Geology of the Hebridean margin of the Rockall Trough

Abstract

SynopsisThe geological structure and history of the Rockall Trough margin to the west of the Outer Hebrides (57°N-59°N) has been inferred from the analysis of bottom samples, seismic, sonar, magnetic, satellite altimeter and surface-ship gravity observations. Much of the continental shelf consists of a shallow platform of Precambrian Lewisian basement, covered by a thin (<300m) blanket of Cenozoic sediments. Apart from areas near the shelf break and immediately west of Lewis, the basement has not undergone the large-scale subsidence typical of many regions adjacent to the Rockall Trough. Beneath the outer shelf, the Lewisian dips steeply towards the deeper water and is covered by a westwardthickening succession (>3km) of Mesozoic and Cenozoic sediments.The eastern margin of the Rockall Trough appears to have been well established as a site of deposition by the end of the Triassic. Further subsidence occurred during the late Jurassic and continued into the Cretaceous when the axial province of the Rockall Trough off the Hebrides was invaded by basic volcanic material. Subsequently, the region was profoundly affected by early Cenozoic igneous activity. The long-term buoyancy of the Lewisian basement under the Outer Hebridean platform and early-formed structural discontinuities within it have influenced the overall pattern of sediment accumulation and the distribution of volcanic activity along the margin. During the later stages of deposition, sedimentation was closely controlled by the presence of early Cenozoic volcanics, by bottom currents and by glacial processes.

Sediment-drift development on the continental margin off NW Britain

“…It should be noted that the megasequences are not composed wholly of drift deposits. On the eastern flank of the Rockall Trough, lower Oligocene reefal sediments (depicted as sequence 3 in Figs 2 and 3) have been reported from the Hebrides Shelf (Jones et al 1986;Stoker 1997). There is also evidence for localized downslope input into the Rockall Trough, including a lowstand fan adjacent to Rockall Bank (sequence 2 in Figs 2 and 3; see also Fig.…”

“…Intra-plate tectonism, linked to intermittent tectonic phases, directly affected the evolution of the continental margin by creating its present morphological expression during a major, mid-Cenozoic, basinsubsidence event which, in turn, led to the onset of bottom currents (Stoker 1997). (Laughton et al 1972;Berggren & Schnitker 1983); (b) BGS boreholes and short cores (see text for details); (c) BGS borehole 88/7,7A (Stoker et al 1994), well 164/25-2, andJones et al (1986). Numbered sections (1-4) refer to upper Eocene to middle Miocene component sequences identified in Rockall Trough (see Fig.…”

Geotechnical and acoustic characteristics of Plio-Pleistocene sediments from the Hebrides Slope

“…The escarpment is steep (up to 28 °) (Evans et al 1989) and convex to the northwest. It is an erosional feature, cut by the onset of bottom currents (Miller and Tucholke 1983) during the mid-Oligocene low sea-level stand (Jones et al 1986;Evans et al 1989). Lower Oligocene carbonates, which form the scarp face (Jones et al 1986), have probably remained largely exposed since the mid-Oligocene, a consequence of the steepness of the escarpment and presence of a northward flowing contour current (Kenyon 1986(Kenyon , 1987.…”

Metagenomics-Based Discovery of Malachite Green-Degradation Gene Families and Enzymes From Mangrove Sediment

“…Therefore, mangrove sediments are suitable for exploring MG degrading microorganisms because of input of carbon in the form of litter which then acts as a substrate for decomposition by microbe. The bioremediation potential of microorganisms isolated from hydrocarbon-contaminated environments was as active as or even higher than those originating from non-contaminated sediments ( Jones et al, 2011 ). For now, a few culturable microorganisms with the degradation activity of dyestuff pollutant are isolated from mangrove sediment microbiome.…”