Showing papers in "Scottish Journal of Geology in 1968"
TL;DR: In this paper, the authors summarise the limited literature on crinoid ecology and palaeoecology and attempt to interpret the depositional environment of certain British crinoidal sediments in the light of experimental observations.
Abstract: Synopsis The paper summarises the limited literature on crinoid ecology and palaeoecology and attempts to interpret the depositional environment of certain British crinoidal sediments in the light of experimental observations. Three types of crinoidal limestone are recognised: muddy limestones deposited in shallow, sheltered waters; poorly washed limestones formed in deeper, open conditions; and clean-washed limestones which may derive in part from the reworking of one or other of the first two types.
73 citations
TL;DR: The late-precambrian Torridonian sediments of the Cape Wrath district, extreme north-west Scotland, unconformably overlie a planar, weathered Lewisian surface.
Abstract: Synopsis The late-Precambrian Torridonian sediments of the Cape Wrath district, extreme north-west Scotland, unconformably overlie a planar, weathered Lewisian surface. The weathered profile present beneath the unconformity is regarded as Torridonian in age, and hence must rank with the oldest palaeosols in the world. This planar surface was partly stripped of its mantle of altered rock prior to burial beneath Torridonian alluvial fan deposits. Where developed on biotite-gneiss, the weathered profile has the chemical characteristics of a modern pedalfer. A pedocal-type soil developed on amphibolite. The chemical and mineralogical changes are suggestive of a warm, moderately humid climate, possibly with dry periods or a dry season. A similarly weathered Lewisian terrain could, in principle, have supplied the bulk of the overlying Torridonian sediments.
40 citations
TL;DR: In this article, the authors considered the Hawick Rocks (Upper Valentian), and have been affected by five main episodes of deformation, three of which are of Caledonian age, forming the structural basis of the area and determining the outcrop distribution.
Abstract: Synopsis The rocks exposed in the coastal sections between Gatehouse and Creetown, Kirkcudbrightshire, are considered to belong to the Hawick Rocks (Upper Valentian), and have been affected by five main episodes of deformation, three of which are of Caledonian age. The first phase produced E.N.E.-W.S.W. similar folds and associated tensional strike faults, forming the structural basis of the area and determining the outcrop distribution. During the second phase these folds were modified, and a new set of concentric folds, comparable in strike but with axial surfaces dipping at around 45° S.S.E., was generated, along with a conjugate set of wrench faults. Folds of the third phase have E.-W. axes and steep eastward plunges. The three phases are equated respectively with F 1 F 2 and F 3 of the Whithorn area (Rust 1965a). The fourth phase gave rise to folds with near-horizontal axial planes, and frequently developed as minor thrusts, and the final deformation gave rise to dextral kink-bands trending N.-S. The two last are correlated with F 4 and F 5 of Whithorn, to which Hercynian and Alpine dates are provisionally allocated. A swarm of dykes was emplaced between the first and second phases, and further dykes were intruded after the second phase.
26 citations
TL;DR: In this paper, the Caledonian histories of these two areas are outlined and correlated, and the structures produced during the subsequent end-Silurian evorogenesis are examined and compared with those formed at this time elsewhere in the British Isles.
Abstract: Synopsis In the light of recent work in the Isle of Man and the Lake District, the Caledonian histories of these two areas are outlined and correlated. The tectonic history of this north-eastern quarter of the Irish Sea region consists of two evorogenic episodes of severe Caledonian deformation. The earlier tectogenesis took place during the Lower Ordovician after the infilling of a rapidly subsiding geosynclinal trough. The importance of this orogenic phase within the British Caledonides is considered by comparison with surrounding areas. The structures produced during the subsequent end-Silurian evorogenesis are examined and compared with those formed at this time elsewhere in the British Isles.
25 citations
TL;DR: The Cairnsmore of Fleet granite is emplaced into Lower Palaeozoic sediments the structure of which is not completely known as mentioned in this paper, but field evidence indicates steep contacts, but gravity results suggest that at depth they are less steep and that the present outcrop is near the roof of a batholith.
