The Middle Jurassic Rattray Volcanic Province is located at the triple junction of the North Sea continental rift system. It has previously been thought to be sourced from three large central volcanoes: the Glenn, Fisher Bank and Ivanhoe volcanic centres. Re-interpretation using 3D seismic and well data shows that no volcanic centres are present and the Rattray Volcanics were instead sourced in fissure eruptions from linear vents, including the Buchan–Glenn Fissure System, a c. 25 km long zone of WSW–ENE-striking linear fissure vents and associated small volcanic edifices across the Buchan–Glenn Horst. The orientation of the fissures is broadly parallel to the Highland Boundary Fault, which intersects the Rattray Volcanics at the Buchan–Glenn Fissure System, implying that Mid-Jurassic magmatism exploited pre-existing crustal structural anisotropies established during the Caledonian Orogeny. The lack of large intrusive complexes beneath the Rattray Volcanics indicates that the pre-Middle Jurassic sedimentary sequences (e.g. the Devonian–Carboniferous Old Red Sandstone Group, the Permian Rotliegend and Zechstein groups and the Triassic Skagerrak Formation) extend further than previously supposed and therefore the presence of possible subvolcanic reservoir and source rock units within the triple junction of the Central North Sea may have been overlooked.
Abstract The UK Rockall Basin is one of the most underexplored areas of the UK Continental Shelf (UKCS), with only 12 exploration wells drilled since 1980. With only one discovery made in 2000 (Benbecula (154/1-1) gas discovery), the general view of the basin from an exploration viewpoint is not positive. However, over the last 15 years, our knowledge of the petroleum systems of the Atlantic Margin has substantially increased. With the recent acquisition of new seismic data by the UK Government as part of the OGA's Frontiers Basin Research Programme, it is a pertinent time to re-examine the prospectivity of the UK Rockall Basin. This paper presents a history of exploration within the UK Rockall Basin, from the first well drilled in the basin in 1980, to the last well, drilled in 2006. We then present new insights into the lack of success during exploration within the basin, in particular by focusing on the extensive Early Cenozoic volcanic rocks within Rockall, to illustrate the wide range of potential interactions with the petroleum system. We also present evidence that points to the potential of a viable intra-basaltic (Rosebank) type play along the eastern flank of the Rockall Basin.
Rift-related magmatism resulting in widespread igneous intrusions has been documented in various basins, including the Faroe Shetland Basin (UK), the Voring and Møre basins (Norway), and along the NW Shelf of Australia. Seismic mapping, combined with fieldwork, has resulted in greater understanding of subsurface intrusive plumbing systems but knowledge of emplacement style and the mechanisms by which intrusions propagate is limited. The interpretation of a 3D seismic dataset from the Exmouth Sub-basin, NW Shelf of Australia, has identified numerous igneous intrusions where a close relationship between intrusions and normal faults is observed. These faults influence intrusion morphology but also form pathways by which intrusions have propagated up through the basin stratigraphy. The steep nature of the faults has resulted in the intrusions exploiting them and thus manifesting as fault-concordant, inclined dykes; whereas in the deeper parts of the basin, intrusions that have not propagated up faults typically have saucer-shaped sill morphologies. This transition in the morphology of intrusions related to fault interaction also highlights how dykes observed in outcrop may link with sills in the subsurface. Our interpretation of the seismic data also reveals subsurface examples of bifurcating intrusions with numerous splays, which have previously only been studied in outcrop. Supplementary material: Figures showing uninterpreted seismic lines are available at https://doi.org/10.6084/m9.figshare.c.4395974
The Northern Kenya Rift is an important natural laboratory for understanding continental rifting processes. However, much of the current understanding of its geological evolution is based on surface outcrops within footwall highs due to a lack of subsurface geological constraints. In this paper, we present an investigation of the Cenozoic stratigraphy and volcano-tectonic relationship of the volcanic sequences within the Turkana Depression (namely the North Lokichar, North Kerio and Turkana Basins). We integrate regional seismic reflection data collected as part of ongoing petroleum exploration in the area with lithological and biostratigraphic data from new wells that were drilled in 2014 and 2015 (Epir-1 and Emesek-1). This has allowed linking and extrapolation of the detailed stratigraphy of the paleontologically important Lothagam site to the volcanic sequences within the Napedet Hills, North Lokichar, North Kerio and Turkana Basins. The site of the Plio-Pleistocene-age Turkana Fault, which separates the North Lokichar Basin from the Turkana and North Kerio Basins, appears previously to have acted as a focus of Middle Miocene volcanism c . 5 Ma prior to the main period of movement on the fault. Our study highlights how subsurface and outcrop information can be combined to give a more in-depth knowledge of the magmatic history within rift basins.
