cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3452978.v1
title: Zircon U–Pb age for the Orkney lamprophyre dyke swarm, Scotland, and relations to Permo-Carboniferous magmatism in northwestern Europe

description: Magmatic zircon in the syenite (bostonite) part of a composite NE–SW-trending cogenetic bostonite–camptonite dyke in Orkney, Scotland, yields a laser ablation inductively coupled plasma mass spectrometry age of 313 ± 4 Ma and <em>ε</em>Hf<sub>(313 Ma)</sub> values of +6 to +11. This suggests that the NE–SW-, east–west- and NW–SE-trending Scottish lamprophyre dyke swarms were emplaced during one late Carboniferous magmatic event, contrasting with published K–Ar dates ranging between <em>c</em>. 325 and 250 Ma. This magmatism is interpreted as a response to late Variscan regional extension or an early response to the Skagerrak mantle plume. Lamprophyre magmatism was initiated some 10 Ma earlier in Scotland than in the Oslo Rift.
DOI: 10.6084/m9.figshare.3452975
title: Some consequences of mechanical stratification in basin-scale numerical models of passive-margin salt tectonics

description: Two-dimensional plane-strain numerical experiments illustrate the effects of variable evaporite viscosity and embedded frictional-plastic sediment layers on the style of salt flow and associated deformation of the sedimentary overburden. Evaporite viscosity exerts a first-order control on the salt flow rate and the style of overburden deformation. Nearly complete evacuation of low-viscosity salt occurs beneath expulsion basins, whereas significant salt is trapped when viscosity is high. Embedded frictional-plastic sediment layers with yield strength partition salt flow and develop transient contractional structures (folds, thrust faults and folded faults) in a seaward salt-squeeze flow regime. Multiple internal sediment layers reduce the seaward salt flow during sediment aggradation, leaving more salt behind to be remobilized during subsequent progradation. This produces more seaward extensive allochthonous salt sheets. If there is a density difference between the embedded layers and the surrounding salt, then the embedded layers fractionate during deformation and either float to the surface or sink to the bottom, creating a thick zone of pure halite. Such a process of ‘buoyancy fractionation’ may partially explain the apparent paradox of layered salt in autochthonous salt basins and pure halite in allochthonous salt sheets.
DOI: 10.6084/m9.figshare.3452975.v1
title: Some consequences of mechanical stratification in basin-scale numerical models of passive-margin salt tectonics

description: Two-dimensional plane-strain numerical experiments illustrate the effects of variable evaporite viscosity and embedded frictional-plastic sediment layers on the style of salt flow and associated deformation of the sedimentary overburden. Evaporite viscosity exerts a first-order control on the salt flow rate and the style of overburden deformation. Nearly complete evacuation of low-viscosity salt occurs beneath expulsion basins, whereas significant salt is trapped when viscosity is high. Embedded frictional-plastic sediment layers with yield strength partition salt flow and develop transient contractional structures (folds, thrust faults and folded faults) in a seaward salt-squeeze flow regime. Multiple internal sediment layers reduce the seaward salt flow during sediment aggradation, leaving more salt behind to be remobilized during subsequent progradation. This produces more seaward extensive allochthonous salt sheets. If there is a density difference between the embedded layers and the surrounding salt, then the embedded layers fractionate during deformation and either float to the surface or sink to the bottom, creating a thick zone of pure halite. Such a process of ‘buoyancy fractionation’ may partially explain the apparent paradox of layered salt in autochthonous salt basins and pure halite in allochthonous salt sheets.
DOI: 10.6084/m9.figshare.3452972
title: A multi-proxy record of the Latest Danian Event at Gebel Qreiya, Eastern Desert, Egypt

