The Mesozoic Ridges of the Southern Porcupine Basin

Abstract

This dissertation presents a review of the geology and geophysics of the principal intra basinal ridges of the southern Porcupine Basin, offshore south-western Ireland. These ridges, namely the Porcupine Median Volcanic Ridge and Porcupine Volcanic Ridge System, are collectively referred to as the Southern Porcupine Basin Ridges. The origin and composition of these ridges is important because they provide insights into both basin development and future hydrocarbon exploration potential of the area. This study is primarily based upon the first detailed interpretation of recently acquired and newly reprocessed long-offset proprietary 2D seismic reflection profiles. The new interpretation indicates that the ridges are fault blocks composed of dominantly sedimentary rock, in contrast to the widely accepted view that the ridges are eruptive features composed of either volcanic rock or metamorphic/serpentinitic mud. Comparison of the tall, elongate, steep-sided morphologies and clear fault_x0002_bounded margins of the Southern Porcupine Basin Ridges with potential modern ridge analogues for all candidate ridge types supports the sedimentary fault block hypothesis. Published potential field modelling studies do not support either an igneous or serpentinitic composition for the ridges, and instead indicate ridge densities which correspond to the Upper Jurassic/Lower Cretaceous basin fill, again consistent with the sedimentary fault block hypothesis. Similar fault block structures have previously been interpreted along strike to the north of the study area, as well as further south along the Atlantic Margin, including the West Galicia Margin, offshore Spain.