bluuebunny/crossref_metadata_2025 huggingface dataset:
Clues to the deep structure of the European Variscides from crustal seismic profiling in North America
Authors: Brewer J. A.
Published: September 2007

COCORP data from two areas of North America where late Palaeozoic deformation occurred provide clues to the deep structure of the Variscides of Europe. These areas are: (1) the southern Appalachians, where deformation culminated in the Alleghenian orogeny, and (2) the Ouachita Mountains, formed during the Ouachita orogeny. The COCORP data show deep structures which were probably formed during collision and overriding of the early Palaeozoic edge of the North American Grenville basement. Two types of reflector sequences are characteristic: (1) subhorizontal or gently dipping reflectors defining the base of crystalline or sedimentary nappes, which in the interior of the orogen pass into: (2) more steeply dipping (25–40°) zones of reflectors, 10–20 km thick, that are possibly offshelf, basinal facies metasedimentary rocks, and slices of basement, stacked and imbricated against, and hence marking the edge of, the North American continent. Similar reflector sequences are observed in seismic data recorded from the European Variscides, suggesting that here similar processes occurred at the southern edge of the Old Red Sandstone continent. Changes in the character of the Variscan front can perhaps be explained in terms of the extent of overthrusting of the continental edge (i.e. the extent of nappe formation).
The land flora of the English and German Zechstein sequences
Authors: Schweitzer H.-J.
Published: September 2007

All species of higher plants described from the Upper Permian Zechstein and related rocks of Germany and England are reviewed, except for those thought to be dubious.

The plants described are:
Neocalamites mansfeldicus
Weigelt,
Sphenopteris dichotoma
Althaus,
S. patens
(Althaus) Geinitz,
S. geinitzi
(Geinitz) Göppert,
S. kukukiana
Gothan et Nagalhard,
Callipteris martinsi
(Kurtze) Zeiller,
Taeniopteris eckardti
Kurtze,
Pseudoctenis middridgensis
Stoneley,
Plagiozamites bellii
nov. spec.,
Sphenobaiera digitata
(Brongniart) Florin,
Pseudovoltzia liebeana
(Geinitz) Florin,
Ullmannia bronni
Göppert,
U. frumentaria
(Schlotheim) Göppert,
Quadrocladus solmsi
(Gothan et Nagalhard) Schweitzer,
Q. orobiformis
(Schlotheim) Schweitzer,
Culmitzschia florini
Ullrich and
Rhenania reichelti
Schweitzer. Of these
Pseudoctenis middridgensis
and
Plagiozamites bellii
are known only from England and
Sphenopteris geinitzi, Quadrocladus solmsi, Q. orobiformis, Culmitzschia florini
and
Rhenania reichelti
only from Germany.

In the Upper Permian there were two plant associations; a hygrophilic
Neocalamites
-Sphenopterid association and a xerophytic
Callipteris
-conifer association. Distinct growth rings in the conifer woods indicate rhythmic changes in the climatic conditions.
The diagenetic history of Cadeby Formation carbonate (EZ1 Ca), Upper Permian, eastern England
Authors: Harwood G. M.
Published: September 2007

The Upper Permian Cadeby Formation (formerly the Lower Magnesian Limestone) crops out from North Yorkshire to Nottinghamshire in eastern England. The Cadeby Formation comprises shallow water carbonates within which penecontemporaneous, eogenetic, mesogenetic and teleogenetic diagenetic events can be defined. Penecontemporaneous events included facies-controlled dolomitization and evaporite calcitization. Pervasive dolomitization, largely independent of facies, was eogenetic. Late eogenetic to early mesogenetic events were dominated by replacive and pore-filling anhydrite crystallization. Both pervasive dolomitization and subsequent anhydrite formation occluded porosity. Other mesogenetic events were of local effect only. Anhydrite to gypsum transformation, together with evaporite dissolution and carbonate leaching, dominate the later near-surface, or telogenetic, events.
Zechstein 1 and 2 Anhydrites: facts and problems of sedimentation
Authors: Richter-Bernburg G.
Published: September 2007

