Ordovician–Devonian intrusions of the Scottish Northern Highlands Terrane have piecemeal geochronology and contested geodynamic significance. We review existing geochronological data and present new in situ U–Pb zircon results from seven of these intrusions. Zircon growth predating emplacement is nearly ubiquitous, related to magma addition to the lower crust during Early Scandian compression. Emplacement ages, structures and petrology vary in relation to major geodynamic processes on the Laurentian margin in the context of Baltica, Ganderia and Avalonia accretion: (1) c . 450–432 Ma Iapetus subduction and back-arc magmatism; (2) c . 432–423 Ma Ganderia accretion, lithospheric foundering, Scandian metamorphism and sinistral transpression; (3) c . 423–415 Ma Late Scandian exhumation and decompression; (4) c . 415–380 Ma Acadian subduction and collision processes. Only c . 423–415 Ma magmatism resulted in production of high radiogenic heat production intrusions of geothermal exploration interest. There is considerable potential in constraining the extent and timing of pre-emplacement zircon growth to relate crustal tectonics and magmatism during orogenesis.
Particles of gold panned from two sites within the Duns area of the Southern Uplands of Scotland are larger by an order of magnitude than those previously reported from the adjacent Lammermuir Hills. The Southern Uplands-Down-Longford Terrane (SUDLT) is geologically diverse and potential local sources include orogenic, intrusion-related, red bed and palaeoplacer models. The populations at both sites are morphologically and microchemically similar. Morphogenetic analyses of the particles suggest that distances from source do not exceed 7.5 km. A minority of the particles panned (containing up to 99% Au with trace Pd, inclusions with Pd to 22.2 wt% and Hg to 13.7 wt%) were chemically identical to those previously reported from the adjacent terrane and attributed to red bed styles of gold mineralization. We also report the discovery of a stockwork, from where detrital gold contained Bi-Te inclusions, which suggests a local magmatic source. However, most of the particles had Ag contents of up to 46 wt%, more typical of an orogenic source. Favourable geochemical conditions within SUDLT basinal muds regionally may indicate that the basins in this terrane were fertile for the capture and concentration of orogenic gold.
Building on a knowledge-based prospectivity analysis conducted by the BGS in 2023, this study assessed the potential for sphalerite, galena, chalcopyrite and pyrite from the Leadhills and Wanlockhead Orefield (LWO), SW Scotland to host critical minerals.Utilizing SEM and LA-ICP-MS, sphalerite was found to be the primary host for Ga, Ge and Ag, while chalcopyrite was identified as the primary host for In, Se and Sn, and galena the primary host for Sb. For sphalerite, the geometric mean concentration of Ge was 200 ppm with a maximum value of 860 ppm. These values indicate significant enrichment of Ge in sphalerite relative to crustal abundances and are comparable to significant Ge-producing deposits like Red Dog, Alaska, and the formerly productive Noailhac-Saint Salvy deposit in France. Cadmium, Se and As were found to be hosted by sphalerite, chalcopyrite and pyrite, respectively. These elements are known to have detrimental effects on human health and ecological and environmental systems. A further orefield-wide assessment of mine waste material to fully document the occurrence of sphalerite in veins and mine waste is recommended.
The ossified remains of several species of tetrapodomorph are found in fossil material collected from a number of coal waste tips from the Scottish Lower Coal Measure Formation in the Midland Valley of Scotland. The recovered fossil material includes well-preserved disarticulated and isolated remains of the megalichthyid Megalichthys pygmaeus Traquair, 1890. Data were collated from an extensive examination of the recovered remains of Megalichthys pygmaeus and the dermal skull bones of Megalichthys hibberti Agassiz, 1835. A comparison study was undertaken encompassing this new information with morphological information acquired from other known megalichthyids, hence a full reconstruction and description of the dermal head of Megalichthys pygmaeus is presented. In addition, a new type specimen commensurate in stratigraphy and locality to that of Traquair's holotype is designated. The paper concludes with an assessment of the current taxonomic position of Megalichthys pygmaeus.
