bluuebunny/crossref_metadata_2025 huggingface dataset:
The Murchison–Sedgwick controversy
Authors: THACKRAY J. C.
Published: December 2007

By the year 1839 Murchison had mapped and described the four groups that made up his Silurian System, defining each on the basis of fossils he had collected during five years fieldwork in South Wales and the Borders. His friend Professor Sedgwick had given only a brief lithological description of the Cambrian rocks of North Wales by this date. As it became clear the two great divisions did not lie one on the other but overlapped at their boundary, Murchison extended his Silurian terminology into Sedgwick's domain. The Professor's inability to give a palaeontological definition of even a restricted Cambrian System led Murchison to extend the Silurian System down to include the oldest fossiliferous strata.

Arguments over the limits and validity of these two Systems scarcely abated with the death of the two chief contestants. British geologists remained in opposing camps until the end of the century, when Lapworth's Ordovician System of 1879 was generally accepted as a compromise for the disputed strata.
The Cornubian batholith, SW England: D/H and
18
O/
16
O studies of kaolinite and other alteration minerals
Authors: SHEPPARD S.M.F.
Published: December 2007

D/H and
18
O/
16
O ratios were determined on minerals and whole-rock samples of fresh granites, granites altered during greisenization and kaolinization of the Hercynian Cornubian batholith, detrital kaolinitic sediments of the Bovey Formation, and modern meteoric waters. The granites are high
−18
O rocks with δ
18
O = 10.8 to 13.2‰ due to melting, assimilation and/or exchange with argillaceous-rich metasediments at depth. Vein-controlled greisening was dominated by meteoric-hydrothermal fluids, Kaolinites from the major china clay deposits are of weathering origin. They are isotopically consistent with having formed in a tropical to warm temperature climate during the Cretaceous-Tertiary. Although intense supergene kaolinization was probably localized by earlier post-magmatic processes, there is no evidence that china clay kaolinites originally formed during hydrothermal activity and subsequently underwent post-formational isotopic exchange.
New Tremadoc strata at outcrop in the Bristol Channel
Authors: Tappin D. R. , Downie C.
Published: December 2007

In September 1972, as part of its offshore mapping programme, the Institute of Geological Sciences, using the chartered drillship MV
Whitethorn,
drilled a shallow borehole in the southern part of Carmarthen Bay. The hole, 72/60, was sited at latitude 51°34-80'N, longitude 4°34-71'W on Continuous Seismic Profile (CSP) 71/3/9 to determine the nature of the Palaeozoic rocks at this location. 5 m of sandy gravel, 3 m of stiff brown clay and 2-5 m of grey mudstone were cored. The mudstone was found to contain a rich assemblage of microplankton including the following taxa:

Acanthodiacrodium ubui?
Martin
Micrhystridium shinetonense
Downie
Cymatiogalea
cf.
multarea
Deunff
Cymatiogalea
cf.
membranispina
Deunff
Acanthodiacrodium angusta
(Downie)
Leiofusa squama
Deunff
Saharidia fragile
(Downie)
Possible chitinozoa
fragments
Acanthodiacrodium
sp. nov.
Acanthodiacrodium
cf.
decipiens
Timofeyev
Dasydiacrodium
sp. nov
Vulcanisphaera
africana Deunff
Micrhystridium robustum
Downie
Polygonium
sp. nov.
Polygonium
sp. nov
Vulcanisphaera
sp. nov.
Priscotheca complanata
Deunff
Archaeohystrichosphaeridium pungens
Timofeyev

The above assemblage is indicative of the Tremadoc and can be equated with that from the Brachiopod Beds of the Shineton Shales. It includes records of several new species, as yet undescribed, which have been recorded by Rasul (1971, unpublished Ph.D. Thesis) from Shropshire. No macrofossils have been found in the core.

The mudstone core is 2.5 m in length and vertically cleaved. It is dark grey, thinly laminated and micaceous. Examination in thin section reveals angular to sub-angular quartz grains tightly packed within a dense matrix of chlorite, which is in places iron stained. Muscovite flakes are orientated along
Palaeomagnetic evidence for the origin of the coastal flexure and dyke swarm in central E Greenland
Authors: Faller A. M. , Soper N. J.
Published: December 2007

The well known coastal flexure of central E Greenland, with its associated dyke swarm, affects a thick pile of Tertiary basalts and the underlying basement gneisses. It is a major tectonic/magmatic feature of this 'trailing edge' type continental margin. The original interpretation of Wager & Deer (1938) envisaged the emplacement of the dykes as a fan-shaped swarm in the convex arc of the flexure. Nielsen (1975, 1978) recognized several episodes of dyke emplacement. He interpreted the main swarm (THOL 1) as earlier than the flexure, emplaced vertically into the horizontal basalt pile and subsequently tilted by antithetic faulting during the formation of the flexure. A palaeomagnetic study of the THOL 1 and later dykes shows that the former were emplaced in their present inclined attitude. This discriminates in favour of Wager's interpretation, while remaining consistent with Nielsen's view of the post-flexural magmatic history. Modifications to Nielsen's scheme are suggested to conform with the new evidence, and the implications in relation to the mechanism of flexuring, the timing of tholeiitic magmatism, and the relationship of both to the early spreading history of this sector of the NE Atlantic, are discussed.
British Lower Palaeozoic black shales and their palaeo-oceanographic significance
Authors: Leggett J. K.
Published: December 2007

