Red Sandstone Sediments Research Articles

Northern Svalbard Composite Tectono-Sedimentary Element

Abstract The Northern Svalbard Composite Tectono-Sedimentary Element (CTSE) comprises Proterozoic, Early Paleozoic and Devonian sedimentary rocks preserved in northern Svalbard and on the adjacent shelf margin between complexes of metamorphic and crystalline basement rocks. The Northern Svalbard CTSE covers four main tectono-sedimentary elements: Tonian synrift, Neoproterozoic–Cambrian post-rift, Ordovician passive margin and late Silurian?/Devonian synextensional basins. The oldest documented sedimentary strata are greywacke and shale deposited after the Greenvillian Orogeny and assumed to be younger than 980–960 Ma. The present CTSE further includes Cambrian–Ordovician sedimentary rocks in Ny-Friesland and Nordaustlandet, while the dominant part of the CTSE are continental Old Red Sandstone sediments of the late Silurian?/Early Devonian Red Bay and Siktefjellet groups and the Early–Late Devonian Andreé Land Group onshore northern Spitsbergen. Locally, the Cambrian–Ordovician formations contain petroleum source rocks with moderate total organic carbon contents and relatively high hydrogen index values, suggesting a good potential for oil generation. There are possible reservoirs, seals and traps in some of the basins but the CTSE generally holds a very limited potential as a petroleum province, particularly as the region is under strict environmental protection.

Euryhaline ecology of early tetrapods revealed by stable isotopes.

The fish-to-tetrapod transition-followed later by terrestrialization-represented a major step in vertebrate evolution that gave rise to a successful clade that today contains more than 30,000 tetrapod species. The early tetrapod Ichthyostega was discovered in 1929 in the Devonian Old Red Sandstone sediments of East Greenland (dated to approximately 365 million years ago). Since then, our understanding of the fish-to-tetrapod transition has increased considerably, owing to the discovery of additional Devonian taxa that represent early tetrapods or groups evolutionarily close to them. However, the aquatic environment of early tetrapods and the vertebrate fauna associated with them has remained elusive and highly debated. Here we use a multi-stable isotope approach (δ13C, δ18O and δ34S) to show that some Devonian vertebrates, including early tetrapods, were euryhaline and inhabited transitional aquatic environments subject to high-magnitude, rapid changes in salinity, such as estuaries or deltas. Euryhalinity may have predisposed the early tetrapod clade to be able to survive Late Devonian biotic crises and then successfully colonize terrestrial environments.

Sedimentological constraints on the late Silurian history of the Highland Boundary Fault, Scotland: implications for Midland Valley Basin development

The relationship between movement on the Highland Boundary Fault and deposition of the Lower Old Red Sandstone in the Midland Valley Basin of Scotland is controversial. Most models favour mid-Silurian to early Devonian sinistral movement on the Highland Boundary Fault and development of a transtensional Midland Valley Basin. To constrain Highland Boundary Fault movement during the late Silurian, we examine the basal Lower Old Red Sandstone alluvial succession exposed adjacent to the Highland Boundary Fault. A lack of synsedimentary fault movement indicators, coupled with an increase in stratal thickness across the fault, indicates that the Highland Boundary Fault was not active during Lower Old Red Sandstone sedimentation. A transtensional basin model cannot be sustained.

The seabed geomorphology and geological structure of the Firth of Lorn, western Scotland, UK, as revealed by multibeam echo-sounder survey

ABSTRACTThis paper presents recently collected swath bathymetry from the Firth of Lorn. 553 km2 of data were collected during 2012–2013 as part of the INIS Hydro (Ireland, Northern Ireland and Scotland Hydrographic Survey) programme.The area proves to consist of bedrock-dominated seabed, divided into narrow, stratigraphically-constrained and glacially-over-deepened basins. The bedrock is composed of late Proterozoic Dalradian metasediments overlain unconformably by Old Red Sandstone (ORS) sediments and lavas of ?Silurian-age. The central region of the Firth of Lorn is dominated by a vertical cliff, up to 150 m high and extending for approximately 24 km. This feature, here termed the Insh Fault, may have originated as a Dalradian extensional fault, been reactivated as an ORS feature and now forms a fault-line scarp with resistant ORS rocks on the downthrown side, flanking the more deeply eroded metasediments exposed in the basin. Tertiary intrusives are common, in particular, swarms of Paleocene dolerite dykes exposed on the sediment-free bedrock surfaces, and can be traced for many kilometres.Evidence for past glaciation is widespread, manifest in the extensive erosion of the bedrock platforms and the abundance of well-preserved moraines and over-deepened basins. The survey region includes the Corryvreckan Whirlpool and Great Race, beneath the tidal flows of which occur submarine dunes.