description: The Latest Danian Event (LDE) is a proposed early Palaeogene transient warming event similar to the Paleocene–Eocene Thermal Maximum, albeit of smaller magnitude. The LDE can be correlated with a carbon isotope excursion (‘CIE-DS1’) at Zumaia, Spain, and the ‘top Chron C27n event’ defined recently from ocean drilling sites in the Atlantic and Pacific, supporting a global extent. Yet, records of environmental change during the LDE (e.g. warming and sea-level fluctuations) are still rare. In this study, we focus on the micropalaeontology (calcareous nannofossils and benthic foraminifera), mineralogy and trace element geochemistry of the LDE in the Qreiya 3 section from the southern Tethyan margin in Egypt. In this section, the LDE is characterized by the occurrence of anomalous beds intercalated within upper Danian shales and marls. The event beds of the LDE are situated above an unconformity on top of a shallowing-upwards sequence deposited in a well-oxygenated outer neritic to upper bathyal marine palaeoenvironment. The lower LDE bed is barren of benthic foraminifera, but contains pyrite and fish remains, and is interpreted as an anoxic level formed during rapid relative sea-level rise. Incursion of a <em>Neoeponides duwi</em> (Nakkady, 1950) benthic assemblage in LDE bed II is interpreted as repopulation of the seafloor after anoxia. The sea-level cycle associated with the LDE is estimated at about 50 m maximum in the Qreiya 3 section. The environmental changes at Qreiya 3 are of supra-regional extent, since a similar sequence of events has been observed at other southern Tethyan locations.
DOI: 10.6084/m9.figshare.3452972.v1
title: A multi-proxy record of the Latest Danian Event at Gebel Qreiya, Eastern Desert, Egypt

description: The Latest Danian Event (LDE) is a proposed early Palaeogene transient warming event similar to the Paleocene–Eocene Thermal Maximum, albeit of smaller magnitude. The LDE can be correlated with a carbon isotope excursion (‘CIE-DS1’) at Zumaia, Spain, and the ‘top Chron C27n event’ defined recently from ocean drilling sites in the Atlantic and Pacific, supporting a global extent. Yet, records of environmental change during the LDE (e.g. warming and sea-level fluctuations) are still rare. In this study, we focus on the micropalaeontology (calcareous nannofossils and benthic foraminifera), mineralogy and trace element geochemistry of the LDE in the Qreiya 3 section from the southern Tethyan margin in Egypt. In this section, the LDE is characterized by the occurrence of anomalous beds intercalated within upper Danian shales and marls. The event beds of the LDE are situated above an unconformity on top of a shallowing-upwards sequence deposited in a well-oxygenated outer neritic to upper bathyal marine palaeoenvironment. The lower LDE bed is barren of benthic foraminifera, but contains pyrite and fish remains, and is interpreted as an anoxic level formed during rapid relative sea-level rise. Incursion of a <em>Neoeponides duwi</em> (Nakkady, 1950) benthic assemblage in LDE bed II is interpreted as repopulation of the seafloor after anoxia. The sea-level cycle associated with the LDE is estimated at about 50 m maximum in the Qreiya 3 section. The environmental changes at Qreiya 3 are of supra-regional extent, since a similar sequence of events has been observed at other southern Tethyan locations.
DOI: 10.6084/m9.figshare.3452969
title: Repeated bottom-water oxygenation during OAE 2: timing and duration of short-lived benthic foraminiferal repopulation events (Wunstorf, northern Germany)

description: Published proxy data for Oceanic Anoxic Event 2 (OAE 2 or Cenomanian–Turonian Boundary Event) and other mid-Cretaceous OAEs indicate widespread anoxic bottom-water conditions. However, increasing evidence shows that anoxia was not permanent but subject to significant fluctuations. We have generated X-ray fluorescence elemental concentration and benthic foraminiferal assemblage records for a short section of OAE 2 black shales from Wunstorf, northern Germany. Two intervals of low sulphur elemental concentration are interpreted as periods of increased oxygenation of bottom waters. This is supported by benthic foraminiferal assemblage data showing repopulation events associated with these intervals. These repopulation events are characterized mainly by the occurrence of agglutinated taxa, with <em>Lingulogavelinella globosa</em> being the only abundant calcareous species. This observation is interpreted in terms of short-term interruptions of the otherwise anoxic bottom-water environment. Comparison with repopulation events during OAE 1b and Quaternary sapropels make it reasonable to speculate that short-term cooling and an associated increase in bottom-water ventilation at the NW European shelf sea are the main trigger mechanisms for the observed repopulation events at Wunstorf. As source area for benthic foraminifera, shallower parts of the Lower Saxony basin are proposed.
DOI: 10.6084/m9.figshare.3452966
title: Unusual mixed silica–carbonate deposits from magmatic–hydrothermal hot springs, Savo, Solomon Islands