A review of Lower Palaeozoic black shale occurrences in the British Isles shows that carbon preservation in sediments, both in deep marine and shelf environments, occurs preferentially during phases of eustatic transgression (Caradoc and Lower Llandovery). Depletion of O
2
in the water column during these times, which in some areas produced anoxic conditions, was probably the result of two oceanographic processes resulting from the sea level rise: (1) the development of a thermocline, which placed bottom waters in deep shelf areas below the level of recycling by wind-driven vertical circulation; (2) increased primary productivity, which caused an expansion of the oxygen minimum zone. This expansion, in ocean waters which were more prone to oxygen-starvation than those of today, resulted in prolonged accumulation of anoxic facies in the abyssal depths of the Iapetus Ocean (the Moffat Shales of the Southern Uplands). Phosphates, analogous to those forming today under oxygen-deficient waters off W-facing continental margins, were deposited in the Caradoc black shale facies of central Wales.
Magnetostratigraphy of the Tertiary igneous succession of Mull, Scotland
Authors: Mussett A. E. , Dagley P. , Skelhorn R. R.
Published: December 2007

Measurements on 8 intrusive igneous bodies belonging to the central intrusive complex of Mull show that the earlier parts of the complex are reversely magnetized, whereas the later parts are normally magnetized.

Interpretation of these results and of published polarities of other parts of the Tertiary igneous succession is ambiguous because of the possibility of overprinting due to the heat of the central complex. Model 1 assumes that all polarities are primary and requires a polarity sequence R-N-R-N-R; Model 2, which assumes overprinting, requires only R-N-R.

A combination of radiometric dating and reference to the polarity time-scale limits the duration of activity to
c
. 3.5 Ma, at about 58 Ma.
Availability of sulphide ores in the ocean crust
Authors: Cann J. R.
Published: December 2007

Comparison of the distribution of sulphide ores in the Troodos ophiolite with the rate and manner of formation of ocean crust suggests that almost all sulphide ore bodies will only be exposed for a few thousand years in the active crestal zone of a ridge before being covered by lava, and that a few hundred such bodies, about 1 every 100 km of ridge crest, are currently exposed. Their rate of formation will be much less than potential mining rates, and sophisticated exploration techniques will be necessary to find them. Artificial generation of ores by controlled circulation may be a better approach eventually.
Ocean-ridge metalliferous and pelagic sediments of the Semail Nappe, Oman
Authors: Fleet A. J. , Robertson A. H. F.
Published: December 2007

The lavas of the Semail ophiolitic nappe of Oman, which formed at and very near a late Cretaceous oceanic spreading axis, are intercalated with, and overlain by a range of metalliferous sediments including cupriferous sulphides, ferruginous ochres and ferro-manganiferous umbers. The lava sequence is divisible into lower and upper informal units. The ‘lower’ lavas contain
small
massive sulphides and ochres which either formed by sea-floor oxidation of sulphides or were directly precipitated. In one area the basal ‘upper’ lavas contain mounds of ferruginous oxide sediments associated with umbers. The mounds may have resulted from bacterial precipitation of sulphides and/or Fe-oxy-hydroxides. Localized umbers deposited from hydrothermal solutions occur throughout and immediately above the ‘upper’ lavas, including areas where sea-floor faulting produced thick accumulations of volcaniclastic breccias. The uppermost umbers are overlain by radiolarites and foraminiferal chalk. Non-calcareous radiolarites are restricted to successions above umbers in some hollows suggesting that dissolution of calcareous pelagic sediment by acid hydrothermal solutions occurred during their ponded accumulation.

Most of the metalliferous deposits and pelagic sediments can be related to a spreading ocean ridge affected by sea-floor fault zones. Others are associated with extrusives which have island-arc affinities and built up as discrete volcanic centres on the sea-floor.
The stratigraphy and petrochemistry of the Lough Nafooey Group (Tremadocian), western Ireland
Authors: Ryan P. D. , Floyd P. A. , Archer J. B.
Published: December 2007

The Lough Nafooey Group is divided into 4 formations. The lowermost Bencorragh Formation consists of spilitic pillowed tholeiites, passing up into the blocky andesite flows, breccias, cherts and basic pillow lavas of the Finny Formation. This is overlain by the Knock Kilbride Formation comprised of spilitized calc-alkali basic to intermediate lavas, often pillowed, that are interbedded with breccias and graptolitic shales. Proximal turbidites containing rhyolite, granite and spilite clasts represent the highest Derry Bay Formation. New palaeontological evidence shows the Knock Kilbride Formation to be of upper Tremadoc (Lancefield 3) age. Petrological and structural studies show that the Lough Nafooey Group was folded and subjected to burial metamorphism prior to the onset of upper Llandovery sedimentation. Assemblages typical of the zeolite, pumpellyite and greenschist facies are recorded. Geochemical studies indicate a similar tectonic setting for the two main phases of eruption of basic lava (Bencorragh and Knock Kilbride formations) and it is suggested that these represent the early development of a Tremadocian island arc possibly related to the Grampian orogeny.
The use of data banks and databases within the Institute of Geological Sciences
Authors: Horder M. F.
Published: December 2007

