Elevated palaeotemperatures prior to Early Tertiary cooling throughout the UK region: implications for hydrocarbon generation

Abstract

Elevated palaeotemperatures prior to Early Tertiary cooling, which affected wide areas of the UK region, have been revealed by Apatite Fission Track Analysis (AFTA™). All available evidence suggests that palaeogeothermal gradients were close to present values and that much of the observed heating was due to greater depth of burial, by 1 to 2 km or more of section that was subsequently removed by uplift and erosion. Uplift and erosion were not restricted to local inversion axes. The palaeotemperature data suggest a broad, regional warping, producing kilometre-scale Tertiary uplift and erosion across a wide area, within which recognized inversion axes represent local regions of maximum uplift and erosion. AFTA data show no thermal effects associated with Cimmerian unconformities, and any heating associated with Cimmerian events was of lesser magnitude than Late Cretaceous to Early Tertiary heating. Over much of the UK region, source rocks attained maximum temperatures and reached peak maturity during this later heating episode. The regional extent of heating at this time and its significance to hydrocarbon source rock maturation have not been fully recognized in the past. The timing of the events described here suggests a link to the development of the Atlantic margin, Laramidé inversion tectonics and the onset of Alpine tectonism. However, definitive answers to such questions must await further research, particularly involving integration of AFTA and other thermal indicators with structural and geophysical data