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In Scotland, the base of the Ballagan Formation has traditionally been placed at the first grey mudstone within a contiguous Late Devonian to Carboniferous succession. This convention places the Devonian–Carboniferous boundary within the Old Red Sandstone (ORS) Kinnesswood Formation. The consequences of this placement are that tetrapods from the Ballagan Formation were dated as late Tournaisian in age and that the ranges of typically Devonian fish found in the Kinnesswood Formation continued into the Carboniferous. The Pease Bay specimen of the fish Remigolepis is from the Kinnesswood Formation. Comparisons with its range in Greenland, calibrated against spores, show it was Famennian in age. Detailed palynological sampling at Burnmouth from the base of the Ballagan Formation proves that the early Tournaisian spore zones (VI and HD plus Cl 1) are present. The Schopfites species that occurs through most of the succession is Schopfites delicatus rather than Schopfites claviger. The latter species defines the late Tournaisian CM spore zone. The first spore assemblage that has been found in Upper ‘ORS' strata underlying the Ballagan Formation (Preston, Whiteadder Water), contains Retispora lepidophyta and is from the early latest Famennian LL spore zone. The spore samples are interbedded with volcaniclastic debris, which shows that the Kelso Volcanic Formation is, in part, early latest Famennian in age. These findings demonstrate that the Ballagan Formation includes most of the Tournaisian with the Devonian–Carboniferous boundary positioned close to the top of the Kinnesswood Formation. The Stage 6 calcrete at Pease Bay can be correlated to the equivalent section at Carham, showing that it represents a time gap equivalent to the latest Famennian glaciation(s). Importantly, some of the recently described Ballagan Formation tetrapods are older than previously dated and now fill the key early part of Romer's Gap.
The lower Mississippian Ballagan Formation of northern Britain is one of only two successions worldwide to yield the earliest known tetrapods with terrestrial capability following the end-Devonian mass extinction event. Studies of the sedimentary environments and habitats in which these beasts lived have been an integral part of a major research project into how, why and under what circumstances this profound step in the evolution of life on Earth occurred. Here, a new palaeogeographic map is constructed from outcrop data integrated with new and archived borehole material. The map shows the extent of a very low-relief coastal wetland developed along the tropical southern continental margin of Laurussia. Coastal floodplains in the Midland Valley and Tweed basins were separated from the marginal marine seaway of the Northumberland–Solway Basin to the south by an archipelago of more elevated areas. A complex mosaic of sedimentary environments was juxtaposed, and included fresh and brackish to saline and hypersaline lakes, a diverse suite of floodplain palaeosols and a persistent fluvial system in the east of the region. The strongly seasonal climate led to the formation of evaporite deposits alternating with flooding events, both meteoric and marine. Storm surges drove marine floods from the SW into both the western Midland Valley and Northumberland–Solway Basin; marine water also flooded into the Tweed Basin and Tayside in the east. The Ballagan Formation is a rare example in the geological record of a tropical, seasonal coastal wetland that contains abundant, small-scale evaporite deposits. The diverse sedimentary environments and palaeosol types indicate a network of different terrestrial and aquatic habitats in which the tetrapods lived.
The first half of the Mississippian or Early Carboniferous (Tournaisian to mid- Viséan), an interval of about 20 million years, has become known as “Romer's Gap” because of its poor tetrapod record. Recent discoveries emphasise the differences between pre-“Gap” Devonian tetrapods, unambiguous stem-group members retaining numerous “fish” characters indicative of an at least partially aquatic lifestyle, and post-“Gap” Carboniferous tetrapods, which are far more diverse and include fully terrestrial representatives of the main crown-group lineages. It seems that “Romer's Gap” coincided with the cladogenetic events leading to the origin of the tetrapod crown group. Here, we describe a partial right lower jaw ramus of a tetrapod from the late Tournaisian or early Viséan of Scotland. The large and robust jaw displays a distinctive character combination, including a significant mesial lamina of the strongly sculptured angular, an open sulcus for the mandibular lateral line, a non-ossified narrow Meckelian exposure, a well-defined dorsal longitudinal denticle ridge on the prearticular, and a mesially open adductor fossa. A phylogenetic analysis places this specimen in a trichotomy with Crassigyrinus and baphetids + higher tetrapods in the upper part of the tetrapod stem group, above Whatcheeria, Pederpes, Ossinodus, Sigournea and Greererpeton. It represents a small but significant step in the gradual closure of “Romer's Gap”.
