cometadata/datacite-titles-descriptions-related-identifiers huggingface dataset:
DOI: 10.6084/m9.figshare.3454958
title: LISPB DELTA, a lithospheric seismic profile in Britain: analysis and interpretation of the Wales and southern England section

description: The Lithospheric Seismic Profile in Britain (LISPB), shot in 1974, included a 310 km profile LISPB DELTA, crossing the Palaeozoic Welsh Basin, the western extent of the Midland microcraton and the Cornubian zone of southern England. This first comprehensive analysis of these data has produced a sub-horizontally layered seismic and associated gravity model that correlates well with surface geology. A north–south decrease in crustal velocity and density corresponds to the change from Avalonian crust into the Rheno-Hercynian zone at the south end of the profile. High velocities and densities in the lowest crustal layer beneath north Wales are proposed to result from Cenozoic and possibly Ordovician igneous intrusive rocks, the former derived from an upwelling plume associated with the opening of the North Atlantic. Examination of the load distribution throughout the model shows that it is strongly correlated with the earthquake distribution along LISPB DELTA. Earthquake focal depth also correlates with heat flow. A simple heat-flow profile has been derived, and the seismic velocity model used to constrain crustal heat production values. A long-wavelength excursion from published data can be explained in terms of an increase in mantle heat flow resulting from a previously identified deep thermal anomaly beneath the Irish Sea.
DOI: 10.6084/m9.figshare.3454958.v1
title: LISPB DELTA, a lithospheric seismic profile in Britain: analysis and interpretation of the Wales and southern England section

description: The Lithospheric Seismic Profile in Britain (LISPB), shot in 1974, included a 310 km profile LISPB DELTA, crossing the Palaeozoic Welsh Basin, the western extent of the Midland microcraton and the Cornubian zone of southern England. This first comprehensive analysis of these data has produced a sub-horizontally layered seismic and associated gravity model that correlates well with surface geology. A north–south decrease in crustal velocity and density corresponds to the change from Avalonian crust into the Rheno-Hercynian zone at the south end of the profile. High velocities and densities in the lowest crustal layer beneath north Wales are proposed to result from Cenozoic and possibly Ordovician igneous intrusive rocks, the former derived from an upwelling plume associated with the opening of the North Atlantic. Examination of the load distribution throughout the model shows that it is strongly correlated with the earthquake distribution along LISPB DELTA. Earthquake focal depth also correlates with heat flow. A simple heat-flow profile has been derived, and the seismic velocity model used to constrain crustal heat production values. A long-wavelength excursion from published data can be explained in terms of an increase in mantle heat flow resulting from a previously identified deep thermal anomaly beneath the Irish Sea.
DOI: 10.6084/m9.figshare.3454955
title: Isotope geochemistry and revised geochronology of the Purrido Ophiolite (Cabo Ortegal Complex, NW Iberian Massif): Devonian magmatism with mixed sources and involved Mesoproterozoic basement

description: In the Purrido Ophiolite (Cabo Ortegal Complex), new U–Pb zircon dating of the amphibolite G03-8 (by laser ablation inductively coupled plasma mass spectrometry) confirms the existence of a dominant Mesoproterozoic zircon population with a refined age of 1155 ± 14 Ma. However, the U–Pb zircon dating of two more amphibolite samples (by sensitive high-resolution ion microprobe) has provided new ages of 395 ± 3 Ma and 395 ± 2 Ma, respectively, interpreted as the crystallization age. Hf isotope data for zircon show that most of the Devonian zircons crystallized from a juvenile depleted mantle source. The Mesoproterozoic zircons have relatively juvenile Hf isotopic composition reflecting some influence of an older component. A few Devonian zircon crystals show evidence of mixing with an older component represented by the Mesoproterozoic zircons. The whole-rock Sm–Nd isotope data indicate an important heterogeneity in the composition of the Purrido amphibolites, only compatible with the generation of their protoliths from two sources. We interpret these puzzling data as resulting from the mixing of a Devonian mantle-derived magma with a Mesoproterozoic basement. These new data provide new perspectives in the interpretation of the most common ophiolites across the Variscan suture in Europe.
DOI: 10.6084/m9.figshare.3454952
title: Provenance and exhumation of an exotic eclogite-bearing nappe in the Caledonides: a U–Pb and Rb–Sr study of the Jæren nappe, SW Norway