The impact of computers on the data collection and associated activities of the Institute of Geological Sciences (NERC) has resulted in an expansion and diversification in the amount and types of data now processed as compared to the early19thcentury, when the Geological Survey used geological maps as an early method of data presentation. The Institute currentlyhas124 million items of computer-readable data available in 14 databank and database systems encompassing the fields of the deep subsurface geology of the UK landmass; hydrogeology; industrial mineral assessment; mineral economics; geochemistry; petrology; geophysics; and the geology of the UK continental shelf. These systems, their usage by the Institute’s geologists and their common features are described. Five common problem areas, namely the availability of adequate support resources, the need for data qualification, the need for data compatibility, the education of the user community and the need for maintaining the future integrity of the data, are briefly discussed. The use of data in these systems for manipulative and predictive purposes and their utilization in the consideration of complex geological and environmental science problems is increasing. This has involved the interrelation of data from more than one system as well as with data from data banks outside the Institute. This will to some degree have an impact on future operations, and a scheme for the interrelation of the Institute’s databanks and databases is discussed.
Fluidization of wet sediments during the emplacement and cooling of various igneous bodies
Authors: Kokelaar B. P.
Published: December 2007

During the emplacement and cooling of igneous bodies, fluidization of wet sediment by water vapour may occur by heating, or by pressure relief during the opening of fractures. Momentary fluidization causes sediment reconstitution and local transport. Continuous fluidization can result in substantial sediment displacement. Theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars. Studies of the emplacement of sills of andesite (Ayrshire), fluid rhyolite (Ramsey Island) and viscous rhyolite (Moelwyn Hills) recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations. The transgressive bases of the subaqueously welded ash-flow tuffs of the Capel Curig Volcanic Formation are consistent with emplacement attended by fluidization of the subjacent sediment. Evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host. Also, fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks, and can cause fractures formed during cooling to be thoroughly pervaded by sediment. Fluidization is commonly associated with the formation of peperites.
A model for the deep structure of the Moine thrust zone
Authors: Soper N. J. , Barber A. J.
Published: December 2007

Seismic refraction and electrical conductivity profiles across northern Scotland, together with geological and other geophysical data, are interpreted in terms of the deep structure of this part of the orthotectonic Caledonides. Our preferred interpretation is that the Moine thrust zone extends to the base of the crust and the Caledonian front is steep; this contrasts with recently proposed ‘ultra thin-skinned’ solutions. The results of the recently completed MOIST deep seismic reflection experiment should, inter alia, test our hypothesis.

In order to test the geometrical feasibility of our interpretation, balanced sections have been constructed to illustrate the crustal evolution of the region during the Caledonian orogeny. These sections permit estimates to be made of crustal shortening, thickening and erosion. Our model requires that the N Highlands were once overlain by major exotic nappes, which by analogy with NW Newfoundland may have been ophiolitic. The proposed regional structural pattern comprises a duplex of crustal dimensions. We suggest that crustal duplex development is an important mechanism in the orogenic deformation of previously thinned and extended passive continental margins.
Ignimbrite depositional facies: the anatomy of a pyroclastic flow
Authors: Wilson C. J. N. , Walker G. P. L.
Published: December 2007

A model is presented for the depositional regimes in a pyroclastic flow, to explain the origin of facies in the Taupo ignimbrite and to compare these with other published examples. In this model, a pyroclastic flow consists of a head, a body and a tail. The head, which is where fluidization caused by air ingestion occurs, generates layer 1 deposits. On lithological grounds these are divided into layers 1(P) which is fines-depleted and rich in pumice, and 1(H) which is fines-depleted and rich in lithics and crystals. Layer 1(P) represents material thrown forwards from the flow head and is termed the jetted deposits. Layer 1(H) represents material sedimented from within the flow head and is termed the ground layer. The body represents the bulk of the flow and the tail is its trailing part which is slowed by ground friction; these parts generate the layer 2 deposits which include the valley-pond ignimbrite and its associated ignimbrite veneer deposit. Localized depositional modes within the body and tail generate distinctive coarse pumice concentration zones and pumiceous lee-side lenses behind obstacles. At its outer limits all of the flow on interfluves is affected by air-ingestion fluidization, producing the distant facies which combines features of both layer 1 and 2 deposits. One important conclusion of this work is that the thicknesses and compositions of the various facies are not related in any simple way to the thickness and composition of the parent flow.
Basalt geochemistry as a test of the tectonic models of Timor
Authors: Berry R. F. , Jenner G. A.
Published: December 2007

Metamorphosed basic volcanic rocks of Permo-Triassic age occur in several distinct geological formations on Timor. Some are found in para-autochthonous units, which have been correlated with similar sequences on the Australian continental shelf; and some occur in apparently allochthonous units, which have been correlated with similar sequences in Malaya and Sumatra. Analyses of the relatively immobile elements, particularly Ti, Zr, Y, Nb, P and the rare earths, from both units revealed that the basalts vary from tholeiitic to mildly alkaline but are all consistent with emplacement in a rift-valley or ocean-floor setting. No difference was detected between the units based on basalt geochemistry, no calc-alkaline basalts similar to those reported in Malaya and Sumatra were found. and the basaltic suites are regionally distributed so as to cross-cut boundaries between the para-autochthonous and allochthonous units. The geochemistry is consistent with the evolution of all the Permo-Triassic units now on Timor as a part of the Australian continental margin but requires revision of detailed interpretations in order to be compatible with an exotic origin for the ‘allochthonous’ units.
A tectonic model for the emplacement of the Main Donegal Granite, NW Ireland
Authors: Hutton D. H. W.
Published: December 2007

