Federico Damián Esteban

Erosional and depositional contourite features at the transition between the western Scotia Sea and southern South Atlantic Ocean: links with regional water-mass circulation since the Middle Miocene

The aim of the present study was to characterise the morpho-sedimentary features and main stratigraphic stacking pattern off the Tierra del Fuego continental margin, the north-western sector of the Scotia Sea abyssal plain (Yaghan Basin) and the Malvinas/Falkland depression, based on single- and multi-channel seismic profiles. Distinct contourite features were identified within the sedimentary record from the Middle Miocene onwards. Each major drift developed in a water depth range coincident with a particular water mass, contourite terraces on top of some of these drifts being associated with interfaces between water masses. Two major palaeoceanographic changes were identified. One took place in the Middle Miocene with the onset of Antarctic Intermediate Water flow and the enhancement of Circumpolar Deep Water (CDW) flow, coevally with the onset of Weddell Sea Deep Water flow in the Scotia Sea. Another palaeoceanographic change occurred on the abyssal plain of the Yaghan Basin in the Late Miocene as a consequence of the onset of Southeast Pacific Deep Water flow and its complex interaction with the lower branch of the CDW. Interestingly, these two periods of change in bottom currents are coincident with regional tectonic episodes, as well as climate and Antarctic ice sheet oscillations. The results convincingly demonstrate that the identification of contourite features on the present-day seafloor and within the sedimentary record is the key for decoding the circulation of water masses in the past. Nevertheless, further detailed studies, especially the recovery of drill cores, are necessary to establish a more robust chronology of the evolutionary stages at the transition between the western Scotia Sea and the southern South Atlantic Ocean.

Geophysical survey in Lago Yehuin, Isla Grande de Tierra del Fuego, Argentina: origin and evolution

A new shallow multichannel seismic survey was carried out in the Llancanelo Lake region (Southern Mendoza Province, Argentina) in order to depict the major Neogene sedimentary-volcanic sequences and regional evolution of a tectonic-volcanic basin located in a key region at the eastern foot of the Andes cordillera. This research is settled on early studies that comprised seismic works reaching depths of 600/700 m as well as geoelectric and electromagnetic surveys reaching the uppermost 80-100 m of the sequences. The processing of the reflection seismic data enabled to obtain a stacked section useful for a preliminary geological interpretation. The obtained results indicated the presence of three major sedimentary units with increasing volcanic (basaltic layers) intercalations with depth that accommodate to the geometry of the depocenter. The entire sequence encompasses most of the Neogene. The previous research set the methodological basis for performing more detailed shallow seismic surveys and allowed defining the strategies for obtaining a better constrained geological model. Seismic transects located north of the lake were densified by adding new profiles. Deep seismic and borehole data from the industry were included in this study in order to provide a regional stratigraphic structure of the Cenozoic sequences and to contribute to the knowledge of the final stages of evolution of the Llancanelo basin.The Cuyania stratigraphic record of the Pygodus serra Zone, and the E. robustus and E. lindstroemi subzones, is discussed in this contribution. Three classical sections have been sampled for conodonts in Precordillera and the San Rafael Block. The studied successions are composed mainly by clastic rocks with variable amount of carbonate. The Ponon Trehue and La Cantera formations start with conglomerates and represent the input of coarse clastic deposits to the Cuyania basin. The Los Azules Formation, in Los Amarillitos section, exhibits a massive sandstone bed with carbonate nodules between the black shale. The key conodonts recovered indicate a late Darriwillian age for the bearing strata, these conodonts specimens from the Ponon Trehue region are compare with those from the Precordillera. Finally, the studied clastic sedimentary successions that record this biozone have been compared, concluding that eustacy did not control the sedimentary change in Cuyania for this time interval.In this contribution we present new specimens of Litopterna recovered during the last decade in Quebrada Fiera (Mendoza Province, Argentina), whose fossiliferous sediments, currently recognized as the base of Agua de la Piedra Formation, are assignable to Late Oligocene (Deseadan South American Land Mammal Age). Two remains mentioned in the first publication on this locality were neither detailed nor described, and they have not been located in the corresponding repository. The new material consists of postcranial fragmentary remains (astragali, calcaneum, and metapodials) of Macraucheniidae (Cramaucheniinae) and an incomplete upper molar (M3) of Proterotheriidae (Proterotheriinae). These few remains of litopterns contrast with the abundance of notoungulates at Quebrada Fiera. A comparative study was carried out with material from Patagonia (Argentina) and taxa recorded in Bolivia and Peru for the same temporal interval. The specimens of Cramaucheniinae are assigned to Coniopternium andinum and the molar of Proterotheriinae to cf. Lambdaconus suinus. This contribution allows us to extend the geographical range of Coniopternium, filling the gap between the Patagonian and lower latitude localities (Bolivia and Peru) in which this genus was found. The record of L. suinus in Quebrada Fiera expands the geographical range of this species outside from Patagonia.ABSTRACT. The aquatic sloth, Thalassocnus, is one of the most intriguing linage of mammal knew from the southern pacific coast of South America during the late Neogene. It was initially recognized in Peru, but recent paleontological surveys also demonstrate its presence in Chile. However, the determination of how many species of Thalassocnus were in Chile remains as an open question. Here, we provide a detailed morphological description of an isolated distal fragment of humerus recovered at the Mina Fosforita member (7-7.5 Ma), Bahia Inglesa Formation (Atacama Region, northern Chile), which shows affinities with Thalassocnus. Morphological comparisons with others forms from Chile and Peru allow us to attribute the CPUC/C/557 specimen to T. natans, though some degree of intraspecific variation is acknowledged. The assessment of the stratigraphic provenance of the materials with previously assigned to Thalassocnus from the Bahia Inglesa, Horcon and Coquimbo formations, permits us to propose that the taxonomic diversity of Thalassocnus in Chile is unequivocal conformed by T. carolomartini, and T. natans. We also admitted the likely presence of T. antiquus and a younger species than T. natans (probably T. yaucensis). Futures discoveries of more complete specimens, and/or the detailed analysis of undescribed specimens from Chile will undoubtedly contribute to illustrate the evolutionary history of this extraordinary and enigmatic clade of organisms.The uppermost Cretaceous continental deposits of the Neuquen Basin (west-central Argentina) have yielded a high diversity vertebrate assemblage, including numerous dinosaur species. The Neuquen Group is the richest dinosaur-bearing unit of the basin and comprises the Rio Limay, the Rio Neuquen and the Rio Colorado subgroups. In this group, there is abundance of isolated, disarticulated or partially articulated sauropods and theropods. However, little is known about the taphonomic history of fossil assemblages. In this study, dinosaur remains from the Rio Neuquen Subgroup (Plottier Formation) found in the Cerro Guillermo area in southern Mendoza are examined. The investigation of fossil occurrences within the study area revealed the existence of different taphonomic modes, from isolated bones until partially articulated skeletons preserved in floodplain and channel settings. SEM-EDS analysis showed the substitution of hydroxyapatite by francolite in the bone microstructure. The presence of fluorine –in one of the cases– suggested a link between the elemental composition and depositional environments: floodplain and fluvial channel. The survey of the vertebrate accumulation types and their sedimentary context allowed documenting a wide range of processes responsible for their genesis, operating within a fluvial-dominated environment. This contribution represents an holistic approach about taphonomic history of Cretaceous dinosaurs for assessing the differential preservation of fossil assemblages in fluvial environments.