The Neoarchaean foreland basement of the Faroe-Shetland terrane (FST) displays abundant evidence for isotopic resetting of U-Pb systems in apatite between c. 1800 and 200 Ma, interpreted to result from episodic heating pulses associated with regional scale tectonic events. Major apparent age peaks of c. 1800-1600 Ma broadly correspond to the timing of Nagssugtoqidian-Laxfordian orogenesis >225 km further south. These are thought to reflect widespread heating during late- to post-orogenic delamination that affected a wide area of the orogenic foreland and resulted in a low-middle greenschist facies static overprint, affecting much of the FST basement. Late- to post-orogenic delamination might also account for major apparent age peaks at c. 1300-1100, 800, and 500-400 Ma, corresponding to, respectively, Grenvillian, Knoydartian and Caledonian orogenic events. However, east-dipping seismic reflectors in the basement west of Shetland may represent the northward extension of the Grenvillian Outer Hebrides Thrust (Zone) and/or Caledonian thrusts and so perturbation of isotherms during west-directed thrusting could therefore also account for these apparent age peaks. Minor apparent age peaks of c. 700, 600, 350 and 200 Ma are most easily interpreted as resulting from enhanced heat flux that accompanied periods of crustal extension prior to and following the Caledonian orogeny.

This study presents the results of a joint Chemostrat–APT study that aimed to produce a suite of radioactive heat production data for basement rocks in the Faroe Shetland Basin to enable more accurate basin modelling to be undertaken. To enable regional studies to be undertaken, the basement has been split into four zones based on similarities. Zone A is formed of high grade metamorphic basement from the Rockall trough (quads 154 & 164) SW of the Laxfordian front. Zone B comprises granodioritic, tonalitic and dioritic Neoarchean aged (2700–2830 Ma) high grade metamorphic basement from the SW of the Rona Ridge and Basin (wells 202/08-1, 204/15-2, 205/161, 205/21-1A, 206/7a-2, 206/08-2, 206/09-2 and 206/12-1) and NE of the Laxfordian front. Zone C contains Neoarchean aged high grade metamorphic basement of a predominantly granitic and quartz rich granitoid composition from the NE of the Rona Ridge (wells 207/01-3, 207/02-1, 208/23-1 and 208/26-1). Zone D differs from the rest of the material in this study in that it is Caledonian ( c. 460 Ma) granitic plutonic basement from Quads 209 (Ereland volcanic centre). Radioactive heat production values were derived from potassium, thorium and uranium data produced from the analysis of eighty-four basement samples by ICP-OES and ICP-MS analysis. Each mapped basement zone was then assigned a mean radioactive heat production value for use in future basin modelling studies; Zone A = 0.21 µWm 3 , Zone B, 0.64 µWm 3 , zone C = 0.88 µWm 3 and zone D = 2.1 µWm 3 . Supplementary material: Tables containing full mineralogical (SI 1) and U-Pb geochronological analytical (SI 2) data at https://doi.org/10.6084/m9.figshare.c.6771540 Thematic collection: This article is part of the New learning from exploration and development in the UKCS Atlantic Margin collection available at: https://www.lyellcollection.org/topic/collections/new-learning-from-exploration-and-development-in-the-ukcs-atlantic-margin

Summary One area where understanding the critical moment of a petroleum system is challenging is the Faroe-Shetland Basin (FSB). Most basin models invoke oil generation beginning in the mid-Cretaceous at ca.100 Ma, predating deposition of Paleogene reservoirs. This time discrepancy has previously been explained by re-migration from intermediary accumulations ("Motel" hypothesis) and/or overpressure retardation of kerogen maturation. The FSB is characterized by thick Cretaceous stratigraphic packages (up to 5 km) which includes a large proportion (up to 2 km) of Paleogene igneous material. Separating sedimentary and igneous material and adding the igneous material at the correct time between ca.58–55 Ma shallows the modelled burial depth of the Upper Jurassic source rocks during the Cretaceous sufficiently to delay maturation by 17 Myr in comparison to previous studies. Additionally, previous studies have invoked crustal radiogenic heat production (RHP) based on Phanerozoic crust averaging ca. 2.8 μW/m3 in the North Sea (300 km to the east). However, the FSB is underlain by significantly older, colder Neoarchean orthogneisses (ca.2.7 – 2.9 Ga), reducing RHP by up to 50% to ca.1.6 μW/m3 (σ = 0.74). Together our model unifies geological, geochronological and geochemical observations, delaying the onset of petroleum expulsion by up to 40 Myr.

