Topographic Configuration Research Articles

Enhanced post-wildfire vegetation recovery in prescribed-burnt Mediterranean shrubland: A regional assessment

The primary objective of prescribed burning (PB) treatment is to promote increased ecosystem resistance to high fire severity and ecosystem adaptive resilience after unplanned wildfires under worsening climates. Yet, empirical evidence involving regional-scale assessments with enough spatial representativeness on how vegetation will respond to PB-wildfire interactions in Mediterranean shrublands is absent. This is particularly relevant to provide comprehensive insights on the effectiveness of PB policies and programs in southern European countries, where shrublands are the main PB target. Here, we investigated the PB effect on vegetation responses in the short-term (1–3 years) after subsequent wildfire encounters in Mediterranean shrublands at the regional scale across mainland Portugal. We leveraged geospatial cloud-computing platforms and remote sensing data (optical and synthetic aperture radar -SAR-) and techniques with physical basis to procure reliable proxies for vegetation fractional cover (FCOVER), vigor (normalized difference vegetation index; NDVI) and structural complexity (cross-polarization ratio of C-band SAR backscatter data; SAR-CR) at the landscape scale throughout the time series. The role of site productivity and topographic configuration variables as putative drivers of vegetation responses was also analyzed. We found that the mitigating effect of PB on wildfire severity translated into stronger vegetation responses in treated areas than in untreated counterparts after the first PB-wildfire encounter. Although FCOVER, NDVI and SAR-CR recovered gradually in both areas, the recovery rate was markedly higher in PB-treated areas 3-years after the PB-wildfire encounter than at earlier times in the time series. The effect of PB treatment was stronger for the FCOVER recovery response than for NDVI and SAR-CR. The effect of the PB treatment on FCOVER and NDVI responses was modulated by site environmental characteristics, such that their differences between PB-treated and untreated counterparts were maximal for both higher altitudes and warmer, drier locations in the landscape.

Autogenic evolution of valley‐confined deltas during sea‐level rise: Insights from numerical and physical modelling

AbstractNearshore incised valleys are important conduits for the transport of sediment, nutrients, pollutants and organic carbon from the continents to the sea. Therefore, it is essential to understand the autogenic evolution of deltas confined within incised valleys and how such evolution is affected by relative sea‐level rise. To date, limited research has focused on how deltas constrained by incised valleys or other forms of antecedent topography respond to rising sea level. An existing theory of autostratigraphy envisages scenarios in which two‐dimensional or unconfined three‐dimensional fan deltas can experience three evolutionary stages under constant rates of relative sea‐level rise and sediment supply: progradation, autoretreat and post‐autobreak transgression. In this work, an integrated study of geometric numerical models and physical experiments is undertaken to investigate autostratigraphic delta evolution for a variety of incised‐valley geometries, under conditions of constant rates of relative sea‐level rise and sediment supply. Results indicate that interplays of antecedent topography (valley geometries) and sediment mass balance expressed in resultant deltaic geometries can result in autogenic changes in shoreline dynamics and river avulsion frequency on deltas. The following primary findings arise. (i) Compared to valleys with rectangular and trapezoidal cross‐sectional profiles, valleys with triangular cross‐sections tend to contain deltas that experience faster rates of progradation, autoretreat and post‐autobreak transgression under rising sea level, and exhibit a more prominent convex‐seaward shoreline trajectory. (ii) The shoreline trajectory is also related to delta topset geometry, becoming more convex‐seaward under decreasing topset slopes. (iii) River avulsion frequency on deltas with rising sea level varies markedly across valleys with different geometries, even under the same rate of relative sea‐level rise; this is attributed to the difference in temporal evolution of shoreline migration for different valley geometries and the resultant difference in the delta topset aggradation. This study highlights complexities in responses of sedimentary systems under the confinement of different topographic configurations that have hitherto largely been overlooked in sequence‐stratigraphic models. The findings provide insight into future shoreline behaviour and river avulsion hazard on confined deltas, and for decoding the stratigraphic record.