Igneous processes within sedimentary basins impact energy resource plays across a range of scales from regional tectonics to reservoir porosity. Understanding these interactions has a direct influence on hydrocarbon, carbon capture, geothermal, hydrogen and helium projects. This volume demonstrates state of the art thinking around these often complex systems.
Tuffs form key stratigraphic markers that assist with determining the timing of volcanic margin development. A number of laterally extensive tuffs are preserved along the North Atlantic Margin in the offshore Faroe–Shetland Basin (FSB), a product of early Palaeogene volcanism associated with the break-up and seafloor spreading between Greenland and NW Europe. These tuffs, which are dominantly basaltic in composition, are widely preserved in the contiguous North Sea Basin. However, less attention has been paid to them in the FSB. This study integrates multiple regional datasets, including 3D seismic data and released commercial well logs, to detail the character and distribution of early Palaeogene tuffs in the FSB. The earliest tuffs are more locally identified by their presence in core, whereas later tuffs are more regionally recognizable, highlighting more widespread volcanism with time. The distribution of tuffs also reveals the timing of formation of the previously enigmatic volcanic centres. Importantly, owing to constraints of vertical resolution in well data, we argue that the number of tuffs in the North Atlantic Margin is probably underestimated, and biased towards basaltic tuffs, which are easier to identify on well logs.
The Rattray Volcanics Member, at the triple junction of the North Sea rift, is here subdivided into two informal sub-members based on analysis of core, wireline and seismic data. The Lower and Upper Rattray Volcanics were emplaced during two distinct phases of volcanism separated by a sustained volcanic hiatus. The presence of hyaloclastite and abundant freshwater algae at the base of the Lower Rattray indicates that large lakes were present in the area prior to the volcanism, possibly indicating that collapse of the regional Jurassic Central North Sea dome began prior to volcanism. Pulsed subsidence probably occurred through the duration of the volcanism with lacustrine conditions becoming re-established during the mid-volcanic hiatus. Sediments were deposited across the Rattray Volcanic Province in fluvial systems and floodplain coal swamps after the final cessation of volcanism, with later marine transgression leading to drowning of the area in the Callovian to Oxfordian. In terms of hydrocarbon prospectivity, no evidence is currently found to confirm the presence of an intra-basaltic play analogous to the Rosebank Field in the Faroe–Shetland Basin, although post-volcanic Pentland Formation sedimentary sequences in the Fisher Bank Basin area indicate the possibility of supra-basaltic prospectivity in the triple junction. Supplementary material: A table containing the complete palynological record is available at https://doi.org/10.6084/m9.figshare.c.4857195
The Faroe–Shetland Basin, NE Atlantic continental margin, hosts a number of important hydrocarbon fields; although deep water and narrow weather windows mean that drilling costs are considerably higher than for other parts of the UK Continental Shelf. Any additional drilling complications are therefore important to predict and negate as such issues can result in avoidable multi-million pound cost implications. This study focuses on the Corona Ridge, an intrabasinal high which contains the Rosebank Field, where a plethora of drilling issues, of enigmatic origin, are common within a key stratigraphic marker known as the Balder Formation. Drilling fluid loss, bit balling, wellbore breakouts and wellbore ‘ballooning’, where lost drilling fluid returns to the wellbore, are all recognized within the Balder Formation along the Corona Ridge. We find that many of the drilling incidents can be traced back to both the lithological character of the Balder Formation and the mid-Miocene tectonic inversion of the Corona Ridge. Moreover, we find that this geological explanation has wider implications for exploration in the region, including the mitigation of drilling incidents in future wells through drill-bit selection. Supplementary material : A table detailing the drilling acronyms and terminology used in this study (adapted from Mark et al. 2018) is available at https://doi.org/10.6084/m9.figshare.c.4290602
We welcome the constructive comments of Manning et al. (2021) that our paper on the palaeogeographical evolution of the Rattray Volcanic Province provides a very valuable synthesis of this suite of rocks. Our paper presented a new evaluation of the stratigraphy and palaeogeographical setting of the Rattray Volcanic Province before, during and after the eruptions. The discussion underlines the fundamental science that can be undertaken and value attached to using subsurface data and cores obtained in the North Sea in general and the Rattray Volcanic Province in particular.
The contribution of Manning et al. (2021) concerns the petrographic identification …
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