The Main Donegal Granite is shown to lie in a major, late stage, NE-SW trending transcurrent sinistral shear zone in the Caledonides of NW Ireland. The zone, which is bent both laterally and upwards around the pluton, has displacements which diminish SW along its length from a maximum of approximately 20 km at the NE end of the pluton. The granite has also been deformed by this sinistral shear but it has a strain component of its own, the nature and development of which indicate that the pluton was accommodated rather than forcefully emplaced in the shear zone. Strain variations between granite and wall rock, and an early plagioclase fabric associated with the petrographic banding of the granite, suggest that intrusion and deformation were more or less synchronous (at around 400 Ma). It is suggested that unconsolidated granite in the shear zone locally created high strain rates and instability which caused the zone to bend, split lengthwise, and progressively create an internal low pressure zone into which the Main Granite was emplaced. The wide variety of emplacement styles of the other, radiometrically synchronous, plutons of the batholith can be attributed to the progressive development of the shear zone: Thorr and Fanad in tension between the zone and a complimentary structure to the N; Ardara and Toories in local compression at the shear zone termination; Rosses in tension on the outer arc of the bending zone; and Trawenagh Bay, as displaced Main Granite magma, in a similar tensional setting during the final stages of deformation.
The Sgurr Beag Slide within Moine rocks at Loch Eilt, Inverness-shire
Authors: Baird A. W.
Published: December 2007

The Sgurr Beag Slide is shown to be a syn- to late-tectonic movement zone of local F
3
age within a regionally developed five phase deformation sequence. It truncates both lithological units and a major F
3
synform, and is associated with the intensification of an F
3
crenulation fabric, the widespread development of boudinage and the tightening of interlimb angles of major and minor F
3
folds. The Moine rocks of the Glenfinnan and Morar Divisions on either side of the slide share the same pre-sliding history of deformation and metamorphism; they both contain minor F
2
folds with strongly developed axial planar mica foliations enhanced in pelitic lithologies by migmatitic segregations, together with less abundant minor F
1
folds. The slide is refolded by isoclinal major F
4
folds and by major open F
5
folds.
Palaeophysiology: the geological context
Authors: Funnell B. M.
Published: December 2007

The palaeophysiology of organisms has undoubtedly affected their ability to colonize and exploit past geological environments; it may also have influenced, through the metabolic by-products produced, the nature of past environments themselves. The importance of physiological evolution for environmental change, and of environmental change for physiological evolution makes it at least as relevant as the study of morphological evolution in understanding the relationship between biological and physical processes in the evolution of the Earth. In this context the relations between bacterial metabolism and Precambrian environments, between plant physiology and atmospheric composition, between metazoan anaerobic metabolism and environmental conditions, and between osmoregulation and salinity changes, are all briefly considered and assessed.
Grampian metamorphic conditions deduced from mafic granulites and sillimanite–K-feldspar gneisses in the Dalradian of Glen Muick, Scotland
Authors: Baker A. J. , Droop G. T. R.
Published: December 2007

Metamorphic conditions of 8 ± 1.5 kbar and 820 ± 50°C are estimated for garnet-clinopyroxene-bearing mafic granulites and associated garnet-sillimanite migmatitic gneisses from the Dalradian sillimanite zone. Revised estimates for the kyanite zone in Glens Avon and Ey (W of the regional andalusite and sillimanite zones) are
c
. 7 kbar at 500-600°C. Results from rocks close to the kyanite-sillimanite isograd in Glen Clova testify to the accuracy of the barometric calibrations.

Textural indications are that sillimanite preceded andalusite in the Glen Muick area: in this region the kyanite-andalusite isograd has no reality. In Glen Muick sillimanite grew synchronously with the development of the dominant steep foliation, and as part of a progressive evolution in metamorphic conditions, not as a separate late overprint. The western segment of the kyanite-andalusite isograd is thought to have developed before the attainment of the P-T conditions recorded in rocks from Glens Avon and Ey.

Metamorphic and geochronological data are examined in the light of the Banff Nappe hypothesis. It is suggested that the eastern high-temperature zones were thrust over the present western kyanite zone and that rocks to the W of the kyanite-andalusite isograd were metamorphosed by thermal relaxation beneath this thrust sheet.
Genesis and mobility of the H
2
O-CO
2
fluid phase during regional greenschist and epidote amphibolite facies metamorphism: a petrological and stable isotope study in the Scottish Dalradian
Authors: Graham C. M. , Greig K. M. , Sheppard S. M. F. , Turi B.
Published: December 2007

During high-pressure, low-temperature greenschist and epidote-amphibolite facies metamorphism in Dalradian rocks of the SW Scottish Highlands, mineral assemblages in metabasites and calcareous metasediments were dominantly controlled by infiltration of hydrous fluids; consequently, mineral assemblages capable of buffering the fluid phase composition were rare. Equilibrium prograde H
2
O-CO
2
fluids usually contained less or much less than about 1–2 mol% CO
2
.

