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A 40 años de la instalación del Laboratorio de Radiocarbono en el Museo de La Plata
(Fundación Museo de La Plata "Francisco Pascacio Moreno", 2017-11) Mari, Florencia; Carbonari, Jorge Eduardo; Huarte, Roberto Andrés
Los términos radiocarbono o carbono-14, que se encuentran ampliamente mencionados tanto en la literatura de divulgación como en la literatura científica, son utilizados con dos significados diferentes; por un lado, designan un método de medición cronológica que tiene por finalidad establecer edades en años de materiales provenientes de investigaciones arqueológicas, paleontológicas y de las geociencias, aplicándose también en estudios medioambientales, forenses y de historia del arte. Por otro lado, esos términos designan al isótopo radioactivo o inestable del carbono –de peso 14– que está presente en cantidades extremadamente pequeñas en la materia orgánica derivada de las plantas y animales, también como materia inorgánica en restos de moluscos y en algunos sedimentos y rocas.
A deformed alkaline igneous rock–carbonatite complex from the Western Sierras Pampeanas, Argentina: Evidence for late Neoproterozoic opening of the Clymene Ocean?
(Elsevier Science, 2008-12) Casquet, C.; Pankhurst, R .J.; Galindo, C.; Rapela, Carlos Washington; Fanning, C. M.; Baldo, Edgardo Gaspar Agustin; Dahlquist, Juan Andrés; González Casado, J. M.; Colombo, Fernando
A deformed ca. 570Ma syenite–carbonatite body is reported from a Grenville-age (1.0–1.2 Ga) terrane in the Sierra de Maz, one of theWestern Sierras Pampeanas of Argentina. This is the first recognition of such a rock assemblage in the basement of the Central Andes. The two main lithologies are coarse-grained syenite (often nepheline-bearing) and enclave-rich fine-grained foliated biotite–calcite carbonatite. Samples of carbonatite and syenite yield an imprecise whole rock Rb–Sr isochron age of 582±60Ma (MSWD= 1.8; Sri = 0.7029); SHRIMP U–Pb spot analysis of syenite zircons shows a total range of 206Pb–238Uages between 433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525±7Ma (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. 433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525±7Ma (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. Sri = 0.7029); SHRIMP U–Pb spot analysis of syenite zircons shows a total range of 206Pb–238Uages between 433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525±7Ma (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. 433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525±7Ma (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. ±60Ma (MSWD= 1.8; Sri = 0.7029); SHRIMP U–Pb spot analysis of syenite zircons shows a total range of 206Pb–238Uages between 433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525±7Ma (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. 433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525±7Ma (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. 206Pb–238Uages between 433 and 612 Ma, with a prominent peak at 560–580Ma defined by homogeneous zircon areas. Textural interpretation of the zircon data, combined with the constraint of the Rb–Sr data suggest that the carbonatite complex formed at ca. 570 Ma. Further disturbance of the U–Pb system took place at 525±7Ma (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. ±7Ma (Pampean orogeny) and at ca. 430–440Ma (Famatinian orogeny) and it is concluded that the Western Sierras Pampeanas basement was joined to Gondwana during both events. Highly unradiogenic 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. 87Sr/86Sr values in calcites (0.70275–0.70305) provide a close estimate for the initial Sr isotope composition of the carbonatite magma. Sm–Nd data yield Nd570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust. 570 values of +3.3 to +4.8. The complex was probably formed during early opening of the Clymene Ocean from depleted mantle with a component from Meso/Neoproterozoic lower continental crust.
A detailed analysis of crevasse and overbank splay units in the Isaac formation (Windermere supergroup), of the southern canadian cordillera
(Geological Society of America, 2008) Khan, Zishann; Arnott, R. W. C; Schwarz, Ernesto; Altosaar, Andrés
Crevasse and overbank splay deposits have been studied in detail within the Isaac Formation. Crevasse splay units (CSU) range from 10 – 20 m thick and extend the length of the study area (> 4 km). Strata within CSU comprise medium to coarse sandstone Ta-c turbidites that range from 0.2 – 1 m thick and are interstratified with thinly-bedded tc-e turbidites. In addition, distinctively matrix-rich sandstone form up to 7 m thick packages intercalated with the turbidites. CSU are interpreted to have been deposited outboard of a crevasse channel that most likely breached the outer-bend channel margin. Episodically a number of high-energy expanding flows went through a hydraulic jump and deposited the matrix-rich sandstone. At other times, or at least locally, flows remained subcritical and deposited the more common turbidites. OSU are common in the outer-bend distal levee setting of a significant channel-levee complex and encased by thinly-bedded turbidites. OSU consist of amalgamated normally graded to planar and cross-stratified medium-bedded, medium sandstone turbidites. OSU are 2 – 4 m thick and extend up to 1 km laterally, however, individual beds within units are laterally discontinuous. Lateral discontinuity is likely the result of rapid flow thinning, filling of topography on the distal levee, and to a lesser extent erosion. As a result, OSU comprise a complex arrangement of sandstone turbidites that commonly offlap and onlap one another locally creating high N:G within the predominantly muddy distal levee. OSU were deposited by turbidity currents that overtopped the channel margin without breaching the levee. These overspilling flows bypassed the proximal levee area because of the steep slope on the backside of the levee, and deposited much of their sediment on the reduced slope over the more distal levee.
