Stratified System Research Articles

Evolution of linear internal waves over large bottom topography in three-layer stratified fluids

Evolutions of internal waves of different modes, particularly mode 1 and mode 2, passing over variable bathymetry are investigated based on a new numerical scheme. The problem is idealized as interfacial waves propagating on two interfaces of a three-layer density stratified fluid system with large-amplitude bottom topography. The Dirichlet-to-Neumann operators are introduced to reduce the spatial dimension by one and to adapt the three-layer system and significant topographic effects. However, for simplicity, nonlinear interactions between interfaces are neglected. Numerical techniques such as the Galerkin approximation, proven effective in previous works, are applied to save computational costs. Shoaling of linear waves on an uneven bottom is first studied to validate the proposed formulation and the corresponding numerical scheme. Then, for two-dimensional numerical experiments, mode transition phenomena excited by locally confined bottom obstacles and quickly varying topographies, including the Bragg resonance, mode-2 excitation, wave homogenization, etc., are investigated. In three-dimensional simulations, internal wave refraction by a Luneberg lens is considered, and good agreement is found in comparison with the ray theory. Finally, in the limiting case, when the top layer can be negligible (for example, a gas layer of extremely small density), the problem is reduced to a two-and-a-half-layer fluid system, where an interface and a surface are unknown free boundaries. In this situation, the surface signature of an internal wave is simulated and verified by introducing the realistic bathymetry of the Strait of Gibraltar and qualitatively compared with the satellite image.

GA-NIFS: An extremely nitrogen-loud and chemically stratified galaxy at z ∼ 5.55

Abstract We report the chemical abundance pattern of GS_3073, a galaxy hosting an overmassive active black hole at z = 5.55, by leveraging observations from JWST/NIRSpec and VLT/VIMOS. Based on the rest-frame UV emission lines, which trace high-density (∼105 cm−3) and highly ionized gas, we derive $\rm \log (N/O) = 0.42^{+0.13}_{-0.10}$. At an estimated metallicity of 0.2 Z⊙, this is the most extreme nitrogen-rich object found by JWST thus far. In comparison, the relative carbon abundance derived is $\rm \log (C/O) = -0.38^{+0.13}_{-0.11}$, which is not significantly higher than those in local galaxies and stars with similar metallicities. We also found potential detection of [Fe vii]λ6087 and [Fe xiv]λ5303, both blended with [Ca v]. We inferred a range of Fe abundances compatible with those in local stars and galaxies. Overall, the chemical abundance pattern of GS_3073 is compatible with enrichment by supermassive stars with M* ≳ 1000 M⊙, asymptotic giant branch (AGB) stars, or Wolf-Rayet (WR) stars. Interestingly, when using optical emission lines which trace lower density (∼103 cm−3) and lower ionization gas, we found a sub-solar N/O ratio, consistent with local galaxies at the same metallicity. We interpret the difference in N/O derived from UV lines and optical lines as evidence for a stratified system, where the inner and denser region is both more chemically enriched and more ionized. Our results suggest that nitrogen loudness in high-z galaxies might be confined to the central, dense, and highly ionized regions of the galaxies, while the bulk of the galaxies evolves more normally.

Groundwater monitoring in challenging environments: an argument for the construction of observation wells based on data from Niamey, Niger

AbstractGroundwater sampling in challenging environments often leads to compromises in following best practices to obtain representative samples from aquifers. This includes collecting samples from existing production or domestic wells instead of using properly constructed monitoring wells or using a bailer instead of a submersible pump for sampling. To address unusual patterns and trends in groundwater chemistry data collected in Niamey, Niger from 2012–2021, a state-of-the-art monthly sampling routine was established for eight wells tapping the basement aquifer. This was based on the hypothesis that the observed changes in groundwater composition were mainly due to differences in sampling technique, and the aim of the study was to gain insights into possible seasonal variations in water composition, to examine if the previously observed trends could be validated and to provide baseline data for future studies. The results indicate that in most cases the long well response zones in the stratified aquifer system led to the collection of water from different strata/aquifers or of strongly mixed samples. Therefore, any sample from those wells is only of limited value for the interpretation of hydrogeological processes. To obtain sound data for the development of groundwater management strategies, the monitoring has to be shifted from existing production wells to properly constructed monitoring wells. In the complex hydrogeological setting of Niamey, with hydraulically interacting aquifers and occurrences of density layering, it is fundamental to ensure that a monitoring well taps one specific depth of one target aquifer and that well-volume purging is applied properly.

