The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Forma...The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Formation. The basal part of this unit, which was deposited in high-gradient topographic relief, is composed of conglomerates and sandstones with thin layers of reworked tuffs. The lithofacies associations of the basal part indicate that the depositional mechanisms were mantled and gravitational flows.The middle part of the unit consists of fine sandstones, limestones, and black siltstones that were deposited in low-energy fluvial and lacustrine environments. The outcrops are located along the NEe SW direction and the major thickest units represented by limestones and siltstones, occur near the southeastern border of this NEeS W depocenter. Since the rhyolitic and trachytic lava flows and tuffs of the Marifil Volcanic Complex are interbedded with the sedimentary sequences of the Puesto Piris Formation,both units are coeval. Zircon Ue Pb age was obtained for a trachytic lava flow(193.4 ±3.1 Ma) suggesting that sedimentation and volcanism are Sinemurian. This extensional episode was recorded in the eastern,western, and southwestern sectors of the North Patagonian Massif, and is possibly associated with the Gondwana supercontinent breakup.展开更多
The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment.Four of these lit...The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment.Four of these lithofacies represent distal glacimarine environments, whereas another one was deposited in proximal glacimarine environments, and the last includes subglacial environments. The organization and configuration of these lithofacies associations represent the advance and retreat of the glacier masses. The maximum glacial advance is correlatable with the G2 glacial interval of the Pennsylvanian Pampa de Tepuel, Las Salinas and Valley Chico, formations of the Extraandean Chubut, and the southern part of Neuquen Cordillera. Contemporaneously, in southern Chile there are marine and glacimarine sediments. The chronostratigraphic relationships between the Silurian to Permian units allow five paleogeographic stages to be distinguished. The middle Silurian-late Devonian igneous rocks represent the first magmatic stage. The second stage, which is transitional to the first, is represented by a marine basin that includes the late Devonian-early Carboniferous Esquel and Rio Pescado formations and the Llanquihue Complex. The third stage(early-late Carboniferous) includes granitoids of the second magmatic event that partially overlapped the first magmatic igneous belt. The fourth stage belongs to the late Carboniferous sedimentation of the Cushamen and equivalent formations. The extended early Permian magmatism was the last Paleozoic event in the studied area.展开更多
The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geol...The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geologic evolution of the Central Patagonian Andes, we carried out geochronologic(U-Pb and^(40)Ar/^(39)Ar), provenance, stratigraphic, sedimentologic, and geochemical studies on the sedimentary and volcanic Cenozoic deposits that crop out in the Meseta Guadal and Chile Chico areas(~47°S). Our data indicate the presence of a nearly complete Cenozoic record, which refutes previous interpretations of a hiatus during the middle Eocene-late Oligocene in the Central Patagonian Andes. Our study suggests that the fluvial strata of the Ligorio Marquez Formation and the flood basalts of the Basaltos Inferiores de la Meseta Chile Chico Formation were deposited in an extensional setting related to the subduction of the Aluk-Farallon spreading ridge during the late Paleocene-Eocene. Geochemical data on volcanic rocks interbedded with fluvial strata of the San Jose Formation suggest that this unit was deposited in an extensional setting during the middle Eocene to late Oligocene. Progressive crustal thinning allowed the transgression of marine waters of Atlantic origin and deposition of the upper Oligocene-lower Miocene Guadal Formation. The fluvial synorogenic strata of the Santa Cruz Formation were deposited as a consequence of an important phase of compressive deformation and Andean uplift during the early-middle Miocene. Finally, alkali flood basalts of the late middle to late Miocene Basaltos Superiores de la Meseta Chile Chico Formation were extruded in the area in response to the suduction of the Chile Ridge under an extensional regime. Our studies indicate that the tectonic evolution of the Central Patagonian Andes is similar to that of the North Patagonian Andes and appears to differ from that of the Southern Patagonian Andes, which is thought to have been the subject of continuous compressive deformation since the late Early Cretaceous.展开更多