A fossorial petalurid trace fossil from the Albian of Patagonia
(Academic Press Ltd - Elsevier Science Ltd, 2020-12) Genise, Jorge Fernando; Sánchez, María Victoria; Poire, Daniel Gustavo; Gonzalez, Mirta Gladys
Maichnus wetkaroae igen. isp. nov., from the Albian of Patagonia, is composed of two or three ellipsoidal oblate chambers connected to shafts that show swellings and concentrically laminated linings. Such laminated linings are also present in chambers, and probably originated by radial backfilling and/or the successive discharges of liquid organic excretions. This unique morphology occurs in paleosols showing evidence of waterlogging. Trace fossil morphology and the occurrence of traces in clusters in waterlogged soils indicate that M. wetkaroae igen. isp. nov. represents larval burrows of fossorial petalurids. This is the first record of Odonatan trace fossils from paleosols and also the oldest one. M. wetkaroae igen. isp. nov. is one of the oldest insect trace fossils recorded from paleosols. It represents the first and unique paleontological evidence of the ancient origin of the burrowing behavior of petalurids postulated only theoretically until now in evolutionary scenarios of Odonata.
A Maastrichtian insect assemblage from Patagonia sheds light on arthropod diversity previous to the K/Pg event
(Nature, 2023-12) Vera, Ezequiel Ignacio; Monferran, Mateo Daniel; Massaferro, Julieta; Sabater, Lara Milena; Gallego, Oscar Florencio; Perez Loinaze, Valeria Susana; Moyano Paz, Damián; Agnolin, Federico; Manabe, Makoto; Tsuhiji, Takanobu; Novas, Fernando Emilio
Insect faunas from the latest Cretaceous are poorly known worldwide. Particularly, in the Southern Hemisphere, there is a gap regarding insect assemblages in the Campanian-Maastrichtian interval. Here we present an insect assemblage from the Maastrichtian Chorrillo Formation, southern Argentina, represented by well-preserved and non-deformed, chitinous microscopic remains including head capsules, wings and scales. Identified clades include Chironomidae dipterans, Coelolepida lepidopterans, and Ephemeroptera. The assemblage taxonomically resembles those of Cenozoic age, rather than other Mesozoic assemblages, in being composed by diverse chironomids and lepidopterans. To the best of our knowledge, present discovery constitutes the first insect body fossils for the Maastrichtian in the Southern Hemisphere, thus filling the gap between well-known Early Cretaceous entomofaunas and those of Paleogene age. The presented evidence shows that modern clades of chironomids were already dominant and diversified by the end of the Cretaceous, in concert with the parallel radiation of aquatic angiosperms which became dominant in freshwater habitats. This exceptional finding encourages the active search of microscopic remains of fossil arthropods in other geological units, which could provide a unique way of enhancing our knowledge on the past diversity of the clade.
A multi-proxy approach to paleoenvironmental changes in the southwestern Río de la Plata area (Argentina) during Late Pleistocene
(Pergamon-Elsevier Science Ltd, 2019-04) Beilinson, Elisa; Raigemborn, María Sol; Rodriguez, Sergio Gabriel; Soibelzon, Esteban; Gasparini, Germán Mariano; Calvo Marcilese, María Lydia Valentina; Cusminsky, Gabriela Catalina; Mari, Florencia; Iacona, Facundo; Soibelzon, Leopoldo Héctor
In the southwestern margin of the Río de la Plata (Argentina), mining works have uncovered deposits that correspond to the last glacio-eustatic cycle (<120 Ky). Because deposits of this cycle are rare in the area, the studied succession provides an opportunity to study the paleoenvironmental and paleoclimatic evolution of the area during that time. Sedimentary analysis reveal an inner estuarine environment impacted by storm surges, followed by fluvial and eolian depositional environments. The paleontological record of the terrestrial deposits indicates open grasslands and semi-arid climatic conditions that can be biostratigraphically assigned to the Lujanian Stage (late Pleistocene). Nevertheless, the chronology of the succession is hereby modified based on OSL ages and geomorphological evidence suggesting that the lower levels of the studied succession are older than previously thought (i.e. MIS 5e instead of MIS 3). Relative changes of sea level are inferred: the estuarine deposits are related to a period of relative high sea-level (i.e. MIS 5e), and the subsequent fluvial system is associated to a global sea-level fall that reached its lowest point during MIS 2.
A Neoproterozoic paleokarstic surface in the upper Villa Mónica Formation, Tandilia System, Argentina: Preliminary constraints on its origin and diagenesis
(Universidade de São Paulo, 2013) Gómez Peral, Lucia; Poire, Daniel Gustavo; Sial, Alcides N.; Arrouy, Maria Julia
The Neoproterozoic sedimentary successions of the Tandilia Basin are constituted by a wide range of sedimentary rocks. We analyse the upper section of the Villa M´onica Formation constituted almost entirely by dolostones. C-isotope pathways and mudstones with dropstones, just below the dolostones, suggest this succession is a probable cap carbonate. Therefore, the model of its diagenetic evolution is consistent with trends of primary marine origin. The age of this unit is still under debate, but stromatolites, Sr isotope data and δ 13C curve suggest Cryogenian age. An uplift registered on top of the formation is related to period of intense erosion and weathering with generation of a karstic surface over the dolostones as a telodiagenetic surface. This important unconformity was situated, from palaeomagnetic studies, in 595 Ma and is characterized by dedolomitization, intense dissolution and precipitation if iron oxide minerals, chert and calcite. Siliceous cementation and replacement have probably occurred when pH dropped during sub-aerial exposure associated to sea-level fall of uncertain relation with glaciations. This surface constitutes the contact between Villa M´onica and Colombo formations, representing an extensive period of erosion, and called “Piedra Amarilla surface”. A few meters below, further evolution of the dissolution processes developed a paleokarstic subsurface recognized by presence of up to 3 m caverns filled by weathered dolomite. C-O isotope data in this level are typical of meteoric fluids interaction showing lower with respect to unaltered dolostone, δ 13C varying from -0.45 to -1.87 and δ 18O VPDB from -6.16 to -10.25 .
