Facies architecture of submarine channel deposits on the western Niger Delta slope: Implications for grain-size and density stratification in turbidity currents

High-resolution bathymetry, seismic reflection, and piston core data from a submarine channel on the western Niger Delta slope demonstrate that thick, coarse-grained, amalgamated sands in the channel thalweg/axis transition to thin, fine-grained, bedded sands and muds in the channel margin. Radiocarbon ages indicate that axis and margin deposits are coeval. Core data show that bed thickness, grain size, and deposition rate strongly decrease with increasing height above channel thalweg and/or distance from channel centerline. A 5 times decrease in bed thickness and 1\u20132 \u3c8 decrease in grain size are evident over a 20 m elevation change (approximately the elevation difference between axis and margin). A simplified in-channel sedimentation model that solves vertical concentration and velocity profiles of turbidity currents accurately reproduces the vertical trends in grain size and bed thickness shown in the core data set. The close match between data and model suggests that the vertical distribution of grain size and bed thickness shown in this study is widely applicable and can be used to predict grain size and facies variation in data-poor areas (e.g., subsurface cores). This study emphasizes that facies models for submarine channel deposits should recognize that grain-size and thickness trends within contemporaneous axis-margin packages require a change in elevation above the thalweg. The transition from thick-bedded, amalgamated, coarser-grained sands to thin-bedded, nonamalgamated, finer-grained successions is primarily a reflection of a change in elevation. Even a relatively small elevation change (e.g., 1 m) is enough to result in a significant change in grain size, bed thickness, and facies

Tendencias mineralógicas y geoquímicas del sistema Vaca Muerta-Quintuco en la sección de Puerta Curaco, Cuenca Neuquina

Los depósitos del sistema Vaca Muerta-Quintuco (Tithoniano-Valanginiano) de la Cuenca Neuquina evidencian el progresivo desarrollo de una plataforma mixta silicoclástica-carbonática, típica de la Fm. Quintuco, por encima de los depósitos de rampa carbonática de la Fm. Vaca Muerta. La localidad de Puerta Curaco exhibe excelentes afloramientos del sistema, que presenta un espesor de 716 m, en donde se efectuaron un perfil litoestratigráfico, mediciones de radioactividad natural espectral (GR) y el muestreo sistemático con el objetivo de analizar las variaciones mineralógicas y geoquímicas de todo el sistema y de la transición entre las dos formaciones. Se definieron cinco intervalos: I1-I5. I1 e I2 se desarrollan en la Fm Vaca Muerta y presentan baja proporción de material clástico y los mayores valores de proxies orgánicos del sistema, vinculándose la respuesta del GR directamente al contenido de U. Por otro lado, la relación V/V+Ni sugiere para la Fm Vaca Muerta una alternancia entre condiciones euxínicas a anóxicas del fondo marino. I3 se desarrolla en la transición entre ambas formaciones y se caracteriza por un aumento brusco en el contenido de minerales arcillosos y una disminución de proxies orgánicos. Esto se asocia a un descenso relativo del nivel del mar. I4 e I5 se desarrollan en la Fm. Quintuco, estando I4 caracterizado nuevamente por sedimentación carbonática, mientras que I5 registra los mayores valores de input clástico, evidenciando el establecimiento final de la plataforma mixta.Se estudiaron los depósitos del sistema Vaca Muerta-Quintuco (Tithoniano-Valanginiano) en la localidad de Puerta Curaco con el objetivo de analizar las variaciones mineralógicas y geoquímicas de la transición desde una rampa carbonática (Formación Vaca Muerta) a una plataforma mixta (Formación Quintuco). Para ello, se realizaron un perfil litoestratigráfico, mediciones de radioactividad natural (GR), estudios mineralógicos (DRX) y geoquímicos (FRX), definiendo cinco intervalos: I1-I5. I1 e I2 se desarrollan en la Formación Vaca Muerta, se encuentran dominados por sedimentación carbonática y presentan los mayores valores de proxies orgánicos del sistema. La respuesta del GR se relaciona directamente con el contenido de U y la relación V/V+Ni sugiere una alternancia entre condiciones euxínicas a anóxicas del fondo marino. I3 se desarrolla en la transición entre ambas unidades, presenta un aumento brusco en el contenido de minerales arcillosos y una disminución de proxies orgánicos, asociándose a un descenso del nivel del mar. I4 e I5 se desarrollan en la Formación Quintuco. I4 se encuentra dominada por sedimentación carbonática, mientras que I5 registra los mayores valores de input clástico, evidenciando el establecimiento de la plataforma mixta. En la Formación Quintuco, la relación V/V+Ni sugiere condiciones de anoxia/disoxia, registrándose una notoria disminución en los proxies orgánicos y una fuerte dependencia del GR con el K y Th. Por lo tanto, la disminución en el contenido orgánico de la Formación Quintuco es causada por la dilución debida al mayor aporte de detritos inorgánicos y no por cambios en la oxigenación del fondo marino.Fil: Capelli, Ignacio Andrés. 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: Scasso, Roberto Adrian. 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: 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: Cravero, Maria Fernanda. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; ArgentinaFil: Minisini, Daniel. Shell Technology Centre Houston; Estados UnidosFil: Catalano, Juan Pablo. 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