The Patagonian Shelf is a very productive region with dif ferent ecosystem structures. A long history of fishing in the Southwestern Atlantic Ocean combined with a complex hydrographic structure, with a permanent fron...The Patagonian Shelf is a very productive region with dif ferent ecosystem structures. A long history of fishing in the Southwestern Atlantic Ocean combined with a complex hydrographic structure, with a permanent front over the shelf-break and dif ferent coastal frontal regions, and a wide non-frontal area in between have made the food web in this area more complex and have resulted in changes to the spatialtemporal scale. Stable isotopes of carbon and nitrogen were used to determine the trophic structure of the Patagonian shelf break which was previously poorly understood. The results indicated that the average δ^(15)N value of pelagic guild(I llex argentinus) was remarkable lower than those of the other guilds. The δ^(13)C values of almost all species ranged from-17‰ to-18‰, but S tromateus brasiliensis had a significant lower δ^(13)C value. Compared with the southern Patagonian shelf, short food chain length also occurred. The impact of complex oceanographic structures has resulted in food web structure change to the temporal-spatial scale on the Patagonian shelf. The Patagonian shelf break can be considered as a separated ecosystem structure with lower δ^(15)N values.展开更多
Ligands present in dissolved organic matter(DOM) form complexes with inorganic divalent mercury(Hg2+) afecting its bioavailability in pelagic food webs. This investigation addresses the influence of a natural gradient...Ligands present in dissolved organic matter(DOM) form complexes with inorganic divalent mercury(Hg2+) afecting its bioavailability in pelagic food webs. This investigation addresses the influence of a natural gradient of DOM present in Patagonian lakes on the bioaccumulation of Hg2+(the prevailing mercury species in the water column of these lakes) by the algae Cryptomonas erosa and the zooplankters Brachionus calyciflorus and Boeckella antiqua. Hg2+accumulation was studied through laboratory experiments using natural water of four oligotrophic Patagonian lakes amended with197Hg2+. The bioavailability of Hg2+was afected by the concentration and character of DOM. The entrance of Hg2+into pelagic food webs occurs mostly through passive and active accumulation. The incorporation of Hg2+by Cryptomonas, up to 27% of the Hg2+amended, was found to be rapid and dominated by passive adsorption,and was greatest when low molecular weight compounds with protein-like or small phenolic signatures prevailed in the DOM.Conversely, high molecular weight compounds with a humic or fulvic signature kept Hg2+in the dissolved phase, resulting in the lowest Hg2+accumulation in this algae. In Brachionus and Boeckella the direct incorporation of Hg from the aqueous phase was up to3% of the Hg2+amended. The dietary incorporation of Hg2+by Boeckella exceeded the direct absorption of this metal in natural water,and was remarkably similar to the Hg2+adsorbed in their prey. Overall, DOM concentration and character afected the adsorption of Hg2+by algae through competitive binding, while the incorporation of Hg2+into the zooplankton was dominated by trophic or dietary transfer.展开更多
We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations on a biotite paraschist and on a tonalitic orthogneiss of the Yaminue Complex,and re-evaluate this complex in the broader context of the tect...We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations on a biotite paraschist and on a tonalitic orthogneiss of the Yaminue Complex,and re-evaluate this complex in the broader context of the tectonic evolution of the Patagonia composite terrane.In the metasedimentary unit (msuYC),the youngest detrital zircon dated at 318±5 Ma(Mississippian/Pennsylvanian boundary) indicates a Pennsylvanian(or younger) depositional age.The three main age populations peak at 474,454 and 374 Ma.Preliminary Hf isotope data for two detrital zircons(447 and 655 Ma) yieldedε(Hf) values of -0.32 and 0.48,indicating that their primary sources contained small amounts of recycled crustal components(of Calymmian age;T_(DM) 1.56 Ga).Zircons from the orthogneiss(miuYC;intrusive into msuYC) show a crystallization age of 261.3±2.7 Ma(Capitanian;late middle Permian) which is broadly coeval with deformation,and Neoarchean-Paleoproterozoic inheritance.Meaningful core-rim relationship between Neoarchean zircon cores and late Permian rims is well defined,indicating the occurrence of Archean crust in this sector of Patagonia.Hf T_(DM) of Permian zircons is mainly Meso-Paleoarchean(2.97-3.35 Ga),with highly negativeε(Hf) values(ca.-33).Hf T_(DM) of inherited Neoarchean zircon cores is also Meso-Paleoarchean(3.14-3.45 Ga) but more juvenile(ε(Hf) = -0.3).Hf isotopes reinforce the presence of unexposed ancient crust in this area. Combining geological and isotope data,as well as geophysical models,we identify the Yaminue Complex within the La Esperanza-Yaminue crustal block flanked by two other,distinct crustal blocks:the Eastern block which forms part of the Patagonia terrane sensu stricto,located in the eastern Patagonian region,and the Western block forming part of the Southern Patagonia terrane.Their origins and timing of amalgamation to form the Patagonia composite terrane are also discussed.展开更多
