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There are two contrasting opinions on the stratigraphic and palaeogeographic distribution of the relatively rare trace fossil Ophiomorpha irregulaire: 1) the trace is mostly restricted to the Upper Cretaceous of the Western Interior Seaway, or 2) it has a post-Palaeozoic record and a worldwide geographic distribution. In this study we document the finding of O. irregulaire in Upper Cretaceous turbidites of the Alta Vista Formation, southern Patagonia, providing additional evidence on the morphology and composition of its pelletal masses, the ethology of its producer and the palaeogeographical and palaeoenvironmental distribution of the trace fossil. The burrow walls are lined with dark mud and their elongate, spiky pellets are formed by a sand core that is also lined with mud. The association with typical fodinichnia, such as Halopoa, Spirophyton, and Zoophycos and the common presence of O. irregulaire in sediments with abundant plant detritus, suggest that the producer was a deposit feeder. Crosscutting relationships and occurrences at several levels within thick-bedded turbidites, suggest a relatively deep tier emplacement of the trace. The finding of the trace in the Southern Hemisphere supports its envisaged worldwide palaeogeographic distribution

A new high-latitude record of the trace fossil Macaronichnus segregatis degiberti is documented from the lower Miocene Punta Basilica beds, Tierra del Fuego, which were previously considered to be ...

Los depósitos marinos del Mioceno temprano en Tierra del Fuego albergan un grupo de gasterópodos struthiolaridos que se destacan por su alta variabilidad morfológica. Desde finales del siglo 19 se interpretó que esta variabilidad reflejaba (1) un grupo de especies altamente diversificado en rápida evolución o (2) una única especie plástica caracterizada por una amplia variabilidad intraespecífica. El estudio morfológico de más de 100 ejemplares del género Perissodonta Martens recolectados en las formaciones fueguinas Carmen silva, Viamonte e Irigoyen indica que parámetros significativos, como la forma del caparazón, la longitud de la espira y el número de ornamentaciones espirales y axiales (líneas espirales finas, cordones, tubérculos) varían continuamente dentro de una amplia gama de valores, favoreciendo una única especie plástica. Los especímenes topotipo de Perissodonta ameghinoi (Ihering), recolectados de la Formación Monte León del Mioceno temprano en la Patagonia, muestran una plasticidad de caracteres similar. Además, material de topotipo reciente de Perissodonta georgiana strebel de las Islas Georgias del sur, una especie considerada sinónimo muy cercano o junior del genotipo de la especie P. mirabilis (smith), indica un grado similar de plasticidad. En consecuencia, los struthiolaridos fueguinos asignados previamente a Perissodonta ameghinoi; P. fueguina (Ihering) o P. densestriata (Ihering) se refieren en este trabajo a P. ameghinoi, un gasterópodo struthiolarido restringido al Mioceno temprano en Tierra del Fuego y Patagonia. The early Miocene marine deposits in Tierra del Fuego bear a group of struthiolariid gastropods that stand out for their high morphological variability. since the end of the 19th century this variability was interpreted as reflecting (1) a highly diversified rapidly evolving group of species or (2) a single, plastic species characterized by ample intraspecific variability. The morphological study of more than 100 specimens of the Fuegian struthiolariid genus Perissodonta Martens collected in the Carmen silva, Viamonte, and Irigoyen formations indicate that significant parameters, such as shell shape, spire length and number of spiral and axial sculptures (cords, threads, tubercles) vary continuously within an ample range of values, favoring a single, plastic species. Topotype specimens of Perissodonta ameghinoi (Ihering), collected from the early Miocene Monte León Formation in Patagonia, show similar plasticity of characters. Furthermore, recent topotype material of Perissodonta georgiana strebel from Islas Georgias del sur, a species considered very close or junior synonym of the genotype species P. mirabilis (smith), indicates a similar degree of plasticity. Accordingly, the Fuegian struthiolariids previously assigned to Perissodonta ameghinoi; P. fueguina (Ihering); or P. densestriata (Ihering) are here referred to P. ameghinoi, a struthiolariid gastropod restricted to the early Miocene in Tierra del Fuego and Patagonia. Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; Argentina

We describe new material of the Subfamily Gaudryceratinae in Antarctica, including five new species: Gaudryceras submurdochi Raffi and Olivero sp. nov., Anagaudryceras calabozoi Raffi and Olivero sp. nov., Anagaudryceras subcompressum Raffi and Olivero sp. nov., Anagaudryceras sanctuarium Raffi and Olivero sp. nov. and Zelandites pujatoi Raffi and Olivero sp. nov., recorded in Santonian to Maastrichtian deposits of the James Ross Basin. The early-mid Campanian Anagaudryceras calabozoi sp. nov. exhibits a clear dimorphism, expressed by marked differences in the ornament of the adult body chamber. Contrary to the scarcity of representative members of the subfamily Gaudryceratinae in the Upper Cretaceous of other localities in the Southern Hemisphere, the Antarctic record reveals high abundance and diversity of 15 species and three genera in total. This highly diversified record of gaudryceratins is only comparable with the Santonian-Maastrichtian Gaudryceratinae of Japan and Sakhalin, which yields a large number of species of Anagaudryceras, Gaudryceras, and Zelandites. The reasons for a similar, highly diversified record of the Gaudryceratinae in these distant and geographically nearly antipodal regions are not clear, but we argue that they probably reflect a similar paleoecological control. Fil: Raffi, María Eugenia. Universidad Nacional de Tierra del Fuego; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; Argentina Fil: Milanese, Florencia Nidia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina

Tide-influenced deposits of the Pennsylvanian Rock Lake Shale Member, Stanton Formation, Missouri and Kansas (U.S.A.), contain well-preserved evidence of the burrowing activities of protobranch bivalves, including locomotion (Protovirgularia) and locomotion-resting (Protovirgularia-Lockeia) trace fossils. Protovirgularia shows three distinct morphotypes, the morphological variability of which was controlled by external factors such as substrate conditions, toponomy, and undertrack deficiency. Extreme morphological modifications of Protovirgularia and/or Lockeia, represented by irregular bilobate structures, probably result from erosion and subsequent partial passive filling of the original biogenic structures. In addition, very well-preserved trace fossils showing intergradation of a fan-shaped cluster of ridges with Protovirgularia-Lockeia structures are interpreted as a compound biogenic structure that represents locomotion, resting, and feeding activities of burrowing protobranch bivalves. Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Mangano, Maria Gabriela. University of Saskatchewan; Canadá Fil: Buatois, Luis Alberto. University of Saskatchewan; Canadá Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Maples, Christopher G.. University of Missouri; Estados Unidos

