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421.
The Cambrian sediments in Howth and Ireland's Eye to the northeast of Dublin have been mapped and the submarine deltaic Censure Group and the overlying Nose of Howth Group, which consists of interbedded turbidites and olistostromes, have been distinguished. Large scale sedimentary disruption has accompanied detachment of quartzitic sandstone beds in the Censure Group, where the bases of detached blocks have slump features while their tops generally do not. This contrasts with the chaotic sedimentary breccias in the olistostromes of the Nose of Howth Group. Blocks in the Censure and Nose of Howth Groups are up to 450 m and 700 m across respectively. The turbidies have come from the southeast and east whereas the slumping appears to have been generated from the southwest. Slumping during sedimentation was followed closely by large-scale folding and sliding of sedimentary or tectono-sedimentary origin, and the bulk appearance of the sediments is due to these sedimentary and tectono-sedimentary mechanisms. The main structure is an easterly facing, steep plunging syncline which locally is associated with a poorly preserved cleavage. This structure predated the main penetrative cleavage which is not axial planar to it.  相似文献   
422.
The simplest magnetic model for the upper 20 km of crust in central Ireland is of two layers. A thin, weakly magnetic upper layer carrying a number of magnetic bodies that can be related to surface geology overlies a magnetic crustal zone whose gross magnetization increases towards the north. The deeper trace of the lapetus Suture in central Ireland forms the boundary between a more magnetic northern crustal area and a less magnetic southern area. A pre-Carboniferous major dextral offset of this suture boundary occurs in the Limerick area. The suture is traced beneath the Dingle peninsula in the far south-west of Ireland. In east-central Ireland, between the Iapetus Suture and Southern Upland Line, the crust contains a large, south-dipping magnetic body with no surface expression, which produces the Virginia magnetic anomaly. The development of magnetic bodies — in particular, volcanic rocks of Carboniferous age — has been controlled by regional stress patterns. The major volcanic centre at Limerick lies at the intersection of two major Caledonian block fault systems just to the north of the surface trace of the Hercynian Front.  相似文献   
423.
In light of global warming and rising relative sea level (RSL), detailed reconstructions of RSL histories and their controlling processes are essential in order to manage coastal-protection challenges. This study contributes to unravelling Holocene RSL change on the East Frisian North Sea coast in high resolution and with a new approach for the German Bight. For the first time, a transfer function (vertical error: 29.7 cm ? ~11% of the mean tidal range) for RSL change based on a combined training set of benthic foraminifers and ostracods from the back-barrier tidal basin of Spiekeroog is applied to the Holocene record of the back-barrier tidal basin of Norderney. The resulting RSL curve for the Norderney tidal basin is corrected for decompaction and shows a deceleration in RSL rise between 6000 and 5000 cal bp. The smallest possible error envelope (~1 m) results from the good suitability of salt-marsh layers between 5000 and 4000 cal bp. The RSL curve provides an approach towards the closure of the common data gap of peat-based curves for the southern North Sea related to a lack of basal peats in the youngest age range, and verifies regional differences in glacial isostatic adjustment.  相似文献   
424.
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