Moray Firth Basin Research Articles

Older than you think: using U–Pb calcite geochronology to better constrain basin-bounding fault reactivation, Inner Moray Firth Basin, western North Sea

Like many rift basins worldwide, the Inner Moray Firth Basin (IMFB) is bounded by major reactivated fault zones, including the Helmsdale Fault and the Great Glen Fault (GGF). The Jurassic successions exposed onshore close to these faults at Helmsdale and Shandwick preserve folding, calcite veining and minor faulting consistent with sinistral (Helmsdale Fault) and dextral (GGF) transtensional movements. This deformation has been widely attributed to Cenozoic post-rift fault reactivation. Onshore fieldwork and U–Pb calcite geochronology of five vein samples associated with transtensional movements along the Helmsdale Fault and a splay of the GGF show that faulting occurred during the Early Cretaceous ( c. 128–115 Ma, Barremian–Aptian), while the Helmsdale Fault preserves evidence for earlier Late Jurassic sinistral movements ( c. 159 Ma, Oxfordian). This demonstrates that both basin-bounding faults were substantially reactivated during the episodic NW–SE-directed Mesozoic rifting that formed the IMFB. Although there is good evidence for Cenozoic reactivation of the GGF offshore, the extent of such deformation along the north coast of the IMFB remains uncertain. Our findings illustrate the importance of oblique-slip reactivation processes in shaping the evolution of continental rift basins given that this deformation style may not be immediately obvious in interpretations of offshore seismic reflection data. Supplementary Material: Appendix A – orthomosaic model obtained from unmanned aerial vehicle (UAV) photography of the Helmsdale locality (GeoTiff format); Appendix B – orthomosaic model obtained from UAV photography of the Shandwick locality (GeoTiff format); Appendix C – geochronology data; and Appendix D – additional thin section microphotographs of sample HD1 showing repeated cycles of syntaxial grain growth are available at https://doi.org/10.6084/m9.figshare.c.6708518

Using UAV-Based Photogrammetry Coupled with In Situ Fieldwork and U-Pb Geochronology to Decipher Multi-Phase Deformation Processes: A Case Study from Sarclet, Inner Moray Firth Basin, UK

Constraining the age of formation and repeated movements along fault arrays in superimposed rift basins helps us to better unravel the kinematic history as well as the role of inherited structures in basin evolution. The Inner Moray Firth Basin (IMFB, western North Sea) overlies rocks of the Caledonian basement, the pre-existing Devonian–Carboniferous Orcadian Basin, and a regionally developed Permo–Triassic North Sea basin system. IMFB rifting occurred mainly in the Upper Jurassic–Lower Cretaceous. The rift basin then experienced further regional tilting, uplift and fault reactivation during the Cenozoic. The Devonian successions exposed onshore along the northwestern coast of IMFB and the southeastern onshore exposures of the Orcadian Basin at Sarclet preserve a variety of fault orientations and structures. Their timing and relationship to the structural development of the wider Orcadian and IMFB are poorly understood. In this study, drone airborne optical images are used to create high-resolution 3D digital outcrops. Analyses of these images are then coupled with detailed field observations and U-Pb geochronology of syn-faulting mineralised veins in order to constrain the orientations and absolute timing of fault populations and decipher the kinematic history of the area. In addition, the findings help to better identify deformation structures associated with earlier basin-forming events. This holistic approach helped identify and characterise multiple deformation events, including the Late Carboniferous inversion of Devonian rifting structures, Permian minor fracturing, Late Jurassic–Early Cretaceous rifting and Cenozoic reactivation and local inversion. We were also able to isolate characteristic structures, fault kinematics, fault rock developments and associated mineralisation types related to these events

Correlating deformation events onshore and offshore in superimposed rift basins: The Lossiemouth Fault Zone, Inner Moray Firth Basin, Scotland

