Controls of δS and δO in dissolved sulphate: Learning from a detailed survey in the Llobregat River (Spain)

The S and O isotopic composition of dissolved SO₄, used as a tracer for SO₄ sources, was applied to the water of the Llobregat River system (NE Spain). The survey was carried out at 30 sites where surface water was sampled on a monthly basis over a period of 2a. The concentration of dissolved SO₄ varied from 20 to 1575 mg L⁻¹. Sulphur isotopic compositions clustered in two populations: one – 93% of the samples – had positive values with a mode of +9‰; the other had negative values and a mode of −5‰. Data for δ¹⁸O_SO4 showed a mean value of +11‰, with no bi-modal distribution, though lower values of δ¹⁸O corresponded to samples with negative δ³⁴S. These values can not be explained solely by the contribution of bedrock SO₄ sources: that is, sulphide oxidation and the weathering of outcrops of sulphates, though numerous chemical sediments exist in the basin. Even in a river with a high concentration of natural sources of dissolved SO₄, such as the Llobregat River, the δ³⁴S values suggest that dissolved SO₄ is controlled by a complex mix of both natural and anthropogenic sources. The main anthropogenic sources in this basin are fertilizers, sewage, potash mine effluent and power plant emissions. Detailed river water sampling, together with the chemical and isotopic characterisation of the main anthropogenic inputs, allowed determination of the influence of redox processes, as well as identification of the contribution of natural and anthropogenic SO₄ sources and detection of spatial variations and seasonal changes among these sources. For instance, in the Llobregat River the input of fertilisers is well marked seasonally. Minimum values of δ³⁴S are reported during fertilization periods – from January to March – indicating a higher contribution of this source. The dual isotope approach, δ³⁴S and δ¹⁸O, is useful to better constrain the sources of SO₄. Moreover, in small-scale studies, where the inputs are well known and limited, the mixing models can be enhanced and the contribution of the different sources can be quantified to some extent.     

Ore lead and sulphur isotope pattern from the low-temperature veins of the Catalonian Coastal Ranges (NE Spain)

The lead isotopic composition of galenas from low-temperature veins of the Catalonian Coastal Ranges (NE Spain) displays a small but distinct range of values: 18.318 ≤²⁰⁶Pb/²⁰⁴Pb ≤ 18.678; 15.678 ≤²⁰⁷Pb/²⁰⁴Pb ≤ 15.767 and 38.534 ≤ ²⁰⁸Pb/²⁰⁴Pb ≤ 39.189. The data define a linear trend in the ²⁰⁸Pb/²⁰⁴Pb versus ²⁰⁶Pb/²⁰⁴Pb diagram that can be interpreted in terms of mixing of lead from different reservoirs. The lead appears to be derived from a solution that preferentially leached granites of Late-Hercynian age. Sulphur isotopic compositions of the galenas range from −8.5 to + 7.3‰ but variations in a single deposit are small (1–2‰), pointing to different sources of sulphur. In a δ³⁴S versus ²⁰⁶Pb/²⁰⁴Pb plot no clear correlation trends appear. Lead isotope data from deposits of similar characteristics situated within the Hercynian orogenic belt as the Linares-La Carolina district (S Spain) and the Inglesiente-Sulcis area (Sardinia) show slight differences indicating a source area of similar lead isotopic composition. In the CCR and Linares-La Carolina districts, the main source of lead is related to the Hercynian granites of each area, although small contributions from metasediments cannot be ruled out. The contribution of lead from metasedimentary rocks is particularly seen in the Sardinian (Hercynian vein-type) ores. Received: 8 August 1996 / Accepted: 5 December 1996     

Geography of contamination: The location of industrial waste dumps in Catalonia

The handling of the solid industrial waste (SIW) generated in Catalonia is one of the main problems of industrial and territorial policy confronting the public bodies controlling this area of activity. The most recent estimates in this regard indicate that the annual production of SIW is 1,700,000 tons and that only 300,000 tons are treated.In this situation it is usual for a large number of industries to eliminate their SIW furtively, it is common practice to dump waste in various unprepared areas. In this article we present a series of hypotheses which we believe allow us to understand the logic that guides the siting of a large number of these dumps.In the first place we demonstrate the importance of a series of conditions derived from the same industrial logic, to wit, a) the cost of transporting the SIW to the dumps, b) the industrial decentralization process and the metropolitan development of Catalonia, c) vertical integration and the appearance of companies especially dedicated to the elimination of waste and, d) the development of land use through revaluation of the land and greater possibilities for control forces furtive dumps to be sited in more and more distant areas.Secondly, we examine the role of public bodies in this process, concentrating on the characteristics of the legal system and the real effectiveness of urban controls. Finally, in third place, an explanation is given of research carried out in the Barcelona area which shows the importance of the conditions examined above.     