The Eycott Volcanic Group of the Lake District Lower Palaeozoic inlier consists of basaltic and andesite and and andesite sheets and associated, mainly coarse, volcaniclastic rocks. The volcanic rocks have been regarded previously as interdigitated with, and equivalent in age to, mudrocks of the upper part of the Skiddaw Group (Tremadoc–Llanvirn). Microfloral evidence has been quoted in support of this interpretation, but has not been substantiated by re-assessment of the critical data. Furthermore, a recent examination of the base of the Eycott Volcanic Group has shown that it rests with angular unconformity on the Skiddaw Group. Skiddaw Group rocks beneath the unconformity range in age from possible late Cambrian to early Llanvirn. The lowest part of the Eycott Volcanic Group, the Over Water Formation, consists of siltstones and tuffaceous sandstones yielding a diverse microflora, and is intercalated with two andesite sheets interpreted herein as sills. Since the currently accepted Llanvirn age for the Eycott Volcanic Group cannot be confirmed, the volcanism may have been penecontemporaneous with the Llandeilo–Caradoc Borrowdale Volcanic Group episode. There are implications for a pre-volcanic tectonic deformation episode.
Dietary intake has been shown to influence acid–base balance in human subjects under tightly controlled conditions. However, the net effect of food groups on alkali/acid loading in population groups is unclear. The aims of the present study were to: (1) quantify estimates of daily net endogenous acid production (NEAP) (mEq/d) in a representative group of British elderly aged 65 years and older; (2) compare and characterise NEAP by specific nutrients and food groups likely to influence dietary acid loading; (3) determine whether geographical location influenced NEAP. The National Diet and Nutrition Survey dataset, consisting of a 4 d weighed record and anthropometric data, was used to estimate dietary acidity. Dietary under-reporters were excluded by analysing only subjects with energy intakes ≥ 1·2 × BMR. NEAP was estimated as the dietary potential renal acid load+organic acid excretion, the latter as a multiple of estimated body surface area. NEAP was lower in women compared with men (P < 0·001), and lower than values reported in a Swedish elderly cohort. Lower dietary acidity was significantly associated with higher consumption of fruit and potatoes and lower consumption of meat, bread and eggs (P < 0·02 to P < 0·001). Lower intakes of fish and cheese were associated with lower NEAP in men only (P < 0·01 to P < 0·001). There were regional differences for NEAP, with higher intakes in Scotland/Northern regions compared with Central/South-Western and London/South-Eastern regions (P = 0·01). These data provide an insight into the acid-generating potential of the diet in the British elderly population, which may have important consequences in this vulnerable group.
Within a largely concealed, caldera-related volcaniclastic succession of the Ordovician
Borrowdale Volcanic Group in the western Lake District, two thick (100–350 m) ignimbrites within
the Fleming Hall Formation exhibit a number of features that in combination make them unusual
deposits. They are both homogeneous with comparatively low-SiO2 (63%) bulk composition, contain
only a moderate crystal content, are generally poor in lithic clasts, show uniformly very dense welding
(yielding parataxitic to massive vitrophyric texture) throughout and lack associated fall-out or surge
deposits. Ignimbrites of comparable bulk composition in this geological setting are usually part of
zoned sheets and/or frequently very crystal-rich. Large-scale, unzoned densely welded ignimbrites are
usually rhyodacitic to rhyolitic. By contrast, ignimbrites of intermediate composition that display
dense welding are relatively small deposits that form by agglutination of hot, plastic spatter.
It is postulated that the Fleming Hall ignimbrites were derived from low column height, low explosivity
eruptions that conserved heat and minimized entrainment of accidental lithic clasts and the formation
of fine ash. The very dense welding and lack of bubble-wall shard vitroclastic textures indicate that
pyroclasts were hot and relatively dry, probably occurring as mildly vesicular (scoriaceous) fragments
which welded or fused together during aggradational deposition rather than by post-depositional compactional
loading. There is little variation in the degree of matrix or melt crystallization throughout the
two ignimbrites, despite the fact that high temperatures must have been maintained for many years following
deposition. Both display virtually ubiquitous development of micropoikilitic glass devitrification
texture, which suggests that the viscosity of the supercooled dacitic melt was sufficiently high,
probably due to initial degassing, to inhibit significant melt crystallization after deposition.
The eruption of the Fleming Hall magmas was probably initiated by the rise or injection of hotter,
more basic, magma, and not by overpressurization due to volatile exsolution resulting from cooling
and crystallization. Foundering of the chamber roof caused forcible and rapid eruption of the magma,
probably along a series of volcanotectonic faults rather than a central vent, and probably flooded the
resultant caldera depression. It is predicted that this type of eruption will not have produced a widely
dispersed deposit, the bulk of which may have been largely contained within its own caldera.
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