Miocene continental margin growth dominated by deposits from ocean currents – an example from offshore Norway

<p>The earliest Cenozoic evolution of the Mid-Norwegian and Lofoten-Vesterålen continental margin (~65-70<sup>o</sup> N) involved rifting, opening and finally seafloor spreading, initiating the Norwegian-Greenland Sea. These events resulted in large morphological and structural variations along the margin, creating accommodation space in a deep- to shallow-marine setting that allowed for accumulation of the Miocene sediments of the Kai- and Molo formations. The Cenozoic seismic stratigraphic correlation between the wide Mid-Norwegian and the narrow Lofoten-Vesterålen margin is poorly established. We therefore here analyze a large database of seismic data and exploration wellbores to give new insights on the sedimentary processes and paleo-environments during the Miocene evolution of this complex continental margin segment.</p><p>Steeply dipping clinoforms of the Molo Formation testify to a Miocene coastal outbuilding on the eastern part of the northern Mid-Norwegian margin. West of this, elongated sediment accumulations oriented in an along-slope SSW-NNE direction characterize the palaeo-slope. These are up to ~200 km long, between 40 and 110 km wide and up to ~520 m thick. An internal divergent reflection configuration characterize the elongated accumulations and they typically display a progressive upslope onlapping relationship onto an overall gently westward-dipping underlying morphology that includes domes, highs and ridges. Small incisions are frequently observed in association with the upslope onlap. These characteristics are altogether typical of contourites deposited from ocean currents. In the Vøring Basin, the internal seismic configuration can be described as consisting of low to moderate amplitude parallel-layered reflections, which are interpreted to represent a deep-water hemipelagic setting.</p><p>On the much narrower Lofoten-Vesterålen margin, parts of the Kai Formation show a seismic reflection configuration similar to what is observed on the northern Mid-Norwegian margin (e.g. elongated character, divergent internal reflections). These sediments are therefore also interpreted to be contouritic- and hemipelagic deposits. In contrast to the northern Mid-Norwegian contourites, the Lofoten-Vesterålen contourites are generally thinner, and they onlap onto an underlying steeply dipping continental slope, a slope which is also characterized by submarine canyons. Downslope of these, depocenters oriented perpendicular to the margin (i.e. slope-parallel), suggest influence of downslope processes through the canyons.</p><p>Our preliminary results show the presence of several contourite build-ups on the investigated margin, indicating the occurrence of a well-established ocean circulation with a persistent current direction along the Norwegian margin during deposition of the Kai Formation. The main source area for these sediments were likely south of the Mid-Norwegian margin. Coastal outbuilding in the Molo Formation and canyon-fed sediment input also testify to a sediment input from the east in the Miocene, and some of these were likely also re-distributed by ocean currents.</p>

The spatial distribution of igneous centres along the Norwegian Atlantic Margin (Møre and Vøring) and their relationship to magmatic plumbing systems

A series of offshore intra-basinal igneous centres have been documented across the North Atlantic Igneous Province including the UK, Ireland and Greenland. However, inconsistent cross-border terminology implies that similar features are not present in the Norwegian offshore, which, in turns, leads to misperceptions of cross-border geological differences. This paper presents evidence for a series of Norwegian igneous centres and suggests a consistent non-genetic cross-border terminology. In the Møre Basin, several igneous centres sit close to the continent–ocean boundary (COB), which have previously been identified as seamounts and/or ‘outer highs’. To provide cross-border consistency these features are consolidated under umbrella terms: igneous centres or volcanic fissures. Further centres are probably present within the Møre Basin (east of the COB) where 3D seismic data were not available. In the Vøring Basin two new igneous centres, one intrusive and one extrusive, are identified within the continental domain. Additionally, a possible deep magmatic upwelling associated with the regionally significant T-Reflector is identified. These igneous centre end-members represent the complexity of the magmatic plumbing across the Norwegian margin. With further data it is likely that further igneous centres will be identified offshore mid-Norway.

