Browsing by Author "Cuitiño, JI"
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Item Open Access An improved approach to age-modeling in deep time: Implications for the Santa Cruz Formation, Argentina(Bulletin of the Geological Society of America, 2020-01-01) Trayler, RB; Schmitz, MD; Cuitiño, JI; Kohn, MJ; Bargo, MS; Kay, RF; Strömberg, CAE; Vizcaíno, SF© 2019 Geological Society of America. Accurate age-depth models for proxy records are crucial for inferring changes to the environment through space and time, yet traditional methods of constructing these models assume unrealistically small age uncertainties and do not account for many geologic complexities. Here we modify an existing Bayesian age-depth model to foster its application for deep time U-Pb and 40Ar/39Ar geochronology. More flexible input likelihood functions and use of an adaptive proposal algorithm in the Markov Chain Monte Carlo engine better account for the age variability often observed in magmatic crystal populations, whose dispersion can reflect inheritance, crystal residence times and daughter isotope loss. We illustrate this approach by calculating an age-depth model with a contiguous and realistic uncertainty envelope for the Miocene Santa Cruz Formation (early Miocene; Burdigalian), Argentina. The model is calibrated using new, high-precision isotope dilution U-Pb zircon ages for stratigraphically located interbedded tuffs, whose weighted mean ages range from ca. 16.78 ± 0.03 Ma to 17.62 ± 0.03 Ma. We document how the Bayesian age-depth model objectively reallocates probability across the posterior ages of dated horizons, and thus produces better estimates of relative ages among strata and variations in sedimentation rate. We also present a simple method to propagate age-depth model uncertainties onto stratigraphic proxy data using a Monte Carlo technique. This approach allows us to estimate robust uncertainties on isotope composition through time, important for comparisons of terrestrial systems to other proxy records.Item Open Access Analysis of the Early-Middle Miocene mammal associations at the Río Santa Cruz (Patagonia, Argentina)(Publicacion Electronica de la Asociacion Paleontologica Argentina, 2019-01-01) Fernicola, JC; Vizcaíno, SF; Susana Bargo, M; Kay, RF; Cuitiño, JI© 2019 Asociacion Paleontologica Argentina. All rights reserved. The Santa Cruz Formation (SCF) records high latitude terrestrial paleoecosystems in the Southern Hemisphere during Burdigalian-early Langhian times (Early-Middle Miocene). Mammalian fossils from Río Santa Cruz (RSC) localities were first collected in the late 19th century, forming the basis for the Santacrucian South American Land Mammal Age. New collections permitt an update of the SCF mammalian species along the RSC. The total taxonomic richness is 95 mammalian species. Many species considered by Ameghino as exclusive for the older Notohippidian stage at similar latitude in the west, are not in fact so. The taxonomic richness in three localities along the RSC is substantially different: 47 species from Barrancas Blancas (BB), 60 from Segundas Barrancas Blancas (SBB) and nine from Yaten Huageno. The faunal composition between BB and SBB is also different: they share 31 species, of which six are present only at BB and 20 only at SBB. More than 85 % of all RSC species are also found at Atlantic coastal exposures of the SCF. In spite of BB (~17.04-16.49 Ma) being closer in age to coastal exposures, and SBB fossils (~16.46-15.63 Ma) being younger than the coastal localities (~17.80-16.30 Ma), the greatest similarity is between SBB and the coast. Faunal differences among the localities may be accounted for local variation in climatic and environmental factors. Previously proposed Santacrucian biozones should be set aside. The exposures of the SCF along the RSC should be considered as the type area of this unit and the Santacrucian fauna.Item Open Access Fossil localities of the Santa Cruz Formation (Early Miocene, Patagonia, Argentina) prospected by Carlos Ameghino in 1887 revisited and the location of the Notohippidian(Journal of South American Earth Sciences, 2014-01-01) Fernicola, JC; Cuitiño, JI; Vizcaíno, SF; Bargo, MS; Kay, RFBetween January and September of 1887 Carlos Ameghino carried out his first geologic and paleontological expedition to the Río Santa Cruz, Patagonia. Based on the fossils and geologic information compiled, in 1887 and 1889, Florentino Ameghino named more than 120 new species of extinct mammals and his Formación Santacruceña and Piso Santacruceño (Santacrucian stage). Data published by both brothers state that the specimens were collected in outcrops by the Río Santa Cruz, between 90 and 200km west of its mouth. However, information in the posthumously published letters and Travel Diary of C. Ameghino allows us to recognize a fourth locality, Río Bote, at about 50km further southwest. In 1900, 1902, F. Ameghino divided the Piso Santacruceño in a younger étage Santacruzienne and older étage Notohippidéen, restricting the geographical distribution of the latter to Kar Aiken locality, northeast of Lago