Time-Transgressive Salinic and Acadian Orogenesis, Magmatism and Old Red Sandstone Sedimentation in Newfoundland

We propose an intimate relationship between Silurian terrestrial red bed sedimentation (Old Red Sandstone), slab breakoff-related magmatism and deformation in the Newfoundland Appalachians. Red bed sedimentation started during the Early Silurian, and records the progressive rise of the Salinic mountains in the tectonic hinterland of the orogen. The red beds were mainly deposited in molasse-style foreland basins in front of an east-propagating terminal Salinic deformation front. New U–Pb zircon dating of volcanic rocks interlayered with the Silurian red beds in key structural locations yielded ages ranging between 425 and 418 Ma, which, combined with the existing geochronological database, suggests that the sedimentary rocks are progressively younger from west to east and overstep the accreted Gondwana-derived terranes. We propose that deposition of the red beds is a good proxy for the time of cratonization of the accreted terranes. Eastward migration of the Salinic deformation front was accompanied by eastward-widening of a slab-breakoff-related asthenospheric window. The latter is interpreted to have formed due to a combination of progressive steepening of the down-going plate following entrance of the leading edge of the Gander margin and its eduction. Gander margin eduction (reversed subduction) is proposed to have been instigated by the trench migration of the Acadian coastal arc built upon the trailing edge of the Gander margin, which developed contemporaneously with the Salinic collision. The resultant thinning of the lithosphere beneath the Salinic orogen, built upon the leading edge of the Gander margin immediately prior to the onset of the Early Devonian Acadian orogeny, set the stage for generation of the widespread bloom of Acadian magmatism.SOMMAIRENous proposons qu’il y a eu une relation intime entre la sédimentation des couches rouges continentales au Silurien (vieux-grès-rouges), un magmatisme lié à une rupture de segments de croûte, et la déformation appalachienne à Terre-Neuve. La sédimentation des couches rouges qui a débuté au début du Silurien témoigne du soulèvement progressif des monts saliniques de l’arrière-pays tectonique de l’orogène. Les couches rouges se sont déposées sous forme de molasses dans des bassins d’avant-pays, à l’avant du front de déformation salinique terminale qui se déployait vers l’est. De nouvelles datations U-Pb sur zircon de roches volcaniques interstratifiées avec des couches rouges siluriennes en des lieux structurels stratégiques montrent des âges qui varient entre 425 Ma et 418 Ma, ce qui, combiné aux bases de données géochronologiques existantes permet de penser que les roches sédimentaires sont progressivement plus jeunes d’ouest en est, et qu’elles surplombent les terranes accrétés du Gondwana. Nous suggérons que les couches rouges sont de bons indicateurs temporels de la cratonisation des terranes accrétés. La migration vers l’est du front de la déformation salinique a été accompagnée par un élargissement vers l’est d’une fenêtre asthénosphérique liée à une rupture de la croûte. Cette dernière aurait été provoquée par la combinaison de l’enfoncement progressif de la plaque qui a suivi l’entrée du bord d’attaque de la marge de Gander, et son éduction. Nous proposons que l’éduction (l’inverse de la subduction) de la marge de Gander a été provoquée par la migration de la fosse tectonique côtière acadienne, induite par la migration du bord d’attaque de la marge de Gander, contemporaine de la collision salinique. L’amincissement de la lithosphère sous l’orogène salinique qui en a résulté, et qui s’est déployé au bord d’attaque de la marge de Gander juste avant l’enclenchement de l’orogénie acadienne au début du Dévonien, a préparé le terrain du déploiement à grande échelle du magmatisme acadien.