A GIS-based fire spread simulator integrating a simplified physical wildland fire model and a wind field model

??This article discusses the integration of two models, namely, the Physical Forest Fire Spread (PhFFS) and the High Definition Wind Model (HDWM), into a Geographical Information System-based interface. The resulting tool automates data acquisition, preprocesses spatial data, launches the aforementioned models and displays the corresponding results in a unique environment. Our implementation uses the Python language and Esri’s ArcPy library to extend the functionality of ArcMap 10.4. The PhFFS is a simplified 2D physical wildland fire spread model based on conservation equations, with convection and radiation as heat transfer mechanisms. It also includes some 3D effects. The HDWM arises from an asymptotic approximation of the Navier–Stokes equations, and provides a 3D wind velocity field in an air layer above the terrain surface. Both models can be run in standalone or coupled mode. Finally, the simulation of a real fire in Galicia (Spain) confirms that the tool developed is efficient and fully operational.     

The influence of enclosing rock type on barite deposits, eastern Pyrenees, Spain: fluid inclusion and isotope (Sr, S, O, C) data

The Rocabruna and Coll de Pal barite deposits, located in the eastern Pyrenees of Spain, fill karstic cavities within carbonate rocks of Cambrian and Devonian age, respectively. The deposits contain barite, chalcopyrite, tetrahedrite, pyrite and minor sphalerite and galena with saddle dolomite and quartz as gangue. Fluid inclusion data from Coll de Pal quartz and dolomite indicate that the mineralizing fluid was a polysaline CaCl₂-rich brine, with temperatures between 125 and 150 °C. C and O isotopic compositions of carbonates in both deposits are consistent with a progressive increase in temperature during deposition. The ³⁴S values of barite, which range from 14.2 to 15.9‰ in Coll de Pal, and from 13.9 to 19.3‰ in Rocabruna, together with ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7118 to 0.7168 in Rocabruna, and from 0.7115 to 0.7136 in Coll de Pal, indicate two different fluid sources. We propose that these deposits formed as a result of mixing between a Ba-rich, sulfate-poor hot fluid, and sulfate-rich solutions of surficial origin. The different Sr isotope ratios in the deposits indicate that the hot Ba-rich fluids involved in each deposit were equilibrated with different rock types (carbonates and shales), in agreement with the geology of the two areas. Received: 22 October 1997 / Accepted: 24 March 1998     

Geotechnical characterization of slump scars,eroded slopes,and correlated deposits on continental margins: Gulf of Lions,Western Mediterranean sea

Abstract

Vertical variations of geotechnical properties in the uppermost sediment layers characterize the main sedimentary processes acting on the construction and destruction of progressive‐type continental slopes. In the Gulf of Lions, the original thicknesses and distribution of the uppermost sedimentary layers of the continental slope and rise, which consist of Holocene muds overlying Pleistocene muds, have been greatly modified by erosion and several kinds of slope failure processes. Each process is typified through sets of geotechnical properties measured in the eroded or slumped sections and in the associated sediment accumulations.

In slump scars, the water‐rich Holocene muds lie on fine, overconsolidated, Pleistocene muds with high plasticity and low shear strength. In bottom current‐eroded slopes, where modern sedimentation is extremely reduced, the Pleistocene muds frequently outcrop and may sometimes be overlain by a very thin layer of Holocene muds. The Pleistocene muds of eroded slopes are overconsolidated and more silty and less plastic than the Pleistocene muds from slopes affected by slope failure, their shear strength being 10 times greater.

Deposits at the toe of slumps are very often formed by several superposed three‐layer units (triplets of interstratified Holocene, transitional, and Pleistocene layers) issued from retrogressive slumping occurring in the slump scars above their head area. The main body of each layer is then relatively undisturbed, showing the usual burial geotechnical gradients due to overburden pressure (i.e., decrease of water content and increase of unit weight and shear strength). At the toe of bottom current‐eroded slopes, a thick and homogeneous layer of Holocene muds overlies the Pleistocene muds; this Holocene layer has unappreciable burial depth gradient of its geotechnical parameters because of a high rate of modem and continuous deposition.     

Tracing seafloor methane emissions with benthic foraminifera: Results from the Ana submarine landslide (Eivissa Channel,Western Mediterranean Sea)

