Thermal Modelling of the Caledonian Basin, Scandinavia and a Northern North Sea Profile

Doktorsavhandling, 1999

The reason for the registered high paleotemperatures of the Scandinavian Alum Shale was investigated by heat flow modelling constrained by vitrinite-like reflectance. The behaviour of the lithosphere under a load was modelled and the paleotemperatures were explained by burial of the Alum Shale in a foreland basin, developing during the Caledonian orogeny. Vitrinite-like reflectance of the Alum Shale and computer modelling implies that the basin was 6.5 km deep at the edge of the mountain range, thinning eastwards and that it ceased 350 km to the east in the present Baltic Sea. The Paleozoic foreland basin was later uplifted and eroded. This study suggests that to create a basin of this magnitude requires a mountain chain similar to the Himalayas and a flexural rigidity in the order of 4 - 10 24 Nm (an effective elastic lithosphere thickness of 87 km). In a thermal maturation study, the problem of vitrinite reflectance suppression in North Sea source rocks was emphasised. The error in paleoheat flow was quantified when estimated from suppressed vitrinite reflectance. In this study, a profile from the northern North Sea was modelled and two models from the Australian North West Shelf were used as references. The estimated heat flow in the northern North Sea model was 40% higher when the vitrinite reflectance data was corrected for suppression (55 mW/m2 instead of 40 mW/m2). If suppression of vitrinite reflectance is not considered, any estimation of hydrocarbon transformation, timing of hydrocarbon generation and the amount of petroleum generated could be erroneous.