AbstractThe separation and characterisation of different deformation events in superimposed basins can be challenging due to the effects of overprinting and/or fault reactivation, combined with a lack of detailed geological or geophysical data. This paper shows how an onshore study can be enhanced using a targeted interpretation of contiguous structures offshore imaged by seismic reflection data. Two deformation events, including evidence of fault reactivation, are recognised and associated with the onshore part of the Lossiemouth Fault Zone (LFZ), southern‐central Inner Moray Firth Basin. The basin is thought to record a history of Permian to Cenozoic deformation, but it is difficult to conclusively define the age of faulting and fault reactivation. However, structures in onshore outcrops of Permo–Triassic strata show no evidence of fault growth, and new interpretation of seismic reflection profiles in the offshore area reveals that Permo–Triassic fills are widely characterised by subsidence and passive infill of post‐Variscan palaeotopography. We propose that sequences of reactivated faulting observed onshore and offshore can be correlated and can be shown in the latter domain to be Early Jurassic–Late Cretaceous, followed by localised Cenozoic reactivation. The workflow used here can be applied to characterise deformation events in other superimposed rift basins with contiguous onshore (surface)—offshore (subsurface) expressions.

New onshore insights into the role of structural inheritance during Mesozoic opening of the Inner Moray Firth Basin, Scotland

The Inner Moray Firth Basin (IMFB) forms the western arm of the North Sea trilete rift system that initiated mainly during the Late Jurassic–Early Cretaceous with the widespread development of major NE–SW-trending dip-slip growth faults. The IMFB is superimposed over the southern part of the older Devonian Orcadian Basin. The potential influence of older rift-related faults on the kinematics of later Mesozoic basin opening has received little attention, partly owing to the poor resolution of offshore seismic reflection data at depth. New field observations augmented by drone photography and photogrammetry, coupled with U–Pb geochronology, have been used to explore the kinematic history of faulting in onshore exposures along the southern IMFB margin. Dip-slip north–south- to NNE–SSW-striking Devonian growth faults are recognized that have undergone later dextral reactivation during NNW–SSE extension. The U–Pb calcite dating of a sample from the synkinematic calcite veins associated with this later episode shows that the age of fault reactivation is 130.99 ± 4.60 Ma (Hauterivian). The recognition of dextral-oblique Early Cretaceous reactivation of faults related to the underlying and older Orcadian Basin highlights the importance of structural inheritance in controlling basin- to sub-basin-scale architectures and how this influences the kinematics of IMFB rifting. Supplementary material: Analytical protocols and analysed sample details are available at https://doi.org/10.6084/m9.figshare.c.5635432

The Goldeneye Field, Blocks 14/29a and 20/4b, UK North Sea

Abstract The Goldeneye gas-condensate field lies in the Moray Firth Basin in the UK Continental Shelf (UKCS) approximately 100 km off the NE coast of Scotland. The field was discovered in 1996 as a normally pressured accumulation with estimated gas-initially-in-place (GIIP) of 810 bcf with a thin oil rim in the Lower Cretaceous Captain Sandstone Member in a three-way, dip-closed structure. Field development included five production wells, with first gas achieved in 2004. Goldeneye was steadily produced under moderate aquifer support until cessation of production (COP) in 2010 following water breakthrough at the wells. Over its lifetime Goldeneye has produced 568 bcf of gas and 23 MMbbl of condensate. Around the time of COP, the UK Carbon Capture and Storage Commercialisation Competition was announced, and Goldeneye was evaluated as a candidate. The removal of significant volumes of hydrocarbons through production left remaining capacity that could be refilled without reservoir pressure significantly exceeding virgin conditions. However, following withdrawal of funding from the UK Government in 2015, the project was put on hold. Since then additional subsurface work has been conducted to support the successful abandonment of the development wells, which had previously been suspended since 2010.

Clay mineral dating of displacement on the Sronlairig Fault: implications for Mesozoic and Cenozoic tectonic evolution in northern Scotland

