Browsing by Author "Ayora, C"
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- ItemChemical and hydrological evolution of the Mulhouse potash basin (France): are "marine" ancient evaporites always representative of synchronous seawater chemistry?(Elsevier, 2008-07-15) Cendón, DI; Ayora, C; Pueyo, JJ; Taberner, C; Blanc-Valleron, MMBrine reaction processes were the most important factors controlling the major-ion (Mg, Ca, Na, K, SO4, and Cl) evolution of brines in the Oligocene, Mulhouse basin (France) evaporite basin. The combined analysis of fluid inclusions in primary textures by Cryo-SEM-EDS with sulfate-delta S-34, delta O-18 and Sr-87/Sr-86 isotope ratios reveals hydrothermal inputs and recycling of Permian evaporites, particularly during advanced stages of evaporation in the Salt IV member. The lower part of the Salt IV evolved from an originally marine input. The basin was disconnected from direct marine inputs and a series of sub-basins formed in an active rift setting where tectonic variations influenced sub-basin interconnections and chemical signatures of input waters. Sulfate-delta S-34 shows Oligocene marine-like signatures at the base of the member. However, enriched sulfate-delta O-18 reveals the importance of synchronous re-oxidation processes. As evaporation progressed other non-marine and/or marine-modified inputs from neighbouring basins became more important. This is demonstrated by increases in K concentrations in brine inclusions and Br in halite, sulfate isotopes trends and Sr-87/Sr-86 ratios. The recycling of previously precipitated evaporites of Permian age was increasingly important with evaporation. This supports the connection of the Mulhouse basin to basins situated north of Mulhouse. The brine evolution eventually reached sylvite precipitation. The chemical signature of the resulting brines is not compatible with global seawater chemistry changes. The fast rate of intra and inter basin brine variations as well as the existence of contemporaneous brines with different chemical signatures, supports our interpretation. The existence of diverse non-marine inputs and associated internal chemical changes to the brine preclude the use of trapped-brine inclusions in reconstructing Oligocene seawater chemistry, without previously identifying all inputs. The general hydrological evolution of the Mulhouse basin is explained as a restricted sub-basin with a first marine stage. This gradually changed to a similar to 40% marine source at the beginning of evaporite precipitation, with the rest of inputs non-marine. The general proportion of solutes did not change greatly over evaporite precipitation. However, as the basin restriction increased the originally marine inputs changed to continental or marine-modified inputs from neighbouring basins north of Mulhouse basin. © 2008, Elsevier Ltd.
- ItemExploring the hydrochemical evolution of brines leading to sylvite precipitation in ancient evaporite basins.(Copernicus Publications, 2010-05-02) Cendón, DI; Pueyo, JJ; Ayora, C; García-Veigas, J; Blanc-Valleron, MMSylvite is a very common mineral in ancient evaporite deposits. Due to the absence of current deposits, the natural geochemical mechanism/s for synsedimentary sylvite precipitation and accumulation are not well understood. Numerous sylvite deposits or portions of them have been described as a result of diagenesis (i.e. Sergipe subbasin, Brasil). However, a number of deposits have been described as synsdimentary or being formed during primary evaporite deposition. It is the last group of deposits that can be studied to better understand the hydrochemical processes taking place in the brine at the onset of sylvite precipitation. The Salt IV sylvite beds from the Mulhouse potash basin, Alsace (France) have been described as synsedimentary in origin (LOWENSTEIN and SPENCER, 1990; CENDON et al., 2008). While sylvite in itself does not contain fluid inclusions viable for micro analysis, primary textures in neighboring halite are used as a proxy to understand brine evolution. Two halite-sylvite cycles from the B1 and B2 layers of the potash lower seam were selected. These exhibited clear primary halite crystal textures with sylvite adapting to an irregular halite sedimentary surface and finishing with a flat surface. The nine halite samples, selected at centimeter scale, provided close to 100 single fluid inclusion analyses, representing both the transition towards sylvite precipitation and the post sylvite precipitation. The fluid inclusion analyses revealed strong fluctuations in K concentration, well over the analytical error (<10%). These variations, in the same halite crystal, seem aligned in growth bands, with fluid inclusions within a certain growth band showing practically identical K concentrations, while neighboring bands exhibit a different concentration. Overall, the closer we are from a sylvite layer the higher K concentrations are. However, strong fluctuations continue when growth bands are compared. This pattern shows cycles of increasing K concentration along parallel growth bands with sharp falls followed by the initiation of a new increasing trend. The small “growth band” scale of the K concentration variations, suggests very sensitive processes within the brine with potential environmental changes (i.e. seasonal variations, day-night temperature fluctuations cycles) leading towards the final mass precipitation of a sylvite layer. © Author(s) 2010