Heterogeneous Basal Thermal Conditions Underpinning the Adélie‐George V Coast, East Antarctica

AbstractAdélie‐George V Land in East Antarctica, encompassing the vast Wilkes Subglacial Basin, has a configuration that could be prone to ice sheet instability: the basin's retrograde bed slope could make its marine terminating glaciers vulnerable to warm seawater intrusion and irreversible retreat under predicted climate forcing. However, future projections are uncertain, due in part to limited subglacial observations near the grounding zone. Here, we develop a novel statistical approach to characterize subglacial conditions from radar sounding observations. Our method reveals intermixed frozen and thawed bed within 100 km of the grounding‐zone near the Wilkes Subglacial Basin outflow, and enables comparisons to ice sheet model‐inferred thermal states. The signs of intermixed or near thawed conditions raises the possibility that changes in basal thermal state could impact the stability of Adélie‐George V Land, adding to the region's potentially vulnerable topographic configuration and sensitivity to ocean forcing driven grounding line retreat.

Impact of Western Ghats orography on the simulation of extreme precipitation over Kerala, India during 14–17 August 2018

The state of Kerala, located in southwest peninsular India, has experienced a series of extremely heavy rainfall events in the past few years, resulting in severe flooding and landslides. Among these events, an extremely heavy rainfall episode (50 to 480 mm/day) occurred during 14–17 August 2018 had led to devastating floods along the southwest coast of India. In this study, we have chosen this event as a case study to analyze the role of orography, using a high-resolution (1-km) cloud-resolving WRF model configuration. We conducted four numerical sensitivity experiments to examine the impact of different topographic configurations, ranging from no-mountain to plateau, moderate, and steep mountain terrains, on the simulation of the extreme rainfall event. The results of the mountain sensitivity experiments indicate that as mountain height increases, simulated low-level wind decelerates quickly. This flow blocking is also manifested in parameters such as reduced upper-air wind intensity, increased dynamical convergence, and increase of vertical velocities at the Western Ghat (WG) mountain barriers, which lead to the variations in moist instability and cloud microphysical processes influencing the horizontal and vertical distribution of solid-phase hydrometeors. Furthermore, the results also show that a reduction in the orography of the WGs decreases the vertical extension of low-level jet winds to upper levels, weakens the tropical easterly flow, and decreases the wind shears between the lower and upper troposphere. In addition, the results suggest that large-scale variations in mountain orography in numerical simulations can affect the simulated magnitude and direction of moisture transport, which may have played a role in determining the magnitude and distribution of simulated rainfall over Kerala.

Is it really keratoconus ‐ topographic mimicry

Aims/Purpose: The aim of this case series is to present eyes with topographic keratoconus configuration, but in which objectifiable no keratoconus exists and thus a so‐called pseudo‐keratoconus is present.Methods: Inclusion criteria were a topographic classification of the cornea as keratoconus by Scheimpflug imaging using the topographic keratoconus classification TKC and a typical elevation data profile with irregular astigmatism and slope (= Ansteilung) of the cornea. Clinical image by slit lamp examination, best‐corrected visual acuity and Scheimpflug tomography of the anterior segment of the eye (Pentacam®, OCULUS, Wetzlar, Germany) were analysed.Results: In our case series, 33 eyes of 23 patients were included. The mean age was 51 (±16) years and the ratio of females to males was balanced. The mean Kmax was 51.1 (±7.1) dioptres. The mean corneal thickness at the thinnest point was 517 (±80) μm. The best‐corrected decimal visual acuity was 0.47 (±0.27). The study eyes were divided into 3 groups according to the underlying cause of the topographic changes. One group included corneal diseases with inferior slope in topography (corneal scar n = 9, Map‐Dot‐Fingerprint dystrophy n = 6, Fuchs endothelial dystrophy n = 5, vortex keratopathy n = 2). The second group had a superior corneal slope that could be interpreted as a superior keratoconus configuration (Map‐Dot‐Fingerprint dystrophy n = 5, irregular astigmatism without other corneal pathology n = 2, Salzmann corneal degeneration n = 1, corneal scar n = 1). The third group included eyes with postoperative newly occurring keratoconus configuration after phototherapeutic keratectomy (n = 2).Conclusions: This case series shows that different corneal pathologies can imitate a topographic keratoconus configuration. The identification – not least at the slit lamp – and differentiation of these pathologies from keratoconus are important in daily practice with regard to counselling of the patients and further treatment.