AbstractTemporary excavations during the construction of the Glendoe Hydro Scheme above Loch Ness in the Highlands of Scotland exposed a clay-rich fault gouge in Dalradian Supergroup psammite. The gouge coincides with the mapped trace of the subvertical Sronlairig Fault, a feature related in part to the Great Glen and Ericht–Laidon faults, which had been interpreted to result from brittle deformation during the Caledonian orogeny (c. 420–390 Ma). Exposure of this mica-rich gouge represented an exceptional opportunity to constrain the timing of the gouge-producing movement on the Sronlairig Fault using isotopic analysis to date the growth of authigenic (essentially synkinematic) clay mineralization. A series of fine-size separates was isolated prior to K–Ar analysis. Novel, capillary-encapsulated X-ray diffraction analysis was employed to ensure nearly perfect, random orientation and to facilitate the identification and quantification of mica polytypes. Coarser size fractions are composed of greater proportions of the 2M1 illite polytype. Finer size fractions show increasing proportions of the 1M illite polytype, with no evidence of 2M1 illite in the finest fractions. A series of Illite Age Analysis plots produced excellent R2 values with calculated mean ages of 296 ± 7 Ma (Late Carboniferous–Early Permian) for the oldest (2M1) illite and 145 ± 7 Ma (Late Jurassic–Early Cretaceous) for the youngest (1M) illite. The Late Carboniferous–Early Permian (Faulting event 1) age may represent resetting of earlier-formed micas or authigenesis during dextral displacement of the Great Glen Fault Zone (GGFZ). Contemporaneous WNW(NW)–ESE(SE) extension was important for basin development and hydrocarbon migration in the Pentland Firth and Moray Firth regions. The Late Jurassic–Early Cretaceous (Faulting event 2) age corresponds with Moray Firth Basin development and indicates that the GGFZ and related structures may have acted to partition the active extension in the Moray Firth region from relative inactivity in the Pentland Firth area at this time. These new age dates demonstrate the long-lived geological activity on the GGFZ, particularly so in post-Caledonian times where other isotopic evidence for younger tectonic overprints is lacking.

Structural development of the Devono-Carboniferous plays of the UK North Sea

Abstract Decades of oil and gas exploration across the North Sea have led to a detailed understanding of its Cenozoic–Mesozoic structure. However, the deeper basin architecture of Paleozoic petroleum systems has been less well defined by seismic data. This regional structural overview of the Devono-Carboniferous petroleum systems incorporates interpretations from more than 85 000 line-kilometres of 2D seismic data and 50 3D seismic volumes, plus a gravity, density and magnetic study, from the Central Silverpit Basin to the East Orkney Basin. A complex picture of previously unmapped or poorly known basins emerges on an inherited basement fabric, with numerous granite-cored blocks. These basins are controlled by Devono-Carboniferous normal, strike-slip and reverse faults. The main basins across Quadrants 29–44 trend NW–SE, influenced by the Tornquist trend inherited from the Caledonian basement. North of Quadrants 27 and 28, and the presumed Iapetus suture, the major depocentres are NE–SW (e.g. the Forth Approaches and Inner Moray Firth basins) to east–west (e.g. the Caithness Graben), and WNW–ESE trending (e.g. the East Orkney Basin), reflecting the basement structural inheritance. From seismic interpretation, there are indications of an older north–south fault trend in the Inner Moray Firth that is difficult to image, since it has been dissected by subsequent Permo-Carboniferous and Mesozoic faulting and rifting.

Implications of Early Cenozoic uplift and fault reactivation for carbon storage in the Moray Firth Basin

Interpretation and depth conversion of an extensive, well-calibrated seismic database provide the basis upon which to map the limits and evaluate the geologic risks of using a saline aquifer target for carbon dioxide ([Formula: see text]) storage in the Moray Firth Basin of the North Sea. The seismic interpretation demonstrates that the Lower Cretaceous (Albian-Aptian) Captain Sandstone Member is a continuous, interconnected reservoir that rises to subcrop in the western areas of the basin as a consequence of Early Cenozoic uplift and tilt. As such, the aquifer forms an open system with few barriers or sizable closures to arrest or entrap light fluids and gases en route to its western subcrop. The new interpretation also indicates that the saline aquifer is cut by several west-southwest/east-northeast-striking reactivated normal faults. Although migration along the faults permitted hydrocarbons to get into structurally elevated traps, such as the Captain Field itself, some faults also breach the seal of the Captain Sandstone Member aquifer, rise to the seabed, and increase the risk of seabed leakage. Consequently, despite its large storage capacity, the dip, subcrop, and fault reactivation affecting the Captain Sandstone Member aquifer all suggest that its use as a site for [Formula: see text] storage remains unproven and is not the best choice for an initial North Sea exemplar. As such, the study highlights the importance of undertaking a robust and forensic geologic screening of any prospective storage site prior to injection.