Astronomical constraints on the duration of the Early Jurassic Pliensbachian Stage and global climatic fluctuations

The Early Jurassic was marked by multiple periods of major global climatic and palaeoceanographic change, biotic turnover and perturbed global geochemical cycles, commonly linked to large igneous province volcanism. This epoch was also characterised by the initial break-up of the super-continent Pangaea and the opening and formation of shallow-marine basins and ocean gateways, the timing of which are poorly constrained. Here, we show that the Pliensbachian Stage and the Sinemurian–Pliensbachian global carbon-cycle perturbation (marked by a negative shift in δ13Cδ13C of 2–4‰2–4‰), have respective durations of ∼8.7 and ∼2 Myr. We astronomically tune the floating Pliensbachian time scale to the 405 Kyr eccentricity solution (La2010d), and propose a revised Early Jurassic time scale with a significantly shortened Sinemurian Stage duration of 6.9±0.4 Myr6.9±0.4 Myr. When calibrated against the new time scale, the existing Pliensbachian seawater 87Sr/86Sr record shows relatively stable values during the first ∼2 Myr of the Pliensbachian, superimposed on the long-term Early Jurassic decline in 87Sr/86Sr. This plateau in 87Sr/86Sr values coincides with the Sinemurian–Pliensbachian boundary carbon-cycle perturbation. It is possibly linked to a late phase of Central Atlantic Magmatic Province (CAMP) volcanism that induced enhanced global weathering of continental crustal materials, leading to an elevated radiogenic strontium flux to the global ocean

Evolution of the Toarcian (Early Jurassic) carbon-cycle and global climatic controls on local sedimentary processes (Cardigan Bay Basin, UK)

The late Early Jurassic Toarcian Stage represents the warmest interval of the Jurassic Period, with an abrupt rise in global temperatures of up to ∼7 °C in mid-latitudes at the onset of the early Toarcian Oceanic Anoxic Event (T-OAE; ∼183 Ma). The T-OAE, which has been extensively studied in marine and continental successions from both hemispheres, was marked by the widespread expansion of anoxic and euxinic waters, geographically extensive deposition of organic-rich black shales, and climatic and environmental perturbations. Climatic and environmental processes following the T-OAE are, however, poorly known, largely due to a lack of study of stratigraphically well-constrained and complete sedimentary archives. Here, we present integrated geochemical and physical proxy data (high-resolution carbon-isotope data (δ13C), bulk and molecular organic geochemistry, inorganic petrology, mineral characterisation, and major- and trace-element concentrations) from the biostratigraphically complete and expanded entire Toarcian succession in the Llanbedr (Mochras Farm) Borehole, Cardigan Bay Basin, Wales, UK. With these data, we (1) construct the first high-resolution biostratigraphically calibrated chemostratigraphic reference record for nearly the complete Toarcian Stage, (2) establish palaeoceanographic and depositional conditions in the Cardigan Bay Basin, (3) show that the T-OAE in the hemipelagic Cardigan Bay Basin was marked by the occurrence of gravity-flow deposits that were likely linked to globally enhanced sediment fluxes to continental margins and deeper marine (shelf) basins, and (4) explore how early Toarcian (tenuicostatum and serpentinum zones) siderite formation in the Cardigan Bay Basin may have been linked to low global oceanic sulphate concentrations and elevated supply of iron (Fe) from the hinterland, in response to climatically induced changes in hydrological cycling, global weathering rates and large-scale sulphide and evaporite deposition

Chronostratigraphic framework and depositional environments in the organic rich Eagle Ford Group

Since the beginning of the century, several authors have hypothesized and documented the presence of bottom currents during the deposition of mudstones, including mudstones rich in organic matter, challenging the assumption that persistent low-energy conditions are necessary prerequisites for deposition of such sediments. More processes responsible for transport and deposition of mudstones means also more processes acting contemporaneously in different parts of a basin. Without a precise and robust chronostratigraphic framework, however, it is not possible to characterize these differences. The new data reported here provide a profoundly different understanding of the controls on sedimentation in distal continental shelf platforms. To enhance the understanding of the different coeval environments of deposition coexisting in a muddy system, the Upper Cretaceous Eagle Ford Group, deposited on the Comanche carbonate platform, has been investigated by integrating sedimentology, mineralogy, geochemistry and palaeoecology and creating age models in different physiographic sectors using biostratigraphy and geochronology. Data from two cores and 41 outcrops were analyzed with a telescopic approach, from grain scale to basin-scale. Nine temporal stages over a ca 8 Myr interval (ca 98 to 90 Ma) were defined in an area that spans 75,000 km**2. Finally, the different environments of deposition recorded within each of the nine stages were interpreted. The construction of the chronostratigraphic framework also allowed: measuring the duration of a basin-wide gradational increase of energy in the water column (ca 1 Myr) and a hiatus confined into the shallower water sector (ca 2 Myr); determining the mean eruption frequency of volcanoes (ca 9 kyr); and the time of inundation of the Western Interior Seaway (97.5 to 97.1 Ma). The context, the outcrops-cores-logs correlations, the large dataset (Supplemental Information), the high-precision and well-calibrated constraints represent an unprecedented contribution for future regional facies models of organic-rich units and for improvements of key aspects in the Industry of Unconventional resources