The James Ross Basin, in the northern Antarctic Peninsula, exposes which is probably the world thickest and most complete Late Cretaceous sedimentary succession of southern high latitudes. Despite its very good exposures and varied and abundant fossil fauna, precise chronological determination of its infill is still lacking. We report results from a magnetostratigraphic study on shelfal sedimentary rocks of the Marambio Group, southeastern James Ross Basin, Antarctica. The succession studied covers a ~1,200 m-thick stratigraphic interval within the Hamilton Point, Sanctuary Cliffs and Karlsen Cliffs Members of the Snow Hill Island Formation, the Haslum Crag Formation, and the lower López de Bertodano Formation. The basic chronological reference framework is given by ammonite assemblages, which indicate a Late Campanian – Early Maastrichtian age for the studied units. Magnetostratigraphic samples were obtained from five partial sections located on James Ross and Snow Hill islands, the results from which agree partially with this previous biostratigraphical framework. Seven geomagnetic polarity reversals are identified in this work, allowing to identify the Chron C32/C33 boundary in Ammonite Assemblage 8-1, confirming the Late Campanian age of the Hamilton Point Member. However, the identification of the Chron C32/C31 boundary in Ammonite Assemblage 8-2 assigns the base of the Sanctuary Cliffs Member to the early Maastrichtian, which differs from the Late Campanian age previously assigned by ammonite biostratigraphy. This magnetostratigraphy spans ~14 Ma of sedimentary succession and together with previous partial magnetostratigraphies on Early-Mid Campanian and Middle Maastrichtian to Danian columns permits a complete and continuous record of the Late Cretaceous distal deposits of the James Ross Basin. This provides the required chronological resolution to solve the intra-basin and global correlation problems of the Late Cretaceous in the Southern Hemisphere in general and in the Weddellian province in particular, given by endemism and diachronic extinctions on invertebrate fossils, including ammonites. The new chronostratigraphic scheme allowed us to calculate sediment accumulation rates for almost the entire Late Cretaceous infill of the distal James Ross Basin (the Marambio Group), showing a monotonous accumulation for more than 8 Myr during the upper Campanian and a dramatic increase during the early Maastrichtian, controlled by tectonic and/or eustatic causes. Fil: Milanese, Florencia Nidia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Olivero, Eduardo Bernardo. Universidad Nacional de Tierra del Fuego; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Raffi, María Eugenia. Universidad Nacional de Tierra del Fuego; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Franceschinis, Pablo Reinaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Gallo, Leandro César. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Skinner, Steven M.. California State University; Estados Unidos Fil: Mitchell, Ross N.. California Institute of Technology; Estados Unidos Fil: Kirschvink, Joseph L.. California Institute of Technology; Estados Unidos. Tokyo Institute of Technology; Japón Fil: Rapalini, Augusto Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina

Recent magnetostratigraphic works from different areas of the James Ross Basin have expanded on chronostratigraphic studies previously based on ammonite, palynomorph and nanoplankton biostratigraphy, and strontium isotope stratigraphy. Here we present a new magnetostratigraphy of Coniacian through Campanian marine sedimentary rocks from Hidden Lake, Santa Marta and Snow Hill Island Formations, on northwest James Ross Island. A total of 189 paleomagnetic directions were obtained along more than 1500 m of stratigraphic thickness from Brandy Bay to Santa Marta Cove areas, identifying three polarity chrons of the global polarity time scale. The local magnetostratigraphic column starts in the upper part of the Cretaceous Normal Superchron C34N (Coniacian) and ends in Chron C33N (middle Campanian). The correlation between the magnetostratigraphy and the age framework given by ammonite biostratigraphy allowed the assignment of precise ages to particular horizons of the Santa Marta Formation. The newly identified geomagnetic polarity reversals are the earliest identified in the James Ross Basin and include: a) C34N/C33R (84.2 Ma, late Santonian – early Campanian) in the Alpha Member of the Santa Marta Formation and b) C33R/C33N (79.9 Ma, middle Campanian) in the upper Beta Member (Santa Marta Formation). By integrating this new data with previous work, we present a complete Upper Cretaceous – lowermost Paleogene chronostratigraphical framework for the basin, spanning both proximal to distal sedimentary facies of the Marambio Group.

We identified six fossil-species of angiosperms based on fossil woods from two small collections from the Beta Member (lower Campanian) of the Santa Marta Formation on James Ross Island: 1) Paraphyllanthoxylon antarcticum sp. nov., a new species of Paraphyllanthoxylon (Angiosperm incertae sedis) which represents the first Antarctic record of that fossil-genus; three previously known Antarctic fossil-species, but from new localities, 2) Laurelites jamesrossii (Laurales), 3) Hedycaryoxylon tambourissoides (Monimiaceae) and 4) Eucryphiaceoxylon eucryphioides (Cunoniaceae); 5) Weinmannioxylon trichospermoides sp. nov., a new species of Weinmannioxylon (Cunoniaceae); 6) and Cretaceoxylon heteropunctatum gen. et sp. nov., a new fossil-genus and fossil-species with uncertain affinity, but with similar wood anatomy and vessel-ray parenchyma pits to the Santalales and Malpighiales. The richness of angiosperm woody species is increased for the Late Cretaceous of Antarctica. The fossil woods are used to interpret ancient forests composition and to make some climatic inferences during the Campanian of the Antarctic Peninsula. Fil: Pujana, Roberto Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Iglesias, Ari. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina Fil: Raffi, María Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego. Instituto de Ciencias Polares, Recursos Naturales y Ambiente; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego. Instituto de Ciencias Polares, Recursos Naturales y Ambiente; Argentina

Recent biostratigraphic and sedimentologic studies in the lower–mid Campanian ammonite-rich shelf deposits of the James Ross Basin, Antarctica made possible a precise reconstruction of facies tracts along an onshore–offshore transect about 70 km in length. In proximal, inner-shelf settings the Santa Marta Formation include trigoniid-rich coquinas and cross-bedded and massive sandstones. In distal, mid- to outer-shelf settings the age-equivalent Rabot Formation consists of bioturbated mudstones and interbedded inoceramid- and brachiopod-rich tempestites. Each of these sedimentary facies is characterized by a very distinctive ammonite facies, whose characterization along a neritic-oceanic gradient offer clues to ammonite habitats. Ammonite facies of proximal settings are dominated by relatively large and ornate kossmaticeratids, with subordinated heteromorphs, desmoceratids, gaudryceratids and tetragonitids. Taphonomy, size–frequency distribution, and non-lethal injuries attributed to arthropods consistently suggest a shallow habitat and a nektobenthic (demersal) mode of life for the kossmaticeratids. Conversely, in distal settings the ammonite facies is dominated by gaudryceratids, including large Anagaudryceras sp., and tetragonitids, with subordinated small kossmaticeratids and large pachydiscids. Restriction to offshore oceanic-influenced facies suggests that these gaudryceratids have a mesopelagic, planktic mode of life. The hamitocone heteromorphs are equally distributed in shallow and deep facies with a high degree of shell fragmentation, particularly in shallow settings. This pattern suggests that hamitocones were exposed to extensive post-mortem drift. Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; Argentina Fil: Raffi, María Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; Argentina

This paper documents calcareous nannofossil assemblages and the bioevents recorded in the Austral basin of Tierra del Fuego, Argentina. Fifty samples from the type section of the Cerro Colorado Formation were analyzed. Nannoflora is moderately preserved and indicates a late Eocene to early Oligocene age for sedimentary rocks of this formation. Biostratigraphic results are based on distribution patterns of calcareous nannofossils assemblages, permitting comparison with the Southern Ocean zonations and some correlations with standard schemes. Our biostratigraphic interpretation shows an almost complete stratigraphic section spanning from the Priabonian to Rupelian Stages and calcareous nannofossil Chiasmolithus oamaruensis to Blackites spinosus zones, or the low latitude zones of Martini NP18 to NP21. The oldest fossiliferous rocks from the type locality of the Cerro Colorado Formation contain Chiasmolithus oamaruensis indicating nannofossil Zone NP18. The Eocene/Oligocene boundary was placed between the last occurrence (LO) of Reticulofenestra oamaruensis and the increasing in abundance (IB) of Reticulofenestra daviesii. Samples taken from the top of the section belong to the Estancia Maria Cristina Beds have Cyclicargolithus abisectus. During the late middle to late Eocene a hiatus is suggested between the Cerro Colorado and Leticia formations evident by a 39 Ma detrital zircon age dating, and the first occurrence (FO) of Dictyococcites bisectus. Furthermore, the presence of C. abisectus in the Estancia Maria Cristina Beds suggests an unconformity with the underlying Cerro Colorado Formation as previously inferred by stratigraphic relationships.

