Zoophycos and related trace fossils from the Chefar El Ahmar Formation,Upper Emsian-Frasnian Ia-Ib (Ougarta,SW Algeria)

The Upper Emsian to Frasnian Ia-Ib strata of the Marhouma area (or “km 30” outcrop), exposed in the Ougarta Range (SW Algeria) belong to the Chefar El Ahmar Formation. On the basis of distinct lithological and palaeontological features, this formation is subdivided into three members (Lower Marly Limestones Member, Middle Marly Limestones Member, and Upper Marly Limestones Member). The studied beds show low to moderate diversity of trace fossil assemblage which contains thirteen ichnotaxa: Chondrites intricatus, Chondrites isp., Chondrites cf. targionii, Circulichnis cf. montanus, Cochlichnus isp., Neonereites biserialis, Neonereites multiserialis, Nereites isp., Palaeophycus isp., Planolites isp., Thalassinoides isp., Zoophycos aff. cauda-galli, and Zoophycos isp. A. The two latter ichnotaxa are the most common trace fossils in the assemblage and occur at three different levels showing different bioturbation intensities. The first Zoophycos-bearing level (Zl 1) is characterised by an overall high bioturbation intensity reflecting a very high oxygenation rate and nutrient supply, allowing the development of large and dense Zoophycos specimens. The second Zoophycos-bearing level (Zl 2) has a considerable reduction of bioturbation intensity as compared to the previous level, with an abundance of Chondrites, which is probably due to radical palaeoecological changes that suggests dysoxic and stressful conditions. The third Zoophycos-bearing level (Zl 3) is characterised by an overall moderate bioturbation intensity. The distribution of trace fossils was influenced by lithology, sedimentation rate, energy level (storm events), bottom oxygenation, and nutrient supply. The lithofacies and trace fossils of the Chefar El Ahmar Formation both indicate a depositional environment fluctuating from the lower shoreface to lower offshore zone.     

Hydrogeology and groundwater management in a coastal granitic area with steep slopes in Galicia (Spain)

Groundwater availability, management and protection are great challenges for the sustainability of groundwater resources in the scattered rural areas of the Atlantic regions of Europe where groundwater is the only option for water supply. This report presents a hydrogeological study of the coastal granitic area of Oia in northwestern Spain, which has unique geomorphological and hydrogeological features with steep slopes favoring the erosion of the weathered granite. The hydrogeological conceptual model of the study area includes: (1) the regolith layer, which is present only in the flat summit of the mountains; (2) the slope debris and the colluvial deposits, which are present in the intermediate and lowest parts of the hillside; (3) the marine terrace; and (4) the underlying fractured granite. Groundwater recharge from rainfall infiltration varies spatially due to variations in terrain slope, geology and land use. The mean annual recharge estimated with a hydrological water balance model ranges from 75 mm in the steepest zone to 135 mm in the lowest flat areas. Groundwater flows mostly through the regolith and the detrital formations, which have the largest hydraulic conductivities. Groundwater discharges in seepage areas, springs, along the main creeks and into the sea. The conceptual hydrogeological model has been implemented in a groundwater flow model, which later has been used to select the best pumping scenario. Model results show that the future water needs for domestic and tourist water supply can be safely provided with eight pumping wells with a maximum pumping rate of 700 m³/day.

     

Modeling disruptions causing domino effects in urban guided transport systems faced by flood hazards

Coastal cities are more vulnerable to floods due to the joint impact of rainfall and tide level. Quantitative risk assessment of disaster-causing factors is critical to urban flood management. This paper presents an integrated method to quantify the hazard degree of disaster-causing factors, rainfall and tide level, and to investigate the optimal management of flooding risk in different disaster-causing factor areas. First, an urban flood inundation model is used to simulate inundated extents in different drainage districts. Then, formulas are put forward to calculate the hazard degree of rainfall and tide level based on inundated extents in different combinations of rainfall and tide level. According to the hazard degree, the main disaster-causing factor could be identified in each drainage district. Finally, the optimal management of flooding risk in different disaster-causing factor areas is selected by disaster reduction analysis and cost–benefit analysis. Furthermore, the coastal city, Haikou of China, is taken as a case study. The results indicate that the hazard degree increases with the increasing distance between the drainage district and the Qiongzhou Strait or the Nandu River in the eastern of Haikou. Heavy rain is the main disaster-causing factor in inland areas, while high tide level is the main disaster-causing factor in island areas. For the area whose main disaster-causing factor is heavy rain, water storage projects could effectively reduce flooding. Meanwhile, pumps are economical choices for the area where tide level is the main disaster-causing factor. The results can provide reference for drainage planning in other coastal areas.     

