Browsing by Author "Taberner, C"

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    Chemical 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, MM
    Brine 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.
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    Palaeohydrology 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, MM
    Brine 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.
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    Sulfate starved subbasins: implications for Permian seawater composition
    (Elsevier B. V., 2006-08-22) Cendón, DI; Pueyo, JJ; Ayora, C; Taberner, C; Peryt, T
    The 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.