David W. Jolley

A revised lithostratigraphic nomenclature for the Palaeogene Faroe Islands Basalt Group, NE Atlantic Ocean

The Palaeogene volcanic succession of the Faroe Islands in the NE Atlantic Ocean is formalised using a purely lithostratigraphic approach and following international guidelines. The Faroe Islands Basalt Group (FIBG) has a gross stratigraphic thickness of ∼6·6 km, dominated by subaerial basalt lava flows, and is subdivided into seven formations. The Lopra Formation forms the basal ∼1·1 km of the Lopra-1/1A borehole, dominated by hyaloclastites, volcaniclastic sandstones and invasive basaltic lavas/sills. It is overlain by the ∼3·25 km-thick Beinisvorð Formation, dominated by laterally extensive basalt sheet lobes separated by minor volcaniclastic lithologies. The Beinisvorð Formation is overlain by the 900 m-thick Enni Formation composed of a mixture of basalt sheet lobes and compound flows with abundant volcaniclastic units, e.g. the Argir Beds, that may require a further subdivision at this stratigraphic level. The new lithostratigraphy allows for more refined biostratigraphical and sequence stratigraphic correlations and prepares for a revised geological map of the Faroe Islands.

Emeishan Basalts, SW China: reappraisal of the formation’s type area stratigraphy and a discussion of its significance as a large igneous province

The late Permian Emeishan Basalt Formation of SW China is one of Earth’s LIPs (large igneous provinces), yet its basic geology remains poorly documented. Recent work on sections close to the type area in Sichuan Province enable us in part to rectify this. Descriptions of the formation and associated units at two areas, one on the lower flanks of Mt Emei and another from a series of outcrops in Ebian County, 50–70 km to the SW, are presented. The basalt pile is 180–270 m thick and in both areas comprises 12 flows that were erupted in relatively quick succession. It rests conformably upon shallow-marine limestones/lignites suggesting emplacement close to sea level. The upper half of the youngest basalt was intensively weathered, but not eroded, prior to it being conformably succeeded by complex body of rocks c. 30 m thick, that includes thin basalts, pyroclastic rocks, tuffs and organic-rich terrestrial sediments. This unit, which has previously been described as a sedimentary package, presumably because intense weathering has obscured the primary lithological fabric in key outcrops, is considered to mark the volcanic waning phase. Uppermost Permian and Triassic terrestrial sediments conformably overlie the terminal volcanic rocks. The sub-regional stratigraphy is compared, as best it can be, with that described from two sections 400 km to the SE; one section matches reasonably well, the other does not, indicating that regional correlations need to be developed carefully. The information is discussed in the context of LIP generator models; several key features of the Emeishan Basalt terrain are at odds with those commonly encountered in LIP’s. The most important conclusion is that the unit marks a prematurely terminated system in which full bloodied rifting leading to the development of an ocean basin never started.

Seismic imaging of 'broken bridges': linking seismic to outcrop-scale investigations of intrusive magma lobes

Three-dimensional seismic datasets have provided unrivalled insights into magma flow within sub-volcanic systems. One of the key revelations is that sills appear to be constructed of a series of discrete magma lobes that form during the emplacement of magma into host-rock. We focus on a large sill, within the Faroe–Shetland Basin, North Atlantic, that is well imaged on seismic data, and identify the presence of ‘broken bridges’ within the sill, developed between elongate magma lobes, and reveal for the first time in three dimensions the development of broken bridges. Critically, by relating the imaged structures to key outcrop-scale examples we confirm that bridge and broken-bridge structures are oriented perpendicular to the magma flow direction. This work thus demonstrates a key link that can be made between seismic-scale investigation of intrusions and sub-seismic (outcrop-scale) processes, highlighting the seemingly scale-invariant nature of the magmatic emplacement process.

The stratigraphy, environment of eruption and age of the Faroes Lava Group, NE Atlantic Ocean