description: The volcanic island of Savo, Solomon Islands, hosts an active hydrothermal system discharging unusual alkaline (pH 7–8) sulphate-rich, chloride-poor fluid, with variable admixtures of Ca–Mg–HCO<sub>3</sub><sup>−</sup>-rich fluid. Hot springs and their outflow streams precipitate a variety of deposits, including travertine, silica sinter and unusual mixed silica–carbonate rocks. Travertine fabrics are dominated by ray-crystal calcite, associated with rapid abiotic precipitation from a supersaturated solution. Sinter is produced by evaporation of thermal waters, and downstream samples contain preserved traces of micro-organisms, which potentially acted as templates for precipitation. Trace element chemistry of sinters and travertines includes anomalously high levels of Te, indicating a magmatic origin for a component fluid in the hydrothermal system. Springs are close to or at saturation with both calcite and amorphous silica. Increased contributions from the Ca–Mg–HCO<sub>3</sub><sup>−</sup> end-member favours calcite formation; this fluid is of low-temperature origin, and as such is favoured by high rainfall. Mixed samples show cyclical changes between silica and carbonate precipitation, potentially as a result of seasonal variation in rainfall.
DOI: 10.6084/m9.figshare.3452969.v1
title: Repeated bottom-water oxygenation during OAE 2: timing and duration of short-lived benthic foraminiferal repopulation events (Wunstorf, northern Germany)

description: Published proxy data for Oceanic Anoxic Event 2 (OAE 2 or Cenomanian–Turonian Boundary Event) and other mid-Cretaceous OAEs indicate widespread anoxic bottom-water conditions. However, increasing evidence shows that anoxia was not permanent but subject to significant fluctuations. We have generated X-ray fluorescence elemental concentration and benthic foraminiferal assemblage records for a short section of OAE 2 black shales from Wunstorf, northern Germany. Two intervals of low sulphur elemental concentration are interpreted as periods of increased oxygenation of bottom waters. This is supported by benthic foraminiferal assemblage data showing repopulation events associated with these intervals. These repopulation events are characterized mainly by the occurrence of agglutinated taxa, with <em>Lingulogavelinella globosa</em> being the only abundant calcareous species. This observation is interpreted in terms of short-term interruptions of the otherwise anoxic bottom-water environment. Comparison with repopulation events during OAE 1b and Quaternary sapropels make it reasonable to speculate that short-term cooling and an associated increase in bottom-water ventilation at the NW European shelf sea are the main trigger mechanisms for the observed repopulation events at Wunstorf. As source area for benthic foraminifera, shallower parts of the Lower Saxony basin are proposed.
DOI: 10.6084/m9.figshare.3452966.v1
title: Unusual mixed silica–carbonate deposits from magmatic–hydrothermal hot springs, Savo, Solomon Islands

description: The volcanic island of Savo, Solomon Islands, hosts an active hydrothermal system discharging unusual alkaline (pH 7–8) sulphate-rich, chloride-poor fluid, with variable admixtures of Ca–Mg–HCO<sub>3</sub><sup>−</sup>-rich fluid. Hot springs and their outflow streams precipitate a variety of deposits, including travertine, silica sinter and unusual mixed silica–carbonate rocks. Travertine fabrics are dominated by ray-crystal calcite, associated with rapid abiotic precipitation from a supersaturated solution. Sinter is produced by evaporation of thermal waters, and downstream samples contain preserved traces of micro-organisms, which potentially acted as templates for precipitation. Trace element chemistry of sinters and travertines includes anomalously high levels of Te, indicating a magmatic origin for a component fluid in the hydrothermal system. Springs are close to or at saturation with both calcite and amorphous silica. Increased contributions from the Ca–Mg–HCO<sub>3</sub><sup>−</sup> end-member favours calcite formation; this fluid is of low-temperature origin, and as such is favoured by high rainfall. Mixed samples show cyclical changes between silica and carbonate precipitation, potentially as a result of seasonal variation in rainfall.
DOI: 10.6084/m9.figshare.3452963
title: <em>P</em>–<em>T</em> constraints and timing of Barrovian metamorphism in the Shetland Islands, Scottish Caledonides: implications for the structural setting of the Unst ophiolite

