The Indo-Pacific ammonite <i>Mayaites</i> in the Oxfordian of the Southern Andes

Oxfordian Iitho- and biostratigraphy of the Chilean and Argentine Andes is reviewed (P. N. Stipanicic). Within the Chacay Group, the Lower to basal Upper Oxfordian La Manga Formation, below, mostly detrital and biogenic, and the Upper Oxfordian Auquilco Formation, above, mainly chemical, are distinguished. The La Manga Formation (with Gryphaea calceola lumachelle) is rich in ammonite faunas, particularly of thc upper Cordatum to lower Canaliculatum Zones. In Neuquén and Mendoza provinces of Argentina, the Plicatilis Zone or Middle Oxfordian has yielded Perísphinctes spp., Euaspidoceras spp., Aspidoceras spp., together with Mayaítes (Araucanites ) stípanícfcí, M. (A.) reyesi, and M. (A.) mulai, Westermann et Riccardi subgen. et spp. nov. The first find of Mayaitidae outside the Indo-Pacific province is discussed in light of _plate-tectonic theory.La revisión Iito- y bioestratigráfica del Oxfordiano de los Andes de Argentina y Chile (P. N. Stipanicic) ha permitido reconocer dentro del Grupo Chacay: 1) abajo, la Formación La Manga, mayormente detrítica y biogénica, del Oxfordiano inferior-superior basa!, y 2) arriba, la Formación Auquilco, mayormente química, del Oxfordiano superior. La Formación La Manga (con lumachelas de Gryphaea calceola) contiene abundante cantidad de amonitas, particularmente de las Zonas de Cordatum superior a Canaliculatum inferior. En las provincias de Mendoza y Neuquén, Argentina, la Zona de Plicatilis (Oxfordiano medio) contiene Perispbinctes spp., Euaspidoceras spp., Aspidoceras spp., conjuntamente con Mayaites (Araucanites) stipanicici, M. (A.) reyesi, y M. (A.) mulai, Westermann et Riccardi subgen. et spp. nov. El primer hallazgo de Mayaitidae fuera de la provincia lndo-Pacífica es discutido tomando en consideración la teoría de tectónica de placas.Universidad Nacional de La Plata (UNLP) - Facultad de Ciencias Naturales y Museo (FCNM

The Indo-Pacific ammonite <i>Mayaites</i> in the Oxfordian of the Southern Andes

Oxfordian Iitho- and biostratigraphy of the Chilean and Argentine Andes is reviewed (P. N. Stipanicic). Within the Chacay Group, the Lower to basal Upper Oxfordian La Manga Formation, below, mostly detrital and biogenic, and the Upper Oxfordian Auquilco Formation, above, mainly chemical, are distinguished. The La Manga Formation (with Gryphaea calceola lumachelle) is rich in ammonite faunas, particularly of thc upper Cordatum to lower Canaliculatum Zones. In Neuquén and Mendoza provinces of Argentina, the Plicatilis Zone or Middle Oxfordian has yielded Perísphinctes spp., Euaspidoceras spp., Aspidoceras spp., together with Mayaítes (Araucanites ) stípanícfcí, M. (A.) reyesi, and M. (A.) mulai, Westermann et Riccardi subgen. et spp. nov. The first find of Mayaitidae outside the Indo-Pacific province is discussed in light of _plate-tectonic theory.La revisión Iito- y bioestratigráfica del Oxfordiano de los Andes de Argentina y Chile (P. N. Stipanicic) ha permitido reconocer dentro del Grupo Chacay: 1) abajo, la Formación La Manga, mayormente detrítica y biogénica, del Oxfordiano inferior-superior basa!, y 2) arriba, la Formación Auquilco, mayormente química, del Oxfordiano superior. La Formación La Manga (con lumachelas de Gryphaea calceola) contiene abundante cantidad de amonitas, particularmente de las Zonas de Cordatum superior a Canaliculatum inferior. En las provincias de Mendoza y Neuquén, Argentina, la Zona de Plicatilis (Oxfordiano medio) contiene Perispbinctes spp., Euaspidoceras spp., Aspidoceras spp., conjuntamente con Mayaites (Araucanites) stipanicici, M. (A.) reyesi, y M. (A.) mulai, Westermann et Riccardi subgen. et spp. nov. El primer hallazgo de Mayaitidae fuera de la provincia lndo-Pacífica es discutido tomando en consideración la teoría de tectónica de placas.Universidad Nacional de La Plata (UNLP) - Facultad de Ciencias Naturales y Museo (FCNM