Geology from rail journeys: the Inverness to Wick Line, Scotland

The Inverness to Wick railway line enables travellers to track the geological history of the far northeast of Scotland, spanning about 1000 million years, and starting in the Neoproterozoic. This history includes the Caledonian Orogeny, the deposition of Old Red Sandstone and Mesozoic sediments, the latter along the faulted margins close to the Great Glen Fault system, and ends with Pleistocene and Holocene deposition and erosion.

Calcrete morphology and karst development in the Upper Old Red Sandstone at Milton Ness, Scotland

Abstract The Upper Old Red Sandstone at Milton Ness, Scotland, is notable for its excellent preservation of calcrete textures, which are comparable with some of the best Quaternary examples. It is also significant for the implications that can be drawn from the association between karst and calcrete, with this example interpreted to have formed entirely within a semi-arid environment. Karst cavities were developed in a mature hardpan calcrete, generated in sandy fluvial sediments with associated aeolian deposits. Subsequent to karst cavity generation, clasts derived from the subaerially exposed hardpan were locally transported and deposited as a laterally traceable bed connecting the tops of all the cavities. Both this bed and the karst infills were subsequently recalcretized in the final phase of the profile’s evolution. Although calcrete-karst associations often are interpreted as the alternation between semi-arid and humid climates, respectively, this example is interpreted to be a result of water accumulating on the nearly impervious hardpan surface under fairly constant semiarid conditions, evidenced by the recalcretization of both the karst infill and the calcrete-derived breccia (‘boulder calcrete’). Additional substrate modification also has taken place by plant roots; the remarkable development of rhizoliths in these Old Red Sandstone sediments should emphasize the need to consider plant influence on other non-marine rocks of post-Silurian age.

Depositional and structural setting of the (?)Lower Old Red Sandstone sediments of Ballymastocker, Co. Donegal

Abstract Approximately 250 m of unfossiliferous sediments attributed to the Old Red Sandstone outcrop onshore at Ballymastocker, Donegal in northwest Ireland. Massive sandstones and trough cross-bedded sandstones pass upwards into coarse purple-brown basal conglomerates. The majority of the clast types, which include quartzite, marble, pelite, schist, vein quartz and metadolerite, are derived from the local Dalradian basement. Acid to intermediate porphyry clasts have no local source and may indicate a source to the northeast in the vicinity of the Devonian Lorne Plateau volcanic rocks in Argyll. The rocks are believed to represent an intermontane alluvial fan environment. The sediments occur in an outcrop of 3 km length against the northern flank of Knockalla Mountain, bounded to the southeast by the NE-SW-trending Caledonian Leannan Fault and resting on fractured Argyll Group Dalradian basement. No unconformable contact is observed and all contacts may be tectonic. Coarsening-up cycles within the sediments may reflect syn-sedimentary tectonic activity. The Devonian rocks are transected by a fracture system implying dextral transpressional activity on the Leannan Fault. The Dalradian basement rocks preserve evidence of sinistral strike-slip movement in late Caledonian times. Slickenfibres observed within the sediments and Dalradian rocks provide evidence for oblique dip-slip movement to the northwest. It is considered that these structures represent the last movement of the ORS basin, dropping it below denudation level, which resulted in its preservation. Movement along the Leannan Fault played a major role in the preservation of the offshore basins in the Islay-Donegal Platform region.

A mid-Frasnian marine incursion into the southern part of the Munster Basin: evidence from the Foilcoagh Bay Beds, Sherkin Formation, SW County Cork, Ireland

