Miguel Ezpeleta

Deep faunistic turnovers preceded the rise of dinosaurs in southwestern Pangaea

The Triassic period documents the origin and diversification of modern amniote lineages and the Late Triassic fossil record of South America has been crucial to shed light on these early evolutionary histories. However, the faunistic changes that led to the establishment of Late Triassic ecosystems are largely ignored because of the global scarcity of fossils from assemblages a few million years older. Here we contribute to fill this gap with the description of a new tetrapod assemblage from the lowermost levels of the Chañares Formation (uppermost Middle–lower Late Triassic epochs) of Argentina, which is older than the other vertebrate assemblages of the same basin. The new assemblage is composed of therapsids, rhynchosaurids and archosaurs, and clearly differs from that of the immediately overlying and well-known historical Chañares vertebrate assemblage. The new tetrapod association is part of a phase of relatively rapidly changing vertebrate assemblage compositions, in a time span shorter than 6 million years, before the diversification of dinosaurs and other common Late Triassic tetrapods in southwestern Pangaea.A Middle–Late Triassic tetrapod assemblage from South America reveals a series of faunal turnovers prior to the rise of dinosaurs in the region.

Estudio palinológico de la formación la veteada en su localidad tipo (Pérmico superior), Sierra de Famatina, La Rioja, Argentina. Granos de polen estriados, plicados y colpados

Abstract. PALYNOLOGICAL STUDY OF LA VETEADA FORMATION AT ITS TYPE LOCALITY (UPPER PERMIAN), FAMATINA RANGE, LA RIOJA PROVINCE, ARGENTINA. STRIATE, PLICATE AND COLPATE POLLEN GRAINS. This is a systematic study of the palynological assemblages recorded in the upper part of the La Veteada Formation (upper La Veteada Association), which constitutes the section of the type locality, La Rioja Province, Argentina. In this contribution, 72 species of striate (monosaccate and bisaccate), plicates and colpate pollen grains are presented. Four new species are described: Meristocorpus veteadensis sp. nov., Lueckisporites biformis sp. nov., Lunatisporites lenticularis sp. nov., and Marsupipollenites costatus sp. nov. and, a new combination, i.e., Striatopodocarpites gopadensis (Bharadwaj and Srivastava) comb. nov is proposed. This palynoflora has a marked dominance of striate pollen grains which have great species diversity of Striatopodocarpites (with 11 species)-Protohaploxypinus (9 species)-Lueckisporites (9 specics)-Lunatisporites (8 species) complex, showing scarse participation of the genera Vittatina, Weylandites, Marsupipollenites, Corisaccites, Staurosaccites and Pakhapites, as well as pollen grains referred to Cordaitales (Potonieisporites, Cannanorop ollis, Caheniasaccites, Plicatipollenites, Barakarites). It shares taxa recorded in the LW (Argentina), Vc-Lv (Brazil) and IS-AC (Uruguay) biozones. Tables include full taxonomic composition of the microflora of the La Veteada Formation at its type locality, the palynostratigraphic correlation of the Neopaleozoic strata of central Argentina, southern Brazil and Uruguay, and the global previous stratigraphic records of the species recorded and discussed herein. The palynoflora of the upper La Veteada Formation is referred to the Late Permian (Lopingian) based on the stratigraphic range of all the recognized species. Consequently, it is considered the youngest Permian palynoflora recorded hitherto in Argentina and South America.

PALYNOLOGY OF THE LA VETEADA FORMATION (LOPINGIAN) AT ITS TYPE LOCALITY, FAMATINA RANGE, LA RIOJA PROVINCE, ARGENTINA. SPORES

Abstract. In this systematic study of palynological assemblages from the upper part of the type section of the La Veteada Formation, 38 species of trilete and monolete spores are described and/or illustrated. Two new species are instituted: Lundbladispora verrucosa and Secarisporites triangularis, and a new combination Secarisporites imperialis (Jansonius) is proposed. Trilete spores comprise a dominant group in the analyzed palynoflora and show a reduced frequency from the base to the top of the section (from 32.2 to 14.5%). Cinguli-cavate spores (derived from herbaceous lycophytes) are dominant and represented by the genera Densoisporites, Lundbladispora and Secarisporites. Smooth and apiculate trilete spores (derived from ferns and sphenopsids) are represented by genera such as Calamospora, Punctatisporites, Granulatisporites, Brevitriletes, Cyclogranisporites and Osmundacidites. This upper section of the La Veteada Formation was deposited in fluvialhypersaline/ brackish lacustrine environments under arid to semiarid climatic conditions. The areas surrounding these water-bodies dominated by evaporites were vegetated mainly by herbaceous lycopsids (Isoetales, Selaginellales, Lycopodiales) and ferns. Pteridophytes (Filicales, Zygopteridales), bryophytes and herbaceous sphenophytes were developed along the river courses and in the surrounding areas of freshwater bodies (ponds and small lakes) on the flood plain. The presence of Densoisporites complicatus, D. nejburgii, D. playfordii, D. solidus, Leptolepidites jonkeri, Lundbladispora brevicula, L. obsoleta, L. springsurensis, L. wilmotti, Ringosporites fossulatus, Secarisporites bullatus, S. imperialis and S. lacunatus confirm a late Permian (Lopingian) age for the upper La Veteada Formation. The palynofloras contain significant proportions of lycopsid tetrads; as is the case with many extra-Gondwanic strata of Lopingian/Early Triassic age.

