Cementstone Group Research Articles

An hydrothermal origin for copper-impregnated prehnite and analcime from Boylestone Quarry, Barrhead, Scotland

Field, petrographic, mineralogical, fluid inclusion and stable isotope studies of prehnite, analcime and calcite in basalt lava of Visean age (about 360 Ma) from Boylestone Quarry, Barrhead, Scotland are all consistent with an hydrothermal origin. In the hydrothermal system, water interacted with hot alkaline basalt soon after eruption. Feldspars were digested in an alkaline solution and alumina and silica were reprecipitated in fractures and veins as the hydrous alumino-silicates analcime and prehnite. The prehnite generally occurs below the analcime in more oxidized host basalt. Minor calcite crystallized late, usually on earlier analcime or prehnite. Fluid inclusion measurements give homogenization temperature ( Th ) of 83–184 °C (mean 145 °C) and salinities c . 1.5 equiv. wt% NaCl for analcime; and c . 46-234°C and c . 26 equiv. wt% NaCl for calcite. Fluid inclusions in analcime appear to contain some SO 2– 4 or CO 2– 3 . Inclusions in calcite associated with prehnite have a lower Ca 2+ :Na + ratio than those in calcite associated with analcime. Using a fluid inclusion temperature of 145 °C for analcime of δ 18 O = 15.6% (V-SMOW) implies δ l8 O for the fluid was 1.4% and this leads to 184 °C for the temperature of precipitation of prehnite of δ 18 O = 12.5%. The δD values of –35% for prehnite are consistent with surface water (seawater or low latitude meteoric water) heated to 180 °C. Two groups of calcite are recognised on fluid inclusion and isotopic evidence: both groups have δD values ranging from —61 to — 117% but one group is characterized by Th > 100 °C and δ 18 O = 20 to 22% (δ 18 O water = 10.3%) and is believed to have formed from surface waters which had exchanged 18 O with igneous rocks at a high temperature whereas the second group with Th = 85 °C and δ l8 0i = 17.2% crystallized from normal surface waters of δ 18 O water = –0.4%. The carbonate δ 13 C data (range –8.3 to –42.4% PDB) attest to the presence of organic-derived carbon dioxide in the hydrothermal fluid, as expected since organic material is observed in some fluid inclusions. The low δ I3 C value, —42.4%, indicates oxidation of methane whereas the higher values point to decarboxyla-tion of organic matter Copper was oxidized and remobilized from disseminated chalcopyrite in basalt and probably from disseminated copper minerals which had resulted from Carboniferous weathering of underlying basalts. Dissolved copper was reprecipitated on cooling and reduction, generally within and above greenish prehnite. The fluid inclusion and isotope studies indicate that the water could well have been mainly meteoric with in addition, some warm Lower Carboniferous seawater and/or saline groundwaters; the water interacted with organic-rich sediments to provide CH 4 and CO 2 then to various degrees with hot igneous rock. The hydrocarbons may have been mobilized into groundwaters by baking of organic sediments in the Cementstone Group. The model is consistent with active volcanogenic geothermal activity during Lower Carboniferous times in the Midland Valley of Scotland.

On the occurrence ofClepsydropsis parvulaGaltier in tournaisian rocks (Cementstone Group) of Berwickshire

On the occurrence of<i>Clepsydropsis parvula</i>Galtier in tournaisian rocks (Cementstone Group) of Berwickshire

Observations on Eristophyton Zalessky, Lyginorachis waltonii Calder, and Cladoxylon edromense sp. nov. from the Lower Carboniferous Cementstone Group of Scotland