Conifer fossil woods from the Santonian to lower Campanian Santa Marta Formation are anatomically studied in detail. The wood flora is dominated by conifers, mainly Araucariaceae. Conifer fossil woods represent 84% of the samples (26 of 31) of the assemblage. The remaining samples are dicotyledon woods which are not included in this study. Woods are mostly calcified and preservation is often excellent. Fossil woods include three species of Agathoxylon, Phyllocladoxylon antarcticum, Cupressinoxylon hallei and a new species of Cupressinoxylon, C. rotundum Pujana sp. nov. The conifer-dominated forests are consistent with the pollen and macrofloras previously described from sediments of the same stratigraphic unit. This fossil wood assemblage contributes to understand the floristic changes that took place in the Cretaceous forests. Fil: Pujana, Roberto Roman. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina Fil: Raffi, María Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Combined research on the structural and stratigraphic evolution of the southeastern Austral Basin identifies three major depositional systems strongly influenced by the tectonic stages of the Fuegian Andes between the Late Cretaceous and the Miocene. During orogenic growth, a submarine ramp system characterized by oblique progradational clinoforms with transverse sediment dispersal, formed adjacent to the deformation front in the wedge-top or proximal foredeep. In moments when the tectonic load and flexural subsidence were reduced, this system was replaced by a progradational-aggradational system with oblique to sigmoidal clinoforms. This occurred during a short span in the middle Eocene, but especially and definitively after contractional deformation ceased in the early Miocene. The third depositional system was long lived, and comprised axial turbidite channel systems located at the clinoform bases, which re-routed sediment toward the deeper foredeep of the western Malvinas Basin. Distinct facies types develop in each depositional system, and their recognition allows evaluating sediment fairways in the foreland basin system. Fil: Torres Carbonell, Pablo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Two paleomagnetic poles of 80 and 75 Ma have been computed from 191 to 123 paleomagnetic samples, respectively, of the marine sedimentary units of the Upper Cretaceous Marambio Group exposed in the James Ross Island, Antarctic Peninsula. Paleomagnetic behaviors during stepwise thermal demagnetization and rock magnetic analyses indicate that magnetization is likely primary and carried by SD-PSD detrital titanomagnetite. Application of an inclination shallowing correction by the elongation-inclination method yielded a significant inclination shallowing affecting the older (ca. 80 Ma) succession exposed in the northwest area of the island. However, the paleomagnetic directions computed from the younger (ca. 75 Ma) succession outcropping in the southeast corner of the island yielded an indeterminate result using the same analysis. The inclination shallowing-corrected 80 Ma paleopole position plus previous ones of ca.110, 90 and 55 Ma were used to construct the Apparent Polar Wander Path (APWP) for the Antarctic Peninsula during the Late Cretaceous-Paleocene. This path confirms that oroclinal bending of the Antarctic Peninsula as well as relative displacement with respect to East Antarctica are negligible since 110 Ma. Comparison with the apparent polar wander path for South America for the 130-45 Ma period suggests that this continent and the Antarctic Peninsula kept a very similar relative paleogeographic position since 110 Ma until 55 Ma, which likely meant a physical link between both continental masses. During that period, both continents underwent a relatively fast southward displacement of around 7° and a clockwise rotation relative to the Earth spin axis that can be bracketed between around 100 and 90 Ma. Oroclinal bending of the Fuegian Andes was likely due to tectonic interactions between the Patagonian-Fuegian Andes and the Antarctic Peninsula promoted, at least partially, by such displacements. By 55 Ma the Antarctic Peninsula probably was starting or about to start its final separation from South America. Fil: Milanese, Florencia Nidia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Rapalini, Augusto Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Slotznick, Sarah P.. University of California at Berkeley; Estados Unidos Fil: Tobin, Thomas S.. University of Alabama at Birmingahm; Estados Unidos Fil: Kirschvink, Joseph. Tokyo Institute Of Technology; Japón Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

The replacement of seed-free plants and gymnosperms by flowering plants during the Cretaceous is one of the most important biotic events in the evolution of life. However, the magnitude of this global turnover remains largely unknown. Here we present sampling-standardized diversity estimates from a high resolution palynological record of the Late Cretaceous (85–66 Ma) from Antarctica, in the context of the past climatic events. Our fossil evidence reveals the occurrence of a rich Campanian flora peaking at c. 80 Ma, with angiosperms as the most diverse group of plants for the first time in Antarctica. This peak of diversity was followed by a period of a stepwise deterioration; 60% of ferns and 40% of gymnosperms became locally extinct from the early/mid-Campanian to the late Maastrichtian. Although angiosperms also faced several extinctions – 25% became extinct – they were far less affected than nonangiosperms. The onset of deterioration of the greenhouse conditions at the end of the Cretaceous – low CO2 and global cooling trends – would have led to our observed pattern of change. Overall, our study reveals the beginning of a profound floristic turnover in the highest southern latitudes that pre-dates the major extinction event of the end of the Cretaceous by 15 Myr. Fil: Barreda, Viviana Dora. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Palazzesi, Luis. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

The sedimentology, petrography, and U–Pb dating of two Eocene volcaniclastic horizons of the Punta Torcida and Leticia formations, Austral basin, Tierra del Fuego, Argentina are interpreted and documented. The volcaniclastic deposits, pumicite breccia and tuffaceous sandstones, are formed by glass shards, plagioclase crystals, and pumiceous and lithic andesitic fragments. Originally deposited as tephra fallout, they have been subsequently reworked and redeposited in marine settings. The final deposits, however, are interpreted essentially as syn-eruptive. U–Pb dating of detrital zircons gave a 46.3 ± 0.4 Ma (early Lutetian) age for the top of the Punta Torcida Formation and 41.9 ± 0.71 (late Lutetian) to 39.6 ± 0.82 (Bartonian) ages for the Leticia Formation. Paleogene volcanic rocks are unknown in the Southern Patagonian-Fuegian Andes; hence the studied volcanic deposits with minimal reworking are important to evaluate the time lag between eruption and true depositional ages in detrital zircons. The resulting dates allow evaluating the timing of the important, basin-wide, intra-Eocene unconformity known from Tierra del Fuego to Lago Argentino, Santa Cruz, Argentina. The documented eruptive phases are related to Andean magmatism, probably located in the outcrop area of the Seno Ano Nuevo suite in the Chilean Archipelago.

Belying previous interpretations on its rarity in southern latitudes, Gaudryceras de Grossouvre is well represented in the Santonian—Campanian of Antarctica. The study of more than 300 specimens from the Santa Marta, Rabot and Snow Hill Island Formations designates five species that characterize four successive stratigraphic intervals: 1) Gaudryceras cf. G. strictum, Santonian, Alpha Member, lower part of the Santa Marta Formation; 2) Gaudryceras santamartense sp. nov., Santonian—early Campanian, Alpha Member, lower mid part of the Santa Marta Formation; 3) Gaudryceras brandyense sp. nov., late early Campanian—?basal mid Campanian, Beta Member, upper part of the Santa Marta Formation; and 4) Gaudryceras cf. G. mite and Gaudryceras rabotense sp. nov., mid Campanian—late Campanian, upper middle part of the Rabot Formation and lower part of the Hamilton Point Member of the Snow Hill Island Formation. There are two differently ornamented neanoconchs characterized by exhibiting dense or sparse strong...