A New depositional model for the Upper Jurassic - Lower Cretaceous mixed carbonate-siliciclastic system in the Neuquén Basin, Argentina
(American Association of Petroleum Geologists, 2010) Zeller, Michael; Verwer, Klaas; Eberli, Gregor P.; Massaferro, José Luis; Schwarz, Ernesto; Spalletti, Luis Antonio
Outcrop subsurface correlation of the Upper Jurassic - Lower Cretaceous mixed carbonate siliciclastic system in the Neuquén Basin reveals a new understanding of the depositional system and in particular of the character of transitions between carbonate and clastic sedimentation. Seismic data imaging the Quintuco Formation in the Loma La Lata Field and outcrops of the time-equivalent Picún Leufú Formation in the southern Neuquén Basin both document a lower prograding unit dominantly composed of siliciclastics with an upwards-increasing carbonate content. An aggrading middle unit can be subdivided into a lower siliciclastic interval capped by a clean carbonate interval which in turn is overlain by an aggrading upper unit in which siltstones and sandstones alternate with minor carbonates. In the outcrop the low angle clinoforms of the lower unit contain facies transitions from quartz sandstone in the topsets to siltstone and shale in the bottomsets. The time equivalent clinoforms in the subsurface are characterized on seismic time-slices by shelf breaks that are paleo-shoreline parallel over hundreds of kilometers. In the middle and the upper unit the carbonates are represented by ooid-skeletal grainstone intervals and oyster floatstone beds in outcrop and subsurface. In each unit, transitions between siliciclastic and carbonate sedimentation occur rapidly at every scale. At a meter scale clastic sandstones alternate rapidly with clean ooid-skeletal grainstones while on a decameter scale siliciclastic silt- and sandstone dominated packages alternate with pure carbonate intervals. The similarity of the stratigraphic architecture of the two areas, which are several hundred kilometers apart, indicates a basin-wide eustatic control rather than a local sediment supply driven process. The consistent clinoform breaks in the subsurface point at longshore currents as the main source for siliciclastic input. This interpretation is corroborated by the general trend of fining of the clastic grainsize from south to north, which is in a more distal position from the continental input in the south. Furthermore it implies that the rapid transitions between siliciclastic and carbonate sedimentation are largely controlled by the available accommodation space on the shelf, with high accommodation allowing transport of sand and silt material for hundreds of kilometers driven by shoreline parallel currents and the concomitant turning off of the carbonate factory.
A new Late Triassic palynological assemblage from western Gondwana (Carrizal Formation, Marayes Basin, Argentina)
(Elsevier France-Editions Scientifiques Medicales Elsevier, 2021-08) Cesari, Silvia Nelida; Drovandi, Juan Martín; Colombi, Carina Ester; Correa, Gustavo Alejandro; Spalletti, Luis Antonio
The Carrizal Formation, exposed in the Marayes-El Carrizal Basin (western Argentina), has been the focus of palaeobotanical studies since the late 1800s. The recent finding of well-preserved palynological assemblages provides the first detailed studies about its palynofloras. In this paper, the 63 taxa identified in the unit are illustrated and discussed, as well as their stratigraphic distribution in equivalent palynological assemblages of Argentina. Some spore species are revised: Uvaesporites hammenii (Herbst) Césari, comb. nov., Retusotriletes wielandii (Jain) Césari, comb. nov. and Lundbladispora stellae (Herbst) Césari, comb. nov. The recognition of Cadargasporites baculatus de Jersey & Paten emend. Reiser & Williams, Craterisporites rotundus de Jersey, Enzonalasporites vigens Leschik, Leptolepidites argenteaeformis (Bolkhovitina) Morbey, Protodiploxypinus americus Dunay & Fisher and Rugulatisporites permixtus Playford, among others, appears to be useful for local and intercontinental correlations. A Carnian age is proposed for the palynofloras.
A new Pliosaurus species (Sauropterygia, Plesiosauria) from the Upper Jurassic of Patagonia: New insights on the Tithonian morphological disparity of mandibular symphyseal morphology
(Paleontological Society, 2018-03) O'gorman, Jose Patricio; Brandoni, Zulma Nelida; Spalletti, Luis Antonio
Most species of the genus Pliosaurus Owen, 1842 come from the Northern Hemisphere, however, a growing number of new specimens are now available from the Southern Hemisphere. Here, a new species of Pliosaurus is described, the second for the genus from the Southern Hemisphere, collected from the upper Tithonian (Jurassic) levels of the Vaca Muerta Formation, Neuquén Province, Patagonia. Pliosaurus almanzaensis new species is characterized by two autapomophies: the angular participating in the mandibular symphysis and the occipital condyle without a notochordal pit or several, irregularly arranged grooves. Additionally, P. almanzaensis n. sp. can be differentiated from other Pliosaurus species by the following characters: trihedral teeth, nine or more symphyseal alveoli, 15-17 post-symphyseal alveoli, and the parasphenoid without a ventral keel. Pliosaurus almanzaensis n. sp. shows that Pliosaurus species with nine or more symphyseal alveoli persisted until the late Tithonian, contrary to previous assumptions that only species with six symphyseal alveoli were present.