Aims In arid communities,it has been proposed that individual plants can extend their roots beyond their canopy exploring neighbour-ing bare ground areas.This becomes relevant in systems where the vegetation is distri...Aims In arid communities,it has been proposed that individual plants can extend their roots beyond their canopy exploring neighbour-ing bare ground areas.This becomes relevant in systems where the vegetation is distributed in patches surrounded by bare soil.However,whether roots of different species may be overlapping under bare ground areas is still controversial.The factors control-ling root responses when no plants appear to be directly influ-encing the gap among patches are still unclear.The aim of our study was to detect perennial grasses responses to an N enrich-ment pulse.Methods In a semi-arid steppe(Patagonia,Argentina),we buried root traps filled with sieved soil with and without N addition,under bare soil patches.Traps were harvested after 4 and 6 months.Trap neighbour-hoods(30 cm in diameter)included at least three of the dominant tussock species.After harvests,we identified species in the traps by root traits and quantified diversity,biomass and specific relative growth rates.Important Findings Bare ground areas show simultaneous root growth of different spe-cies.Diversity of perennial grass roots was higher with N addition than without it in the first harvest(4 months),but this difference disappeared in the second harvest(6 months).Root biomass was maximal after 6 months in N addition traps.Species preferred by herbivores(Bromus pictus and Poa ligularis)showed rapid growth and responses to N addition.Differences between harvests may be an indicative that N pulses interact with rising temperatures and soil water content as growing season progress.展开更多
基金part of the research project "Gondwánico y Patagonídico del Macizo Nordpatagónico occidental" (24/H121) granted by the Universidad Nacional del Sur, "Significado y evolución de los eventos tectonomagmáticos Gondwánicos y Patagonídicos del norte de Patagonia" (11220150100184CO) granted by CONICET
文摘The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Formation. The basal part of this unit, which was deposited in high-gradient topographic relief, is composed of conglomerates and sandstones with thin layers of reworked tuffs. The lithofacies associations of the basal part indicate that the depositional mechanisms were mantled and gravitational flows.The middle part of the unit consists of fine sandstones, limestones, and black siltstones that were deposited in low-energy fluvial and lacustrine environments. The outcrops are located along the NEe SW direction and the major thickest units represented by limestones and siltstones, occur near the southeastern border of this NEeS W depocenter. Since the rhyolitic and trachytic lava flows and tuffs of the Marifil Volcanic Complex are interbedded with the sedimentary sequences of the Puesto Piris Formation,both units are coeval. Zircon Ue Pb age was obtained for a trachytic lava flow(193.4 ±3.1 Ma) suggesting that sedimentation and volcanism are Sinemurian. This extensional episode was recorded in the eastern,western, and southwestern sectors of the North Patagonian Massif, and is possibly associated with the Gondwana supercontinent breakup.
文摘The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment.Four of these lithofacies represent distal glacimarine environments, whereas another one was deposited in proximal glacimarine environments, and the last includes subglacial environments. The organization and configuration of these lithofacies associations represent the advance and retreat of the glacier masses. The maximum glacial advance is correlatable with the G2 glacial interval of the Pennsylvanian Pampa de Tepuel, Las Salinas and Valley Chico, formations of the Extraandean Chubut, and the southern part of Neuquen Cordillera. Contemporaneously, in southern Chile there are marine and glacimarine sediments. The chronostratigraphic relationships between the Silurian to Permian units allow five paleogeographic stages to be distinguished. The middle Silurian-late Devonian igneous rocks represent the first magmatic stage. The second stage, which is transitional to the first, is represented by a marine basin that includes the late Devonian-early Carboniferous Esquel and Rio Pescado formations and the Llanquihue Complex. The third stage(early-late Carboniferous) includes granitoids of the second magmatic event that partially overlapped the first magmatic igneous belt. The fourth stage belongs to the late Carboniferous sedimentation of the Cushamen and equivalent formations. The extended early Permian magmatism was the last Paleozoic event in the studied area.
