Southern Uplands Research Articles

CLARKSON E. & UPTON B. 2006. Edinburgh Rock. The Geology of Lothian. xvi + 239 pp. Edinburgh: Dunedin Academic Press. Price £17.95 (hard covers). ISBN 1 903765 39 0

The late 18th century ‘Edinburgh Enlightenment’ was a remarkable period of intellectual development in many fields of science, but it was the progress in geological understanding, initiated by James Hutton and colleagues, that justifies the city’s claim to be the birthplace of the modern discipline. It is tempting to think that the particular interest in geology was fostered by the setting in which enlightenment occurred, the stone-built, older parts of Edinburgh nestling beneath a spectacular, rugged backdrop. In Edinburgh Rock due homage is paid to the city’s geological heritage, but the authors extend their brief across its Lothian hinterland to present a broader picture. Thus the archetypal Edinburgh rocks – the volcanic masses of Castle Rock and Arthur’s Seat, the latter spectacularly cross-cut by the Salisbury Crags sill – are integrated with other well-known localities such as Hutton’s Unconformity on the East Lothian coast and the renowned fossil localities of West Lothian. In the process the reader is taken through 450 million years of Earth history, from the Ordovician strata of the Southern Uplands to the glacial deposits of the Quaternary ice age. Euan Clarkson and Brian Upton are well placed to tell the story. Both are eminent Edinburgh academics but with a long history of support for local amateur societies …

Using prey densities to estimate the potential size of reintroduced populations of Eurasian lynx

In previous centuries human activities had a profound effect on the distribution of Eurasian lynx ( Lynx lynx) in Europe. The species has since been reintroduced to several areas but still much former range remains unoccupied. A relatively poor coloniser, it is likely that further reintroductions will be required to restore the species to potentially suitable areas. However, in the human-modified landscapes of Europe, where extensive wooded habitats are often fragmented, it is important to assess the potential lynx population size that could be supported in the available habitat. A previous study identified two networks of potential lynx habitat in Scotland. The present study further explores the feasibility of reintroducing lynx to Scotland by estimating the potential population size for the identified habitat by considering the availability of prey. An examination of lynx and wild ungulate densities from four areas in Europe, revealed a highly significant relationship between lynx density and the density of ungulate biomass. Based on the biomass represented by the densities of roe, red, sika and fallow deer occurring in two potential lynx habitat networks in Scotland, it was predicted that habitat in the Highlands could support 2.63 lynx 100 km −2, while the Southern Uplands could support 0.83 lynx 100 km −2. Applied to the amount of identified habitat, it is estimated that a Highlands habitat network could support around 400 lynx, and a Southern Uplands network, around 50. Scotland could support a large population of Eurasian lynx, which at current estimates, would be the fourth largest in Europe.

Palaeomagnetism of the Loch Doon Granite Complex, Southern Uplands of Scotland: The Late Caledonian palaeomagnetic record and an Early Devonian episode of True Polar Wander

The Southern Uplands terrane is an Ordovician–Silurian back-arc/foreland basin emplaced at the northern margin of the Iapetus Ocean and intruded by granite complexes including Loch Doon (408.3 ± 1.5 Ma) during Early Devonian times. Protracted cooling of this 130 km 3 intrusion recorded magnetic remanence comprising a predominant (‘A’) magnetisation linked to initial cooling with dual polarity and mean direction D / I = 237 / 64° ( α 95 = 4°, palaeopole at 316°E, 21°N). Subsidiary magnetisations include Mesozoic remanence correlating with extensional tectonism in the adjoining Irish Sea Basin (‘B’, D / I = 234/− 59°) and minority populations (‘C’, D / I = 106/− 2° and ‘D’, D / I = 199/1°) recording emplacement of younger (∼ 395 Ma) granites in adjoining terranes and the Variscan orogenic event. The ‘A’ directions have an arcuate distribution identifying anticlockwise rotation during cooling. A comparable rotation is identified in the Orthotectonic Caledonides to the north and the Paratectonic Caledonides to the south following closure of Iapetus. Continental motion from midsoutherly latitudes (∼ 40°S) at 408 Ma to equatorial palaeolatitudes by ∼ 395 Ma is identified and implies minimum rates of continental movement between 430 and 390 Ma of 30–70 cm/year, more than double maximum rates induced by plate forces and interpreted as a signature of true polar wander. Silurian–Devonian palaeomagnetic data from the British–Scandinavian Caledonides define a 430–385 Ma closed loop comparable to the distributed contemporaneous palaeomagnetic poles from Gondwana. They reconcile pre-430 Ma and post-380 Ma APW from this supercontinent and show that Laurentia–Baltica–Avalonia lay to the west of South America with a relict Rheic Ocean opening to the north which closed to produce Variscan orogeny by a combination of pivotal closure and right lateral transpression.