Argentino. However, 15 of the 54 species that F. Ameghino listed as exclusively Notohippidian stage already had been named on specimens collected South to the Río Santa Cruz in 1887, two year prior to C. Ameghino's first visit to Kar Aiken. Based on historical information and several expeditions to the Río Santa Cruz and its environs, in this contribution we establish the geographical locations of the 1887 localities, formalize their names, evaluate the stratigraphic position of the fossil-bearing levels, and analyze the geographic extension of the Notohippidian, inferring that Río Bote is where C. Ameghino first collected species that came to define the Notohippidian. © 2014 Elsevier Ltd.Item Open Access Fossil Localities Of The Santa Cruz Formation (Lower Miocene, Patagonia, Argentina) Prospected By Carlos Ameghino In 1887. The Problem Of The Notohippidian Stage(South American Journal of Earth Sciences, 2014) Fernicola, JC; Cuitiño, JI; Vizcaíno, SF; Bargo, MS; Kay, RFItem Open Access Fossil vertebrates of the early-middle Miocene Cerro Boleadoras Formation, northwestern Santa Cruz Province, Patagonia, Argentina(Andean Geology, 2022-09-01) Vizcaíno, SF; Bargo, MS; Pérez, ME; Aramendía, I; Cuitiño, JI; Monsalvo, ES; Vlachos, E; Noriega, JI; Kay, RFThe early-middle Miocene continental Cerro Boleadoras Formation (CBF) crops out in the area of Cerro Boleadoras and Cerro Plomo on the western slope of the Meseta del Lago Buenos Aires, northwestern Santa Cruz Province, Argentina. The lower levels of the CBF consist of laterally extensive medium to pebbly sandstone beds with trough cross-bedding, interpreted as fluvial channel deposits, interbedded with tabular fine-grained floodplain deposits. Recent fieldwork provided fossil vertebrates from these levels with an estimated age between ~16.5 Ma and 15.1 Ma (late Burdigalian-early Langhian). The studied section temporally overlaps with the middle or upper sections of the Santa Cruz Formation (SCF) in the Austral-Magallanes Basin of southern Patagonia, the Río Frías Formation in Chile, and the lower Collón Curá Formation of northern Patagonia. We compile an integrated faunal list for this locality, including specimens from previous collections, and discuss its chronological and paleoenvironmental implications. The taxa list includes most of the groups recorded in the SCF: one anuran, three birds, and at least 33 mammals (metatherians, xenarthrans, litopterns, notoungulate typotheres and caviomorph rodents), indicating a Santacrucian age sensu lato. We also recorded a testudine, which constitutes the southernmost record of tortoises in South America and worldwide. Faunal dissimilarities between the vertebrate fossil content of the CBF and the mentioned sections of the Santa Cruz, Río Frías and Collón Curá formations may reflect ecologic, climatic and geographic differences rather than temporal ones. The co-occurrence of arboreal or semiarboreal, browsing, frugivorous, and grazing mammals suggests the presence of both forested and open environments for the area occupied by the CBF rocks. However, it is not possible to discern whether these two environments coexisted or alternated, and whether one environment predominated over the other. Marker taxa, such as the chinchillid rodents Prolagostomus and Pliolagostomus, and the typothere Pachyrukhos indicate a trend to aridification during the Miocene in southern Patagonia, as previously reported for the upper part of the SCF along the Río Santa Cruz and south to the Río Coyle, along the Atlantic coast and the Río Gallegos.Item Open Access Insights on the controls on floodplain-dominated fluvial successions: A perspective from the early–middle miocene santa cruz formation in río chalía (patagonia, argentina)(Journal of the Geological Society, 2021-01-01) Cuitiño, JI; Raigemborn, MS; Bargo, MS; Vizcaíno, SF; Muñoz, NA; Kohn, MJ; Kay, RFThe Santa Cruz Formation (SCF) in Río Chalía (Austral Basin, Patagonia, Argentina) is a well-exposed fluvial succession with abundant and diverse fossil vertebrates accumulated during the Miocene Climatic Optimum (MCO). Using facies analysis, characterization of stratigraphic architecture, U–Pb geochronology and vertebrate palaeontology, we assess the timing and interplay of controlling factors on the sedimentation, including tectonics, global sea level, climate and sediment supply. Throughout the succession, there occurred a constant aggradation of the floodplain-dominated fluvial system. Seven zircon U–Pb ages constrain the time of accumulation between c. 18 and 15.2 Ma, under a relatively constant sedimentation rate of 150 ± 50 m myr–1 . The large number of fossil vertebrates indicates a Santacrucian fauna, showing no recognizable changes through the section. The basin-scale, low-gradient anastomosed fluvial system of the SCF records a period of about 3 myr of relatively constant environmental conditions controlled by continuous basin subsidence and high sediment supply conditioned by explosive volcanism together with weathering of uplifting terrains in the Andes. In addition, the system was influenced by a temperate to