description: An integrated <em>in situ</em> monazite laser-ablation inductively coupled plasma mass spectrometry and metamorphic equilibria study is used to establish the <em>P</em>–<em>T</em> conditions and timing of Barrovian metamorphism in the Shetland Islands, Scottish Caledonides. The results have implications for the structural setting of the Unst ophiolite, which was obducted onto metasedimentary rocks of the Dalradian Supergroup. Metapelites in the footwall of the ophiolite yield U–Pb ages between 462 and 451 Ma with <em>P</em>–<em>T</em> conditions varying from <em>c</em>. 7.5 kbar and 550 °C directly below the ophiolite to <em>c</em>. 10 kbar and 775 °C at structurally deeper levels. The timing of peak metamorphism corresponds closely to that of Grampian (<em>c</em>. 450–470 Ma) metamorphism in mainland Scotland and Ireland, and Taconic (<em>c</em>. 450–460 Ma) metamorphism in the Appalachians, thus confirming the near-synchroneity of this important arc accretion event along the Laurentian margin. There is a significant metamorphic contrast between the low-grade rocks associated with the Unst ophiolite and the <em>P</em>–<em>T</em> conditions recorded in its footwall. If published K–Ar ages of <em>c.</em> 470 Ma broadly record obduction of the ophiolite, its present basal contact is probably a younger tectonic break that was associated with the excision of at least <em>c</em>. 10 km of crustal section.
DOI: 10.6084/m9.figshare.3452963.v1
title: <em>P</em>–<em>T</em> constraints and timing of Barrovian metamorphism in the Shetland Islands, Scottish Caledonides: implications for the structural setting of the Unst ophiolite

description: An integrated <em>in situ</em> monazite laser-ablation inductively coupled plasma mass spectrometry and metamorphic equilibria study is used to establish the <em>P</em>–<em>T</em> conditions and timing of Barrovian metamorphism in the Shetland Islands, Scottish Caledonides. The results have implications for the structural setting of the Unst ophiolite, which was obducted onto metasedimentary rocks of the Dalradian Supergroup. Metapelites in the footwall of the ophiolite yield U–Pb ages between 462 and 451 Ma with <em>P</em>–<em>T</em> conditions varying from <em>c</em>. 7.5 kbar and 550 °C directly below the ophiolite to <em>c</em>. 10 kbar and 775 °C at structurally deeper levels. The timing of peak metamorphism corresponds closely to that of Grampian (<em>c</em>. 450–470 Ma) metamorphism in mainland Scotland and Ireland, and Taconic (<em>c</em>. 450–460 Ma) metamorphism in the Appalachians, thus confirming the near-synchroneity of this important arc accretion event along the Laurentian margin. There is a significant metamorphic contrast between the low-grade rocks associated with the Unst ophiolite and the <em>P</em>–<em>T</em> conditions recorded in its footwall. If published K–Ar ages of <em>c.</em> 470 Ma broadly record obduction of the ophiolite, its present basal contact is probably a younger tectonic break that was associated with the excision of at least <em>c</em>. 10 km of crustal section.
DOI: 10.6084/m9.figshare.3452957
title: Evolution of fluid chemistry and fluid-flow pathways during folding and faulting: an example from Taemas, NSW, Australia

description: In the Taemas area, New South Wales, Australia, a swarm of hydrothermal calcite and quartz veins is hosted in upright, open to close folded limestones and shales. Overprinting relationships and vein geometries demonstrate that the vein swarm formed progressively during fold growth and associated reverse faulting. Textures preserved in veins reveal that veins formed via hundreds to thousands of individual dilation and mineral precipitation events. Bedding-parallel flexural slip during fold growth was associated with laminated vein development, and limb-parallel stretching during fold growth was associated with the formation of bedding-orthogonal extension veins. The presence of subhorizontal extension fractures and severely misoriented reverse faults imply that fluid pressures exceeded lithostatic levels, at least transiently, during the development of the vein swarm. Vein δ<sup>18</sup>O compositions increase upwards through the Murrumbidgee Group in response to a progressive reaction of an externally derived, upwards-flowing low-δ<sup>18</sup>O fluid (of probable meteoric origin) with host limestones. Vein δ<sup>18</sup>O and <sup>87</sup>Sr/<sup>86</sup>Sr compositions vary spatially and temporally within the same outcrop, and within individual veins. These variations are inferred to be caused by the ascent of packages of fluid along constantly changing flow pathways caused by multiple permeability creation–destruction cycles associated with fault slip and fault sealing. Vein trace and rare earth element (REE) concentrations are more variable, probably reflecting rapid rock buffering along fluid pathways on length scales of less than 10 m. Our results indicate that fluid-flow pathways change dynamically during crustal shortening, with pathways switching between states of low and high permeability during episodic fault slip and associated fracture development.
DOI: 10.6084/m9.figshare.3452957.v1
title: Evolution of fluid chemistry and fluid-flow pathways during folding and faulting: an example from Taemas, NSW, Australia