Abstract: Synopsis The Cairnsmore of Fleet granite is emplaced into Lower Palaeozoic sediments the structure of which is not completely known. The granite exhibits a decrease in biotite content towards the centre, and passes into a biotite-muscovite granite. The outer contact is everywhere sharp and the aureole restricted in width except in the N.E. and S.W. Field evidence indicates steep contacts, but gravity results suggest that at depth they are less steep and that the present outcrop is near the roof of a batholith. The foliation (flow and shear) is generally concordant with the contact except in the S. and S.W. and has the form of a dome structure slightly offset to the S.W. relative to the outcrop. There appears to be no relation between the foliation and the joints and veins in the granite.
22 citations
TL;DR: In this paper, major and minor structures in the Moinian and Dalradian rocks of the Monadhliath Mountains are described and the tectonic history of the area outlined.
Abstract: Synopsis Major and minor structures in the Moinian and Dalradian rocks of the Monadhliath Mountains are described and the tectonic history of the area outlined. Early major structures, isoclinal recumbent folds with north-east trending axial planes, are refolded by Late asymmetric folds with north-east trending axial planes dipping steeply to the south-east. These episodes of folding are correlated with those described elsewhere in the Ballappel Foundation and the Iltay Dalradians.
20 citations
TL;DR: The interpretation of Bailey and Macgregor (1912) and Bailey (1922) is revised in this article, where the presence of three major, isoclinal and recumbent folds is demonstrated.
Abstract: Synopsis The interpretation of Bailey and Macgregor (1912) and Bailey (1922) is revised. The presence of three major, isoclinal and recumbent folds is demonstrated. Their geometry and facing is described by reference to minor structures, sedimentary structures and the overall stratigraphy. The Glen Orchy Antiform, around which the primary structures are folded, possibly developed together with the primary folds. It is not associated with any minor secondary structures. The structure of the Glen Orchy area raises important questions in the interpretation of the overall structure of the Moine and Dalradian.
19 citations
TL;DR: In this article, the Lewisian rocks north-west of Loch Tollie corresponding deformation during three successive phases of the Laxfordian orogeny is shown in meta-sediments, hornblende-schists, amphibolites and acid gneisses.
Abstract: Synopsis In the Lewisian rocks north-west of Loch Tollie corresponding deformation during three successive phases of the Laxfordian orogeny is shown in meta-sediments, hornblende-schists, amphibolites and acid gneisses. Isoclinal folds, some drag folds and open folds and associated axial planar schistosity/foliation and mineral and intersection lineations were developed during the main phase of deformation. Asymmetrical folds, of which the Tollie anticline is the most prominent, refold the isoclinal folds and the associated main phase structures. Antiforms predominate, the synforms being largely represented by shear-belts. This mid phase deformation produced the dominant N.W.-S.E. trend of the lithological layers and the main phase foliation and the pattern of alternating belts of south-easterly and north-westerly plunging main phase lineation. After the emplacement of acidic veins and sheets, late phase deformation resulted in the development of steeply-plunging brittle folds and shear-belts with pseudo-tachylite.
16 citations
TL;DR: In this article, the Ordovician encrinurid trilobites Cybeloides girvanensis (Reed) and C. loveni (Linnarsson) were redescribed.
Abstract: Synopsis The Ordovician encrinurid trilobites Cybeloides girvanensis (Reed) and C. loveni (Linnarsson), formerly assigned to the genus Paracybeloides, are redescribed. Specimens of Cybeloides from several British localities are identified with the former species. A teratological pygidium of C. loveni is noted. It is suggested that the development of spines in these species was, at least partly, an adaptation for attaining a concealed position.
16 citations
TL;DR: The first full description of Mixopterus dolichoschelus is made possible, with dorsal and ventral reconstructions, of a large eurypterid from the Upper Silurian inliers in Lanarkshire and Ayrshire, Scotland.