The distribution and lithology of the anhydrite rocks of Zechstein 1 and Zechstein 2 were significantly influenced by the contemporary geography of the basin. Thick ‘pletholitic’ shallow-water deposits with large-scale synsedimentary derangements lie near the margins and pass laterally, with steep boundaries, into thin laminated deep-water rocks on the basin floor. Five sub-cycles (I–V) have been recognized in cored boreholes in the Z1 Werraanhydrit throughout the German Zechstein basin and permit correlation with the Zechstein 1 sequence of the southern North Sea Basin; although not complete in every place, each sub-cycle generally comprises flaser anhydrite overlain by laminated anhydrite. The abrupt changes of facies at the contacts between the sub-cycles cannot be attributed to eustatic sea-level changes but are caused by changes of the climate, water currents and related effects; the periodicity must have resulted from factors originating outside the basin.

The following new adjectives are proposed, primarily for varieties of anhydrite although they may prove to be equally applicable to other sedimentary rock types: ‘Pletholitic’—from the Greek ‘plethos’, an indefinable mass—applicable to thick anhydrite rock with a diffuse, cloudy or chicken-wire structure and fabric but with little overall stratification.

‘Stratobolic’—from the Greek ‘bolos’, lump—anhydrite rock with extremely irregular small-scale and medium-scale bedding but with a strong sense of stratification
en masse
. This term includes ‘flaser’, which is mainly applied to stratobolic rocks with bedding of an exceptionally anastomosing character.

‘Lamellitic’—from the German ‘Lamellenanhydrit’—unusually uniformly and evenly laminated anhydrite, including some varved anhydrite. This term is proposed because the word ‘laminated’ is used in a range of senses and does not adequately stress the uniformity and continuity of bedding in some thinly and evenly layered anhydrite rocks.
Zechstein salt correlation: England-Denmark-Germany
Authors: Richter-Bernburg G.
Published: September 2007

A correlation of the Zechstein strata of England and Germany is presented. It is based on strong similarities in the distribution, thickness and lithology (including lithological succession) of the various evaporites in the two sequences and, particularly, on an upwards change in colour from mainly grey to mainly red between the second and third cycles; this change probably indicates a basin-wide change in the oxidation state of the Zechstein Sea. By these criteria, it is suggested that strata of the Don and Aislaby groups of England together are equivalent to the deposits of the Werra Cycle in Germany and that those of the Teesside Group are correlatives of the German Stassfurt sequence.
Sedimentary environments of the lowest Zechstein sediments in the Lubin region, SW Poland
Authors: Tomaszewski J. B.
Published: September 2007

The lowest Zechstein sediments in the Lubin area form the ‘copper-bearing series’ and contain the copper ore deposit of the Foresudetic Monocline. Observations, measurements and sampling of the lowest Zechstein sediments were taken over an area of
c.
25 km
2
in the underground galleries of the Lubin copper mine. Chemical and mineralogical analysis of the samples was then carried out. Additional data on the ore body and the thickness of particular lithologies were supplied by the mine’s geological service. These data enabled the construction of isopach maps for the copper bearing series, plus reconstruction of the sedimentary environments.
Evolution of the southern margin of Tethys (North Australian region) from early Permian to late Cretaceous
Authors: Audley-Charles M. G.
Published: September 2007

A mid-Permian rifting episode appears to have removed continental blocks (now forming parts of Asia) from Australian Gondwana, but the present continental margin of Northern Australia-central New Guinea was formed by a later episode of rifting during the Jurassic. With the exception of the north-west Australian offshore region west of the Scott Plateau, this rifted continental margin has been greatly modified during the Cainozoic by collisions with arc-trench systems. Collision resulted in fold and thrust mountains, locally with ophiolite emplacements, that now characterize most of northern New Guinea and the Banda Arc. The identification of the Australia-New Guinea rifted continental margin in what is now the fold and thrust mountain belt of New Guinea, islands of the Outer Banda Arc, East Sulawesi, and Buton, rests largely on stratigraphic correlation and the recognition of the pre-rift sequence, breakup unconformity, and the post-breakup marine transgression and prolonged subsidence in these now highly deformed rocks. One implication of the Jurassic continental rifting is that the pre-rift rocks of the region accumulated in an intracratonic basin of eastern Gondwana. Another important implication is that the continental blocks rifted from the Northern Australia-central New Guinea margin must have drifted northwards towards Asia as the Mesozoic Tethys ocean spread across the tropics and equatorial region. These continental fragments of Gondwana collided with parts of south-east Asia that had been derived from Gondwana in an earlier phase of rifting.
The nature, extent, and subsequent dispersal of the Permian Tethys
Authors: Waterhouse J. B.
Published: September 2007