Impact of oil emplacement on diagenesis in Cretaceous oil sands

Abstract Seventeen thin sections of Cretaceous oil sands from the Neuquen Basin (Argentina), Sergipe-Alagoas Basin (Brazil), Western Canadian Sedimentary Basin (Canada), Junggar Basin (China), Lower Saxony Basin (Germany), Kangerlussuaq Basin (Greenland), Arabian Basin (Kuwait), Chad Basin (Nigeria), Dahomey Basin (Nigeria), Western Moray Firth Basin (UK), Wessex Basin (UK) and Utah (USA) were examined using the scanning electron microscope (SEM) to improve our understanding on how oil emplacement impairs the progress of diagenesis. Our results show that diagenetic processes affecting sandstones prior to oil emplacement include burial/compaction, silica/calcite cementation, calcite replacement of detrital grains/cements as well as the development of silica overgrowth. Most diagenetic processes were inferred to cease upon oil emplacement into the pores of the sandstones, however, diagenetic processes such as the alteration of detrital grains/cements and precipitation of authigenic minerals/metallic compounds were observed to occur after oil emplacement into the pores of the sandstones. Oil was emplaced in some of the studied Cretaceous oil sands at a relatively early stage when the sandstones were not compacted or cemented. Such Cretaceous oil sands were observed to have had anomalously high porosities of above 38% prior to oil emplacement. The only cement observed in these oil sands are the viscous heavy oils (bitumens) associated with them. Upon extraction of these heavy oils, the oil sands collapse into unconsolidated sands. Occurrence of these bitumen supported Cretaceous sands implies availability of migrating oils while some of the Cretaceous sands were depositing in various basins. Oil emplacement occurred in some of the studied Cretaceous oil sands after the sandstones had undergone some diagenetic processes which did not destroy all their pore spaces. Such Cretaceous oil sands were observed to have had moderate to high porosities of 10%–30% prior to oil emplacement, with some of these sandstones showing evidence of silica overgrowth. Emplacement of oil into the pores of such sandstones is believed to have stopped further development of the silica overgrowth that would have led to the total loss of porosity in these Cretaceous reservoir sands. In some of the studied Cretaceous oil sands, oil emplacement occurred when the sands had experienced a long history of diagenetic events leading to almost total loss of porosity. Common diagenetic features observed in such Cretaceous oil sands include sutured quartz grain-grain contacts and quartz overgrowth.

Goldeneye: Tomorrow Never Dies (or a field Only Lives Twice)

Abstract The Goldeneye gas–condensate field lies in the Moray Firth Basin of the North Sea and illustrates the potential for further field life after the normal end of production. It was discovered in 1996 in a three-way dip-closed structure in the Lower Cretaceous Captain Sandstone. Five development wells were drilled from a single production platform and first gas was produced in 2004. The field pressure decline indicated partial aquifer support and no compartmentalization. Approaching the end of production, the opportunity arose to propose Goldeneye as a store for CO 2 . The cap-rock seal was capable of containing gas and the removed hydrocarbons left a significant volume that could be refilled without raising pressures above original conditions. The field's good reservoir properties were favourable for injection, the wellstock and infrastructure were modern, and CO 2 sources were available close by. The different requirements of a storage project called for a detailed understanding of the overburden to guard against possible leak paths and to identify secondary containment. Furthermore, greater understanding of the aquifer was needed as it limits storage volumes through its impact on reservoir pressures. Updated interpretation, analysis and modelling demonstrated that Goldeneye is an excellent potential CO 2 storage site, which gives it a possible second span of life helping to offset UK CO 2 emissions.