Optimized Irrigated Water Management Using Numerical Flow Modeling Coupled with Finite Element Model: A Case Study of Rechna Doab, Pakistan

The fate of agriculture in Pakistan is predominantly concerned with excessive water mining threats to the subsurface water resources. The current study integrates the Visual MODFLOW-2000 application to estimate the water balance of an aquifer bounded by the Chenab River in the West and the Ravi River in the East, which covers an area of about 2.98 million hectares. An assimilated method of groundwater flow is employed to characterize the flow dynamics of the Rechna Doab aquifer. The Digital Elevation Model (DEM) produced by the Shuttle Radar Topography Mission (SRTM) and a mesh of discretized cell size (2500 m) were incorporated into the model design. The conceptual model of the alluvial aquifer involves trifold vertical boundaries (an initial fold thickness set up to 150 m). The model input parameters are precipitation, seepage through irrigation, return flow, recharge, hydraulic conductivity and evapotranspiration. Empirical relations are established (at the basin scale) for the discharge input of irrigation canals. Model results confirm that groundwater flow follows the topographic configuration of the study area (i.e., northeast to southwest), and the seepage from irrigating canals and rainfall appeared to be the main source of groundwater recharge among various resources. The zone budget study under steady state simulation showed that the total direct recharge to the aquifer is calculated as 522,910 acre foot. The simulated water balance of the studied aquifer reflects more fluctuations in river leakage. The predictive optimized model reflects an adaptation of canal lining and installation of additional tube wells that will minimize canal seepage by 70% and lead to the reclamation of 37,000 acres of water-logged land for normal cropping.

The effects of diachronous surface uplift of the European Alps on regional climate and the oxygen isotopic composition of precipitation

Abstract. This study presents the simulated response of regional climate and the oxygen isotopic composition of precipitation (δ18Op) to different along-strike topographic evolution scenarios. These simulations are conducted to determine if the previously hypothesized diachronous surface uplift in the Western and Eastern Alps would produce δ18Op signals in the geologic record that are sufficiently large and distinct to be detected using stable isotope paleoaltimetry. We present a series of topographic sensitivity experiments conducted with the water-isotope-tracking atmospheric general circulation model (GCM) ECHAM5-wiso. The topographic scenarios are created from the variation of two free parameters, (1) the elevation of the Western–Central Alps and (2) the elevation of the Eastern Alps. The results indicate Δδ18Op values (i.e., the difference between δ18Op values at the low- and high-elevation sites) of up to −8 ‰ along the strike of the Alps for the diachronous uplift scenarios, primarily due to changes in orographic precipitation and adiabatic lapse rate driven localized changes in near-surface variables. These simulated magnitudes of Δδ18Op values suggest that the expected isotopic signal would be significant enough to be preserved and measured in geologic archives. Moreover, the simulated slight δ18Op differences of 1 ‰–2 ‰ across the low-elevation sites support the use of the δ–δ paleoaltimetry approach and highlight the importance of sampling far-field low-elevation sites to differentiate between the different surface uplift scenarios. The elevation-dependent rate of change in δ18Op (“isotopic lapse rate”) varies depending on the topographic configuration and the extent of the surface uplift. Most of the changes are significant (e.g., −1.04 ‰ km−1 change with slope error of ±0.09 ‰ km−1), while others were within the range of the statistical uncertainties (e.g., −0.15 ‰ km−1 change with slope error of ±0.13 ‰ km−1). The results also highlight the plausible changes in atmospheric circulation patterns and associated changes in moisture transport pathways in response to changes in the topography of the Alps. These large-scale atmospheric dynamics changes can complicate the underlying assumption of stable isotope paleoaltimetry and therefore require integration with paleoclimate modeling to ensure accurate reconstruction of the paleoelevation of the Alps.