Experimental and numerical evaluation of single-layer covers placed on acid-generating tailings

This study focuses on the reclamation work being performed on two former acid-generating tailings sites, located in Quebec, Canada. At both sites, the tailings were partially oxidized due to extended exposure, and the pore water is acidic. The reclamation solution applied to control acid mine drainage is a monolayer cover, made of non acid-generating tailings in one case and a till in the other. The goal of this project was to assess the response of the tailings-cover systems under various conditions. Tailings samples were collected in situ and characterized in the laboratory. Large column tests were conducted to evaluate the hydrogeological and geochemical behaviour of the covered tailings following wetting and drying cycles. The instrumented columns were designed to reproduce some of the existing site conditions and provide representative results for longer term analyses. Volumetric water content, suction, and oxygen concentrations were also monitored over time. The experimental data were used to validate different numerical models including those constructed with Vadose/W (GeoSlope Int.). Additional simulations were conducted under field conditions to evaluate the effect of various influence factors such as the depth of the water table, climatic conditions and the thickness of the cover. The combination of experimental and numerical results show how the behaviour and efficiency of a monolayer cover placed over reactive tailings depend on these factors, highlighting the importance of hydrogeological properties and water table depth. In many instances, the cover materials were prone to desaturation, especially when the water table was deeper than about 2 m below the tailings-cover interface. These results tend to indicate that relatively thin monolayer covers would not be able to prevent oxygen ingress under some of the conditions observed in the field. Desaturation of the cover and/or reactive tailings is due to a combination of drainage and evaporation. In such cases, increasing the thickness of the monolayer cover only has a limited effect. A discussion follows on the practical implications of these laboratory experiments and the numerical simulations for field design of reclamation measures at these two tailings impoundments.     

Biogeochemistry and dynamics of settling particle fluxes at the Antikythira Strait (Eastern Mediterranean)

For the first time, a 12-month trap experiment was conducted on both sides of the strait between Crete and Antikythira Island (Eastern Mediterranean Sea) from June 1994 to June 1995 as part of the PELAGOS experiment. Analyses of major chemical constituents, including carbohydrates and stable lead isotopes and Scanning Electron Microscope studies were performed on the trap samples. Total mass fluxes varied between 1 and 1273 mg m⁻² d⁻¹. The lowest fluxes observed were in summer and autumn 1994, when stratification of the water column was at its deepest. In general, mass fluxes exhibited very low values throughout this experiment confirming the strong oligotrophy of this area. The mean contents of the major constituents (carbonates, opal, lithogenic fraction) were quite similar during the survey and between traps, with the exception of organic carbon contents, which were highest (7–10%) in summer 1994, i.e. during the period of lowest mass fluxes. During the first 6-month deployment (summer–autumn 1994) there was an important mass flux peak, which was depleted in organic carbon, at the Ionian near-bottom trap. This event coincided with a violent wind episode, which may have caused the resuspension of particles, which were then transported down the steep continental slope on the Ionian side of the strait. A smaller peak in mass flux occurred at the Aegean near-bottom trap, coincident with rainfall. Both these events indicate that environmental factors can control flux variations in an oligotrophic environment. During the second 6-month deployment (winter–spring 1995) there was another important increase in mass fluxes, which occurred at all three traps, although in the Ionian traps mass flux peaks were delayed by one to two sampling intervals. The distance between the two mooring sites gives a rough estimate of a minimum horizontal advection speed of 2 cm s⁻¹ for this particulate transfer from the Aegean to the Ionian area. This estimate is in good agreement with the measured current velocities.     