Knowledge, attitude and practice regarding thirst management in surgical patients among intensive care unit nurses: A cross-sectional study.

The prevalence of thirst in intensive care unit (ICU) surgical patients is high, and its impact is significantly harmful. Nurses play a crucial role in managing thirst. It is essential to develop targeted training programmes for nurses, focusing on their knowledge, attitude and practice (KAP). To investigate KAP regarding thirst management in surgical patients among ICU nurses and the potential influencing factors related to demographic characteristics. This is a cross-sectional study. From August to September 2023, a self-developed questionnaire was distributed online in the ICUs of 14 tertiary general hospitals in Shanghai, China. This questionnaire aimed to assess the KAP of ICU nurses concerning thirst management. Influencing factors were analysed using ANOVA and the rank-sum test. Spearman correlation analysis and stratified regression analysis were employed to evaluate the relationship among KAP. The study was reported according to the STROBE checklist. A total of 530 valid questionnaires were obtained online with a response rate of 86.60%. While ICU nurses generally held a positive attitude towards thirst management, there was a noticeable deficiency in knowledge and a lack of standardization in practice. Nurses with higher educational levels, lower academic titles, who had received training and who were familiar with the consensus and guidelines on thirst management had better attitude towards managing thirst. Younger nurses, those with less ICU working experience, lower academic titles, who had received training and who were acquainted with the guidelines showed better practice. It was observed that knowledge and attitude both had a significant positive influence on practice. KAP regarding thirst management of surgical patients among ICU nurses are interconnected and require enhancement. Targeted training, focused on the identified weakness and influencing factors, needs to be carried out. An innovative and stratified training system can improve the quality of practice, as well as contributing to the professional development of ICU nurses. Further, the findings of the study provide a foundational understanding of thirst management, promoting the advancement of related scientific research.

Enhanced temperature regulation in compound heating systems: Leveraging guided policy search and model predictive control

With the widespread application of solar-energy-air-source heat pump composite heating, optimizing the regulation of air temperature in heating zones, enhancing system thermal comfort, and reducing energy consumption have become crucial. To ensure residential comfort while minimizing HVAC system energy costs, a control method combining guided policy search (GPS) with model predictive control (MPC) is proposed for composite heating systems. This method replaces state estimation in MPC with policy search and substitutes the offline trajectory optimization used in guided policy search with MPC, thus integrating the strengths of both approaches. This strategy not only improves control precision but also reduces energy consumption and enhances system robustness. The GPS-MPC control algorithm was validated against reinforcement learning and MPC. A simulation model was developed and validated on a real physical platform. Simulations compared the control effects of on-off control and MPC on pump frequency, flow rate, stratified thermal storage tank temperature, component, and system energy consumption. The data results indicate that the GPS-MPC algorithm offers superior predictive accuracy, efficiency, and robustness in composite heating control systems compared to conventional methods. Under the GPS-MPC strategy, indoor temperature fluctuations, pump frequency response speed, and energy consumption were significantly improved, with temperature fluctuation limited to only 0.8 °C, and the system achieving energy savings of over 12 %.

