Early Cenozoic Regional Exhumation and Mid-Cretaceous
Basin Inversion in the Southern North Sea Using Apatite Fission Track Analysis
Green, Paul F.1,
Ian R. Duddy1, Richard J. Bray2 (1) Geotrack
International Pty Ltd, Melbourne, Australia (2) Exploration Consultants Ltd,
Henley-on-Thames, Oxon, England
The Southern North Sea is a
classic location for studying basin inversion, evidenced by erosion of Late
Cretaceous Chalk from structures such as the Sole Pit Axis. Areas where Chalk
is preserved are commonly regarded as stable, non-inverted platforms, e.g. the
East Midlands Shelf (EMS) of the UK sector.
AFTA (Apatite Fission Track Analysis) data from 8 offshore wells
and numerous onshore wells, integrated with vitrinite reflectance data, shows
that the EMS has undergone deeper burial prior
to regional exhumation which began in the Early Cenozoic, ca. 60 Ma. Estimates
of additional section deposited above the preserved Chalk and subsequently
eroded from the EMS during Cenozoic exhumation are up to ~1 km across the EMS, and are highly consistent with previous estimates
derived from compaction studies in both Chalk and Triassic mudstones.
AFTA data from wells located along the eastern flank of the Sole
Pit axis show evidence of larger amounts of exhumation compared to EMS wells, and an earlier onset of cooling in the
interval 110 to 95 Ma. In these wells, higher amounts of additional burial are
also required to explain Triassic compaction data compared to Chalk values.
These observations are interpreted as revealing mid-Cretaceous inversion of the
Sole Pit Axis, prior to regional Early Cenozoic exhumation.
definition of thermal histories of hydrocarbon source rocks afforded by
resolution of these two major tectonic episodes provides a clearer
understanding of petroleum systems in the region, for example allowing
assessment of the remigration of earlytrapped hydrocarbons.