Antarctica has played a key role connecting all major land-masses of Gondwana, even during periods of their break up through the Cretaceous and Paleogene. The largely ice-covered rocks of Antarctica undoubtedly contain countless clues about the paleogeographic and biotic connections of southern Gondwana. The Antarctic Peninsula is the region that has provided and that likely will provide the most informative fossil remains from the Cretaceous–Paleogene. In particular, during the past two decades, geologic and paleontological explorations of the James Ross Basin, Weddell Sea, have revealed that this basin, located off the northeast tip of the Antarctic Peninsula (West Antarctica), contains one of the most important records of Late Cretaceous and early Paleogene life in the Southern Hemisphere.

Re-evaluation of the fossil penguin Palaeeudyptes gunnari from the Eocene Leticia Formation, Argentina: additional material, systematics and palaeobiology. Alcheringa 40, xx–xx. ISSN 0311-5518 Eocene penguins are known mostly from Antarctic specimens. A previously documented partial skeleton consisting of a pelvis, femur, tibiotarsus and fibula, from the middle Eocene Leticia Formation, Tierra del Fuego Province, Argentina, has been prepared and re-described. Re-analysis favours assignment to Palaeeudyptes gunnari, a species widely recorded in the Eocene of Antarctica. A new isolated coracoid belonging to an indeterminate species reveals new information about diving kinematics and swimming abilities. Palaeobiological attributes and morphology of the fossils indicate that both specimens belonged to large penguins with poor diving capability and wing propulsion systems similar to those of extant taxa. These penguin remains are the only vertebrate fossils thus far recorded from the Leticia Formation, and provide important insights into the relationships of South American and Antarctic penguins during the Paleogene. The presence of Palaeeudyptes in Argentina supports an Eocene connection between the South American and Antarctic penguin faunas. Carolina Acosta Hospitaleche [acostacaro@fcnym.unlp.edu.ar], CONICET. División Paleontología Vertebrados, Museo de La Plata Paseo del Bosque s/n, 1900 La Plata, Facultad de Ciencias Naturales y Museo, UNLP, Argentina; Eduardo Olivero [emolivero@gmail.com], CONICET. Centro Austral de Investigaciones Científicas (CADIC-CONICET), B. Houssay 200, 9410 Ushuaia, Tierra del Fuego, Argentina. Fil: Acosta Hospitaleche, Carolina Ileana Alicia. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

The irregular meandering, endichnial trace fossil Nereites biserialis characterized by alternating biserial row of dimples flanked by even to lobate laminae of sediment, best observed in weathered exposures of tidal sandy siltstones and silty sandstones, are extremely abundant in the outcrops at the base of the Maastrichtian López de Bertodano Formation in Antarctica. Polished sections, perpendicular to bedding, show that the dimples represent voids left by eroded terminal backfilled muddy globular fecal masses inside the central tunnel of the burrow and that the globular fecal masses are totally surrounded by a terminal-radial backfill of lobate, crescentic laminae of the enveloping zone. While uniserial to multiserial pustules of the external hyporelief are known in several ichnospecies of Nereites, the alternating biserial row of fecal masses inside the central tunnel is a diagnostic ichnospecific feature, accordingly Nereites biserialis (Seilacher) is considered a valid ichnospecies. Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Problems of endemism and diachronous extinctions make global correlation of coeval strata in the mid Campanian-Maastrichtian of the James Ross Basin problematic. To provide a more precise chronological framework, we present two magnetostratigraphies of Campanian strata from the Rabot Formation that crops out at Hamilton Norte (200 m thick) and Redonda Point (340 m thick) in James Ross Island. Sampled sections consist of poorly-consolidated, drab-colored fine sandstones and mudstones. Bulk susceptibility logs of both sections show a similar pattern of relatively low values at the lower and upper levels with significantly higher values at mid-levels that confirms the lithostratigraphic correlation between sections. Rock magnetic studies suggest that this change is not attributable to a ferrimagnetic fraction but to a paramagnetic contribution of presumed detrital origin. Stepwise thermal demagnetization showed dominant unblocking temperatures higher than 400 °C. Progressive hybrid low-temperature cycling, low-field AF and thermal demagnetization in a controlled N2 atmosphere, reveals a two-polarity characteristic component of possible primary origin. Rock magnetic experiments suggest that detrital titano-magnetite is the most likely remanence carrier. Anisotropy of magnetic susceptibility results show sedimentary fabrics, indicating that beds were not significantly buried or compacted. Magnetostratigraphies produced at each locality demonstrate a consistent change from reverse to normal polarity remanence in the middle of the sections. Biostratigraphic constraints identify this reversal as the C33r/C33n transition, indicating a 79.90 Ma depositional age for this level of the Rabot Formation. The remanence directions yield a mean whose corresponding paleopole is consistent with two recently obtained Upper Cretaceous reference paleopoles for the Antarctic Peninsula. Our data support the lack of tectonic rotation or oroclinal bending of this region since the Late Cretaceous. Fil: Milanese, Florencia Nidia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Kirschvink, Joseph L.. Caltech Division Of Geological And Planetary Sciences; Estados Unidos. Tokyo Institute Of Technology; Japón Fil: Rapalini, Augusto Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina

We thank Panero for his interest in our paper. However, we consider his interpretations somewhat incomplete and misleading, principally because he reports results using methods that we did not apply in our study, and underestimates the importance of pollen morphological characters in phylogenetic studies. We respond to each of these points with the aim of clarifying his misinterpretations about our paper., Facultad de Ciencias Naturales y Museo

Cretaceous sedimentary rocks of the James Ross Basin offer a unique Austral record of the transition from mild mid-Turonian–early Campanian to relatively cold Maastrichtian palaeoclimatic conditions. After deposition of deep-marine Lower to Upper Cretaceous sediments and tectonic inversion of the basin, the Upper Cretaceous–Danian Marambio Group reflects the development of a shelf extended for more than 100 km into the Weddell Sea. The expansion of the shelf area was punctuated by three major transgressive–regressive cycles: the N (Santonian–early Campanian); NG (late Campanian–early Maastrichtian); and MG (early Maastrichtian–Danian) sequences. Faunal groups sensitive to changing water-mass conditions, such as ammonites and inoceramids, exhibit unusual patterns of diversity changes and/or early extinctions. In the N Sequence ammonite generic richness is minimum in the Santonian, then it increases gradually to an early Campanian maximum and decreases in the latest early Campanian. This pattern is typical for transgressive–regressive cycles, where broadening of the shelf during peak transgression controls maximum diversity. The molluscs Scaphitidae, Nostoceratidae, Inoceramidae, and most Trigoniidae disappeared from Antarctica during the early Campanian. By the early–late Campanian boundary, the last Antarctic inoceramids show a distinctive shell structure that probably reflects thermal stress. In the nearby Tierra del Fuego region, deep-marine inoceramids disappeared by the early Maastrichtian, concomitant with a marked change from anoxic–dysoxic to well-oxygenated bottom conditions. The ammonites of the NG and MG sequences are dominated by kossmaticeratids, both in generic richness (which is much lower than in the N Sequence) and specimen abundance, but their diversity pattern do not reflect the expansion of the shelf during peak transgression. Dominance of the Kossmaticeratidae, concomitant with a known Austral temperature decline in the seawater, supports the idea that kossmaticeratids were stenothermal ammonites that flourished in Antarctica when the water masses had attained their preferred temperature and were displaced towards lower latitudes when a certain minimum threshold temperature was reached in the late Maastrichtian. These diversity changes and local extinctions closely match published temperature-cooling trends in the southern ocean and the oxygenation event at the inoceramid extinction level in Tierra del Fuego probably reflects cooling and enhanced bottom ventilation, promoted by circulation of deep Antarctic waters. Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