Doggerland was a landmass occupying an area currently covered by the North Sea until marine inundation took place during the mid-Holocene, ultimately separating the British landmass from the rest of Europe. The Storegga Event, which triggered a tsunami reflected in sediment deposits in the northern North Sea, northeast coastlines of the British Isles and across the North Atlantic, was a major event during this transgressive phase. The spatial extent of the Storegga tsunami however remains unconfirmed as, to date, no direct evidence for the event has been recovered from the southern North Sea. We present evidence of a tsunami deposit in the southern North Sea at the head of a palaeo-river system that has been identified using seismic survey. The evidence, based on lithostratigraphy, geochemical signatures, macro and microfossils and sedimentary ancient DNA (sedaDNA), supported by optical stimulated luminescence (OSL) and radiocarbon dating, suggests that these deposits were a result of the tsunami. Seismic identification of this stratum and analysis of adjacent cores showed diminished traces of the tsunami which was largely removed by subsequent erosional processes. Our results confirm previous modelling of the impact of the tsunami within this area of the southern North Sea, and also indicate that these effects were temporary, localized, and mitigated by the dense woodland and topography of the area. We conclude that clear physical remnants of the wave in these areas are likely to be restricted to now buried, palaeo-inland basins and incised river valley systems.

The concept of a critical moment in a petroleum system (the time of highest probability of entrapment and preservation of oil and gas) has underlain petroleum exploration for over 25 years. However, one area where understanding the critical moment is challenging is the Faroe-Shetland Basin (FSB; offshore UK). Isotopic dating of oils suggests that petroleum generation began between ca. 68 and 90 Ma; however, most basin models invoke an earlier generation beginning in the mid-Cretaceous at ca. 100 Ma, predating deposition of Paleocene and Eocene reservoirs. This time discrepancy has previously been explained by remigration from intermediary accumulations ("motel" hypothesis) and/or overpressure retardation of kerogen maturation. The FSB is characterized by a thick Cretaceous stratigraphic package (up to 5 km) that includes a large net thickness (up to 2 km) of Paleogene igneous material. In our model, separating sedimentary and igneous material and adding the igneous material at the correct time between ca. 58 and 55 Ma shallows the modeled burial depth of the Upper Jurassic source rocks during the Cretaceous sufficiently to delay maturation by 17 m.y. in comparison to results of previous studies. Additionally, previous studies have invoked crustal radiogenic heat production (RHP) based on the Phanerozoic crust averaging similar to 2.8 mu W/m(3) in the North Sea (300 km to the east). However, the FSB basement is composed of significantly older, colder Neoarchean orthogneisses (ca. 2.7-2.9 Ga), reducing RHP by up to 50% to similar to 1.6 mu W/m(3) (sigma = 0.74). For the first time, our model unifies geological, geochronological, and geochemical observations, delaying the onset of petroleum expulsion by up to 40 m.y. in comparison to previous models.