Magnetic polarity sequences from downhole measurements in ODP holes 998B and 1001A,leg 165, Caribbean Sea

The magnetostratigraphy of sediments drilled at two sites (998 and 1001) in the Caribbean Sea during the Ocean Drilling Program (ODP) Leg 165 is established directly from downhole measurements. For the first time in the ODP, the magnetostratigraphy of sediments is determined from both logging magnetic data and paleomagnetic analysis of core material for an age interval of about 16 m.y. across the Cretaceous/Tertiary boundary. The total magnetic induction and the susceptibility of the surrounding sediment were recorded in situ and continuously by the GHMT (Geological High-sensitivity Magnetic Tool). The aim of processing these data is to determine the magnetic polarity. At Site 998 (Cayman Rise), no paleomagnetic results are available from the recovered cores given a hard secondary overprint. Nonetheless, a magnetostratigraphic sequence from early Miocene to late Oligocene is proposed from the analysis of the GHMT data. The comparison with biostratigraphic results shows the accuracy of the resulting magnetic polarity. At Site 1001 (Hess escarpment), cores were recovered in two holes thus allowing the comparison of the magnetostratigraphic results obtained from the GHMT data and from paleomagnetic analysis of core samples over a length of 200 m representing about 16 m.y. from early Eocene to late Cretaceous times. The sedimentation rates computed from the determined magnetochrons are very similar and correspond to the ones obtained from shipboard biostratigraphic results. One of the most striking result obtained from the magnetostratigraphic results, especially the GHMT data, at Site 1001, is the abrupt decrease in the sedimentation rate across the K/T boundary. This suppressed sedimentation lasted at least 4 Ma after the K/T event.     

An ultraviolet-selected galaxy redshift survey – II. The physical nature of star formation in an enlarged sample

We present further spectroscopic observations for a sample of galaxies selected in the vacuum ultraviolet (UV) at 2000 Å from the FOCA balloon-borne imaging camera of Milliard et al. This work represents an extension of the initial study by Treyer et al. Our enlarged catalogue contains 433 sources (≃3 times as many as in our earlier study) across two FOCA fields. 273 of these are galaxies, nearly all with redshifts z ≃0–0.4. Nebular emission-line measurements are available for 216 galaxies, allowing us to address issues of excitation, reddening and metallicity. The UV and H α luminosity functions strengthen our earlier assertions that the local volume-averaged star formation rate is higher than indicated from earlier surveys. Moreover, internally within our sample, we do not find a steep rise in the UV luminosity density with redshift over 0< z <0.4. Our data are more consistent with a modest evolutionary trend, as suggested by recent redshift survey results. Investigating the emission-line properties, we find no evidence for a significant number of AGN in our sample; most UV-selected sources to z ≃0.4 are intense star-forming galaxies. We find that the UV flux indicates a consistently higher mean star formation rate than that implied by the H α luminosity for typical constant or declining star formation histories. Following Glazebrook et al., we interpret this discrepancy in terms of a starburst model for our UV-luminous sources. We develop a simple algorithm which explores the scatter in the UV flux–H α relation in the context of various burst scenarios. Whilst we can explain most of our observations in this way, there remains a small population with extreme UV–optical colours which cannot be understood.     