ABSTRACTFifteen specimens of Eristophyton stems from the Lower Carboniferous Cementstone Group of Berwickshire and East Lothian have been examined. Three possess medullary rays comparable to E. waltonii Lacey, the others have rays like E. beinertianum (Göpp.) Zalessky. In one specimen assigned to E. waltonii a leaf-trace subdivides outside the secondary xylem to form an arc of six separate bundles. Another stem of E. waltonii has attached closely spaced petiole bases one of which is clearly identifiable as Lyginorachis with six vascular bundles arranged in an arc. Stems of Eristophyton from five localities occur associated with petioles or rachises possessing a U-shaped vascular bundle with abaxial ridges like L. waltonii Calder. As these may occur mixed with rachises agreeing with L. brownii Calder the latter is regarded as synonymous. Detached petioles found associated with E. beinertianum may possess four or six basal bundles. The evidence suggests that the U-shaped petiolar bundle passes down into four then six basal bundles and such petioles are associated with both E. waltonii and E. beinertianum. Calder (1935, pl. 1, fig. 2) showed dichotomy in the petiole bundle.In addition different rachises are known possessing a more massive U-shaped bundle but lacking sclerotic nests and sparganum outer cortex. These are assigned to Cladoxylon edromense sp. nov. Cortical nests occur in both E. waltonii and L. waltonii and may be compared with the sclerotic plates in the compressions of Diplotmema dissectum Brongn. and D. patentissimum Ett.. The evidence supports the view that Eristophyton is a pteridosperm with bifurcate fronds known as L. waltonii Calder when petrified and comparable to Diplotmema when compressed.

Nodular carbonates in the Lower Carboniferous, Cementstone Group of the Tweed Embayment, Berwickshire: evidence for a former sulphate evaporite facies

Synopsis A small number of coarsely crystalline nodular carbonate beds of calcite and dolomite are intercalated within lacustrine sediments in the Lower Carboniferous Cementstone Group of the Tweed area. Textural and mineralogical features indicate that they represent former nodular anhydrite beds which developed in lake marginal sabkhas. The close association of these replaced sulphates with beds of cementstone (finely crystalline dolomites) favours a sabkha model for cementstone dolomitisation in which sulphate precipitation helps to promote the requisite Mg/Ca ratios in the dolomitising brines. Two main stages of diagenesis, each dominated by mineral replacement, appear to have affected the sulphate facies subsequent to its formation: initially the anhydrite was subject to partial gypsification and then, at a later stage of diagenesis, dolomite and calcite replacements of sulphate occurred.

Observations on the Lower Carboniferous Lycopod Oxroadia gracilis Alvin

ABSTRACTA stem-base of Oxroadia gracilis is described showing 12 distal rhizophores and 72 roots. The rhizophores branch in a manner interpreted as dichotomy in successive planes at right angles. Each has a siphonostele which may possess medullary tracheids. Root-traces are monarch and wedge-shaped in section and their departure leaves ramular gaps in the siphonostele. The largest root may have functioned as a tap-root formed earlier than the rhizophores and exogenous. Only two out of ten known rooting specimens show rhizophores.An aerial stem with leaves shows secondary xylem up to the level of the probable second dichotomies.Leaves have slightly decurrent clasping bases forming low cushions and are recurved. Ligules (when preserved) occur in deep cavities of leaf-bases. In the apical region young leaves are small, recurved, and grooved distally below, giving a pseudo-forked appearance in cross sections of the stem.Only incomplete strobili are known.Comparisons are made with ‘Lepidodendron’ saalfeldense Solms-Laubach, and Trabicaulis ftabellilignis Meyer-Berthaud; these are considered co-generic.Oxroadia is recorded from the Oil-Shale Group (late Viséan or Asbian) near Kinghorn, Fife, Scotland; and from the Cementstone Group (late Tournaisian or Courceyan) East Lothian, Scotland; Berwickshire, Scotland; and Northumberland, northern England.

Actinopterygian fish from the Dinantian of Foulden, Berwickshire, Scotland

ABSTRACTThe four stem-group neopterygians from Foulden are redescribed: Carboveles ovensi White, Aetheretmon valentiacum White, Strepheoschema fouldenensis White and Fouldenia ottadinica White. Carboveles is shown to be a junior synonym of Phanerosteon Traquair, Fouldenia ottadinica White is synonymised with Styracopterus fulcratus (Traquair), Strepheoschema rhodesi Moy-Thomas with S. fouldenensis White and Aetheretmon whitei Moy-Thomas with A. valentiacum White. The family Strepheoschemidae is erected to comprise Strepheoschema and Aetheretmon, characterised by paired ventral ridge scales in front of the pelvic fins. Cosmoptychius striatus (Agassiz), recorded here from Foulden for the first time, is widespread in the geologically younger Oil Shale Group. The Foulden actinopterygian fauna is identical to that of the Cementstone Group at Coomsdon Burn, Northumberland, although with two additional taxa. Styracopterus fulcratus occurs also at a further two Cementstone Group localities in Scotland.

