The measured shallow temperature field in Britain

The move towards a lower carbon society is likely to lead to a greater utilization of geothermal heat as the UK meets the challenge of its EU renewable obligation to source 15% of its energy from renewables by 2020. The shallow temperature field can be estimated, but measured temperatures are the most accurate approach for defining the shallow heat resource. Available measured temperature data have been used to compile maps of temperatures at depths below ground level of 100, 200, 500 and 1000 m. From these data regional trends and anomalies have been defined. From a consideration of all of the data a geothermal gradient of 28 degrees C km(-1) has been calculated for the upper 1 km of the sedimentary crust, which is slightly above the previously quoted value of 26 degrees C km(-1). Elevated temperatures have been mainly observed in eastern and southern England and have been attributed to convection within some of the thicker Permo-Triassic sandstones and the thermal blanketing effect of Triassic and Jurassic argillaceous rocks. Some of the depressed temperatures are associated with thick sequences of Carboniferous arenaceous rocks.