The Neuquén composite section: magnetostratigraphy and biostratigraphy of the marine lower Jurassic from the Neuquén basin (Argentina)

Paleomagnetic and biostratigraphic data from five marine sedimentary sections in the Argentine Neuquén basin have allowed to construct the Lower Jurassic Neuquén Composite Section. This composite section comprises 14 reversed and 11 normal polarity Zones, in relation to 17 Andean ammonite Assemblage Zones, spanning the Hettangian^Toarcian (Early Jurassic). It represents the first paleomagnetic data of Lower Jurassic marine successions in the Southern Hemisphere. The Neuquén composite Section was correlated to the International Mesozoic Polarity Time Scale which, for the Lower Jurassic, comprises 54 polarity Zones and 16 Standard ammonite Zones. The correlation between the regional and the international biomagnetostratigraphic scales supports but also refines the correlation between the Andean and Standard ammonite zonations. Correlation between the Neuquén composite Section and the polarity sequences recorded in each section helped to assign several unfossiliferous stratigraphical levels to the corresponding biozones.Facultad de Ciencias Naturales y Muse

The Neuquén composite section: magnetostratigraphy and biostratigraphy of the marine lower Jurassic from the Neuquén basin (Argentina)

Paleomagnetic and biostratigraphic data from five marine sedimentary sections in the Argentine Neuquén basin have allowed to construct the Lower Jurassic Neuquén Composite Section. This composite section comprises 14 reversed and 11 normal polarity Zones, in relation to 17 Andean ammonite Assemblage Zones, spanning the Hettangian^Toarcian (Early Jurassic). It represents the first paleomagnetic data of Lower Jurassic marine successions in the Southern Hemisphere. The Neuquén composite Section was correlated to the International Mesozoic Polarity Time Scale which, for the Lower Jurassic, comprises 54 polarity Zones and 16 Standard ammonite Zones. The correlation between the regional and the international biomagnetostratigraphic scales supports but also refines the correlation between the Andean and Standard ammonite zonations. Correlation between the Neuquén composite Section and the polarity sequences recorded in each section helped to assign several unfossiliferous stratigraphical levels to the corresponding biozones.Facultad de Ciencias Naturales y Muse

The Neuquén composite section: magnetostratigraphy and biostratigraphy of the marine lower Jurassic from the Neuquén basin (Argentina)

Paleomagnetic and biostratigraphic data from five marine sedimentary sections in the Argentine Neuquén basin have allowed to construct the Lower Jurassic Neuquén Composite Section. This composite section comprises 14 reversed and 11 normal polarity Zones, in relation to 17 Andean ammonite Assemblage Zones, spanning the Hettangian^Toarcian (Early Jurassic). It represents the first paleomagnetic data of Lower Jurassic marine successions in the Southern Hemisphere. The Neuquén composite Section was correlated to the International Mesozoic Polarity Time Scale which, for the Lower Jurassic, comprises 54 polarity Zones and 16 Standard ammonite Zones. The correlation between the regional and the international biomagnetostratigraphic scales supports but also refines the correlation between the Andean and Standard ammonite zonations. Correlation between the Neuquén composite Section and the polarity sequences recorded in each section helped to assign several unfossiliferous stratigraphical levels to the corresponding biozones.Facultad de Ciencias Naturales y Muse