Abstract The Munster Basin of southern Ireland contains a thick (7 km +) succession of Old Red Sandstone sediments interpreted as the product of various alluvial processes. The present study presents a preliminary sedimentological and palynological analysis of a grey succession informally known as the Foilcoagh Bay Beds, which is the lowest unit of the Sherkin Formation exposed in the southern part of the basin. Sedimentological analysis of the succession suggests that it is the product of sinuous distributary channels, flanked by permanently flooded overbank areas that endured occasional crevasse splay floods. These conditions evolved into a protected lagoon or lake that received periodic high energy floodings from an adjacent marine environment. Palynological study has refined the age of the Foilcoagh Bay Beds as mid-Frasnian time. Palynofacies analysis has provided direct evidence of marine influence as revealed by the presence of marine microfossils and abundant amorphous organic matter at some dark grey mudrock levels. This suggests deposition in a well-established lacustrine or lagoonal environment in which anoxic conditions prevailed at intervals and which was subjected to a period of marine incursion. The recognition of a marine influence in the Munster Basin at an early stage in its history has several important implications, including the following (1) previous models for the basin that suggested an enclosed centripetally draining entirely non-marine system have to be re-evaluated; (2) the drainage pattern and direction of the marine incursion were probably controlled by localized subsidence along an east-east direction; initiation of subsidence associated with the development of the east-west-trending South Munster Basin may have commenced much earlier than previously considered; (3) the occurrence of marine conditions has been tentatively correlated with the Rhinestreet mid-Frasnian sea-level highstand; (4) the recognition of marine conditions early in the known history of the basin provides a pathway for fish to have entered the basin; (5) the basin may have had a marine connection throughout much of Late Devonian time, opening the possibility for base-level control of the alluvial systems within the basin by external eustatic factors.

The calculation of base cation release from the chemical weathering of Scottish soils using the profile model

To investigate the weathering rates of different soil parent materials which occur in Scotland, a study has been undertaken in which detailed soil mineralogy has been used to calculate base cation release. To calculate base cation release, this data, and supplementary soil chemistry and physical attribute data, have provided the input to the PROFILE model. The model is a multi-layer, steady state, deterministic model in which the soil is represented by a series of mixed tank reactors, each of which has the mineralogical, physical and chemical attributes measured for individual soil horizons. The major parent materials from which Scottish soils have developed are glacial till, derived from acid to basic igneous rocks, schist and other metamorphic types, Lower Palaeozoic greywackes and shales, Old Red Sandstone sediments, Carboniferous sediments and Permo-Trias sediments. For each of the parent materials, three soil profiles were analysed and used with the PROFILE model. The base cation release rates, calculated for these parent materials in the top 50cm of the soil profile, varies between 0.2 and 3.2 keq/ha/yr, although, for a given parent material, the range was usually quite small. In general, these results compare very favourably with those suggested for the calculation of critical loads using an empirical approach proposed at Skokloster. In comparison with current rates of deposition, this suggests many of these soils are being acidified and that for many soil-plant combinations, the critical load may be exceeded.

Discussion on vitrinite reflectivity and the structure and burial history of the Old Red Sandstone of the Midland Valley of Scotland

Gerald M. Friedman writes: the paper by Marshall et al. 1994 uses vitrinite reflectivities from Lower Old Red Sandstone (ORS) sediments of the Midland Valley of Scotland to interpret burial and uplift history. Vitrinite reflectivies give values of 1.3% for the Stonehaven Group (Kincardineshire) and 1.3% for the Strathmore Group (Perthshire). They conclude that 'the Stonehaven Group reflectivity values are considerably lower than expected under the 9 km of sediments aggregated for the Lower ORS of Kincardineshire and demonstrate a maximum burial of 3 to 5 km’. The ORS correlates with the Devonian red beds of the Appalachian Basin. Here carbonized plant debris in uppermost Middle Devonian strata within the eastern Catskill Mountains of New York have been converted to anthracite (Friedman & Sanders 1982). The anthracite has a vitrinite reflectance of 2.5%. This implies a level of organic metamorphism (LOM) of 16. A similar degree of thermal activity is implied by the black colour (Staplin kerogen alteration index of 4) of the associated (possibly recycled) carbonized kerogen; a conodont alteration index of 4; and authigenic chlorite and local sericite fillings of the interparticle pores of interbedded sandstones. The specimens are about 350 Ma old. If 200 Ma is taken as the duration of exposure to the maximum geothermal temperature, then the LOM of 16 and other thermal indicators imply a maximum temperature of 190 °C. Using a geothermal gradient of 26°C km −1 , a former depth of burial of 6.5 km is implied. Such a former depth is consistent with

