Journal of the Geological Society, London, Vol. 153, 1996, pp. 823-826, 1 fig, 3 tables. Printed in Northern Ireland

Thereare two major problems in accepting either of these interpretations. Firstly, there is no convincing A late Vendian age for the Kinlochlaggan evidence of boulderbeds, or of known glacial deposits, Boulder Bed (Dalradian)? occurring at either of these stratigraphical levels elsewhere in the Dalradian rocks of Scotland or Ireland; and secondly, there is no evidence for a second, pre-Vendian glacial event RICHARD H. S. EVANS'& P. W. GEOFF elsewhere in the North Atlantic region. Indeed, to explain TANNER thelatter anomaly,Hambrey (1983) suggested that the Department of Geology and Applied Geology, Kinlochlaggan Boulder Bed may provide evidence unique in University of Glasgow, Glasgow G12 8QQ, UK Scotland fora pre-Vendian glacial event belonging to the 'Present address: ShelI P. D.C.(Nigeria) Ltd, Sturtian Glacial Period (c.800 Ma). PO Box 263, Port Harcourt, Nigeria The alternativeproposed here is to correlate the Kinlochlaggan Boulder Bed with thePort Askaig Tillite found at the base of the Argyll Group (Table 1). The latter is a glaciomarine till (Spencer 1985; Eyles 1988)which provides a chronostratigraphic marker within the Dalradian The Kinlochlaggan Boulder Bed occursin Neoproterozoic sequence,and is the basis for astratigraphical correlation Dalradian rocks of the GrampianMountains of Scotland. It is between the Scottish and Irish Dalradian successions. currently thought to represent a glacial event (c. 800 Ma) unique in The Port Askaig Tillite has been correlated with tillites the North Atlantic region, and be part of a sequence correlated by different workers with either the Grampianor Appin groups.We of lower Vendian age (c. 650Ma) which are found correlate the Boulder Bed with the Port Askaig Tillite of Vendian throughout the NorthAtlantic area in Scandinavia, (c. 650Ma) age, and deduce that the sequence in which it occurs Greenland, Spitzbergen, and Svalbard (Hambrey 1983; belongs to the younger Argyll Group. The latter is preserved within Harland et al. 1993). The Varanger Ice Age which gave rise the D2 KinlochlagganSynform, and a previously unrecognized to this depositoccurred at the time of initial breakup of discontinuity of regional importance may separate inverted Argyll Rodinia(Young 1995), andimmediately prior to the Group rocks from the underlying Grampian Group. opening of Iapetus at 600-570Ma ago (Torsvik et al. 1995). An older glacial episode at 750Ma is characteristic of the NorthAmerican Cordillera (see Young 1995) but has not Keywords: Dalradian, Proterozoic, Scotland, tillite. been reported from the North Atlantic region. Support for the recognition of a single glacial event in NE Laurentia (including the Dalradian block), and Baltica, comes from Although the stratigraphy of the Neoproterozoic Dalradian the recentreconstruction of Rodinia (Dalziel 1991) which rocks in Scotland is well established (Harris et al. 1994), shows that Laurentia straddled the equator at 750 Ma, and stratigraphical and palaeogeographicalproblems posed by that it was only when asubsequent clockwise rotation of the discovery of the Kinlochlaggan BoulderBed (Treagus theseunits caused them to move to >30"S (Torsvik et al. 1969) in the Grampian Mountains remain unresolved. Two 1995) that the first glaciation occurred at c. 650 Ma. conflicting interpretations of its stratigraphical age have The aims of this note are to report the discovery of new been proposed, namely that it lies either within the exposures of the Kinlochlaggan Boulder Bed found by the Lochaber subgroup (Treagus 1969, 1981; Thomas 1979), or authorsand P. R. Thomas on Aonach Beag, proposea at the base of the Grampian Group (Piasecki & Temperley late-Vendian (c.650 Ma) age for the deposit, and examine 1988) (Table 1). some of the implications arising from this proposal.This work is based on 1:lOOOO reconnaissance mapping by R.H.S.E. of the Dalradian rocks from Kinlochlaggan 17 km Table 1. Relative stratigraphical ages of the Port SSW to Aonach