A new record of late Ediacaran acritarchs from La providencia group (Tandilia System, Argentina) and its biostratigraphical significance
(Pergamon-Elsevier Science Ltd, 2019-08) Arrouy, Maria Julia; Gaucher, Claudio; Poire, Daniel Gustavo; Xiao, Shuhai; Gómez Peral, Lucia; Warren, Lucas V.; Bykova, Natalia; Quaglio, Fernanda
A well preserved assemblage of organic-walled microfossils is described from the Alicia and Cerro Negro formations of the La Providencia Group. The microbiota is dominated by Leiosphaeridia species (L. minutissima, L. tenuissima, L. crassa and L. jacutica) and comprises colonial sphaeroids (Synsphaeridium sp.) and filamentous microfossils of the genus Siphonophycus. The assemblage is assigned to the Late Ediacaran Leiosphere Palynoflora (LELP), which is consistent with the occurrence of the discoidal fossil Aspidella (<565 Ma) in the overlying unit. The distribution of microfossils within the Alicia Formation is mainly controlled by the shallowing upward trend and thus, environmental factors. This is indicated by the abundance and size of filaments, which tend to occur near to the paleoshore in shallow water settings. Furthermore, large leiospheres also occur in shallower facies together with filaments, in accordance with existing models for acritarch ecology and distribution in the Proterozoic marine successions. The absence of acanthomorphic acritarchs is thus interpreted as a real evolutionary trend, and not as a result of preservational or environmental biases. Regarding the preservation of microfossils, a higher Thermal Alteration Index for the Alicia Formation, compared with older and younger units, is interpreted as a result of hydrothermal overprint and/or contact metamorphism by basic dikes.
A new species of Plohophorus Ameghino (Cingulata, Glyptodontidae) from the latest Pliocene–earliest Pleistocene of the Pampean Region (Argentina): the last survivor of a Neogene lineage
(Cambridge University Press, 2023-08) Quiñones, Sofía Inés; Cuadrelli, Francisco; de los Reyes, Martin; Luna, Carlos Alberto; Poire, Daniel Gustavo; Zurita, Alfredo Eduardo
Within xenarthrans, two large groups are recognized, Pilosa (anteaters and sloths) and Cingulata (armoured xenarthrans). The latter contains Glyptodontidae, one of the most bizarre and enigmatic groups of animals that ever lived. Recent phylogenetic proposals show an early Miocene divergence into two clades, one of northern origin (Glyptodontinae) and the other with its oldest records in the early–middle Miocene of southern South America, which groups most of the recognized diversity. Although knowledge of the ‘austral clade’ has increased recently, several taxa need urgent taxonomic and phylogenetic studies to understand their evolutionary history. One case is represented by the ‘Plohophorini’, a tribe that traditionally included several genera (Plohophorus, Pseudoplohophorus, Phlyctaenopyga, Stromaphorus and Stromaphoropsis), from the late Miocene–Pliocene of the Pampean and North-Western regions of Argentina, and Uruguay. A new and terminal species of Plohophorus, P. avellaneda sp. nov., coming from the El Polvorín Formation (Pampean region of Argentina) is here reported and described, and represents the first case of a Neogene genus of glyptodont crossing the Plio–Pleistocene boundary (c. 2.53 Ma). In addition, the palaeohistological analysis on the osteoderms (the first for ‘Plohophorini’) reveals some characters not observed in other glyptodonts, highlighting its potential phylogenetic importance. The phylogenetic analysis corroborates that the well-characterized species of ‘Plohophorini’ of Uruguay and the Pampean region of Argentina (‘eastern Plohophorini’) constitute a natural group within the austral clade, since both species of Plohophorus (P. avellaneda + P. figuratus) cluster together, and are the sister taxa of Ps. absolutus + Ps. benvenutti. Along the evolutionary history of Plohophorini an increase in body mass is observed, reaching its maximum with P. avellaneda sp. nov. (c. 471 ka). Despite the high frequency of late Pliocene records, Plohophorini disappear completely from the fossil record during the Pleistocene, suggesting that this character was negatively selected.
A Paleocene lowland macroflora from Patagonia reveals significantly greater richness than North American analogs
(Geological Society of America, 2007-12) Iglesias, Ari; Wilf, Peter; Johnson, Kirk R.; Zamuner, Alba Berta; Cúneo, N. Rubén; Matheos, Sergio Daniel; Singer, Bradley S.
Few South American macrofloras of Paleocene age are known, and this limits our knowledge of diversity and composition between the end-Cretaceous event and the Eocene appearance of high floral diversity. We report new, unbiased collections of 2516 compression specimens from the Paleocene Salamanca Formation (ca. 61.7 Ma) from two localities in the Palacio de los Loros exposures in southern Chubut, Patagonia, Argentina. Our samples reveal considerably greater richness than was previously known from the Paleocene of Patagonia, including 36 species of angiosperm leaves as well as angiosperm fruits, flowers, and seeds; ferns; and conifer leaves, cones, and seeds. The floras, which are from siltstone and sandstone channel-fills deposited on low-relief floodplain landscapes in a humid, warm temperate climate, are climatically and paleoenviromnentally comparable to many quantitatively collected Paleocene floras from the Western Interior of North America. Adjusted for sample size, there are >50% more species at each Palacio de los Loros quarry than in any comparable U.S. Paleocene sample. These results indicate more vibrant terrestrial ecosystems in Patagonian than in North American floodplain environments ∼4 m.y. after the end-Cretaceous extinction, and they push back the time line 10 m.y. for the evolution of high floral diversity in South America. The cause of the disparity is unknown but could involve reduced impact effects because of greater distance from the Chicxulub site, higher latest Cretaceous diversity, or faster recovery or immigration rates.