CFD-DEM modeling of turbidity current propagation in channels with two different topographic configurations

Submarine turbidity currents are a special type of sediment gravity flow responsible for turbidite deposits, attracting great interests from scientists and engineers in marine and petroleum geology. This paper presents a fully coupled computational fluid dynamics (CFD) and discrete element method (DEM) model to quantitatively analyze the turbidity current propagation in channels with two different topographic configurations. An appropriate drag force model is first incorporated in the CFD-DEM scheme, and two benchmark cases, including a single-particle sedimentation case and an immersed granular collapse case, are conducted to verify the accuracy of the developed CFD-DEM model. The model is then employed to investigate the fluid and particle dynamics of turbidity currents flowing over a flat bed (FB), and three obstacle-placed beds with different heights (OPB, OPB_1 and OPB_2). The CFD-DEM results indicate that the front position of turbidity current in the FB case is well consistent with the classic lock-exchange experiment. Results also show that the presence of the obstacle can clearly diminish the inter-particle collisions and the particle kinetic energy, weaken the particle-fluid interactions, and further make more sediment particles settle in front of the obstacle. Increase of obstacle height can result in diverse flow morphology of particles and fluids, and intensify the influences of obstacle on particle dynamics of turbidity currents. We show that our models enable reproducing the typical process of turbidity current propagation, and further can provide more valuable insights in understanding the turbidite-related geological phenomena from the point of view of particulate flow.

Selection of Optimum Land Leveling Design Method for Surface Irrigation

Land leveling or land grading of surface irrigated fields improve irrigation water distribution and application efficiencies, conserve water and increases crop productivity. Land formation for irrigation face many constraints (ensuring proper slopes, prevention of flood, ensuring canal water command over the field, optimizing earthwork, minimizing truck travel distances, proper equipment utilization). Design engineers traditionally, perform site formation design manually by plane shape, least squire or linear programming methods. Such methods are with different characteristics. The main objective this study is to select and compare performance of these three design methods for proper land leveling design. Consequently, the basic theory of these alternative design methods are reviewed and their performance using data surveyed from five fields in Khartoum North-Sudan, each with different soil surface topographic configurations, is analyzed. The statistical analysis revealed that the linear programming method is the most appropriate design method. Employing the linear programming design method revealed that design slopes in row and cross row directions are within the acceptable range (0.1 to 0.5, the ratio of Cut/fill volumes is within the recommended range (1.1 to 1.3), uniformity of distribution of design elevations of grid points are acceptable and within the target limits (80%), while their deviation is at 80% of grid points around the mean before leveling.

Old name, new face: A systematic analysis of flexor digitorum superficialis muscle with “chiasma antebrachii”

The gross anatomy of the forearm flexors, particularly that of the flexor digitorum superficialis (FDS) muscle, has been described and graphically illustrated in several anatomical books and atlases starting in the middle of the century before last. However, in anatomical dissection studies as well as in clinical-anatomical courses training muscle-specific targeted injections due to movement disorders such as dystonia or spasticity, it has become apparent that there is a need for a closer investigation of the complex construction of the FDS muscle. To this end, we studied the structure of the muscle bellies and tendons of FDS on 46 human body donates that have been used either in our dissection or clinical-anatomical training courses. With this, we demonstrate here the topographical configuration of the individual muscle belly for each of digits 2 through 5 and the exact paths of their tendons until their passing through the carpal tunnel. Furthermore, we demonstrate the presence of a chiasm of the FDS tendons for the digits 2 and 3, approximately 3–4 cm proximal of the carpal tunnel. Thus, we introduce herewith the terminology “chiasma antebrachii”. These findings were confirmed in situ by imaging of fixed human body donates via MRI and corroborated by MRI and ultrasound imaging in two volunteers. Taken together, the present findings enable an updated understanding of the complex organization of the heads, bellies, and tendons of FDS that is relevant not only for anatomical teaching but also clinical interventions.