Abstract Palaeogene volcanism on the NW margin of the Faroe-Shetland Basin is represented by the Faroes Lava Group, within an age range of 57.5–60.56 Ma. The volcanic sequence comprises >1000 m of basaltic volcaniclastic rocks deposited in estuarine or marginal lagoons, overlain by three laterally-extensive formations of subaerial facies basaltic lavas: Lower, c. 3250 m; Middle, c. 1400 m; Upper, at least 900 m (top not preserved). The Lower and Upper formations comprise high-volume sheet flows, commonly with ferrallitized tops, interbedded with reddened, thin, fluvial claystone and basaltic siltstone deposits. Laterally-impersistent coals occur within the Lower Lava Formation. The Coal-bearing Formation (c. 20 m) was deposited in an overbank floodplain environment during an hiatus in the volcanism between the Lower and Middle formations. The Volcaniclastic Sandstone Sequence comprises hydroclastic and pyroclastic deposits which post-date the Coal-bearing Formation and represent a return to volcanism, prior to the eruption of the Middle Lava Formation which is mainly characterized by inflated pahoehoe flows. The onshore sequence of the Faroes Lava Group can be correlated with basaltic flows within the Faroe-Shetland Basin, where lavas in Well 205/9-1 are interpreted to be of Lower Lava Formation affinity, possibly erupted from a local vent system. Seismic and gravity mapping and modelling suggest that the offshore extension of the Lower Lava Formation, together with the oldest part of the Middle Lava Formation, comprise subaqueous hyaloclastites deposited in a prograding Gilbert-type lava delta system. The youngest part of the Middle Lava Formation and all of the Upper Lava Formation occur as subaerial facies lavas within the basin.

The evolution of the North Atlantic Igneous Province and the opening of the NE Atlantic rift

The papers in this volume represent a step forward in our knowledge of the geological evolution of the North Atlantic from the Cretaceous-Palaeogene boundary through to the early Eocene. With the increase in hydrocarbon exploration activities in the Faroe-Shetland Basin (Fig. 1), new interpretations of the regional geology have become increasingly important, and the accuracy of the time frame for this work is vital to our understanding of the sequence of volcanic and sedimentary events. The synthesis of data relating to Palaeogene volcanism and sedimentation along the Norwegian Margin by Eldholm et al. emphasizes the importance of transfer zones, possibly inherited from the Proterozoic basement, in the distribution of sediments and volcanic products during rifting (Fig. 2). Furthermore, subsequent uplift and the development of marginal highs are invoked as factors which affected water circulation within the basins, leading to a deterioration in the Eocene climate. This work identifies the relevance of the North Atlantic Igneous Province (NAIP) as an influence on environmental systems on a global scale. Ar-Ar and Pb-U isotopic age data show that the main period of continental flood basalt volcanism in the NAIP extended from c. 60.5 Ma through to c. 54.5 Ma (Table 1). Biostratigraphical analysis of these volcanic-sedimentary sections (Jolley et al. 2002) shows that the onset of this interval equates to the Late Paleocene Thermal Maximum (LPTM). New isotopic dating of the oldest part of the volcanic sequence on the Faroe Islands, the Lower Formation, by Waagstein et al. has further confirmed the age

Palaeosurface palynofloras of the Skye lava field and the age of the British Tertiary volcanic province

Abstract Collection and palynological analysis of intratrappean boles, mudstones, sands, conglomerates and coals from the Skye lava field has allowed the reconstruction of geomorphological features and vegetation distribution on five palaeosurfaces. These palaeosurfaces show a changing pattern of streamside, swamp and upland vegetation which fall into three forest types: mixed mesophytic, upland Taxodiaceae and montane conifer forest. Comparisons of the Skye palynofloras with others analysed from the intra and intertrappean beds of the Antrim, Mull and Small Isles lavas, gives evidence of three (possibly four) main phases of British Tertiary volcanic province extrusive activity. In comparison to complete palynological records from the Faeroe-Shetland Basin, Skye and Antrim palynofloras can be dated as ranging from 58.23 Ma to 57.99 Ma, while those of the Mull Lavas, and coals below the Faeroe Islands Middle/Upper Basalts indicate initiation and resumption of extrusion after 55.00 Ma. Evidence of the age of palynofloras from the intratrappean beds of Eigg and Muck is limited, and does not dispute the Chron 27r age suggested by isotopic analysis (c. 62 Ma). Finally palynological evidence is presented showing two major subsidence phases, and one uplift phase during the 0.24 Ma existence of the Skye Lava field. It is suggested that altitudes in excess of 1200 m were experienced during thermal doming related to the emplacement of the Cuillin centre. The relative timing of this and other volcanic events is compared to subsidence patterns in the marine sedimentary record.

