Norberto Malumián

Mesozoic-Cenozoic stratigraphy of the Fuegian Andes, Argentina

The stratigraphy of the Argentinean Fuegian Andes reveals contrasting Mesozoic-Cenozoic tectonic regimes. The Lemaire Formation, submarine complex of bimodal volcanites, breccias, and sedimentary rocks; the Yahgan Formation, volcaniclastic apron of deep-marine andesite-rich turbidites and mudstones; and the Beauvoir Formation, slope mudstones, all evidence late Jurassic early Cretaceous extension and consequent origination of the Rocas Verdes Marginal Basin. The basal late Cretaceous ductile deformation, isoclinal folding, and metamorphism of these rocks indicate a compressional tectonic regime that resulted in the closure of the marginal basin. The Fuegian Andes were uplifted by the late Campanian; subsequent propagation of the compressional deformation and subsidence by tectonic loading along the northern orogenic margin originated the Austral and Malvinas foreland basins. The Turonian-lower Campanian “Estratos de Buen Suceso” represents the final stages of the closure of the marginal basin and/or the beginning of the foreland basins. During the late Campanian to mid Miocene, the foraminiferal assemblages allow precise dating of the main tectonic events and with the associated trace fossils and sedimentary facies, the general characterization of the depositional settings. The thrust and fold belt of the Austral/Malvinas basins includes three depocenters: 1) the Bahia Thetis (upper Campanian-Maastrichtian), Policarpo (upper Maastrichtian/Danian), and Tres Amigos (upper Paleocene) Formations, mostly turbidite settings with cosmopolitan agglutinated foraminifers; 2) the Rio Claro Group, upper Paleocene-lower Eocene; and 3) the La Despedida Group, representing the extended upper mid Eocene-upper Eocene transgression with endemic foraminifers. A fourth depocenter, the Oligocene-mid Miocene Cabo Domingo Group mostly deposited below the calcite compensation depth and characterized by widespread agglutinated foraminifers, represents the last and deepest foredeep, originated just north of the fold belt during the waning compressional phase. Reduced exposures of mid Eocene bryozoan limestones, the Rio Bueno Formation, and fluvial upper Eocene lower Oligocene, the Punta Cactus and Sloggett Formations, conform reduced exposures within the fold belt. The late Miocene-Pliocene, shallow marine “estratos de la Maria Luisa” and Irigoyen Formation, the latter with foraminifers suggesting an Atlantic-Pacific connection, record Cenozoic transcurrency and pull-apart basins.

Estratigrafía del Cretácico Superior-Paleoceno del área de Bahía Thetis, Andes fueguinos, Argentina: acontecimientos tectónicos y paleobiológicos

Se caracteriza la evolucion estratigrafica del Cretacico superior-Paleoceno de las cuencas de antepais Austral-Malvinas en la porcion mas interna de la faja plegada y corrida del extremo oriental de los Andes fueguinos. En la bahia Thetis se reconocen tres Formaciones: 1) Bahia Thetis, fangolitas oscuras, tobas, turbiditas arenosas y conglomerados resedimentados, con ammonites y foraminiferos del Campaniano tardio-?Maastrichtiano inferior; 2) Policarpo, fangolitas arenosas, tobaceas, bioturbadas con ammonites, foraminiferos y dinoquistes del Maastrichtiano en su parte inferior-media y con foraminiferos y dinoquistes del Daniano en su parte superior; y 3) Tres Amigos (n. nombre), conglomerados, areniscas y fangolitas, con dinoquistes y foraminiferos del Paleoceno austral. Estas tres formaciones, sumadas a los estratos de la bahia Buen Suceso (Santoniano-Campaniano inferior), de la caleta Falsa de Policarpo-Rio Bueno (Maastrichtiano a Eoceno medio basal), y del cabo Campo del Medio (Eoceno), integran sobre la costa atlantica una columna estratigrafica compuesta, relativamente completa del Santoniano al Eoceno superior. Dataciones paleontologicas e inferencias tectonicas en cuerpos conglomeradicos y discordancias, acotan la edad de tres pulsos principales de levantamiento de los Andes fueguinos en el Campaniano tardio-?Maastrichtiano temprano; Paleoceno medio-tardio; y Eoceno medio basal, respectivamente. Los ultimos inoceramidos hallados son del Campaniano temprano, pero probablemente su desaparicion en los Andes Fueguinos ocurra en el Maastrichtiano, conjuntamente con un marcado cambio de condiciones de fondo, de disoxicas-anoxicas en el Campaniano tardio-?Maastrichtiano inferior a oxicas en el Maastrichtiano tardio

Miocene foraminifera from the Neuquén Basin, Argentina: stratigraphic and paleoenvironmental implications

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.