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.     

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.     

The Petrology of the Lower Old Red Sandstone Lavas of the Eastern Sidlaw Hills, Perthshire, Scotland

The calc-alkaline lava sequence of the eastern Sidlaw Hillsforms a small part of an extensive volcanic province of LowerOld Red Sandstone (Devonian) age in Scotland and N. England.The Sidlaw lavas ranging from olivine basalt to dacite are allporphyritic with combinations of olivine, plagioclase, clinopyroxene,orthopyroxene, and opaque oxide pheno-crysts. Chemically, thelavas are slightly more alkalic than modern calc-alkaline lavas.There is considerable variation in the ‘incompatible elements’.The differentiation of the lavas can be accounted for by fractionationof olivine+plagioclase+minor ore from a chemically variable,immediately parental magma at low pressure (c. 1 kb P_H2O). Itis suggested that fractionation of variable amounts of olivineand clinopyroxene from an olivine tholeiite at moderate P_H2Ocould give rise to this chemically variable, high alumina, immediatelyparental magma.     

Remagnetization and fluid flow in the Old Red Sandstone along the Great Glen Fault, Scotland

The Devonian Old Red Sandstone in the vicinity of the Great Glen Fault (GGF) in Scotland contains two different components residing in hematite: a postfolding Carboniferous CRM1 in the Loch Ness area and a Cretaceous or perhaps Triassic CRM2 near Hilton. The CRM1 could be related to major fluid flow events in the Late Paleozoic which caused hematite authigenesis and remagnetization along other faults in Scotland. The CRM2 near Hilton was also related to a fluid event in the Cretaceous or Triassic which caused hematite authigenesis. The presence of different CRMs residing in hematite along different segments of the GGF is similar to what has been reported for other major faults in Scotland.     

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.     

Pteraspidomorphs (Vertebrata), the Old Red Sandstone,and the special case of the Brecon Beacons National Park,Wales, U.K.

Pteraspidomorphi are Ordovician to Devonian, jawless vertebrates devoid of paired fins that have developed a variety of phenotypes of mostly demersal aquatic animals of the neritic province. Some, however, were active swimmers in the water column or near to the surface. They show many convergences in adaptive variations with the other ossified agnathan vertebrates or ostracoderms, that is the osteostracans, galeaspids and pituriaspids. They are traditionally known as Old Red Sandstone (ORS) fish, and have been interpreted as fresh-water inhabitants. However, recent palaeoecological and sedimentological analyses have shown that they were near-shore, shallow-marine fishes in the Ordovician, that they occupied marine environments on the Silurian Baltic platform and a wide variety of environments in the Devonian, including those of the ORS (lagoonal, estuarine, deltaic, and open platform). Their peak of diversity was reached in the Early Devonian, and they all disappeared before the Frasnian-Famennian boundary biotic crisis. Within Earth sciences, they are used in biostratigraphy, palaeoecology, and palaeobiogeography. They are good tools for dating siliciclastic sedimentary series of the Silurian and Devonian, including the ORS, and they are good markers of the margins of Ordovician to Devonian palaeocontinents (Laurentia, Baltica, Siberia, Gondwana).     

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.     

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.     

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.     

Enigma variations: the stratigraphy,provenance, palaeoseismicity and depositional history of the Lower Old Red Sandstone Cosheston Group,south Pembrokeshire,Wales

The Lower Devonian (Lochkovian‐Emsian) Cosheston Group of south Pembrokeshire is one of the most enigmatic units of the Old Red Sandstone of Wales. It consists of a predominantly green, exceptionally thick succession (up to 1.8 km) within the red c. 3 km‐thick fill of the Anglo‐Welsh Basin, but occupies a very small area (27 km²). Four formations—Llanstadwell (LLF), Mill Bay (MBF), Lawrenny Cliff (LCF) and New Shipping (NSF)—group into lower (LLF + MBF) and upper (LCF + NSF) units on stratigraphical and sedimentological criteria. Two palynostratigraphic associations (Hobbs Point and Burton Cliff) are recognised in the LLF. Overall, the Cosheston succession comprises a fluvial, coarsening‐upward megasequence, mostly arranged in fining‐upward rhythms. It is interpreted as the fill of an east‐west graben bounded by faults to the north and south of the Benton and Ritec faults, respectively. Both ‘lower Cosheston’ formations were deposited by east‐flowing, axial river systems draining a southern Irish Sea landmass. Drainage reversal, early in the deposition of the LCF, resulted in ‘upper Cosheston’ lateral, SW‐flowing rivers which carried predominantly second‐ and multi‐cycle detritus. The ‘lower Cosheston’ is characterized by an abundance of soft‐sediment deformation structures, probably seismically triggered by movements along the graben's northern bounding fault. A minimum average (≥ mesoseismic) earthquake recurrence interval of c. 4000 yr is estimated for the MBF. This and the correlative Senni Formation of south‐central Wales form a regionally extensive green‐bed development that represents a pluvial climatic interval. Copyright © 2006 John Wiley & Sons, Ltd.     

