Apatite fission track analysis (AFTA) is a method of obtaining thermal history information in sediments. In sections that have been hotter in the past, AFTA provides estimates of maximum palaeotemperatures, and the time at which a sedimentary section began cooling from maximum palaeotemperatures. It is useful for studying the thermal history of sequences containing source rocks, and can provide information critical to the understanding of the timing of oil generation. Integration of AFTA and vitrinite reflectance (VR) data allows a coherent thermal history framework to be established and a formal method of analysing palaeogeothermal gradients has been developed by combining AFTA and VR data. This approach allows definition of the major facets of thermal history based on directly measurable parameters, rather than on assumed values of palaeo-heatflow, and provides rigorous estimates of the amount of uplift and erosion. The case study demonstrates the application of this approach to the East Midlands Shelf region. Here AFTA data have revealed an episode of maximum palaeotemperatures prior to cooling commencing at around 60 Ma. Combined AFTA and VR data show that this cooling was due to kilometre-scale early Tertiary uplift and erosion under near normal geothermal gradients. Our estimates of uplift and erosion are significantly greater than those of pervious workers and show that uplift and erosion was not restricted to the recognized axes of inversion, but was regional in extent. This has implications for the evolution of source rock maturity in this region and in other basins in around the UK where AFTA has indicated early Tertiary heating and where the extent and amount of Tertiary uplift and erosion may have also been underestimated by previous workers.

No abstract

No abstract

No abstract

Studies of inverted basins based solely on the preserved section provide only partial insight into the thermal and tectonic history of basin development. Equally important is that part of the history represented by section removed by erosion during inversion. Thermal History Reconstruction, involving application of Apatite Fission Track Analysis (AFTA TM) and Vitrinite Reflectance (VR) to define the timing and magnitude of key erosional and/or thermal episodes, and integration of this information with data from the preserved section, provides a more complete description. Case histories from the UK, New Zealand and Australia are presented to demonstrate this approach. Much of northern and eastern England, the Irish Sea and the Southern North Sea was affected by heating apparently due largely to additional burial, followed by early Tertiary cooling due to regional uplift and erosion, synchronous with recognized basin inversion events. Heating associated with this episode caused generation of hydrocarbons throughout the region. Areas conventionally regarded as not inverted appear to have been subjected to km-scale uplift and erosion, which was not restricted to classic 'inversion axes'. Failure to allow for these effects can lead to a significant underestimation of regional maturity trends. Thermal History Reconstruction is also essential in areas that have undergone more than one episode of inversion. For example in Inner Moray Firth well 12/16---1 maximum palaeotemperatures in the Carboniferous section were reached prior to Hercynian inversion and the chances of preserving any hydrocarbons generated from Carboniferous or older source rocks appear poor. In southeastern Australia, early Cretaceous rift basins underwent mid-Cretaceous inversion at a time of high palaeogeothermal gradients (c. 60°C km-1), and basement margins were also inverted at that time. Again, early generation implies that the chances of preservation of hydrocarbons are small. By integrating stratigraphic and structural relationships within the preserved section with data on the palaeo-thermal history of a section derived from direct measurements of palaeotemperature profiles, the complete history of hydrocarbon generation may be reconstructed with confidence.