The landscape context of the Antonine Wall: a review of the literature

The landscape, environmental and land use changes before, during and after Antonine occupation are examined for the region of central Scotland between the Southern Uplands and the Grampian Highlands, principally from the published literature. The purpose is to synthesize and make available a range of new palaeoenvironmental data, to evaluate critically these new data-sets, to search for significant shifts in landscape or land use and to characterize their timings and effects, thus placing the Antonine occupation in a coherent landscape context. It is established that economic expansion in the region occurred in the later Iron Age, demonstrably before Roman military occupation. This expansion developed from Bronze Age and earlier Iron Age small-scale farms and gathered pace in the last cal 200–300 years BC, for crop growing as well as pasture, and was continued rather than intensified in the first two centuries cal AD. It is difficult to see differences in this economic expansion north and south of the Antonine Wall itself, or east and west of the Forth–Clyde isthmus, but it is tentatively suggested that in the foothills of the Southern Uplands the Romans entered a landscape already decaying. Roman influence is perhaps recognizable at some localities in a reduction of cereal production and the expansion of grazed pasture, assumed to represent a restructuring of the native economy to support a new market. It is presumed that imports of foodstuffs continued to be important to Roman forces during Antonine occupation, although possible reconstructions of the sediments in the Forth and Clyde estuaries suggest these may not have provided ideal harbours. There is little evidence that this increased pastoral economy imposed stresses on soils or plant communities, and the market seems to have been readily supplied within the agricultural capacity of the landscape. Nevertheless, the native economy was probably artificially buoyed by the Roman presence, and withdrawal eventually led to what is best described as an agricutural recession, not population collapse.

The electric field in northern England and southern Scotland: implications for geomagnetically induced currents

SUMMARY Magnetotelluric (MT) data, in the form of MT tensors, are used to estimate directly the size and spatial distribution of the electric field in northern England and southern Scotland with the aim of predicting the flow of geomagnetically induced currents (GIC) in power networks in the region. MT and Geomagnetic Deep Sounding data from a number of different field campaigns, at a period of 750 s, are employed. The MT data are cast in the form of telluric vectors, which allow a joint hypothetical event analysis (HEA) of both Geomagnetic Deep Sounding and MT data. This analysis reveals qualitatively the pervasive effects of electric field distortion in the region. Two approaches are taken to understand how the spatial structure of the regional electromagnetic field is affected by local distortions, and what the origin of these distortions might be. The dimensionality, and form of electric field distortion, of the MT tensors is investigated using the Weaver et al. and Bahr classification schemes, and by examining the misfit of a galvanic distortion model as a function of rotation angle. At sites where the galvanic distortion model is found to be appropriate the regional MT tensors are recovered using tensor decomposition techniques. It is found that recovering the regional MT response reconciles the geometry of induced currents implied by the MT data with that of the Magnetic Variation anomalies. Lilley’s central impedances are used to calculate rotationally invariant effective telluric responses. In the Southern Uplands the magnitude of the effective telluric response is approximately 0.25-0.5 mV km −1 nT −1 , but as the Southern Uplands Fault is approached it rises steadily to 3 mV km −1 nT −1 . In the Midland Valley, the effective telluric response is approximately 0.5 mV km −1 nT −1 which rises steadily to 2.5 mV km −1 nT −1 as the Southern Uplands and Highland Boundary Faults are approached to the southeast and northwest, respectively. Therefore, the increase in the magnitude of the effective telluric response correlates with the approach of a major tectonic boundary such as the Southern Uplands Fault. These results show that the induced electric field strength varies considerably throughout the central Scotland region. In addition, the HEA indicates that due to lateral changes in conductivity structure the direction of the electric field deviates significantly from the regional direction implied by the polarization azimuth of the primary geomagnetic induction. Therefore, any attempts to model the flow of GIC in the region need to account for the spatial variation of both the magnitude and azimuth of the electric field.

Breccia dikes and crater‐related faults in impact craters on Mars: Erosion and exposure on the floor of a crater 75 km in diameter at the dichotomy boundary

