Origins of elements building travertine and tufa: New perspectives provided by isotopic and geochemical tracers
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Titre | Origins of elements building travertine and tufa: New perspectives provided by isotopic and geochemical tracers |
Type de publication | Journal Article |
Year of Publication | 2016 |
Auteurs | Teboul P.-A, Durlet C., Gaucher E.C, Virgone A., Girard J.-P, Curie J., Lopez B., Camoin G.F |
Journal | SEDIMENTARY GEOLOGY |
Volume | 334 |
Pagination | 97-114 |
Date Published | APR 1 |
Type of Article | Article |
ISSN | 0037-0738 |
Mots-clés | Calcareous tufa, Major elements, Stable isotopes, Trace elements, Travertine |
Résumé | Fluid/rock interaction represents a major process in the formation of calcitic or aragonitic travertine and tufa (CATT). In most cases, CATT is associated to limestone dissolution somewhere along the hydrogeological pathway. However, a wide array of other substratum (basalts, rhyolites, carbonatites, ultramafics, granites, dolomites, evaporites) can act as potential source of elements involved in the formation of CATT. This study reports on the evaluation of potential geochemical tracers linking CATT to their substratum, and unravelling the origin of elements. A large database was established from available literature data as well as new data acquired in the frame of this study for a set of Modern to Recent CATT (Ligurian ophiolites, Italy; the Chaine des Puys, Limagne graben and Paris Basin, France; Reunion Island, Indian Ocean; Jebel Oust, Tunisia). Four most reliable tracing methods are identified (1) delta C-13 and delta O-18 cross-plot allows distinguishing epigean (min delta C-13 = -27.2 parts per thousand, max delta C-13 = 0.9 parts per thousand, mean delta C-13 = - 12.3 parts per thousand for N = 314) from hypogean systems (min delta C-13 = -4 parts per thousand, max delta C-13 = 11.7 parts per thousand, mean delta C-13 = -2.87 %. for N = 198). Very low delta C-13 values (<-12 parts per thousand) and delta O-18>-4 parts per thousand associated to negative delta C-13 values are specifically indicative of an ultramafic source rock. (2) Barium and strontium cross-plot helps to discriminate different groups of source rocks amongst the hypogean CATT: (i) source rocks composed of mixed limestones, evaporites, and dolomites are characterised by low barium (<100 ppm) and high strontium (>400 ppm) contents, (ii) mafic and granitic source rocks are undifferentiated and display similar barium (from 15 to 930 ppm) and high strontium (>200 ppm) contents, (iii) the carbonatite group is characterised by its exceptional high barium and strontium values. In epigean CATT, a pure limestone source rack usually relates to very low barium and strontium contents (<50 ppm and <70 ppm respectively), whereas mixed limestone, evaporite and dolomite source rocks generally display low strontium content (<580 ppm) with higher barium content (>50 ppm). (3) Relatively high beryllium content (>30 ppm) in CATT seems to indicate a pure granitoid source. (4) High chromium concentrations (>20 ppm) are systematically documented in Modern CATT located on an ultramafic substratum. The definition of diagnostic compositional fields for actively forming or recently formed CATT is influenced by many factors including water composition, water temperature, dissolved gas composition and concentration, biological activity, position in the sedimentary body and early diagenesis, in addition to substratum lithology. However, the results of this study illustrate that, despite these many factors, the combined use of Ba, Sr, Be, Cr, delta C-13, and delta O-18 may be valuable to discriminate the rock lithology prevailing in the hydrogeological or palaeo-hydrogeological reservoir of CATT. (C) 2016 Elsevier B.V. All rights reserved. |
DOI | 10.1016/j.sedgeo.2016.01.004 |