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\subsection{Temperature estimation using $\Delta_{47}$}  Using the clumped isotope composition of carbonate minerals as a geothermometer is a young and developing technique. Critical to it's successful application is a robust calibration between $\Delta_{47}$ and temperature. At present there exist several different calibrations (references). These are illustrated in Figure 4. There is a range in both the temperature sensitivity (gradient) and offset of the different calibrations. Here we simply point out The differences between calibrations are laboratory dependent and  that for measurements of samples when converted to temperature only make geological sense when the local $\Delta_{47}$ - $T$ relationship is used. For  this study we have used the temperature calibration determined at UEA using biogenic carbonates (bivalves and foraminifera)  and travertine samples collected from sites with well characterized temperatures: \[{\Delta _{47}} = \frac{{0.0389 \times {{10}^6}}}{{{T^2}}} + 0.2139\]  where T is in Kelvins. As with most previous studies the calibration has been made over a restricted temperature range (0-56$^{\circ}$C that lies (0-56$^{\circ}$C). For the most part this range is  below the temperaturerange  of most of the  samples collected reported  in this study. of these calibrations We  have been made over a restricted range of temperatures based on confidence, however, that  the collection of biogenic carbonates from environments with known temperature (e.g. references). More recently calibrations calibration can be extrapolated to higher temperatures. In Figure 4 we  have become available plotted data obtained in our laboratory  forinorganically precipitated calcites. However these have not served to resolve the origin of  the differences.  What is clear from these studies is that differences between calibrations are laboratory dependent. i.e. measurements $\Delta_{47}$ value  ofunknown samples when converted to  a temperature only make geological sense when the local Δ47 - T calibration is used. If another laboratories calibration is used then unrealistic temperatures are often estimated. This points to significant methodological issues associated with Carrara marble  samplepreparation and mass spectrometry  that have yet to be resolved. We don’t discuss these here. For this study we have used the UEA determined calibration to translate Δ47 values for carbonates into temperature.    (6)  This calibration is based on (i) biogenic carbonates (bivalves had been crushed  and foraminifera) collected from environments with known environmental temperature; (ii) natural inorganic calcites from travertines precipitated experimentally re-crytallised  at spring heads with known temperature, 600$^{\circ}$C  and (iii) experimental inorganic carbonates precipitated or recrystallised at known temperatures. A single 1000MPa in a solid media apparatus before rapidly quenching(Bernasconi, 2014 pers. comm.) Our extrapolate  calibration is consistent across passes very close to  the mean of these high  temperature range covered by the data. Also, our  calibration from 0 - 600°C. We note that within measurement error this calibration is indistinguishable with lies very close to  the theoretical line calculations  of Guo et al. (2009). the temperature dependence of heavy isotope clumping in calcite \citep{Guo:2009fy}. These observations gives us confidence in extrapolating our calibration to cover the range of temperatures expected in the upper crust.