Small round holes or pits, Oichnus Bromley, are rare trace fossils in Mississippian shells, but are a locally common feature of crinoid pluricolumnals in some sites of the British Isles. Numerous examples have been found from mudrocks in the Brigantian (Mississippian) Blackhall Limestone, Lower Limestone Formation, at Trearne Quarry, near Beith, north Ayrshire. Until now, all have been assigned to Oichnus simplex Bromley. These trace fossils are typically associated with growth deformities of the pluricolumnals, which are commonly swollen and more rarely grow a lip around the pit. A new specimen, Oichnus isp. cf. O. paraboloides Bromley, adds to the ichnological diversity of Trearne Quarry. It is likely the spoor of a different producer to O. simplex. Oichnus isp. cf. O. paraboloides infests the stem of Rhabdocrinus scotocarbonarius (Wright) and is an elongate, rounded, slot-like depression with sloping sides. It infested the live crinoid as established by the swollen growth reaction of the stem.
A recent discovery of Brittaniclus rankini from below the Blackhall Limestone at Blairskaith Quarry, near Torrance is described and two old-collection specimens of Cyclidae from the Hurlet Limestone at Trearne, near Beith are re-evaluated. This is the first record of Brittaniclus from the Lower Limestone Formation. Brittaniclus is already well known from the Limestone Coal Formation (Serpukhovian, Carboniferous) of the Glasgow area and from the Glencartholm Volcanic Beds (Visean, Carboniferous) and appears to represent a free-swimming marine pancrustacean that is best preserved in non-marine lagoonal shales. One of the specimens from Trearne is incomplete and is here referred to Cyclus radialis due to the well-defined thoracic ridges on the dorsal carapace. The other specimen is the first record of a new species of Magnitocyclus, a genus which has previously only been found from the Visean to Serpukhovian of Russia. It is named here as M. trearnensis sp. nov.
Models of crustal growth must take account of areas of old crust which have been reworked in addition to the volume of juvenile crust generated. In this case study the Coire Uaigneich Granophyre in south-central Skye is viewed as a microcosm of the process of crustal reworking. Here we show that the granophyre is the product of the partial melting of Neoproterozoic Torridonian sandstone, triggered by the thermal energy from the Cuillins intrusion. Our evidence is based upon a study of areas of partial melting within xenoliths of Torridonian arkose in the granophyre and from the presence of restitic Proterozoic and Archean zircons in the granophyre. However, we find that the difference in composition between partial melts of fused Torridonian xenoliths and the granophyre itself suggests that the granophyre is the product of the mixing of two melts - one fused Torridonian and a more mafic melt, probably derived from the Cuillins intrusion. This view is supported by trace element modelling of the partial melting of Torridonian sandstone and the presence of a younger generation of euhedral, igneous-looking zircons in the granophyre which have a weighted average 206Pb/238U age of 58.92 +/- 0.06 Ma, identical to that of the Cuillins intrusion.
The Highland Border Complex (HBC; e.g. River North Esk, Stonehaven) is here interpreted as part of a Cambrian-Early Ordovician hyperextended continent-ocean transition zone that was tectonically emplaced onto the South Laurentian margin related to Early Ordovician collision with a volcanic arc to the SE (Midland Valley). All HBC units include terrigenous sediment. Basalts range from variably-enriched alkaline type (North Esk) to mid-ocean ridge-like (Stonehaven). They include radiolarian chert and hydrothermal metalliferous deposits. A local conglomerate with stretched clasts (North Esk) includes chert and ultramafic detritus with chromite. During and after emplacement, cross-cutting high-strain zones developed in response to progressive left-lateral or oblique ductile syn-metamorphic to brittle post-metamorphic stresses. Three main collision-related deformation events affected both the HBC and the adjacent Dalradian (North Esk), the first two under greenschist-facies metamorphic conditions. Following peak metamorphism, the HBC and Dalradian in the Highland Border rotated to near vertical (Downbend). After exhumation via orogenic collapse and/or erosion, the Lower Old Red Sandstone (LORS) transgressed the Highland Border. In the North Esk, the basal LORS (Devonian Lintrathen ignimbrite) unconformably overlies the HBC, precluding this contact as the Highland Boundary Fault. The North Esk Fault and Highland Boundary Fault (Stonehaven) can be broadly correlated as a long-lived crustal discontinuity.