Abstract— Environmental conditions on Mars are conducive to the modification and erosion of impact craters, potentially revealing the nature of their substructure. On Earth, postimpact erosion of complex craters in a wide range of target rocks has revealed the nature and distribution of craterrelated fault structures and a complex array of breccia and pseudotachylyte dikes, which range up to tens of meters in width and tens of kilometers in length. We review the characteristics of fault structures, breccia dikes, and pseudotachylyte dikes on Earth, showing that they occur in complex network‐like patterns and are often offset along late‐stage crater‐related faults. Individual faults and dikes can undulate in width and can branch and bifurcate along strike. Detailed geological analyses of terrestrial craters show that faults and breccia dikes form during each of the major stages of the impact‐cratering process (compression, excavation, and modification). We report here on the discovery of prominent, lattice‐like ridge networks occurring on the floor of a highly modified impact crater 75 km in diameter near the dichotomy boundary of the northern lowland and southern upland. Interior fill and crater‐floor units have been exhumed by fluvial and eolian processes to reveal a unit below the crater floor containing a distinctive set of linear ridges of broadly similar width and forming a lattice‐like pattern. Ridge exposures range from ˜1–4 km in length and ˜65–120 m in width, are broadly parallel, straight to slightly curving, and are cross‐cut by near‐orthogonal ridges, forming a box or lattice‐like pattern. Ridges are exposed on the exhumed crater floor, extending from the base of the wall toward the center. On the basis of the strong similarities of these features to terrestrial crater‐related fault structures and breccia dikes, we interpret these ridges to be faults and breccia dikes formed below the floor of the crater during the excavation and modification stages of the impact event, and subsequently exhumed by erosion. The recognition of such features on Mars will help in documenting the nature of impact‐cratering processes and aid in assessment of crustal structure. Faults and breccia dikes can also be used as data for the assessment of post‐cratering depths and degrees of landform exhumation.

The tectonomagmatic evolution of Scotland

ABSTRACTScotland has a magmatic record covering much of the period 3100–50 Ma. In this review, we pull together information on Scotland's igneous rocks into a continuous story, showing how magmatic activity has contributed to the country's structural development and assessing whether the effects of older magmatic events can be recognised in later episodes.The oldest igneous rocks are part of supracrustal sequences within the Lewisian Gneiss Complex, formed when Scotland was part of the supercontinent Kenorland. The supracrustal rocks were intruded between 3100 and 2800 Ma by granodiorites and tonalites, which were metamorphosed and deformed in a major tectonothermal event between 2700 and 2500 Ma. The break-up of Kenorland (2400–2200 Ma) was marked by the intrusion of mafic dyke swarms of tholeiitic affinity. The convergence of continental masses to form the supercontinent Columbia resulted, at ∼1900 Ma, in a series of subduction-related volcanic rocks and gabbro–anorthosite masses. Subsequent continent–continent collision formed a series of granite–pegmatite sheets at ∼1855 Ma and ∼1675 Ma and reworked much of the earlier rocks in the amphibolite facies. Columbia was breaking up by 1200 Ma, an event marked by remnants of basaltic magmatism in the NW of the country. Re-assembly of the continental fragments to form the supercontinent Rodinia resulted in the Grenville Orogeny, which in Scotland was marked by basement reworking but no confirmed magmatic activity. Early attempts to split Rodinia produced a rift-related, bimodal, mafic–felsic sequence in the Moine Supergroup of the Northern Highlands, at least some of the mafic rocks having mid-ocean ridge basalt affinities. Crustal thickening during a disputed orogenic event, the Knoydartian, may have caused regional migmatisation. The final break-up of Rodinia occurred in Scotland at ∼600 Ma, when very extensive tholeiitic magmatism characterised the later parts of the Dalradian Supergroup, while a series of granites intruded the Moine and Dalradian successions.Ordovician and Silurian times saw the closure of the Iapetus Ocean and the convergence of Laurentia, Avalonia and Baltica. The collision of a major arc system with Laurentia caused the Grampian event (480–465 Ma) of the Caledonian Orogeny, marked by ophiolite obduction, the generation of (largely) anatectic granites, volcanism in the Midland Valley and Southern Uplands, and intrusion of a major gabbro–granite suite in the NE. The late-Caledonian events (435–420 Ma) were largely post-collisional and were marked by the emplacement of alkaline igneous intrusions in the NW, calc-alkaline granitic intrusions over much of the country, widespread volcanic activity and regional dyke swarms. Laurentia, Avalonia and Baltica amalgamated to form the supercontinent Laurussia. Magmatic activity recommenced at 350 Ma, when intra-plate alkaline magmatism affected much of southern Scotland, in particular, through into Permian times. The alkaline magmatism was interrupted at ∼295 Ma by a short-lived event in which tholeiitic magmas were intruded as sills and dykes in a swarm ∼200 km wide. In the early Palaeogene, lithospheric attenuation related to proto-North Atlantic formation and the splitting of Pangaea was complemented by the arrival of the Iceland mantle plume. Huge volumes of mafic magma were emplaced as lava fields, central complexes and regional swarms, locally increasing crustal thickness by 30%

Chitinozoan biostratigraphy in the Dob's Linn Ordovician-Silurian GSSP, Southern Uplands, Scotland

The Dob's Linn section has recently been confirmed as the Global Stratotype Section and Point (GSSP) for the Ordovician-Silurian boundary. Within the framework of the present study, the Dob's Linn sections yielded, for the first time, chitinozoans with biostratigraphical and correlative value. In the North Cliff trench, the Armoricochitina reticulifera Biozone has been recognised, allowing correlation with the Newport Sands section of the Cardigan area in Wales, which has good graptolite control. In the GSSP trench around the Ordovician—Silurian boundary, a fauna dominated by Cyathochitina and Ancyrochitina spp. has been recovered; the chitinozoans were in ascending order attributed to the Ancyrochitina ellisbayensis, Ancyrochitina laevaensis and Belonechitina ?postrobusta biozones, allowing correlation with several other sections in Laurentia (Ellis Bay) and Baltica, and the global chitinozoan biozonation for the Silurian System.