- ItemOrigen de las altas concentraciones de amonio, arsénico y boro en el acuífero Niebla-Posadas en la proximidad de la actividad minera de Cobre Las Cruces (Gerena-Sevilla)(Geological and Mining Institute of Spain, 2015) Scheiber, L; Ayora, C; Vázquez-Suñé, E; Cendón, DI; Soler, A; Baquero, JCNot available
- ItemOrigin of high ammonium, arsenic and boron concentrations in the proximity of a mine: natural vs. anthropogenic processes(Elsevier, 2016-01-15) Scheiber, L; Ayora, C; Vázquez-Suñé, E; Cendón, DI; Soler, A; Baquero, JCHigh ammonium (NH4), arsenic (As) and boron (B) concentrations are found in aquifers worldwide and are often related to human activities. However, natural processes can also lead to groundwater quality problems. High NH4, As and B concentrations have been identified in the confined, deep portion of the Niebla-Posadas aquifer, which is near the Cobre Las Cruces (CLC) mining complex. The mine has implemented a Drainage and Reinjection System comprising two rings of wells around the open pit mine, were the internal ring drains and the external ring is used for water reinjection into the aquifer. Differentiating geogenic and anthropogenic sources and processes is therefore crucial to ensuring good management of groundwater in this sensitive area where groundwater is extensively used for agriculture, industry, mining and human supply. No NH4, As and B are found in the recharge area, but their concentrations increase with depth, salinity and residence time of water in the aquifer. The increased salinity down-flow is interpreted as the result of natural mixing between infiltrated meteoric water and the remains of connate waters (up to 8%) trapped within the pores. Ammonium and boron are interpreted as the result of marine solid organic matter degradation by the sulfate dissolved in the recharge water. The light δ15NNH4 values confirm that its origin is linked to marine organic matter. High arsenic concentrations in groundwater are interpreted as being derived from reductive dissolution of As-bearing goethite by dissolved organic matter. The lack of correlation between dissolved Fe and As is explained by the massive precipitation of siderite, which is abundantly found in the mineralization. Therefore, the presence of high arsenic, ammonium and boron concentrations is attributed to natural processes. Ammonium, arsenic, boron and salinity define three zones of groundwater quality: the first zone is close to the recharge area and contains water of sufficient quality for human drinking; the second zone is downflow and contains groundwater suitable for continuous irrigation but not drinkable due to high ammonium concentrations; and the third zone contains groundwater of elevated salinity (up to 5940 μS cm− 1) and is not useable due to high ammonium, arsenic and boron concentrations. © 2015, Elsevier B.V.
- ItemPalaeohydrology of the Mulhouse Basin: are fluid inclusions in halite tracers of past seawater composition?(Goldschmidt, 2007-08-19) Cendón, DI; Ayora, C; Pueyo, JJ; Taberner, C; Blanc-Valleron, MMBrine reactions processes were the most important factors controlling the major-ion evolution in the Oligocene, Mulhouse Basin (France) evaporite basin. The combined analysis of fluid inclusions in primary textures in halite by Cryo-SEM-EDS with sulfate-δ34S, δ18O and 87Sr/86Sr isotope ratios reveals hydrothermal inputs and recycling of Permian evaporites, particularly during advanced stages of evaporation in the Salt IV member which ended with sylvite formation. The lower part of the Salt IV evolved from an originally marine input. Sulfate-δ34S shows Oligocene marine-like signatures at the base of the member (Fig.1). However, enriched sulfate-δ18O reveals the importance of re-oxidation processes. As evaporation progressed other non-marine or marine-modified inputs from neighbouring basins became more important. This is demonstrated by an increase in K concentrations in brine inclusions, Br in halite and variations in sulfate isotopes trends and 87Sr/86Sr ratios. The recycling of previously precipitated evaporites was increasingly important with evaporation. Therefore, regardless of the apparent marine sequence (gypsum, halite, potassic salts), the existence of diverse inputs and the consequent chemical changes to the brine preclude the use of trapped brine inclusions in direct reconstruction of Oligocene seawater chemistry.
