Hydrography, Surface Geology and Geomorphology of the Deep Water Sedimentary Basins to the West of Ireland

Abstract

This desk study involved the assembly, review and analysis of public domain and available data from an extensive deep water area offshore to the west of Ireland. All major bathymetric and sedimentary basins, in addition to associated shallow plateau and bank areas, were considered. Particular emphasis was placed on the Porcupine Seabight and Rockall Trough as these were considered to be the main areas of interest for the proposed 1996 AIRS (Atlantic Irish Regional Survey) project. Only relatively brief summaries are given for the Hatton Basin, Hatton Bank and the area further west. Also, as the GLORIA side-scan sonar system used in the project is effective only in deeper waters (continental slope and abyssal depths), a considerable portion of the shallow shelf has been ignored. The primary goal of this study was to assemble a large existing data base on the above areas and to present this in a concise format. An introduction for each area describes the geological location and bathymetric characteristics. This is followed in each case by a description of the hydrography, in particular the characteristics of the water column and bottom current dynamics. Finally, an overview of the main geological and geomorphological features is given. Little reference will be made to the pre-Pleistocene geology of the region, with the focus of the project being on the modern sediments. The water column over much of the study area is seen to be highly stratified, with a number of distinct layers of various origin evident. Vigorous bottom currents are also clearly present in many areas, often at significant depth, and undoubtedly have an influence on seafloor sedimentation patterns. Sediment influx related to the cessation of the last glacial cycle has had a profound influence on the sea bed geomorphology. In a number of areas, massive sediment drifts or accumulations are evident, in addition to large scale mass-wasting and slope failure features which determine slope and basin floor character. Vigorous early post-glacial sea bed currents probably determined the distribution of much of the glacial sediment, but currents capable of transporting fine sand to silt grade sediments have been recorded and are still active today.