基金funded by Fondecyt Projects(Nos. 1151146 and 1110914)Programa de Fomento y Transferencia tecnológica en Exploración Minera, código BIP № 30114940-0, PIP CONICET 2015-2017 No. 11220150100426,UBACYT 2015-2017 No. 20020150100166BA, PICT 2016 No. 2252, NSF EAR-165031the Yale Institute for Biospheric Studies
文摘The Central Patagonian Andes is a particular segment of the Andean Cordillera that has been subjected to the subduction of two spreading ridges during Eocene and Neogene times. In order to understand the Cenozoic geologic evolution of the Central Patagonian Andes, we carried out geochronologic(U-Pb and^(40)Ar/^(39)Ar), provenance, stratigraphic, sedimentologic, and geochemical studies on the sedimentary and volcanic Cenozoic deposits that crop out in the Meseta Guadal and Chile Chico areas(~47°S). Our data indicate the presence of a nearly complete Cenozoic record, which refutes previous interpretations of a hiatus during the middle Eocene-late Oligocene in the Central Patagonian Andes. Our study suggests that the fluvial strata of the Ligorio Marquez Formation and the flood basalts of the Basaltos Inferiores de la Meseta Chile Chico Formation were deposited in an extensional setting related to the subduction of the Aluk-Farallon spreading ridge during the late Paleocene-Eocene. Geochemical data on volcanic rocks interbedded with fluvial strata of the San Jose Formation suggest that this unit was deposited in an extensional setting during the middle Eocene to late Oligocene. Progressive crustal thinning allowed the transgression of marine waters of Atlantic origin and deposition of the upper Oligocene-lower Miocene Guadal Formation. The fluvial synorogenic strata of the Santa Cruz Formation were deposited as a consequence of an important phase of compressive deformation and Andean uplift during the early-middle Miocene. Finally, alkali flood basalts of the late middle to late Miocene Basaltos Superiores de la Meseta Chile Chico Formation were extruded in the area in response to the suduction of the Chile Ridge under an extensional regime. Our studies indicate that the tectonic evolution of the Central Patagonian Andes is similar to that of the North Patagonian Andes and appears to differ from that of the Southern Patagonian Andes, which is thought to have been the subject of continuous compressive deformation since the late Early Cretaceous.
基金Supported by the National Key Technology R&D Program of China(No.2013BAD13B03)the National Natural Science Foundation of China(No.41776185)the Special Fund for Agro-Scientifi c Research in the Public Interest of China(No.201203018)
文摘The Patagonian Shelf is a very productive region with dif ferent ecosystem structures. A long history of fishing in the Southwestern Atlantic Ocean combined with a complex hydrographic structure, with a permanent front over the shelf-break and dif ferent coastal frontal regions, and a wide non-frontal area in between have made the food web in this area more complex and have resulted in changes to the spatialtemporal scale. Stable isotopes of carbon and nitrogen were used to determine the trophic structure of the Patagonian shelf break which was previously poorly understood. The results indicated that the average δ^(15)N value of pelagic guild(I llex argentinus) was remarkable lower than those of the other guilds. The δ^(13)C values of almost all species ranged from-17‰ to-18‰, but S tromateus brasiliensis had a significant lower δ^(13)C value. Compared with the southern Patagonian shelf, short food chain length also occurred. The impact of complex oceanographic structures has resulted in food web structure change to the temporal-spatial scale on the Patagonian shelf. The Patagonian shelf break can be considered as a separated ecosystem structure with lower δ^(15)N values.
基金funded by Agencia Nacional de Promoción Científica y Tecnológica (ANPCyT PICT 200700393)Consejo Nacional de Investigaciones Científicas y Tcnicas(CONICET PIP 11220100100064)+1 种基金International Atomic Energy Agency(IAEA TCP ARG7007)Universidad Nacional del Comahue(Program 04-B166)
文摘Ligands present in dissolved organic matter(DOM) form complexes with inorganic divalent mercury(Hg2+) afecting its bioavailability in pelagic food webs. This investigation addresses the influence of a natural gradient of DOM present in Patagonian lakes on the bioaccumulation of Hg2+(the prevailing mercury species in the water column of these lakes) by the algae Cryptomonas erosa and the zooplankters Brachionus calyciflorus and Boeckella antiqua. Hg2+accumulation was studied through laboratory experiments using natural water of four oligotrophic Patagonian lakes amended with197Hg2+. The bioavailability of Hg2+was afected by the concentration and character of DOM. The entrance of Hg2+into pelagic food webs occurs mostly through passive and active accumulation. The incorporation of Hg2+by Cryptomonas, up to 27% of the Hg2+amended, was found to be rapid and dominated by passive adsorption,and was greatest when low molecular weight compounds with protein-like or small phenolic signatures prevailed in the DOM.Conversely, high molecular weight compounds with a humic or fulvic signature kept Hg2+in the dissolved phase, resulting in the lowest Hg2+accumulation in this algae. In Brachionus and Boeckella the direct incorporation of Hg from the aqueous phase was up to3% of the Hg2+amended. The dietary incorporation of Hg2+by Boeckella exceeded the direct absorption of this metal in natural water,and was remarkably similar to the Hg2+adsorbed in their prey. Overall, DOM concentration and character afected the adsorption of Hg2+by algae through competitive binding, while the incorporation of Hg2+into the zooplankton was dominated by trophic or dietary transfer.