- ItemRecent and old groundwater in the Niebla-Posadas regional aquifer (southern Spain): implications for its management(Elsevier Science B.V., 2015-04-01) Scheiber, L; Ayora, C; Vazquez-Sune, E; Cendón, DI; Soler, A; Custodio, E; Baquero, JCThe Niebla-Posadas (NP) aquifer in southern Spain is one of the main groundwater sources for the lower Guadalquivir Valley, a semiarid region supporting an important population, agriculture and industry. To contribute to the understanding of this aquifer the assessment of sustainable use of groundwater, the residence time of groundwater in the NP aquifer has been estimated using H-3, C-14 and Cl-36. Along the flow paths, recharged groundwater mixes with NaCl-type waters and undergoes calcite dissolution and is further modified by cation exchange (Ca-Na). Consequently, the water loses most of its calcium and the residual delta C-13(DIC) in the groundwater is isotopically enriched. Further modifications take place along the flow path in deeper zones, where depleted delta C-13(DIC) values are overprinted due to SC42- and iron oxide reduction, triggered by the presence of organic matter. Dating with H-3, C-14 and Cl-36 has allowed the differentiation of several zones: recharge zone (<0.06 ky), intermediate zone (0.06-20 ky), deep zone 1(20-30 ky), and deep zone 2 (>30 ky). An apparent link between the tectonic structure and the groundwater residence time zonation can be established. Regional faults clearly separates deep zone 1 from the distinctly older age (>30 ky) deep zone 2. From the estimated residence times, two groundwater areas of different behavior can be differentiated within the aquifer. © 2015, Elsevier B.V.
- ItemSulfate starved subbasins: implications for Permian seawater composition(Elsevier B. V., 2006-08-22) Cendón, DI; Pueyo, JJ; Ayora, C; Taberner, C; Peryt, TThe Zechstein evaporites represent a vast 1,000,000 km2 evaporitic basin of the Late Permian that extended from the British Isles to Poland and beneath the North Sea. The Zechstein evaporites of northern Poland precipitated in a subbasin of the Zechstein Sea forming the Peribaltic Gulf. Fluid inclusions in halites of the Polish Zechstein oldest Halite (Na1) have been analyzed by Cryo-SEM-EDS together with the δ34S δ18O of accompanying sulfates and Br contents in halite. The A1d (anhydrite) and Na1(halite and anhydrite) were chosen as they have the potential to better represent the original source of brine, minimizing common recycling processes within evaporitic basins. Fluid inclusions have major-ion compositions similar to evaporated modern seawater. Sulfate isotopes generally coincide with previous values for Permian evaporites assigned as marine in origin. However variations in both δ34S and δ18O are considerable when compared to smaller marine-continental settings such as the South Pyrenean basin (Ayora et al., 1994, Cendón et al., 2003). We postulate that the further restriction from the main Zechstein basin could have caused brines to be extremely sensitive to SO4-concentration variations, the result being that the Peribaltic Gulf could have been periodically starved of sulfate. This was registered by several isotopic reservoir effects during anhydrite and halite precipitation in the A1d and Na-1 cycles. Brines trapped in primary halite fluid inclusions in our data set are similar to those expected from the evaporation of modern seawater, except for SO4 always being depleted when compared to modern values. The palaeogeographic setting of the basin could explain why brines were depleted with respect to SO4, without the need to invoke more complicated global processes, such as secular variations in seawater chemistry. While these findings do not deny possible variation in seawater chemistry over the Phanerozoic, they reinforce the need for accurate interpretation of evaporitic precipitates. © 2006 Published by Elsevier Ltd.