Occurrence and development of folding related to normal faulting within a mechanically heterogeneous sedimentary sequence: a case study from Inner Moray Firth, UK

Abstract Folds associated with normal faults are potential hydrocarbon traps and may impact the connectivity of faulted reservoirs. Well-calibrated seismic reflection data that image a normal fault system from the Inner Moray Firth basin, offshore Scotland, show that folding was preferentially localized within the mechanically incompetent Lower–Middle Jurassic pre-rift interval, comprising interbedded shales and sandstones, and within Upper Jurassic syn-rift shales. Upward propagation of fault tips was initially inhibited by these weak lithologies, generating fault propagation folds with amplitudes of c. 50 m. Folds were also generated, or amplified, by translation of the hanging wall over curved, convex-upward fault planes. These fault bends resulted from vertical fault segmentation and linkage within mechanically incompetent layers. The relative contributions of fault propagation and fault-bend folding to the final fold amplitude may vary significantly along the strike of a single fault array. In areas where opposite-dipping, conjugate normal faults intersect, the displacement maxima are skewed upwards towards the base of the syn-rift sequence (i.e. the free surface at the time of fault initiation) and significant fault propagation folding did not occur. These observations can be explained by high compressive stresses generated in the vicinity of conjugate fault intersections, which result in asymmetric displacement distributions, skewed towards the upper tip, with high throw gradients enhancing upward fault propagation. Our observations suggest that mechanical interaction between faults, in addition to mechanical stratigraphy, is a key influence on the occurrence of normal fault-related folding, and controls kinematic parameters such as fault propagation/slip ratios and displacement rates.

Origin of heavy oil in Cretaceous petroleum reservoirs

Research Article| June 01, 2016 Origin of heavy oil in Cretaceous petroleum reservoirs Timothy Bata; Timothy Bata Search for other works by this author on: GSW Google Scholar John Parnell; John Parnell School of Geosciences, University of Aberdeen, AB24 3UE, United Kingdom Search for other works by this author on: GSW Google Scholar Stephen Bowden; Stephen Bowden School of Geosciences, University of Aberdeen, AB24 3UE, United Kingdom Search for other works by this author on: GSW Google Scholar Adrian Boyce Adrian Boyce Scottish Universities Environmental, Research Centre, East Kilbride, Glasgow G75 0QF, United Kingdom Search for other works by this author on: GSW Google Scholar Bulletin of Canadian Petroleum Geology (2016) 64 (2): 106–118. https://doi.org/10.2113/gscpgbull.64.2.106 Article history received: 21 May 2015 accepted: 30 Sep 2015 first online: 03 Oct 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Timothy Bata, John Parnell, Stephen Bowden, Adrian Boyce; Origin of heavy oil in Cretaceous petroleum reservoirs. Bulletin of Canadian Petroleum Geology 2016;; 64 (2): 106–118. doi: https://doi.org/10.2113/gscpgbull.64.2.106 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyBulletin of Canadian Petroleum Geology Search Advanced Search Abstract Much of the world’s heavy oil is found in Cretaceous reservoir rocks due to a combination of tectonic, climatic, geological, and biological factors. Here we study Cretaceous oil sands from the Neuquén Basin (Argentina), Sergipe-Alagoas Basin (Brazil), Alberta (Canada), Dahomey Basin (Nigeria), Uinta Basin (USA), Western Moray Firth Basin (United Kingdom), and Wessex Basin (United Kingdom) to improve our understanding of the origin of the heavy oils. Our results indicate that the oils were generated as conventional light oil, which later degraded into heavy oils, rather than thermally cracked oils from over matured source rocks. All the studied Cretaceous oil sands are enriched in the polar fraction, and the total ion current (TIC) fragmentogram of the saturate fractions show unresolved complex mixture (UCM) humps indicating that the oils have undergone biodegradation. Sterane data for the Cretaceous oil sands show a selective increase in the C29 regular steranes relative to C27 and C28 regular sterane, which is also consistent with biodegradation. There is also evidence for diasterane degradation in some samples which are related, suggesting severe biodegradation. The trisnorhopane thermal maturity indicator showed that the Cretaceous oil sands have thermal maturity levels equivalent to 0.66–1.32% Ro, consistent with an early to late oil window. 25-norhopanes were not detected in any of the studied Cretaceous oil sands despite sterane degradation. This strongly suggests that biodegradation in the Cretaceous oil sands occurred at shallow depths rather than at greater depths. Pyrite associated with the Cretaceous oil sands was found to be consistently isotopically light. The isotopic fractionation between these pyrites and contemporary seawater sulfate was calculated using the mean δ34S values and the established seawater composition curve. This fractionation exceeded the maximum known kinetic isotope fractionation of approximately 20‰ that is possible from non-biogenic mechanisms, such as thermochemical sulfate reduction. This strongly suggests that the pyrite precipitated from an open system by means of microbial sulfate reduction as part of the biodegradation process. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Preliminary assessment of the petrology of the Hopeman Sandstone (Permo-Triassic), Moray Firth Basin, Scotland