The interpretation and application of regional geochemistry: lessons from the Paratectonic Caledonides

Synopsis The Southern Uplands (southern Scotland) and Lake District (northern England) terranes contain thick and extensive sequences of macroscopically homogeneous, Lower Palaeozoic wacke-type sandstone. There is a close spatial relationship between the outcrop of biostratigraphically defined rock units and distinctive patterns of element distribution in stream sediments derived from those units, with the stream sediment patterns indicating cryptic compositional variations that are not otherwise apparent. Analysis of the stream sediment composition relative to whole-rock values shows that it is not a direct surrogate for the underlying bedrock. Instead, elevation and depletion trends for any given element are controlled by the nature of its mineral host(s) and provide a previously unappreciated means of assessing the detrital mineralogy, and hence provenance of the bedrock sandstones. Stream sediment composition also provides a valuable alternative means of evaluating possible correlation between different stratigraphical sandstone units. Further, since the fine-grained matrix to the wacke sandstones makes a major contribution to the stream sediment, an assessment of the latter allows variations in matrix composition to be taken into account. Examples are given from the Silurian turbidite sequences of the central and southern Southern Uplands (Gala, Hawick and Riccarton groups; the affinity of the Ross Formation with the Hawick Group is demonstrated) and the southern Lake District (Windermere Supergroup).

Fine-scale biostratigraphy within the Stimulograptus sedgwickii Zone (Silurian: Llandovery) at Dob’s Linn, Southern Uplands

Synopsis A 1.89-m section excavated from the Stimulograptus sedgwickii Biozone (Silurian: Llandovery, Aeronian) at Dob’s Linn, Southern Uplands, Scotland, representing some 0.2 Ma of deposition, shows pronounced, quantitatively established patterns of graptolite abundance and diversity. The most striking signature comprises several marked peaks in abundance of the distinctive taxon Neolagarograptus tenuis (Portlock) within this interval. Such ‘bloom events’, if recognized further afield, may provide very fine-scale stratigraphic resolution, seemingly akin to the ammonite biohorizons of the Jurassic. Taxonomic richness as a whole decreases upwards and appears associated with bentonite layers, suggesting that volcanic ash falls might have led to local extinctions of graptolite populations with little or no subsequent recovery. Repetition of the analysis on a duplicate section along-strike at Dob’s Linn showed comparable patterns, demonstrating the robustness of the methodology.

Geochronology of a granitoid boulder from the Corsewall Formation (Southern Uplands): implications for the evolution of southern Scotland

Synopsis A U–Pb monazite age of 474 ± 2 Ma has been determined for a weakly foliated granite boulder > 1 m in diameter from the Corsewall conglomerate, SW Scotland. The clast contains xenoliths and partly assimilated xenoliths of regionally metamorphosed rock from which the monazites have been derived. The age constrains the original emplacement of the pluton to between 474 ± 2 and c. 458 Ma, the age of the deposit in which the boulder is found. This age confirms an earlier Rb–Sr muscovite Ordovician age for boulders of this type and contradicts a pre-existing age of 1265 Ma used to suggest a source in Newfoundland and a post-Caradoc major lateral displacement of the Southern Uplands. The monazite age reaffirms that a basement-arc complex once existed north of the Southern Uplands and was the principal contributor of sediment to Ordovician–Silurian basins of southern Scotland. A source for the metamorphic detritus in the Dalradian block is unlikely, as the boulders would have been transported for > 150 km through zones of actively accreting terranes and marginal basins. The possibility of Archaean crust within this basement complex is further suggested by the Sm–Nd systematics of the granite boulders at Corsewall Point.