Plant miospores from the Dinantian of Foulden, Berwickshire, Scotland

ABSTRACTPlant miospore assemblages obtained from eight beds of the Foulden sequence, ranging from Bed 1 to Bed 17, are basically similar to each other in stratigraphical significance. The presence of Convolutispora circumvallata, Crassispora trychera and Schopfltes claviger and the absence of Lycospora pusilla suggest assignment to the Schopfites claviger-Auroraspora macra (CM) Biozone. This indicates the Courceyan Stage of the British Dinantian and the late Tournaisian (Tn3) of the Belgian Series. Comparable miospore assemblages have been described from Cementstone Group localities elsewhere in Berwickshire, East Lothian, Ayrshire and northern England. Preservation, and lack of marine palynomorphs and scolecodonts, suggest non-marine deposition. The presence of vitrinite fragments and megaspores as well as miospore tetrads suggests little transport before deposition.

Sedimentology of the Dinantian of Foulden, Berwickshire, Scotland

ABSTRACTThe Berwickshire Cementstone Group was deposited on a coastal plain crossed by meandering rivers flowing S into a marine gulf, the Northumberland basin. Sedimentation was mainly by overbank flooding onto an alluvial plain which largely dried out between floods. The resulting sediments include poorly-stratified mudstones and siltstones and crevasse splay sheet sandstones. The depositional environment of the cementstones is not clear. Lacustrine and tidal flat origins are considered. Semi-permanent floodplain lakes were very rare, but in one the uniquely fossiliferous Foulden Fish Bed was deposited. This lake was shallow and filled by repeated influxes of sediment carried from rivers by sheetfloods. On entering the lake, these sheetfloods may have become density underflows from which thin, graded siltstones or sandstones were deposited. These floods carried plant debris into the lake and rapidly buried the remains of the lake fauna. The salinity of the lake cannot be determined, but the input of both fresh and saline waters can be envisaged. There is no evidence that the lake was permanently eutrophic. The mortality of the animals may have been due to changes in water chemistry produced by hot dry spells of weather followed by storms and floods.

Introduction to the palaeontology of the Dinantian of Foulden, Berwickshire, Scotland

ABSTRACTThe Foulden Site of Special Scientific Interest is one of the few Cementstone Group localities that yields significant fauna and flora. Excavations in 1980 and 1981 removed a 1·3 m2 slab of the Fish Bed for laboratory study of the vertical and spatial distribution of the biota. Layer by layer analysis revealed an almost mutually exclusive relationship between the vertical distribution of the palaeoniscoid fishes and malacostracan crustaceans, as well as a horizon crowded with juvenile acanthodians. Elongate elements of this biota showed slight preferred orientations at that prolific horizon. Some 27 m of strata including the Fish Bed, Plant Bed and Shell Bed are recorded in detail, and their biota noted. Interim results of work on the main groups collected are summarised in associated papers in this part of Transactions. Brief reports are given here on the euryhaline marine bivalve mollusc Modiolus latus (Portlock), a rare durophagous bradyodont shark tooth and an Eogyrinus-like amphibian scute.

The resemblance between the Lower Carboniferous cupules ofHydraspermacf.tenuisLong andSphenopteris bifidaLindley and Hutton

SynopsisSix new specimens of petrified cupules ofHydraspermacf.tenuisfrom Oxroad Bay, East Lothian (Cementstone Group) have been examined. Sections of one show a close similarity in size and shape to compressed cupules ofSphenopteris bifidaL. and H. from the Lewis Burn (Scremerston Coal Group or lower Viséan) of Northumberland. The conclusion reached is that cupules ofHydraspermacf.tenuisLong are petrified equivalents of the compressed cupules ofSphenopteris bifidaL. and H. The morphological significance of this identification is discussed.

