Sedimentology of the Old Red Sandstone (Siluro-Devonian) in the Clee Hills area,Shropshire, England

The sequence of approximately 1300 m is divided by a major unconformity (Middle Devonian) into the thick Lower Old Red Sandstone (Siluro-Devonian), resting disconformably on Ludlovian (Silurian) marine strata, and the much thinner Upper Old Red Sandstone (Upper Devonian) overlain by the Carboniferous.The Lower Old Red Sandstone commences with littoral sediments (Downton Castle Formation) followed by tidal mud-flat deposits (Temeside Formation) formed after a brief marine transgression. The predominant remainder of the sequence (Ledbury Formation, Ditton Group, Abdon Group, Woodbank Group), characterized by fining-upwards cyclothems, records the establishment during a marine regression of extensive and persistent alluvial plains. Prior to Ditton Group times, detritus came from relatively distant regionally metamorphosed rocks lying to the north or west of the Clee Hills. Subsequently, apparently as the result of river-capture or drainage-reversal consequent on the commencement of the final (mid-Devonian) phase of Caledonian movement, high-level crustal rocks closer at hand (largely Wales) replaced the metamorphics as the sources of sediment, the earlier Lower Old Red Sandstone itself being recycled. To judge from the calcretes preserved in the alluvial formations, the area lay near the Equator and experienced a relatively dry hot climate.The Upper Old Red Sandstone likewise reveals fining-upwards cyclothems. The overlying Carboniferous rocks evidence the renewed marine transgression of the area, after the removal of the effects of the mid-Devonian movements.     

Facies change in upper devonian and lower carboniferous rocks of Southern Ireland

In south-west Ireland 8,000 ft (2,440 m) of marine sandstones and mudstones, the Cork Beds (?Upper Famennian to E Zone, Carboniferous, in age), overlie the Old Red Sandstone. Farther north the Old Red Sandstone is succeeded by thin Lower Limestone Shales overlain by thick Waulsortian bank limestones. A critical section (North Ringabella) west of Cork Harbour, in which 6,500 ft (1,981 m) of Old Red Sandstone and Cork Beds is exposed, is described and divided into ten formations. By comparison with sections to the south the upper beds of the Old Red Sandstone are shown to pass southward into marine sandstones (Cork Beds) of ?Upper Famennian age. The successions in the Cloyne and Cork Synclines are described and reveal the progressive northward change in the Lower Carboniferous from the argillaceous Cork Facies through a zone of isolated bank limestones (Cloyne) to a thick, 4,000 ft (1,219 m), Waulsortian bank complex (Cork). Finally an attempt is made with use of isopachyte maps to reconstruct the palaeogeography of southern Ireland in Upper Devonian and Lower Carboniferous times.     

Deposits of a near-coastal fluvial plain — the toe head formation (upper devonian) of southwest cork,EIRE

The Toe Head Formation of southwest Cork occurs in a thick, conformable sequence of Upper Devonian and Lower Carboniferous sedimentary rocks. It occupies a position between typical terrestrial “red-beds” and tidal flat and marine shelf sediments. The rocks are predominantly arenaceous and grey-green in colour. The formation is described in terms of five major lithofacies which are: (1) large-scale bedded sandstone facies, (2) rippled sandstone facies; (3) interbedded facies; (4) mudrock facies; and (5) mudcrack association facies. Simple statistical analysis of sequential organisation shows a crude pattern of fining-upwards sequences. The facies are interpreted to represent a spectrum of fluvial channel and flood plain environments, this interpretation being supported by the unidirectional palaeocurrent pattern. In view of the overall stratigraphical succession, a near-coastal fluvial plain is suggested. The formation is shown to be roughly equivalent to the Upper Old Red Sandstone of the Geological Survey (1860–1864) and to extend at least from Seven Heads to Dunmanus Bay.     

