Boron isotope geochemistry of N a‐bicarbonate, N a‐chloride, and C a‐chloride waters from the N orthern A pennine F oredeep basin: other pieces of the sedimentary basin puzzle

The boron stable isotope ratio δ 11 B of 12 water samples representative of three chemical facies (fresh N a‐bicarbonate, brackish N a‐chloride, saline, and brine C a‐chloride) has been analyzed. Interpretation of the δ 11 B data, along with the chemical compositions, reveals that N a‐carbonate waters from the N orthern A pennine are of meteoric origin, with boron contributions from clay desorption and mixing with seawater‐derived fluids of N a‐chloride or C a‐chloride compositions. The comparison of our new results with the literature data on other sedimentary basins of M editerranean, and worldwide, confirms the contribution of N a‐bicarbonate waters to the genesis of mud volcano fluids. The N a‐chloride sample of S alvarola ( SAL ), which may represent the end‐member of the mud volcanoes, and the C a‐chloride brine water from S alsomaggiore ( SM ) indicate boron release from clays compatible with the diagenetic process. The empirical equation:δ 11 B = [ 5.1364 × ln(1/B) mg l − 1] + 44.601 relating boron concentration and the stable isotope composition of the fluids observed in this study and the literature is proposed to trace the effect of diagenesis in sedimentary basins. A geothermometer associated to the diagenetic equation is also proposed:T ∘ C = [ δ 11 B − 38.873( ± 1.180 ) ] / [ − 0.164( ± 0.012 ) ]The application of this equation to obtain reservoir temperatures from δ 11 B compositions of waters should be carefully evaluated against the results obtained from other chemical and isotopic geothermometers from other basins around the world.