description: In the Taemas area, New South Wales, Australia, a swarm of hydrothermal calcite and quartz veins is hosted in upright, open to close folded limestones and shales. Overprinting relationships and vein geometries demonstrate that the vein swarm formed progressively during fold growth and associated reverse faulting. Textures preserved in veins reveal that veins formed via hundreds to thousands of individual dilation and mineral precipitation events. Bedding-parallel flexural slip during fold growth was associated with laminated vein development, and limb-parallel stretching during fold growth was associated with the formation of bedding-orthogonal extension veins. The presence of subhorizontal extension fractures and severely misoriented reverse faults imply that fluid pressures exceeded lithostatic levels, at least transiently, during the development of the vein swarm. Vein δ<sup>18</sup>O compositions increase upwards through the Murrumbidgee Group in response to a progressive reaction of an externally derived, upwards-flowing low-δ<sup>18</sup>O fluid (of probable meteoric origin) with host limestones. Vein δ<sup>18</sup>O and <sup>87</sup>Sr/<sup>86</sup>Sr compositions vary spatially and temporally within the same outcrop, and within individual veins. These variations are inferred to be caused by the ascent of packages of fluid along constantly changing flow pathways caused by multiple permeability creation–destruction cycles associated with fault slip and fault sealing. Vein trace and rare earth element (REE) concentrations are more variable, probably reflecting rapid rock buffering along fluid pathways on length scales of less than 10 m. Our results indicate that fluid-flow pathways change dynamically during crustal shortening, with pathways switching between states of low and high permeability during episodic fault slip and associated fracture development.
DOI: 10.6084/m9.figshare.3452954
title: Pressure–temperature evolution and thermal regimes in the Barrovian zones, Scotland

description: We constrain the <em>P</em>–<em>T</em> evolution of the Barrovian metamorphic zones from the southwestern to the northeastern coasts of Scotland using thermobarometry and pseudosection analysis based on mineral composition data, garnet zoning profiles and 2D garnet maps. Twenty-five samples were investigated from the garnet to the sillimanite zones. In the western half of the field area there was relatively high-<em>P</em> metamorphism (0.9–1.1 GPa) followed by near-isothermal decompression. In and around the Barrovian type area of Glen Clova maximum pressures were also high (<em>c</em>. 0.8–0.9 GPa); however, peak-<em>T</em> conditions were driven by a brief (of the order of 1 Ma or less) thermal pulse or pulses during exhumation at <em>c</em>. 0.6 GPa. Pressures at peak-<em>T</em> conditions along the eastern coast were the lowest observed, <em>c</em>. 0.4–0.5 GPa. These rocks were probably affected by the same thermal pulse activity evident around Glen Clova. All three regions initially developed during regional metamorphism associated with thermal relaxation of tectonically overthickened crust. The eastern part of the sequence, including Glen Clova, is fundamentally different from the western part because it required additional advective heat input to achieve peak thermal conditions. This heat was probably supplied by synorogenic magmas (e.g. Newer Gabbros) and the associated elevated crustal heat flow.
DOI: 10.6084/m9.figshare.3452954.v1
title: Pressure–temperature evolution and thermal regimes in the Barrovian zones, Scotland

description: We constrain the <em>P</em>–<em>T</em> evolution of the Barrovian metamorphic zones from the southwestern to the northeastern coasts of Scotland using thermobarometry and pseudosection analysis based on mineral composition data, garnet zoning profiles and 2D garnet maps. Twenty-five samples were investigated from the garnet to the sillimanite zones. In the western half of the field area there was relatively high-<em>P</em> metamorphism (0.9–1.1 GPa) followed by near-isothermal decompression. In and around the Barrovian type area of Glen Clova maximum pressures were also high (<em>c</em>. 0.8–0.9 GPa); however, peak-<em>T</em> conditions were driven by a brief (of the order of 1 Ma or less) thermal pulse or pulses during exhumation at <em>c</em>. 0.6 GPa. Pressures at peak-<em>T</em> conditions along the eastern coast were the lowest observed, <em>c</em>. 0.4–0.5 GPa. These rocks were probably affected by the same thermal pulse activity evident around Glen Clova. All three regions initially developed during regional metamorphism associated with thermal relaxation of tectonically overthickened crust. The eastern part of the sequence, including Glen Clova, is fundamentally different from the western part because it required additional advective heat input to achieve peak thermal conditions. This heat was probably supplied by synorogenic magmas (e.g. Newer Gabbros) and the associated elevated crustal heat flow.