The evolution of the Dogger Bank, North Sea: a complex history of terrestrial, glacial and marine environmental change

This paper presents a summary of the results of a detailed multidisciplinary study of the near surface geology of the Dogger Bank in the southern central North Sea, forming part of a site investigation for a major windfarm development undertaken by the Forewind consortium. It has revealed that the Dogger Bank is internally complex rather than comprising a simple “layer cake” of the Quaternary sediments as previously thought. Regional and high-resolution seismic surveys have enabled a revised stratigraphic framework to be established for the upper part of this sequence which comprises the Eem (oldest), Dogger Bank, Bolders Bank formations and Botney Cut Formation (youngest), overlain by a typically thin Holocene sequence. Detailed mapping of key horizons identified on the high-resolution seismic profiles has led to the recognition of a series of buried palaeo-landsystems which are characterised by a range of features including; glacial, glacifluvial and fluvial channels, a large-scale glacitectonic thrust-moraine complex with intervening ice-marginal basins, a lacustrine basin and marine ravinement surfaces. Interpretation of these buried landscapes has enabled the development of an environmental change model to explain the evolution of the Dogger Bank. This evolution was driven by the complex interplay between climate change, ice sheet dynamics and sea level change associated with the growth and subsequent demise of the British and Irish and Fennoscandian ice sheets during the Weichselian glaciation. Following the decay of these ice sheets the Dogger Bank entered a period of significant climatic and environmental flux which saw a terrestrial landscape being progressively inundated as sea levels rose during the Holocene

The Late Weichselian-Holocene transition in the Barents Sea: sedimentological and early diagenetic studies

Gravity cores and grab samples from the Barents Sea (Fig. 1) were studied with respect to mineralogy, grain size distribution. total carbon content and ‘Rock Eval’ pyrolysis. The samples were classified as either Late Weichselian or Holocene according to Bjarlykke et al. (1978) and Elverhoi & Solheim (1983)

Landslide Material Control on Tsunami Genesis ‐ The Storegga Slide and Tsunami (8100 y BP)

Tsunami generation from sub‐aqueous landslides is controlled by landslide kinematics, which in turn is governed by the material properties of the slide mass. Yet, the effect of the material properties on tsunami‐genesis is poorly understood. Geomorphological observations of landslide run‐out put constraints on the landslide dynamics. In addition, observations of tsunami run‐up heights can improve our understanding of how the landslide material transforms from initiation to final run‐out. The giant prehistoric Storegga Slide off the mid‐Norwegian coast caused a well documented ocean‐wide tsunami that offers a unique setting for coupling landslide material models to tsunami generation models. In this study we simulate the dynamics of the Storegga Slide and tsunami using the depth‐averaged landslide model BingClaw, which implements visco‐plastic rheology and remolding, and couple it to a standard tsunami propagation model. A broad sensitivity study varying the landslide material strength parameters in BingClaw showed that the initial soil yield strength and remolding rate are most important for the tsunami‐genesis, but that the residual strength determined the final run‐out distance. BingClaw parameters were further optimized to obtain the observed run‐out distance and to minimize the relative error of the tsunami run‐up heights. As detailed time‐dependent three‐dimensional representations of landslide parameters cannot be determined field investigation of the landslide itself, these simulations of the Storegga Slide and tsunami can help in the selection of plausible parameter ranges for prognostic modeling in quantitative hazard assessments.Landslide Material Control on Tsunami Genesis ‐ The Storegga Slide and Tsunami (8100 y BP)publishedVersio

The size and frequency of icebergs and bergy bits derived from tidewater glaciers in Kongsfjorden, northwest Spitsbergen

Tidewater glaciers constitute over 1000 or 20% of the coast of Svalbard. The dimensions and frequency of the occurrence of icebergs and bergy bits produced from these tidewater glaciers in Kongsfjorden, northwest Spitsbergen, were measured during the summers of 1991 and 1992. In 1991, 35-40% of 275 observed icebergs and bergy bits were 2 m in freeboard. This is interpreted to be the result of a major calving event prior to the 1992 observations. Side-scan sonar data on sea floor morphology showed frequent scouring by iceberg keels to a depth of 35 m, but no scouring below 40 m, thus defining the maximum iceberg keel depth and the depth to which sediment reworking by these keels occurs. Calculations of the melt rate of icebergs allows an estimation of the life expectancy of icebergs calved into Kongfjorden. Melting by forced convection lies between approximately 0.1 and a maximum of 1.0 m d?1, depending on iceberg relative velocity, size and water temperature. Melting linked to wave action is also approximately 0.5-1.0 m d?1. These calculations imply that icebergs of the dimensions commonly observed in Kongsfjorden will seldom survive travelling beyond the fjord mouth. Radar observations of iceberg occurrence from FS POLARSTERN during its summer 1991 circumnavigation of Svalbard also showed that no larger icebergs were escaping beyond the mouths of the major fjords of western and northern Spitsbergen. Iceberg derivation from Spitsbergen fjords is therefore not likely to be an important mechanism for sediment rafting and deposition on the continental shelf and in the deep ocean, but it is of significance to local fjord sedimentation. Comparison with evidence on iceberg dimensions from the Barents Sea and an East Greenland fjord shows that the larger icebergs there are derived from parent ice masses with quite different characteristics than those calving into the Spitsbergen fjords

Geotechnical properties of shelf sdiments from the Prydz Bay

This paper presents a geotechnical characterization of the glacigenic sediments in Prydz Bay, East Antarctica, based on the shipboard physical properties data obtained during Leg 119, combined with results of land-based analyses of 24 whole-round core samples. Main emphasis is placed on the land-based studies, which included oedometer consolidation tests, triaxial and simple shear tests for undrained shear strength, permeability tests in oedometer and triaxial cell, Atterberg limits, and grain-size analyses. The bulk of the tested sediments comprise overconsolidated diamictites of a relatively uniform lithology. The overconsolidation results from a combination of glacial loading and sediment overburden subsequently removed by extensive glacial erosion of the shelf. This leads to downhole profiles of physical properties that have been observed not to change as a function of the thickness of present overburden. A number of fluctuations in the parameters shows a relatively systematic trend and most likely results from changes in the proximity to the ice sheet grounding line in response to variations in the glacial regime. Very low permeabilities mainly result from high preconsolidation stresses (Pc'). Pc' values up to 10,000 kPa were estimated from the oedometer tests, and empirical estimates based on undrained shear strengths (up to 2500 kPa) indicate that the oedometer results are conservative. The diamictites generally classify as inactive, of low to medium plasticity, and they consolidate with little deformation, even when subjected to great stresses. This is the first report of geotechnical data from deep boreholes on the Antarctic continental shelf, but material of similar character can also be expected in other areas around the Antarctic