Formation and evolution of the Asian landscape during the Cenozoic

<p>Asia has a unique set of landscapes, notably characterized by the highest plateau in the world, the strongest monsoon circulation, and an immense arid region. When and how this landscape was formed have long been investigated, but explanations remain elusive. In this paper, through a synthesis of both terrestrial and marginal marine sedimentary records and numerical simulation analyses, we propose that tectonic uplift/deformation and global cooling during the Cenozoic have controlled the evolution of Asian topography and climate, respectively, and, the Asian landscape. The Asian landscape has undergone three main stages of evolution, <i>viz</i>: development of low-relief topography and warm-dry climate during the Eocene (~50-34 Ma); emergence of high relief topography in the southwest, along with a diverse range of landforms elsewhere, associated with a warm monsoon-arid climate coupling system during the Oligocene to early Pliocene (34-3.0 Ma); and development of the typical Asian summer and winter monsoon circulation and present landscape since the late Pliocene, accompanied by significant global cooling. Our analyses reveal that the distribution of river catchments, flora, fauna and soils are controlled by tectonic uplift/deformation and palaeoclimate changes. Stepwise evolution of the Asian landscape since ~50 Ma was driven by tectonic deformation and global temperature changes, each of which may play different role(s) in landscape evolution. For instance, the India-Asia collision played a vital role in the formation of the Asian topographic configuration in the middle Eocene, which generated regional atmospheric circulation. On the other hand, global cooling during the late Pliocene played an important role in generating the modern-like Asian landscape including the rapid accumulation of loess deposits, strengthening of the Asian monsoon circulation, and the evolution of modern topography. To summarize, we broadly propose a three-stage history of landscape evolution in Asia during the Cenozoic. The detailed processes of Asian landscape evolution and the specific roles of tectonism and global temperature in controlling Asian landscapes and palaeoclimate evolution need to be further investigated.</p>

Decoding of groundwater recharge in deep aquifers of foreland Basins using stable isotopes (δ18O and δD) and anion-cation analysis: A case study in the southern Llanos Basin, Colombia

The topographic and structural configuration of the deformation front in foreland basins has implications in the process of hydrologic recharge of deep aquifer systems. Deep aquifer systems are favored when tectonic deformation has exhumed aquifer units to the surface, creating a connection between the surface and subsurface. The indirect water recharge processes established by this connection allow meteoric water to infiltrate and travel long distances through a basin. Therefore, establishing recharge zones and determining the influence of meteoric waters in deep aquifers represents a challenge to understand the dynamics and hydraulic potential of this type of system. This study presents new oxygen and hydrogen isotopic data from 162 samples of surface water and 109 samples from groundwater. Groundwater samples were taken from deep wells (700 m–4000 m deep) that penetrated the aquifer units that make up the Basal Flow Unit (BFU) present in the southern Llanos basin in Colombia. In addition, anion (−) and cation (+) analysis (HCO3−, CO3−2, SO4−2, Cl−, Na+, K+, Ca+2, Mg+2) was performed on 67 surface water samples and 93 groundwater samples from wells to evaluate their composition and existing relationship with the recharge areas. We used these isotope compositions (δ18O - δD) and hydrochemical data to identify the provenance and degree of influence of meteoric waters in the Basal Flow Unit. Thus, we evaluated the isotopic behavior of the Andean Foreland in Colombia. These data allowed us to propose the altitude ranges of the recharge zones for a deep regional aquifer (BFU) that extends along the southern Llanos basin in Colombia. The δ18O and δD values from surface water sources showed consistency with respect to the isotopic behavior reported in global datasets (GMWL), the Local Meteoric Water Line (LMWL) established for Colombia, and data from IAEA-GNIP stations examined in this study. The new δ18O and δD analysis, together with datasets from previous studies carried out in the area, made it possible to establish the Local Meteoric Water Line for the Llanos basin following the equation δD = 7.8 (±0.10) x δ18O + 11.66 (±0.75). δ18O and δD values of groundwater samples taken in the deep wells follow the proposed Llanos Local Meteoric Water Line. It supports a high influence of meteoric waters in the Basal Flow Unit, from areas close to the recharge zones up to more than 300 km away to the east of the basin and suggesting its origin from approximate altitude ranges that vary between 580 m and 2060 m, related to the La Macarena Range and the eastern flank of the Eastern Cordillera. The physicochemical data was used as an additional proxy and showed the lowest ion concentrations in proximity to the recharge zones, recognizing in general groundwater with low concentrations of Cl− (4.1–1278 mg/L) and Na (4.7–1749 mg/L) along the BFU present in the southern Llanos basin.