The Hopeman Sandstone is a cross-bedded sandstone of Permo-Triassic age that crops out in coastal exposures in northeastern Scotland. Although the unit has traditionally been interpreted as an aeolian deposit, partly on the assumption of well-sorted, well-rounded quartz sand and lack of micas, no detailed thin-section studies have been published to confirm these conclusions. The following report employs petrographical analysis to quantify the sorting, rounding and mineral composition of the Hopeman Sandstone. Our results indicate that the formation is not as well sorted or well rounded as previously suggested and that it contains significant orthoclase and trace amounts of muscovite, which may suggest that depositional models for at least some facies within the unit need to be revised. This report serves as a preliminary analysis of unusual textural trends across the Hopeman Sandstone and should prompt additional research to further characterize and interpret the sedimentology of the formation.

Seismic geomorphology and sequence stratigraphy as tools for the prediction of reservoir facies distribution: an example from the Paleocene and earliest Eocene of the South Buchan Graben, Outer Moray Firth Basin, UKCS

Abstract A seismic stratigraphic analysis constrained by well and wireline log data has been undertaken on the Paleocene and earliest Eocene succession of the South Buchan Graben (Quadrants 20 and 21), Outer Moray Firth Basin (OMFB). Two principal sequences have been described relating to two regressive/transgressive second-order cycles of relative sea-level change. The Maureen, Andrew, Glamis Tuff and Balmoral sandstone members are expressed as a stacked set of lowstand basin floor fans separated by mudstone intervals representing four cycles of third-order relative sea-level change. The Sele and Balder formations contain both basinal and shelfal packages as an expression of two cycles of third-order relative sea-level change. The Forties Sandstone Member is deposited within highly mounded, levee-confined channels downlapped by a prograding slope succession with well-defined clinoforms and deltaic topsets attributed to the Dornoch and Beauly formations. The individual parasequences of the prograding wedge are related to higher-order eustatic fluctuations with incision and slope fans, attributed to the Cromarty Sandstone Member, deposited during periods of relative sea-level lowstand. It is demonstrated that through the integration of lithostratigraphic, seismic geomorphological and sequence stratigraphic analyses an understanding of depositional environments and the distribution of facies within them can be obtained. The identification of basinal and slope features with reservoir potential, along with an understanding of their chronostratigraphic relationship to sealing facies, play an important role in regional play fairway mapping and risk analysis in this area and beyond. Future prospectivity within mature basins, such as the OMFB, relies on subtle stratigraphic traps typical of lowstand systems tracts, where the main risk is associated with reservoir quality and containment.

A revision of the Jurassic (Bathonian to Oxfordian) lithostratigraphy of the onshore Moray Firth Basin, north-east Scotland

Abstract Bathonian to Oxfordian strata occur onshore in two principal locations over 30 km apart on the coast of the Moray Firth, at Brora and Balintore. The existing lithostratigraphy has the same formation names applied to both successions despite profound differences, exemplified in their schemes of local members. Furthermore, three of the formation names include the same place name, and use obsolete lithological terms. We consider that all the Bathonian to Oxfordian members are satisfactory, and propose their retention with original names, with one exception, to provide continuity with the superseded formational scheme. We propose retention of the Brora Coal Formation as currently defined. The Brora Argillaceous, Brora Arenaceous and Balintore formations at Brora are unsatisfactory in a modern context and we propose: i) a new Strathsteven Mudstone Formation, which is mudstone-dominated, and generally coarsens-upwards. ii) a Clynekirkton Sandstone Formation, which is sandstone-dominated and generally coarsens upwards. This formation scheme employs unique geographical names and modern and appropriate lithological terminology. Furthermore, the boundary between the Strathsteven and Clynekirkton formations is placed at a junction that is a change from mud- and silt-dominated lithologies to silt- and fine- and medium-grained sand and is mappable. We consider that the Callovian–Oxfordian succession at Balintore should be assigned to a single formation, viz. the revised Balintore Formation. Apart from the basal Brora Roof Bed, the succession at Balintore does not lithologically resemble that at Brora, and the scheme of the Brora Argillaceous Formation, Brora Arenaceous Formation, and the Balintore Formation as previously defined is unworkable here.

