Abstract

The dynamic seascapes found in continental margin settings generally host many vertical structures, such as fault escarpments and submarine canyon systems. This terrain is exemplified on the Irish Atlantic Margin (IAM) by the Porcupine Bank Canyon (PBC). Bedrock has been found here in the past, however, surveying in these areas continues to be a difficult task due to issues regarding access and sampling conditions. As a result, a lack of both knowledge and detail generally exists for offshore outcrop, which is in stark contrast to typical terrestrial geological data. Modern advances in marine robotics and seafloor imaging techniques has allowed for renewed offshore scientific expeditions in deep marine settings, being guided by high-resolution topographical data (gathered through multibeam echosounding) and Remotely Operated Vehicles (ROVs). Here, updated high-resolution bathymetric data, coupled with bedrock samples that have been drilled in-situ and a series of video transects spread out across the PBC have been used to develop methods for offshore geological ‘fieldwork’, through marine bedrock mapping and sample characterisation, whilst also using footage to recreate the seafloor through Structur-from-Motion (SfM) photogrammetry, in order to produce accurately scaled, lifelike, geological outcrop models. The steps presented within this thesis with regards to bedrock mapping tie in with marine geomorphometry and habitat suitability modelling techniques. This attempts to quantitatively describe the surface of the seafloor, and identify key terrain attributes for which bedrock has previously been encountered and proven to occur. Further terrain data can then be reclassified based on the interquartile ranges (IQRs) for these characteristic sections, identifying potential occurrence of outcrop in non-surveyed areas. This study applies these methods across more than 2000 km2 of canyon terrain, and have yielded a 60% accuracy for bedrock predictions. These geological maps, coupled with high-definition video footage and physical rock samples, have allowed for a reappraisal of the bedrock encountered within the PBC. Bedrock samples indicate an underlying basement rock of lower greenschist facies metamorphosed igneous rocks.