description: The provenance and exhumation history of paragneisses that enclose the 471–458 Ma eclogites in the Caledonian Jæren nappe, SW Norway, were constrained by performing U–Pb analysis on detrital zircon and Rb–Sr dating of mica. Zircon grains from four samples were analysed by laser ablation inductively coupled plasma mass spectrometry, providing detrital U–Pb ages between 3130 and 620 Ma. These data suggest Laurentian provenance, implying the existence of an early Caledonian (Taconian) HP fragment of Laurentian crust in the southern Scandinavian Caledonides. Several rims and recrystallized zircon patches yielded U–Pb ages averaging at 469 ± 6 Ma (2σ). These are identical to the Lu–Hf ages of the eclogites and underscore the importance of Taconian metamorphism in this part of the Caledonides. The main phengite Rb–Sr age cluster at 424.4 ± 4.6 Ma provides time constraints on the amphibolite-facies recrystallization of former high-Si phengite. Five out of seven biotite Rb–Sr ages were identical, yielding a weighted mean age of 413.6 ± 2.6 Ma. Low-Si phengite and biotite in three samples gave <em>c</em>. 400 Ma ages. The Rb–Sr data record the mid-crustal emplacement of the exotic Jæren nappe and its subsequent unroofing along the western edge of Baltica during the backsliding and collapse of the Scandian orogenic front.
DOI: 10.6084/m9.figshare.3454952.v1
title: Provenance and exhumation of an exotic eclogite-bearing nappe in the Caledonides: a U–Pb and Rb–Sr study of the Jæren nappe, SW Norway

description: The provenance and exhumation history of paragneisses that enclose the 471–458 Ma eclogites in the Caledonian Jæren nappe, SW Norway, were constrained by performing U–Pb analysis on detrital zircon and Rb–Sr dating of mica. Zircon grains from four samples were analysed by laser ablation inductively coupled plasma mass spectrometry, providing detrital U–Pb ages between 3130 and 620 Ma. These data suggest Laurentian provenance, implying the existence of an early Caledonian (Taconian) HP fragment of Laurentian crust in the southern Scandinavian Caledonides. Several rims and recrystallized zircon patches yielded U–Pb ages averaging at 469 ± 6 Ma (2σ). These are identical to the Lu–Hf ages of the eclogites and underscore the importance of Taconian metamorphism in this part of the Caledonides. The main phengite Rb–Sr age cluster at 424.4 ± 4.6 Ma provides time constraints on the amphibolite-facies recrystallization of former high-Si phengite. Five out of seven biotite Rb–Sr ages were identical, yielding a weighted mean age of 413.6 ± 2.6 Ma. Low-Si phengite and biotite in three samples gave <em>c</em>. 400 Ma ages. The Rb–Sr data record the mid-crustal emplacement of the exotic Jæren nappe and its subsequent unroofing along the western edge of Baltica during the backsliding and collapse of the Scandian orogenic front.
DOI: 10.6084/m9.figshare.3454943
title: Enhancing tectonic and provenance information from detrital zircon studies: assessing terrane-scale sampling and grain-scale characterization

description: Determining detrital zircon U–Pb ages has become the method of choice for single- mineral-based provenance studies focused on the identification of potential source regions of siliciclastic sediments. Advances in microanalytical methods have significantly accelerated the acquisition rate of U–Pb ages, thus allowing for more statistically significant zircon age datasets to be acquired than previously. However, several studies have demonstrated limitations of relying solely on detrital zircon as a provenance proxy. To further assess the utility of this provenance indicator we measured U–Pb ages of detrital zircon derived from modern sediment collected from the French Broad River and its tributaries that drain portions of the Appalachian Orogen in southeastern USA. The results demonstrate that significant detrital zircon age variations occur along the length of the river. The age variations suggest that characterization of entire sedimentary formations by analysis of single samples may be misleading and that a multiple-sample approach is required. In addition, by incorporating high-magnification cathodoluminescence images with Th/U for each detrital grain, a more robust interpretation can be made regarding zircon source.
DOI: 10.6084/m9.figshare.3454943.v1
title: Enhancing tectonic and provenance information from detrital zircon studies: assessing terrane-scale sampling and grain-scale characterization

