Subsidence of the Scotian Basin: A Theoretical Model

Abstract

The development of a continental margin basin such as the Scotian Basin depends on various factors, exponential thermal contraction, sedimentary loading and the physical properties of the lithosphere underlying the basin.

From recent studies of the Scotian Basin it is concluded that the Basin has subsided exponentially with time with an exponential time constant of 50 m.y. to 60 m.y. in the western half of the Basin and 70 to 80 m.y. in the eastern half, since the final breaking apart of Africa and North America (160 to 170 m.y. ago). Sedimentation has also played an important role in the subsidence history of the Scotian Basin. During early stages of basin development sedimentation was rapid and constant. Later it gradually slowed and the Basin became an area of deep marine sedimentation (approximately 70 m.y. to 40 m.y. b.p.). Sedimentation rates then increased refilling the basin to its present shelf environment.

The modelling of a basin representing regional isostatic adjustment in a simplified Scotian Basin was done in three stages. First, the point load response of a viscoelastic plate (simulating the lithosphere) was found. Second, convolutions were evaluated representing a square load. Finally, the square loads were applied to a 500 x 500 km grid representing the Scotian Basin. The viscoelastic plate used to simulate the lithosphere underlying the Basin had varying flexural rigidities and viscous time constants. The best results were obtained when the flexural rigidity was taken as 1025 n.m. and the viscous time constant was 105 to 106 yrs. Sediment influx into the oceanic side of the theoretical Basin was kept at a constant 1000 meters per 20 m. yrs., a reasonable approximation to the observed sedimentation rates. Sediment influx onto the continental margin was assumed to be just sufficient to fill the subsiding area.

The model results obtained for a 160 m.y. time history gave a close approximation of the sediment accumulation in the Scotian Basin. We suggest minor improvements that would give model results that more closely represent subsidence in the Scotian Basin.

Keywords: Pages: 200 Supervisor: Chris Beaumont