Abstract: Synopsis New material of Mixopterus dolichoschelus, a large eurypterid from the Upper Silurian inliers in Lanarkshire and Ayrshire, Scotland has made possible the first full description of the form, with dorsal and ventral reconstructions. In many features (shape of prosoma, nature of the large ‘walking’ legs (III)) M. dolichoschelus differs significantly from the Norwegian Mixopterus kiaeri Stormer and it is proposed that the Scottish species be placed in a new genus for which the name Lanarkopterus is proposed. A comparison of the enlarged, spinose legs (III) in Megalograptus, Lanarkopterus and Mixopterus suggests a new interpretation of joint numeration in the last two genera.
15 citations
TL;DR: In this paper, a late Caledonian phase of regional metamorphism is outlined in the Western Highlands and a major break in the zoning along the line of the Great Glen Fault is identified.
Abstract: Synopsis A late Caledonian phase of regional metamorphism is outlined in the Western Highlands. Minor intrusions associated with the Newer Granites are found to exhibit varying degrees of regional metamorphism in which the zonal ‘isograds’ trend about north-east-south-west, approximately parallel to and increasing in grade towards the Great Glen. There is a major break in the zoning along the line of the Great Glen Fault.
TL;DR: In this paper, the ages of sandstones and interbanded andesitic and basaltic lavas, rhyolites and tuff are considered, and it is argued that because the sandstones are of two different facies, they are unlikely to be of the same age.
Abstract: Synopsis The ages of sandstones and interbanded andesitic and basaltic lavas, rhyolites and tuff are considered. It is argued that because the sandstones are of two different facies, they are unlikely to be of the same age. One facies is of typical Old Red continental type and contains fish of Middle Devonian age. Isotopic age determinations on a series of volcanic rocks associated with these sandstones indicate a recrystallisation at 300 m.y. ago and a possible origin age at 370 m.y. ago. In the case of the second facies of sandstone neither isotopic ages nor geological evidence from associated lavas indicate whether it is older or younger than the first. An isotopic age from a granite which cuts the second facies of sandstone indicates that the sandstone must be older than 330 m.y., whilst ages determined from interbedded lavas indicate a local recrystallisation or alteration at about 230 m.y. ago.
TL;DR: The origin of the Glenelg eclogites is reviewed and an hypothesis of tectonic emplacement from a deeper metamorphic source in the uppermost mantle preferred as discussed by the authors.
Abstract: Synopsis A nepheline normative eclogite containing almandine-rich garnet and Na 2 O-rich (5.47 per cent) pyroxene is described. The origin of the Glenelg eclogites is reviewed and an hypothesis of tectonic emplacement from a deeper metamorphic source in the uppermost mantle preferred. It is suggested that the rocks were originally basic magmas or accumulates from such magmas originally crystallised near the crust-mantle boundary.
TL;DR: In this article, the remains of Coleoptera collected by James Bennie at the end of the last century from Late Glacial deposits in Edinburgh are described and the fauna is indicative of a marshy environment rather than a lake as had hitherto been assumed.
Abstract: Synopsis Remains of Coleoptera, collected by James Bennie at the end of the last century from Late Glacial deposits in Edinburgh, are described. All the fragments recognised can be identified with living species, but five of them are not now found living in Britain. The fauna is indicative of a marshy environment rather than a lake as had hitherto been assumed. For the most part the fauna indicates sub-arctic conditions with a somewhat more continental climate than prevails in Edinburgh at the moment. There are however certain anomalous associations in this assemblage which may be reconciled to some extent by assuming that the climatic regime of Late Glacial Edinburgh has no precise equivalent anywhere in Europe today. An attempt is made to put together a picture of a climatic regime that might have been acceptable to all the species in this fauna.
TL;DR: In this article, the garnets from a vent at Elie, Fife have been collected and analyzed, and a primary precipitate origin from a magma in depth is proposed.
