Palaeobathymetric evolution of the Nova Scotia rifted margin during the Central Atlantic Ocean opening

The palaeobathymetric evolution of rifted margins during continental breakup is complex. We investigate the subsidence of Late Triassic to Early Jurassic evaporitic sequences in the proximal and distal parts of the Scotian margin that formed during the opening of the Central Atlantic Ocean.

We use a 3D flexural backstripping technique, which incorporates decompaction and post-breakup reverse thermal subsidence modelling applied to key stratigraphic intervals through the Jurassic down to the Late Triassic base salt. The isostatic evolution of rifted margins depends on crustal thinning, lithosphere thermal perturbation and melt production during rifting and breakup. Quantitative analysis of seismic reflection and gravity anomaly data together with subsidence analysis have also been used to determine crustal thickness variations and ocean–continent transition structure, and to constrain the along strike variability in breakup related magmatism and crustal composition.

Reverse post-breakup subsidence modelling to the Late Triassic base salt restores this horizon at breakup time to near sea level in the proximal domains of the Scotian margin where the continental crust was only slightly thinned during rifting. In contrast, predicted palaeobathymetry of the base salt surface restored to breakup time is greater than 2 to 3 km in the distal parts of the margin where the continental crust was highly thinned (<10km) close to the ocean-continent-transition. One possible interpretation of this is that while the proximal salt underwent post-rift thermal subsidence only, the distal salt was deposited during the latest stage of rifting focused along the distal domains of the Scotian margin, where it underwent additional tectonic subsidence from crustal thinning. This observed difference between the subsidence of proximal and distal salt has been observed elsewhere on the South Atlantic margins (e.g., the Angolan Kwanza margin) and illustrates the complexity of the subsidence and palaeobathymetric evolution of distal rifted margins during breakup.

The deposition of Triassic evaporites occurred before and after the emplacement of the Central Atlantic Magmatic Province (CAMP). The impact of the CAMP on rifting, crustal structure and palaeobathymetric evolution of the Nova Scotia remains to be determined. We do not exclude an additional positive dynamic topography effect at breakup time related to the CAMP magmatic event.