We made a detailed facies analysis of well exposed Eocene foredeep and wedge-top successions in the SE Austral Basin of eastern Tierra del Fuego, Argentina, contributing to a better understanding of its patterns of sand dispersal. The analysis reveals that these successions constitute portions of turbidite systems with recurrent facies associations, interpreted as channel, channel-margin and levee depositional elements. The channel facies, paleocurrents and interpreted paleogeography suggest that the studied successions form the transfer zone of the turbidite systems that fed the foreland basin. We hypothesize that the SE Austral Basin, which forms the transition between the Austral and Malvinas Basins, acted as an east-west conduit for sediments sourced at the Fuegian Andes and transported to a deeper depositional zone in the SW Malvinas Basin. The fill of the channels in the transfer zone involved a large amount of turbidity flows, which in addition to the evidence of levee confinement in the studied deposits suggests that the sandier portion of the flows was able to reach the depositional zone, were mostly unconfined (sheeted) sand bodies may have formed. In addition, overbank sand bodies were deposited within the transfer zone, associated to processes of flow overspill. Both types of sand bodies constitute potential reservoirs in this hydrocarbon producing basin, implying that the Eocene SE Austral Basin, and the ultimate zone of deposition in the SW Malvinas Basin may constitute major prospects for hydrocarbon exploration. The proposed model define a new perspective for future research on the sedimentologic and stratigraphic evolution of the SE portion of the Austral Basin.

Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Austral de Investigaciones Cientificas; Argentina

El sistema de cuenca de antepaís Austral-Malvinas adyacente al orógeno Fueguino comprende sedimen-titas marinas expuestas en el norte de Península Mitre, incluyendo 550 m de la antefosa del Paleoceno tardío-Eoceno temprano, y más de 2.900 m de la subcuenca María Luisa, depocentro de techo de cuña ('wedge-top') del Eoceno medio tardío-?Mioceno. La columna se subdivide en las formaciones La Barca (100 m, Paleoceno superior), Punta Noguera (450 m, Eoceno inferior), Leticia (30 m, Eoceno medio superior), Cerro Colorado (935 m, Eoceno medio superior-Eoceno superior), Puesto José (nom. nov., 1.600 m, Oligoceno) y Malengüena (nom. nov., 216 m, ?Mioceno). La microfauna de la Formación Malengüena se distingue por el dominio de Globocassidulina cf brocha, y por su peculiar preservación, ambas características no reconocidas previamente en la porción argentina de la cuenca Austral. Se verifican discordancias sintectónicas entre el límite Paleoceno-Eoceno y el Eoceno medio, asociadas a una etapa de orogénesis regional: en el Eoceno más alto-Oligoceno basal, relacionada localmente con el anticlinal Campo del Medio; en el Oligoceno 'medio', asociada al retrocorrimiento Malengüena; y en el Mioceno ?inferior, relacionada con estructuras profundas de la faja corrida y plegada.The orogenic margin of the Austral-Malvinas foreland basin system is formed by a marine succession exposed at northern Península Mitre, composed of 550 m of the late Paleocene-early Eocene foredeep, and more than 2,900 m of the late middle Eocene-?Miocene María Luisa wedge-top sub-basin. The succession is subdivided in the following formations: La Barca (100 m, upper Paleocene), Punta Noguera (450 m, lower Eocene), Leticia (30 m, upper middle Eocene), Cerro Colorado (935 m, upper middle Eocene-upper Eocene), Puesto José (nom. nov, 1,600 m, Oligocene) and Malengüena (nom. nov, 216 m, ?Miocene). The foraminiferal content of the Malengüena Formation is distinguished by the dominance of Globocassidulina cf. brocha, and by its particular preservation, features not previously recognized in the Argentinean part of the Austral Basin. Syntectonic unconformities are recognized between the Paleocene-Eocene boundary and the middle Eocene, related to regional orogénesis; in the uppermost Eocene-lowermost Oligocene, locally related to the Campo del Medio anticline; in the 'mid' Oligocene, associated with the Malengüena backthrust; and in the ?lower Miocene, related to deep structures of the thrust-fold belt.

U/Pb detrital-zircon geochronology of eleven sandstones collected from Cretaceous through Oligocene strata of the eastern Magallanes foreland basin of southernmost Argentina records a dramatic provenance shift near the end of the middle Eocene at ca. 39 Ma. From the Late Cretaceous through most of the middle Eocene, detrital zircons reaching the foreland basin were dominantly contributed from ≤ 140 Ma sources, most likely derived from the Patagonian–Fuegian magmatic arc. In contrast, detrital-zircon populations of sampled upper Eocene and Oligocene strata are dominated by 150–190 Ma and pre-Mesozoic grains presumably derived from ignimbrites and granitoids associated with the break-up of Gondwana and from metasedimentary rocks of the Cordillera Darwin metamorphic complex, respectively. Exposures of these units occur in the hinterland of the Fuegian Andes thrust belt and inboard of the Patagonian–Fuegian batholith, suggesting that middle to late Eocene shortening in the rear of the Fuegian orogenic wedge structurally dammed batholith-derived sediment from reaching the foreland basin while contributing Jurassic and pre-Mesozoic detritus from hinterland thrust sheets. The timing of this interpreted deformation is in agreement with (1) independent structural, stratigraphic, and thermochronometric evidence of middle Paleogene deformation in the Fuegian Andes, and (2) marine Nd isotope ratio data that reveal initial penetration of Pacific water through the Drake Passage, thereby suggesting a possible link between the kinematics of the Fuegian Andes, the opening of Drake Passage, and if related, the Oi-1 glaciation of Antarctica.

Like other secondary soft-bottom dwellers, serpulid and sabellid tube worms used particular strategies in order to cope with their earlier loss of mobility. This is expressed by the transition from irregular to genomically programmed morphologies of their calcareous shells that guarantee a stable horizontal resting position. In contrast to permanent recliners, however, this attitude was probably only the starting position for active resurrection after the muddy tail of storm sediments had settled on top of the displaced animal.

At Snow Hill and Seymour islands, northeastern Antarctic Peninsula, the early Maastrichtian part of the Marambio Group consists in ascending stratigraphic order of a) fossiliferous mudstone and sandstone of the Snow Hill Island Formation (> 140 m thick), b) glauconitic beds of the Haslum Crag Sandstone (ca. 200 m thick), and c) the mudstone-rich basal Lopez de Bertodano Formation (ca. 400 m thick). The study of fourteen sedimentary sections located along the depositional strike reveals complex arrangements of facies associations and stratal architecture for these units. The Snow Hill Island Formation consists of coarsening and thickening upward successions, 3–7 m thick, of interbedded mudstone and sandstone recording prograding deltaic lobes. Above a marked unconformity, the Haslum Crag Sandstone, bioturbated glauconitic sandstone and mudstone with inclined heterolithic stratification, records the incision, migration, and filling of relatively large and deep subtidal channels. Deeply incised into the Haslum Crag Sandstone, the Lopez de Bertodano Formation includes transgressive estuarine and shallow marine deposits that fill a previous fluvially and/or tidally scoured depression. The Haslum Crag Sandstone consists of forced regressive deposits formed during relative sea-level falls, and documents a rare case of sharp-based, tide-influenced sandstone encased in marine and estuarine mudstone. The main differences between the Haslum Crag Sandstone and other forced regressive, wave-influenced sharp-based sandstones are twofold: a) it records basal erosion by tidal processes — an erosional feature not as yet fully documented in forced regressions, and b) it records a rare case of tide-influenced deposits originating during overall regressive conditions. The great thicknesses of tide-influenced forced regressive deposits (Haslum Crag Sandstone) and the transgressive, estuarine deposits (Lopez de Bertodano Formation) suggest the occurrence of several high-frequency sea-level changes, probably driven by tectonic processes.

