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Revision of the La Veteada Formation in its stratotype (La Rioja, Argentina) : Age, stratigraphy and paleoenvironmental significance
No full textThe La Veteada Formation, in the Sierra de Famatina (west of Argentina), is one of the few records of Early Triassic age in South America verified by isotopic age and palynological assemblages. This unit is composed of sandstones, mudstones, shales, limestones, and marls, with some levels of gypsum, chert, and tuff levels. In its stratotype, the La Veteada Formation rests on Late Permian red beds of the Talampaya Formation and is covered by Neogene breccias and conglomerates belonging to the Del Crestón Formation. The unit is divided into three associations of sedimentary facies. Facies association A (80 m thick) is a red bed succession composed of mudstone and fine-grained sandstone, together with some levels of chert and gypsum. Facies association B (58 m thick) is greenish-gray to yellowish-gray and comprises limestones, marls, shales, and fine- to coarse-grained sandstones. This facies includes stromatolites and several levels of shales and marls where rich palynological assemblages were recovered. Finally, facies association C (24 m thick) is made up of yellowish-gray marls, mudstones, and sandstones. In this section, stromatolites are missing, thin levels of gypsum appear, and evidence of subaerial exposition as mud cracks and raindrop imprints are frequent at the top of the facies. The lithology, sedimentary structures, and vertical stacking of facies suggest that the La Veteada Formation was deposited in a lacustrine environment, which evolved from a shallow ephemeral playa lake system (facies association A) to a perennial lake, in which carbonate production increased compared to clastic sedimentation (facies association B). Regarding the facies association C, the increase in clastic supply, the missing stromatolites, and the presence of gypsum levels suggest a progressive shallowing of the lake and the likely transition to a palustrine environment. The Early Triassic age of the La Veteada Formation is indicated from two different lines of research. Firstly, a zircon U-Pb age of 249.66±0.11 Ma obtained from a tuff level at the middle part of the facies association A. Secondly, the presence of palynological species identified in other Early Triassic units worldwide. The La Veteada Formation records the filling of the embryonic extensional basins formed at the earliest Triassic. Moreover, this unit shows the evolution of depositional environments after the late Permian massive extinction event.pp.127-14
Revision of the La Veteada Formation in its stratotype (La Rioja, Argentina) : Age, stratigraphy and paleoenvironmental significance
Get PDFThe La Veteada Formation, in the Sierra de Famatina (west of Argentina), is one of the few records of Early Triassic age in South America verified by isotopic age and palynological assemblages. This unit is composed of sandstones, mudstones, shales, limestones, and marls, with some levels of gypsum, chert, and tuff levels. In its stratotype, the La Veteada Formation rests on Late Permian red beds of the Talampaya Formation and is covered by Neogene breccias and conglomerates belonging to the Del Crestón Formation. The unit is divided into three associations of sedimentary facies. Facies association A (80 m thick) is a red bed succession composed of mudstone and fine-grained sandstone, together with some levels of chert and gypsum. Facies association B (58 m thick) is greenish-gray to yellowish-gray and comprises limestones, marls, shales, and fine- to coarse-grained sandstones. This facies includes stromatolites and several levels of shales and marls where rich palynological assemblages were recovered. Finally, facies association C (24 m thick) is made up of yellowish-gray marls, mudstones, and sandstones. In this section, stromatolites are missing, thin levels of gypsum appear, and evidence of subaerial exposition as mud cracks and raindrop imprints are frequent at the top of the facies. The lithology, sedimentary structures, and vertical stacking of facies suggest that the La Veteada Formation was deposited in a lacustrine environment, which evolved from a shallow ephemeral playa lake system (facies association A) to a perennial lake, in which carbonate production increased compared to clastic sedimentation (facies association B). Regarding the facies association