The Dalradian Supergroup represents an important phase of Neoproterozoic sedimentation on the eastern margin of Laurentia, yet its early depositional history and palaeogeographical context remain incompletely understood. This study integrates lithostratigraphic, sedimentological and detrital zircon U-Pb data to refine correlations between the early Dalradian Supergroup of mainland Scotland and the Colonsay and Bowmore groups of the Inner Hebrides. Multidimensional scaling of detrital zircon age spectra, coupled with lithological and geochemical similarities, supports a threefold subdivision of the Colonsay Group that parallels the Glenshirra Group and the Corrieyairack and Glen Spean subgroups of the Grampian Group of the mainland Dalradian. Coarse fluvial-deltaic and alluvial fan deposits in the initial basin infill of the Colonsay Group yield unimodal Paleoproterozoic zircon populations dominated by local Makkovik-Ketilidian-Rhinnian basement sources, whereas younger shallow-marine sediments show increasing Grenville-aged input. These trends, mirrored in the Glenshirra and Grampian Group succession, suggest a shared tectonic regime and sediment routing system. The Bowmore Group, although tectonostratigraphically distinct, displays detrital zircon signatures comparable with the upper part of the Glen Spean Subgroup and early Appin Group of the Dalradian Supergroup. Collectively, the data support early Dalradian sedimentation within a foreland basin setting, potentially initiated during the mid-Tonian Knoydartian Orogeny. Shifts in the detrital zircon spectra are interpreted here to record a transition from proximal to more distal sediment sourcing in a flysch setting, the progressive infilling of topographic lows and the expansion of a molasse apron across eastern Laurentia.
The Victorian stonemason and polymath Hugh Miller's seminal 1841 book The Old Red Sandstone continues to attract critical acclaim due to its engaging delivery to the reader, of the science of geology as it was then understood, in eloquent and descriptive prose. Since Miller's time the study and elucidation of geological data have become far more sophisticated and focused but, due to the comparative lack of rigour in the formative years of the science, some of his explanations of the Middle Devonian geology and palaeontology of Cromarty have either become misunderstood or would benefit greatly from a refresh. Here we provide a chronology of Miller's early discoveries and his evolving understanding of Cromarty geology and how it impacted his contemporaries, and subsequent researchers and the history of geological science. In particular, the work of his son, as a surveyor with the British Geological Survey, is described in the context of his role in Cromarty geology. We re-evaluate the literature, which, in concert with fieldwork dating back to 1991, provides an up-to-date reconciliation of the Middle Devonian geology of the Cromarty area generally, including its historically and scientifically important fossil-bearing fishbeds.
A newly discovered specimen of potential fish Mortichnia is described from the Middle Devonian Achanarras Limestone Member (Lower Caithness Flagstone Subgroup, NE Scotland). Fish trace fossils have previously been reported only rarely from the Achanarras Limestone Member, despite the wealth of fish specimens recovered from the world famous Achanarras Quarry, Caithness, Scotland. The trace comprises curved grooves or furrows to the rear of the fossil remains of a juvenile Pterichthyodes fish.
The studied succession, located on Mainland Orkney and the island of Westray lies in cyclic flagstones of Middle Devonian lake laminites. The lake bed of each cycle is constrained above and below by marginal lake facies that reflect a transition from open playa to permanent lake and vice versa, referred to as transition sequences. Abundant sedimentary structures in these sequences, previously described as subaqueous shrinkage cracks or subaqueous cracks are reinterpreted as gypsum pseudomorphs. The study shows the small structures to have prismatic, lensoid and clustered forms of gypsum in graded stages of growth and supports a new perception of the palaeoclimate and its close interdependence with periodic gypsum growth. A lake model reconstruction of lake floor morphology and its link to seasonal palaeoclimate illustrates the case for the presence of limited size pseudomorphs. It is suggested that the occurrence of consistently small pseudomorphs is a consequence of a strongly regular, wet/dry tropical monsoon palaeoclimate, coupled with an extremely low gradient lake floor, allowing short-term gypsum growth in strongly evaporating conditions across widely oscillating lake shorelines, the remarkable preservation of pseudomorphs being a consequence of dolomitization.