Lake Champlain Zooplankton Community Dynamics Following an Extreme Flood Event

Lake Champlain, the sixth largest freshwater lake in the U.S., is a deep thermally stratified temperate zone lake system. Recently, flood events have impacted the Northeastern U.S. more frequently than in past decades, resulting in increased turbidity and other impacts in northern temperate lakes. This study represents an unprecedented analysis of the impacts of major spring and summer flooding in 2011 on Lake Champlain zooplankton communities. Few studies exist on flood impacts on lake systems, especially in natural un-impounded lakes. Our results illustrate the impacts of large-scale flooding on planktonic communities in deep stratified temperate lakes and the differential responses among species based on autecological traits. Community responses include flood-adapted increase during the flood event (Ceriodaphnia reticulata and Eubosmina coregoni), a flood-intolerant decline (Asplanchna spp. and Keratella cochlearis) or a delayed flood intolerance (Daphnia retrocurva, Mesocyclops edax, and Polyarthra spp.). Our results suggest that large, temperate lakes such as Lake Champlain will experience community shifts in zooplankton composition during future extreme flood events associated with climate change-related weather patterns in the Northeastern U.S.

Second-Class Care: How Immigration Law Transforms Clinical Practice in the Safety Net.

This article examines how U.S. immigration law extends into the health care safety net, enacting medical legal violence that diminishes noncitizens' health chances and transforms clinical practices. Drawing on interviews with health care workers in three U.S. states from 2015 to 2020, I ask how federal citizenship-based exclusions within an already stratified health care system shape the clinical trajectories of noncitizens in safety-net institutions. Focusing specifically on cancer care, I find that increasingly anti-immigrant federal policies often reshape clinical practices toward noncitizens with a complex, life-threatening condition as they approach a "specialty care cliff" by (1) creating time penalties that keep many noncitizens in a protracted state of injury and (2) deterring noncitizens from seeking care through threats of immigration enforcement. Through these processes, medical legal violence also creates the potential for moral injury among health care workers, who must adapt clinical practices in response to socio-legal boundaries of belonging.

Material characterization revealing production models of the Late Ming silver hairpins

The Site of Jiangkou in Pengshan, Sichuan province revealed the largest assemblage of silver artefacts ever known in China. These artefacts were collected by Zhang Xianzhong, the rebellion general of the Late Ming and Early Qing period, from Sichuan and adjacent provinces, and sunk in the Minjiang River after his failure in 1644 CE. This research focuses on silver hairpins from this assemblage and explores their production system via detailed typological investigation and material characterization. According to their style, forming techniques and material provenance, the Jiangkou hairpins can be divided into three groups corresponding with three different types of production workshops. The first group was made in independent silversmiths mainly serving non-official civilians. Metallographic analysis shows they were made with varied forming techniques, including forging, folding, casting and welding. They were alloyed with varied amount of copper. The other two types have much more standardized forming techniques and are associated with the commercial workshops capable of mass production and government institutions. The commercial workshops commonly used forging-annealing method to make their hairpins and maintained a well consistent chemical composition across their products. The silver hairpins made by government institutions were all cast into shape, suggesting a highly standardized system. This type of hairpins were mostly found in tombs of royal families and high elites. This research revealed a stratified silver production system in the Late Ming period and demonstrated the strength of material characterization in revealing production organization models.

Piezoelectric layer guided in-plane surface waves with flexoelectricity and gradient effects

With the rapid advancement of 5 G technology, the demand for surface acoustic wave (SAW) devices is experiencing exponential growth. Precisely forecasting the speed at which Rayleigh waves propagate, taking into account size effects and flexoelectric properties, is vital for enhancing SAW device design. To address this need, the study explores Rayleigh wave propagation in a stratified system consisting of a nanoscale piezoelectric guiding layer atop an isotropic elastic substrate. The governing equations, boundary conditions, and interface continuity conditions between the guiding layer and substrate are established through the Hamiltonian principle. Following this, the dispersion equations for Rayleigh waves under electric open-circuit and electric short-circuit conditions are derived and solved numerically. Additionally, the effects of flexoelectricity, inertial gradients, strain gradients, electric field gradients, and the piezoelectric guiding layer thickness on the phase velocity of Rayleigh waves are extensively explored. Our findings indicate that flexoelectricity and strain gradients elevate the phase velocity, while inertial gradients and electric field gradients result in a decrease in the phase velocity. As the frequency of Rayleigh waves increases, the impact of these factors becomes more prominent. In addition, it is observed that electric field gradients play a less significant role compared to inertial gradients and strain gradients. The findings of this study could offer valuable insights for the advancement of miniaturized SAW devices designed for high-frequency service.