Beag (Fig. 1). Much of the area is remote Askaig Tillite and Kinlochlaggan Boulder Bed and mountainousand for the major part there is no pre-existing Geological Survey map or memoir. Dalradian Supergroup The Kinlochlaggan Boulder Bed. Atthe type locality Group Subgroup [NN 547689751 (Fig. 1, loc. A)near Kinlochlaggan, Inverness-shire, two non-bedded sub-vertical 7 m thick Argyll Easdale boulder beds separated by a 6 m feldspathic quartzite occur Islay within a 43 msequence of psammites and semi-pelites Port Askaig Tillite (Treagus 1969, 1981). Boulders are most common in the lower (western) boulder bed, where they range up to 33 cm Appin Blair Atholl across and are set in an homogeneous rock packed with Ballachulish matrix-supported clasts 0.3-3cm across. Small clasts of Kinlochlaggan Boulder Bed* quartzite, semi-pelite,pelite, andalkali-granite occur Lochaber alongside alarger (45 cm) stone of pink alkali-granite (Treagus 1969). Treagus (1981) reportedthree further Grampian Kinlochlaggan BoulderBed? occurrences of boulderbed (Fig. 1, loc. B),but no description was given. *After Treagus (1981). The Kinlochlaggan BoulderBed, or its mapped t Winchester & Glover (1988). stratigraphical equivalent, the Kinlochlaggan Biotite Schist, 823

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hasbeentraced along strike from Kinlochlaggan [NN5476 89751 to AonachBeag [NN4579 74181. Near ARGYLL GROUP ss . ,l Aonach Beag [NN4554 73751 (Fig. 1, loc. C), the Boulder 0Kinlochlaggan Quartate Bed consists of two boulder bed horizons, 2-3 m and 5-6 m thick, separated by a thin band of impurequartzite. The mKmlochlaggan Boulder Bed (A-C)

structurally lower band is non-bedded and shows numerous, APPIN GROUP small (0.2-0.5 cm), pink, feldspathic clasts set in a quartzose KinlochlagganEiotite Schlst. matrix, with some stones up to 20 cm across. Nearly all of Colre na Colchllle Lnnestone, thestones are of pink (generally foliated)alkali-granite, and Colre Cheap Kyanite Schist with some of semi-pelite and psammite, and one of basic Kinlochlaggan Llmestone and igneous rock. Theupper band is non-bedded a massociated pelites ‘gritty-looking’ psammite which in thin section is seento - SEQUENCE MISSING contain numerous feldspar and granite clasts upto 1cm GRAMPIAN GROUP long, set in a fine-grained quartz-feldspar-biotite matrix. In 0Banded Psammite their sequence and lithology the boulder beds on Aonach Beag are closely similar to those at Kinlochlaggan. - Formationboundary

-e - Fault Previous stratigraphic sequence. Carruthers (1923), working mainly to the south of the area described here, was careful to point outthat there was a structural sequencefrom ‘Moine’ rocks to a quartzite and a limestone belonging to the ‘Lochaber Series’ of the Dalradian. Anderson (1947) recognized that the Dalradian rocks between Aonach Beag and the River Spey (4.5 km NNE of Kinlochlaggan) lie in the core of a major synform and, based on two observations of cross-bedding in the Kinlochlaggan Quartzite, named it the Kinlochlaggan Syncline. Anderson suggested thatthe Kinlochlaggan Limestone may be equated with the Ballachulish Limestone,but recognized that some of the stratigraphicunits seenat Ballachulish were missing at Kinlochlaggan. This interpretation of the Boulder Bed asa glacial deposit of early Dalradian age, laid down well before the widely recognized Port Askaig Tillite (Treagus 1969, 1981) (Table 2), and preserved within an early fold closure in older rocks, is internally consistent and has attracted general support (i.e. Johnson 1991). The alternative possibility, implied by Piasecki & Temperley (1988), thatthe Fig. 1 An outline geological map of the Kinlochlaggan Synform, the Dalradian-likerocks at Kinlochlaggan may be correlated axial trace of which runs through the unit shown in solid black on with a unit of kyanite-bearing pelite, marble, quartzite and the main map. Only the main Quartzite outcrop is shown and many amphibolite found at the base of the Grampian Group (the thin bands of quartzite and other rock types are omitted for clarity, Ord