The Upper Oligocene–Miocene deposits of the foreland Austral Basin of Tierra del Fuego represent the youngest foredeep fill, developed in front of the adjacent fold and thrust belt. They consist of superbly exposed, sub-horizontal clastic successions of more than 600 m of sedimentary thickness. The study of 11 sections by means of facies analysis and sequence stratigraphic criteria enabled the identification of five depositional sequences (SI–SV), bounded by unconformities (dI-dV) involving hiatuses of different magnitudes. The basal sequence (SI) includes two members: A, mudstone dominated, deposited by cohesive flows; and B, glauconite-rich, sandstone dominated, deposited by episodic turbidity currents. The remaining sequences (SII–SV) are composed of complex arrangements of fine conglomerates, coarse- to fine-grained sandstones, and mudstones that were deposited mainly by hyperpycnal flows. The basal unconformities of the SI to SIV involve minor hiatuses, while that of the SV is a major order unconformity. Two types of clinofom geometries are recognized in the foredeep sequences. Type a clinoforms present a wedge shaped geometry and characterize the foredeep infill during the compressional tectonic regime. Regarding this clinoform type, SI is situated closer to the orogen and shows variations in the bedding dip with development of internal unconformities. SII to SIV are situated towards the foreland and are characterized by subhorizontal conformable beds of large lateral extension. Type b clinoforms, with sigmoidal geometry, show a clear northeast progradation related to a progressive foredeep fill under tectonic quiescence. This clinoform type characterizes the deposits in SV. The recognition of hyperpycnites and different types of clinoform geometries in these sequences incorporates new concepts in reservoir prospects, which are critical for the evaluation of the petroleum system in the Austral Basin.

Field work in the frontal part of the foreland thrust-fold belt of the Fuegian Andes reveals complex relationships between stratigraphy and structure. Construction of balanced cross-sections allows us to infer the geometry and kinematics of structures controlling the thrust-fold belt evolution. The sequential restoration of these cross-sections to their undeformed state reveals the architecture of the Austral foreland basin in relation to the evolving deformation front. This front was developed after incorporation of the Paleocene-earliest Eocene foredeep of the basin to the thrust-fold belt. A wedge-top depozone formed over this former foredeep, bounded by the late-middle to late Eocene thrust front. The wedge-top basin was filled by a quartz-rich sandstone-dominated succession of Andean provenance. The same succession filled the foredeep formed northwards of the deformation front, active from late-middle Eocene. Further reactivation of compression led to backthrusting of the wedge-top clastic succession in the late Eocene, and to subsequent foreland propagation of the deformation, manifested by a sequence of low angle thrusts that affected the foredeep. The foredeep migrated forelandwards as the tectonic load advanced, to finally act as a passive depozone after the earliest Miocene, when the propagation of the deformation front stopped. The paleogeographic reconstruction from late Paleocene to earliest Miocene shows a strong linkage between tectonics and sedimentation in the Atlantic coast of the frontal Fuegian Andes. Fil: Torres Carbonell, Pablo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Dimieri, Luis Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Geológico del Sur. Universidad Nacional del Sur. Departamento de Geología. Instituto Geológico del Sur; Argentina

Different morphotypes of vertically embedded ammonoid shells are abundant in the 1-km-thick deposits of the Santa Marta Formation, Antarctica, that record the evolution of a deep-water delta system. Vertical shells deposited in water depths well below the theoretical limit imposed by hydrodynamic and hydrostatic analyses are preserved as isolated specimens, dense concentrations associated with abundant wood fragments (pod preservation), or as dense concentrations inside and around large ammonites (sheltered preservation). Taphonomic analysis indicates that (1) vertical shell orientation is primary; (2) postburial reworking was minimum or absent, as indicated by consistent shell orientation parallel to regional paleocurrents and complete preservation of fragile shells with phragmocones filled with drusy calcite; and (3) vertical orientation is not biased towards a preferred morphotype. Rapid sedimentation, including deposition from high- and low-density currents, tempestites, and weak bottom currents carrying a dense suspension of ammonoid shells and wood fragments, was one of the main factors controlling the vertical preservation below the limits imposed by theoretical hydrostatic analyses. Another important factor was the plugging of the siphuncular tube with clay particles during transportation. The clay plug was stiff enough to resist the ambient hydrostatic pressure, avoiding or delaying the waterlogging of the phragmocone.

A new elasmosaurid, Vegasaurus molyi, gen. et sp. nov., from Vega Island, James Ross Archipelago, Antarctica, is described. The holotype and only specimen of this species (MLP 93-I-5-1) was collected from the lower Maastrichtian Cape Lamb Member of the Snow Hill Island Formation. Vegasaurus molyi is the only Antarctic elasmosaurid and one of only a few Late Cretaceous elasmosaurids from the Southern Hemisphere whose postcranial anatomy is well known. Vegasaurus molyi is distinguished from other elasmosaurids by the following combination of characters: cervical region with 54 vertebrae with elongated centra, dumbbell-shaped articular faces and lateral ridge present in the anterior and middle parts of the neck but absent in the posterior-most cervical vertebrae; scapula with ventral ramus bearing a strong ridge in the anteromedial corner of its dorsal surface; ilium shaft with expanded distal end, divided into two parts forming an angle of 140°opening anteriorly; and humerus with anterior knee and prominent posterior projection with accessory posterior articular facet. Preliminary phylogenetic analysis places V. molyi within a clade that includes the Late Cretaceous Wedellian aristonectine elasmosaurids, Aristonectes and Kaiwhekea. This indicates a close relationship between Aristonectinae and non-Aristonectinae Late Cretaceous Weddellian elasmosaurids and suggests a Weddellian origin for the Aristonectinae. Fil: O'gorman, Jose Patricio. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleontología Vertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Salgado, Leonardo. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Marenssi, Sergio Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina

The Asteraceae (sunflowers and daisies) are the most diverse family of flowering plants. Despite their prominent role in extant terrestrial ecosystems, the early evolutionary history of this family remains poorly understood. Here we report the discovery of a number of fossil pollen grains preserved in dinosaur-bearing deposits from the Late Cretaceous of Antarctica that drastically pushes back the timing of assumed origin of the family. Reliably dated to ∼76–66 Mya, these specimens are about 20 million years older than previously known records for the Asteraceae. Using a phylogenetic approach, we interpreted these fossil specimens as members of an extinct early diverging clade of the family, associated with subfamily Barnadesioideae. Based on a molecular phylogenetic tree calibrated using fossils, including the ones reported here, we estimated that the most recent common ancestor of the family lived at least 80 Mya in Gondwana, well before the thermal and biogeographical isolation of Antarctica. Most of the early diverging lineages of the family originated in a narrow time interval after the K/P boundary, 60–50 Mya, coinciding with a pronounced climatic warming during the Late Paleocene and Early Eocene, and the scene of a dramatic rise in flowering plant diversity. Our age estimates reduce earlier discrepancies between the age of the fossil record and previous molecular estimates for the origin of the family, bearing important implications in the evolution of flowering plants in general., Los datos utilizados en este trabajo pueden accederse haciendo clic en "Documentos relacionados"., Facultad de Ciencias Naturales y Museo

