Anatomy and Sequence Architecture of the early Post-Rift in the Neuquén Basin (Argentina): A Response to Physiography and Relative Sea-level Changes

A detailed architectural and sequence stratigraphic analysis was carried out in the early-post-rift succession of central Neuque´n Basin (Middle Jurassic Cuyo Group), integrating outcrop and subsurface information from a 3,000 km2 area. Sedimentary facies analysis allowed the definition of six marine facies associations, which are grouped in two main depositional systems. During the late Toarcian to early Bathonian a storm- and wave-dominated shoreface to offshore system was developed. This is overlain by a late Bathonian–early Callovian fluvio-deltaic depositional system. The sequence stratigraphic analysis of this succession identified parasequences limited by marine flooding surfaces with little evidence of erosion. Parasequences could be grouped into four parasequence sets that show the evolution of the depositional systems and can be interpreted in terms of shoreline trajectories. In this sense, a log-term transgressive event defined by a complicated retrogradational stacking pattern and spanning for almost 10 My is identified for the older deposits. This succession is eventually replaced by a progradational unit that represents highstand conditions. The Cuyo succession identified in this part of the basin is completed by the development of a regressive surface and the onset of a deltaic depositional system with no parasequence development but indicating an abrupt basinward facies shift. The long-term transgression that dominates the early post-rift succession in this part of the basin is interpreted to represent a period of sustained accommodation creation produced by the combination of thermal subsidence, differential compaction of syn-rift deposits, and eustatic rise under a relatively low sediment supply. Changes in the stacking pattern of retrogradational parasequence sets are thought to be produced by changes in the bathymetry of the topography being flooded, which is a relic of a complex array of footwalls and shoulders generated during the syn-rift stage. Regional changes in thickness and timing for the early post-rift succession could be therefore the result of the relatively passive infill of an inherited topography of the syn-rift, suggesting that most of the accommodation was already created before the onset of the long-term transgressive trend that characterizes the post-rift succession in this part of the basin. The Cuyo Group succession reported here reflects the complexity in terms of depositional styles, sequence stratigraphic patterns, and controls that can be expected during the early-post rift infill of syn-rift structural depressions. Therefore, the results of this study can provide useful lessons for post-rift systems having prolific hydrocarbon production worldwide (e.g., in the Northern North Sea, Norwegian Sea, Thailand, and Argentina and Chile).Fil: Veiga, Gonzalo Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Schwarz, Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Spalletti, Luis Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Massaferro, Jose L. YPF S.A; Argentin

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In laboratory experiments we measured the saturation effects on the acoustic properties in carbonates and the results question some theoretical assumptions. In particular, these laboratory experiments under dry and wet conditions show that shear moduli do not remain constant during saturation. This change in shear modulus puts Gassmann's assumption of a constant shear modulus into question and also explains why velocities predicted with the Gassmann equation can be lower or higher than measured velocities. Background and experimental setup. Porosity is the most important factor controlling sonic velocity but our data document that pore type, pore fluid compressibility and variations in shear modulus due to saturation are also important factors for velocities in carbonate rocks. Most laboratory research on saturation effects has been carried out in sandstone, despite the fact that about half of the world's oil and gas reserves are in carbonates. Only a few studies had investigated the effect of saturation on velocity in carbonate rocks. Rafavich et al. (1984) conclude that porosity is the major factor influencing velocity and that pore-fluid type has no statistically relevant influence. In contrast, Japsen et al. The aim of the study described in this article was to further investigate the effect of saturation on different carbonates. We selected 30 limestone samples from Cretaceous and Miocene reservoirs with porosities from 3% to over 30%, and having different texture and pore types. Measuring sonic velocity under dry and saturated conditions on a single sample under variable confining pressure is an experimental challenge, because the sample might be altered during pressurization. To overcome this experimental dilemma we selected macroscopically homogeneous samples and cut them in half. Samples with nearly identical porosities (less the 2% variation) in both halves were used for this experiment. One half of each sample was measured first under dry conditions using variable hydrostatic confining pressure in steps from 2 MPa up to a maximum of 80 MPa and back down to 2 MPa. If, upon completion of the pressure cycle, no hysteresis effect was detected, the sample was considered unaltered and measured under saturated conditions. Otherwise, the second half of the sample was used for measurements under saturated conditions. The samples were saturated with degassed, distilled water for at least 12 hours under vacuum conditions to assure complete saturation. During the measurement, the pore fluid pressure was kept constant at 2 MPa. The same effective pressure steps as used in the dry sequence were measured. A single compressional wave and two orthogonally polarized shear waves were simultaneously measured at center frequency of 1 MHz. Effect of saturation on V P , V S , and V P /V S ratio. Gas-water substitution causes an increase in bulk modulus and in compressional-wave velocity (V P ). In we exclude the bulk moduli stiffening effect, then the increased bulk density due to water-filled pores slightly reduces both the shear-wave velocity (V S ) and V P . This density effect solely does not change the V P /V S ratio Many compressional velocities of our water-saturated samples are higher than the dry samples, and most shearwave velocities decrease in the saturated samples

Global attitudes in the management of acute appendicitis during COVID-19 pandemic: ACIE Appy Study

Background: Surgical strategies are being adapted to face the COVID-19 pandemic. Recommendations on the management of acute appendicitis have been based on expert opinion, but very little evidence is available. This study addressed that dearth with a snapshot of worldwide approaches to appendicitis. Methods: The Association of Italian Surgeons in Europe designed an online survey to assess the current attitude of surgeons globally regarding the management of patients with acute appendicitis during the pandemic. Questions were divided into baseline information, hospital organization and screening, personal protective equipment, management and surgical approach, and patient presentation before versus during the pandemic. Results: Of 744 answers, 709 (from 66 countries) were complete and were included in the analysis. Most hospitals were treating both patients with and those without COVID. There was variation in screening indications and modality used, with chest X-ray plus molecular testing (PCR) being the commonest (19\ub78 per cent). Conservative management of complicated and uncomplicated appendicitis was used by 6\ub76 and 2\ub74 per cent respectively before, but 23\ub77 and 5\ub73 per cent, during the pandemic (both P < 0\ub7001). One-third changed their approach from laparoscopic to open surgery owing to the popular (but evidence-lacking) advice from expert groups during the initial phase of the pandemic. No agreement on how to filter surgical smoke plume during laparoscopy was identified. There was an overall reduction in the number of patients admitted with appendicitis and one-third felt that patients who did present had more severe appendicitis than they usually observe. Conclusion: Conservative management of mild appendicitis has been possible during the pandemic. The fact that some surgeons switched to open appendicectomy may reflect the poor guidelines that emanated in the early phase of SARS-CoV-2