On the basis of the sedimentary and biotic facies characteristics of Permian strata deposited in different climatic zones, scepticism is expressed about some recent palaeogeographical reconstructions that demand a vast wedge-shaped Tethys in Asia, or movement over considerable latitudes of allochthonous terranes.
Unexpected microfaunal communities within the Triassic Tethys
Authors: Kristan-Tollmann Edith
Published: September 2007

Modern research has demonstrated a remarkable uniformity in Triassic faunas throughout the Tethyan region. This is true not only for planktonic and pelagic elements but also for vagile and sessile benthic organisms, and involves a surprisingly large number of species of macro- and microfauna, including numerous zone fossils. In this work, further striking microfossil examples are selected from potentially important groups that have been little utilized previously for biogeographical research.
Structure and palaeogeography of the western Tethys during the Jurassic: tests based on ammonite palaeobiogeography
Authors: Thierry Jacques
Published: September 2007

Comparisons between the recently proposed palaeogeographical reconstructions for the Tethys and the palaeobiogeography of Jurassic ammonites are important in the study of the structural evolution and the palaeogeography of the Tethys and its margins. The geographical distribution of Jurassic ammonites is considered to be due to a combination of historical and ecological factors, with the existence of biota and bioma (
sensu
Croizat 1958). ‘Boreal’ and ‘Tethyan biota’ are used and preferred to the ‘Boreal’ and ‘Tethyan realms’ (or provinces), as previously used to designate ammonite communities with similar geological and evolutionary history; several ‘Bioma’ are defined for faunal communities with similar morphofunctionary adaptations (for instance on very shallow platforms or in deep oceanic regions). The overlap of biota and bioma better explains the compound ammonite faunas. The recently proposed new maps of the Tethys show that in the west the oceanic areas are much more restricted in area than in previous reconstructions; a large oceanic region is constantly extended throughout the Jurassic, only in its eastern part. Subsequently, the total area west of the so-called Apulian Plate, and in Western Europe, takes a prominent part in the faunal ammonite distribution. The Arctic Basin sometimes acted as an evolutionary trap, where Boreal faunas were totally isolated from the Tethyan ones; sometimes an important eustatic transgression allowed faunal exchanges to be made between Boreal and Tethyan stocks. Several examples, taken from the Pliensbachian to the Callovian, serve to demonstrate the influence on ammonite distributions of either the possible deep-oceanic areas or very shallow platforms and emergent areas.
Gondwana, Tethys, and terrestrial vertebrates during the Mesozoic and Cainozoic
Authors: Rage Jean-Claude
Published: September 2007

During the Triassic, free dispersal of terrestrial vertebrates was possible in Pangaea; however provinciality appeared in Gondwana. Distribution of Triassic vertebrates may be explained even if the Earth diameter did not expand and if Pacifica did not exist. During the Jurassic, a free land communication persisted between Gondwana and Laurasia, and provinciality is not demonstrated. A Gondwanan pattern emerged during the Cretaceous, but since that time it is not possible to identify a global difference between Gondwanan faunas and Laurasian ones. An African/South American terrestrial community developed until the Aptian. Subsequently, the opening of South Atlantic hindered interchanges between these two areas, but did not end them; exchanges might have taken place then via trans-Atlantic filter, or sweepstakes, routes. For the Cretaceous/Eocene time interval, crossings of the Tethys occurred intermittently, the major event being the interchange that took place between North and South America by latest Cretaceous. By the Cretaceous/Palaeocene transition, a terrestrial route probably linked the still southern Indian Plate to Laurasia. It is uncertain whether this route reached Madagascar. After the Eocene/Oligocene transition, exchanges between Gondwanan continents vanished, whereas exchanges between Gondwanan areas and Laurasia sometimes occurred.
Tectonics from fossils? Analysis of reef-coral and sea-urchin distributions from late Cretaceous to Recent, using a new method
Authors: Rosen Brian R. , Smith Andrew B.
Published: September 2007