Spatially variable seismic underground motions in layered porous seabed medium induced plane wave

In ocean engineering anti-seismic filed, the marine environment is usually regarded as the coupling field of seawater-layered porous seabed-elastic bedrock. This paper presents a theoretical method to study the spatially variable seismic underground motions in stratified seabed system. Based on the potential flow theory, Biot's porous model and random vibration theory, the transfer function and coherence function model of the underground seismic motions in the marine coupling field are derived. On the basis of the above theoretical derivation, the program of the spatial variability seismic underground motions of the coupling field is simulated and developed, and its accuracy and effectiveness are verified. Moreover, the effects of soil stiffness and overlying seawater level on the seismic response are also analyzed. Numerical results show that spatially variable seismic underground motions are significantly different from those on the ocean bottom. The simulation of spatially variable seismic underground motions for layered seabed field is significant for both theoretical study and ocean engineering application.

Politics of School Choice in Germany: The Abolition of the Binding Recommendation in Baden-Wuerttemberg and Saxony

ABSTRACT The German school system is known for its stratified secondary school system following the four-year elementary school. While access to grammar schools was strictly regulated in German school history, most federal states have now strengthened the will of parents and abolished the tradition of binding elementary school recommendations. New in the group of Laender that do not have a binding Gymnasium recommendation are Baden-Wuerttemberg and Saxony. By analyzing parliament debates, this paper analyzes why Baden-Wuerttemberg and Saxony abolished the binding elementary school recommendation and have strengthened parental choice for secondary schools.

Optimal design of air distribution systems in large indoor spaces during the construction of walls: A case study on liquefied natural gas terminal storage tanks

Efficiently organizing indoor airflow is crucial for optimizing the working environment in large-scale wall construction projects, particularly when constructing liquefied natural gas membrane tanks. This helps prevent membrane corrosion, optimize construction time, and mitigate future safety risks. However, due to their size, these tanks often experience air stratification, posing challenges in meeting simultaneous temperature, humidity, and uniformity requirements during construction. To effectively address this issue, this study developed Computational Fluid Dynamics models that numerically simulated three commonly used ventilation systems: displacement ventilation system, stratified ventilation system, and fabric duct air supply system. Laboratory experiments were conducted to validate the accuracy of numerical simulation. Additionally, response surface methodology (RSM) was used to determine optimal combinations of air supply parameters for superior environmental uniformity control. The findings indicate that the fabric air supply system is more suitable than displacement and stratified ventilation systems for achieving environmental uniformity control in large spaces. It can limit wall temperature nonuniformity coefficient up to 9 % during summer and provide better uniformity in air velocity during winter conditions. Moreover, under summer conditions, the optimal range for air supply speed is between 9.62 m/s - 11.22 m/s with temperatures ranging from 16 °C to 19 °C, while under winter conditions, the optimal range is between 18.3 m/s −19.3 m/s with temperatures ranging from 33.0 °C to 35.0 °C.The optimal design of the ventilation system is advantageous for various building construction scenarios with stringent temperature and humidity requirements, particularly for large-scale buildings.

Exploring conceptualisations of vocational education in China: how the hierarchical education system mirrors social hierarchy

This research examines conceptualisations of Chinese vocational education. The parallel routes of academic and vocational education sort students into either strand with standardised exams. However, the status of academic and vocational work has been established through a culture of Confucianism. In order to examine current conceptualisations of vocational education, website-based commenting was used as an e-research method. Postings on the Chinese internet community Zhihu (知乎) were analysed for word frequency and user voice and examined through the lens of vocational system classification theory. It was found that Chinese socio-historical perspectives inform societal perceptions of education; that social divides reinforce academic/vocational educational divides, and that the stratified educational system of China further contributes to vocational education’s unsatisfying learning environment. Since addressing societal perspectives is particularly complicated, it is recommended that those who seek to reduce educational inequality work to improve the educational quality and student experience of vocational education.

