Linking sedimentation rates and large‐scale architecture for facies prediction in nonmarine basins (Paleogene,Almazán Basin,Spain)

This article focuses on the relationships between the large‐scale stratigraphic architecture of the Almazán basin infill and the sedimentation rates (SR) calculated for precise time intervals. Our aim was to improve the understanding of the timing and causes of the architectural changes, their significance in terms of accommodation space and sediment supply and their relationship with climate and tectonics. The study area includes the Gómara fluvial fan, the main sediment transfer system of the Almazán basin during Paleogene times. Its large‐scale architecture shifted through time between a stacking pattern of low density ribbon‐like and high density sheet‐like channel fills. Laterally to the fluvial system, mudstone and evaporitic mudstone units represented evaporitic mudflats which passed laterally into palustrine/lacustrine limestone units interpreted as lakes and ponds. Stacked calcretes occurred in distal alluvial and distal floodplain settings. A magnetostratigraphy encompassing 2600 m guided by available fossil mammal biochronology has provided a temporal framework that spans the complete Paleogene infill of the basin, from Late Lutetian to Late Oligocene, filling a gap in the Cenozoic chronostratigraphy of Spanish basins. This permits to constrain the kinematics of the structures both in the basin and in its margins, and to provide the timing for the depositional sequences. These data, combined with a magnetostratigraphic map, where magnetic reversals were traced through the Gómara monocline, allow a detailed analysis of the SR variability across the fluvial system and its adjacent depositional environments. The results show that high sedimentation rates (around 30–40 cm kyr^?1) are related to fluvial environments with low density ribbon‐shaped channels, while low SR (around or below 10 cm kyr^?1) are related to high density sheet‐like channels. Laterally, mud dominated environments with high SR (15–20 cm kyr^?1) grade into palustrine/lacustrine carbonated environments with low SR (around 9 cm ky^?1). The lowest SR (about 3 cm kyr^?1) are related to the development of stacked calcrete profiles in distal floodplain and in the connection of distal alluvial and palustrine/lacustrine units.     

Regional magma plumbing and emplacement mechanisms of the Faroe‐Shetland Sill Complex: implications for magma transport and petroleum systems within sedimentary basins

The movement of magma through the shallow crust and the impact of subsurface sill complexes on the hydrocarbon systems of prospective sedimentary basins has long been an area of interest and debate. Based on 3D seismic reflection and well data, we present a regional analysis of the emplacement and magmatic plumbing system of the Palaeogene Faroe‐Shetland Sill Complex (FSSC), which is intruded into the Mesozoic and Cenozoic sequences of the Faroe‐Shetland Basin (FSB). Identification of magma flow directions through detailed seismic interpretation of approximately 100 sills indicates that the main magma input zones into the FSB were controlled primarily by the NE–SW basin structure that compartmentalise the FSB into its constituent sub‐basins. An analysis of well data shows that potentially up to 88% of sills in the FSSC are <40 m in thickness, and thus below the vertical resolution limit of seismic data at depths at which most sills occur. This resolution limitation suggests that caution needs to be exercised when interpreting magmatic systems from seismic data alone, as a large amount of intrusive material could potentially be missed. The interaction of the FSSC with the petroleum systems of the FSB is not well understood. Given the close association between the FSSC and potential petroleum migration routes into some of the oil/gas fields (e.g. Tormore), the role the intrusions may have played in compartmentalisation of basin fill needs to be taken fully into account to further unlock the future petroleum potential of the FSB.     

The Asturian Basin within the North Iberian margin (Bay of Biscay): seismic characterisation of its geometry and its Mesozoic and Cenozoic cover