The succession of the Lower Old Red Sandstone (Siluro-Devonian) along the Ross-Tewkesbury Spur Motorway (M.50), Hereford and Worcester

The motorway cuts approximately 1900 m of strata, of which about 56 per cent are continuously exposed in numerous long sections, a new standard being afforded for the Lower Old Red Sandstone in the southern Welsh Borders. The succession recognized is: LOWER OLD RED SANDSTONE Brownstones (L. Dev.) at least 795 m St. Maughan's Group (L. Dev.) 630 m Raglan Marl Group (Siluro-Dev.) 385 m Clifford's Mesne Sandstone (Sil.) at least 9 m LUDLOW SERIES (Silurian) at least 5 m The uppermost Ludlow Series and the Clifford's Mesne Sandstone are exposed in the core of the May Hill-Woolhope upfold. They are overlain in the complimentary syncline to the west by the Raglan Marl Group, St. Maughan's Group and Brownstones, in ascending order. Above the Clifford's Mesne Sandstone, there is a progressive upward increase in the number and thickness of sandstone relative to mudstone beds. Pedogenic limestones are largely concentrated in two short stratigraphic intervals. The lowest, mainly in the uppermost Raglan Marl Group but reaching into the St. Maughan's Group, includes the “Psammosteus” Limestone recognised elsewhere in the area. The second concentration occurs in the uppermost St. Maughan's Group. Vertebrates in the Raglan Marl Group and the St. Maughan's Group allow the Downtonian and Dittonian “stages” to be recognized.     

Fluviodeltaic sedimentology and ichnology of part of the Silurian Grampians Group,western Victoria

The mid‐Silurian Major Mitchell Sandstone of the Grampians Group outcrops at Mt Bepcha, western Victoria, represent a prograding fluviodeltaic sequence comprising four lithofacies and five ichnofacies. The stratigraphically lowest Interbedded Sandstone/Siltstone Facies is characterised by thin sandstone and siltstone beds with soft‐sediment deformation and scours with gravelly lag deposits. This lithofacies contains Thalassinoides, Palaeophycus, Rhizocorallium and intrastratal burrows, together indicative of the Cruziana Ichnofacies, and is interpreted as a shallow‐marine depositional environment on a low‐energy delta front with minor tidal influences. The overlying Massive Sandstone Facies lacks silt, and consists of predominantly massive and some plane‐laminated sandstone, abundant Skolithos linearis , rare Palaeophycus and a single small Cruziana problematica ; the trace‐fossil assemblage is assigned to the Skolithos Ichnofacies. This facies is believed to have been deposited in a marine high‐energy shoreface environment with continuously shifting sands, affected by periodic flooding events from the mouth of a nearby river. Above this is the Trough Cross‐bedded Facies, which contains trough cross‐bedding with gravelly lag deposits, a northwest palaeocurrent direction and large Taenidium barretti burrows (Burrowed Ichnofacies). This facies also contains abundant plane‐laminated sandstone with a northeast‐southwest palaeocurrent direction and ichnofossils of Scoyenia and Daedalus , representing the Scoyenia Ichnofacies. The Trough Cross‐bedded Facies is interpreted to have been deposited in shallow low‐sinuosity channels by overbank‐flooding events, most likely on a delta plain. The uppermost facies, the Plane‐laminated Facies, contains thin beds of current‐lineated, plane‐laminated graded coarse to fine sandstone that preserve arthropod trackways (Arthropod Ichnofacies). This facies was deposited on a periodically sheet‐flooded, subaerially exposed delta plain.     

Age of the peel sandstone group,isle of man

An Early Devonian age for the continental, red‐bed succession of the Peel Sandstone Group can be defined on the basis of: (1) a derived marine fauna of late Wenlock (Homerian) age, (2) a Scoyenia ichnofacies assemblage (including Beaconites and Diplichnites) characteristic of latest Silurian to Early Devonian (Lower Old Red Sandstone magnafacies) sediments in the British Isles, (3) a microflora of late Lochkovian to Pragian age, (4) a detrital palaeomagnetic remanence that pre‐dates local, Acadian palaeomagnetic directions and coincides with a prominent, southerly, Late Silurian to Early Devonian excursion in the local apparent polar wander path, and (5) a mid‐Devonian palaeomagnetic remanence that overprints (?)Acadian, thrust‐related folding. Data presented in this study confirm previous suggestions (Allen and Crowley 1983) that the Peel Sandstone Group represents a rare example of Early Devonian sedimentation preserved on the northern margin of the former Eastern Avalonia microcontinent. Potential correlations and linkages with other Lower Old Red Sandstone successions exposed in the Anglo‐Welsh Basin are developed and discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Palynofloras from tournaisian lacustrine and tidal sequences in slieve bloom,counties laois and offaly,Ireland