Abstract: Synopsis The garnets from a vent at Elie, Fife, have been collected and analysed. This analysis is compared with recent analyses of pyrope from, a number of other environments. On the basis of this comparison and the occurrence of the pyrope as xenocrysts in the vent agglomerate of Elie Ness Neck, a primary precipitate origin from a magma in depth is postulated.
TL;DR: In this paper, three separate depositional units are described from the Esk and upper Tyne basins, each unit comprises a till grading upwards into glacio-fluvium.
Abstract: Synopsis Three separate depositional units are described from the Esk and upper Tyne basins. Each unit comprises a till grading upwards into glacio-fluvium. The tills from the basal and middle units together correspond to what has previously been described as the Basal Boulder Clay of the area. Stone counts suggest the basal till was derived from a westerly quadrant. The high proportion of greywacke in the intermediate till suggests it was derived from a southerly quadrant. The topmost depositional unit is represented chiefly by the Roslin Till, previously described as the Southern Upland Readvance Boulder Clay. This till is confirmed as the product of a local glacial readvance, but the stone count throws doubt on the former assumption that this readvance was from the Southern Uplands. No organic material is known to occur between the three depositional units. Mechanical analyses do not serve to distinguish the three tills.
TL;DR: In this article, the Lower Old Red Sandstone of southern Kintyre is divided into three formations: Breccias, conglomerates and sandstones, which are similar to those of Arran.
Abstract: Synopsis The Lower Old Red Sandstone of southern Kintyre is divided into three formations The aggregate thickness (excluding the island of Sanda) is 1200 m Breccias, conglomerates and sandstones are described which are similar to those of Arran Also described are pyroclastic sediments, which are kaolinitic Three volcanic vents in the Southend region have been re-investigated and are thought to illustrate three stages in the same sequence of igneous activity The composition of the sediments and palaeocurrent observations show that the sediment was derived from the north or north-west The thickness of the Lower Old Red Sandstone succession is compared with that of other successions in the Midland Valley, and the differences are explained in terms of the geometry of crustal movement The position and nature of the Highland Boundary Zone is briefly discussed It is suggested that it extended across southern Kintyre during Lower and Middle Devonian times as a relatively broad zone of southward down-warping
TL;DR: In this paper, the formation of complex folds along narrow N.W.-S.E. master joints in gneiss has been studied, where the vertical and horizontal surfaces represent cross-sections near to or within the steep limb of a steep limb.
Abstract: Synopsis Complex patterns, of folds with horizontal axes perpendicular to the foliation in gneiss, occur on vertical foliation surfaces. Similar complex patterns, of corresponding folds with vertically disposed axes, occur on horizontal surfaces. The vertical and horizontal surfaces represent cross-sections near to or within the steep limb of N.W.-S.E. monoclinal fold belts which cut rocks of a crystalline basement. Heterogeneous flow appears to have been operative in the formation of the complex folds. Local intensely developed small-scale folding along narrow N.W.-S.E. fold belts possibly resulted from their coincidence with pre-existing N.W.-S.E. master joints in the basement.
TL;DR: In this paper, the field relationships and textural and mineralogical features of basic syenites, ultrabasic rocks and dolomites associated with leucocratic syenite in the Loch Ailsh intrusion were investigated.
Abstract: Synopsis The field relationships and textural and mineralogical features of basic syenites, ultrabasic rocks and dolomites associated with leucocratic syenites in the Loch Ailsh intrusion demonstrate that both basic syenites and ultrabasic rocks are the products of reaction between dolomite and syenite.
TL;DR: The metamorphic history of these Moine and Lewisian rocks in the Moine nappe of Skye is as complicated as the structural history, one of the principal difficulties being the recognition of equilibrium assemblages.
Abstract: Synopsis The metamorphic history of these Moine and Lewisian rocks in the Moine nappe of Skye is as complicated as the structural history, one of the principal difficulties being the recognition of equilibrium assemblages. Detailed work on an important garnet-hornblende-biotite-epidote assemblage in gneissic rocks indicates that the highest metamorphism was probably of lower almandine amphibolite fades and that it occurred early in the structural history of the area. Later retrograde changes took place in schistose rocks nearer the Moine thrust plane. Co-existing chlorite-actinolite assemblages, analysed in detail, indicate a metamorphic grade probably not much lower than the almandine amphibolite facies.