The isochron technique for dating geological events is widely used in many fields of isotope geochemistry. However, data sets can be complex, and many samples may not behave as closed systems, resulting in excess scatter around a regression line. In certain data sets, however, excess scatter may result when geological samples are partially reset or when samples are comprised of multiple components recording different geological processes separated in time and/or initial isotope composition. Here we introduce a new approach for investigating evidence of such multicomponent mixtures within isochron space. We provide a mathematical framework to resolve the number of mixture components, without requiring any prior knowledge of this number. Crucially, the model reports the proportion of each individual sample that belongs to each mixture component, allowing the user to return to the samples and independently test model outputs with other techniques. It is important to distinguish accurate and meaningful ages and initial daughter isotope compositions from the meaningless values that are caused by mismatch between geological processes and the models that we use to describe them. First, we demonstrate our new model on a synthetic data set to show that it can successfully separate distinct isochrons in a complex mixture. We further validate our approach with a previously published data set using the 187Re‐187Os system in bitumen and 147Sm/144Nd system in magmatic rocks. We identify discrete components in these data sets and using complementary geological observations discuss the implications of treating these scattered data as recording multiple geological processes.

Chemical weathering of silicate rocks is a primary drawdown mechanism of atmospheric carbon dioxide. The processes that affect weathering are therefore central in controlling global climate. A temperature-controlled "weathering thermostat" has long been proposed in stabilising long-term climate, but without definitive evidence from the geologic record. Here we use lithium isotopes (delta Li-7) to assess the impact of silicate weathering across a significant climate-cooling period, the end-Ordovician Hirnantian glaciation (similar to 445 Ma). We find a positive delta Li-7 excursion, suggestive of a silicate weathering decline. Using a coupled lithium-carbon model, we show that initiation of the glaciation was likely caused by declining CO2 degassing, which triggered abrupt global cooling, and much lower weathering rates. This lower CO2 drawdown during the glaciation allowed climatic recovery and deglaciation. Combined, the data and model provide support from the geological record for the operation of the weathering thermostat.

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 Loch Shin Line is a geological–geophysical lineament associated with a zone of mantle-derived appinites, granites and strike-slip faulting that runs NW–SE across the Moine Nappe, northern Scotland. U–Pb zircon and Re–Os molybdenite dating of the Loch Shin and Grudie plutons, which lie immediately SW of the NW–SE Loch Shin–Strath Fleet fault system, yield c . 427–430 Ma ages that overlap within error. They also coincide with previously obtained U–Pb zircon ages for the Rogart pluton, which lies along-strike to the SE. Field and microstructural observations confirm the similarity and contemporaneous nature of the plutons and associated sulphide mineralization. Fluid inclusion analyses place further constraints on the P – T – X conditions during regional late Caledonian exhumation of the Moine Nappe. Synchronous to slightly younger brittle dextral strike-slip faulting along the WNW–ESE Loch Shin–Strath Fleet Fault System was probably antithetic to sinistral movements along the nearby Great Glen Fault Zone. Our findings support the hypothesis that the Loch Shin Line acted as a deep crustal channelway controlling the ascent and emplacement of Silurian magmas into the overlying Moine Nappe. We propose that this deep structure corresponds to the southeastern continuation of the Precambrian-age Laxford Front shear zone in the buried Lewisian autochthon. Supplementary Material: Field photographs, photomicrographs and fluid inclusion information are available at http://www.geolsoc.org.uk/SUP18859.