Microchemical characterisation of natural gold and artefact gold as a tool for provenancing prehistoric gold artefacts: A case study in Ireland

The importance of Au to ancient societies has encouraged many archaeologists to search for the sources exploited in antiquity. These projects generally involve detailed studies of artefacts and comparison of their chemical characteristics with those reported for natural Au. However, descriptions of natural Au are frequently inadequate for provenancing studies, and the compositional variability of the material is not widely recognised. The present study describes a new approach to gold provenancing using the technique of microchemical characterisation in which populations of gold grains are classified according to the alloy compositions and the assemblages of microinclusions of other minerals. This technique, originally developed to identify sources of alluvial gold during Au exploration, has proved applicable to provenancing studies in four main areas. Firstly, microchemical characterisation of artefacts grouped according to archaeological criteria can indicate the number of sources exploited in relation to time and artefact taxonomy. Secondly, knowledge of the total variation in chemical characteristics of natural Au from a particular region provides an excellent database for provenancing and reduces the need for exhaustive sampling. Thirdly, it is possible to predict how Au alloys were modified during fabrication as a consequence of assimilation of mineral inclusions. Finally, identification of inclusion phases in artefact Au can provide information on metallurgical practices. These principles have been applied to the search for the source of Au used for the unique traditions of prehistoric Irish metalworking. Studies of 180 Irish Au artefacts belonging to four major metalworking traditions dating from the Early Bronze Age (2400 BC) to the Iron Age, (150 BC) show that each group exhibits distinctive Ag and Cu contents. Parallel studies of 2267 natural Au grains from 58 alluvial localities and four bedrock localities throughout Ireland reveal a broad pattern of alloy compositions consistent with style of mineralisation and host geology. The ranges of Ag contents of Early Bronze Age and Middle Bronze Age artefacts suggests that the Au source lies within Lower Palaeozoic sedimentary rocks of the Southern Uplands Terrane and significantly, that the same source (or sources) were used in both periods. A different source of relatively Ag-rich Au (most probably at Croagh Patrick, Co. Mayo), was exploited in the Late Bronze Age. Iron Age artefacts have Ag contents higher than natural Irish Au. Evidence for evolution of metallurgical practice during the Bronze Age is provided by the increasing Cu content of the gold alloys (to levels far in excess of natural gold) and the nature of inclusions in artefacts of different ages. Elevated Sn in Cu-rich alloys suggests deliberate or accidental alloying with bronze. This approach has provided the first clear indication that only a few individual indigenous Irish sources of Au were used during the Bronze Age and that their relative importance changed over time. Future archaeological investigations may adopt a geographical focus that was not previously possible.

Clay mineral assemblages in British Lower Palaeozoic mudrocks

AbstractLower Palaeozoic rocks crop out extensively in Wales, the Lake District of northern England and the Southern Uplands of Scotland; they also form the subcrop concealed beneath the English Midlands and East Anglia. These mainly marine sedimentary rocks were deposited in basins created during plate tectonic assembly of the various terranes that amalgamated to form the British Isles, 400-600 Ma ago. Final amalgamation occurred during the late Lower Devonian Acadian Orogeny when the basins were uplifted and deformed, producing belts of cleaved, low-grade metasediments, so-called slate belts, with a predominantly Caledonian (NE-SW) trend. The clay mineralogy of mudrock lithologies - including mudstone, shale and slate - found in these belts is reviewed. Using X-ray diffraction data from the <2 μm fractions of ~4500 mudrocks samples, clay mineral assemblages are summarized and discussed in terms of diagenetic and low-grade metamorphic reactions, and the metapelitic grade indicated by the Kübler index of illite crystallinity.Two sequences of clay mineral assemblages, or regional assemblages, are recognized. Regional Assemblage A is characterized by a greater diversity of clay minerals in assemblages from all metapelitic grades. It includes K-rich, intermediate Na/K and Na-rich white micas, chlorite and minor amounts of pyrophyllite. Corrensite, rectorite and pyrophyllite are found in the clay assemblages of contact or hydrothermally altered mudstones. K-white micas are aluminous and phengite-poor, with b cell dimensions in the range 8.98-9.02 Å. Regional Assemblage B has fewer clay minerals in assemblages from a range of metapelitic grades. Phengite-rich K-mica is characteristic whereas Na- micas are rare, and absent in most assemblages; chlorite is present and minor corrensite occurs in mudrocks with mafic-rich detritus. Minor amounts of kaolinite are sporadically present, but dickite and nacrite are rare; pyrophyllite and rectorite are generally absent. The b cell dimensions of K-white mica in Regional Assemblage B are in the range 9.02-9.06 Å. The two regional assemblages are found in contrasting geotectonic settings. Regional Assemblage A is characteristic of the extensional basin settings of Wales, the northern Lake District and the Isle of Man. These basins have a history of early burial metamorphism associated with extension, and syn-burial or post-burial intrusive and extrusive volcanic activity. Intermediate Na/K mica probably developed from hydrothermal fluids generated around submarine volcanic centres. Deep diagenetic and low anchizonal clay mineral in these basins may develop a bedding-parallel microfabric. Chlorite-mica stacks also occur in the extensional basins and the stacking planes represent another type of bedding-parallel microfabric. Both types of microfabric are non-tectonic and developed by burial during the extensional phase of basin evolution. Regional Assemblage B is developed in the plate-convergent settings of the Southern Uplands and the southern Lake District. In the accretionary complex of the Southern Uplands the processes of burial diagenesis, metamorphism and tectonism were synchronous events. In both plate- convergent basins, low temperatures and tectonic fabric-formation had an important role in clay mineral reactions, whereas hydrothermal fluids played no part in clay genesis.