Trearne Quarry in north Ayrshire, south-west Scotland, is a Brigantian (Mississippian) age Site of Special Scientific Interest (SSSI) with a diverse marine biota. The crinoids are notable, many species being known from well-preserved cups and columns showing pitted infestations. The horizon considered herein is named, informally, the Ureocrinus bockschii bed. The named species is a dendrocrinidea cladid that is the most common species from this site. The calyx seems to have had an inherent robustness as they are more common than any other crinoid species. The U. bockschii bed yields only rare disarticulated calyx plates of other crinoid species. Pits, Oichnus simplex Bromley, in stems are more likely to be domiciles of unmineralized infesting organisms rather than evidence for gastropod parasitism or predation. Crinoid attachment structures are rare. The associated fauna is limited, including brachiopods, corals ( Othoceras sp.), bryozoans ( Rhabdomeson sp.), the bellerophontid Euphemites urii (Fleming) and rare fishes, Petalodus acuminatus (Agassiz).
Two malacostracan crustacean genera are described from the Langsettian (upper part of the Bashkirian, Lower Pennsylvanian) of the Scottish coal fields in the Midland Valley of Scotland. One is the youngest occurrence of TealliocarisPeach, 1908 and was found at Polkemmet Colliery near Whitburn, West Lothian. It is recognized as a new species, Tealliocaris elliotti, based on the presence of eight spines on its scaphocerites and lateral convergent carinae of the telson. The other crustacean is a unique specimen from the Ardenrigg Colliery at Wester Bracco, North Lanarkshire in similar shales of Langsettian age. There are no distinguishing characters preserved that would identify it as a new species, but it can be placed in PalaeocarisMeek and Worthen, 1865 based on the well-preserved features of the tail fan. This is the first record of this genus in Scotland, although specimens of Minicaris brandiSchram, 1979 from the Namurian (Serpukhovian, Upper Mississippian) shales of Bearsden are now here also considered to be a species of Palaeocaris.
A geochronological and isotopic study grounded by field observations is presented on the southern-most Lewisian orthogneisses of Iona, southwest Scotland. Syenitic orthogneisses in western Iona and granodioritic orthogneisses in the east have yielded indistinguishable SIMS U-Pb zircon c . 2710 Ma protolith ages, among the youngest recorded from the Lewisian. Whole-rock Sm-Nd and zircon Lu-Hf data indicate largely juvenile Neoarchaean crustal additions. Based on this evidence, a north-south trending mylonite zone separating eastern and western Iona is unlikely to be a terrane boundary. Extensive reworking during the “late Laxfordian” deformational event between 1779-1753 Ma (bracketed between pre-tectonic migmatisation and post-tectonic granitic pegmatite intrusion) likely corresponds to accretion of the Rhinns Complex to the Nuna/ Columbia supercontinent. Zircon Lu-Hf data indicate that late Laxfordian melts were largely derived from the Neoarchaean orthogneisses. K-feldspar Pb isotope ratios in the orthogneisses have likely been reset during late Laxfordian metamorphism while those in a post-tectonic syenitic pegmatite, with a U-Pb zircon age of 1688 ± 8 Ma are considered to be original and consistent with an exotic source. Correlation of the Iona Lewisian with Coll and Tiree is possible but the younger age of the Iona orthogneisses does not support correlation with the Rona terrane.
There is little known of the diversity of Silurian crinoids in Scotland. Rather than wait in hope for a new Lagerst & auml;tte, our knowledge of the fauna can be improved by recognizing imperfectly preserved specimens, such as disarticulated columnals. Pentagonopentagonalis (col.) annulus sp. nov. is here recorded from the Llandovery (Rhuddanian) Mulloch Hill Sandstone Formation of Ayrshire. It is known only from disarticulated columnals, most without counterpart, and rare pluricolumnals. The column is xenomorphic, and columnals can vary from pentagonal (probably proximal) to rounded or circular (more distal?), each with a moderately broad lumen that is similarly shaped. There is no areola and the articulation is radial symplectial. Pluricolumnals are heteromorphic, perhaps N3231323. This morphospecies is described to demonstrate something of the wealth of information and inference that may be gleaned from even the most unpromising material.