Vitrinite reflectivity and the structure and burial history of the Old Red Sandstone of the Midland Valley of Scotland

Vitrinite reflectivities from Lower Old Red Sandstone (ORS) sediments of the Strathmore region in the Midland Valley of Scotland give values of 1.2% for the Stonehaven Group (Kincardineshire), 0.9% for the Arbuthnott Group (Angus) and 1.3% for the Strathmore Group (Perthshire). These values are corroborated by clay mineral diagenesis studies. The Stonehaven Group reflectivity values are considerably lower than expected under the 9 km thickness of sediments aggregated for the Lower Old Red Sandstone of Kincardineshire and demonstrate a maximum burial of some 3 to 5 km. These results together with detailed vitrinite reflectivity measurements in the Dundee Formation, consideration of post-Devonian burial history and kinetic burial modelling, show that the present level of Lower ORS thermal maturation results from Late Carboniferous maximum burial. This is confirmed by comparison with a vitrinite reflectivity gradient from the Strathclyde Group of Fife. To reconcile the vitrinite reflectivity data with the stratigraphy and structure of the Lower Old Red Sandstone, burial models invoking structural repetition, depocentre migration and structurally assembled stratigraphy are considered. It is concluded that the Lower Old Red Sandstone is a structurally assembled series of basins with the Cowie Formation of the Stonehaven Group being part of a separate depositional succession and structurally juxtaposed into its present position as part of an apparently contiguous sequence.

Effect of drainage on characteristics of some soils of the Orkney Islands

Three soil profiles with different degrees of drainage impedance developed on glacial till derived from Middle Old Red Sandstone sediments in the Orkney Islands were characterized texturally, chemically and mineralogically. Particular features of these soils were the high organic matter contents (9-50%) of the surface horizon soils resulting from high rainfall and cool temperatures. The high exchangeable Na+ and K+ contents in surface horizons of two of the pedons are a result of salt spray. The clay mineralogy and the nature and amount of aluminosilicate gel were affected by drainage class. In general, chlorite dominates the clay fraction of the imperfectly drained soil. However, with increasing impedence it was gradually displaced by mica which ultimately predominates in the very poorly drained saline gley. Vermiculitization occurred in the better drained soils. The poorly drained soils were distinguished by the absence of chlorite. Goethite was present in all soils but lepidocrocite occurred only when drainage was strongly impeded. Hematite was never present in these soils.

Genetic types of manganese oxide deposits in Scotland; indicators of paleo-ocean-spreading rate and a Devonian geochemical mobility boundary

There are over 70 occurrences of manganese oxides throughout Scotland; of these, only 13 are sufficiently well developed to be worthy of description. The deposits are categorized on the basis of the formation processes; eight are supergene ground-water or soil deposits, three formed by weathering, and two are hydrothermal in origin. The chemistry of marine sedimentary exhalative deposits can be related to the paleospreading rate of the once-active ridge and, under favorable conditions of stratigraphic preservation, be used to estimate the halfwidth of the ancient ocean. This approach yields estimates of 5 cm yr (super -1) and about 1,000 km for the spreading rate and maximum half-width of the Ordovician Iapetus ocean, respectively: figures which compare favorably with earlier estimates from faunal migration studies.Several of the Scottish manganese outcrops are associated with Old Red Sandstone (Devonian) sediments--a continental fluvial-lacustrine facies in northern Scotland. Diagenetic remobilization, with subsequent oxidation and deposition, of the manganese within the lacustrine sediments led to the formation of a manganese-rich horizon in the uppermost sections of the Old Red Sandstone sedimentary pile. Previously immobile in the pre-Devonian inorganic reaction-dominant regime, manganese mobility increased dramatically with the introduction of large quantities of organic acids following terrestrial colonization by plants. Climate change from arid to tropical with increased vegetation development promoted the formation of thick, organic-rich soils with the concomitant increase in available manganese-chelating ligands. Organomanganese reactions fundamentally changed the pattern of manganese mobility in the postcolonization surficial environment, making the Devonian a stratigraphic geochemical boundary. These changes in weathering processes would also affect the dispersal patterns of other metals which form organo complexes, gold being an obvious example.

