DougalEARTH Ltd.

United Kingdom

DougalEARTH Ltd.

United Kingdom
Time filter
Source Type

Corseri R.,Volcanic Basin Petroleum Research AS | Senger K.,University Center in Svalbard | Selway K.,University of Oslo | Abdelmalak M.M.,University of Oslo | And 4 more authors.
Tectonophysics | Year: 2017

A highly conductive body (0.1–0.8 Ω·m) is identified at mid-crustal depth (8–13 km) in the north Gjallar Ridge from magnetotelluric (MT) data and further investigated in light of other remote-sensing geophysical data (seismic reflection, gravity, aeromagnetic). A commercial 3D controlled-source electromagnetic survey was conducted in the Vøring Basin in 2014 and, although primarily designed for hydrocarbon exploration, good quality MT data were extracted at periods ranging from 100 to 103 s. Dimensionality analysis indicates clear 1D to 2D characteristics in the MT data. 2D inversion was carried out on four profiles (totalling ~ 94 km) oriented perpendicular to the electromagnetic strike and one profile along strike (~ 45 km), using a 1D subset of the data. All inversions converged quickly to RMS values close to unity and display a very good agreement with borehole resistivity data from well 6705/10-1 located in the survey area. A striking feature on all profiles is a highly conductive (0.1–0.8 Ω·m) body at 8–13 km depth. To explain the prominent conductive anomaly, integration of geophysical data favours the hypothesis of electrical conduction across well-connected mineral network in pre-Cretaceous sediments. Seismic interpretation suggests a link between the conductor and intruded sedimentary successions below a detachment level and associated low-angle faults. In the Vøring Basin, low magnetic signal and temperature at the conductor's depth indicate that such thick mineral deposits could display non-magnetic behaviour while occurring well below the magnetite Curie isotherm (~ 585 °C). Natural occurrences and magnetic properties of common iron-sulphide minerals favour a geological interpretation of mid-crustal conductivity as thick pyrrhotite deposits formed in intrusion's contact metamorphic aureoles. © 2017 Elsevier B.V.

Watton T.J.,Durham University | Watton T.J.,Statoil | Wright K.A.,DONG Energy | Jerram D.A.,DougalEARTH Ltd | And 2 more authors.
AAPG Bulletin | Year: 2014

Offshore sequences of volcaniclastic rocks (such as hyaloclastite deposits) are poorly understood in terms of their rock properties and their response to compaction and burial. As petroleum exploration targets offshore volcanic rifted margins worldwide, understanding of volcanic rock properties becomes important both in terms of drilling and how the rocks may behave as seals, reservoirs, or permeability pathways. The Hawaiian Scientific Drilling Project phase II in 2001 obtained a 3 km-(2-mi)-long core of volcanic and volcaniclastic rocks that records the emergence of the largest of the Hawaiian islands. Core recovery of 2945 m (9662 ft) resulted in an unparalleled data set of volcanic and volcaniclastic rocks. Detailed logging, optical petrology, and major element analysis of two sections at depths 1831-1870 and 2530-2597 m (6007-6135 and 8300-8520 ft) are compared to recovered petrophysical logs (gamma ray, resistivity, and P-wave velocity). This study concludes deviation in petrophysical properties does not seem to correlate to changes in grain size or clast sorting, but instead correlates with alteration type (zeolite component) and bulk mineralogy (total olivine phenocryst percentage component). These data sets are important in helping to calibrate well-log responses through hyaloclastite intervals in areas of active petroleum exploration such as the North Atlantic (e.g., Faroe-Shetland Basin, United Kingdom, and Faroe Islands, the Norwegian margin and South Atlantic margins bordering Brazil and Angola). © 2014. The American Association of Petroleum Geologists. All rights reserved.