Bansubgroup, Glover & Winchester 1989), is less especially around Aonach Beag (see Thomas 1979, fig.1). Locations certain(Winchester & Glover 1988), andno boulder or A-C are referred to in the text; heights of triangulation points are pebble beds have been reported from this subgroup. in m. (a) Inset map showing the location of the main map (K) and the area (in black) underlain by the Lochaber to Southern Highland Revised stratigraphic sequence. Thesequence proposed Groups of the Dalradian Supergroup. I, Islay; L, Loch Linnhe; 0, here, with the older rocks occupying the core of the Glen Orchy; R, Glen Roy; S, Schiehallion. Kinlochlaggan Synform, is shown in Table 3. Not all of the units are present or recognizable throughout the area due to CoireCheap Kyanite Schist. Dark-coloured, commonly their local structural excision or attenuation. The sequence graphitic, quartz-biotite-muscovite schist characterized by is based solely upon the mapped continuity and repetition of abundant kyanite prisms (up to 3cm long), with andesine units aroundand across fold structures, as sedimentary and rare garnet. way-up structures are extremely rare. Coire nu CoichilleLimestone. A thin (to3m) finely GrampianGroup. Grey, coarse-grainedpsammites with alternating quartzo-feldspathic and micaceous layers. Table 2. Correlation of the Dalradian Kinlochlaggan sequence with that at Ballachulish (after Treagus 1981) AppinGroup. Sr6n Gharbh PeliticSchist. Muscovite- biotite schist, commonly with migmatitic quartzo-feldspathic, Kinlochlaggan Limestone Ballachulish Limestone segregations, and contains small garnets (1-2 mm). Pelite and semi-pelite Leven Schist KinlochlagganGlencoe BoulderQuartziteBed The KinlochlagganLimestone is a grey, coarse-grained Pelite and semi-pelite Binnein Schist (up to 3 mm), predominantly calcite limestone up to 10 m Kinlochlaggan Quartzite Binnein Quartzite thick which locally developsa cm-scale banding atthe MOINE (now GRAMPIAN GROUP) margins of the units. It is locally dolomitic, and weathers to Psamrnitic schists Eilde Schist a buff- or orange-coloured surface.

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banded grey to yellow limestone with minor biotite, pyrite, (a) We equate the Kinlochlaggan Quartzite with the Islay and quartz; locally seen as a blue-green diopside marble. ( = Schiehallion) Quartzite, andthe Coire nan Coichille KinlochlagganBiotite Schist. A grey to reddish-brown Limestone with the Islay Limestone,and the White biotite-quartz-oligoclase-muscovite schist, calcareous in Limestone at Schiehallion (Treagus 1987). part, which contains widely dispersed small garnets (up to (b)The Kinlochlaggan Limestone at Kinlochlaggan 0.4 mm). consists of three calcite limestones separated by pelitic schist KinlochlagganBoulder Bed. This lies adjacent tothe (Anderson 1947) which compares with three limestones Kinlochlaggan Quartzite on Aonach Beag, but at Kinloch- separated by three schist horizons in the type section of the laggan there is an unexposed gap of about 80 m between the Dark Limestones and Dark Schists at Schiehallion (Treagus two units. Along the NW limb of the Synform, abanded & King 1978). In both cases the schists are graphitic, and schist member consisting of alternating thin layers of kyanite- or sillimanite-bearing. Amajor study of the psammite, quartzite, and pelite, is found at about the same geochemistry of Dalradian limestones (Rock 1986) showed level as the Boulder Bed (Thomas 1979). that the Kinlochlaggan Limestonehas a clear Lower KinlochlagganQuartzite. A grey-white quartzite, locally Dalradian affinity, and Wright (1988) has pointed out that with pink feldspathic layers and occasional bedding-parallel its very high Sr content is an unusual feature which it shares hematitic bands. Both of Anderson’s (1947) localities for with other Blair Atholllimestones such as the Islay and cross-bedding were thoroughlysearched but no definitive Lismore Limestones. way-up evidence was found.Although clear cross-bedding (c) Throughout their outcrop, the Blair Atholl schists are (albeit in strongly