Biogeographical distribution is seen as a product of small- and large-scale factors, of which only the latter are important in palaeogeographical reconstruction. We review here previous methods for assessing the historical sequence of major events that have caused biogeographical distributions, and we argue that the most rigorous of these is cladistic biogeography. We also advocate our own new method, which uses parsimony analysis of taxa shared between sample localities. In not being dependent on prior phylogenetic analysis, this method is especially suitable for taxonomic groups which lack an adequate phylogeny.

This new method takes contemporaneous distributional data from one or more narrow stratigraphic time planes (including the present), and generates a cladogram of sample localities for each of them. We interpret these cladograms as hypotheses of historical sequences of divergences between biotas, for which the sample localities provide geographical control. Congruence between cladograms from different organic groups and time planes provides an indication of those events which are most likely to have been the result of major (e.g. tectonic) historical factors. This method avoids prejudgement of areas of endemicity. We also argue that because younger major historical events can destroy the biogeographical patterns produced by older events, we can reach a more complete understanding of historical biogeography by using a combination of Recent and fossil data. The method however requires refinement and we summarize some of its present problems.

We present area cladograms for Recent and Lower Miocene corals and echinoids, and for Eocene and late Cretaceous (Campanian-Maastrichtian) echinoids. Although these should be tested against area cladograms based on other taxa, we conclude, amongst our preliminary results, that: (1) the present Indo-Pacific fauna is a young biogeographical entity, not older than the Lower Miocene; (2) prior to this, Pacific faunas had been isolated since a time older than the Upper Eocene; and (3) the faunas of the Atlantic and western Tethys have been distinct from those of the Indian Ocean and eastern Tethys since a time long before the ‘terminal Tethyan event’ (Miocene), and since as far back, at least, as the late Mesozoic.
Geophysical framework and the Appalachian-Caledonide connection
Authors: Haworth R. T. , Hipkin R. , Jacobi R. D. , Kane M. , Lefort J. P. , Max M. D. , Miller H. G. , Wolff F.
Published: September 2007

Gravity and magnetic data from the Appalachian-Caledonide area demonstrate the overall continuity of the orogen while identifying its segmentation into areas of contrasting structural style. The extension of this segmentation into ‘drift’-covered areas (e.g. the southern U.S.A.) and offshore areas (e.g. around Newfoundland and the British Isles) provides an orogen-wide framework into which structural detail established at outcrop can be accommodated. Linear gravity and magnetic anomalies often reflect contrasts within the Precambrian basement that have controlled tectonic events to the present. Such basement structure has been investigated by deep seismic profiling, which has also identified large-scale thrusting throughout the Appalachians and the Caledonides with some thrusts even extending into the upper mantle. Speculation to greater depths based on conductivity and P-wave travel-time residuals suggests that traces of the early Palaeozoic collision zone may still exist in the lower crust and upper mantle beneath the northern Appalachians. The loading imposed by thrust sheets during that collision produced foreland basins in the eastern USA whose form and sedimentary record indicate the magnitude and duration of thrusting. Palaeomagnetic results suggest transcurrent movement in Devonian-Carboniferous time, but the early Palaeozoic collisional choreography has not yet been uniquely defined.
Early deformation in the Caledonian-Appalachian orogen
Authors: Rast Nicholas , Sturt B. A. , Harris A. L.
Published: September 2007

Deformation isotopically dated at 1100–1000 Ma has been recorded in the Moine rocks of N Scotland and may be related to the latest stages of Grenville orogenesis of N America. Late Precambrian orogenesis is widely recorded in the dispersed fragments of Avalonia particularly in the eastern Appalachians, eastern Newfoundland and southern Britain. Localized evidence for late Cambrian-early Ordovician orogenesis is forthcoming in the Appalachians (Penobscot) in Scandinavia (Finnmarkian) and in Scotland and Ireland (Grampian).
Early Palaeozoic metamorphism in the Scandinavian Caledonides
Authors: Bryhni Inge
Published: September 2007