Geomorphological controls on the evolution of a new streamflow in the piedmont of the southern of Sierras Pampeanas: A case study of the Río Nuevo, West-central Argentina

Our understanding of the geomorphological processes that drive river formation and hydrological settings that favour them is still under development, facing the difficulties of knowledge fragmentation and the mismatch of temporal scales, particularly in arid or semi-arid regions. In this study, we provided new evidence on the link between river formation and hydrological settings by analysing the extremely rapid development of a new river (Rio Nuevo) network in the Morro basin, San Luis, West-Central Argentina. The geomorphology and the morphoevolution of the new hydrographic basin were documented in view of its morpho-litho-stratigraphy and structural characteristics of the river valley. Six main geomorphological units in relation with the formation of the new river were identified. Three of these units predated such formation, two other geomorphological units accompanied the onset of river formation and were also subject to rapid expansion while the last one (lagoons and wetlands) is still stable due to the river rapid expansion as a result of water table level rise. The evaluation of these geomorphological characteristics has provided a better understanding of the process that governs the formation of rivers in semiarid areas, contributing to the prediction and management of future transformations. Further geomorphological controls associated with topographic configuration and tectonic processes were also inferred.

Non-Invasive Prospection Methods in the Roman City of Balsa (Luz de Tavira-Portugal): Revealing the Real Townscape

Ever since Estácio da Veiga, at the end of the 19th century, identified the ruins of the Roman city of Balsa under Torre d’Aires estate (Luz de Tavira-Portugal) and its surroundings, the scientific questions about this Roman city have been constantly increasing. Despite the historical importance of this city, referenced in classical literature, the archaeological knowledge about it remains very scarce due to the difficulties around implementing any durable scientific research projects. Therefore, much of that written about the topographical features and configuration of the city has no unequivocal scientific support. Finally, 2019 saw the launch of this ongoing project “Balsa, searching for the origins of the Algarve”, which aims to ascertain the main features concerning the city’s extent and configuration, mainly through non-invasive methods. Since 2017, geomagnetic and geo-radar surveys have spanned several hectares and successfully identified many traces of the Roman city while discarding the existence of others in certain locations. In the last two years, the geo-radar surveys have intensified and established the boundaries to the Roman city as well as parts of its layout, remnants of buildings, and even fossilised agricultural crops in addition to other geophysical anomalies, whether or not they are subsequently confirmed by diagnostic pits.

EEG microstates in resting condition in young indians

Objectives: The map topography analysis gives an idea of temporal dynamics of electric fields, which is reference independent, making the results unambiguous. These topographic maps remain stable for 80 to 100 milliseconds, abruptly shifting to a new topographic map configuration and remains stable in that state are called the ‘functional microstates’ as described by Lehmann et al (1987). There has been no study done in the resting state eye closed and eye open conditions showing the microstate maps in healthy Indian subjects in resting eyes open and resting eyes closed condition using 128 channel EEG. So our study aim was to assess the microstates in resting eyes closed and eyes open condition. And to compare the microstate parameters such as mean duration, global explained variance (GEV) and time coverage between eyes closed and eyes open condition. Materials and Methods: A cross-sectional and observational study on 20 indian subjects (Mean age- 26.65 and (SD) - 2.78 years) was done on resting eyes closed and eyes open conditions. After EEG acquisition using 128 channel EEG machine, EEG was preprocessed and microstate analysis using CARTOOL software was performed on the EEG data. Results: After microstate analysis four maps topography were obtained. There was statistically non-significant difference observed in microstate maps between resting eyes closed and resting eyes open condition for the all parameters i.e. mean duration, time coverage and GEV. Conclusion: Our findings suggests that, both eyes closed and eyes open conditions were similar to each other in terms of stability and predominance of Maps.