To Mix or Not to Mix: Details of Magma Storage, Recharge, and Remobilization during the Pacheco Stage at Misti Volcano, Peru (≤21–2 ka)

Abstract We investigate ten of the most recent tephra-fall deposits emplaced between ≤21 and 2 ka from the Pacheco stage of Misti volcano, Peru, to elucidate magma dynamics and explosive eruption triggers related to magma storage, recharge, and remobilization. Whole-rock, glass, and mineral textures and compositions indicate the presence of broadly felsic, intermediate, and mafic magmas in a chemically and thermally stratified magma storage system (Zones 1–3) that interact to differing extents prior to eruption. Intermediate magmas are defined by plagioclase + amphibole + two-pyroxenes + Fe-Ti oxides and phase equilibria indicate they formed at ~300 to 600 MPa and ~950°C to 1000°C. Intermediate magmas dominate the Pacheco stage and either erupted alone as hybridized magmas or mingled with minor volumes of cool felsic magmas (~800°C) in which only plagioclase + Fe-Ti oxides are stable. Felsic magmas do not exclusively comprise any tephra-fall deposit emplaced during the Pacheco stage but were remobilized by recharge and mixing with intermediate magmas in order to erupt. Furthermore, felsic-hosted amphibole cognate to the intermediate magmas are reacted despite the felsic magmas being water saturated, which suggests they are staged above the amphibole stability limit (≤200 MPa). The cryptic presence of mafic magmas is indicated by high-An plagioclase cores (An74–88), rare anhedral olivine (Fo77–80), and possibly high Mg# augite and amphibole (up to Mg# 84 and 77, respectively). The dearth of basalt to basaltic andesite melts recorded in erupted glasses and exclusivity of high-An plagioclase to crystal cores signals mafic magmas are staged deeper in the crust than the intermediate magmas. Periodic interactions between these magmas tracked via glass compositions and crystal exchange reveal an alternation between the production of mingled magmas and their eruption shortly after a recharge event, followed by a period of homogenization and eruption of hybridized magmas. As such, we identify magma recharge as a key mechanism by which half of the explosive eruptions were triggered in the Pacheco stage. A >100°C increase in Misti’s fumarole temperatures from 1967 to 2018 coincident with changes in fumarolic gas compositions is consistent with degassing of a mafic recharge magma, signaling that Misti could produce similar explosive eruptions in the future.

Exploring normative frameworks of fairness through (relational) institutional habitus in Oxford's undergraduate admissions process.

In the UK's stratified HE system the question of who is able to access the most selective and prestigious universities is fraught with issues of fairness. This paper explores how decision-makers in Oxford's undergraduate admissions process construct norms of fairness and how such norms inform their reflexive considerations and actions around admissions decisions. Framing such norms as multiple institutional habituses, the paper considers how decision-makers compromise and negotiate between institutional habituses in tension. Further, it presents an augmented conception of institutional habitus - the relational institutional habitus - which offers a conceptual tool to make sense of the existence of multiple contested institutional norms and their partial and fragile reconciliation in institutional action.

Groundwater, salt and contaminant transport in a coastal aquifer system with a low‐permeability layer in the intertidal zone