Development of intra-basaltic lava-field drainage systems within the Faroe–Shetland Basin

The Faroe–Shetland Basin, located on the NW continental shelf of the UK, represents arguably the last frontier area of hydrocarbon exploration of the UK territorial waters. The basin contains an aerially extensive lava sequence, which forms part of the Palaeogene-aged North Atlantic Igneous Province (NAIP). In 2004, a major oil and gas discovery was made within the Palaeocene–Eocene lavas in the form of the Rosebank Field. Unusually, the reservoir intervals are a series of intra-basaltic fluvial clastic sequences separated by basalt lava flows, hyaloclastites and volcaniclastic sediments, giving rise to a new hydrocarbon play concept. The discovery has led to an increased emphasis on trying to understand the detailed stratigraphy of the offshore lava fields within the Faroe–Shetland Basin, as well as the nature of the regional intra-basaltic drainage systems and sediments that form the reservoir intervals in Rosebank. In this paper we show a regional integrated three-dimensional (3D) seismic and well analysis of the lava sequences within the area of the Corona Ridge, exploring the age relationships and spatial distribution of the sequence T40 and T45 Palaeocene lava field. In particular, we note the occurrence of an intra-basaltic (sequence T40, Colsay Member) drainage network that appears to represent a major drainage pathway within the Faroe–Shetland Basin lava fields. Few published studies have dealt with drainage system development on lava but our preliminary analysis appears to indicate that lava flow-field morphology plays a dominant role in controlling the development and evolution of a drainage system.

Two large meteorite impacts at the Cretaceous-Paleogene boundary

The end-Cretaceous mass extinction has been attributed by most to a single asteroid impact at Chicxulub on the Yucatan Peninsula, Mexico. The discovery of a second smaller crater with a similar age at Boltysh in the Ukraine has raised the possibility that a shower of asteroids or comets impacted Earth close to the Cretaceous-Paleogene (K-Pg) boundary. Here we present palynological and δ 13 C evidence from crater-fi ll sediments in the Boltysh impact crater. Our analyses demonstrate that a post-impact fl ora, formed on the ejecta layer, was in turn devastated by the K-Pg event. The sequence of flrecovery from the K-Pg event is directly comparable with that in middle North America. We conclude that the Boltysh crater predated Chicxulub by ~2–5 k.y., a time scale that constrains the likely origin of the bodies that formed the two known K-Pg craters.

Frontier exploration and the North Atlantic Igneous Province: new insights from a 2.6 km offshore volcanic sequence in the NE Faroe–Shetland Basin

The Lagavulin exploration well 217/15-1Z penetrated a c. 2.6 km thick volcanic sequence dominated by extrusive basaltic rocks spanning the Paleocene–Eocene boundary in the NE Faroe–Shetland Basin. The well comprises one of the thickest drilled sequences through the North Atlantic Igneous Province. Integrated analysis of drill cuttings and wireline-log data reveals key volcanic lithofacies: (1) tabular lava flows; (2) compound lava flows; (3) hyaloclastite; (4) volcaniclastic rocks. The volcanic facies reveal two major sub-aqueous to subaerial sequences consistent with lava delta progradation. These sequences are separated by a volcanic hiatus represented by extensive reddened soils, which preceded the re-submergence of the area. Emergence followed by submergence of the first lava delta is interpreted to record an intra-T40 transient uplift event near the Paleocene–Eocene boundary. Basalts from the lower c. 1.3 km have low TiO2 (<1.5 wt%) and low Zr/Y (2–3), with olivine-phyric picrites towards the base (Mg# 70–82; olivine Fo85–91). The hiatus correlates precisely with a change to high-TiO2 (2.5–3.2 wt%), high-Zr/Y (>4) compositions, which dominate the upper sequence. The associated change in lava geochemistry, transient uplift and volcanic hiatus appears consistent with a transient pulse of hot buoyant plume material passing beneath the area. Supplementary material: All raw geochemical data and supplementary analyses are available at http://www.geolsoc.org.uk/SUP18888.

Understanding basin sedimentary provenance: evidence from allied phytogeographic and heavy mineral analysis of the Palaeocene of the NE Atlantic

The drilling of hydrocarbon exploration wells in the Faroe–Shetland Basin has provided an expanding sample resource that provides material for testing recently developed palynology-based sediment transport analysis. This technique has been verified by comparison with heavy mineral analysis; both approaches have been used to identify sediment sources and input points along the strike of the Palaeocene West Shetland Platform. Integration of heavy mineral and palynological data has provided a basis for understanding arenaceous and argillaceous sediment distribution and sourcing. In addition to a source from the western, Greenland side of the basin, four argillaceous and four arenaceous sedimentary sources have been identified along the strike of the West Shetland Platform. These vary in temporal and spatial distribution, and thus provide a history of sediment source evolution. This analysis supports a persistent difference in source between the Corona Basin and the Flett and Judd Sub-basins. Although source variation and overlap between basins is evident, transfer zones represent both conduits for and barriers to effective sediment transport. Both palynological and heavy mineral evidence identifies the former presence of Late Namurian–Westphalian strata on the West Shetland Platform, which were removed by subsequent erosion.