Three fluid infiltration events are recognized. During prograde greenschist facies metamorphism, metabasic sills were infiltrated by large volumes of CO
2
-bearing hydrous fluid; carbon isotope studies indicate that the CO
2
was locally derived by widespread oxidation of graphite or other organic carbon in adjacent metasediments. This may have occurred under approximately lower greenschist facies conditions as a result of mixing of fluids of varying
f

O
2

, initiated by thermal expansion of water during heating, decompression and consequent hydraulic fracturing. In the epidote-amphibole facies (garnet zone), dehydration reactions in metabasites generated large quantities of water, which removed carbonate from metabasites on a regional scale and infiltrated calcareous metasediments to produce assemblages containing grossular, diopside, K-feldspar, amphibole, clinozoisite and sphene. A late retrograde infiltration of CO
2
,-bearing hydrous fluid under lower greenschist facies conditions generated assemblages containing K-feldspar + chlorite + rutile ± dolomite in calcareous rocks and albite prophyroblast schists in zones of intense secondary deformation.

Large-scale infiltration of fluid into greenschist-facies metadolerite sills was intimately related to, and possibly controlled by, penetrative deformation and, in the absence of a penetrative deformation, grain-boundary diffusion by itself was an ineffectual mechanism of fluid transport.
Soviet and British stratigraphical classifications compared
Authors: Holland C. H.
Published: December 2007

Significant features of Soviet stratigraphical classification are briefly reviewed in comparison with procedures accepted by the Geological Society in Britain. There is much similarity and, in any case. there is a more widespread tendency for views to converge.
Metamorphism and tectonics of the Himalaya
Authors: Windley Brian F.
Published: December 2007

Metamorphism connected with the main growth and deformation stages of the Himalaya ranges from mid-Cretaceous to the Quaternary. Northward subduction gave rise in the early to mid-Cretaceous to an island are complex with greenschists, amphibolites, granulites and blueschists in the W (Kohistan-Ladakh) and an Andean-type margin with greenschist-amphibolite grade metamorphism in the E (India and Tibet). Ophiolitic nappes were thrust southwards over the Indian continental margin in the Palaeogene during the final stages of closure of the southern arm of Tethys. The Indus-Zangbo Suture bifurcates westwards and between the two sutures lies the Kohistan-Ladakh island arc which was converted to an Andean-type arc in the Palaeocene-Eocene. The Karakorum Range underwent northward subduction at least during the late Cretaceous to give rise to a complex and prominent calc-alkaline batholith. Post-collisional southward thrusting of crustal slabs over the Indian continental margin took place in the early Miocene with production of high-grade metamorphism, inverted isograds and crustal melt granites. Later southward thrusting in the Pliocene to Quaternary gave rise to localized low-grade recrystallization against the thrusts.
Metamorphic studies: research in progress
Authors: Brown Michael
Published: December 2007

Report of a meeting of the Metamorphic Studies Group held at Burlington House,
16
March
1983.
The meeting was organized
by
Dr M. Brown.

A Metamorphic Studies Group Meeting on ‘Metamorphic studies: research in progress’ together with the second Annual General Meeting of the Group were held on 16 March 1983; approximately 65 members of the Group participated in the meeting. A total of 13 papers was presented, covering a wide range of interests in metamorphic geology and including a mixture of old faces and new contributors; it was disappointing that only four of the papers were given by current research students, although it remains the policy of the Group to encourage research students to contribute to its meetings.

The morning session, chaired by Professor Bernard Leake, was opened by Brown, who presented an account of the metamorphic history preserved within cordierite-bearing pelitic gneisses from Timor in eastern Indonesia. The rocks, which form part of the Mutis Complex, are allochthonous, having been located in SE Asia during Mesozoic time and having been emplaced onto Australian continental rise deposits by thrusting during the mid-Pliocene collision between the Banda Arcs, now separated from SE Asia by the Banda Sea marginal basin, and the Australian continental margin. Estimated metamorphic conditions resulting from decompression under high temperatures evolved from T > 750°C and P ≃ 10 kbar through T ≃ 700°C and P ≃ 5 kbar at P

H
2
<O

< 0.5 P
total
to T = 550-600°C and P ≃ 2 kbar.

This uplift path
Conditions of high grade metamorphism in the Dalradian of Connemara, Ireland
Authors: Barber J. P. , Yardley B. W. D.
Published: December 2007

In E Connemara, Ireland, Dalradian metasediments were initially metamorphosed to kyanite-staurolite grade at pressures above 7kbar. The subsequent emplacement of basic to intermediate magmas, accompanied by uplift and erosion, produce a steepening of the geothermal gradient and led to the formation of migmatitic garnet–cordierite–sillimanite-gneisses in the highest grade regions in the S. Cation exchange equilibria between coexisting mineral pairs suggest that partial melting took place under high temperatures (≃ 750°C) and moderate pressures (4.5–6 kbar). Fluid inclusion studies and andalusite occurrences from migmatite leucosomes suggest that crystallization of the melts occurred at lower pressures (<3.5 kbar) than melting, implying that uplift and erosion occurred while the rocks were hot.
Triassic sediments of the Inner Moray Firth, Scotland: early rift deposits
Authors: FROSTICK L. , REID I. , JARVIS J. , EARDLEY H.
Published: December 2007

