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Thermal histories of Permian and Triassic basins in Britain derived from fission track analysis

Abstract Permian and Triassic rifting in northern Europe resulted in the deposition and preservation of alluvial sediments within discrete graben structures throughout the UK. The sediments are mostly continental red-bed facies which contain little or no organic materials for vitrinite reflectance palaeotemperature estimation. However, the sandstones commonly contain detrital apatite from which fission track age and track length data can be readily derived, and the elusive low temperature thermal history quantified. Published and new fission track data from over 80 Permian and Triassic sandstones in Britain reveal contrasting thermal histories. Triassic rocks of northwest Scotland have seen only moderate palaeotemperatures (60–75°C), reached during the Mesozoic, in contrast to the Cheshire and Irish Sea Basins which experienced greater maximum palaeotemperatures (80–110°C) during the Late Cretaceous (Lewis et al. 1992b). In southwest England, maximum palaeotemperaturs of 70–80°C (∼95°C in the basin centre at Wytch Farm) were reached during the Lower Cretaceous. The Permian and Triassic sediments of this study indicate that maximum burial is not restricted to the Late Cretaceous and that, in the southwest especially, temperatures peaked much earlier, during the Lower Cretaceous. This implies a significant variation throughout Britain in both Mesozoic cover and its subsequent exhumation.