foldedrocks) shows thatthe Quartzite highly aluminous and are characterized by the development youngs towards the Grampian Group at two locations [NN of abundant large kyanite prisms, as in the Coire Cheap 4715 7577 and 4531 7352) this observation should be treated Kyanite Schist of the Kinlochlaggan area,or, at higher with caution. grade, by abundant faserkiesel (Connemara).Garnet is Aonach BeagBanded Semi-pelite. A grey gneissose characteristically scarce in these rocks, as at Kinlochlaggan. psammite/semi-pelitecharacterised by centimetre-scale Althoughdetaileda correlation is not possible at compositional layering, thin quartzose bands, and abundant present, we consider that the above similarities provide good quartzo-feldspathic andquartz segregations, which is not support for the correlation of the Kinlochlaggan succession distinguished from theGrampian Group on Fig. 1 as the with formations in the Blair Atholl-Islay subgroups of the outcrop width is generally

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Table 3. New stratigraphical sequence proposed for the Kinloch- ANDERTON.R. 1985. Sedimentationand tectonics in the Scottish Dalradian. lagganDalradian, and its possible correlationwith the Islay Scottish Journal of Geology, 21,407-436. CARRUTHERS, R. G. 1923. The geology of Corrour and the Moor of Rannoch. sequence (Harris et al. 1994) Memoirs of the Geological Survey of Scotland. DALZIEL, I. W. D. 1991. Pacific margins of Laurentia and East Kinlochlaggan sequence Islay sequence Antarctica-Australia as a conjugate rift pair: evidence and implications for an Eocambrian supercontinent. Geology, 19, 598-601. Argyll Group EYLES, C. H. 1989. Glacially- and tidally-influenced shallow marine sedimentation of the Late Precambrian Port Askaig Formation, Scotland. Aonach BeagBanded Semi-pelite Port Ellen Phyllite Palaeogeography. Palaeoclimatology, Palaeoecology, 68, 1-25. Kinlochlaggan Quartzite Islay Quartzite GLOVER,B.W.. KEY, R. M,,MAY, F.. CLARK,G. C., PHILLIPS,E. R. & Kinlochlaggan Boulder Bed Port Askaig Tillite CHACKSFIELD.B. C. 1995. ANeoproterozoic multi-phase rift sequence: Kinlochlaggan Biotite Schist theGrampian and Appin groups of thesouthwestern Monadhliath Mountains of Scotland. Journal of the Geological Society, London, 152, Appin-Argyll boundary 39 1-406. HAMBREY,M. J. 1983. Correlation of LateProterozoic tillites in theNorth Coire na Coichille Limestone Islay Limestone Atlantic region and Europe. Geological Magazine, 120, 209-320. Coire Cheap Kyanite Schist Mullach Dubh Phyllite HARLAND,W. B., HAMBREY.M. J. & WADHAMS,P. 1993. Vendian geology of Kinlochlaggan Limestone Ballygrant Limestone Svulburd. Norsk Polarinstirutt Skrifter, 193. HARRIs, A. L., HASELOCK.P. J.. KENNEDY,M. J. & MENDUM,J. R. 1994. The Sron Gharbh Pelitic Schist Baharradail Phyllite DalradianSupergroup in Scotland,Shetland and Ireland. In: GIBBONS, Sequence missing W. & HARRIS, A.L. (eds) A revised correlation of Precambrian rocks in the British Isles. Geological Society, London. Special Reports 22, 33-53. Grampian Group JOHNSON,M. R. W. 1991. Dalradian. In: CRAIG,G. Y. (ed.) Geology of Scotland. 3rd. edition. Geological Society. London, 125-160. LEAKE, B. E. & TANNER,P.W. G. 1994. The geology of the Dalradian and associated rocks of Connemara. western Ireland. The Royal Irish found within a 100 m of the NW boundary of the Academy, Dublin. Kinlochlaggan Quartzitenear AonachBeag (Fig. 1). It LITHERLAND,M. 1980. The stratigraphy of the Dalradian rocks around Loch separatesthe Aonach BeagBanded Semi-pelite (equated Creran. Argyll. Scottish Journal of Geology, 16, 105-123. PIAsErKI,M. A. J. & TEMPERLEY,S. 1988. TheCentral Highland Division. with the Killiekrankie Schist foundabove the quartziteat In: WINCHESTER,J. A. (ed.) Later Proterozoic stratigraphy of the Schiehallion; Table 3) tothe southeast, from the main Northern Atlantic regions. Blackie, Glasgow, 46-53. GrampianGroup outcrop to the northwest. The tectonic RAST, N. & LITHERLAND,M. 1970. Thecorrelation of the Ballachulish schist is locally platy in character, and commonly contains