C, the increase in clastic supply, the missing stromatolites, and the presence of gypsum levels suggest a progressive shallowing of the lake and the likely transition to a palustrine environment. The Early Triassic age of the La Veteada Formation is indicated from two different lines of research. Firstly, a zircon U-Pb age of 249.66±0.11 Ma obtained from a tuff level at the middle part of the facies association A. Secondly, the presence of palynological species identified in other Early Triassic units worldwide. The La Veteada Formation records the filling of the embryonic extensional basins formed at the earliest Triassic. Moreover, this unit shows the evolution of depositional environments after the late Permian massive extinction event.pp.127-14
Evaluación geológica de puntos de encuentro transitorio en la comuna de San Pedro de Atacama en caso de erupción del volcán Láscar, región de Antofagasta
No full textInforme Técnico -- Unidad Ejecutora: Unidad de Geología y Peligros de Sistemas Volcánicos, Santiago51 p
First report of Euthyneura (Heterobranchia: Gastropoda) in the Early Jurassic of Southern Patagonia, Argentina
No full textThe present paper aims at the description of two new species of Euthyneura (Heterobranchia: Gastropoda) in the Early Jurassic (early Pliensbachian) marine deposits of the Chubut Basin at southern Patagonia, Argentina. The new species Cossmannina australis nov. sp. and Cylindrobullina caquelensis nov. sp. were found at the Cerro Caquel locality located in the western slope of Sierra de Tecka and río Tecka valley. The new locality yielded the ammonite Eoamaltheus sp. (E. meridianus Hillebrandt Zone, upper part of Ibex Zone to Davoei Zone) which allowed to assign an early Pliensbachian age for the marine deposits at the studied area, providing also new evidence of the oldest record within the Early Jurassic in the Sierra de Tecka region. The new report of Euthyneura in the Chubut Basin extends the palaeobiogeographical distribution of this clade into the southern hemisphere during the earliest Pliensbachian.pp.291-30
Review of bomb and ash flows : Genesis and case studies of a subset of block and ash flow deposits
No full textPyroclastic density currents with an abundance of cauliflower-shaped bombs are an uncommon type of deposit, called bomb and ash flow (BoAF) deposits in several papers. Although they are similar to block and ash flow (BAF) deposits (e.g., rich in juvenile blocks and breadcrusted bombs), they are often related to eruptions of mafic to intermediate magmas. In the current study, we analyze and compare historical and prehistorical BoAF-generating eruptions at Asama and Aso (Japan), Mayon (Philippines), Mt. Spurr (United States), Fuego (Guatemala), Arenal (Costa Rica), Cotopaxi and Tungurahua (Ecuador), and Láscar and Tilocálar volcanoes (Chile). Our review indicates that BoAFs show a substantial contribution of juvenile rounded material but with different rheologies and fragmentation mechanisms. This juvenile material is typically basaltic or andesitic, as it is more susceptible to form volcanic bombs with scoriaceous cauliflower textures. Thus, BoAFs could be a subset of the BAF deposits. The study and recognition of this type of deposit in volcanic sequences could be misinterpreted as a ballistic bomb deposit or even a hot bomb-rich lahar deposit, therefore, its appropriate interpretation is fundamental for volcanic hazard assessment.pp.346-37
Minuta : Socavón Av. Bernardo Philippi, Frutillar Bajo, comuna de Frutillar, región de Los Lagos
No full textMinuta técnica2 p
Visita técnica por remociones en masa, Pasaje Loma Baja, sector Ricardo Lagos de la comuna de Curanilahue, región del Biobío
No full textInforme Técnico -- Unidad Ejecutora: Asistencias Técnicas y Emergencias Geológicas, Dirección Regional Sur. Concepción11 p
Remoción en masa en estero Toninas, Ruta-7, comuna de Puerto Montt, región de Los Lagos
No full textInforme Técnico -- Unidad Ejecutora: Oficina Técnica de Puerto Varas14 p
Caracterización de los deslizamientos ocurridos en invierno 2022 en la comuna de Calbuco, región de Los Lagos
No full textInforme Técnico -- Unidad Ejecutora: Oficina Técnica Puerto Varas21 p
Remociones en masa : ¿Cuáles son las zonas más sensibles a sufrir estos procesos y cómo podemos minimizar sus consecuencias?
No full textCorresponde a anexo de BSNGM 16371 DVD: Zonificación de áreas expuestas a peligros de remoción en masa en la región de Antofagasta ; Xterrae Geologí