The Triassic-Jurassic boundary in the Andes of Argentina

The Arroyo Malo Formation at Alumbre Creek, on the northern bank of the Atuel River, west central Argentina, comprises a c. 300 m thick continuous marine succession across the Triassic-Jurassic System boundary, consisting of massive and laminated pelites indicative of a slope depositional environment. Late Triassic invertebrates, including ammonoids, nautiloids, bivalves, gastropods, brachiopods and corals are restricted to the lower 150 m. Beds between 125-135 m from the bottom yield Choristoceras cf. marshi Hauer, a species found in the Marshi/Crickmayi Zone of Europe and North America, together with loose fragments of Psiloceras cf. pressum Hillebrandt, coeval with the lower to middle part of the Hettangian Planorbis Zone. About 80 m higher are beds yielding Psiloceras cf. rectocostatum Hillebrandt, a species that gives name to an Andean biozone partially coeval with the Johnstoni and Plicatulum Subzones, upper Planorbis Zone. Other fossils recorded in the Rhaetian strata of this section are foraminifers, ostracods and plant remains identified as Zuberia cf. zuberi (Szaj.) Freng. and Clathropteris sp. The section was also sampled for conodonts and radiolarians, thus far with negative results. A palaeomagnetic study is underway.La Formazione Arroyo Malo ad Alumbre creek, sulla sponda settentrionale del fiume Atuel, Argentina centro-occidentale, comprende una successione marina continua spessa circa 300 m attraverso i! limite Triassico-Giurassico, ed e costituita da peliti massive e laminate indicative di un ambiente deposizionale di scarpata. Gli inverttfjrati del Ttiassico superiore, che includono ammonoidi, nautiloidi, bivalvi, gasteropodi, brachiopodi e coralli sono limitati ai primi 150 m. Gli strati fra i 125-135 m dalla base hanno dato Choristoceras cf. marshi Hauer, una specie trovata nella Zona a Marshi/Crickmayi di Europa e Nord America, insieme con frammenti sparsi di Psiloceras cf. pressum Hillebrandt, coeva con la parte mediana della Zona a Planorbis dell'Hettangiano. Circa. 80 m piu in alto ci sono strati contenenti Psiloceras cf. rectocostatum Hlllebrandt, una specie che da i! no me ad una biozona andina parzialmente coeva con le Sottózone a Johnstoni e Plicatulum, Zona a Planorbis superiore. Altri fossili documentati negli strati del Retico di questa sezione sono foraminiferi, ostracodi e resti di piante identificati come Zuberia cf. zuberi (Szaj.) Freng. e Clathropteris sp. La sezione e stata anche campionata per quanto riguarda conodonti e radiolari, finora con risultati negativi. Uno studio paleomagnetico e in corso.Fil: Riccardi, Alberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; ArgentinaFil: Damborenea, Susana Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; ArgentinaFil: Manceñido, Miguel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; ArgentinaFil: Iglesia Llanos, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología. Instituto de Geofísica "Daniel Valencio"; Argentin

The Triassic-Jurassic boundary in the Andes of Argentina

The Arroyo Malo Formation at Alumbre Creek, on the northern bank of the Atuel River, west central Argentina, comprises a c. 300 m thick continuous marine succession across the Triassic-Jurassic System boundary, consisting of massive and laminated pelites indicative of a slope depositional environment. Late Triassic invertebrates, including ammonoids, nautiloids, bivalves, gastropods, brachiopods and corals are restricted to the lower 150 m. Beds between 125-135 m from the bottom yield Choristoceras cf. marshi Hauer, a species found in the Marshi/Crickmayi Zone of Europe and North America, together with loose fragments of Psiloceras cf. pressum Hillebrandt, coeval with the lower to middle part of the Hettangian Planorbis Zone. About 80 m higher are beds yielding Psiloceras cf. rectocostatum Hillebrandt, a species that gives name to an Andean biozone partially coeval with the Johnstoni and Plicatulum Subzones, upper Planorbis Zone. Other fossils recorded in the Rhaetian strata of this section are foraminifers, ostracods and plant remains identified as Zuberia cf. zuberi (Szaj.) Freng. and Clathropteris sp. The section was also sampled for conodonts and radiolarians, thus far with negative results. A palaeomagnetic study is underway.Facultad de Ciencias Naturales y Muse

Calibración estratigráfica multidisciplinaria de la transición Jurásico-Cretácico en la Cuenca Neuquina

Se realizaron estudios sistemáticos de detalle en la Formación Vaca Muerta con el fin de lograr una calibración multidisciplinaria integrada de la transición jurásico/cretácica en la Cuenca Neuquina. Aunque esta unidad se caracteriza por presentar una bioestratigrafía basada en amonites, la distribución temporal de las biozonas es todavía un tema de importante debate. En esta contribución se presentan los resultados integrados de la sección Arroyo Loncoche (sur de Mendoza), en donde exhaustivos estudios cicloestratigráficos, paleomagnéticos y bioestratigráficos han permitido elaborar un robusto esquema de correlación cronoestratigráfico para el intervalo Tithoniano-Berriasiano. La calibración estratigráfica propuesta para la sucesión tithoniano-berriasiana andina presenta dos puntos clave: 1) La base de la Formación Vaca Muerta muestra un patrón de polaridades que solo sería compatible con la parte superior de la Zona de Hybonotum (Tithoniano Inferior bajo). 2) La posición del límite Jurásico - Cretáceo está ubicada dentro del tercio inferior de la Zona de S. koeneni.Detailed systematic studies are being carried out in the Vaca Muerta Formation in order to achieve an integrated multidisciplinary calibration of the Jurassic/Cretaceous transition in the Neuquén Basin. Although this unit has a very well established ammonite biostratigraphy, the temporal distribution of biozones is yet a matter of hot debate. In this contribution we present the results of a well constrained integrated data from the Arroyo Loncoche section (southern Mendoza), where comprehensive cyclostratigraphic, paleomagnetic and biostratigraphic sampling/data allowed us to elaborate a very strong chronostratigraphic scheme for the Tithonian-Berriasian interval.Fil: Kietzmann, Diego Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Iglesia Llanos, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Ivanova, Daria K.. Bulgarian Academy of Sciences; BulgariaFil: Kohan Martinez, Melisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Sturlesi, Magalí Aldana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentin

