Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract -Flood basalts in associated volcanic rifted margins, such as the North Atlantic Igneous Province, have a significant component of lavas which are preserved in the present day in an offshore setting. A close inspection of the internal facies architecture of flood basalts onshore provides a framework to interpret the offshore sequences imaged by remote techniques such as reflection seismology. A geological interpretation of the offshore lava sequences in the Faroe-Shetland Basin, using constraints from onshore analogues such as the Faroe Islands, allows for the identification of a series of lava sequences which have characteristic properties so that they can be grouped. These are tabular simple flows, compound-braided flows, and sub-aqueously deposited hyaloclastite facies. The succession of volcanic rocks calculated in this study has a maximum thickness in excess of 6800 m. Down to the top of the sub-volcanic sediments, the offshore volcanic succession has a thickness of about 2700 m where it can be clearly identified across much of the area, with a further 2700 m or more of volcanic rock estimated from the combined gravity and seismic modelling to the north and west of the region. A large palaeo-waterbody is identified on the basis of a hyaloclastite front/apron consisting of a series of clinoforms prograding towards the eastern part of the basin. This body was > 500 m deep, must have been present at the onset of volcanism into this region, and parts of the water body would have been present during the continued stages of volcanism as indicated by the distribution of the hyaloclastite apron.

Quantifying the facies architecture of flood basalt provinces is important as it can be used to understand the physical volcanology and rock property variations throughout the lava sequence. The 3D facies architecture and internal heterogeneity of the Skye Lava Field, for example, provides important insights into the evolution of the British Tertiary Igneous Province, and valuable information to aid in the exploration of potential offshore reservoirs underlying significant flood lavas along the North Atlantic margin. The volcanic stratigraphy of the Talisker Bay area of Skye comprises: (1) lower compound-braided lavas (flow lobes <3 m thick); (2) transitional lavas (flows <8 m thick); (3) upper tabular-type lavas (flows <20 m thick), representing a relative increase in eruptive volume. A 3D model of the lava sequence was reconstructed using detailed digital geological mapping, revealing estimated volumes of: the lower sequence (12.7 km 3 ), the transitional sequence (7.4 km 3 ) and the upper sequence (17.0 km 3 ). The lower sequence lavas formed on the flanks of a shield volcano and were sourced from the NE. Volcanological features such as lava feeder tubes, pahoehoe textures and lobes indicate a scale of volcanism similar to that of present-day Hawaii. The within-flow heterogeneity of the basalts is characterized using an ‘intrafacies scheme’, allowing comparison of variations in lithofacies with characteristic (geophysical) rock properties of compressional-wave velocity and density.

International audience20 magnetotelluric (MT) soundings were collected on the Isle of Skye, Scotland to provide a high-resolution three-dimensional (3-D) electrical resistivity model of a volcanic province within the framework of a project jointly interpreting gravity, seismic, geological and MT data. The full 3-D inversion of the MT data jointly interpreted with gravity data reveals upper crustal structure. The main features of the model are interpreted in conjunction with previous geological mapping and borehole data. Our model extends to 13 km depth, several kilometres below the top of the Lewisian basement. The top of the Lewisian basement is at approximately 7–8 km depth and the topography of its surface was controlled by Precambrian rifting, during which a 4.5 km thick sequence of Torridonian sediments was deposited. The Mesozoic sediments above, which can reach up to 2.2 km thick, have small-scale depocentres and are covered by up to 600 m of Tertiary lava flows. The interpretation of the resistivity model shows that 3-D MT inversion is an appropriate tool to image sedimentary structures beneath extrusive basalt units, where conventional seismic reflection methods may fail

Thick successions of basalt and basaltic-andesite lavas flows were extruded during continental break-up and they cover pre-existing sedimentary basins often of interest for hydrocarbon exploration. With conventional seismic acquisition and processing methods, it is difficult to image both the internal architecture of the volcanic succession as well as the underlying sub-basalt structure. The use of synthetic data can help us to understand the poor sub-basalt imaging quality and to develop effective acquisition and processing approaches useful for real data. Moreover, non-seismic methods have been successful in improving understanding of overall geometries of sub-basalt targets. Therefore, integration of seismic and non-seismic data seems to yield promising results and needs to be explored further. From all these considerations, the necessity of a realistic 3D basalt model that would allow simulating realistic seismic and non-seismic data, on one hand to test seismic acquisition and processing techniques, and on the other to develop strategies for geophysical data integration into a common methodology to overcome the sub-basalt imaging problem. A complex 3D model was built adapting all the information available from interpretation of seismic data, log data, gravity data, and geological observation. Seismic and non-seismic synthetic data have been produced on the model. In this paper we present the methodology to develop the 3D model as well as the initial results from data simulations. The model and the data are available to the public, through the authors of the present paper.