Devonian extensional tectonics versus Carboniferous inversion in the northern Orcadian basin

The Old Red Sandstone (Middle Devonian) Orcadian basin was formed as a consequence of extensional collapse of the Caledonian orogen. Onshore study of these collapse-basins in Orkney and Shetland provides directions of extension during basin development. The origin of folding of Old Red Sandstone sediments, that has generally been related to a Carboniferous inversion phase, is discussed: syndepositional deformation supports a Devonian age and consequently some of the folds are related to basin formation. Large-scale folding of Devonian strata results from extensional and left-lateral transcurrent faulting of the underlying basement. Spatial variation of extension direction and distribution of extensional and transcurrent tectonics fit with a model of regional releasing overstep within a left-lateral megashear in NW Europe during late-Caledonian extensional collapse. Later inversion (probably during the Upper Carboniferous) is characterized by E–W to NE–SW contraction. It induced reactivation of extensional faults as thrusts, development of small-scale folds and thrusts, and right lateral transcurrent movement of the major faults such as the Great Glen and Walls Boundary faults.

Genesis of coffinite and the U-Ti association in lower old red sandstone sediments, Ousdale, Caithness, Scotland

The mineralogy of a fault-related uranium occurrence, in clastic rocks overlying granite, is described from borehole material. Coffinite is the only important uranium mineral. Other notable minerals are sulphides, fluorite, calcite and hydrocarbon. Coffinite is epigenetic and paragenetically late, rimming sulphides and hycrocarbon. It occurs partly in spatial association with a TiO2 mineral (probably anatase). This U-Ti association is attributed to adsorption of U by altered Ti-minerals prior to growth of the U mineral. Thus is has similarities with many diagenetic occurrences, though their mineralogy is usually different (the U-Ti association being represented by uranotitanates). The latter are attributed to local supersaturation of TiO2, which did not occur at Ousdale because Ti was relatively mobile in the fluids. Coffinite + TiO2 + quartz is interpreted as a stable low-temperature assemblage. The mineralogy thus indicates a hydrothermal uranium mineralization of an unusual type (without prominent uraninte), formed from relatively low-temperature fluids containing complexing agents which mobilized Ti.

Upper Old Red Sandstone sedimentation in the Buchan oilfield, North Sea

Synopsis A fining and maturing upwards fluvial sequence of Devonian to Viséan age forms the reservoir section of the Buchan oilfield. An upward transition occurs from mainly bed-transport deposits to bed-transport plus suspension deposits. The lower part of the sequence comprises multi-storey sand bodies deposited in mobile-channel belts and during sheetfloods. The upper part of the sequence is characterised by a greater number of fining-upward cycles, an increase in the amount of fine grained material and an increase in the number of cornstone horizons. It was deposited in a system of channels and associated flood basins, over which waning-flow sheetflood deposition periodically occurred. The upward change in facies and sedimentation style is interpreted as being due to the combined influences of three processes: a) a rise in sea level that raised river base levels; b) a change in climate and c) a decrease in the sediment supply from the soure area, which was possibly a granitic intrusion to the WNW of the field.