Mechanism of emplacement and crystallisation history of the northern margin and centre of the Galway Granite, western Ireland

ABSTRACTThe main phase (∼400 Ma) emplacement of the central and northern part of the reversely zoned Galway Granite was incremental by progressive northward marginal dyke injection and stoping of the 470–467 Ma Connemara metagabbro-gneiss country rock. The space was provided by the synchronous ESE-opening, along the strike of the country rocks, of extensional fractures generated successively northward by a releasing bend in the sinistrally moving Skird Rocks Fault or an equivalent Galway Bay Fault. This fault is a prolongation of the Antrim–Galway (a splay off the Highland Boundary Fault) and Southern Upland Faults. The ESE-strike of the spalled-off rocks controlled the resultant ESE-elongated shape of the batholith. The magma pulses (∼5–30 m in thickness) were progressively more fractionated towards the northern margin so that the coarse Porphyritic (or Megacrystic) Granite (GP; technically granodiorite) in the centre was followed outwards by finer grained, drier and more siliceous granite, until the movements opening the fractures ceased and the magma became too viscous to intrude. ‘Out-of-sequence’ pulses of more basic diorite-granodiorite (including the Mingling–Mixing Zone) and late main phase, more acid, coarse but Aphyric Granite, into the centre of the batholith, complicated the outward fractionation scheme. The outward expansion, caused by the intrusions into the centre, caused a foliation and flattening of cognate xenoliths within the partly crystallised northern marginal granite and in the Mingling–Mixing Zone to the south.Late phase (∼380 Ma) central intrusions of the newly-discovered aphyric Shannapheasteen Finegrained Granite (technically granodiorite), the Knock, the Lurgan and the Costello Murvey Granites, all more siliceous and less dense than the GP, were emplaced by pushing up the already solid and jointed GP along marginal faults. This concentration of lighter granites plus compression shown in thrusting, caused overall fault uplift of the Central Block of the Galway batholith so that the originally deepest part of the GP is exposed where there is the most late phase granite. Chemical analyses show the main and late phase magmas, including late dykes, were very similar, with repetition of the same fractionation except that the late phase magmas were drier and more quickly cooled, giving finer grained rocks.

The Use of the Common Pb Isotope Composition of Detrital K-Feldspar Grains as a Provenance Tool and Its Application to Upper Carboniferous Paleodrainage, Northern England

K-feldspar is a common detrital mineral in sandstones. It contains little U or Th, and hence the common Pb isotope composition of unaltered K-feldspar is that of the source rock. Pb isotope variations in igneous and metamorphic crustal rocks define broad spatial patterns that make the Pb signature of detrital K-feldspar grains a useful provenance tool. However, it is unclear how robust this signal is, and to what extent it can be modified by weathering, transport, burial diagenesis, and/or exposure to hydrothermal fluids. This study reports an evaluation of the technique, using two granite–arkose pairs (from Helmsdale, northern Scotland, and Shap, northwest England) where the composition of the detrital grains can be compared to feldspars in the granite from which they were derived. The results of this test have informed a pilot study using the Pb isotope composition of detrital K-feldspar in Upper Carboniferous fluvial sedimentary rocks of northern England to constrain the sediment routing. Pb isotope compositions have been measured using an in situ high-resolution single-grain technique that can distinguish original composition, heterogeneity, and subsequent alteration within individual sand grains. The results for the granite–arkose pairs show that the common Pb isotope signature of the detrital K-feldspar grains matches the in situ feldspars in the source granites. The signal is independent of grain size (medium-grained sand to granules), but alteration along a paleo-regolith at Helmsdale has resulted in perturbations in Pb composition and an increase in the errors on the analyses. The application of the technique to arkosic Carboniferous (Serpukhovian–Bashkirian) Millstone Grit Group sandstones in the Pennine Basin reveals two discrete populations of K-feldspars that cannot be distinguished petrographically. Matching of the compositions to potential sourcelands to the north and northeast of the basin suggest a far-traveled (> 500 km) source of K-feldspar from the Archean–Paleoproterozoic Lewisian rocks of northwest Scotland or their extension to the north, but also an equally important proximal source emanating from the Southern Uplands Belt of Scotland in what would have been the lower part of the hinterland drainage basin of the Millstone Grit.