Spatial-temporal network analysis of the public bicycle sharing system in Medellín, Colombia

The bicycle sharing system in Medellin has become one of the alternatives in the city to achieve more sustainable transportation. To know how people use it on a daily basis is a fundamental resource to plan future expansions and to make the most out of the public investments. Therefore, we present an analysis of the bicycle sharing system and the emerging patterns according to its usage, based on exploratory data analysis and network theory approaches, we characterize users (single-trip vs. multi-trip users, female vs. male, and young vs. adult users). The results show that the main challenges for the future planning of the bicycle sharing system in Medellin are the inclusion of female users, which represents half of the potential users but are less prone to use the system. We also consider the foresight of the placement of new stations and infrastructure according to the purpose of the trip, the topographical configuration of the city, and the articulation with the integrated transportation system in the city.

Fill‐and‐Spill, Tilt‐and‐Repeat (FaSTaR) cycles: Stratigraphic evolution above a dynamic submarine stepped slope

AbstractThe classic fill‐and‐spill model is widely applied to interpret topographic controls on depositional architecture and facies distributions in slope successions with complicated topography. However, this model implies a constant topographic configuration over the lifespan of a turbidite system. In contrast, the impact on patterns of erosion and deposition above dynamic slopes whose topographic configuration varies spatially over time remains poorly investigated. Here, using high‐resolution 3D seismic reflection data and more than 100 wells from a 40 km long stepped slope system (Campos Basin, offshore Brazil), we document the evolution of a sand‐prone turbidite system active during the Oligocene–Miocene transition. This turbidite system was influenced by vertical and lateral deformation, and we propose a new stratigraphic model to explain the resultant depositional architecture. Two depocentres were identified as steps, with channels on the proximal step, and channel–lobe complexes on the distal step, bounded by sediment bypass‐dominated ramps. Lateral stepping of channels on the proximal step, and oblique stacking of the down‐dip lobe complexes, each cut by through‐going channels, indicate multiple fill‐and‐spill cycles. A persistent north‐east‐ward stepping and thickening on the steps are interpreted to reflect lateral tilting of the seafloor driven by salt tectonics. The dynamic substrate prevented the establishment of a single long‐lived conduit across the proximal step, as recorded in systems with fixed topographic configurations. The filling of through‐going channels with mud at the end of each cycle suggests waxing‐to‐waning sediment supply cycles and periods of sand starvation when the lateral tilting dominated and drove avulsion of the feeder channels towards topographic lows. This study demonstrates that subtle dynamic slope deformation punctuated by discrete sediment supply cycles results in complex stratigraphic patterns with multiple phases, and multiple entry and exit points. Repeated cycles of fill‐and‐spill, tilt‐and‐repeat are likely to be present in other stepped slope systems.