description: Determining detrital zircon U–Pb ages has become the method of choice for single- mineral-based provenance studies focused on the identification of potential source regions of siliciclastic sediments. Advances in microanalytical methods have significantly accelerated the acquisition rate of U–Pb ages, thus allowing for more statistically significant zircon age datasets to be acquired than previously. However, several studies have demonstrated limitations of relying solely on detrital zircon as a provenance proxy. To further assess the utility of this provenance indicator we measured U–Pb ages of detrital zircon derived from modern sediment collected from the French Broad River and its tributaries that drain portions of the Appalachian Orogen in southeastern USA. The results demonstrate that significant detrital zircon age variations occur along the length of the river. The age variations suggest that characterization of entire sedimentary formations by analysis of single samples may be misleading and that a multiple-sample approach is required. In addition, by incorporating high-magnification cathodoluminescence images with Th/U for each detrital grain, a more robust interpretation can be made regarding zircon source.
DOI: 10.6084/m9.figshare.3454940
title: A refined chronology for the Cambrian succession of southern Britain

description: Three dated (U–Pb, zircon) ash beds from biostratigraphically constrained Avalonian successions of Shropshire (England) and Pembrokeshire (Wales) delimit the traditional ‘Lower'–‘Middle' Cambrian boundary and resolve a problematic regional correlation. In Shropshire, a date of 514.45 ± 0.36 [0.81 including tracer calibration and <sup>238</sup>U decay constant errors] Ma from near the top of the Lower Comley Sandstone Formation provides a maximum age for the boundary between Cambrian Stages 3 and 4, and a date of 509.10 ± 0.22 [0.77 including tracer calibration and <sup>238</sup>U decay constant errors] Ma from the basal Quarry Ridge Grits, Upper Comley Sandstone Formation, provides a minimum age for the boundary between Cambrian Stages 4 and 5 (and thus Series 2 and 3). These dates offer a calibration of early metazoan evolution by directly constraining the age of the intervening Comley Limestones, which contain diverse small shelly fossils in addition to trilobites, and also a key early occurrence of exceptional, three-dimensionally preserved arthropods. In Pembrokeshire, an ash bed from the Caerfai Bay Shales Formation dates to 519.30 ± 0.23 [0.77 including tracer calibration and <sup>238</sup>U decay constant errors] Ma, equivalent to a horizon low in the Lower Comley Sandstone Formation of Shropshire, possibly around the level at which trilobites make their first local appearance.
DOI: 10.6084/m9.figshare.3454940.v1
title: A refined chronology for the Cambrian succession of southern Britain

description: Three dated (U–Pb, zircon) ash beds from biostratigraphically constrained Avalonian successions of Shropshire (England) and Pembrokeshire (Wales) delimit the traditional ‘Lower'–‘Middle' Cambrian boundary and resolve a problematic regional correlation. In Shropshire, a date of 514.45 ± 0.36 [0.81 including tracer calibration and <sup>238</sup>U decay constant errors] Ma from near the top of the Lower Comley Sandstone Formation provides a maximum age for the boundary between Cambrian Stages 3 and 4, and a date of 509.10 ± 0.22 [0.77 including tracer calibration and <sup>238</sup>U decay constant errors] Ma from the basal Quarry Ridge Grits, Upper Comley Sandstone Formation, provides a minimum age for the boundary between Cambrian Stages 4 and 5 (and thus Series 2 and 3). These dates offer a calibration of early metazoan evolution by directly constraining the age of the intervening Comley Limestones, which contain diverse small shelly fossils in addition to trilobites, and also a key early occurrence of exceptional, three-dimensionally preserved arthropods. In Pembrokeshire, an ash bed from the Caerfai Bay Shales Formation dates to 519.30 ± 0.23 [0.77 including tracer calibration and <sup>238</sup>U decay constant errors] Ma, equivalent to a horizon low in the Lower Comley Sandstone Formation of Shropshire, possibly around the level at which trilobites make their first local appearance.
DOI: 10.6084/m9.figshare.3454937
title: Neoproterozoic loess and limits to snowball Earth