Evidence for the historical exploitation of possible bedrock gold in the upper Mennock Water, Wanlockhead, Dumfries and Galloway

Synopsis Microchemical characterization of gold grains collected from a probable site of old gold processing at the confluence of the Mennock Water and Whitestone Cleuch in the Leadhills–Wanlockhead auriferous area has led to the identification of a type of gold previously unrecorded in the area. Within the Leadhills–Wanlockhead gold region the alluvial gold is dominated by a type which contains typically 10–12% Ag, little or no Cu and Hg, and an opaque inclusion suite containing sulphides (about 60%) and sulpharsenides (about 40%). Alluvial gold grains recovered from the Mennock Water and Whitestone Cleuch during this study are of this type. In contrast, gold grains recovered from the base of pits at the study site contain between 5.6 and 7.4% Ag, negligible Cu and Hg, and an opaque mineral inclusion suite characterized by pyrite, chalcopyrite, galena, sphalerite and tetrahedrite. Sulpharsenides are absent. This microchemical signature is more similar to that previously recorded in alluvial gold from two other sites in the Southern Uplands: the Tweed headwaters and the Glengaber Burn. The distinctive microchemical signature of gold from the study site has not been observed in any other gold grains recovered from the Mennock Water catchment ( c. 20 km 2 ) or elsewhere in the Leadhills–Wanlockhead region. These grains frequently exhibit textures incompatible with any fluvial transport, but characteristic of gold grains liberated through crushing ore. Thus, the evidence from gold composition and grain textures suggests that a distinctive bedrock source of gold was crushed and presumably beneficiated at this site. This discovery represents evidence for an unrecorded site of possible in-situ gold exploitation.

Precipitation analysis and agricultural water availability in the Southern Highlands of Yemen

AbstractRain‐fed agriculture with supplementary irrigation, usually referred to as ‘water harvesting on terraced fields’ is the traditional irrigation technique in the Ta'izz area, located in the southern uplands of the Yemen Mountain Massif. The non‐traditional method of groundwater irrigation has recently led to overuse and depletion of aquifers. A new orientation towards the traditional agricultural irrigation techniques is necessary for the purpose of sustainability. This requires a better scientific understanding of these irrigation systems. In order to understand the design and management of water harvesting schemes, rainfall analysis and the identification of prevailing rainfall patterns is required. A statistical rainfall analysis was conducted to detect the probability of rainfall exceedance during the vegetation period from May until October. Rainfall supply was then measured against water requirements of the prevailing crop Sorghum bicolore. To explore the beneficial effect of the local runoff irrigation schemes, also referred to as water harvesting schemes, water‐harvesting factors were introduced. The rainfall is supplemented by a water‐harvesting factor to show the amplifying effect of those water‐harvesting measures.Analysis results show that a lack of rainfall during the end of the first rainy season and an intermediate dry period under pure rain‐fed conditions can be mitigated by the local runoff irrigation schemes. A fairly reliable and sufficient rainfall characterizes the second rainy season. Copyright © 2005 John Wiley & Sons, Ltd.

Athyrium distentifolium Tausch ex Opiz (A. alpestre (Hoppe) Rylands ex T. Moore‐non‐Clairv.) including A. distentifolium var. flexile (Newman) Jermy

Woodsiaceae. Athyrium distentifolium, Alpine lady-fern. Fronds bi-pinnate, ovate-lanceolate, yellow-green 20 cm to over 100 cm, arising in a 'shuttlecock' from a central crown. Stipe straight, one fifth to one quarter the length of the blade with pale brown scales, usually broad, but occasionally narrow. Pinnae widely spaced near base of the frond, and sometimes deflexed, crowded near the tip, meeting the rachis at an angle of 900 at the midpoint of the blade, or slightly ascending. Pinnules broadest at the base, tapering to a point. Sori circular, with irregular filaments making up a rudimentary indusium when young, soon obscured as the sori grow. Sori concentrated in the upper part of the frond, becoming sparse towards the base. Number of sori varies with size of frond. Plants frequently infertile (McHaffie et al. 2002). Athyrium distentifolium var.flexile Newman's lady-fern. Fronds bi-pinnate, narrow, blue-green, 10-40 cm, arising from a central crown, erect or sharply angled near the base of the rachis to lie nearly flat against the substrate. Stipe short, one sixth to one eighth the length of the blade, often densely covered with broad, pale scales that may continue beyond the midpoint of the blade. Blade broadest near the base, or nearer the mid-point. Pinnae close together near base of frond, often strongly deflexed to at least half way up the frond. Uppermost pinnae widely spaced. Pinnules taper towards the base. Sori circular, sometimes with only a few sporangia; rudimentary indusium visible while the sorus is still immature. Sori concentrated at base of the frond, becoming less frequent towards the tip. Plants usually fertile (McHaffie et al. 2002). Athyrium distentifolium is a chionophilous fern that grows at altitudes or latitudes which ensure long-lying winter snow cover. Deep snow provides insulation from severe winters, and prevents early growth in a mild spring. Only a limited number of species can tolerate these conditions and this reduces competition. Although previously known as a Scandinavian and continental European species, A. distentifolium was not recognized in Britain until 1844 (Newman 1851). Within Britain it is found only in Scotland where it is confined to the remote Highlands. Soon after it was identified, another similar taxon of uncertain taxonomic status was described (Backhouse 1852). Subsequent research has determined that this is a recessive variety which is now known as A. distentifolium var.flexile. Both taxa are covered in this account.