Palaeomagnetic re-examination of the basal Caithness Old Red Sandstone; aspects of local and regional tectonics

A palaeomagnetic re-examination of the basal strata of the Caithness Old Red Sandstone has given results that are fully compatible with previous palaeomagnetic findings in this region. After structural correction the dominant remanence component has D = 205°, I = +3°, α₉₅ = 6.4° (N = 27). The existence of this shallow inclined magnetization in the Middle Devonian strata of Caithness invalidates the model, proposed by Van der Voo and Scotese (1981), involving a ca. 2000 km sinistral offset along the Great Glen Fault in the Carboniferous. However, the available data are in favour of a few hundred kilometres sinistral movement along this fracture zone. However, the possibility of there having been a much larger transcurrent shift between Europe and North America in late/post-Devonian times, accumulated along various fracture zones within the Caledonian fold belt, is discussed. On the basis of an inferred overprinted magnetization, it is tentatively concluded that the tectonic deformation of the Old Red Sandstone of Caithness has a mid-Jurassic or younger age.     

Review of plant evolution and its effect on climate during the time of the Old Red Sandstone

A substantial decrease in atmospheric carbon dioxide (CO₂) concentration during the mid-Palaeozoic is likely to have been the consequence partially of the evolution of rooted land plants. The earliest land plants evolved in the Ordovician but these were small cryptophytes without any roots. Much of the evidence for the evolution of vascular plants comes from the Old Red Sandstone of South Wales and the Welsh Borderland. Plants with large rooting systems evolved during the Middle Devonian and resulted in an increase in chemical weathering of silicate rocks. This, in turn, caused a contemporaneous drop in atmospheric CO₂ concentration from approximately 25 times present concentration in the Cambrian to twice the present concentration by the late Carboniferous. The supposed mechanism for CO₂ removal from the atmosphere involves oceanic carbonate precipitation, enhanced by plant-enhanced chemical weathering of Ca and Mg silicates.     

The Hydrolysis of Al(III) in NaCl solutions: A Model for M(II), M(III), and M(IV) Ions

Understanding the identity and stability of the hydrolysis products of metals is required in order to predict their behavior in natural aquatic systems. Despite this need, the hydrolysis constants of many metals are only known over a limited range of temperature and ionic strengths. In this paper, we show that the hydrolysis constants of 31 metals [i.e. Mn(II), Cr(III), U(IV), Pu(IV)] are nearly linearly related to the values for Al(III) over a wide range of temperatures and ionic strengths. These linear correlations allow one to make reasonable estimates for the hydrolysis constants of +2, +3, and +4 metals from 0 to 300°C in dilute solutions and 0 to 100°C to 5 m in NaCl solutions. These correlations in pure water are related to the differences between the free energies of the free ion and complexes being almost equal $$ \Updelta {\text{G}}^\circ \left( {{\text{Al}}^{3 + } } \right) - \Updelta {\text{G}}^\circ \left( {{\text{Al}}\left( {\text{OH}} \right)_{j}^{{\left( {3 - j} \right)}} } \right) \cong \Updelta {\text{G}}^\circ \left( {{\text{M}}^{n + } } \right) - \Updelta {\text{G}}^\circ \left( {{\text{M}}\left( {\text{OH}} \right)_{j}^{{\left( {n - j} \right)}} } \right) $$ The correlation at higher temperatures is a result of a similar relationship between the enthalpies of the free ions and complexes $$ \Updelta {\text{H}}^\circ \left( {{\text{Al}}^{3 + } } \right) - \Updelta {\text{H}}^\circ \left( {{\text{Al}}\left( {\text{OH}} \right)_{j}^{3 - j} } \right) \cong \Updelta {\text{H}}^\circ \left( {{\text{M}}^{n + } } \right) - \Updelta {\text{H}}^\circ \left( {{\text{M}}\left( {\text{OH}} \right)_{j}^{n - j} } \right) $$ The correlations at higher ionic strengths are the result of the ratio of the activity coefficients for Al(III) being almost equal to that of the metal. $$ \gamma \left( {{\text{M}}^{n + } } \right)/\gamma \left( {{\text{M}}\left( {\text{OH}} \right)_{j}^{n - j} } \right) \cong \gamma \left( {{\text{Al}}^{3 + } } \right)/\gamma \left( {{\text{Al}}\left( {\text{OH}} \right)_{j}^{3 - j} } \right) $$ The results of this study should be useful in examining the speciation of metals as a function of pH in natural waters (e.g. hydrothermal fresh waters and NaCl brines).