Lower Carboniferous pteridosperm cupules and the origin of angiosperms

SynopsisFour new petrified specimens of cupules assigned toHydraspermacf.tenuisLong are described from the Cementstone Group of Oxroad Bay, East Lothian. In one of these specimens four ovules are present. Three of the specimens are interpreted as representing a pair of cupules derived from a single megasporophyll showing dichotomy so that each cupule is termed a hemi-cupule and has two lobed halves which represent quarters of the entire megasporophyll. In the fourth specimen five cupules are present, each possessing two lobed halves not sub-divided into quarters.Hydraspermais thus interpreted as showing two kinds of cupules designated mega-cupules and paired hemi-cupules. The theory is developed that angiosperm carpels have evolved from the two kinds of pteridosperm cupules.

Some Lower Carboniferous pteridosperm cupules bearing ovules and microsporangia

SynopsisTwo pairs of detached fossil cupules from the Cementstone Group of the East Lothian coast are described. One pair (specimen 1) contains 16 ovules agreeing with the seed genus Hydrasperma Long as well as 8 microsporangia containing spores. The second pair (specimen 2) has neither ovules nor microsporangia.The ovules present in specimen 1 have about 9 free apical tentacles and as many longitudinal ridges on the bodies of the ovules. The central column is very well developed, about as long as the ovule body and obconical in shape. In it some of the cells have bars of thickening on the walls like transfusion cells. Each cupule-pair has a common stalk which divides to become the two inverted cupules. In specimen 1 each cupule has a wall consisting of two valves united above but subdivided into tapering lobes below, i.e. distally. Ovules are borne below the concave upper region of each cupule (sessile laminar placentation). In this specimen each cupule-valve is subdivided into two smaller portions, one of which bears 8 microsporangia. The latter appear to be terminal and reflexed and almost sessile.The laminar placentation in Hydrasperma supports the view that this type of placentation in angiosperms is primitive and the bisexual cupule-pair here described suggests that the primitive fertile fronds from which cupules (and presumably carpels) evolved were originally capable of bearing both mega- and microsporangia.

Observations on Carboniferous seeds of Mitrospermum, Conostoma and Lagenostoma

SynopsisMitrospermum bulbosum sp. nov. is described from a single specimen found in the Lower Carboniferous Cementstone Group of Berwickshire. It is a platyspermic seed about 14 mm diameter. The nucellus is free from the integument laterally and contains a single megaspore above which is a pollen chamber and well-developed apical beak. The integument is cordate at the base around a bulbous chalazal region with two membranous wings which terminate above as two flat lobes having a V-shaped sinus between. At the base of this sinus is the micropyle which surrounds the apex of the nucellar beak.Mitrospermum compressum Arber has been re-investigated from 21 specimens and evidence adduced to show that the micropylar canal expands upwards and opens between two short apical lobes.Conostoma oblongum Will, has been re-investigated from 20 specimens. It possesses four integumental bundles; sometimes there are two basal lobes but no integumental flanges; no free apical lobes have been seen and the seed was sessile, not having a wide pedicel.A specimen of Lagenostoma ovoides Will, with a mature prothallus is briefly described from longitudinal sections. At the upper end the prothallus has three archegonia and a circular trough surrounding the ‘tent-pole’.

23.—Psalixochlaena berwickense sp. nov., a Lower Carboniferous Fern from Berwickshire

SynopsisPsalixochlaena berwickense sp. nov. is described from specimens found in the Cementstone Group of Berwickshire. The incomplete fossils consist of short cylindrical stems, 0·7–1·5 mm diameter, and probably represent portions of one or more branching rhizomes. Attached petioles have not been seen but one detached fragment shows a resemblance in structure to the petioles of P. cylindrica (Williamson) Holden. Branching of the stem is by trifurcate laterals and this distinguishes it from P. cylindrica but bears a superficial resemblance to Rowleya trifurcata Long.

XIII.—A new interpretation of Lepidodendron calamopsoides Long and Oxroadia gracilis Alvin

SynopsisA petrified lycopod found in a loose block of calciferous sandstone from the Cementstone Group in Berwickshire possesses a rooting stem-base similar to others previously assigned to Lepidodendron calamopsoides (Long 1964) but it shows continuity with a dichotomously branched stem about 15 cm. long, lacking leaves, but otherwise resembling Oxroadia gracilis (Alvin 1965). The diagnosis of Lepidodendron calamopsoides has been emended to include only axes bearing lepidodendroid leaf cushions as previously described. The new specimen, and others with like roots are tentatively assigned to Oxroadia gracilis Alvin.