The origin, evolution and provenance of the Northern Belt (Ordovician) of the Southern Uplands Terrane, Scotland: a heavy mineral perspective

The heavy mineral components of Ordovician greywacke turbidites of the Southern Uplands (subduction-accretion prism) Terrane were studied using high-resolution heavy mineral analysis. Diagnostic heavy minerals and the discovery of hitherto unreported species provide a new insight into the interplay of sediment fluxes, tectonic controls and provenance. Each formation is characterized by distinctive heavy mineral suites, indicating that the sediments of successive or laterally-equivalent formations were sourced from different and rapidly-changing lithologies. Appreciable variations were detected even in greywacke packages within an individual formation, indicating that these changes were taking place at a very fast rate. Detritus came from either an eroding Dalradian or a similar Barrovian metamorphic complex and its superjacent obducted ophiolite complex to the northeast, and from oceanic island arcs and collapsing seamounts to the south. The rapid appearance of metamorphic detritus, following a short period of ophiolite stripping, indicates that post-subduction-flip exposure of and erosion into the metamorphic complex was fast, suggesting extensional unroofing. The chemical similarity of detrital garnet with Scottish Grampian garnet may suggest derivation from that complex and, therefore, that the Southern Uplands Terrane has not travelled, sinistrally, more than about 200 km with respect to the Scottish Highlands. The absence of detrital staurolite in the greywackes raises the possibility that stripping either did not reach abundant staurolite levels or that staurolite was a relatively uncommon mineral in the source area. The former explanation is unlikely because, in western Ireland, a similar Dalradian stripping sequence involves the appearance of staurolite in the first arrival of metamorphic detritus. However, possibly, in western Ireland, the Dalradian source was extensionally unroofed to a much deeper structural level than was Scotland in the same time interval. Only the Shinnel Formation shows spatial detrital consistency, indicating that, by Shinnel times, the Dalradian hinterland had achieved a relatively uniform level of erosion. The discovery of lawsonite, as part of a ferroglaucophane-glaucophane blueschist assemblage in the Portpatrick Formation, is important yet enigmatic. Ordovician crosstie-winchite-ferroglaucophane-phengite assemblages are known throughout the northwestern Appalachian/Caledonian belt and may have provided the source for the Portpatrick blueschist-facies detritus. However, a possible source was from the Cadomian blueschist belt of Anglesey, then on the southern margin of the Iapetus Ocean. This is supported by garnets with sodic/calcic amphibole inclusions, unknown in the Dalradian. Perhaps Cadomian ‘terrane fragments’ were rifted from the southern margin of Iapetus to drift towards and collide with Laurentia to shed detritus into the Laurentian margin trench.

Terrane and basement discrimination in northern Britain using sulphur isotopes and mineralogy of ore deposits

Abstract This study of four well characterized and adjacent terranes in Northern Britain outlines the sulphur isotope variations, assesses the overall importance of crustal and mantle sulphur, and presents a model that can be applied to terrane distinction throughout the North Atlantic Caledonides. The characteristics of metal components within the mineralization provide additional information that can be related to the nature of underlying basement and events from the onset of sedimentation to the cessation of mineralization within stratigraphically linked packages of rock. The δ 34 S data show that the dominant crustal units in each terrane, whether upper crustal sediments or cratonic basement, provide the main alternative sulphur source to the mantle and act also as the main contaminant of subcrustal melts. The δ 34 S values of granitoid-related mineralization are either within the subcrustal melt-range of −3‰ to +3‰ or deviate toward the values of major crustal units in the terrane, i.e. toward 34 S depletion in the Southern Uplands and toward 34 S enrichment in the Lakesman and Grampian terranes. More complex mineralization in the Northern Highland terrane is linked to the presence of thick North Atlantic craton beneath upper crustal metasediments. Across the region the vein systems beyond the influence of magmatic components represent homogenized sulphur, metals and fluids from local upper crustal units. The sulphur isotope data and style of mineralization for the British terranes are compared with terranes of similar age along strike in Eastern Canada revealing notable correlations.