Water mass transformation along the Indonesian throughflow in an OGCM

The oceanic pathways connecting the Pacific Ocean to the Indian Ocean are described using a quantitative Lagrangian method applied to Eulerian fields from an ocean general circulation model simulation of the Indonesian seas. The main routes diagnosed are in good agreement with those inferred from observations. The secondary routes and the Pacific recirculation are also quantified. The model reproduces the observed salt penetration of subtropical waters from the South Pacific, the homohaline stratification in the southern Indonesian basins, and the cold fresh tongue which exits into the Indian Ocean. These particular water mass characteristics, close to those observed, are obtained when a tidal mixing parameterization is introduced into the model. Trajectories are obtained which link the water masses at the entrance and at the exit of the Indonesian throughflow (ITF), and the mixing along each trajectory is quantified. Both the ITF and the Pacific recirculation are transformed, suggesting that the Indonesian transformation affects both the Indian and Pacific stratification. A recipe to form Indonesian water masses is proposed. We present three major features of the circulation that revisit the classical picture of the ITF and its associated water mass transformation, while still being in agreement with observations. Firstly, the homohaline layer is not a result of pure isopycnal mixing of the North Pacific Intermediate Water and South Pacific Subtropical Water (SPSW) within the Banda Sea, as previously thought. Instead, the observed homohaline layer is reproduced by the model, but it is caused by both isopycnal mixing with the SPSW and a dominant vertical mixing before the Banda Sea with the NPSW. This new mechanism could be real since the model reproduces the SPSW penetration as observed. Secondly, the model explains why the Banda Sea thermocline water is so fresh compared to the SPSW. Until now, the only explanation was a recirculation of the freshwater from the western route. The model does not reproduce this recirculation but instead shows strong mixing of the SPSW within the Halmahera and Seram Seas, which erodes the salinity maximum so that its signature is not longer perceptible. Finally, this work highlights the key role of the Java Sea freshwater. Even though its annual net mass contribution is small, its fresh salinity contribution is highly significant and represents the main reason why the Pacific salinity maxima are eroded.     

Contrasted turbulence intensities in the Indonesian Throughflow: a challenge for parameterizing energy dissipation rate

Microstructure measurements were performed along two sections through the Halmahera Sea and the Ombai Strait and at a station in the deep Banda Sea. Contrasting dissipation rates (??) and vertical eddy diffusivities (K _z ) were obtained with depth-averaged ranges of \(\sim [9 \times 10^{-10}-10^{-5}]\) W kg^??1 and of \(\sim [1 \times 10^{-5}-2 \times 10^{-3}]\) m² s^??1, respectively. Similarly, turbulence intensity, \(I={\epsilon }/(\nu N^{2})\) with ν the kinematic viscosity and N the buoyancy frequency, was found to vary seven orders of magnitude with values up to \(10^{7}\). These large ranges of variations were correlated with the internal tide energy level, which highlights the contrast between regions close and far from internal tide generations. Finescale parameterizations of ?? induced by the breaking of weakly nonlinear internal waves were only relevant in regions located far from any generation area (“far field”), at the deep Banda Sea station. Closer to generation areas, at the “intermediate field” station of the Halmahera Sea, a modified formulation of MacKinnon and Gregg (2005) was validated for moderately turbulent regimes with 100 < I < 1000. Near generation areas marked by strong turbulent regimes such as “near field” stations within strait and passages, ?? is most adequately inferred from horizontal velocities provided that part of the inertial subrange is resolved, according to Kolmogorov scaling.     

Characterization of wood-laden flows in rivers

Inorganic sediment is not the only solid-fraction component of river flows; flows may also carry significant amounts of large organic material (i.e. large wood), but the characteristics of these wood-laden flows (WLFs) are not well understood yet. With the aim to shed light on these relatively unexamined phenomena, we collected home videos showing natural flows with wood as the main solid component. Analyses of these videos as well as the watersheds and streams where the videos were recorded allowed us to define for the first time WLFs, describe the main characteristics of these flows and broaden the definition of wood transport regimes (adding a new regime called here hypercongested wood transport). According to our results, WLFs may occur repeatedly, in a large range of catchment sizes, generally in steep, highly confined single thread channels in mountain areas. WLFs are typically highly unsteady and the log motion is non-uniform, as described for other inorganic sediment-laden flows (e.g. debris flows). The conceptual integration of wood into our understanding of flow phenomena is illustrated by a novel classification defining the transition from clear water to hypercongested, wood and sediment-laden flows, according to the composition of the mixture (sediment, wood, and water). We define the relevant metrics for the quantification and modelling of WLFs, including an exhaustive discussion of different modelling approaches (i.e. Voellmy, Bingham and Manning) and provide a first attempt to simulate WLFs. We draw attention to WLF phenomena to encourage further field, theoretical, and experimental investigations that may contribute to a better understanding of flows in river basins, leading to more accurate predictions, and better hazard mitigation and management strategies. © 2019 John Wiley & Sons, Ltd.