A paleopedological approach to understanding Eocene environmental conditions in southern Patagonia, Argentina
(Elsevier Science, 2022-09) Raigemborn, María Sol; Lizzoli, Sabrina; Hyland, Ethan; Cotton, Jennifer; Gómez Peral, Lucia; Beilinson, Elisa; Krause, Javier Marcelo
The Eocene Las Flores and Koluel-Kaike formations in southern Patagonia (~48° S, Golfo San Jorge Basin, Argentina) are pedogenically modified fluvial and fluvio-eolian successions, respectively, which document early-middle Eocene environments at mid-paleolatitudes in the Southern Hemisphere. In order to reconstruct the paleoenvironment for the Las Flores and Koluel-Kaike formations, we performed a multiproxy and coordinated study of sediments and paleosols of both units, considering abiotic components. Using detailed sedimentology and paleopedology (macro- and micromorphology), bulk paleosol geochemistry and clay mineralogy, and organic carbon concentrations and stable isotope (δ13Corg) compositions, we show that the Las Flores and Koluel-Kaike paleosols are overall Ultisol-like paleosols, mineralogically and chemically consistent with a high to high-moderate degree of weathering, and developed on different parent materials (sedimentary with sandy and silty texture vs. silty volcaniclastic). Climate proxies and a comparison with modern Ultisols with similar features suggest that these paleosols formed under a broadly tropical-temperate and humid-subhumid climate with distinct seasonality. Overall, these combined data record long-term environmental conditions during the Paleogene (early-middle Eocene), and preserve a record of Eocene terrestrial climate in the Southern Hemisphere. This research is relevant for understanding latitudinal climatic gradients during warm periods like the Eocene, a key knowledge gap for future predictions, and these sites are particularly important because mid-latitude reconstructions in the Southern Hemisphere are the poorest resolved.
A review of Devonian–Carboniferous magmatism in the central region of Argentina, pre-Andean margin of SW Gondwana
(Elsevier Science, 2021-10) Dahlquist, Juan Andrés; Morales Camera, Matías Martín; Alasino, Pablo Horacio; Pankhurst, Robert; Stipp Basei, Miguel Angelo; Rapela, Carlos Washington; Moreno Moreno, Juan Antonio; Baldo, Edgardo Gaspar Agustin; Galindo Francisco, Carmen
We review a widespread project database for Devonian–Carboniferous magmatism in the Sierras Pampeanas and Frontal Cordillera between 27° and 35°S, including petrological, geochemical, geochronological, and isotope data, with compiled data from the literature and some new results. We distinguish four main magmatic domains: 1) Devonian Arc, 2) Devonian Foreland, 3) Carboniferous Arc, and 4) Carboniferous Retro-Arc. Devonian segmented subduction led to two oceanic slab configurations: 1) flat-slab subduction in the outboard region and resubduction >800 km inland from the trench, including lithosphere delamination of the upper plate and break-off of the subducted oceanic slab, along with asthenospheric mantle upwelling (31°–33° 30′S), and 2) normal subduction (34° - 35°S). In the first configuration the arc magmatism was absent, but voluminous foreland magmatism was developed, including small-scale high silica adakite. The second geodynamic setting took place during the latest Devonian and Carboniferous when the oceanic slab roll-back occurred. Arc and retro-arc magmatism were developed coetaneously between 27° and 31°S, with northwest migration that could be explained by movement relative to hot asthenospheric mantle. The arc is represented by calc-alkaline granitoids, whereas retro-arc magmatism consisted of (a) metaluminous to weakly peraluminous A-type granites, and (b) strongly peraluminous A-type granites, these latter with sometimes incomplete isotopic homogenization of the parental magma. Devonian–Carboniferous magmatic evolution here is explained by segmented tectonic subduction and a switch-off and switch-on geodynamic model. Magmatic activity was mainly continuous from ca. 390 to 320 Ma, although compositional variations occurred through time and space (foreland, arc, and retro-arc). Major involvement of mantle sources in the genesis of the Carboniferous arc granites at 28°–30°S contrast with a dominant continental signature in the granites of the Devonian arc at 34°–35°S. These differences are explained by two different configurations in the subduction system related to advance (28°–30°S) or retreat (34°–35°S) of the subducted ocean slab. The main conclusion of this work is that the complex interaction of oceanic and continental plates can produce different types of magmatism (or its absence): subduction processes do not consist only of an oceanic plate sinking under a continental plate.