andPerthshire Dalradian successions. Geological Magazine, 107, 259- 272. lenticular ribbons of quartz. ROCK,N. M. S. 1986. Chemistry of theDalradian (Vendian-Cambrian) rnetalirnestones, British Isles. Chemical Geology, 56, 289-311. Discussion. Our speculation that, over a large area of the SMITH,T. E. 1968. Tectonics in UpperStrathspey, Inverness-shlre. Scottish Central Highlands,majora structural discontinuity has Journal of Geology, 4,68-84. SPENCER,A. M. 1985 Mechanisms andenvironments of deposition of late brought inverted Dalradian rocks on top of, or into contact Precambrian geosynclinal tillites: Scotland and East Greenland. with, an upward younging Grampian Group sequence prior Palaeogeography, Palaeoclimatology. Palaeoecology, 51, 143.157. to the D2 deformation, conflicts with previous structural and THOMAS,P. R. 1979. New evidence for a Central Highland Root Zone. In: stratigraphical interpretations (Thomas 1979, 1980), and has HARRIS,A. L., HOLLAND,C. H. & LEAKE.B. E. (eds) The Caledonides of no analogue in the regional structure of the Dalradian block. the British Isles-reviewed. Geological Society, London. Special Publications, 8, 205-211. In our current state of knowledge it is impossible to decide - 1980. Thestratigraphy and structure of the Moine rocks N of the whether this tectonic contact was initiated during Vendian Schiehallion Complex,Scotland. Journal of the Geological Society. syn-sedimentaryrift-related extensional events (i.e. Glover London, 137,469-482. et al. 1995) or during the early contractional phase of the TORSVIK,T. H.. LOHMANN,K. C. & STuRr. B. A. 1995. Vendian glaciations and their relation to the dispersal of Rodinia: paleomagnetic constraints. Grampian orogeny. The answers to this and other problems Geology, 23,727-730. posed here can only be sought by means of adetailed TREAOIJS,J. E. 1969. The Kinlochlaggan Boulder Bed. Proceedings of the stratigraphical and structural synthesis of the Kinlochlaggan Geological Society, London, 1654, 55-60. Synform, and of the largely unmapped surrounding area. - 1981. The Lower Dalradian Kinlochlaggan Boulder Bed,central Scotland. In: HAMBREY,M. J. & HARLAND.W. B. (eds) Earth’s pre-Pleistocene glacial record. Cambridge University Press, Cambridge, We are indebted to P. R. Thomas for providing unstinting 637-639. encouragement, advice, and critical input throughoutthe work. - 1987. The structuralevolution of theCentral Highlands ofScotland. R.H.S.E. was supported by a NERC Studentship; publication is by Transactions of the Royal Society of Edinburgh: Earth Sciences, 78, 1-15. permission of Shell PetroleumDevelopment Company (Nigeria) - & KING.G. 1978. Acomplete Lower Dalradian succession in the Schiehallion district, Central Perthshire. Scottish Journal of Geology 14, Ltd. We thank J. R. Mendum, S. Robertson & J. E. Treagus 157.166. for valuable discussions and for incisive commentsonthe WINCHESTER,J. A. & GLOVER,B. W. 198X. The Grampian Group, Scotland. script. Correspondenceto P. W. G. Tanner (e-mail: In: WINCHESTER,J. A. (ed.) Later Proterozoic stratigraphy of the [email protected]). Northern Atlantic regions. Blackie, Glasgow, 146.161. - & - 1989. TheGrampian Group: a major late Proterozoic clastic References sequence in the Central Highlands of Scotland. Journal of the Geological Society, London, 146, 85-96. ANDERSON.J. G. C. 1947. The Kinlochlaggan Syncline,southern WRIGHT,A. E. 1988. The Appin Group. In: WINCHESTER,1. A. (ed.) Later Inverness-shire. Transactions of the GeologicalSociety of Glasgow, 21, Proterozoic strarigraphy of the North Atlantic regions. Blackie. Glasgow, 97-1 15. 177-199. - 1956. The Moinian andDalradian rocks betweenGlen Roy and the YOUNG.G. M. 1995. AreNeoproterozoic glacial deposits preserved on the MonadhliathMountains, Inverness-shire. Transactions uf the Royal margins of Laurentiarelated to the fragmentation of two supercon- Society of Edinburgh, 63, 15-36. tinents? Geology. 23, 153.156.

Received 6 June 1996; accepted 3 July 1996 Scientific editing by Cordon Taylor.

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