New petrographic and geochemical insights from inoceramid bivalve shells of lower Campanian (Marambio Group, James Ross Basin, Antarctica) show that they suffered significant palaeoenvironmental stress just before their disappearance in the southern high latitudes. Inoceramid data have mainly been derived from shell fragments of the large form Antarcticeramus rabotensis Crame & Luther, collected at stratigraphical levels marking the early disappearance of inoceramids in the James Ross Basin (10 m.y. before the Cretaceous/Tertiary boundary in Antarctica). Cathodoluminescence studies and minor and trace element intra-shell variations in A. rabotensis shells, along with their whole shell geochemistry (major, minor, and trace elements, including REE), have revealed evidence of only weak diagenesis but significant palaeoenvironmental stress. The most relevant evidence of such adverse palaeoenvironmental conditions in A. rabotensis shells is reflected by marked growth interruptions in the normal shell layering, including the occurrence of a previously undetected inner aragonitic nacreous layer formed of alternating aragonitic and calcitic sublayers. The weak diagenesis produced characteristic geochemical intra-shell variations, which have subsequently been detected in the inoceramid shell microstructure, especially in the inner aragonitic nacreous layer.

The major structural and tectonic features of the Fuegian Andes provide an outstanding onshore geological framework that aids in the understanding of the tectonic evolution of the Scotia Arc, mainly known from offshore studies. The orogenic history of the Fuegian Andes (Late Cretaceous-Miocene) is thus compared and integrated with the tectonic history of the Scotia Sea. Late Cretaceous-Paleocene structures in the Fuegian Andes suggest a N-directed contraction consistent with an oroclinal bending of the southernmost South America-Antarctic Peninsula continental bridge. This N-directed contraction in the Fuegian Andes continued during the spreading of the West Scotia Ridge, between 40-50 and 10 Ma ago. The onset of major strike-slip faulting in Tierra del Fuego is here considered to be not older than the late Miocene, consistent with the recent history of the North Scotia Ridge; thus forming part of a tectonic regime superposed to the prior contraction in the Fuegian Andes. Fil: Torres Carbonell, Pablo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Dimieri, Luis Vicente. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Geológico del Sur; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Bohoyo, Fernando. Instituto Geológico y Minero de España; España Fil: Galindo Zaldívar, Jesús. Universidad de Granada; España

One of the very few crinoid records in Patagonia is that of the abundant columnals of the genus Isselicrinus found in several localities in shallow marine, glauconitic sandstones of the Leticia Formation (upper middle Eocene of Tierra del Fuego Island). Some of them, up to 10 cm long, are preserved in a position almost perpendicular to the stratification, which is attributed to episodes of high sedimentation rate. The Isselicrinus remains occur either almost alone or associated with solitary corals, gastropods, bivalves, rare nautilids, shark teeth, penguin bones and well-preserved specimens of Ophiura elegantoides. The associated microfossils, mainly Foraminifera, are characterised by the anomalous abundance and dominance of large Nodosariacea. These records reflect a peculiar success of a retrograde, dense, suspension-feeding crinoid population as a regional extension of previously described distribution in the Antarctic upper Eocene. Uno de los pocos registros de crinoideos en Patagonia está representado por abundantes columnas del género Isselicrinus, en areniscas glauconíticas someras de la Formación Leticia (Eoceno Medio superior de Tierra del Fuego). Algunas columnas, de hasta 10 cm de largo, están preservadas en forma casi perpendicular a la estratificación, posición que se atribuye a episodios de alta tasa de sedimentación. Los restos de Isselicrinus se presentan en forma aislada o están asociados a corales solitarios, gastrópodos, bivalvos, escasos nautiloideos, dientes de tiburones, huesos de pingüinos, y ejemplares bien preservados de Ophiura elegantoides. Los microfósiles asociados, principalmente foraminíferos, se caracterizan por la dominancia y abundancia anómala de grandes conchillas de Nodosariacea. Estos registros reflejan un peculiar éxito de poblaciones suspensívoras, retrógradas y densas, de crinoideos y demuestran una extensión regional de poblaciones similares descriptas para el Eoceno superior de Antártida

A new ichnotaxon, Paradictyodora antarctica, is proposed for complex spreite trace fossils from the Upper Cretaceous of Antarctica and Eocene of Tierra del Fuego, Argentina. This complex, three-dimensional, vertical spreite structure enlarges upwards, displaying a prismatic-to-conical shape that consists of subvertical folded laminae, produced by the lateral migration of a subvertical J-shaped tube anchored at its base. Overall morphology and mode of formation distinguishes this new ichnotaxa from other ichnogenera such as Daedalus, Dictyodora, and Heimdallia. Paradictyodora occurs in fodinichnia-dominated ichnocoenosis developed in distal fine-grained deposits of deepwater fan delta systems.

Deep marine Paleocene to Oligocene turbidites are exposed in several localities along the Atlantic coast of Península Mitre, Tierra del Fuego (Olivero and Malumián, 2008; Torres Carbonell et al., 2009). At Cabo Leticia (Fig. 1), the Paleocene sandstone-conglomerate package of the Cabo Leticia Formation is transitionally covered by the La Barca Formation, which consists of two members; a lower upper Paleocene sandstonemudstone dominated LB1 Member and an upper organic-rich mudstone-dominated LB2Member. At Punta Noguera (Fig.1), the La Barca Formation is interpreted to underlie lowermost Eocene turbidites of the Punta Noguera Formation (Olivero et al., 2002; Malumián, et al., 2009). The late Paleocene age of the lower LB1 Member of the La Barca Formation was initially established on the basis of foraminifera and dinocysts (Olivero et al., 2002; Malumián and Caramés, 2002). New studies at Punta Ainol (Fig. 1) have also found a diagnostic late Paleocene assemblage of calcareous benthic foraminifera contained in organic-rich mudstones interpreted as part of the LB2 Member, which suggests a late Paleocene age for the whole formation (Sample PT Sur, Torres Carbonell et al., 2009).Agglutinated foraminifera are dominant in the La Barca Formation, and only two isolated horizons preserve calcareous benthic foraminifera (Malumián and Jannou, 2010), whereas planktonic foraminifera and calcareous nannofossils have not been previously found in the formation (Malumián and Jannou, 2010). As part of ongoing research devoted to the study of calcareous nannofossils from Tierra del Fuego, we have analyzed samples from the La Barca Formation, both at its type locality in Cabo Leticia and from the mudstones exposed at Punta Ainol. None of the samples processed from the type locality of the La Barca Formation were fertile. Nevertheless, the organic-rich mudstones samples from Punta Ainol are fossiliferous and contain calcareous nannofossils that correlate with other Paleocene-Eocene assemblages from the Southern Hemisphere. Thus, the main goal of our study is to document the nannofossil assemblages and to interpret their stratigraphic and paleoenvironmental implications. Fil: Bedoya Agudelo, Erika Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego, Antártida e Islas del Atlántico Sur. Instituto de Ciencias Polares, Recursos Naturales y Ambiente. Departamento de Biología; Argentina Fil: Concheyro, Andrea. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina Fil: Torres Carbonell, Pablo Juan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Martinioni, Daniel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego, Antártida e Islas del Atlántico Sur. Instituto de Ciencias Polares, Recursos Naturales y Ambiente. Departamento de Biología; Argentina