Tournaisian miospore assemblages are used to determine the age of some plant-bearing horizons in the Old Red Sandstone succession of the Slieve Bloom Mountains, Counties Laois and Offaly, Ireland, and the sedimentology and conditions of deposition of the productive lithologies are described. The age of the marine transgression which terminated continental sedimentation is indicated, and the associated depositional environment is discussed. Comparisons are made with other micro- and macrofloras from Ireland, Britain, Canada, the U.S.S.R. and Bear Island.     

Palaeogeographic significance of pedogenic carbonates in the topmost Upper Old Red Sandstone of the Scottish border basin

The alluvial depositional surface of the Scottish Border Basin in youngest Upper Old Red Sandstone times is thought to have been dissected and subsequently disrupted and buried as an effect of magma formation and lava eruption. Lengthy periods of surface stability occurred during these events, as implied by the occurrence of up to two thick carbonate palaeosols over much of the Old Red outcrop.     

The structure of the Taff Gorge area,Glamorgan, and the stratigraphy of the Old Red Sandstone—Carboniferous Limestone transition

Lithostratigraphical and structural mapping of the Taff Gorge area, Glamorgan, has revealed a number of E-W trending folds and thrusts. These were developed during the early stages of the Hercynian deformation as a result of an approximately N-S principal compressive strain. Coeval with the folding, a conjugate set of sub-vertical wrench faults, symmetrical about the principal compressive strain, divided the area into tectonic blocks and to some extent controlled the progressive development of folds and thrusts within the individual blocks. Later Hercynian deformation gave rise firstly to oblique-slip and finally to dip-slip movement on the faults. The lithological transition between the Old Red Sandstone and Carboniferous Limestone is described in detail, including the diagenetic history of the limestones. Marine horizons are shown to be present within the dominantly fluviatile Old Red Sandstone, and the base of the Carboniferous Limestone is defined at the base of the lowest limestone of the continuous marine sequence. Studies of spores, macroplants, conodonts and brachiopods indicate that the whole of the Upper Old Red Sandstone and Lower Limestone Shale in the Taff Gorge are of Tournaisian age.     

Comparison of the vertebrate faunas of the Lower Old Red Sandstone of the Anglo-Welsh Basin with contemporary faunas in Scotland

The Lower Old Red Sandstone terranes of the Midland Valley of Scotland and the Anglo-Welsh Basin have been considered as separate realms due to the rarity of fish species common to both areas. Although in the first half of the 19th century the osteostracan Cephalaspis lyelli was thought to occur in both terranes this was shown in be incorrect in the latter part of that century. It was not until 1968 that it was demonstrated that the thelodont agnathan Turinia pagei occurred in both terranes. This species has a much wider distribution across the whole of the Old Red Sandstone continent, but its presence in both realms indicates they were connected either directly or indirectly. In 2012 it was suggested that the osteostracan Janaspis watsoni might be present in both basins and in 2013 the acanthodian Parexus recurvus was shown to definitely occur in both. Here we show that other acanthodian genera and species were present in both regions during the Lochkovian (earliest Devonian). Co-specific plants also occur in both terranes during the Lochkovian. As there is no evidence of a marine connection to the Midland Valley in the Lochkovian, the only logical conclusion is that the connection between the two terranes was fluvial.     

The ‘old red sandstone’ of county mayo,Northwest Ireland

The distribution and stratigraphic relations of the Old Red Sandstone of the Clew Bay area. County Mayo are described. They comprise two groups both dominated by conglomerates, one Lower Devonian and one Middle Devonian, which have differing clast contents and which are separated by faults. The sediments are described in terms of five facies which are all interpreted as alluvial fan deposits. Provenance data from palaeocurrents and clast composition suggest transport predominantly to the west-northwest but one formation shows an opposite sense of transport. The rocks are folded about northeast-southwest axial traces and are affected by numerous faults. Structures are more complex than those of the Lower Carboniferous rocks which unconformably overlie the Devonian. A similar tectonosedimentary setting to the Old Red Sandstone of parts of the Scottish Caledonides is indicated.     