Depósitos sinorogénicos en el antepaís neopaleozoico del cinturón de Famatina, centro-oeste de Argentina: implicancias paleoambientales, paleogeografías y tectonosedimentarias

RESUMEN:En el cinturon de Famatina, ubicado entre las provincias geologicas argentinas de Sierras Pampeanas y Precordillera, se describe y analiza una sucesion de conglomerados de -400 m, considerada en trabajos previos como la seccion superior del intervalo postglacial neopaleozoico del Grupo Paganzo (Pensilvaniano tardio). En este trabajo estos conglomerados (Formacion Las Pircas nom.nov.), extensamente desarrollados en Famatina, son separados como una unidad litoestratigrafica diferente asociada a un episodio de deformacion, sobre la base de: 1. la presencia de una discordancia angular en su base, 2. un fuerte contraste litofacial con la unidad glacial subyacente y 3. su organizacion estratigrafica interna. El analisis de facies indica un predominio de depositos de abanicos aluviales proximales, que pasan en transicion hacia sistemas fluviales entrelazados y desarrollo local de depositos lacustres. La recurrencia de megacapas con bloques y conglomerados de composicion granitica indica una significativa exhumacion de basamento, sugiriendo actividad tectonica coetanea. Asimismo, los estudios de procedencia indican participacion de clastos de areniscas fluviales pensilvanianas y volcanitas acidas ordovicicas que actualmente se exponen en la sierra de Famatina. Esto es compatible con el analisis de paleocorrientes, que muestra una dispersion de los sedimentos hacia el oeste. La posicion de los altos topograficos de basamento al este del arco principal, junto con evidencias de plegamiento, sugieren una etapa de deformacion de zocalo dentro del antepais no descrita con anterioridad. Esto permite explicar la fuente principal de esta cuna clastica depositada de este a oeste parcialmente equivalente a la Formacion Tupe en el ambito de Precordillera. Este modelo de antepais puede ser comparado con el antepais fragmentado moderno de los Andes Centrales.ABSTRACT:In the Famatina belt, western Argentina, a -400 m thick conglomerate succession is extensively developed and has been previously considered as the uppermost section of a postglacial interval (late Pennsylvanian) of the Paganzo Group. Here we separate it as a different lithostratigraphic unit (Las Pircas Formation, nom. nov.) with a significant tectonic meaning based on: 1. the angular discordance at its base; 2. the strong lito facial contrast with the underlying glacial unit and 3. its internal stratigraphic organization. Facies analyses indicate topographically controlled proximal alluvial fans succeeded by braided fluvial systems, and local development of lacustrine deposits. Granite bearing-megaboulder beds and conglomerates indicate significant basement exhumation and tectonic unroofing. Clast composition also depicts early Pennsylvanian sandstones and Ordovician volcanic rocks mainly exposed in the central part of Famatina (at present). Paleocurrent analyses are compatible with a dispersal pattern mostly to the west. The position of basement topographic high further east from the main contemporaneous arc together with evidences of folding allow us to interpret previously unrecognized basement thrusting within the foreland. This may have been the main source for the westward coarse arkosic clastic wedge known in the Argentine Precordillera as the Tupe Formation and equivalents. This late Pennsylvanian-Early Permian foreland model can be compared with the modern broken foreland of the Central Andes.

Mantle Influence on Andean and Pre-Andean Topography

Mantle convection can drive long-wavelength and low-amplitude topography, which can occur synchronously and superimposed to tectonics. The discrimination between these two topographic components, however, is difficult to assert. This is because there are still several uncertainties and debates in the geodynamic community, for example, the scales and rates of dynamic topography. Geological, geomorphological, geophysical measurements, and/or landscape analyses might assist to validate models. In this contribution, we provide new geological evidences along the Central and Patagonian Andes, which demonstrate that dynamic topography has been an important component on the South American landscape formation as well as in the ancient western Gondwana. Our examples in the Argentine Pampas show that dynamic topography is required to explain not only the basin subsidence but also the whole observed topography. We also suggest that the dynamic components in this region are much lower than numerical models (average dynamic subsidence rates of ~0.04 mm/yr—this work— which contrast with the ~0.1 mm/yr estimated in the US). We also propose two strategies to analyze ancient cases. The first requires of comparing a total elevation proxy, like the equilibrium lines (or ELA) in glaciated areas, with model topography derived from geochemical studies of mantle rocks. A second strategy was the analysis of the Triassic rifting evolution of western Argentina (post-rift sag deposits). Sag deposit thicknesses exceed 2 km, which do not correlate with the 100 m thick thermal calculated by rift subsidence modeling.