Keiding J.K.,German Research Center for Geosciences | Trumbull R.B.,German Research Center for Geosciences | Veksler I.V.,German Research Center for Geosciences | Veksler I.V.,TU Berlin | Jerram D.A.,DougalEARTH Ltd.
Geology | Year: 2011

Ultra-magnesian olivines in basaltic rocks or magma are here defined by a forsterite proportion [Fo = Mg/(Mg + Fe) in molar percent] greater than the maximum Fo91.5 known from Earth's mid-ocean ridge systems. They are relatively common in Archean komatiites and have been also reported from several Phanerozoic large igneous provinces. The presence of ultra-magnesian olivines is generally interpreted as evidence for melts with extremely high MgO concentration (komatiites) and high eruption temperatures. Such melts are considered to be hallmarks of a hotter mantle in the early Earth and of thermal anomalies related to Phanerozoic mantle plumes. Here we show that the link between ultra-magnesian olivines and komatiitic melts is not straightforward. The composition of melt inclusions trapped in ultramagnesian olivine (Fo93.3) from the Etendeka province of Namibia contradict the predicted 24 wt% MgO for parental melts and 1680 °C mantle potential temperature. Instead, the trapped melts do not exceed 17.5 wt% MgO, and the maximum potential temperature indicated by these compositions is 1520 °C. We show that ultra-magnesian olivines can also be produced by protracted melt extraction from the mantle source, and that this process also leaves a distinctive depletion in incompatible trace elements. © 2011 Geological Society of America.

Jerram D.A.,University of Oslo | Jerram D.A.,DougalEARTH Ltd. | Jerram D.A.,Queensland University of Technology | Svensen H.H.,University of Oslo | And 6 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

The Siberian Traps large igneous province was formed during the end-Permian, about 252. Ma ago. Basaltic melt was injected into the organic and salt rich Tunguska sedimentary basin, forming interconnected sill complexes and associated hydrothermal vent complexes. Thick deposits of basaltic tuff and tephra covered the paleosurface before the onset of flood volcanism, commonly taken as direct evidence for the explosive nature of the initial phase of volcanism. The field work in this study revealed that tuffs are virtually absent along a 150. km long transect along the Dyupkun lake and Kureika river, even though tuff is shown on available geological maps. Towards the south and west, the transition between the end-Permian sediments and the flood basalts is either characterized by thin (2-5 m) to no tephra deposits (Khantaika area), hyaloclastites and associated lake-deposited tephra (Kureika area), or massive tephra deposits from local eruptive centers (Severnaya area). The new results can be put into the context of other studies about volcanic tuff horizons in Siberia, and questions the notion of province-scale explosive volcanism in Siberia during the onset of flood volcanism. Moreover, the main thicknesses of explosive tuff deposits, up to 700 m, are located in the central and southern parts of the province where the LIP erupted through thick Cambrian salt and carbonate sequences. Since numerous phreatomagmatic pipes are present in these areas, we suggest a causal relationship between deep magma-sediment interactions, explosive eruptions and the resulting environmental stress that initiated the end-Permian mass extinction. © 2015 Elsevier B.V.

Jones M.T.,University of Oslo | Jerram D.A.,University of Oslo | Jerram D.A.,DougalEARTH Ltd. | Jerram D.A.,Queensland University of Technology | And 2 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

The correlation between large igneous provinces (LIPs), extinction events, and rapid climate change suggests that volcanism can have a detrimental impact on Earth surface conditions. Changes in atmospheric and ocean chemistry, particularly the climate-sensitive carbon and sulphur cycles, are among the most probable processes for inducing global environmental stress. However, the interactions and feedbacks between volcanism and these cycles are numerous and complex, making the characterisation of the response to a LIP challenging. Here we summarise the sources and sinks of carbon and sulphur from large scale volcanism and magmatism using information from modern and ancient systems. For the sources, we review the current understanding of volcanic emissions, and explore the relative contributions and importance of magma-derived degassing versus volatile release from sediments affected by igneous intrusions and lava. In addition, we explore the various ways in which LIPs can reduce atmospheric concentrations of these same elements. The relative influences of each source and sink are in part determined by the mode of LIP emplacement and eruption style, along with the subsequent timescales of such effects. We focus on a few key examples, including the Siberian Traps, the Paraná-Etendeka, and the Central Atlantic Magmatic Province (CAMP), to demonstrate how the environmental impact can vary considerably with differing modes of emplacement, LIP duration, and eruption styles. In particular, we show that the host rocks can have a dominant role as a source or sink of emissions, depending on the lithologies affected by the LIP emplacement. © 2015 Elsevier B.V.

