An attempt to interpret the temperature profile of the KTB pilot drillhole (Germany) by paleoclimatic considerations

The temperature profile of the KTB pilot drillhole, T(z)_KTB-PH,is distinctly nonlinear: a temperature deficit ΔT (relative to a linear temperature-depth profile) is especially pronounced in the depth range 500–3500 m. The depth dependence of the deficit, Δ(z) is compared to be anticipated effect of surface paleoclimatic variations, ΔT_pc(z), at the drillsite on the temperature profile. The latter can be calculated from available paleo-climatic models. If ΔT_pc(z) is added to T(z)_KTB-PH, a nearly linear temperature-depth curve results with an average geothermal gradient of 27.9°C/km. This, together with an average vertical thermal conductivity of 3.0 W/mK, estimated from KTB drillcore data, implies a heat flow density at the KTB site of 84 mW/m². This modelled value is in good agreement with heat flow determinations in the adjacent Eger graben structure (Western Bohemian massif).