A Laboratory Model for a Meandering Zonal Jet

AbstractThe meandering jet streams of the Northern Hemisphere influence the weather for more than half of Earth's population, so it is imperative that we improve our understanding of their behavior and how they respond to climate change. Here, we describe a novel laboratory model for a meandering zonal jet. This model comprises a large rotating annulus with a series of topographic ridges, and an imposed radial vorticity flux. Flow interactions with the topographic ridges operate to concentrate the zonal transport into a narrow jet, which supports the development and propagation of Rossby waves. We investigate the dynamics of the jet for a range of rotation rates, imposed radial vorticity fluxes, and topographic ridge configurations. The circulations are classified into two distinct regimes: predominantly zonal or predominantly meandering. The flow regime can be quantified by the ratio of the Ekman dissipation and jet advection timescales, which gives an indication of whether disturbances arising from the flow‐topography interaction are dissipated faster than the time taken to circuit the annulus; if not, these disturbances will reencounter the topography, and thus be reinforced and amplified. For predominantly zonal flows, the radial vorticity flux is split equally between the standing meanders and transient eddies. For predominantly meandering flows, standing meanders perform 79% of the radial vorticity flux, with 18% accommodated by the transient eddies. Our experiments indicate that the Arctic amplification associated with climate change will tend to favor predominantly zonal flow conditions, suggesting a reduced occurrence of atmospheric blocking events caused by the jet streams.

Late Cretaceous through Cenozoic Paleoenvironmental History of the Bagua Basin, Peru: Paleoelevation Comparisons with the Central Andean Plateau

Located in northern Peru, at the lowest segment of the Central Andes, the Bagua Basin contains a Campanian to Pleistocene sedimentary record that archives the local paleoenvironmental and tectonic history. We present new δ18O and δ13C signatures of pedogenic carbonate nodules from paleosols in the Campanian–Maastrichtian Fundo El Triunfo Formation and in the upper Eocene–middle Miocene Sambimera Formation to reconstruct the isotopic composition of paleo-meteoric water and the floristic biome. We compare these results to modern isotopic values from a newly obtained modern water transect to interpret the environmental evolution of this area and its relationship with the neighboring Eastern Cordillera. A ~2‰ δ18O depletion between the latest Cretaceous and the latest Eocene reflects a shift from a coastal to inland environment. A negative δ18O shift of ~3‰ from the middle Miocene to the present day reveals the establishment of the Eastern Cordillera as an orographic barrier for the moisture traveling westward, sometime after deposition of the top of the Sambimera Formation at ~13 Ma. A shift in the δ13C signature from ~−25‰ in the Campanian–Miocene deposits to ~−23‰ in modern–Holocene times suggests a change in biome from dominant C3 plants to a mixture of C3 and C4 plants. This environmental shift reflects both the late Miocene global C4 expansion and the transition to more arid conditions in the basin. The Campanian–middle Miocene environmental reconstruction of the Bagua Basin indicates a steady paleoelevation setting in the northernmost Central Andes during most of the Cenozoic and constrains the uplift of the Eastern Cordillera to the late Miocene–Pleistocene. This paleoelevation history contrasts with that of the Central Andean Plateau, which is characterized by two major episodes of surface uplift: early–middle Miocene and late Miocene–Pliocene. The contrasting modern topographic configuration of the Central Andean Plateau and the northernmost Central Andes gives rise to the question of what factors created such a dramatic difference in topographic evolution of the two regions that shared an overall common tectonic history. We discuss the possible factors responsible for this contrasting topographic configuration and suggest that the diachronous flat slab episodes are likely a major factor, resulting in greater shortening and crustal thickness and, ultimately, in earlier surface uplift episodes occurring in the Central Andean Plateau.

Efeitos causados por obstáculos na hidrodinâmica de correntes de turbidez: uma abordagem experimental

ABSTRACT This research aims to evaluate the effects of the presence of obstacles on turbidity currents hydrodynamics. Nine physical simulations of a poorly sorted mixture of water and coal (Cvol = 5%; D50 = 47 μm) were run in a laboratory test channel with three flow discharges (5, 10 and 15 L.min-1) in three different topographic configurations: runs without obstacles; runs with three 3 cm-high obstacles and runs with three 6 cm-high obstacles. The results showed that greater height of obstacles leads to greater blockage of the flow, causing changes on vertical profiles of velocity shape, flow regime (supercritical to subcritical), geometry and flow circulation in the zone between obstacles. Obstacle height reduction by 50% led to similar behavior of the turbidity current as the no-obstacles condition. After passing over the sequence of the obstacle, the turbidity current tended to regenerate a hydrodynamic structure comparable to the no-obstacles conditions.