Estimating the Magnitude of Exhumation From 2D and 3D Seismic Velocity Datasets: A Case Study From Slyne Basin, Offshore Northwestern Ireland

Abstract

Abstract Exhumation describes vertical displacements of rocks from maximum depth of burial that results from the removal of overburden material. In this study we invert seismic velocity profiles from 2D and 3D seismic reflection datasets to constrain the distribution and the magnitude of exhumation within the Slyne Basin, offshore NW Ireland. The method has already been successfully applied to 2D datasets offshore Britain and Africa; this study is the first attempt to extract exhumation estimates from 3D seismic data. Inversion of 3D seismic velocity data yields a continuous map of exhumation across the entire 3D footprint. Exhumation estimates from 2D seismic sections agree with estimates from co-located 3D data. However, there is greater scatter in the 2D-derived exhumation estimates, most easily seen at line ties. This scatter in the 2D measurements arises because 2D seismic stacking velocities are less well constrained than 3D velocities. Together, the 2D and 3D seismic stacking velocity profiles can be used to estimate exhumation patterns on spatial scales >10 km to an accuracy of ±200 m. Many estimated changes in exhumation are associated with geological structures, suggesting confidence in the results. The margins of Slyne Basin have undergone about 1 km more erosion than the basin centre to form the Jurassic-Miocene composite unconformity. Inversion anticlines in the centre of the basin have undergone a few hundred metres more erosion at their crests than at their flanks. There is good agreement between 3D seismic-derived exhumation estimates and existing exhumation estimates using traditional techniques applied to borehole data. Overall, our results show that regional exhumation can be mapped in hitherto unprecedented detail using good quality seismic stacking velocity data.