A review of the Famatinian Ordovician magmatism in southern South America: Evidence of lithosphere reworking and continental subduction in the early proto-Andean margin of Gondwana
(Elsevier Science, 2018-12) Rapela, Carlos Washington; Pankhurst, Robert J.; Casquet, César; Dahlquist, Juan Andrés; Fanning, Christopher Mark; Baldo, Edgardo Gaspar Agustín; Galindo Francisco, Carmen; Alasino, Pablo Horacio; Ramacciotti, Carlos Dino; Verdecchia, Sebastián Osvaldo; Murra, Juan Alberto Félix; Stipp Basei, Miguel Angelo
Along the proto-Pacific margin of Gondwana, from Venezuela to northeastern Patagonia, the Early–Middle Ordovician Famatinian orogeny was the first orogenic event following assembly of the supercontinent. Previous isotope studies of the igneous and (meta-)sedimentary rocks of southwestern Gondwana yield ambiguous implications for the role of juvenile mantle addition during the early crustal growth at the supercontinental margin. To interpret the geological and tectonic evolution of the orogen and the magma sources in different episodes we look at evidence from a large area of southern South America, including the 700 × 600 km type sector of the orogen in the Sierras Pampeanas (27°–33°S), the Precordillera, and northeastern Patagonia. Previous geological, geochemical and geochronological results are reviewed together with new U—Pb SHRIMP crystallization ages, 177Hf/176Hf and 18O/16O data for dated zircon, and whole-rock Sr and Nd isotope compositions. Four geological domains are recognized in the Sierras Pampeanas (Western, Central, Eastern and Foreland Famatinian domains). Magmatism is mostly restricted to the interval 463 ± 4 to 486 ± 7 Ma, with the most intense period of emplacement between 468 and 472 Ma constituting a magmatic flare-up. Granitoid emplacement in both northeastern Patagonia and the Cordon de Lila (Puna Altiplano, Chile) was effectively synchronous with that in the Sierras Pampeanas, defining a continuous belt. Combined geochemical and isotopic data (whole-rock Sr, Nd; Hf, O in zircon) indicate that the source of calcic metaluminous suites is the subcontinental lithosphere – both mantle and mafic lower crust – with variable contamination by the Early Paleozoic metasedimentary country rocks. The lithospheric mantle involved is assumed to underlie the outcropping 1330–1030 Ma age basement of the Western Domain, which exhibits tectonic characteristics of active continental margin in the north and oceanic arc-back arc in the south. The latter sector is the potential source of some minor Famatinian igneous rocks with less evolved isotopic compositions, although a restricted asthenospheric addition cannot be discarded in this case. Minor peraluminous granites are spatially associated with the metaluminous sequence, but major highly-peraluminous batholiths occur on the eastern flank of the Central Domain. Field relations and geochemical/isotopic evidence indicate that the most obvious source of these crustal melts was the very thick post-early Cambrian metasedimentary sequence comprising the host country rocks. Episodic tectono-magmatic evolution of the Famatinian magmatic belt in two overlapping stages is invoked to explain different characteristics in the four recognized domains in the type sector: • ca. 474–486? Ma, roll-back stage. This is a mainly extensional interval involving asthenospheric upwelling and thinning of the subcontinental mantle; full development of the marine ensialic basins and early emplacement of both metaluminous granites and highly-peraluminous batholiths in the Central and Eastern Famatinian domains. Trondhjemite plutons with an adakitic signature were emplaced in the Foreland Domain• ca. 468–472 Ma, slab break-off stage. Steepening of the oceanic slab and arc migration to the southwest ended with slab break-off due to subduction of continental crust during continental collision with the Precordillera terrane. This stage produced voluminous metaluminous magmatism at the western edge of the Central Domain (the flare-up episode), K-bentonites in the Precordillera, leucogranites in the Western Domain and scattered metaluminous and peraluminous plutons in all Famatinian domains.Both slab roll-back and break-off stages developed during a high-T regime typical of hot orogens. Although asthenospheric mantle was a necessary heat source for lithospheric melting, its material contribution to the growth of Early Paleozoic crust was apparently very minor. Recycling of Mesoproterozoic lithosphere, including the subcontinental mantle, coupled with crustal melting of Early Paleozoic metasedimentary sequences, accounts for most Famatinian magmatism. Comparable results from the Central Andes and East Antarctica confirm that the early stages of the Terra Australis orogen in SW Gondwana were dominated by lithospheric reworking processes.
