Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

The Caledonian Orogen in northern Scotland comprises two major thrust nappes: the Moine and the Sgurr Beag Nappe. The Moine Nappe contains early Neoproterozoic Morar Group rocks (Moine Supergroup) and basement inliers. This paper describes the structure and stratigraphy of the Knoydart peninsula, a key area within the southern Moine Nappe. The geology of Knoydart is dominated by a thick internally coherent sequence of Morar Group rocks. This sequence is shown to be deformed by large-scale, west-vergent and west-facing Caledonian (early Palaeozoic) folds that represent D2 within the southern Moine Nappe. Subsequent D3 deformation led to refolding or tightening of F2 folds, so that the major Morar Antiform is, in essence, a composite F2/F3 fold. F2 and F3 folds are broadly co-axial, but F3 folds have steeper axial planes. The F2/F3 folds refold a regional-scale, originally recumbent, isoclinal F1 fold nappe of probable Knoydartian (mid-Neoproterozoic) age. The F1 fold nappe is cored by a thin sliver of basement gneiss; the lower limb comprises migmatitic Morar Group rocks, exposed in the Morar Window. The upper limb of the F1 fold nappe occupies most of Knoydart and is stratigraphically coherent and right-way-up. Within this sequence, the upper unit of the Lower Morar Psammite is barely deformed, preserving trough-cross-bedding and large-scale channels in thick beds. This suggests braided river deposition, similar to the Torridon Group west of the Moine Thrust and the Morar Group in the northern part of the Moine Nappe. On the basis of lithological similarity and stratigraphic disposition, it is suggested that the lowermost part of the Morar Group in Knoydart correlates with the Neoproterozoic Sleat Group on Skye

Progress report on the geology of 1:50k sheet 64W (Newtonmore)

This report describes the results of solid geology fieldwork in 1:50 000 sheet 64W (Newtonmore) resulting from the 2002 summer mapping season. A full revision of the solid geology at 1:10 000 scale was completed in the north-western part of the sheet (Sheet NN69SE) while rapid mapping/reconnaissance of the solid geology has been carried out in the remaining 85% of the sheet area The superficial geology of the sheet has been completely revised and will be described in a separate report. The north-western part of the sheet contains the transition from the deeper water graded sandy and silty turbidite deposits of the Corrieyairack Subgroup upwards (and south-eastwards) into the shallow water sand-dominated deposits of the Strathtummel Subgroup. East of the A9 trunk road, the Gaick region is confirmed as a single lithostratigraphical package in the Strathtummel Subgroup recording shallow water depositional conditions, greatly thickened by D2 recumbent folding. Axial surfaces of these folds dip gently east overall with gently east plunging to subhorizontal fold axes. Axial traces are generally N-S trending. The main regional (biotite) schistosity is axial planar to these folds and locally, can be seen clearly deforming an earlier bedding near-parallel biotite fabric. The available evidence for stratigraphical younging is limited to a few well-washed river sections but shows that regional facing is always to the south in S2 across the Gaick region. No large-scale F1 folds are recognised with the exception of those at Crubenmore on the A9. Minor undulations of the main regional fabric mean that the sheet dip varies between gently north to gently east across open upright north-east-plunging folds, in marked contrast to the conspicuous pattern of reclined, north-west verging D3 folds deforming the main regional (S2) schistosity in Glen Truim and farther north-west. There appear to be no other major fold sets across this part of the Gaick region The Drummochter Dome thus takes the form of a stack of recumbent D2 folds, modified by steep zones to the north-west (Geal CharnOssian Steep Belt) and south-east (Tummel Steep belt and correlatives). The pattern of early recumbent folds and later steep belts is similar to that seen in the higher structural levels south of the Boundary Slide which include the Tay Nappe

A stratigraphic framework for the early Neoproterozoic successions of the Northern Highlands of Scotland.