Palaeomagnetic study of Lower Jurassic marine strata from the Neuquén Basin, Argentina: A new Jurassic apparent polar wander path for South America

A thorough palaeomagnetic study in four marine sedimentary sections from the Neuquén Basin in west-central Argentina was carried out. Sections are several hundreds meters-thick and consist of ammonite-bearing beds with intercalated volcanics. Two magnetic components carried by titanomagnetites were identified in the studied sections, one soft corresponding most likely to a present-day remagnetisation and a harder one which is interpreted as the primary magnetisation of the sections, based on optical studies and the results of field tests of palaeomagnetic stability, bearing an Early Jurassic age. As a result, two new palaeomagnetic poles for stable South America are presented: one for the Hettangian–Sinemurian located at 223° E, 51° S, A95=6°, N=25, and the other for the Pliensbachian–Toarcian located at 67° E, 74° S, A95=5°, N=52. These and other poles from the literature were used in this study to construct a refined Late Triassic to Jurassic APW path for stable South America, which differs significantly from previous models in showing a cusp between the Sinemurian and the Pliensbachian, indicative of large apparent polar wander. The same feature is observed in other continents of Pangea, like Eurasia. Palaeolatitudes of the Neuquén Basin indicate that South America was subject to considerable N–S movements during the Late Triassic and lowermost Early Jurassic. These latitudinal movements of Pangea are consistent with displacements recorded for marine faunas from South America and Eurasia.Facultad de Ciencias Naturales y Muse

Cyclostratigraphy of the Tithonian Interval at Las Tapaderas section, Vaca Muerta Formation, Southern Mendoza Neuquén Basin, Argentina

La Formación Vaca Muerta en la sección de Las Tapaderas está caracterizada por una sucesión rítmica de margas y calizas. La sección se extiende desde la Zona de Virgatosphinctes andesensis hasta la Zona de Substeueroceras koeneni (Tithoniano inferior- Berriasiano inferior) donde es cubierta por los depósitos volcaniclásticos de la Formación Loma Seca (Pleistoceno superior). El análisis de facies permitió reconocer seis litofacies, que fueron agrupadas en dos facies correspondientes a los subambientes de cuenca y rampa externa distal, dentro del contexto de una rampa carbonática. El análisis secuencial, basado en el reconocimiento de superficies de inundación, permitió identificar tres secuencias depositacionales compuestas de carácter regional. La primera secuencia depositacional tiene un espesor de 20 m y abarca las biozonas de Virgatosphinctes andesensis hasta el tercio inferior de Windhauseniceras internispinosum (Tithoniano medio alto a superior bajo). La segunda secuencia depositacional tiene un espesor de 27 m y se extiende desde el tercio inferior de Windhauseniceras internispinosum hasta alcanza la base de la Zona de Substeueroceras koeneni (Tithoniano superior). La tercera secuencia depositacional presenta 30 m de espesor y abarca la Zona de Substeueroceras koeneni (Tithoniano superior ? Berriasiano inferior). El análisis cicloestratigráfico se basó en el reconocimiento de ciclos elementales marga/caliza o marga/marga. Una serie temporal construida a partir de los espesores de los ciclos elementales fue analizada mediante series de Fourier. Se identificaron 220 ciclos elementales que se asignan al ciclo de precesión (~21 ka), 53 ciclos de excentricidad de baja frecuencia (79 y 132 ka) y 11 ciclos de excentricidad de alta frecuencia (410 ka). El análisis espectral permitió también reconocer la presencia del ciclo de oblicuidad (46 ka), el cual ha sido registrado erráticamente en la Formación Vaca Muerta. Estos datos permitieron la construcción de una escala orbital para esta sección, que es consistente con los resultados publicados previamente por los autores y la precisa ubicación del límite Jurásico-Cretácico en esta sección. Asimismo se calculó una tasa de sedimentación de 10-19 m/Ma para esta sección.The Vaca Muerta Formation at Las Tapaderas section is characterized by a rhythmic succession of marlstone and limestone. The section spans the Virgatosphinctes andesensis Zone to the Substeueroceras koeneni Zone (Lower Tithonian - Lower Berriasian) where it is covered by volcaniclastic deposits of the Loma Seca Formation (Upper Pleistocene). Facies analysis allowed the recognition of six lithofacies, which were grouped into two facies corresponding to the basin and distal outer ramp sub-environments, within a carbonate ramp system. Sequence stratigraphic analysis, based on the recognition of flooding surfaces, allowed the identification of three composite depositional sequences of a regional nature. The first depositional sequence is 20 m thick and spans the Virgatosphinctes andesensis to the lower third of Windhauseniceras internispinosum Zones (Lower Tithonian to lowermost Upper Tithonian). The second depositional sequence is 27 m thick and extends from the lower third of Windhauseniceras internispinosum to the base of the Substeueroceras koeneni Zones (Upper Tithonian). The third depositional sequence is 30 m thick and covers the Substeueroceras koeneni Zone (Upper Tithonian - Lower Berriasian). The cyclostratigraphic analysis was based on the recognition of marlstone/limestone and marlstone/marlstone elementary cycles. A time series built from thickness of elementary cycles was analyzed using Fourier series: 220 elementary cycles were identified which are assigned to the precession cycle (~21 ky), 53 low frequency eccentricity cycles (79 and 132 ky) and 11 high frequency eccentricity cycles (~ 410 ky). The spectral analysis also allowed to recognize the presence of the obliquity cycle (46 ky), which has been erratically recorded in the Vaca Muerta Formation. These data allowed the construction of an orbital scale for this section, which is consistent with the results previously published by the authors and the precise location of the Jurassic-Cretaceous boundary in this locality. Likewise, a sedimentation rate of 10-19 m/Ma was calculated for this section.Fil: Kietzmann, Diego Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Palacio, Juan Pablo. YPF - Tecnología; ArgentinaFil: Iglesia Llanos, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentin

Palaeomagnetic study of the El Quemado complex and Marifil formation, Patagonian Jurassic igneous province, Argentina

The upper Jurassic El Quemado Complex was sampled at 36 sites from five localities in the cordilleran foothills of southern Patagonia between Lago Argentino and Lago Posadas–Sierra Colorada, and the middle Jurassic Marifil Formation at 12 sites in the Somuncur´a Massif near Camarones. The main lithology was ignimbrite, with minor tuff and lava. Petrographical and SEM observation show that the El Quemado rocks suffered an intense, high-temperature alteration which resulted in transformation of most primary Ti-magnetite in pseudobrookite, rutile and minor Ti-haematite and Fe hydrated oxides. A similar, less pronounced alteration occurred in the Marifil rocks. 40Ar/39Ar dating of El Quemadowas possible for one sample from Sierra Colorada and yielded an age of 156.5 ± 1.9 Ma. Magnetic mineralogy measurements (isothermal remanence, hysteresis loop, Curie balance) show that the remanent magnetization is dominated by PSD low-Ti magnetite, often associated to a minor high-coercive mineral (haematite). Secondary magnetization components are usually absent or weak at El Quemado sites, strong at Marifil. They were completely erased by thermal and AF demagnetization and a characteristic remanence (ChRM) stable up to temperatures higher than 550◦C or peak-field values of 100 mT was successfully isolated. The virtual geomagnetic pole (VGP) from the Marifil Formation (83◦S, 138◦E) is in agreement with the literature data for Jurassic rocks from stable South America. The El Quemado VGPs fall in two groups. The localities to the north of latitude 48◦S (Lago Posadas, Sierra Colorada) yield a VGP (81◦S, 172◦E) close to that of Marifil, whereas those south of latitude 49◦S (Lago San Mart´ın, Lago Argentino) show a highly elongated VGP distribution consistent with counter-clockwise block-rotation about vertical axes. These rotations were likely caused by thrust sheets which were rotating counter-clockwise at the same time they were advancing towards the foreland. The amount of rotation varies according to the location of the sampling sites in the thrust and fold belt.Facultad de Ciencias Naturales y Muse

Tracking the Late Jurassic apparent (or true) polar shift in U-Pb-dated kimberlites from cratonic North America (Superior Province of Canada)

Different versions of a composite apparent polar wander (APW) path of variably selected global poles assembled and averaged in North American coordinates using plate reconstructions show either a smooth progression or a large (∼30°) gap in mean paleopoles in the Late Jurassic, between about 160 and 145 Ma. In an effort to further examine this issue, we sampled accessible outcrops/subcrops of kimberlites associated with high-precision U-Pb perovskite ages in the Timiskaming area of Ontario, Canada. The 154.9 ± 1.1 Ma Peddie kimberlite yields a stable normal polarity magnetization that is coaxial within less than 5° of the reverse polarity magnetization of the 157.5 ± 1.2 Ma Triple B kimberlite. The combined ∼156 Ma Triple B and Peddie pole (75.5°N, 189.5°E, A95 = 2.8°) lies about midway between igneous poles from North America nearest in age (169 Ma Moat volcanics and the 146 Ma Ithaca kimberlites), showing that the polar motion was at a relatively steady yet rapid (∼1.5°/Myr) pace. A similar large rapid polar swing has been recognized in the Middle to Late Jurassic APW path for Adria-Africa and Iran-Eurasia, suggesting a major mass redistribution. One possibility is that slab breakoff and subduction reversal along the western margin of the Americas triggered an episode of true polar wander