Patterns of Triassic sedimentation in the Inner Moray Firth are examined in the light of a new model of continental rift sedimentation that has been developed in the Tertiary to Recent rifts of East Africa. The major tectonic control during the Trias was the Great Glen fault to the northwest, which can be shown to have been moving in dip-slip fashion at this time. The structure of the Firth appears to have resembled the simple half-graben that makes up the great East African rift system. Deposits both thicken and get finer towards the fault. Sediments found in off-shore wells are dominated by laminated fine sand and silty-clay with sporadic evaporites. Similar sequences are characteristic of, or associated with, ephemeral lakes in modern semi-arid continental rift settings. No alluvial fans have been detected close to the faulted margin. Again, this is consistent with general patterns of sedimentation against boundary faults in the Kenyan rift. The coarsest sedimentary sequences in the Moray Firth are on the unfaulted margin to the south around Burghead. They consist of fluviatile, lake shore and aeolian deposits. The fluvial sediments show evidence of tectonically induced cycles of sedimentation which are interpreted in terms of waves of detritus working down the drainage system. Beds dominated by pebbly horizontal laminae and reminiscent of steep, straight and shallow ephemeral streams alternate with troughed sands of deeper, more sinuous, but equally ephemeral rivers. These are the coarsest sediments of the unfaulted margin of the basin. However the lack of thick conglomerate sheets, which are a feature of East African sequences at equivalent positions within the rift basin, suggests only small-scale fault activity and a relatively subdued topography during Triassic times. This is supported by evidence of extensive calichification during the Rhaetic which produced a top-Trias marker horizon found throughout the Inner Moray Firth.
Geological aid to developing countries
Authors: STOW DORRIK A. V.
Published: December 2007

Report of the inaugural meeting of the UK section of the Association of Geoscientists for International Development (AGID-UK), now affiliated to the Geological Society, held in Burlington House, 15 February 1988.

AGID is a unique international association of geoscientists with some 90% of its 2500 membership drawn from over 100 Third World countries. After nearly 15 years in existence, it is still the only organization devoted to the application of science to the problems of developing countries. It works in co-operation with local, national and international groups on programmes related to the development of natural resources, environmental planning and geoscience education. Perhaps its most important function is the informal grassroots contact and worldwide collaboration between individual geoscientists who share many of the same problems and the determination to solve them.

The theme of the meeting was to explore the role that UK geologists could play towards these ends. Four speakers were invited to address aspects of ‘geological aid’ from personal experience.

Global geoscience.
Anthon R. Berger
(Ottawa, editor of
Episodes)
began by suggesting that ‘geological aid’ was a somewhat outmoded concept. However since geosciences are global in outlook, it is imperative that a proper understanding is developed of the natural forces that lead to global changes and of their interaction with society. It is also imperative to communicate effectively both the results of such research and any consequent warnings to planners, politicians and policymakers. None of this can be done without the full participation of Third World Scientists in the
Kinematics of the Alpine plate-margin: structural styles, strain and motion along the Penninic–Austroalpine boundary in the Swiss–Austrian Alps
Authors: RING U. , RATSCHBACHER L. , FRISCH W. , BIEHLER D. , KRALIK M.
Published: December 2007

A structural and kinematic analysis of parts of the Alpine suture zone, i.e. the Arosa Zone and the edges of the overlying Austroalpine and underlying Penninic units, is presented. The Arosa Zone is interpreted as part of an accretionary wedge formed by the overriding of the Austroalpine units, the northern part of the Adriatic plate, over the Penninic units. Structures, strain and stretching trajectories indicate that two main deformation events followed each other discontinuously. The earlier event was a WSW- to NW-directed thrusting under noncoaxial deformation and led to melange-type structures. The second event, less penetrative in the Arosa Zone and with a downward increase in strain and noncoaxial flow, formed N- to NE-verging folds and imbrication zones. West-directed displacement commenced in the Early Cretaceous and the motion changed to a prevailing northerly direction during the Eocene, as revealed by sediments involved in thrusting and by radiometric dating of the mylonites.

The kinematic history deduced from structural analysis agrees with the history obtained by recent work on plate margin sediments. We correlate the anticlockwise rotation of the Adriatic plate relative to Europe between about 130 and 60 Ma with the west-directed motion in the Arosa Zone. A change to relative N-S motion during the Lower Tertiary led to the N to NE directed displacements. A direct relationship thus exists between the motion of the Adriatic plate and the resulting deformation along its northern margin during the early history of the Eastern Alps.

Partitioning in brittle and ductile deformation and structural slicing under noncoaxial deformation is responsible for the melange-type structures.
Changes in marine isotopic composition and the late Ordovician glaciation
Authors: MARSHALL JAMES D. , MIDDLETON PAUL D.
Published: December 2007

Well-preserved brachiopod shells and marine cements from limestone coquinas which cap carbonate mudmounds in the Siljan area of central Sweden have the heaviest stable oxygen and carbon isotope values yet reported for Lower Palaeozoic marine sediments. The coquinas formed during the eustatic regression at the onset of the late Ordovician glaciation: the isotopic compositions reflect simultaneous shifts in both carbon and oxygen (more than 5‰ δ
13
C and up to 2º‰ δ
18
O) away from more normal Lower Palaeozoic values in similar carbonates from within the mounds. Oxygen isotope data are consistent with a change in the isotopic composition of the sea water probably accompanied by a decrease in temperature. The changes in carbon values suggest enhanced deposition of organic carbon, a process which would have decreased
p
CO
2
in the ocean and the atmosphere and thus contributed to rapid global cooling.
The Dinantian stratigraphy of the East Midlands: a seismostratigraphic approach
Authors: EBDON C. C. , FRASER A. J. , HIGGINS A. C. , MITCHENER B. C. , STRANK A. R. E.
Published: December 2007