The Upper Old Red Sandstone-Carboniferous junction at Burnmouth, Berwickshire

Synopsis A conformable junction between the Upper Old Red Sandstone and Lower Carboniferous rocks (Cementstone Group) exposed at Burnmouth in Berwickshire is described. The stratigraphic and palaeogeographic significance of the junction is discussed.

VIII.—Some specimens of Mazocarpon, Achlamydocarpon and Cystosporites from the Lower Carboniferous Rocks of Berwickshire

SynopsisA detached sporophyl and megasporangium of Mazocarpon pettycurense Benson is described. It formed twelve megaspores.Achlamydocarpon scoticum sp. nov. is described from detached sporophylls and megasporangia. The latter opened by means of three slits in the distal region so making pollination possible.A specimen of Cystosporites devonicus Chaloner and Pettitt is recorded from ash beds at the base of the Cementstone Group.

A preliminary study of sandstone sedimentation in the Lower Carboniferous of the Tweed Basin

Synopsis The sedimentology of the sandstones is used, together with the available stratigraphic information, to demonstrate the changes in depositional environment which take place in the Tweed Basin during Lower Carboniferous times. The characters of the sandstones of the Cementstone Group indicate deposition in a dominantly fluvial environment, the Fell Sandstone is interpreted as a thick widespread shallow marine deposit and the sandstones of the Scremerston Coal Group are mainly of fluvial origin. An attempt is made to fit these observations into a regional palaeogeographic pattern.

XIV.—Some Lower Carboniferous Fructifications from Berwickshire, together with a Theoretical Account of the Evolution of Ovules, Cupules, and Carpels

SynopsisTwo new species of petrified seedsEosperma edromense, andAnasperma burnensegen. et sp. nov. are described from the Cementstone Group of Berwickshire.Anaspermashows that the anatropous condition existed among Palæozoic ovules; it has a single integument with two lateral apical lobes.Rachides ofStauropteris berwickensissp. nov. and associated megasporangia are also described.An account is given of the theory of the telomic origin of the first ovular integument. The second (outer) integument in Angiosperm ovules may therefore have evolved after the establishment of anatropy, either from the first integument or as an overgrowth of the chalaza. Evidence is cited to support the theory that Angiosperm carpels have evolved from dorsiventral bivalved cupules.

VII.— The Heads of Ayr Vent

I. INTRODUCTION The twin headlands of the Heads of Ayr are located on the coast four miles south of the town of Ayr. They occupy about half-a-mile of coast and provide excellent vertical (cliff) and horizontal (wave-cut platform) sections through a volcanic vent of Carboniferous age. The vent was first mentioned by Geikie (1869), and later briefly referred to by Burns (1888), Smith (1895) and Boyle (1908). Tyrrell (1920) was the first to publish a detailed description of its structure and petrography, and this was later augmented by Eyles (1929). The Heads of Ayr vent is emplaced in gently-dipping sediments belonging to the Cementstone Group of Lower Carboniferous age. It has no large plug intrusion and, apart from a few small monchiquitic basalt bosses, is composed entirely of pyroclastic rocks which are bedded towards the west and imbedded towards the east. This spatial distinction between the two types of pyroclastic deposit is not found in most other Lower Carboniferous vents, perhaps, in part due to poorer exposures of them. The detailed field survey was carried out using enlarged maps of the coastal strip along Heads of Ayr, made from aerial photographs on a scale of 1:1250. It was found possible to trace directly from the photographs many of the structural features of the coast, especially the folding in the bedded pyroclastic rocks of the western end. II. STRUCTURE The vent is naturally divisible into an eastern part and a western part separated by the central recess. These divisions which were This 250-word extract was created in the absence of an abstract The author wishes to acknowledge the advice of colleagues in the Department of Geology, University of Glasgow, and to thank Professor T. Neville George and Dr. D. S. Weedon for their encouragement in the present work and for their critical reading of the manuscript.