TL;DR: In this article, a channel structure, linguiform mounds, ridged flame structures, a bellerophontid roll-mark and rilled tool-marks are described from Kirkcudbrightshire.
Abstract: Synopsis A channel structure, linguiform mounds, ridged flame structures, a bellerophontid roll-mark and rilled tool-marks are described from Kirkcudbrightshire.
TL;DR: In this paper, the initial forms of the intrusions were deduced as members of a dyke-swarm trending roughly east and west, and it was suggested that the apparent contrast may have a bearing on the orientation of the direction of Laxfordian compression.
Abstract: Synopsis In Great Bernera, Lewis, many small basic bodies intruded after the formation of the Scourian gneiss complex were deformed and metamorphosed as a result of Laxfordian orogenic activity. These bodies, now represented by meta-dolerites, appear as contorted bands and lenticles whose outcrop-pattern is determined by the effects of two principal phases of folding. An attempt is made to deduce the initial forms of the intrusions and it is suggested that they were emplaced as members of a dyke-swarm trending roughly east and west. The structures produced by Laxfordian deformation of the metadolerites are compared with those exhibited by deformed metadolerites of the same generation in the Loch Laxford region of the Scottish mainland, and it is suggested that the apparent contrast may have a bearing on the orientation of the direction of Laxfordian compression.
TL;DR: A conformable junction between the Upper Old Red Sandstone and Lower Carboniferous rocks (Cementstone Group) exposed at Burnmouth in Berwickshire is described in this article.
Abstract: Synopsis A conformable junction between the Upper Old Red Sandstone and Lower Carboniferous rocks (Cementstone Group) exposed at Burnmouth in Berwickshire is described. The stratigraphic and palaeogeographic significance of the junction is discussed.
TL;DR: In this article, it was shown that although an unconformity is almost certainly present in the north, this does not apply to the southern part, where exposed contacts are vertical and strongly transgressive to the sheet-dip of volcanic rocks.
Abstract: Synopsis According to existing accounts Lower Old Red Sandstone volcanic rocks, together with basal pockets of sediments, rest unconformably upon the quartzitic Moinian and Dalradian inside the north-eastern part of the cauldron-subsidence. Remapping of the ground has shown that although an unconformity is almost certainly present in the north, this does not apply to the southern part, where exposed contacts are vertical and strongly transgressive to the sheet-dip of the volcanic rocks. Here the junction is believed to mark the north-eastern margin of a linear vent, the south-western margin of which is covered by volcanic rocks. Most of the rocks previously regarded as sedimentary are now known to be volcanic. They consist of dykes of quartzitic explosion-breccia (formed underground) together with larger amounts of extruded explosion-breccia (vent-breccia) occupying the postulated linear vent, as well as a minor volcanic neck. The little undoubted sediment that exists is not in situ, but is present as inclusions, up to 100 ft across, in the volcanic rocks.
TL;DR: In a recent paper by Matthews and Cheeney as mentioned in this paper, a number of analyses of coexisting garnet, biotite, hornblende and epidote from gneisses are presented and discussed.
Abstract: SIRS,—In a recent paper by Matthews and Cheeney (1968, p. 20) a number of analyses of co-existing garnet, biotite, hornblende and epidote from gneisses are presented and discussed. The analysis of hornblende 95052, which is an aluminotschermakite (Leake 1968), is of particular interest. Matthews and Cheeney calculate this analysis to a basis of 23 (O) but as Borg (1967) has convincingly shown the unsatisfactory nature of using 23 (O) as a basis for calculating amphibole formulas, the ions have been recalculated to the more usual basis of 24 (O, OH) (Table 1). The analysis then gives Si 6-21, Al[4] 1-79 and Al[6] 1-26 which is the