Six tectonically controlled seismic sequences have been identified in the Dinantian succession of the Widmerpool Gulf, East Midlands and they have also been recognized in outcrop sections in Derbyshire and the Bowland Basin. These correlations are made possible by integrating and calibrating sequence boundaries with the biostratigraphical evidence from foraminifers, conodonts and palynomorphs and relating these to the tectonostratigraphical evolution of the basin. It is suggested that the current chronostratigraphical stages of the Dinantian do not always reflect major regional stratigraphical events and that the seismic sequence stratigraphy erected herein may provide a more applicable chronostratigraphical subdivision of the Dinantian of the East Midlands and northern England.
Late Palaeogene-Neogene evolution of the triple junction region near Maraş, south-central Turkey
Authors: KARIG D. E. , KOZLU H.
Published: December 2007

The Maraº region of Turkey includes the Anatolian-Arabian-African triple junction. The African-Arabian margin is marked by left-lateral transtension along the Dead Sea (Kara Su) rift. Motion on the Anatolian-Arabian boundary is partitioned between the left-lateral East Anatolian fault and a fold-thrust belt termed the Engizek zone, equivalent to the Bitlis suture further east. The African-Anatolian boundary lies along the Cyprus-Misis-Andirin trend and is expressed near the triple junction as the Aslantaº-Iskenderun zone, now undergoing slow left-lateral transtension. The Neogene evolution of these boundaries is largely recorded in the stratigraphy and structure of the basins that lie along the Anatolian-Arabian (Lice basin) and Anatolian-African (Aslantaº-Iskenderun basin) boundaries. These basins appear to have developed in the early Miocene along major strike-slip zones. Large half graben in the pre-Neogene 'basement' of the western (Misis-Andirin block) developed contemporaneously with motion on the Anatolian-African boundary. These extensional features evolved subsequent to the intense shattering of the Mesozoic carbonate sequence in the Misis-Andirin block and its mixing with panels of deep water Palaeogene strata to form an extensionally disrupted assemblage. Transpression and conversion of both Anatolian-African and Anatolian-Arabian boundaries to fold-thrust belts occurred in the late Miocene. Transpression continues along the Anatolian-Arabian boundary but transtension has recurred along the Anatolian-African boundary since the Pliocene.
Basin evolution within and adjacent to the Tien Shan Range, NW China
Authors: ALLEN M. B. , WINDLEY B. F. , CHI ZHANG , ZHONG-YAN ZHAO , GUANG-REI WANG
Published: December 2007

Two late Palaeozoic collisions produced the ancestral Tien Shan Range. Extension following the younger collision, preceded a phase of thermal subsidence associated with fluvial and lacustrine sedimentation throughout the Jurassic, Cretaceous and early Tertiary. This thermal subsidence was interrupted by renewed movement on Palaeozoic reverse faults, caused by the Mesozoic collisions at the southern margin of Asia. The India/Asia collision in the early Tertiary has produced widespread thrusting in the Tien Shan, which in turn is responsible for the formation of active foreland basins at the southern and northern margins of the range and similar basins within the range itself. This compression produced uplift and relief, and consequent erosion gave rise to alluvial fans, braidplains and ephemeral lakes in an extremely arid environment.
The Lower Carboniferous Stainmore Basin, N. England: extensional basin tectonics and sedimentation
Authors: COLLIER R. E. LI.
Published: December 2007

Recently released industry seismic data image a 6 km thick Dinantian succession in the Stainmore Basin, and are used to interpret deposition in response to extensional subsidence. The basin is bounded to the north by the Lunedale–Wigglesworth–Butterknowle en echelon suite of normal faults. An early (?Courceyan–?Arundian) syn-rift sequence more than 4 km thick includes footwall-derived clastic fans. A basinal terrigenous sequence deposited through the Arundian, Holkerian and early Asbian contrasts with coeval carbonates on the Ravenstonedale Shelf and the Askrigg Block. Deposition continued in the basin whilst the Alston block and northern parts of the basin were emergent during early Asbian times. A late Asbian relative base level rise and the possible cessation of active rifting allowed both basin and structural highs to be inundated by shallow marine carbonates. Rhythmic ‘Yoredale’ sedimentation followed.

Dinantian depositional patterns reflect the interplay between active extensional faulting, a suspected local inversion event, changes in sediment influx rates, sea level variations and differential rates of compaction between basement highs and the basin. However, error margins on the available biostratigraphy and timing of active faulting prevent the detailed separation of these variables and their impact on sedimentation in the Dinantian.
A precise U-Pb zircon age for the Inishtrahull syenitic gneiss, County Donegal, Ireland
Authors: DALY J. S. , MUIR R. J. , CLIFF R. A.
Published: December 2007

Smd zircon fractions from the deformed alkaline igneous complex on Inishtrahd, County Donegal, Ireland yield near-concordant U-Pb ages of 1779 * 3 Ma interpreted as dating the igneous crystallization of the gneiss's precursor. Sm-Nd depleted mantle model ages range from 1912 Ma to 1978 Ms. The similarity of the model ages and the crystallization age indicates that the protoliths were derived from a depleted mantle source essentially uncontaminated by older crust. The isotopic data confirm previous tentative correlations of the Inishtrahull rocks with those of Islay in southwestern Scotland. Archaean crust is apparently absent from this region, consistent with recent models placing a southern limit on the Archaean along the line of the Great Glen fault zone.