Early Palaeozoic metamorphism is represented in several of the nappes of the Scandinavian Caledonides, although it is often severely overprinted by late Silurian-early Devonian events. It is defined particularly in N Norway where the Finnmarkian phase probably reached peak conditions at about 535 Ma with extensive cooling and uplift at about 485 Ma. On Spitsbergen there was a phase of low- to high-grade metamorphism of jadeite-glaucophane type prior to the late Ordovician-Silurian.
Pre-Arenig metamorphism in the Appalachians
Authors: Laird Jo
Published: September 2007

Our understanding of the distribution of pre-Arenig metamorphism in the Appalachians is rudimentary because of polymetamorphism, complex structure and the need for further combined field, structural, isotopic and petrological studies. Available data indicate that in the northern Appalachians pre-Arenig metamorphism is preserved in distinct terranes often collectively referred to as Avalonia. In Maritime Canada 800–700 Ma dates on amphibolite-facies gneisses are interpreted as metamorphic ages. Amphibolite- to greenschist-facies metamorphism is older than 600 Ma granitic rocks. Several areas in eastern New England may record late Proterozoic to early Ordovician amphibolite- to greenschist- facies metamorphism. In the central Appalachians metamorphism older than about 500 Ma is granulite facies in southeastern Pennsylvania and amphibolite to greenschist facies in northern Virginia. Except in the Grenville basement, metamorphism in the southern Appalachians is generally inferred to be Arenig or younger.
Arenig-Llandovery stratigraphy and faunas across the Scandinavian Caledonides
Authors: Bruton David L. , Harper David A. T.
Published: September 2007

The nature and development of Arenig-Llandovery sedimentary environments is reviewed with reference to 18 allochthonous-parautochthonous sections in the Scandinavian Caledonides. The faunas suggest that age constraints are imprecise, and direct correlations with sequences on the adjacent platform are difficult. However, it is possible to recognize a northerly transition from near-shore to offshore facies on Hardangervidda and a platform to slope transition in Jämtland and E Jotunheimen during the early Ordovician. There is no direct evidence of a distinct Finnmarkian orogenic event (late Cambrian-early Ordovician) in the lower Allochthon, while the central Scandinavian upper Allochthon, containing N American shelly fossils, has a pre-Caradoc history far removed from that of the Baltic platform. In the Bergen area no fossils older than Ashgill age are known and the youngest marine rocks are early Llandovery. Locally-important features of the platform sequences, including breaks in sedimentation, the deposition of bentonites, basement faulting and the early termination of marine sedimentation (late Llandovery in the N and W), cannot be directly related to discrete tectonic events in the orogen.
Arenig to Wenlock regional metamorphism in the Paratectonic Caledonides of the British Isles: a review
Authors: Oliver G. J. H.
Published: September 2007

Between Arenig and Wenlock times the various terranes of the Paratectonic Caledonides in the British Isles were metamorphosed by a variety of processes such as sedimentary burial in volcanic arcs, inter-arc basins and fore-arc and back-arc basins (e.g. Wales, SE and W Ireland, the Lake District and the Midland Valley of Scotland), tectonic burial in an accretionary prism (e.g. Ballantrae, the Southern Uplands and the Longford-Down Massif), hydrothermal alteration associated with the generation of oceanic crust (e.g. Ballantrae and the Highland Border Complex, the Southern Uplands and the Tyrone spilites), dynamothermal metamorphism accompanying obduction of oceanic mantle and crust (e.g. Ballantrae and the Highland Border complexes) and tectonic burial by nappes (e.g. the NW Foreland beneath the Moine Thrust). The region has suffered low-grade regional metamorphism ranging from zeolite facies through prehnite-pumpellyite and pumpellyite and pumpellyite-actinolite facies into greenschist facies, with the localized development of amphibolite and granulite facies.
The development of the Iapetus Ocean from the Arenig to the Wenlock
Authors: McKerrow W. S.
Published: September 2007