This report sets out a revised stratigraphic framework for the for the late Mesoproterozoic and early Neoproterozoic successions of the Northern Highlands of Scotland. The late Mesoproterozoic comprises the Stoer Group that, despite its small outcrop, is well exposed and studied. No major changes as to subdivision are proposed for this group. The classic subdivision of Torridonian and Moine Supergroup for the early Neoproterozoic sedimentary rocks of the Northern Highlands of Scotland has become incompatible with new datasets (detrital zircon dates, radiometric dating of metamorphic and igneous events, sedimentological studies) and is now stratigraphically invalic. Supergroup status for the Moine is not warranted, since there is no stratigraphic continuity (as previously thought) between the Morar and Glenfinnan groups. Instead, the successions are grouped into two new Supergroups: an older Wester Ross Supergroup and a younger Loch Ness Supergroup. This subdivision is now compatible with the broad subdivisions in the wider North Atlantic region. The Wester Ross Supergroup includes the Sleat, Torridon and Morar groups, and likely the Iona, Tarskavaig (Skye), and Sand Voe, Yell Sound and Westing (Shetland) groups. These units were deposited between c. 1000-950 Ma, sourced from the Grenville orogen and deposited in a broad foreland-basin setting. Some Wester Ross Supergroup units (and equivalents in Greenland and Svalbard) have been affected by c. 950-910 Ma Renlandian metamorphic and igneous events, and deposition must thus predate this orogeny. The Loch Ness Supergroup includes the Glenfinnan and Loch Eil groups, as well as the Badenoch Group in the Grampian Highlands. Contacts between the Glenfinnan and Morar groups are sheared everywhere and there is no evidence for stratigraphic continuity. The Loch Ness Supergroup was deposited between c. 900 and 870 Ma and is at least partly associated with an extensional tectonic event. The Wester Ross Supergroup and the Loch Ness Supergroup, together with the late (<720 Ma) Neoproterozoic Dalradian Supergroup, can be correlated with the three major Megasequences recognised in the wider Neoproterozoic Northern Atlantic setting, each recording major tectonic events in the Laurentian sector of Rodinia. The late Mesoproterozoic Stoer Group remains distinct. All early Neoproterozoic Formation and Members across the Northern Highlands have been critically assessed and the terminology has been rationalised

Joint-bounded crescentic scars formed by subglacial clast-bed contact forces: implications for bedrock failure beneath glaciers

Glaciers and ice sheets are important agents of bedrock erosion, yet the precise processes of bedrock failure beneath glacier ice are incompletely known. Subglacially formed erosional crescentic markings (crescentic gouges, lunate fractures) on bedrock surfaces occur locally in glaciated areas and comprise a conchoidal fracture dipping down-ice and a steep fracture that faces up-ice. Here we report morphologically distinct crescentic scars that are closely associated with preexisting joints, termed here joint-bounded crescentic scars. These hitherto unreported features are ca. 50–200 mm deep and involve considerably more rock removal than previously described crescentic markings. The joint-bounded crescentic scars were found on abraded rhyolite surfaces recently exposed (< 20 years) beneath a retreating glacier in Iceland, as well as on glacially sculpted Precambrian gneisses in NW Scotland and various Precambrian rocks in Ontario, glaciated during the Late Pleistocene. We suggest a common formation mechanism for these contemporary and relict features, whereby a boulder embedded in basal ice produces a continuously migrating clast-bed contact force as it is dragged over the hard (bedrock) bed. As the ice-embedded boulder approaches a preexisting joint in the bedrock, stress concentrations build up in the bed that exceed the intact rock strength, resulting in conchoidal fracturing and detachment of a crescentic wedge-shaped rock fragment. Subsequent removal of the rock fragment probably involves further fracturing or crushing (comminution) under high contact forces. Formation of joint-bounded crescentic scars is favoured by large boulders at the base of the ice, high basal melting rates, and the presence of preexisting subvertical joints in the bedrock bed. We infer that the relative scarcity of crescentic markings in general on deglaciated surfaces shows that fracturing of intact bedrock below ice is difficult, but that preexisting weaknesses such as joints greatly facilitate rock failure. This implies that models of glacial erosion need to take fracture patterns of bedrock into account