A review on depositional systems, bioevents and paleogeography of the Valanginian-Hauterivian Neuquén Sea: Refining sedimentary and biological signals linked to the dynamics of epeiric seas
(Elsevier Science, 2022-11) Schwarz, Ernesto; Remirez, Mariano Nicolas; Lazo, Dario Gustavo; Veiga, Gonzalo Diego; Isla, Manuel Fermín; Echevarria, C.; Toscano, Agustina Gabriela; Garberoglio, Ricardo Miguel
Epeiric seas were common in deep times, but modern analogues are rare. Large-scale reconstruction of ancient examples is usually limited by available data, which also hampers the conceptualization of their variability and key controlling parameters. In this study we summarize and integrate a large stratigraphic dataset of a relatively small, semi-restricted Cretaceous epeiric sea in southwestern Gondwana to identify key sedimentary and biological signals that are used to discuss oceanographic connection with adjacent oceans, areal distribution of sediments entering the marine basin, sediment dispersal pathways within it, and the resulting stratigraphy. The Valanginian–Hauterivian Pilmatué-Lower Centenario study interval represents an exceptional record of well-dated marine and continental sediments deposited in the Neuquén Sea, which occupied a back-arc setting and was semi-connected with the proto-Pacific Ocean across a volcanic arc. The study interval is organized in three transgressive-regressive sequences (Lower, Middle, and Upper) defined by the integration of genetically linked depositional systems, macrobenthic bioevents, and stratal patterns. Detailed paleogeographic reconstructions show a consistent east-west proximal-distal depositional trend and a major fluvial system located in its southeastern apex. This continental-scale delivery system was responsible for the vast volume of sands and muds brought into the sea. The degree of connection between the Neuquén Sea and the adjacent ocean was evaluated by considering onlap stratal relationships, incursion of pandemic fauna, onset and deactivation of tidal offshore fields, and contribution of plankton-derived carbonate mud (a proxy to paleoproductivity). These criteria indicate that the maximum volume of watermasses within the semi-restricted sea was reached not during initial flooding (i.e., base of Lower Sequence), but most probably near the Valanginian/Hauterivian boundary (base of Middle Sequence). Dispersal pathways within the distal marine settings of the Neuquén Sea were reconstructed by integrating geographical thickness variations, composition of muds, and seafloor oxygenation levels. Results allow defining a non-uniform, along-depositional strike scenario, with a locus of siliciclastic deposition westwards of major deltaic systems, and lower accumulation towards the northwestern and southwestern areas. The northwestern region, having maximum carbonate contribution and lower oxygen levels, is inferred to have been more prone to water-column stratification over time. Some of the key attributes reconstructed for the Neuquén Sea (namely significant restriction, major sediment supply in one apex, asymmetric distribution of sediments in the distal settings) are comparable with configurations observed in the present Persian Gulf and the Adriatic Sea and departing from others such as the Baltic Sea and the Gulf of Carpentaria. Comparisons with ancient examples such as the Western Interior Sea and the North American Seaway suggest contrasting paleogeographic models, but at the same time reinforce the value of these key parameters to produce better discrimination between the possible spectrum of epeiric seas. In that sense, building classifications for epeiric seas based on these key parameters, such us size, degree of connection with the open ocean, sediment entry points, and sediment dispersal pathways, appears as the next challenge for more comprehensive reconstructions of these environments worldwide.
A revisited Silurian-Lower Devonian brachiopod biostratigraphy of North Patagonian Massif, Ventania system and Southern Paraná Basin. A regional correlation
(International Comission on Stratigraphy. International Union of Geological Sciences, 2015) Siccardi, Aron
The fist collections of Silurian-Devonian brachiopods fromSouth America were realized by Charles Darwin (1833) inthe Malvinas Islands, during his voyage on the H.M.S. Beaglearound the world and they were lately described by Morris andSharpe (1846). After that Clarke?s monograph (1913) provided anapproach on systematics and paleobiogeography of this fauna.Contemporary works were mainly focused in the Proto-Andeanmargin but the Silurian-Devonian faunas from the Atlanticoutcrops (Fig. 1) especially those of North Patagonian Massif(Müller, 1965), Ventania (Andreis, 1964), Eastern Paraguay(Harrington, 1950; Wolfart, 1961) and Uruguay (Méndez-Alzola,1938), remained poorly studied.The Silurian brachiopods reviewed come from Sierra GrandeFormation (Northern Patagonia) and Vargas Peña Formation(Eastern Paraguay, Parana Basin). This two sections bearingiron levels, ranging from iron coating to oolitic ironstones. Fromthe Sierra Grande Formation two oolitic iron levels are recognised; below the fist iron level it is found the fauna described asHeterorthella freitana-Clarkeia antisiensis (Müller, 1965); belowthe second iron level, the suggested presence of Conularia quichua-Bainella sp hinted a Lower Devonian age. However, recentstudies (Siccardi et al. 2014), allowed recognized the Llandoverianbrachiopods Eostropheondonta chilcaensis (BENEDETTO,1995), Heterorthella? sp, Dalmanella? sp, Hindella? sp. andRessellerids (Resserella?, Vysbiella?). In addition, a trilobite assemblage dominated by Eoleonaspis sp, supports theLlandoverian age (Rustán et al. 2013). The Vargas Peña Formationis included in the siliciclastic sequence of the Itacurubí Group(Hirnantian-Lower Silurian) and its brachiopod faunas knownfrom are composed by Anabaia paraguayensis (HARRINGTON,1950), accompanied of scarce inarticulates (Obolidae? indet.);the age assigned to this assemblage is Aeronian to late Telychian(Tortello et al. 2012 and references therein). Even though, in theParaguayan outcrops oolitic ironstones have not been found, theyare mentioned in subsurface drills.Fig.1. Outcrop location. (A) Eastern Paraguay. (B) Uruguay (DuraznoDepartment). (C) Sierra de la Ventana. (D) Sierra Grande.The Lower Devonian brachiopod faunas that integrate thisstudy have been collected from outcrops of the Lolén Formation(Sierra de la Ventana) and the Cordobés Formation (Uruguay,Durazno Department). In the base of the Lolén unit, the uppermostin the Ventana Group (Silurian?