microphyte components (chloroccocalean microalgae).

<p>A, B (SEM): <i>Pediastrum</i> spp.; BAFCB meb 262. C: <i>Botryoccocus</i> sp. (SEM); BAFCB meb 262. D, E: Zygnemataceae spores (LM); BAFCB pm 260. Scales A, B, C = 1000 µm; D, E = 10 µm.</p

Free-floating microphyte components (chloroccocalean microalgae).

<p>A, B (SEM): <i>Pediastrum</i> spp.; BAFCB meb 262. C: <i>Botryoccocus</i> sp. (SEM); BAFCB meb 262. D, E: Zygnemataceae spores (LM); BAFCB pm 260. Scales A, B, C = 1000 µm; D, E = 10 µm.</p