warm and subhumid climate favoured by the MCO before the onset of the Andean rain shadow, together to high global sea levels.Item Open Access Paleoenvironments and paleoecology of the Santa Cruz Formation (early-middle Miocene) along the Río Santa Cruz, Patagonia (Argentina)(Journal of South American Earth Sciences, 2021-08) Kay, RF; Vizcaíno, SF; Bargo, MS; Spradley, JP; Cuitiño, JIItem Open Access Patagonian Aridification at the Onset of the mid‐Miocene Climatic Optimum(Paleoceanography and Paleoclimatology) Trayler, RB; Kohn, MJ; Bargo, MS; Cuitiño, JI; Kay, RF; Strömberg, CAE; Vizcaíno, SFItem Open Access Reconstructing Cenozoic Patagonian biotas using multi-proxy fossil records(Journal of South American Earth Sciences, 2021-12-01) Palazzesi, L; Vizcaíno, SF; Barreda, VD; Cuitiño, JI; del Río, CJ; Goin, F; González Estebenet, MS; Guler, MV; Gandolfo, MA; Kay, R; Parras, A; Reguero, MA; Zamaloa, MDCThe fossil record from Cenozoic sediments provides a great deal of information that has direct bearing on the early assembling of modern Patagonian ecosystems. In this synthesis, we revise selected fossil marine and terrestrial records from the last 66 Ma with the aim of understanding major shifts of Patagonian biotas. From the Paleocene to the mid Eocene this region supported outstandingly diverse terrestrial assemblages that show strong connections to modern-day Australasia (e.g. gum trees, casuarinas, monotremes). Nearshore marine biotas confirm peak warmth conditions, with tropical species with Tethyan affinities. The late Eocene and early Oligocene marks the onset of a period of overall regional cooling, drying, and increasingly variable ecological conditions. The rise of palm-dominated flammable biomes in hinterlands and the prevalence of Gondwanan gallery forest (e.g. southern beeches and podocarps) along river-sides supported the existence of mosaic habitats maintained by edaphic and regional climatic conditions. This shift in landscapes reflects the evolution of a wide range of herbivorous mammals (e.g. Notoungulata, Litopterna, and Astrapotheria). The late Oligocene and early-to-mid Miocene witnessed a dramatic modification of landscapes including the incursion of high sea-level episodes, the emergence of specialized coastal (i.e. salt-marsh) plant taxa and the expansion of large herbivorous mammals with predominantly high-crowned teeth (e.g. Notoungulata: Hegetotheriidae, Interatheriidae, and Mesotheriidae). The cooling trend of this interval was interrupted by a mid-Miocene transient warming event, with the dispersion of terrestrial (e.g. platyrrhine monkeys, palms) and marine (e.g. Tuberculodinium vancampoae) elements with tropical affinity into southernmost South American regions. Seasonally-dry conditions increased towards the end of the Miocene, yet subtropical species persisted either in terrestrial (e.g. malpighs, passion vines, capybaras), and marine (e.g. Subtropical and Caribbean molluscs) environments. The increasing aridity caused by the Andean uplift wiped out most of the forest species and promoted the diversification of open-habitat species; the emergence of the current grass-dominated Patagonian Steppe occurred later on, probably during the Quaternary.Item Open Access U-Pb geochronology of the Santa Cruz Formation (early Miocene) at the Río Bote and Río Santa Cruz (southernmost Patagonia, Argentina): Implications for the correlation of fossil vertebrate localities(Journal of South American Earth Sciences, 2016-10-01) Cuitiño, JI; Fernicola, JC; Kohn, MJ; Trayler, R; Naipauer, M; Bargo, MS; Kay, RF; Vizcaíno, SF© 2016 Elsevier Ltd.The early Miocene Santa Cruz Formation (SCF) in southern Patagonia hosts the Santacrucian South American Land Mammal Age (SALMA), whose age is known mainly from exposures along the Atlantic coast. Zircon U-Pb ages were obtained from intercalated tuffs from four inland sections of the SCF: 17.36 ± 0.63 Ma for the westernmost Río Bote locality, and 17.04 ± 0.55 Ma-16.32 ± 0.62 Ma for central Río Santa Cruz localities. All ages agree with the bounding age of underlying marine units and with equivalent strata in coastal exposures. New ages and available sedimentation rates imply time spans for each section of ~18.2 to 17.36 Ma for Río Bote and 17.45-15.63 Ma for central Río Santa Cruz (Burdigalian). These estimates support the view that deposition of the SCF began at western localities ~1 Ma earlier than at eastern localities, and that the central Río Santa Cruz localities expose the youngest SCF in southern Santa Cruz Province. Associated vertebrate faunas are consistent with our geochronologic synthesis, showing older (Notohippidian) taxa in western localities and younger (Santacrucian) taxa in central localities. The Notohippidian fauna (19.0-18.0 Ma) of the western localities is synchronous with Pinturan faunas (19.0-18.0 Ma), but older than Santacrucian faunas of the Río Santa Cruz (17.2-15.6 Ma) and coastal localities (18.0-16.2 Ma). The Santacrucian faunas of the central Río Santa Cruz localities temporally overlap Colloncuran (15.7 Ma), Friasian (16.5 Ma), and eastern Santacrucian faunas.