Multiphase brittle tectonic evolution of the Mid-Norwegian margin, central Norway, reconstructed by remote sensing, paleostress inversion and K-Ar fault rock dating

<p>Basement terranes commonly contain complex fault networks developed during repeated episodes of brittle deformation. The Mid-Norwegian margin (from 62 to 63.8 °N) exposes a complexly fractured terrane formed mainly by Caledonian basement rocks. The margin recorded a prolonged brittle deformation history spanning the Devonian to Paleogene time interval. It is characterised by a pervasive NE-SW structural grain due to the ductile-brittle multiphase activity of the Møre-Trøndelag Fault Complex (MTFC).</p><p>In order to develop a time-constrained tectonic model of the area, we applied a multidisciplinary approach combining remote sensing, field work, paleostress inversion, microstructural analysis, mineralogical characterization, clumped isotope thermometry on carbonates and K-Ar dating of fault rocks from key representative faults. We present herein the preliminary structural-geochronological data of a still ongoing study of two regions along the Mid-Norwegian margin, the Hitra-Frøya and Kråkenes-Runde areas. These key areas represent the intersection regions between the Mid-Norwegian- and the other sectors of the margin.</p><p>The brittle structural record of the entire Mid-Norwegian margin was analysed by remote sensing of lineaments using high resolution LiDAR data followed by ground-truthing of the obtained results during field work. Three main sets of lineaments were identified: i) (E)NE-(W)SW-trending lineaments, parallel to the coastline and to the MTFC; ii) N(NW)-S(SE)-trending lineaments; iii) WNW-ESE-trending lineaments. The main sets of faults and fractures were further characterised by their fault rock association and coating. All generations of faults contain thin coatings of chlorite, variably thick epidote and quartz mineralisations and calcite veins and coatings, locally associated with acicular zeolite. Samples of calcite and related gouges were collected from different sets of faults. Carbonate clumped isotope thermometry constrains the range of temperature of calcite growth between 140 and 30 °C, indicating that calcite precipitated at different thermal conditions during a multiphase structural evolution. K-Ar data collected so far from synkinematic illite separated from fault gouges yield Jurassic-Paleogene ages.</p><p>The structural network of the margin is interpreted as reflecting a sequence of different deformation episodes. In order to resolve the orientation of the stress field for each recorded event, we applied paleostress inversion with the Win-Tensor software [1]. The preliminary results suggest that at least three tectonic stages affected the margin. A NE-SW strike-slip dominated transpression possibly reflects the late stages of the Caledonian orogenic cycle. A pure and oblique extensional (E)NE-(W)SW stage is associated with the Jurassic North Sea rifting, followed by a NW-SE Paleogene extensional reactivation observable throughout the margin.</p><p>To conclude, a new multidisciplinary database for the reconstruction of the brittle deformation history of the Mid-Norwegian margin is presented. The proposed approach aims to define the temporal and structural characterisation of each single tectonic episode. Such an approach is also pivotal toward the correlation with the deformation history of the corresponding offshore domains, as well as the comparison in time with other segments of the Norwegian margin.</p><p>[1] Delvaux, D. and Sperner, B. (2003). Stress tensor inversion from fault kinematic indicators and focal mechanism data: the TENSOR program. Geological Society, London, Special Publications, 212: 75-100</p>

Tidally influenced iceberg motion: sub-metre resolution imaging of iceberg ploughmarks using autonomous underwater vehicles in the Weddell Sea

<p>Linear to curvilinear depressions interpreted as iceberg ploughmarks are identified on the continental shelf beyond Larsen C Ice Shelf in about 350 m water depth using multibeam echo-sounding at sub-metre horizontal resolution. Detailed imaging of ploughmark morphology demonstrates the presence of irregularly spaced ridges extending across the full ploughmark width. These ridges have an arcuate shape in plan-view, are up to 2 m high, 20-40 m wide, show occasional presence of subdued debris-flow lobes on their distal side and have an asymmetric cross-profile in which the seafloor deepens beyond their slightly steeper side. The ridges are interpreted to have been produced when the iceberg moved backwards under the falling tide, which pushed up a ridge of sediment behind the iceberg keel, before it continued on its original trajectory under the rising tide. Similar features, which we term ‘iceberg tidal ridges’, can be identified at lower resolution on bathymetric and three-dimensional seismic data from the mid-Norwegian margin, suggesting the broader implications of the interpretations presented here. For example, the mapping of delicate ridges preserved within iceberg ploughmarks can be used to reconstruct past oceanic circulation including the former direction and strength of ocean currents.</p>