AbstractLow‐permeability layer (LPL), formed by natural deposit or artificial reclamation and commonly found below the intertidal zone of coastal groundwater system, can retard the ingress of seawater and contaminants, and shorten the travel time of the land‐sourced contaminant to the marine environment compared with a homogenous sandy coastal aquifer. However, there is limited understanding on how an intertidal LPL, a condition occurred in a coastal aquifer at Moreton Bay, Australia, influences the groundwater and contaminant transport across the shallow beach aquifer system. We characterized the aquifer hydrological parameters, monitored the in situ groundwater heads, and constructed a 2‐D numerical model to analyses the cross‐shore hydrological processes in this stratified system. The calibrated model suggests that in the lower aquifer, the inland‐source fresh groundwater flowed horizontally towards the sea, upwelled along the freshwater–saltwater interface, and exited the aquifer at the shore below the LPL. Whereas in the upper aquifer, the tidally driven seawater circulation formed a barrier that prevented fresh groundwater from horizontal transport and discharge to the beach above the LPL, thereby directing its leakage to the lower aquifer. A contaminant represented by a conservative tracer was ‘released’ the upper aquifer in the model and results showed that the spreading extent of the contaminant plume, the maximum rate of contaminant discharge to the ocean, and its plume length decreased compared with a simulation case in a homogenous sandy aquifer. Sensitivity analysis was also conducted to investigate the characteristics of the LPL, including its continuity and hydraulic conductivity, which were found to vary along the beach at Moreton Bay. The result shows that with a lower hydraulic conductivity and continuous layer of LPL reduced the groundwater exchange and contaminant transport between upper and lower aquifer. The findings from the combined field and modelling investigations on the impact of an intertidal LPL on coastal aquifer systems highlight its significant implications to alter the groundwater and mass transport across the land–ocean interface.

Synchronic distribution of the dinoflagellate Protoceratium reticulatum and yessotoxins in a high stratified fjord system: Tidal or light modulation?

Protoceratium reticulatum is the main yessotoxin-producer along the Chilean coast. Thus far, the yessotoxin levels recorded in this region have not posed a serious threat to human health. However, a bloom of P. reticulatum during the austral summer of 2022 caused the first ban of shellfish collection, due to the high toxin levels. A bloom of P. reticulatum during the austral summer of 2020 allowed an evaluation of the fine-scale distribution of the dinoflagellate during a tidal cycle. High-resolution measurements of biophysical properties were carried out in mid-summer (February 18–19) at a fixed sampling station in Puyuhuapi Fjord, Chilean Patagonia, as part of an intensive 24-h biophysical experiment to monitor the circadian distributions of P. reticulatum vegetative cells and yessotoxins. High P. reticulatum cell densities (>20 × 103 cells L–1) were found in association with a warmer (14.5–15 °C) and estuarine (23.5–24.5 g kg–1) sub-surface water layer (6–8 m). P. reticulatum cell numbers and yessotoxins followed a synchronic distribution pattern consistent with the excursions of the pycnocline. Nevertheless, the surface aggregation of the cells was modulated by the light cycle, suggesting daily vertical migration. The yessotoxin content per P. reticulatum cell ranged from 9.4 to 52.2 pg. This study demonstrates both the value of fine-scale resolution measurements of biophysical properties in a highly stratified system and the potential ecosystem impact of P. reticulatum strains producing high levels of yessotoxins.

Establishment of glioma prognosis nomogram based on the function of meox1 in promoting the progression of cancer

BackgroundGliomas stand out as highly predominant malignant nervous tumors and are linked to adverse treatment outcomes and short survival periods. Current treatment options are limited, emphasizing the need to identify effective therapeutic targets. The heterogeneity of tumors necessitates a personalized treatment approach with an effective grouping system. Meox1 has been implicated in promoting tumor progression in diverse cancers; nonetheless, its role in gliomas remains unelucidated. Material/methodsUtilized immunohistochemistry to assess the expression of Meox1 protein in glioma tissues. Proliferation and invasion assays were conducted on wild-type and meox1-overexpressed glioma cells using the CCK8 and Transwell assays, respectively. The expression levels of meox1 and its related genes in gliomas were obtained from Chinese Glioma Genome Atlas (CGGA), along with the corresponding patient survival periods. LASSO regression modeling was employed to construct a scoring system for patients with gliomas, categorizing them into high-/low-risk groups. Additionally, a nomogram for predicting the survival period of patients with glioma was developed using multivariate logistic analysis. ResultsWe attempted, for the first time, to demonstrate heightened expression of Meox1 in glioma tumor tissues, correlating with significantly increased invasion and proliferation abilities of glioma cells following meox1 overexpression. The scoring system effectively stratified patients with glioma into high-/low-risk groups, revealing differences in the survival period and immunotherapy efficacy between the two groups. The integration of this scoring system with other clinical indicators yielded a nomogram capable of effectively predicting the survival period of individuals with gliomas. ConclusionsOur study established a stratified investigation system based on the levels of meox1 and its related genes, providing a novel, cost-effective model for facilitating the prognosis prediction of individuals with glioma.