-Middle Devonian), an assemblage composed by Cryptonella sp, Schellwienella sp, Leptocoeliasp and Derbyia sp was originally mentioned by Andreis (1964)Following contributions (Isaacson, 1975, 1991), have also mentioned the presence of Proboscidina arcei ISAACSON, 1977. Thefauna of the Lolen Formation is characterized by the low diversity and the strong deformation. However, the new collection fromthe recent fild works has allowed to confim the presence of thetaxon previously described, as well as to identify the brachiopodsMutationelidae? indet, Orbiculoidea? sp, and Pleurothyrella?sp.,accompanied by the bivalves Nuculites sp. The age suggestedfor this brachiopod assemblage is Lochkovian-Pragian (SuarezSoruco, 2000). Devonian brachiopods from Uruguay registeredin the Cordobés Formation (Durazno Group) are more diversifidand associated to the Cordobés Formation, a dominantly shalysequence. An Emsian faunal assemblage, dominated by the brachiopods Australocoelia palmata (MORRIS AND SHARPE,1846) and Orbiculoidea bainii? SHARPE, 1856, accompaniedby the less abundant Derbyina? sp., Pleurochonetes falklandicus (MORRIS AND SHARPE, 1846), Iridistrophia? sp. andGigadiscina collis (CLARKE,1913) has been herein recognized.The mixed dominance could be explained due to the overlap of theOrbiculoidea and Australocoelia communities.According to the available data the Silurian correlationswith others South American basins could be based on keyfaunal assemblages and sedimentary events: oolitic ironstonesin the Proto-Andean margin and the glacial event in the Northeastern Brazil. The presences of oolitic ironstones between thefaunas considered would provide an additional correlation tool.The oolitic ironstones are well-known from the Proto- Andeanmargin and having a biostratigraphical control. The oldest agesdefied are Late Rhuddanian and the youngest, Late Telychian.When considering the hypothesis of the ironstones deposition andthe glaciation events (Caputo, 1998), they could be traced as aresponse of interglacial early transgressive stages, during the lastpulse of the Early Palaeozoic Glacial event. In the Sierra GrandeFormation the Eostropheondonta and Ressellerids associationdominate the brachiopod assemblage having an Ordovician mark,plus the absence of Ordovician key genera indicate a (Lower?)Rhuddanian age. Wenlockian faunas have not been registered inthe studied sections. The correlations proposed are schematisedin Fig.2.Within the Lower Devonian interval, three key species couldbe recognised: Proboscidina arcei, Scaphiocoelia boliviensisWHITFIELD, 1890 and Australocoelia palmata. The fist one,apart from being founded in Sierra de la Ventana, it is abundantduring Lochkovian-Pragian times in several Bolivian localitiesand South Africa (Uppermost Nardouw Subgroup, BaviaanskloofFormation. Meanwhile Scaphiocoelia is traditionally proposed asa Pragian key genus, but it restricted to Bolivia and South Africaand records from others basins (Brazil and Precordillera) are confusing. During the Emsian stage, Australocoelia palmata becamea common (and dominant) component of most of the shallowwater brachiopod assemblages.
A Seismic Monitoring Tool for Tidal-Forced Aquifer Level Changes in the Río de la Plata Coastal Plain, Argentina
(Multidisciplinary Digital Publishing Institute, 2024-02) Galone, Luciano; Panzera, Francesco; Colica, Emanuele; Fucks, Enrique Eduardo; Carol, Eleonora Silvina; Cellone, Francisco Aldo; Rivero, Lluís; Agius, Matthew R.; D´Amico, Sebastiano
Ambient seismic noise has gained extensive applications in seismology and plays a pivotalrole in environmental seismic studies. This study focuses on the Río de la Plata Coastal Plain, employingthe horizontal-to-vertical spectral ratio (HVSR) method on ambient seismic noise recordsto analyze subsurface dynamics. The region’s hydrogeology is complex, featuring partially interconnectedcoastal aquifers. The HVSR analysis reveals two peaks, with P0 associated with thesediment-basement interface and P1 linked to a shallower stratigraphic discontinuity. Temporalanalysis of P1 highlights cyclical patterns correlated with estuarine levels, suggesting a relationshipbetween variations in seismic velocities and tidal dynamics. Comparisons with aquifer data supportthe hypothesis that tidal variations influence subsurface mechanical properties, impacting the HVSRfunction. The study hints at the potential of ambient seismic noise analysis as a non-invasive and costeffectivemethod for studying coastal aquifers and understanding groundwater dynamics. Ongoingresearch aims to further explore these relationships for enhanced groundwater resource management.
A Silurian - Devonian marine platform-deltaic system in the San Rafael Block, Argentine Precordillera-Cuyania terrane: Lithofacies and provenance
(Geological Society Publications House, 2009-05) Manassero, Marcelo Jorge; Cingolani, Carlos Alberto; Abre, Paulina
The San Rafael Block is included as a part of the pre-Andean region, in the southern sector of the Argentine Precordillera-Cuyania terrane, within the western Gondwana margin. The Río Seco de los Castaños Formation (Upper Silurian-Lower Devonian) is one of the major marine-siliciclastic pre-Carboniferous units, and is interpreted as a distal to proximal silty platform-deltaic system. The dominant sedimentary processes were wave and storm action and the source areas were located to the east, close to the study area. The rocks are mainly of immature arkosic sandstones showing both recycled orogen and continental block provenances. Sedimentological characteristics of conglomerate-filled channels and an organic-matter-rich bed are described. X-ray diffraction analyses of the clay minerals from the sequences show that very low-grade metamorphic conditions acted during the Early Carboniferous. Geochemical analyses indicate moderate to strong weathering, and potassium metasomatism. Zr/Sc ratios lower than 22, no important enrichments of Zr, Th/Sc ratios, high Sc and Cr concentration and the Eu-anomalies indicate a provenance from a less evolved upper continental crust. TDM ages and ε Nd are within the range of the Mesoproterozoic basement and Palaeozoic supracrustal rocks from the Precordillera-Cuyania terrane. Probable sources, tectonic setting and land-sea interactions are discussed. © The Geological Society of London 2009.

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