The Green Castle Sandstone Formation: A new name for the Cwmffrwd Formation (Old Red Sandstone) preoccupied by an Ordovician Member

The Geological Survey’s Framework Report on the Old Red Sandstone of the Anglo-Welsh region includes a proposal for a new formational name, the Cwmffrwd Formation, for the basal formation of the Daugleddau Group in Carmarthenshire, S. Wales.The name is preoccupied by the Early Ordovician Cwmffrwd Member of the Carmarthen Formation and a new name, the Green Castle Sandstone Formation is proposed for the Cwmffrwd Formation.     

Facies relationships in the Upper Devonian-Lower Carboniferous of southwest Ireland and adjacent regions

In southwest Ireland 2,500 m of Upper Famennian to basal Namurian marine sandstones and mudstones, the Cork Beds, overlie rocks of Old Red Sandstone facies. Coastal exposures of the Cork Beds are interpreted as showing gradual upward change from alluvial strata, through thick subtidal and shelf sediments to pyritic muds. A review of recent palaeontological evidence shows that the thick shallow marine part of the Cork Beds is older than the major development of lime-stones north of the Cork Harbour—Kenmare Une, whose equivalents to the south are in the condensed basinal sediments. The Lower Carboniferous portion of the Cork Facies is shown to be thicker in South Cork than in West Cork. In Lower Carboniferous times a positive area–the Glandore High–separated two sub-basins with different depositional histories. Six palaeogeographic maps are used to demonstrate the progressive shift of facies belts as Lower Carboniferous marine transgression progressed. Finally, brief comparison is made with rocks of the same age in southwest England.     

Stratigraphical relationships and sedimentary environments of the silurian—early Old Red Sandstone of Pembrokeshire

In Pembrokeshire, northward Hercynian thrusting has brought together Silurian and Old Red Sandstone rocks of widely different stratigraphical and sedimentological successions. Five structurally separate blocks are centred from south to north on Freshwater, Marloes, Winsle, Rosemarket and Haverfordwest.     

Process regime change on a Silurian siliciclastic shelf: controlling influences on deposition of the Gray Sandstone Formation,Pembrokeshire, UK

Shallow marine deposits comprising the Silurian Gray Sandstone Formation (GSF) exhibit pronounced process regime changes through time. The formation was deposited on the southern shelf of the Lower Palaeozoic Welsh Basin (UK), and conformably overlies the Coralliferous Formation. The basal Lithofacies Assemblage A (of Sheinwoodian age) is dominated by a storm‐dominated process regime, comprising shoreface and offshore shelf facies associations. The overlying Lithofacies Assemblage B records a mixed process regime, with units being deposited under both storm‐ and tide‐influenced conditions. Tidal‐influence prevailed during deposition of the overlying Lithofacies Assemblage C, with proximal to distal facies variations across a significant tide‐influenced river delta being observed. A return to storm‐dominated shoreface conditions is seen in the succeeding Lithofacies Assemblage D. Lithofacies Assemblage E (Homerian age) records the return of a tide‐influenced river delta to the area, prior to the conformable transition into the overlying Old Red Sandstone (ORS) Red Cliff Formation (of Ludlow age). Northward thickening of the formation across southern Pembrokeshire into the Musselwick Fault indicates a tectonic control on sedimentation, the formation infilling accommodation space developed in an intra‐shelf half‐graben. Recurring changes in process regime from storm‐ to tide‐influenced sedimentation may be related to the onset and subsequent cessation of tidal resonance in sub‐basins across the shelf area which itself was probably controlled by episodic tectonism. It is proposed that the Coralliferous and Gray Sandstone formations comprise the newly erected Marloes Group. Copyright © 2009 John Wiley & Sons, Ltd.     