The first application of the Re–Os isotope geochronometer to ORR demonstrated that the Re–Os data, although imprecise, could yield the depositional age of sedimentary successions (Ravizza and Turekian 1989), a remarkable outcome given the analytical challenges and data uncertainties at the time. Today, utilizing new analytical and mass spectrometry techniques (see below) and the most accurate Re decay constant (1.666 10 11 year ; Smoliar et al. 1996) has permitted the determination of precise (in some cases 1 % uncertainty) depositional ages for ORR that possess 0.5 wt% total organic carbon (TOC) (e.g., Cohen et al. 1999; Georgiev et al. 2011; Kendall et al. 2009a; Selby and Creaser 2005a; Xu et al. 2009; Cumming et al. 2012). These studies have provided the foundation to apply the Re–Os organic-rich sedimentary rock geochronometer to yield ages throughout geological time for stratigraphic boundary intervals and major Earth events (e.g., rise of oxygen, Proterozoic glaciations etc.; Selby and Creaser 2005a; Selby 2007; Anbar et al. 2007; Xu et al. 2009; Rooney et al. 2011; Yang et al. 2009). Rhenium–osmium geochronology of ORR utilizes the isochron method, which yields the initial Os isotope composition (Os/Os) for the sampled unit, taken to represent the Os/Os composition of the water column at the time of deposition (Ravizza and Turekian 1989; Cohen et al. 1999; Peucker-Ehrenbrink and Ravizza 2000, 2012). In addition to ORR, hydrocarbon products of such matured rocks, for example, crude oil and bitumen, have been shown to also be enriched in both Re and Os at the ppb and ppt level, respectively (Barre et al. 1995; Woodland et al. 2001; Selby and Creaser 2005b; Selby et al. 2007; Finlay et al. 2011). The hydrocarbon Re–Os isotope data from several petroleum systems has shown that Re–Os systematics of hydrocarbons can provide the timing of petroleum generation from an oil source rock (Selby et al. 2005; Selby and Creaser 2005b; Finlay et al. 2011), with the initial Os/Os value derived from Re–Os hydrocarbon data interpreted to reflect the Os/Os inherited from the source rock at the time of petroleum expulsion (Selby and Creaser 2005b; Rooney et al. 2012).

In the Archaean basement rocks of the Assynt and Gruinard terranes of the mainland Lewisian Complex in NW Scotland, a regional suite of quartz-pyrite veins cross-cut regional Palaeoproterozoic (Badcallian, ca. 2700Ma; Inverian, ca. 2480Ma) fabrics and associated Scourie dykes. The quartz veins are overprinted by amphibolite-greenschist facies Laxfordian deformation fabrics (ca. 1760Ma) and later brittle faults. The hydrothermal mineral veins comprise a multimodal system of tensile/hybrid hydraulic fractures which are inferred to have formed during a regional phase of NW-SE extension. The almost orthogonal orientation of the quartz veins (NE-SW) to the Scourie dykes (NW-SE) are incompatible and must result from distinct paleostress regimes suggesting they are related to different tectonic events. This hypothesis is supported by Rhenium–Osmium dating of pyrite that yields an age of 2249±77Ma, placing the vein-hosted mineralisation event after the oldest published dates for the Scourie Dykes (2420Ma), but before the youngest ages (1990Ma). Sulphur isotope analysis suggests that the sulphur associated with the pyrite is isotopically indistinguishable from primitive mantle. The presence of the ca. 2250Ma quartz-pyrite veins in both the Assynt and Gruinard terranes confirms that these crustal units were amalgamated during or prior to Inverian deformation. The absence of the veins in the Rhiconich Terrane is consistent with the suggestion that it was not finally amalgamated to the Assynt Terrane until the Laxfordian.

Trace element compositions of raw clay, fired clay and Roman ceramic building material (CBM) from Carpow Roman fortress, Newburgh, Scotland and the city of York, England have been determined through the use of inductively coupled plasma-mass spectrometry (ICPMS). It is confirmed that the firing of clay does not disturb any of the sample’s trace element composition and that trace element protolith identification is an applicable tool for fingerprinting the source of material used in CBM construction. It is also demonstrated through the particular proportions of LREE/HREE; Th/Co; La/Sc; La/Lu; Eu/Sm values on CBM from Carpow that these material were likely manufactured from clay used in the York Roman tile manufacturing industry, therefore suggesting importation. The transport of CBM from York to Carpow provides a useful addition to known examples of the long-distance shipping of CBM. It is postulated that similar analysis to that conducted here could be used to identify important trade networks within the Roman Empire.