The hypothesis that benthic foraminifera are useful proxies of local methane emissions from the seafloor has been verified on sediment core KS16 from the headwall of the Ana submarine landslide in the Eivissa Channel, Western Mediterranean Sea. The core MS312 from a nearby location with no known methane emissions is utilised as control. The core was analysed for biostratigraphy, benthic foraminiferal assemblages, Hyalinea balthica and Uvigerina peregrina carbon and oxygen stable isotope composition, and sedimentary structures. The upper part of the core records post-landslide deglacial and Holocene normal marine hemipelagic sediments with highly abundant benthic foraminifera species that are typical of outer neritic to upper bathyal environment. In this interval, the δ¹³C composition of benthic foraminifera indicates normal marine environment analogous to those found in the control core. Below the sedimentary hiatus caused by the emplacement of the slide, the foraminiferal assemblages are characterised by lower density and higher Shannon Index. Markedly negative δ¹³C shifts in benthic foraminifera are attributed to the release of methane through the seabed. The mean values of the ¹³C anomaly in U. peregrina are ? 0.951 ± 0.208 in the pre-landslide sediments, and ? 0.269 ± 0.152 in post-slide reworked sediments deposited immediately above the hiatus. The δ¹³C anomaly in Hyalinea balthica is ? 2.497 ± 0.080 and ? 2.153 ± 0.087, respectively. To discard the diagenetic effects on the δ¹³C anomaly, which could have been induced by Ca–Mg replacement and authigenic carbonate overgrowth on foraminifera tests, a benthic foraminifera subsample has been treated following an oxidative and reductive cleaning protocol. The cleaning has resulted, only in some cases, in a slight reduction of the anomaly by 0.95% for δ¹³C and < 0.80% for δ¹⁸O. Therefore, the first conclusion is that the diagenetic alteration is minor and it does not alter significantly the overall carbon isotopic anomaly in the core. Consequently, the pre-landslide sediments have been subject to pervasive methane emissions during a time interval of several thousand years. Methane emissions continued during and immediately after the occurrence of Ana Slide at about 61.5 ka. Subsequently, methane emissions decreased and definitely ceased during the last deglaciation and the Holocene.     

Overpressure within upper continental slope sediments from CPTU data,Gulf of Lion,NW Mediterranean Sea

Data from in situ piezocone tests (CPTU) and laboratory analyses are utilized for the interpretation of the stress history of Quaternary sedimentary sequences in the upper continental slope of the Gulf of Lion, northwestern Mediterranean Sea. A CPTU based preconsolidation pressure profile referenced to the current effective stress indicates that the deposit is underconsolidated from 12 meters below the seafloor (mbsf) down to at least 150 mbsf. Excess pore pressure below 12 mbsf is further supported by results from oedometer and dissipation tests. Subseafloor pockmarks and indications of free gas in seismic reflection profiles reveal four main overpressure sources (SI–SIV) with overpressure ratios >0.3 at subseafloor depths coinciding with levels where the dominantly silty-clayey sediment contains increased proportions of sand. We relate the excess pore pressure related to free gas due to gas exsolution processes and sea level variations driven by Pleistocene sea level changes.     

Eivissa slides, western Mediterranean Sea: morphology and processes

After obtaining full-coverage swath bathymetry data in 1995 and very high-resolution acoustic profiles in 2002, four slides at the Balearic Margin of the Eivissa Channel in the western Mediterranean Sea were revisited in 2004 when side-scan sonar data were collected using a MAK-1M deep-towed acoustic system. These new findings, higher in resolution than those for the swath bathymetry, show two main features previously undetected within these submarine landslides: (1) a series of step-forming inclined and detached slabs oriented perpendicular to the slide movement and located in the uppermost part of the slides, and (2) arcuate regular positive ridges oriented also normal to the slide movement and located in the depositional lobes of some of the slides. The former are interpreted as extensional ridges, suggesting a retrogressive post-failure evolution of the slides. The latter are interpreted as compression ridges, related to plastic deformation of the sediment before movement freezing. Moreover, the new data show that fluid escape features are even more widespread in the Eivissa Channel than previously thought, dozens of new pockmarks less than 20 m in diameter having been identified.     

Quaternary stratal architecture of the Barcelona prodeltaic continental shelf (NW Mediterranean)

The Barcelona continental shelf is part of a 6–20 km wide canyon-bounded shelf located off the city of Barcelona (NE Spain). This study integrates newly acquired high-resolution single channel seismic reflection profiles and available lithological information of the Barcelona shelf to describe its late Quaternary architecture and the role of global glacio-eustatic fluctuations and local factors in its development.

Four major sequence boundaries are identified throughout the seismic dataset. They are tentatively correlated with the four last 4th order (100–120 ka) high-amplitude late Quaternary glacio-eustatic lowstands. Most of the stratigraphic record is formed by falling stage systems tracts with forced-regressive deposits, which confers a general progradational vertical stacking pattern. Transgressive systems tracts are represented by continuous units confined directly off river sources and on previously eroded surfaces. Stillstand deposits are difficult to recognize in the available dataset. The uppermost seismic unit corresponds to the Holocene shore-parallel Besos and Llobregat joint prodelta affected by the prevailing south-westward circulation.

The general architecture of the late Quaternary Barcelona shelf deposits is determined by global glacio-eustatic cycles. However, the lateral variability of the seismic units depends largely on local factors such as (i) the position of sediment sources (essentially the Llobregat River); (ii) differential subsidence and, especially, sediment compaction; (iii) erosive processes such as canyon incision, mass wasting or wave base dynamics; and (iv) underlying geomorphic restrictions.