Brackish water faunas from the St Maughans Formation: The Old Red Sandstone section at Ammons Hill,Hereford and Worcester,UK, re-examined

The disused railway cutting at Ammons Hill, Hereford and Worcester, exposes a sequence of beds belonging to the Devonian St Maughans Formation of Lochkovian (Gedinnian) age. The beds are of Old Red Sandstone facies, but contain brackish water faunas. These faunas occur at a level generally considered to be above the level of marine influence that affected the older Raglan Mudstone Formation of mainly Přídolí Series age. The section, described by King in 1934, is now overgrown, but was excavated in 1986 by the British Geological Survey during its survey of the Worcester 1:50000 sheet. The evidence of the section calls for slight amendment of Allen's (1985) model of an interrupted transition from marine deposition in Ludlow time to freshwater deposition in Gedinnian time that was complete by the time of the formation of a regionally extensive calcrete palaeosol, the Psammosteus Limestone. Subsequent transgressive events took place before the establishment of apparently wholly fluvial and floodplain environments.     

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.     

Studies in fluviatile sedimentation: Implications of pedogenic carbonate units. Lower Old Red Sandstone,Anglo-Welsh outcrop

Carbonate units occur in varying numbers in the fine-grade members of the alluvial fining-upwards cyclothems present in the Lower Old Red Sandstone of the Anglo-Welsh outcrop. They closely resemble contemporary soil-carbonates (calcretes) and hence show that the local Siluro-Devonian climate was relatively hot with a comparatively low seasonal rainfall. Compared with contemporary calcretes, the units suggest that sites on the alluvial plains were denied river-borne sediments for periods each in the general order of 10⁴ years. The pedogenic interpretation of the carbonate units, developed in the light of the behaviour of rivers today, leads to alternative models for the geomorphology of the Siluro-Devonian alluvial plains and for their gross subsurface structure. Geomorphologically, the plains at any instant presented depositionally active and inactive areas in juxtaposition. Under some circumstances the relief was provided only by alluvial ridges. Under others, relief was afforded by valley sides and perhaps river terraces, in addition to ridges. Knowledge of the character of the Lower Old Red Sandstone in vertical sequence leaves as plausible three alternative gross structures for the alluvial pile beneath the plains. They differ chiefly in the lateral variability and connectedness of the palaeosols and place hitherto unavailable limits on the three-dimensional character of the cyclothems.     

Caledonide influences on the Old Red Sandstone fluvial systems of the Oslo Region,Norway

Red or buff‐coloured sandstones and siltstones of fluvial origin comprise approximately 80% of the Ringerike Group, a late Silurian Old Red Sandstone (ORS) sequence that crops out extensively in the Oslo Region of southern Norway. These fluvial sediments are lithostratigraphically ascribed to two laterally equivalent formations—the Stubdal Formation (to the north of Oslo) and the Skien Formation (to the south of Oslo). The fluvial strata of each of the two formations have a distinct style of sandbody geometry, facies, provenance, and palaeocurrent direction. Within the Stubdal Formation, shallow channelized sandbodies, low‐ to upper‐flow regime sedimentary structures, a Caledonide provenance and a palaeoflow toward the southeast are evident. Within the Skien Formation, sandbody geometry is entirely sheet form, with upper‐flow regime sedimentary structures, a provenance from Precambrian rocks to the northern and local parts of the Oslo Region and a palaeoflow toward the east. No stratal contact can be seen between the two fluvial formations, due to a 15 km break in exposure between the southernmost Stubdal Formation and the northernmost Skien Formation. Relationships with adjacent formations indicate that they are diachronous, lateral equivalents. Given the abrupt change in sedimentary style between the two formations, it is proposed that a barrier had developed within the foreland basin, diverting the ORS fluvial systems in southern Norway, from a southward (north of Oslo), to an eastward direction (south of Oslo). This diversion had implications for depositional gradient, fluvial regime and provenance, resulting in the differences visible in the deposits of those rivers. The barrier invoked is arguably a Caledonide blind thrust fault that developed a topographic high, running east–west through the vicinity of Oslo, during the late Silurian. Copyright © 2004 John Wiley & Sons, Ltd.