Pre-Caledonian orthogneisses in Scotland and Ireland, south of the Great Glen fault zone, have generally been correlated with the late Archaean Lewisian Complex of northwestern Scotland (e.g.
Wilkinson 1907
;
McCallien 1930
; Bowes & Hopgood 1975;
Dixon et al. 1990
) although Aftalion & Max (1987) concluded that the Lewisian was absent from the Annagh Division gneisses of north Mayo, Ireland. There are now several lines of evidence to suggest that Archaean crust may be absent southeast of the Great Glen fault zone (e.g.
Fitches et al. 1990
;
Daly 1990
;
Halliday et al. 1985
).

A large area of pre-Caledonian basement, here termed the Rhinns Complex, is thought to be present within the fault-bounded Colonsay-West Islay block (Fig. 1;
Bentley et al. 1988
;
Fitches et al. 1990
;
Marcantonio et al. 1988
)), which extends from Colonsay in
The Oligocene Xanthi pluton, northern Greece: a granodiorite emplaced during regional extension
Authors: KOUKOUVELAS I. , PE-PIPER G.
Published: December 2007

The Xanthi pluton is one of a series of Oligocene subduction-related granodiorites in northern Greece. Its emplacement was controlled by major faults. It is located on the ENE-trending Kavala–Komotini fault zone, which probably originated as a strike-slip fault. Geophysical data show that the pluton is laccolith-shaped, extending many kilometres south of the fault. Andesitic dykes several million years older than the pluton indicate a NE–SW-directed extensional stress field. Mineral lineations plunging to the SW reflect continued extension during cooling of the pluton. Subsequent jointing and dykes of aplite and lamprophyre reflect continued extension. Although this could result from extensional pull-apart at a bend during dextral strike-slip motion on the Kavala–Komotini fault, there is no evidence for subsequent strike-slip deformation. Furthermore, two similar laccolithic plutons are unrelated to the Kavala–Komotini fault and the regional extent of thick Oligocene sediments suggests an extensional environment. During the extension that created a ramp space along the listric fault bounding the Xanthi basin, into which the granite was intruded, the Kavala–Komotini fault acted as a transfer fault. Reactivation of early joints occurred during late Oligocene–Early Miocene compression. Faults within the pluton parallel to the Kavala–Komotini fault accompanied extension during Neogene basin formation. Emplacement of subduction-related magma into ramp space developed along listric faults, to produce laccolith-like plutons, may be a common feature of back-arc extension.
Sequence stratigraphy of carbonate-evaporite basins: models and application to the Upper Permian (Zechstein) of northeast England and adjoining North Sea
Authors: TUCKER MAURICE E.
Published: December 2007

The successions of carbonate-evaporite basins, which are periodically cut off from the world ocean, are considered in terms of their sequence stratigraphy. Two basin types are distinguished: those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation. It is argued that, following relative sea-level falls, sequences begin with the evaporites, precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin-centre halite fills in the second. The evaporites pass up into carbonate sediments which are mainly deposited on shallow-water platforms around the basin during transgressive and highstand systems tracts. The concepts and models developed are applied to the Zechstein (Upper Permian) strata of northeast England and adjoining North Sea. Seven sequences are proposed, with some containing thin parasequences. The sequence approach to carbonate—evaporite basins, which considers both basin margin and basin centre facies, gives a more encompassing perspective of sedimentation than the traditional cycle concept, with its emphasis on the basin centre.
Progressive deformation of the South Stack and New Harbour Groups, Holy Island, western Anglesey, North Wales
Authors: PHILLIPS EMRYS
Published: December 2007

The Monian Supergroup of western Anglesey comprises three major lithostratigraphic units: the South Stack (oldest), New Harbour and Gwna Groups. In northern and western Anglesey, deformation and metamorphism each increase in intensity downward through the Monian Supergroup, especially towards the base of the New Harbour Group. The variation in style and apparent intensity of deformation recorded by the South Stack and New Harbour Groups were governed by gross lithological differences. A correlation is proposed between the deformation histories of the New Harbour and South Stack Groups. Early deformation of the supergroup produced a pervasive bedding-parallel S1 fabric (chlorite) in both the New Harbour and, to a lesser extent, South Stack Groups. Development of the major, SE-verging F2 Penrhyn Mawr and Rhoscolyn anticlines, and associated minor folds also produced an axial planar S2 pressure solution and crenulation cleavage (phengite). The Rhoscolyn anticline was subsequently modified by the localized development of recumbent, mesoscale F3 folds with an axial planar pressure-solution cleavage (phengite to phengitic muscovite). The F3 event may have accompanied an episode of thrust faulting. Deformation of the South Stack and New Harbour Groups was accompanied by a progressive regional greenschist facies metamorphic event. The simplest interpretation of the deformation history of the Monian Supergroup involves a progressive SE-directed shear event which occurred prior to the deposition of an Ordovician overstep sequence on Anglesey.