A Lower Old Red Sandstone lake in the offshore Orcadian Basin

Lower Old Red Sandstone (ORS) sediments have been recorded from a number of localities onshore around the margins of the Orcadian Basin ([Westoll 1977][1]; [Mykura 1983][2]; [Mykura and Owens 1983][3]). Similar sediments have not previously been reported from offshore but [Mykura (1983)][2] suggested that a number of isolated basins of this age might exist in the Moray Firth. One of these predicted basins has recently been penetrated by a borehole drilled by Burmah Oil Exploration Ltd. The Burmah well 12/27–1 lies about 45 km northeast of Lossiemouth, and is located to the south of the Great Glen Fault (Fig. 1). Approximately 3200 feet (976 m) of Lower Devonian sediments are recorded in the well. The miospore populations recovered are extremely sparse, and include carbonised examples of Emphanisporites annulatus, E. robustus, Calamospora spp. and Retusotriletes spp. These limited assemblages together with the total absence of all characteristic Middle or late Devonian taxa suggests an early Devonian age for the sediments (B. Owens, pers. com.). The carbonisation recorded is commonly found in Devonian spores from onshore sequences (J. Marshall, J. Brown and S. Hindmarsh, verbal communication to Orcadian Basin conference, Cambridge, September 1984). Downhole logs and well cuttings indicate that the lithology is fine grained throughout the 3200 feet. Three short cores have been cut and these are composed predominantly of mid to dark grey coloured, slightly micaceous claystones with interbedded dark grey siltstones up to about 4 feet (1.2 m) thick. Variable amounts of dolomite are found throughout, sometimes comprising . . . [1]: #ref-3 [2]: #ref-1 [3]: #ref-2

The soil clays of Great Britain: II. Scotland

AbstractThe soils of Scotland are relatively young, being developed mainly on glacial drift deposited some 10 000 years ago. Only a small number of genetic soil types are represented, but this is more than compensated for by the wide variety of parent materials from which the drift ultimately derives. The major parent materials include granite and granitic gneiss, gabbro, basalt/andesite, mica-schist and related metamorphic rock types, Lower Palaeozoic greywackes and shales, Old Red Sandstone sediments, Carboniferous sediments, fluvioglacial sands and gravels, and estuarine silts and clays. The clay mineralogy of the soil associations developed on these parent materials is described and the origin of the clay minerals is interpreted. It is concluded that the influence of inheritance is predominant, but that the effects of pre-glacial weathering and Holocene pedogenesis can also be discerned. Inheritance has contributed a wide variety of clay minerals to the soils, including illite, kaolinite, chlorite, smectite and a number of interstratified minerals, pre-glacial weathering has resulted in the widespread formation of kaolinite and halloysite, irrespective of soil parent material or drainage class, and recent pedogenesis has brought about the transformation of inherited layer silicates by vermiculitization processes, with concomitant interlayer alumination, particularly in surface horizons.

Miospores, correlation and age of some Scottish Lower Old Red Sandstone sediments from the Strathmore region (Fife and Angus)

Abstract. The age of some Lower Old Red Sandstone sediments (Arbuthnott Group) is reassessed and confirmed as Lower Devonian (lower Gedinnian) on the basis of a reinvestigation of spore assemblages. The data upon which this age assessment is based are provided by recent palynological researches in the Welsh Borderland, the type area of the Gedinnian (Belgium), and the graptolite-bearing parastratotype for the Silurian-Devonian boundary (Podolia). Samples from the Arbuthnott Group at Wormit (Fife), associated with rocks dated as 407± 6 Ma by Thirlwall (1983) and regarded by him as Silurian, have yielded miospore assemblages of early but not earliest Devonian when compared with the Podolian Silurian-Devonian sequence. Samples throughout the sequence of the Arbuthnott Group as exposed in Angus and Fife have yielded miospores. These assemblages, occurring at levels above and below the Wormit samples, are all of lower Gedinnian age. The whole of the spore-bearing succession of the Arbuthnott Group, which is about 1,800 m thick, belongs to the micrornatus-newportensis Zone (lower and middle subzones) and is equivalent to part of the lower Ditton Group of Brown Clee Hill (Shropshire) of 20 to 30 m in thickness. There is no critical palaeontological evidence for age in the strata associated with the Arbuthnott Group, neither in the underlying Dunnottar and Crawton Groups nor in the overlying Garvock Group so the exact position of the Silurian-Devonian and Gedinnian-Siegenian boundaries is uncertain. A new spore Anteturma, namely Cryptosporites, is proposed. Qualisaspora fragilis gen. et sp. nov. is described herein and appears to have potential as an index fossil for the lower Dittonian of the British Isles. Some regional differences also occur as ?Dibolisporites sp. A and ?Samarisporites sp. A occur in beds dated as lower Gedinnian in Sotland whereas spores of similar sculpture and structure are present higher in the Anglo-Welsh sequence in beds dated as lower Siegenian.