基金financial support from Research Grant PiP- 11220090100181(CONICET,Council for Scientific and Technical Research of Argentina) and SEGEMARBSE(Back-Scattered Electrons) images were carried out using facilities at the CMCA(Centre for Microscopy,Characterization,and Analyses),which is supported by funding from UWA and the governments of Western Australia and Australia
文摘We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations on a biotite paraschist and on a tonalitic orthogneiss of the Yaminue Complex,and re-evaluate this complex in the broader context of the tectonic evolution of the Patagonia composite terrane.In the metasedimentary unit (msuYC),the youngest detrital zircon dated at 318±5 Ma(Mississippian/Pennsylvanian boundary) indicates a Pennsylvanian(or younger) depositional age.The three main age populations peak at 474,454 and 374 Ma.Preliminary Hf isotope data for two detrital zircons(447 and 655 Ma) yieldedε(Hf) values of -0.32 and 0.48,indicating that their primary sources contained small amounts of recycled crustal components(of Calymmian age;T_(DM) 1.56 Ga).Zircons from the orthogneiss(miuYC;intrusive into msuYC) show a crystallization age of 261.3±2.7 Ma(Capitanian;late middle Permian) which is broadly coeval with deformation,and Neoarchean-Paleoproterozoic inheritance.Meaningful core-rim relationship between Neoarchean zircon cores and late Permian rims is well defined,indicating the occurrence of Archean crust in this sector of Patagonia.Hf T_(DM) of Permian zircons is mainly Meso-Paleoarchean(2.97-3.35 Ga),with highly negativeε(Hf) values(ca.-33).Hf T_(DM) of inherited Neoarchean zircon cores is also Meso-Paleoarchean(3.14-3.45 Ga) but more juvenile(ε(Hf) = -0.3).Hf isotopes reinforce the presence of unexposed ancient crust in this area. Combining geological and isotope data,as well as geophysical models,we identify the Yaminue Complex within the La Esperanza-Yaminue crustal block flanked by two other,distinct crustal blocks:the Eastern block which forms part of the Patagonia terrane sensu stricto,located in the eastern Patagonian region,and the Western block forming part of the Southern Patagonia terrane.Their origins and timing of amalgamation to form the Patagonia composite terrane are also discussed.
基金Funding was provided by grants from FONCyT(PICT 00462)Universidad de Buenos Aires Ciencia y Técnica(UBACyT G0032)to MR Aguiar.
文摘Aims In arid communities,it has been proposed that individual plants can extend their roots beyond their canopy exploring neighbour-ing bare ground areas.This becomes relevant in systems where the vegetation is distributed in patches surrounded by bare soil.However,whether roots of different species may be overlapping under bare ground areas is still controversial.The factors control-ling root responses when no plants appear to be directly influ-encing the gap among patches are still unclear.The aim of our study was to detect perennial grasses responses to an N enrich-ment pulse.Methods In a semi-arid steppe(Patagonia,Argentina),we buried root traps filled with sieved soil with and without N addition,under bare soil patches.Traps were harvested after 4 and 6 months.Trap neighbour-hoods(30 cm in diameter)included at least three of the dominant tussock species.After harvests,we identified species in the traps by root traits and quantified diversity,biomass and specific relative growth rates.Important Findings Bare ground areas show simultaneous root growth of different spe-cies.Diversity of perennial grass roots was higher with N addition than without it in the first harvest(4 months),but this difference disappeared in the second harvest(6 months).Root biomass was maximal after 6 months in N addition traps.Species preferred by herbivores(Bromus pictus and Poa ligularis)showed rapid growth and responses to N addition.Differences between harvests may be an indicative that N pulses interact with rising temperatures and soil water content as growing season progress.