Seven stratigraphic units reflect the tectonic evolution of the Argentinian Fuegian Andes: Basement (Paleozoic-Jurassic); Lemaire Formation (Upper Jurassic); Yahgan-Beauvoir formations (Lower Cretaceous); Cerro Matrero Formation (Upper Cretaceous); Río Claro Formation (Paleocene); La Despedida Group (Eocene); and Cabo Peña Formation (uppermost Eocene-Lower Oligocene). Basement rocks (garnet, quartz-sericite, and chlorite schists; and amphibolites) are unconformably covered by the Lemaire Formation (rhyolites; basalts; slates; and acidic volcaniclastic breccias, tuffs, conglomerates, and turbidites), formed during extensional tectonism. The post-rift Yahgan Formation (deep-marine black mudstones, andesitic volcaniclastic turbidites and tuffs) interfingers northward with the Beauvoir Formation (slope and platform black mudstones), and covers the Lemaire Formation unconformably. The Yahgan Formation represents an andesitic. volcaniclastic apron, coeval with a Pacific volcanic-arc, filling a marginal basin floored with oceanic crust. The Late Cretaceous compressional orogeny resulted in tectonic inversion, closure of the marginal basin, peak metamorphism and folding, and initial uplifting of the Fuegian Andes. By the latest Cretaceous-earliest Paleogene, the Andes were exposed to subacrial erosion, and the lowest Danian Río Claro Formation bears clear evidence of an Andean clastic provenace. The Río Claro Formation represents the first molasse deposits of the foreland stage of evolution of the Fuegian Andes. Earliest Paleogene north-verging thrust propagation deformed the Río Claro Formation and older units, producing northward depocenter migration. La Despedida Group rests unconformably on the Río Claro Formation and is involved in the thrust and fold belt. Important Eocene compression resulted in thrusting of central Andean basement schists and the Lemaire Formation over Lower Cretaceous and continental Paleogene rocks, respectively. In the Argentinian Fuegian Andes, the compressional orogeny ceased by the Late Eocene and the subhorizontal Cabo Peña Formation unconformably overlies folded La Despedida Group strata. Field mapping suggests a left-lateral offset of 20-30 km of Cretaceous-Eocene rocks along the Magallanes-Fagnano Fault System: this is clear evidence that the strike-slip regime has been active since at least the latest Eocene. Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Martinioni, Daniel Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

The stratigraphy and preliminary interpretation of a new locality with glacial deposits in a previously interpreted ice-free area in Tierra del Fuego are presented. These deposits consist of basal proglacial gravels (at least 4–5 m thick) covered by the Drift Cabo Campo del Medio. The drift consists of a lower, 2 m thick, lodgment till and a upper, 7 m thick, glaciotectonized composite till, reflecting basal glacier shearing and upthrusting of glaciofluvial deposits and lodgment till, with superimposed deformation by gelifluction. These two main drift packages are interpreted as ground moraines, reflecting two corresponding glacial advances with an intervening recess of the glacier front. The altitude of the Drift Campo del Medio, well above younger fluvioglacial deposits related to the Last Glaciation, the degree of erosional modifications, and its external position, to the NE of the Last Glaciation moraine system, are evidence suggesting that the Drift Cabo Campo del Medio was related to a glaciation older than the Penultimate Glaciation. The finding of this locality sheds new light on the old controversy of total vs partial ice coverage of the island.

The Fuegian thrust-fold belt (TFB) forms the thin-skinned outer wedge of the Andes in Tierra del Fuego. Using subsurface and outcrop data from two areas (Western and Eastern) of the TFB front in Argentina we aimed to verify and characterize the apparent structural variations along the strike. Both areas reveal pro- and retro-vergent fault-related folds detached at similar horizons, with a youngest early to middle (?) Miocene deformation age. However, the Western Area has gentle, large-wavelength folds whereas the Eastern Area is characterized by a very tight structural geometry, with closer fold geometries. This difference manifests itself in the shortening of analogous structures: below 5.5% in the west as against ~22% in the Eastern Area. Our findings verify structural style variations along the strike and suggest that the Eastern Area endured higher strain. We evaluate two possible causes of this strain gradient, assuming homogeneous regional shortening: (i) lateral rheological variations at the base of the thrust wedge, namely the occurrence of more competent beds which would have restrained the propagation of the detachment toward the east; and (ii) the effect of strong buttressing in the eastern TFB exerted by the Río Chico arch basement promontory during deformation. Published results, together with our current subsurface and outcrop data, rule out significant rheological gradients in a preferred direction along the TFB. On the other hand, we present evidence of the nucleation of frontal thrusts above basement steps at the Río Chico arch western margin, which comprise local buttresses. We speculate that this buttressing was mantained along the TFB front and is enhanced toward the east, where forward TFB propagation was hindered due to the southern projection of the Río Chico promontory. This would explain the higher strain and more complex structural style in the Eastern Area. La faja corrida y plegada Fueguina (FCP) comprende el cinturón de piel fina en el antepaís de los Andes en Tierra del Fuego. Con la finalidad de verificar y caracterizar posibles variaciones estructurales a lo largo del frente de la FCP en Argentina, hemos analizado datos de subsuelo y superficie en dos áreas (occidental y oriental). Ambas revelan pliegues relacionados con fallas, tanto provergentes como retrovergentes, que despegan en niveles similares, y tienen una edad mínima miocena temprana a media (?). Sin embargo, en el área occidental el plegamiento es suave y de alta longitud de onda mientras que en el área oriental la estructura es muy apretada, con pliegues más cerrados. Esta diferencia se manifiesta al comparar el acortamiento en estructuras análogas: menor a 5,5% en el oeste contra ~22% en el área oriental. Por lo tanto, queda verificada la existencia de variaciones en el estilo estructural a lo largo del rumbo, y se pone en evidencia que el área oriental fue sometida a mayor deformación. Evaluamos dos causas posibles para este gradiente de deformación, asumiendo una magnitud de acortamiento regional homogénea: (i) variaciones laterales en la reología de la base de la FCP, por ejemplo capas más competentes hacia el este que podrían haber dificultado la propagación del despegue en ese sector, y (ii) una fuerte obstaculización al avance de la FCP en el este, ejercida por el promontorio de basamento del Arco Río Chico. La información publicada previamente, así como los datos de este trabajo, descartan un gradiente reológico significativos en una dirección preferencial a lo largo de la FCP. Al contrario, nuestros datos evidencian localización de corrimientos frontales sobre escalones en el basamento del Arco Río Chico en el área occidental, que localmente obstaculizan el avance de la deformación. Especulamos con que este efecto obstaculizador se mantuvo a lo largo del frente de la FCP, con mayor intensidad hacia el este, donde el avance de la FCP fue restringido por la proyección austral del arco Río Chico. De esta manera se puede explicar la mayor deformación y el estilo estructural más complejo en el área oriental.

Fine-grained sandstones and siltstones of Late Cretaceous to Eocene age in Antarctica and Tierra del Fuego yield an association of well-known shallow-marine trace fossils. Among them stick out complex spreite burrows, which are formally described as Euflabella n. igen. and subdivided into five ichnospecies with different burrowing programs and occurrences. As shown by concentrations of diatoms, radiolarians, foraminifers, and calcispheres in particular backfill lamellae, the unknown trace makers lived on fresh detritus from the surface as well as the burrowed sediment. In some ichnospecies, vertical sections show that the spreite is three-dimensionally meandering in upward direction and that upper laminae tend to rework the upper backfill of the folds underneath. This could mean a second harvest, after cultivated bacteria had time to ferment refractory sediment components, which the metazoan trace maker had been unable to digest before. Fil: Olivero, Eduardo Bernardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Cientificas; Argentina; Fil: Lopez Cabrera O., Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Cientificas; Argentina