description: Neoproterozoic tillites overlain by limestones and dolostones (cap carbonates) have been interpreted as evidence of abrupt climate change from glaciers to tropical seas on the assumption that cap carbonates were marine. This assumption is here challenged by evidence for loess deposition of the Nuccaleena Formation of South Australia from granulometry (angular, randomly oriented, silt, modal diameter 7ϕ) and sedimentary structures (climbing-translatent cross-stratification, linear dunes). In addition, a variety of palaeosols in the Nuccaleena Formation have red clayey horizons, replacive micritization, expansion cracks, and thufur mounds, as well as low carbon and oxygen isotope values, high strontium isotope ratios, and geochemical evidence of leaching and clay formation. This cap carbonate has no definitively marine features, and is here interpreted as periglacial loess overlying the fluvioglacial–intertidal Elatina Formation, so it is not a record of abrupt global warming from snowball Earth. Other cap carbonates around the world differ in various ways, and may have formed in different depositional environments, but could profitably be reconsidered from the new perspective of the loess depositional model proposed here.
DOI: 10.6084/m9.figshare.3454937.v1
title: Neoproterozoic loess and limits to snowball Earth

description: Neoproterozoic tillites overlain by limestones and dolostones (cap carbonates) have been interpreted as evidence of abrupt climate change from glaciers to tropical seas on the assumption that cap carbonates were marine. This assumption is here challenged by evidence for loess deposition of the Nuccaleena Formation of South Australia from granulometry (angular, randomly oriented, silt, modal diameter 7ϕ) and sedimentary structures (climbing-translatent cross-stratification, linear dunes). In addition, a variety of palaeosols in the Nuccaleena Formation have red clayey horizons, replacive micritization, expansion cracks, and thufur mounds, as well as low carbon and oxygen isotope values, high strontium isotope ratios, and geochemical evidence of leaching and clay formation. This cap carbonate has no definitively marine features, and is here interpreted as periglacial loess overlying the fluvioglacial–intertidal Elatina Formation, so it is not a record of abrupt global warming from snowball Earth. Other cap carbonates around the world differ in various ways, and may have formed in different depositional environments, but could profitably be reconsidered from the new perspective of the loess depositional model proposed here.
DOI: 10.6084/m9.figshare.3454931
title: Tectonic escape of a crustal fragment during the closure of the Rheic Ocean: U–Pb detrital zircon data from the Late Palaeozoic Pulo do Lobo and South Portuguese zones, southern Iberia

description: The Pulo do Lobo Zone, which crops out immediately north of the allochthonous South Portuguese Zone in southern Iberia, is classically interpreted as a polydeformed accretionary complex developed along the southern margin of the Gondwanan parautochthon (Ossa–Morena Zone), during the late Palaeozoic closure of the Rheic Ocean. This closure was a major event during the amalgamation of Pangaea. U–Pb laser ablation inductively coupled mass spectrometry dating of detrital zircons from late Palaeozoic Devono-Carboniferous clastic units in the South Portuguese Zone and Pulo do Lobo Zone yield contrasting age populations and attest to the exotic nature of both zones. Detrital zircons from the South Portuguese Zone display populations typical of detritus derived from either Gondwana (Ossa–Morena Zone), or peri-Gondwanan terranes. In contrast, rocks from the Pulo do Lobo Zone contain populations consistent with derivation from Baltica, Laurentia or recycled early Silurian deposits along the Laurentian margin. An example of one such deposit is the Southern Uplands terrane of the British Caledonides. Taken together, these data can be reconciled by a model involving tectonic transport of a crustal fragment that was laterally equivalent to the Southern Uplands terrane between the allochthonous South Portuguese Zone and Gondwana as a result of an early Devonian collision between an Iberian indenter with Laurussia.
DOI: 10.6084/m9.figshare.3454931.v1
title: Tectonic escape of a crustal fragment during the closure of the Rheic Ocean: U–Pb detrital zircon data from the Late Palaeozoic Pulo do Lobo and South Portuguese zones, southern Iberia