Detecting climate-driven ecological changes in high-altitude lakes in the Sierra Nevada, California

Over the past several decades, increasing climate instability in the Sierra Nevada, California, expressed primarily as reduced winter precipitation and higher temperatures, has led to more frequent drought. High-altitude lakes in this region have been characterized as pristine ecosystems, but growing evidence suggests that they are responding acutely to climate change. To address this, we analyzed the diatom assemblages of two 210Pb dated sediment cores (Gull and June Lakes) from the eastern Sierra Nevada with the aim of assessing their sensitivity to and timing of responses to climate change at the end of the neoglacial (~1450 CE to ~1850 CE) and identifying how climate drivers can impact diatom communities. The nutrient cycles of both lakes have been disrupted by changes in thermal stratification, driven by increasing temperatures, as interpreted from the shift from a Stephanodiscus corruscus dominated ecosystem to a Stephanodiscus minutulus dominance. In this case, the June Lake (the deeper lake) diatom assemblage shifted from an assemblage representative of well mixed conditions to one representative of a stratified system before Gull Lake as a response to increasing temperatures and a strengthened thermocline. We relate the asynchronous change in the thermocline stability to basin morphology, where the deeper lake with a deeper thermocline is more sensitive to increasing temperatures. Further, generalized additive models (GAMs) allowed us to identify the onset of ecological change in both lakes, pointing to the termination of the Little Ice Age (LIA; ~1850 CE), revealing an acute response to changing climate.

Dynamic re-sedimentation of lacustrine carbonates in the Búzios Field, pre-salt section of Santos Basin, Brazil

The huge oil accumulations in the South Atlantic Pre-Salt section have driven studies that seek a greater understanding of the origin and evolution of these important reservoirs. Lacustrine carbonate intraclastic deposits correspond to the main reservoirs in the Búzios Field, currently with the highest daily production wells in the world, and in other Santos Basin fields. However, few studies were dedicated to these deposits due to the great complexity of Pre-Salt deposits and the lack of analogs. These factors have generated intense controversies in the interpretation of their depositional models. A systematic petrographic characterization allowed detailed characterization of the textures and primary constituents in the rift and sag sections of a well in the Búzios Field. The bioclastic accumulations of the rift Itapema Formation, show features indicative of reworking, such as abrasion, fragmentation and disarticulation of the bivalve bioclasts. Moreover, the bioclasts occur mainly within intraclasts and as nuclei of ooids, characteristics of multicycle redeposition. The massive structure of these deposits, the lack of characteristic wave structures, their distribution in lows and conspicuous mixing with stevensitic grains indicate their gravitational redeposition, as result of the intense tectonic activity during the rift phase. The sag phase Barra Velha Formation deposits are composed of intraclasts eroded from the in situ spherulites and shrubs. These rocks are predominantly massive, lack subaerial exposure features, and display features that point to dynamic and multicyclic reworking. Furthermore, they occur intercalated with in situ deposits in high frequency, even at a thin section scale. These aspects, along with the consistency of isotope values, the widespread spatial distribution and preservation of stevensite across diverse Pre-Salt areas, suggest that gravitational, waves and currents redeposition models should be reevaluated. We propose that internal waves, generated by perturbations of the chemocline of a meromictic, stratified lacustrine system promoted recurrent reworking of the in situ deposits. This generated intraclastic levels with multicycle redeposition aspects, often interlayered with the characteristic in situ deposits. Understanding the processes that generated these deposits will contribute to reduce exploration risks and optimize hydrocarbon production from the intraclastic reservoirs.