Stratigraphic development of an Upper Jurassic deep marine syn‐rift succession, Inner Moray Firth Basin, Scotland

AbstractThe stratigraphic development of an Upper Jurassic syn‐rift succession exposed at outcrop in the Inner Moray Firth Basin has been investigated using high‐resolution biostratigraphy and sedimentology. A continuous 970 m thick section, exposed in the hangingwall of the Helmsdale Fault was logged in detail. The succession spans 8 Ma and contains eight lithofacies types, which indicate deposition in a deep marine setting. Boulder beds contain large, angular clasts, with bed thicknesses typically >2 m and poor sorting suggesting deposition by debris flows. An inverse clast stratigraphy is observed; the oldest boulder beds contain sandstone clasts of Upper Old Red Sandstone (ORS) with younger debris flows containing clasts of Middle ORS calcareous siltstone. A marked change from siliciclastic to carbonate dominated sedimentation occurred during the Early Tithonian, interpreted primarily as a result of change in lithologies in the footwall catchment from sandstone to calcareous siltstone, which reduced supply of siliciclastic sediment. Secondary factors are identified as increased aridity in the Early Tithonian, which reduced sand supply from the hinterland and a third‐order Early Tithonian eustatic sea‐level rise, which trapped coarser clastic sediment within the hinterland. Biostratigraphy allows calculation of variations in sedimentation rates with recognition of: (1) an early rift phase characterised by sandy turbidite deposition, when sedimentation rates averaged 0.08 m/ky, (2) a rift climax phase from the Early Kimmeridgian where sedimentation rates increased steadily to a maximum of 0.64 m/ky in the Early Tithonian, with strata dominated by boulder scale clast‐supported debris flows and (3) a late stage of rifting from the mid Tithonian, where sedimentation rates decreased to 0.07 m/ky. Overall sedimentation rates are comparable to those of other deep marine rift basins. Unroofing a resistant lithology on the footwall of a rift has important implications for siliciclastic sediment supply in rift basins.

Introduction and rationale

This special thematic issue of Petroleum Geoscience results from a meeting held at Birmingham University on 14 May 2008 to commemorate the work of the late Dr Ken Thomson and which was attended by individuals from both academia and industry. Photograph of Ken taken on a boat off the coast of the Trotternish Peninsula, Isle of Skye in 2002 during a field trip investigating the interplay between igneous and sedimentary processes in the Palaeogene Igneous Province (photo courtesy of Donny Hutton). Ken Thomson, a lecturer in Earth Sciences at the University of Birmingham, died suddenly while at work in April 2007. He was aged only 42. Ken began his career as a medic at Manchester University, but realized his true calling and transferred to Geology, graduating in 1990. He then moved to the Department of Geology & Geophysics at The University of Edinburgh, undertaking a Shell–Esso-funded PhD concentrating on the basin dynamics of the Inner Moray Firth Basin under the supervision of John Underhill. After completing his PhD he took up a position at the University of Oxford as the BP Exploration Junior Research Fellow in Geophysics, before moving on to a lectureship in petroleum geology at Durham University in 1995, before finally taking up the position at …

Lower Cretaceous deep-water sandstone plays in the UK Central Graben

Abstract Up to the present, exploration of the UK Lower Cretaceous deep-water sandstone play has been confined largely to the Moray Firth basins. The Lower Cretaceous of the Central Graben area has been modelled previously as predominantly shale-prone, and hence unattractive to exploration. There is a growing realization that this may not be the case. Since seismic imaging of Lower Cretaceous sandstones is known to be poor whether hydrocarbon-bearing or water-wet, a robust depositional model must be constructed from well and regional geological data in order to predict sandstone distribution and geometry, and hence to aid identification of potential hydrocarbon traps. Of the hundreds of wells drilled in the Central Graben area that targeted deeper Jurassic-Triassic reservoirs, virtually all have been located on the flanks of the graben, or on intra-graben highs. However, 71 of these wells have proved sandstones or traces of sandstone within the Lower Cretaceous, giving grounds for optimism that more substantial deep-water sandstone developments may be present within the graben depocentres. Twenty-six leads have been identified within these depocentres; most of these are located within stratigraphic traps in interpreted detached basin floor fans.