Jerram D.A.,University of Oslo | Jerram D.A.,DougalEARTH ltd. | Jerram D.A.,Queensland University of Technology | Widdowson M.,University of Hull | And 7 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

Plume-induced lithospheric uplift and erosion are widely regarded as key features of large igneous province (LIP) emplacement, as is the coincidence of LIP eruption with major extinction and oceanic anoxic events (OAE). The Emeishan LIP, which erupted during the Capitanian (previously termed 'end Guadalupian') extinction event, has provided the most widely discussed example of axisymmetric doming above a rising mantle 'plume'; advocates have argued that in excess of 500m of uplift occurred over >30000 km2 causing extensive radially distributed erosion and alluvial fan formation. However, the recognition of submarine hydromagmatic and phreatomagmatic-style volcanism, as well as syn-volcanic marine sediments interbedded in the eruptive succession, now requires further examination to this simple plume-uplift model.Here we present data from newly discovered sections from the center of the putative uplifted area (around Lake Er Hai, SW Yunnan Province,) that provide a more complete history of the Emeishan volcanism. These reveal that platform carbonate deposition was terminated by rapid subsidence, followed quickly by the onset of volcanism. Importantly, these eruptions also coincide with widespread losses amongst fusulinacean foraminifera and calcareous algae. For at least the lower two thirds of the 4-5 km thick lava pile, eruptions continued at or below sea level, as testified by the presence of voluminous mafic volcaniclastic deposits, pillow lavas, and development of syn-volcanic reefal limestones in the Emeishan inner zone. Only in the later stages of eruption did terrestrial lava flows become widely developed. This onset of volcanism in a submarine setting and the consequent violent, phreatomagmatic-style eruptions would have had a profound effect on marine fauna and exacerbated any volcanically induced climate effects during the Capitanian. The late Permian of SW China at the time of the Emeishan was an extended area of thinned lithosphere with epeiric seas, which appear to have been sustained through the onset of LIP emplacement. Therefore, while there remains substantial geochemical support of a plume origin for Emeishan volcanism, LIP emplacement cannot be ubiquitously associated with regional pre-eruption uplift, particularly where complex lithospheric structure exists above a plume. © 2015 Elsevier B.V.

Watton T.J.,Durham University | Jerram D.A.,DougalEARTH Ltd. | Jerram D.A.,Queensland University of Technology | Thordarson T.,University of Edinburgh | Davies R.J.,Durham University
Journal of Volcanology and Geothermal Research | Year: 2013

Analysis of the spatial lithofacies variability within lava-fed delta formations in southern Iceland has revealed complex three-dimensional volcanic architectures in hyaloclastite deposits in non-glacial settings. Two depositional environments are studied, (a) lava entering a marine embayment (Stóri-Nupur) and; (b) lava advancing into a body of water of the flanks of a Surtseyan cone (Hjörleifshöf{eth}i). Interaction between environmental factors such as shoreline geomorphology, water depth, wave energy levels, the nature of the lava transport system, lava supply rate all affect the resulting lava deltas creating complex lithofacies arrangements and stacking patterns. Recognised here are two types of hyaloclastite deltas. One of syn-sedimentary origin (Hjörleifshöf{eth}i) and one derived from primary fragmentation processes (Stóri-Nupur). Syn-sedimentary systems are dominated by destabilisation of the hyaloclastite pile leading to reworking downslope and share similarities to alluvial delta systems. Conversely, primary fragmented systems are controlled by waxing and waning cycles in volcanic effusivity whereby the hyaloclastite unit recorded is not the product of one lava flow rather than one eruptive event. © 2012 Elsevier B.V.

Wright K.A.,Durham University | Davies R.J.,Durham University | Jerram D.A.,Dougalearth Ltd | Morris J.,Statoil | Fletcher R.,Statoil
Basin Research | Year: 2012