This study demonstrates that petroleum and source rocks are enriched in Pt and Pd to the ppb level, and that the 187Os/188Os composition coupled with the Pt/Pd value permits the fingerprinting of petroleum to its source. Oils from the United Kingdom Atlantic Margin (sourced from the Upper Jurassic Kimmeridge Clay Fm.) as well as source rock samples have been analysed for Pt and Pd. When the Pt/Pd value is compared with 187Os/188Os (calculated at the time of oil generation; Osg) the values from both the known source and the oils are similar, demonstrating that they can be used as an oil to source fingerprinting tool. This inorganic petroleum fingerprinting tool is particularly important in heavily biodegraded petroleum systems where traditional fingerprinting techniques (e.g. biomarkers) are severely hampered, e.g. the world's largest oil sand deposit, the West Canadian Oil Sands (WCOS). This has caused the source of the WCOS to be hotly debated, with no present day consensus between inputs from potential source units e.g. Exshaw and Gordondale Fms. 187Os/188Os and Pt/Pd fingerprinting of the oil sands shows that the majority of the petroleum have similar 187Os/188Os and Pt/Pd values, supporting the hypothesis of one principal source. Analysis of the potential source rocks establishes that the principal source of the oil sands to be from the Jurassic Gordondale Fm., with a minor Exshaw Fm. input. Thus, the combination of previously pioneered Re–Os petroleum geochronology with 187Os/188Os and Pt/Pd values of petroleum permits both a temporal and spatial understanding of petroleum systems.

We demonstrate that the Re-Os system can be used to understand the temporal evolution of a petroleum system as well as aid in the identification of source units. Traditional geochemical methods (high-performance liquid chromatography, carbon isotope, gas chromatography, and biomarker analysis) indicate that the main source of 18 oils analyzed for Re-Os geochronology from the United Kingdom Atlantic margin (Clair, Schiehallion, Cuillin, and Foinaven fields) is Late Jurassic marine shales. This is supported by the Os isotopic composition (Os-187/Os-188) of the Late Jurassic source (similar to 0.9-2.4) at the timing of oil generation being similar to that of the oil (68 Ma; 0.92-1.12), indicating that the Re-Os system can potentially be used to fingerprint the source of an oil. The Re-Os data for the 18 oils yield an age (68 +/- 13 Ma) that agrees with both the relative (basin models) and absolute (Ar-Ar geochronology) timing of oil generation, indicating that that Re-Os oil geochronology records oil generation events.

The research in this thesis is presented in paper format with each of four chapters representing one complete study. Chapter two presents Re–Os and geochemical fingerprint data for UK Atlantic margin oils. organic and δ13C geochemical data demonstrate that the oil is sourced from Upper Jurassic marine shales and the Re–Os data yields an age of 68 ± 13 Ma. Comparison of this date with published basin histories and Ar-Ar geochronology demonstrate that Re–Os ages correspond with the timing of oil generation. Furthermore the similarities between oil and source rock 187Os/188Os at the time of oil generation (Osg) indicates that Osg can be used to identify oil source units. Chapter three demonstrates, through the analysis of Kimmeridge Clay Fm. core and North Sea oil, that unradiogenic mantle like values within oils from wells in the Viking Graben and East Shetland Basin cannot be inherited from source. It is hypothesised that they are caused by contamination by a hydrothermal fluid sourced from either Cenozoic intrusive units or the mantle. Strain localisation is suggested to have caused the main basin bounding faults within the Viking Graben and East Shetland Basin to be of sufficient depth to act as conduits for hydrothermal fluid to propagate through and contaminate oils within reservoirs. Chapter four investigates how Osi values across the Ordovician/Silurian boundary GSSP at Dob’s Linn, Scotland, tracks the Hirnantian glaciation within a globally important source unit: the Ordovician/Silurian “Hot” Shales. During the Late Katian, Osi values increase from 0.28 – 1.08, providing evidence for increased silicate weathering of radiogenic continental crust. A decrease to less radiogenic Osi (~0.60) occurs at the base Hirnantian and marks the onset of the Hirnantian Glaciation. This is ascribed to Hirnantian ice cover and reduced chemical weathering rates cutting the supply of radiogenic material. In the Late Hirnantian an abrupt increase in Osi values to ~1.1 over 19 cm of stratigraphy, is attributed to the leaching of exposed radiogenic glacial deposits and increased weathering of silicate terrane during deglaciation. Chapter five applies the Platinum Group Elements, specifically Pt/Pd ratios, to identify oil source units. It is demonstrated that asphaltenes from the well constrained UK Atlantic margin petroleum system contain similar Pt/Pd and Osg values to the known source unit. A further study of the poorly constrained West Canadian Tar Sands demonstrates that Pt/Pd ratios in source rocks are not affected by hydrocarbon maturation and are distinct between differing potential source units. Comparison of the Tar Sands with potential source units demonstrates that the Tar Sands are mainly sourced from the Lower Jurassic Gordondale Fm., with minor input from the Devonian/Mississippian Exshaw Fm.

