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First results from shallow stratigraphic boreholes on the eastern flank of the Rockall Basin, offshore western Ireland

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journal contribution
posted on 30.04.2020, 14:20 authored by P. HAUGHTON, D. PRAEG, P. SHANNON, G. HARRINGTON, K. HIGGS, L. AMY, S. TYRRELL, T. MORRISSEY
Selected sections from four RSG consortium boreholes are displayed. These serve to highlight some of the key stratigraphic units and contacts along the eastern margin of the Rockall Basin. The cores were acquired using the MV Bucentaur in 1999 in a bid to constrain the stratigraphic evolution of the basin by coring Mesozoic and Tertiary stratigraphy tied via high resolution site survey seismic grids to regional industry seismic lines. Borehole 11/20-sb01 on the Erris High cored the flanks of a Palaeogene (?), shallow water tuff cone, and two core sections illustrate the volcaniclastic facies and evidence for post-eruption injection of the cone by soft carbonate sediment. Borehole 16/28-sb01 was drilled on the slopes north of the Porcupine High, and selected cored sections illustrate the basalt in which the hole terminated (a flow or a sill?), overlain by a thin Maastrichtian or older sandy grainstone. This is truncated by a subtle but significant unconformity, above which a deepening upward Eocene section is preserved. Borehole 83/20-sb01 on the western flank of the Porcupine High above the Bróna Basin reached the Jurassic, which is here overlain by a diverse Cretaceous section recording an upward evolution from shallow to deeper water ('brownsand' to 'greensand' to chalkey marl). A major phosphatised and Mn-impregnated surface cuts into the Cretaceous (the C30 surface?) and is onlapped by Miocene slope sediments. Borehole 83/24-sb02 lies SW of 83/20-sb01 deeper on the slope. It also cored a Cretaceous section (here the 'brownsand' unit) siting unconformably on an older Jurassic and/or Carboniferous interval. At this site, the Cretaceous is overlain by Eocene pelagic carbonates that were removed by erosion up dip.