Middle and Upper Jurassic (Callovian to Kimmeridgian) palynology of the onshore moray firth basin, northeast Scotland

The Brora Coal, Brora Argillaceous, Brora Arenaceous, Balintore and Kimmeridge Clay formations of the onshore Moray Firth Basin represent an important Middle to Upper Jurassic (Callovian to Lower Kimmeridgian) reference section close to hydrocarbon‐rich North Sea basins. This composite succession at Brora and Balintore is c. 233 m thick; it is mudstone/siltstone‐dominated and largely rich in zonal and subzonal ammonites. For example, the Callovian succession at Brora is virtually complete, with coverage of all seven ammonite zones. All the five formations examined have yielded abundant palynofloras. The lithostratigraphic units sampled, except the Brora Coal Formation, have yielded rich associations of dinoflagellate cysts. The majority of the Inverbrora Member of the Brora Coal Formation at its type section at Brora is of early Callovian age based on dinoflagellate cysts; this member yielded Meiourogonyaulax caytonensis and Mendicodinium groenlandicum and these species preclude a Bathonian age. This member has been previously attributed to the late Bathonian. Dinoflagellate cysts are diverse and abundant in the overlying Brora Argillaceous to Kimmeridge Clay formations, therefore indicating open marine conditions. The stratigraphic distributions and relative proportions of these Callovian to Lower Kimmeridgian dinoflagellate cyst floras are largely consistent with those reported elsewhere in northern Europe, and the established dinoflagellate cyst biozonations can be readily applied to the Inner Moray Firth Basin. Some taxa, such as Gonyaulacysta dentata, are of distinct Boreal affinity. Furthermore, some minor stratigraphic anomalies were noted, including the range base of Scriniodinium crystallinum being in the early Oxfordian at Balintore. In England and Germany, this bioevent occurs in the late Callovian. Some notable dinoflagellate cyst abundance phenomena were observed. An example of this is the prominence of Korystocysta spp. in the Middle Callovian. This and other quantitative phenomena are of correlative significance. Marine palynomorph diversity increased markedly during the Callovian, stabilizing in the Lower Oxfordian. A suite of characteristic dinoflagellate cysts became extinct in the Middle Oxfordian, and some typically Late Jurassic elements became more prominent at this time. The early Kimmeridgian palynofloras from Ethie are entirely typical of this interval elsewhere in Europe.

Cenozoic vertical motions in the Moray Firth Basin associated with initiation of the Iceland Plume

It is likely that the Iceland mantle plume generated transient uplift across the North Atlantic region when it initiated in earliest Cenozoic time. However, transient uplift recorded in sedimentary basins fringing the region can be overprinted by the effects of permanent uplift. Identifying and quantifying transient uplift can only be achieved in areas which have a well‐constrained stratigraphic record and across which the relative importance of permanent and transient uplift varies (e.g., the Moray Firth Basin, North Sea). By analyzing the subsidence of 50 boreholes from the Moray Firth Basin (MFB), residual vertical motions unrelated to rifting have been isolated. Transient uplift of 180–425 m occurred during Paleocene times. The western MFB has also been affected by permanent Cenozoic uplift, with denudation decreasing from 1.3 ± 0.1 km in the west of the basin to zero denudation east of 1°W. Dynamic support above the Iceland Plume led to transient uplift of the entire MFB in early Paleocene times, peaking in latest Paleocene times. In early Eocene times the effect of the plume waned, and subsidence occurred. Paleocene permanent uplift of the NW British Isles is generally accepted to have been due to magmatic underplating of the crust emplaced during the British Tertiary Igneous Province (61–58.5 Ma). The cause of Neogene uplift events is poorly understood, but it could also be associated with the Iceland Plume.