A wide‐angle seismic profile across the western peninsulas of SW Ireland was performed. This region corresponds to the northernmost Variscan thrust and fold deformation. The dense set of 13 shots and 109 stations along the 120 km long profile provides a detailed velocity model of the crust.
Abstract A Bouguer gravity map of Ireland and the surrounding shallow seas has been produced in the form of a vertically illuminated shaded relief image. This method of presentation accentuates subtle trends in the gravity field which reflect complex density variations present in the crust beneath Ireland. These can be correlated with well known geological features in the onshore region, such as Caledonian granites and major faults. The large normal fault systems which bound offshore Mesozoic basins are clearly indicated by strong gravity lineaments with a similar underlying Caledonian trend. In many cases these can be traced onshore to known Caledonian faults. Transverse Caledonian and Variscan tectonic trends are also highlighted by the method.
Cold‐water coral mounds occur in discrete clustered populations over a broad region from the glaciated Norwegian continental margins to the non‐glaciated margins of Iberia and northwest Africa. Here we report on an interesting correlation between the Holocene growth of a mound population west of Ireland and early Holocene paleoclimatic variations in the North Atlantic region, notably the well documented ‘8,200 yr cold event’. An age structure for the population is calculated from growth rate estimates for the coral framework constructor Lophelia pertusa and a previously formulated population growth model. The model growth curve for the Holocene period fits the observed data well, except for a significant deflection in the data trend at about 8,500 calendar years ago. This corresponds to the time that the glacial lakes Agassiz and Ojibway, which were once dammed by a remnant of the Laurentide ice sheet, drained catastrophically into the Labrador Sea and triggered the ‘8,200 yr event’. This cold period may also have played a role in triggering major submarine landslides, such as the Storegga Slide.
F-10 SLOPE FAILURE MASS FLOW AND BOTTOM CURRENT PROCESSES IN THE ROCKALL TROUGH B.M. O’REILLY 1 P.W. READMAN 1 and P.M. SHANNON 2 1 The margins of the Rockall Trough currently the focus of oil and gas exploration interest incorporate an environmentally-important and lightly studied shelf region. This valuable natural laboratory contains information on slope stability sediment transport nutrient upwelling current and biological activity at a shelf/slope/basin-floor transition. An extensive high-resolution sidescan sonar survey was carried out in the Irish sector of the Rockall Trough in June/July 1998. The TRIM (TOBI Rockall Irish Margins) project (Shannon et al. 2001) funded
Magnetostratigraphical results from various historical, Holocene, Lateglacial and Glacial deposits from Central Jutland, Vendsyssel, the Baltic Sea and Schleswig‐Holstein are illustrated and discussed. Although only a few archaeomagnetic case studies have yet been made in Denmark, magnetic datings with accuracies of about ±50 years have been obtained on mediaeval kilns by comparing with a dipole transformed modification of the British archaeomagnetic master curve. Furthermore, a study of the expected east–west orientation of some 330 Romanesque churches in Denmark seem to indicate that about 25% of these churches were magnetically orientated; thus some kind of a magnetic compass may have been in common use in the twelfth century in Denmark. Radiocarbon‐dated Holocene lake sediments from lake Skanderborg reveal a distinct pattern of magnetic secular variation with fairly short time constants, which may be useful in magnetostratigraphical correlations of other lake sediments. Also Lateglacial and Early Postglacial sediments from the southern Baltic Sea show systematical magnetic patterns, whereas glacial boulder clay at the bottom shows disturbed directions, obviously moulded by the moving ice. Lateglacial Younger Yoldia clay from North Jutland shows well‐developed short periodic swings as well as an extreme declination variation of some 80° to 90°, the so‐called ‘Nørre Lyngby declination excursion’ around 14,000 B.P. A sequence of Older Yoldia clay at the same site furthermore shows significantly low inclination values, the so‐called ‘Rubjerg low inclination excursion’ of an age between 23,000 B.P. and 40,000 B.P. Finally, a well‐clustering palaeomagnetic direction from a Weichselian glacial boulder clay from Timmerhorn north of Hamburg is discussed from a hierarchical, statistical point of view.
Abstract Results of palaeoecological studies involving pollen analytical, chemical and palaeomagnetic investigations on a 3 m core from Lough Doo, NE County Mayo, are presented. The record, which commences shortly after 7000 BP, shows a sharp Alnus expansion coinciding with a decline in Pius at 6400 BP, an elm decline taking place in the context of severe soil erosion and the final decline of Pinus occurring as the chemical record indicates onset of severe reducing conditions in the catchment. Pine becomes extinct at or shortly before 3200 BP in the context of increased farming activity and the expansion of blanket bog in the adjacent upland areas. A later feature (c. 1880 BP) is the expansion of Taxus to 7.1% of total pollen. On the basis of the palynological evidence, it is concluded that there were no major Neolithic Landnam phases, which contrasts sharply with the evidence for widespread woodland clearance and the laying out of extensive and regular field systems in the northern coastal part of County Mayo. In the upper part of the core a severe inversion of 14 C dates is recorded. On the basis of the palaeomagnetic and pollen evidence this began at c. 1500 BP and is considered to have been initiated in the context of woodland clearance and a renewal in farming activity.
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