The Indo-Pacific ammonite <i>Mayaites</i> in the Oxfordian of the Southern Andes

Oxfordian Iitho- and biostratigraphy of the Chilean and Argentine Andes is reviewed (P. N. Stipanicic). Within the Chacay Group, the Lower to basal Upper Oxfordian La Manga Formation, below, mostly detrital and biogenic, and the Upper Oxfordian Auquilco Formation, above, mainly chemical, are distinguished. The La Manga Formation (with Gryphaea calceola lumachelle) is rich in ammonite faunas, particularly of thc upper Cordatum to lower Canaliculatum Zones. In Neuquén and Mendoza provinces of Argentina, the Plicatilis Zone or Middle Oxfordian has yielded Perísphinctes spp., Euaspidoceras spp., Aspidoceras spp., together with Mayaítes (Araucanites ) stípanícfcí, M. (A.) reyesi, and M. (A.) mulai, Westermann et Riccardi subgen. et spp. nov. The first find of Mayaitidae outside the Indo-Pacific province is discussed in light of _plate-tectonic theory.La revisión Iito- y bioestratigráfica del Oxfordiano de los Andes de Argentina y Chile (P. N. Stipanicic) ha permitido reconocer dentro del Grupo Chacay: 1) abajo, la Formación La Manga, mayormente detrítica y biogénica, del Oxfordiano inferior-superior basa!, y 2) arriba, la Formación Auquilco, mayormente química, del Oxfordiano superior. La Formación La Manga (con lumachelas de Gryphaea calceola) contiene abundante cantidad de amonitas, particularmente de las Zonas de Cordatum superior a Canaliculatum inferior. En las provincias de Mendoza y Neuquén, Argentina, la Zona de Plicatilis (Oxfordiano medio) contiene Perispbinctes spp., Euaspidoceras spp., Aspidoceras spp., conjuntamente con Mayaites (Araucanites) stipanicici, M. (A.) reyesi, y M. (A.) mulai, Westermann et Riccardi subgen. et spp. nov. El primer hallazgo de Mayaitidae fuera de la provincia lndo-Pacífica es discutido tomando en consideración la teoría de tectónica de placas.Universidad Nacional de La Plata (UNLP) - Facultad de Ciencias Naturales y Museo (FCNM

Ecological reconstruction of a mixed Middle Triassic forest from Argentina

The palaeoecology of an in situ Middle Triassic forest known as the Darwin Forest, from the Paramillo Formation of Argentina, is described based on palaeobotanical, sedimentological and spatial analyses. The palaeoforest grew on an andisol soil that developed on volcaniclastic floodplain deposits. The volcanic detritus and the rhythmic amalgamation of upper flow-regime tractional deposits overlying the andisol indicate that the forest was buried rapidly by a subaerial, cool and wet pyroclastic base surge flow. The plant community was reconstructed by quantitative mapping of the fossilized stumps integrated with taxonomic and sedimentological information. The Darwin Forest had a tree density of 427-759 per ha, with an upper stratum (20-26 m) of corystosperms and a second stratum (16-20 m) of conifers. Estimated biomass is equivalent to modern dry monsoonal forest. The understorey was composed of ferns (Cladophlebis spp.). Quantitative growth-ring analysis of Araucarioxylon protoaraucana suggests that these trees were evergreen and, together with vegetation structure and sedimentary data, indicate that the forest developed under dry, subtropical, strongly seasonal conditions.Fil: Brea, Mariana. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; ArgentinaFil: Artabe, Analia Emilia Eva. División Paleobotánica, Facultad de Ciencias naturales y Museo, Universidad Nacional de La Plata; ArgentinaFil: Spalletti, Luis Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentin

Tectonic Setting of the Tordillo Formation in the Aconcagua Fold-and-Thrust Belt

At the northwestern Mendoza province, the Mesozoic infill of the Neuquén Basin is tectonically repeated in the Aconcagua fold-and-thrust belt. Particularly, the Tordillo Formation (commonly associated with the Kimmeridgian) represents a local low stand period of sea level, with mainly alluvial and fluvial sediments. Toward the western sector of the belt, it interfingers with volcanic and volcaniclastic materials and presents a marked increase in the thickness. This unit was studied in two localities at the Blanco River valley, at the undeformed sector and over the second thrust that produces a second repetition of the Upper Jurassic and Lower Cretaceous sequences in the Aconcagua fold-and-thrust belt. This transect exposes facies variations and a significant increase in thickness to the west. Additionally, provenance analysis and paleocurrent directions indicate that the sediment supply was located to the E-SE, and that the underlying units were exhumed at the time of deposition of the Late Jurassic red beds. A consistent thickness increment of the Upper Jurassic deposits to the west through the Aconcagua fold-and-thrust belt suggests that sedimentation was controlled by NNW-directed structures. This is also supported by facies analyses that demonstrate high topographic breaks affecting a smooth westdipping fluvial ramp toward the volcanic arc. These features support an extensional setting for the deposition of the Tordillo Formation at the latitudes of the Aconcagua fold-and-thrust belt, as other authors have proposed for the Malargüe fold-and-thrust belt to the south. Plate tectonic reconstructions suggest trench rollback during this time previous to the westward migration of the South American plate, which is consistent with the back-arc extension proposed in the previous works.Fil: Acevedo, Eliana Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Rosselot, Eduardo Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Martos, Federico Exequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Fennell, Lucas Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; ArgentinaFil: Folguera Telichevsky, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

Seed cone anatomy of Cheirolepidiaceae (Coniferales): Reinterpreting Pararaucaria patagonica

• Premise of the study: Seed cone morphology and anatomy reflect some of the most important changes in the phylogeny and evolutionary biology of conifers. Reexamination of the enigmatic Jurassic seed cone Pararaucaria patagonica reveals previously unknown systematically informative characters that demonstrate affinities with the Cheirolepidiaceae. This paper documents, for the first time, internal anatomy for seed cones of this important extinct Mesozoic conifer family, which may represent the ghost lineage leading to modern Pinaceae. • Methods: Morphology and anatomy of cones from the Jurassic La Matilde Formation in Patagonia are described from a combination of polished wafers and thin section preparations. New photographic techniques are employed to reveal histological details of thin sections in which organic cell wall remains are not preserved. Specific terminology for conifer seed cones is proposed to help clarify hypotheses of homology for the various structures of the cones. • Key results: Specimens are demonstrated to have trilobed ovuliferous scale tips along with a seed enclosing pocket of ovuliferous scale tissue. Originally thought to represent a seed wing in P. patagonica, this pocket-forming tissue is comparable to the flap of tissue covering seeds of compressed cheirolepidiaceous cones and is probably the most diagnostic character for seed cones of the family. • Conclusions: Pararaucaria patagonica is assigned to Cheirolepidiaceae, documenting anatomical features for seed cones of the family and providing evidence for the antiquity of pinoid conifers leading to the origin of Pinaceae. A list of key morphological and anatomical characters for seed cones of Cheirolepidiaceae is developed to facilitate assignment of a much broader range of fossil remains to the family. This confirms the presence of Cheirolepidiaceae in the Jurassic of the Southern Hemisphere, which was previously suspected from palynological records.Fil: Escapa, Ignacio Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; Argentina. University of Alberta; CanadáFil: Rothwell, Gar. State University of Oregon; Estados Unidos. Ohio University; Estados UnidosFil: Stockey, Ruth. State University of Oregon; Estados UnidosFil: Cúneo, Néstor Rubén. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; Argentin