Basin Thermal Structure in the Chilean-Pampean Flat Subduction Zone

Flat-slab segments are considered refrigerated areas given that the asthenospheric wedge is forced to shift hundreds of kilometres away from the trench, and the flat and coupled subducting plate acts as a thermal insulator. Although lithospheric-scale thermal analysis based on numerical modelling and geophysical observations abound, studies on the thermal history of sedimentary basins are scarce. In this contribution, we present a temperature data compilation from more than 60 oil wells within the Chilean-Pampean flat-slab segment and the transitional zones to normal subduction to the north and south in the south-central Andes. The geothermal gradient data are correlated with basin-basal heat flow estimated from 1D modelling, Curie point depths derived from aeromagnetic surveys, and previous crustal and lithospheric thicknesses estimations. Their distribution evidences a quite good consistency and correlation from region-to-region. Our modelling demonstrates that sedimentation changes are not sufficient to explain the variations illustrated in the geothermal gradient map, and that basal heat flux variations are required to reproduce the reported values. According to our results, the coldest basins develop over the flat slab or cratonward regions, whereas the highest temperatures on areas where the slab plunges. This suggests that the flat-slab geometry as well as the lithospheric structure affects the thermal state within the upper crust and particularly the sedimentary basins. Further studies will allow improving our database as well as the knowledge about the radiogenic contribution of the lithosphere and the asthenospheric heat input to the basins basal heat flow.

Gymnosperm pollen grains from the La Veteada Formation (Lopingian), Paganzo Basin, Argentina: biostratigraphic and palaeoecological implications

ZAVATTIERI, A.M., GUTTIÉRREZ, P.R. & EZPELETA, M., January 2018. Gymnosperm pollen grains from the La Veteada Formation (Lopingian), Paganzo Basin, Argentina: biostratigraphic and palaeoecological implications. Alcheringa 42, 277–300. ISSN 0311-5518. This work forms the concluding part of a series of systematic studies of typical Gondwanan Permian palynofloras from the type section of the La Veteada Formation in the Paganzo Basin, central-western Argentina. It deals with the description and/or illustration of the non-taeniate monosaccate, bisaccate and polysaccate gymnosperm pollen species that are richly represented in the La Veteada Formation and are attributed to 25 genera. These taxa are allied to, or derived from, a diverse range pteridosperms (corystosperms, peltasperms), conifers (including Voltziales) and cordaites; Ginkgoales, Cycadales and Gnetales also have some representation. The new species, Jugasporites vellicoites, is instituted and the new combination, Alisporites angustus (Ouyang & Norris) comb. nov. et emend., is proposed. New evidence to support a Lopingian age for the palynoflora, considered to be the youngest Permian palynoflora recorded hitherto in South America, is based on a summary of the published information about its composition, together with an assessment of previous records of the diversity of gymnosperm taxa analysed in this contribution. The co-occurrence of several species of taeniate pollen (described in a previously published part of our work) and the gymnosperm taxa documented here, which have not been reported before from South America, differentiates the palynoflora of the upper La Veteada Formation from all others so far described from this continent. The high ratio of pollen versus spores, plus the botanical and palaeoecological inferences of the gymnospermous component of the formation’s palynoflora, reflects a parent vegetation adapted to relatively dry conditions. Such a low-humidity environment is consistent with the sedimentological evidence, which suggests that, through the Lopingian, semi-arid to arid climates dominated the southern South American basins. Ana María Zavattieri* (amz@mendoza-conicet.gov.ar) Unidad de Paleopalinología, Departamento de Paleontología IANIGLA, CCT-CONICET-Mendoza, Av. Adrián Ruiz Leal s/n, M5502IRA, Mendoza, Argentina; Pedro Raúl Gutiérrez (pedroraulgutierrez@gmail.com) Museo Argentino de Ciencias Naturales ‘B. Rivadavia’—CONICET, Sección Paleopalinología, Área Paleontología, Av. Ángel Gallardo 470, C1405DJR Buenos Aires, Argentina; Miguel Ezpeleta (miguelezpeleta@gmail.com) Centro de Investigaciones en Ciencias de la Tierra, Universidad Nacional de Córdoba—CONICET, Ciudad Universitaria, Av. Vélez Sarsfield 1611, X5016GCA Córdoba, Argentina.