Silicate weathering is a natural regulator of atmospheric carbon dioxide (CO 2 ), where the majority of carbonate is stored in the oceans. In some instances, carbonates may form via bedrock weathering in terrestrial landscapes, but this is commonly noted in ultramafic rock due to its desirable mineralogy. In Northwest Scotland, carbonate minerals surround felsic, intermediate, and mafic igneous bedrock. Their abundance suggests that these rocks could potentially be targeted for carbonation, given the absence of other known cation sources nearby. We present geochemical and mineralogical data for bedrock samples and mineralogy and stable carbon and oxygen isotope data for the carbonate samples. Whole rock geochemistry demonstrates that major abundancies of CaO and MgO are present in the bedrock samples and would be sourced from plagioclase and pyroxene minerals which are target minerals for CO 2 mineralisation. The stable carbon and oxygen isotope data demonstrate that there are likely mixed carbon sources (atmospheric and organic), while other environmental factors including temperature, CO 2 degassing/ evaporation, and nearby waters influence the isotopic composition. Results suggest that rocks traditionally overlooked in CO 2 mineralisation studies have the potential to serve as a feedstock for carbonation, given the abundance of secondary carbonates found in NW Scotland.
In 1860 Pander described a new species of fish from the Givetian of Scotland using the invalid name Osteolepis microlepidotus, which was a synonym of Osteolepis macrolepidotus. In 1948 Jarvik published a monograph on this fish, giving it the name Osteolepis panderi. However, he did not designate a type specimen or a type locality. This was due to Jarvik's mistake in thinking he had to choose a specimen from one of the specimens used by Pander and being unable to view Pander's collection in Saint Petersburg (then Leningrad) owing to World War II and the subsequent Cold War. Osteolepis microlepidotus first appeared in print in 1829, but Sedgwick and Murchison's description was inadequate for erecting a species. Shortly after, Agassiz described specimens of O. microlepidotus, which were later shown to be specimens of O. macrolepidotus. Jarvik should have chosen one of the specimens he used as he erected the species O. panderi. After a seven-decade delay NMS G.1903.130.35 in the National Museums of Scotland is chosen as the lectotype from the many specimens used by Jarvik in his description of the species. Skinnet Farm Quarry in Caithness, Scotland is also chosen as type locality for this species.
Two species of the closely related monobathrid crinoid from the Lower Paleozoic of Scotland, namely Macrostylocrinus cirrifer Ramsbottom (Upper Ordovician, Katian) and Macrostylocrinus silurocirrifer Brower (Lower Silurian, Telychian), are similar in having elongate, unbranched radices proximally. These were not cirri, as suggested by their names, but were radices that were more or less inflexible, lacking contractile tissues. The function of these radices was uncertain. In the absence of contractile tissues, they could not have been for grasping other upright structures and crinoids do not need help to balance, their posture being maintained by mutable collagenous tissues. It is possible, but unlikely, that they may have acted to direct feeding currents towards the crown. Most probably, in an analogy to the post-Paleozoic isocrinids, the stem acted like a ‘conveyor belt’, the proximal, radicular and upright part being carried away from the cup as further columnals are inserted, eventually forming a distal, recumbent attachment structure. The elongate radices would have stabilized the dististele, but, unlike isocrinids, the arms of Macrostylocrinus spp. were not adapted for crawling and thus escaping predators. Both M. silurocirrifer (type species) and M. cirrifer are included in Macrostylocrinus ( Scotimacrostylocrinus ) subgen. nov.
The Lealt Shale Formation is known for its superb preservation of aragonitic molluscs. As fish otoliths are primarily composed of aragonite, and because of the semi-stable nature of this polymorph, records of otoliths become increasingly rare in deep time. Therefore, the Lealt Shale Formation provides a window through which to expand knowledge of Middle Jurassic otoliths. A total of 753 otoliths have been collected, representing 10 species: three in Archaeotolithus, five in Leptolepis, one Archengraulis and a teleost incertae sedis (juveniles only). Four species are new: Archaeotolithus eiggensis, Archaeotolithus invernizziae, Leptolepis flexuosus and Leptolepis skyensis. Two species remain in open nomenclature and the remaining species are known from the Middle Jurassic of southern England and continental Europe: Archaeotolithus doppelsteini, Leptolepis densus, Leptolepis rotundatus and Archengraulis productus. The Lealt Shale Formation was deposited in a low-salinity lagoonal environment with variable freshwater influx and a probably tenuous link to marine waters, resulting in a complex palaeosalinity history. The relevance of the specific environment for the composition of the fish fauna as documented by otoliths is discussed. The evolution of the otolith morphospace during the Jurassic is discussed in the light of the new finds.