Here we present initial 187Os/188Os (Osi) values integrated with δ13Corg for the first Paleozoic section — the Ordovician/Silurian boundary GSSP at Dob's Linn, Scotland. Our 187Os/188Os data tracks major changes in climate that occurred during the Late Ordovician (Hirnantian glaciation), which coincides with the second largest known mass extinction. During the complanatus and early anceps Biozones Osi values increase from 0.28–1.08. This provides evidence for a period of increased silicate weathering of radiogenic continental crust, likely from the Caledonian Orogen. This increase in weathering was likely the driving mechanism for the drawdown in atmospheric CO2 and global cooling that resulted in the onset of the Hirnantian Glaciation. A decrease to less radiogenic Osi occurs at the base Hirnantian extraordinarius Biozone and coincides with the trend to more positive δ13Corg values that mark the onset of the Hirnantian Glaciation. The trend in Osi during this interval is ascribed to Hirnantian ice cover and reduced chemical weathering rates cutting the supply of radiogenic material to the Iapetus Ocean. The reduction in silicate weathering enabled atmospheric CO2 to return back to greenhouse levels, causing rapid deglaciation during the mid persculptus Biozone. This period is marked by an abrupt increase in Osi values from 0.6 to 1.08 over 19cm of stratigraphy and coincides with the deglacial limb of the δ13Corg profile. We interpret the Osi data to reflect the leaching of exposed radiogenic 187Os/188Os bearing glacial deposits and increased weathering of radiogenic 187Os/188Os silicate terrane during the deglaciation. Previous workers have identified the Hirnantian glaciation primarily through δ13C stratigraphy. However, our Os isotope data indicate that an initial mechanism (i.e. increased silicate weathering) was the driving mechanism behind the Hirnantian Glaciation and subsequent mass extinction. Thus, by coupling Osi and δ13Corg proxies we provide the most direct evidence for the initiation and cessation of the Hirnantian glaciation. Furthermore, this study demonstrates the first use of 187Os/188Os chemostratigraphy for the Paleozoic as a proxy for reconstructing the Earth's climate system, particularly palaeoceanography.

United Kingdom North Sea oils sourced from the Kimmeridge Clay Formation contain unradiogenic (similar to 0.17 to similar to 0.48) and radiogenic (similar to 1.04 to similar to 3.34) Os-187/Os-188 values. The unradiogenic Os-187/Os-188 values are spatially associated with the main basin-bounding faults of the Viking Graben and East Shetland Basin. In contrast, the radiogenic Os-187/Os-188 values are associated with North Sea basins located farther away from the basin boundary faults. We suggest that crustal thinning and strain localization within the Viking Graben and East Shetland Basin are sufficient to have allowed basin-bounding faults to propagate to sufficient depth to act as conduits for mantle-derived fluids to interact with oil. This hypothesis is supported by previous geochemical data for North Sea oil fields. Furthermore, we demonstrate the use of Os isotopes as an important tracker of crustal-scale fluid dynamics and petroleum migration pathways in extensional basins.