Thermally subsiding basins and the insulating effect of sediment with application to the Cambro- Ordovician Great Basin sequence, western USA
Tectonic subsidence of thermally generated basins is sensitive to the insulating effect of sediment. Compacting sediment reduces thermal subsidence, increases apparent stretching factors and reduces uncertainty in estimates of the breakup age. The transient effect of sediment insulation on the shape of the subsidence curve is considered by comparing model results with an exponential fit from 16 to 144Myr after breakup. Misfits are dependent on the model parameters used, the degree of stretching, the degree of sediment compaction and the bottom boundary condition used in modelling. The magnitude of the misfit ranges up to 90 m (uncorrected for eustatic loading). These effects may alter the interpretation of backstripping results. Application to a data set from the Cambro-Ordovician miogeocline of the Great Basin, western USA, increases apparent stretching factors and reduces uncertainty in the predicted earliest Cambrian breakup age. In this case the misfits to exponential subsidence are quite large ( ~ 300m) so that correction for the insulating effect of sediment does not eliminate a probable eustatic signal consistent with the Sauk sequence. If a eustatic signal is assumed, correction for model error suggests that the thermal parameters used are an improvement over those previously adopted and that the base of the lithosphere thins as sediments are added at the surface.