Consequences of limited sediment supply for long-term evolution of offshore tidal sand waves, a 3D model perspective

Field data show that offshore tidal sand waves in areas where sediment supply is limited have different characteristics (shape and dimensions) compared with their counterparts in areas with sufficient sediment supply. So far, only the initial formation of tidal sand waves on a sediment-starved shelf has been studied with a 2DV model that ignores variations along the crests. In this study, a 3D non-linear morphodynamic model is used to investigate the effects of sediment availability on the long-term evolution of offshore tidal sand waves. Overall, the simulated sand waves have characteristics that resemble those of observed sand waves. The mature sand waves that develop in the case of limited sediment supply (i.e., thickness of erodible sediment layer is smaller than the height of sand waves) are more three-dimensional, i.e., having isolated and more irregular crestlines compared with those in the case of sufficient supply. With decreasing sediment supply, sand waves have larger spacings between successive crests, smaller heights and they migrate faster. These differences in the characteristics of the sand waves start to occur once the hard bed underneath the erodible sediment layer is exposed

Calcium-activated potassium channels:Implications for aging and age-related neurodegeneration

Population aging, as well as the handling of age-associated diseases, is a worldwide increasing concern. Among them, Alzheimer's disease stands out as the major cause of dementia culminating in full dependence on other people for basic functions. However, despite numerous efforts, in the last decades, there was no new approved therapeutic drug for the treatment of the disease. Calcium-activated potassium channels have emerged as a potential tool for neuronal protection by modulating intracellular calcium signaling. Their subcellular localization is determinant of their functional effects. When located on the plasma membrane of neuronal cells, they can modulate synaptic function, while their activation at the inner mitochondrial membrane has a neuroprotective potential via the attenuation of mitochondrial reactive oxygen species in conditions of oxidative stress. Here we review the dual role of these channels in the aging phenotype and Alzheimer's disease pathology and discuss their potential use as a therapeutic tool

Revision of the solid geology shown on the 'Assynt District' special geological map : a report on the 2002 fieldwork