description: The Pulo do Lobo Zone, which crops out immediately north of the allochthonous South Portuguese Zone in southern Iberia, is classically interpreted as a polydeformed accretionary complex developed along the southern margin of the Gondwanan parautochthon (Ossa–Morena Zone), during the late Palaeozoic closure of the Rheic Ocean. This closure was a major event during the amalgamation of Pangaea. U–Pb laser ablation inductively coupled mass spectrometry dating of detrital zircons from late Palaeozoic Devono-Carboniferous clastic units in the South Portuguese Zone and Pulo do Lobo Zone yield contrasting age populations and attest to the exotic nature of both zones. Detrital zircons from the South Portuguese Zone display populations typical of detritus derived from either Gondwana (Ossa–Morena Zone), or peri-Gondwanan terranes. In contrast, rocks from the Pulo do Lobo Zone contain populations consistent with derivation from Baltica, Laurentia or recycled early Silurian deposits along the Laurentian margin. An example of one such deposit is the Southern Uplands terrane of the British Caledonides. Taken together, these data can be reconciled by a model involving tectonic transport of a crustal fragment that was laterally equivalent to the Southern Uplands terrane between the allochthonous South Portuguese Zone and Gondwana as a result of an early Devonian collision between an Iberian indenter with Laurussia.
DOI: 10.6084/m9.figshare.3454928
title: Fjord systems and archives: a review

description: Fjords are glacially over-deepened semi-enclosed marine basins, typically with entrance sills separating their deep waters from the adjacent coastal waters which restrict water circulation and thus oxygen renewal. The location of fjords is principally controlled by the occurrence of ice sheets, either modern or ancestral. Fjords are therefore geomorphological features that represent the transition from the terrestrial to the marine environment and, as such, have the potential to preserve evidence of environmental change. Typically, most fjords have been glaciated a number of times and some high-latitude fjords still possess a resident glacier. In most cases, glacial erosion through successive glacial/interglacial cycles has ensured the removal of sediment sequences within the fjord. Hence the stratigraphic record in fjords largely preserves a glacial-deglacial cycle of deposition over the last 18 ka or so. Sheltered water and high sedimentation rates have the potential to make fjords ideal depositional environments for preserving continuous records of climate and environmental change with high temporal resolution. In addition to acting as high-resolution environmental archives, fjords can also be thought of as mini-ocean sedimentary basin laboratories. Fjords remain an understudied and often neglected sedimentary realm. With predictions of warming climates, changing ocean circulation and rising sea levels, this volume is a timely look at these environmentally sensitive coastlines.
DOI: 10.6084/m9.figshare.3454928.v1
title: Fjord systems and archives: a review

description: Fjords are glacially over-deepened semi-enclosed marine basins, typically with entrance sills separating their deep waters from the adjacent coastal waters which restrict water circulation and thus oxygen renewal. The location of fjords is principally controlled by the occurrence of ice sheets, either modern or ancestral. Fjords are therefore geomorphological features that represent the transition from the terrestrial to the marine environment and, as such, have the potential to preserve evidence of environmental change. Typically, most fjords have been glaciated a number of times and some high-latitude fjords still possess a resident glacier. In most cases, glacial erosion through successive glacial/interglacial cycles has ensured the removal of sediment sequences within the fjord. Hence the stratigraphic record in fjords largely preserves a glacial-deglacial cycle of deposition over the last 18 ka or so. Sheltered water and high sedimentation rates have the potential to make fjords ideal depositional environments for preserving continuous records of climate and environmental change with high temporal resolution. In addition to acting as high-resolution environmental archives, fjords can also be thought of as mini-ocean sedimentary basin laboratories. Fjords remain an understudied and often neglected sedimentary realm. With predictions of warming climates, changing ocean circulation and rising sea levels, this volume is a timely look at these environmentally sensitive coastlines.