The distribution and structure of the Mesozoic and Cenozoic cover within the central part of the North Iberian Margin (Bay of Biscay) is analysed based on a dense set of 2D seismic reflection lines and logs. The integration of well data allows the recognition of seven seismostratigraphic units and the construction of a surface that illustrates the 3D morphology of this area at the time of the Jurassic rifting. The study zone comprises what is known as Le Danois Bank, a basement high, and the Asturian Basin, one of the sedimentary basins originated during the Iberian rifting at the end of the Paleozoic. Its development continued with the oceanisation of the Bay of Biscay as a failed arm of the Atlantic rift; later, during the Cenozoic, a drastic change in tectonic regime induced the partial closure of Biscay and building up the Cantabrian?Pyrenean chain along the northern border of Iberia. This compressional period left its imprint in the Asturian Basin sediments in the form of a mild inversion and general uplift. The geometry of the basin bottom appears as an asymmetric bowl thinning out towards the edges, with a main E‐W depocenter, separated by E‐W striking faults from a secondary one. Those bounding faults show twisted trends in the north, interpreted as a consequence of the compressional period, when a transfer zone in a N‐S direction formed between the two E‐W striking deformation fronts in Biscay. This study shows that the transfer zone extends further to the west, reaching the longitude of Le Danois Bank. The maximum thickness of the filling within the Asturian Basin is estimated in more than 10 km, deeper than assessed in previous studies. The recognition of frequent halokynetic structures at this longitude is another observation worth to remark. Based on this study, it is suggested that the basin formed on top of a distal basement block of stretched crust limiting with the hyperextended rifted domain of Biscay. This location largely conditioned its deformation during the late compression.     

High‐resolution evolution of terrigenous sediment yields in the Provence Basin during the last 6 Ma: relation with climate and tectonics

Basin‐wide correlation of Messinian units and Plio‐Quaternary chronostratigraphic markers (5.3 Ma, 2.6 Ma, 0.9 Ma and 0.45 Ma), the mapping of total sediment thickness and the determination of overall sedimentary volumes enabled us to provide a high‐resolution quantitative history of sediment volumes for the last 6 Ma along the Gulf of Lions margin. The results point to (i) a dramatic increase in terrigenous sediment input during the Messinian Salinity Crisis. This increased sedimentation reflects enhanced regional fluvial erosion related to the dramatic fall of Mediterranean base‐level. Stronger weathering due to a regional wetter climate probably also increased erosional fluxes. (ii) A sediment input three times higher during the Plio‐Quaternary compared to the Miocene seems in agreement with published measurements from World's ocean. However, the timing of this increase being uncertain, it implies that the trigger(s) also remain(s) uncertain. (iii) A decrease in detrital volume around 2.6 Ma is attributed to a regional change in the drainage pattern of rivers in the northwestern Alps. (iv) This study also highlights the Mid‐Pleistocene Revolution around 0.9 Ma, which resulted in an almost doubling of sediment input in the Provencal Basin.     

Reliability-based design of R/C water tank structures under seismic action

Based on a reliability level 2 method, a procedure is proposed to design reinforced concrete structures for elevated tanks subjected to seismic action, with a specified probability of failure in a 50-year design life. To evaluate the probability of failure the ultimate limit state is obtained when the top column displacement demanded by the earthquake, a random variable, reaches the allowable displacement, which is here treated as deterministic. The seismic action is characterized probabilistically by the power spectral density function of the ground acceleration, which is obtained from a design spectrum. The strength and ductility of an annular column section of confined reinforced concrete for cyclic loads are evaluated with design aids. Design charts are made for a given tank capacity and specified seismic zone that allow one to choose different combinations of strength, stiffness and ductility for the same tolerable probability of failure. A step by step method is suggested for the design of the annular column section, choosing finally the most convenient design. The advantage of this methodology is shown through a numerical example.     

Simulation of a long-lived meso-β scale convective system over the mediterranean coast of spain. Part I: Numerical predictability

Summary An unusually long-lived (33 hours), devastating (local maximum rainfall rate over 800 mm/24 hr) meso--scale (diameter smaller than 200 km) convective system that occurred over the Mediterranean coast of Spain has been simulated reasonably well by means of a regional numerical model. Several runs of the model including parameterized convection and boundary conditions of varying degrees of complexity have been performed. In most of these experiments, the main characteristics of the event, namely its, stationarity and duration, are captured. The direct relationship between the Lagrangian lifetime of a meteorological system and its degree of deturministic predictability seems to be corroborated by the results: It appears that the meso--scale forcing that preceded and favoured the MCS was especially well predictable, and once initiated, the simulated MCS seems to have several feedback mechanisms helping to extend its life. Results are encouraging, because they reveal that it might be possible to predict very severe episodes of small MCSs such as the one shown here sufficiently in advance.With 15 Figures