The report provides an overview of the main findings from the first field season in the Assynt District of the Moine Thrust Project. Detailed mapping in the eastern part of the Assynt halfwindow has resulted in a new interpretation of the geometry and behaviour of the Ben More Thrust. This reinterpretation of the thrust satisfactorily resolves the conflicts between the various previous models. The remapping confirmed that the Ben More Thrust can be traced, as shown on the published 1923 Assynt District geological map, along the western flank of Na Tuadhan to Bealach a’ Mhadhaidh. The Ben More Thrust is then traced to [NC 30026 24416] where it is displaced across a steep reverse fault to [NC 30514 23953]. It then continues NNW as a readily traceable feature placing gneisses of the Lewisian Gneiss Complex over quartzite along Leathaid Riabhach [NC 298 252]. Here the Ben More Thrust progressively steepens into a sub-vertical structure that has gneiss to the NE and quartzite to the SW. The thrust follows a prominent gully along Leathaid Riabhach to A’ Chailleach. From here the Ben More Thrust more or less follows the top of a monoclinally folded quartzite that forms the summit of Beinn Uidhe and is exposed in the valley floor NW of A’ Chailleach. It retains thrust geometry with hangingwall gneisses and footwall quartzites and becomes a steep feature that approximately follows ‘Glen Beag’ (the un-named glen south of the Stack of Glencoul). The Ben More Thrust meets, but does not displace the Glencoul Thrust at the head of Loch Glencoul. Therefore it is proposed that there is a branch line here where the two thrusts meet so that all the rocks NE of Loch Glencoul and east of Loch Beag are part of the Ben More Thrust Sheet. Figure 2.7 in the report provides a clear pictorial description of the geometry of the Ben More Thrust in the northern part of the Assynt half-window. A significant new ductile structure has been identified within the Ben More Thrust Sheet, termed the Coire a’ Mhadhaidh Detachment, that mostly follows the Lewisian gneisses/quartzite contact. It has been traced from the northern limits of the Loch Ailsh intrusion across Ben More Assynt, along the eastern slopes of Na Tuadhan, across Cailleach an t-Sniomha to the west of Gorm Loch Mòr and immediately west of the Stack of Glencoul into Glen Coul (Figure 2.1 in the report). The sense of shearing in the detachment is almost always top-to-west. Similar smaller shears have also been recognised within the Lewisian gneisses in the thrust sheet. However, no ductile shearing was noted at the gneiss/quartzite contact below the Ben More Thrust. Several of the complex imbricate structures mapped by previous workers were revisited. The imbricates in the Loch an Eircill–Loch nan Caorach area appear to be simpler than shown on the published Assynt District map. An alternative solution is provided for the southern termination of the Glencoul Thrust south of Inchnadamph although it is noted that more detailed work needs to be done, notably south of Conival. Brief descriptions are given of Moine rocks above the Moine Thrust in the north-eastern part of the Assynt District map. There appears to be a lateral facies change with semipelitic schists dominant in upper Glen Cassley and psammites becoming dominant to the north. Fabrics associated with several deformation phases have largely obliterated sedimentary structures although transposed bedding traces can be seen between a spaced foliation that controls the flaggy character of the psammites. Widely spaced traverses across the major Lewisian outcrop areas, within the Assynt half-window as well as in the western foreland to the thrust belt, largely confirmed the work of the primary surveyors. Thus all of the Lewisian comprises orthogneisses, mostly hornblende-gneisses but with more felsic pyroxene-bearing gneisses in the north, that all contain ultramafic and mafic pods and layers. The traces of the various Scourie dykes are correctly shown on the published Assynt District map. The Canisp Shear Zone has been traced eastwards, south of Canisp, eventually disappears under Cambrian quartzites. A second parallel shear has also been delineated north of Loch Assynt. The polyphase nature of ductile deformation in the Lewisian gneisses elucidated by previous workers is confirmed. However, the deformation state of the gneisses is extremely variable on all scales, with intense deformation confined to specific (shear) zones that vary in thickness from several centimetres up to hundreds of metres. Descriptions of the numerous minor intrusions and the Quaternary deposits studied during the fieldwork are given in separate reports

Drag forces at the ice-sheet bed and resistance of hard-rock obstacles:The physics of glacial ripping

Glacial ripping involves glaciotectonic disintegration of rock hills and extensive removal of rock at the ice-sheet bed, triggered by hydraulic jacking caused by fluctuating water pressures. Evidence from eastern Sweden shows that glacial ripping caused significant subglacial erosion during the final deglaciation of the Fennoscandian ice sheet, distinct from abrasion and plucking (quarrying). Here we analyse the ice drag forces exerted onto rock obstacles at the base of an ice sheet, and the resisting forces of such rock obstacles: glaciotectonic disintegration requires that ice drag forces exceed the resisting forces of the rock obstacle. We consider rock obstacles of different sizes, shapes and fracture patterns, informed by natural examples from eastern Sweden. Our analysis shows that limited overpressure events, unfavourable fracture patterns, low-Transmissivity fractures, slow ice and streamlined rock hamper rock hill disintegration. Conversely, under fast ice flow and fluctuating water pressures, disintegration is possible if the rock hill contains subhorizontal, transmissive fractures. Rock steps on previously smooth, abraded surfaces, caused by hydraulic jacking, also enhance drag forces and can cause disintegration of a rock hill. Glacial ripping is a physically plausible erosion mechanism, under realistic glaciological conditions prevalent near ice margins.</p

Gneiss, fractures and saprolite: field geology for hydrogeology of the central Cauvery Catchment, south India

This report describes the geological observations and interpretations made following two reconnaissance field trips in October 2017 and April 2018 by Maarten Krabbendam and Romesh Palamakumbura, in the central Cauvery catchment in South India. The goal of the reconnaissance was to provide geological constraints to hydrogeological modelling to be undertaken as part of the UPSCAPE Project. The main geological constraints dealt with are fractures and the character of the regolith