Detailed seismic stratigraphic analysis of 2D seismic data over the Faroe-Shetland Escarpment has identified 13 seismic reflection units that record lava-fed delta deposition during discrete periods of volcanism. Deposition was dominated by progradation, during which the time shoreline migrated a maximum distance of ~44km in an ESE direction. Localised collapse of the delta front followed the end of progradation, as a decrease in volcanic activity left the delta unstable. Comparison with modern lava-fed delta systems on Hawaii suggests that syn-volcanic subsidence is a potential mechanism for apparent relative sea level rise and creation of new accommodation space during lava-fed delta deposition. After the main phase of progradation, retrogradation of the delta occurred during a basinwide syn-volcanic relative sea level rise where the shoreline migrated a maximum distance of ~75km in a NNW direction. This rise in relative sea level was of the order of 175-200m, and was followed by the progradation of smaller, perched lava-fed deltas into the newly created accommodation space. Active delta deposition and the emplacement of lava flows feeding the delta front lasted ~2600 years, although the total duration of the lava-fed delta system, including pauses between eruptions, may have been much longer. © 2011 The Authors. Basin Research © 2011 Blackwell Publishing Ltd, European Association of Geoscientists & Engineers and International Association of Sedimentologists.

Polozov A.G.,RAS Institute of Geology and Mineralogy | Svensen H.H.,Center for Earth Evolution and Dynamics | Planke S.,Center for Earth Evolution and Dynamics | Planke S.,Volcanic Basin Petroleum Research AS VBPR | And 5 more authors.
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2016

A number of mechanisms have been proposed to explain the end-Permian crisis. Many of them explore the link between this catastrophe and the Siberian Traps. We test the hypothesis that eruption of thermogenic gas generated in contact aureoles around igneous sills intruded into evaporite sequences of the Tunguska Basin triggered the crisis. In particular, we test the idea that the aspect that breccia pipes represent conduits for voluminous gas migration from the deep basins to the atmosphere. This contribution sheds new light on the pipe formation based on new field and borehole observations and electron microscopy analyses. Of more than three hundred mapped magnetite-bearing basalt pipes, 43 are classified as diatremes. The diatremes are usually circular or elliptical, with multiple zones of brecciation reaching the surface, sometimes with preserved in-filled crater lakes. The pipe diameter on the surface varies from a few tens of meters for small single diatremes to about a kilometer. The largest crater lake area is 2.7km2. We have conducted a detailed study of the breccias in the Sholokhovsk basalt pipe located within the Nepa potash deposit in the Tunguska Basin, Siberia, Russia (about N 59° and E 107°) and find that the breccias are cemented by carbonate matrix (calcite, dolomite) and halite. Breccia clasts are altered at various temperatures, evidenced by growth of albite and garnet from basaltic glass, and diopside, garnet, magnetite and chlorine-bearing amphibole (up to 1.8% Cl) in altered magmatic clasts. These mineral assemblages suggest high temperature interactions with evaporites within the pipe conduits. The large number of pipes support that degassing of halogen-rich volatiles was a widespread and violent process with implications for the end-Permian crisis. © 2015 Elsevier B.V.

Cross J.K.,Royal Holloway, University of London | Roberge J.,National Polytechnic Institute of Mexico | Jerram D.A.,DougalEARTH Ltd.
Journal of Volcanology and Geothermal Research | Year: 2012

The explosive activity of Popocatépetl Volcano is a threat to the surrounding densely populated areas and it is therefore important to recognize indicators of change in eruptive style (explosive to dome building) within a short period of time. In this study we present results of vesicle size distributions (VSDs) and compositional analysis of matrix glass from juvenile clasts from five of the main plinian eruptions of Popocatépetl (ca 23-1.2. ka), the 2001 small eruption during partial dome collapse and four eruptions during 1997 (May 11th and June 14th, 15th and 30th). Major element analysis of matrix glass (WDS-EPMA) allows the estimation of the depth from which the erupted magma went into disequilibrium (between crystals and melt), by calculating the equilibrium pressure using the quartz-albite-orthoclase ternary system of Blundy and Cashman (2001). Quantitative interpretation of texture in juvenile (pumice or scoria) clasts via VSD analysis using CSD software was used to link physical changes experienced by magma during ascent, with conditions responsible for eruptions. The extent and style of vesiculation in juvenile clasts is also related to eruption style and duration and has specifically allowed the recognition of changes in vesicular texture that represent variations from explosive to dome building activity (Mangan and Sisson, 2000; Adams et al., 2006). This study highlights a more complicated story in terms of magma storage, than that previously accepted for the Popocatépetl volcanic system and is an important contribution to ongoing research at the volcano. © 2012 Elsevier B.V.

Loading DougalEARTH Ltd. collaborators
Loading DougalEARTH Ltd. collaborators