In addition to the large continents of N America, Scandinavia and Gondwana, the regions around the early Palaeozoic Iapetus Ocean contained several small terranes. These included an island arc, which collided with various parts of N America to produce, in succession, the Grampian, Humberian and Taconic orogenies. They also included the terrane of Avalonia, a later Precambrian arc which had rifted off a margin of Gondwana by the middle Ordovician. Large sinistral strike-slip faults in Scotland suggest a total displacement of around 1500 km, so that by the Silurian an elongate Scotland lay to the W of Norway. Continental collisions took place in three stages: a Llandovery stage, perhaps related to eastward subduction below Svalbard, when W-verging nappes were emplaced in E Greenland, a later Silurian (Scandian) stage when westward subduction below Scotland can be related to E-verging nappes in Norway, and an early Devonian stage when Avalonia collided with N America (Acadian orogeny).
Wenlock to mid-Devonian volcanism of the Caledonian-Appalachian orogen
Authors: Thirlwall M. F.
Published: September 2007

Volcanic rocks of Siluro-Devonian age form two distinct petrological provinces in the Caledonian-Appalachian orogen roughly corresponding to regions which last suffered major deformation in the Permo-Carboniferous or the Siluro-Devonian. In France, Germany and SW England the minor volcanism was dominantly marine and mostly produced enriched tholeiites. Abundant volcanism about 410 Ma old in Scotland is calcalkaline and related to subduction on the NW margin of Iapetus, while volcanism in Shetland, E Greenland and Norway is rather younger and more acidic but is calc-alkaline, at least in Shetland. Apart from a metatholeiite in Alabama, Siluro-Devonian volcanism in N America is restricted to New England and the Canadian Appalachians where two major volcanic belts run NE-SW. Chemical data for these rocks are limited but do suggest that at least some rocks in both belts are related to subduction processes. This need not necessarily greatly constrain tectonic models.
Wenlock to Givetian deformation in the British Isles and the Canadian Appalachians
Authors: McKerrow W.S.
Published: September 2007

A combination of stratigraphic evidence and dates on igneous rocks suggests that the climax of Caledonian deformation in the British Isles and of Acadian deformation in the Canadian Appalachians both occurred during the middle to late Emsian stage, or about 397 to 390 Ma ago. In addition to this event, many small regions show uplift and/or deformation spasmodically throughout Silurian and Devonian time, both before and after the Emsian.
Silurian to Lower Carboniferous tectonism in the Appalachians of the USA
Authors: Osberg P. H.
Published: September 2007

In New England highly deformed Silurian and lower Devonian beds are overlain unconformably by middle Devonian sediments. Early structures include westward-verging recumbent folds and thrusts, while younger features include local development of back-folding and upright folds with a NE trend. In the central and southern Appalachians the recognition of Acadian structures is not clearly documented, except for the Talladega Belt. Middle and upper Devonian molasse occurs to the W of the central Appalachians.
Timing and geometry of collision, terrane accretion and sinistral strike-slip events in the British Caledonides
Authors: Soper N. J.
Published: September 2007

Recent geotectonic interpretations of the British Caledonides invoked E-W closure between two plates, Laurentia and ‘Europe’, to produce the N-S striking N Atlantic Caledonides and dextral strike-slip along the NE-SW-oriented British sector of the Iapetus suture. However, this model does not satisfy the following important new lines of evidence: the provinciality of Cambro-Ordovician shelf fauna, which indicates oceanic separation between Laurentia, Baltica and a third plate or terrane (‘Cadomia’) of which S Britain forms a part; the Y-shaped configuration of the orogen comprising the Appalachians, N Atlantic Caledonides and the N German-Polish zone which marks collision sutures between three plates rather than two; the evidence of sinistral, not dextral, transpressive displacements in both the orthotectonic Caledonides and the slate belts of Britain.

The ‘three-plate’ model for the British Caledonides which was proposed to accommodate these lines of evidence is developed further in terms of terrane accretion: Ordovician to mid-Silurian accretion events affected the Laurentian margin before the closure of Iapetus and produced the orthotectonic Caledonides of Scotland and Ireland; the Laurentia-Baltica collision closed the northern arm of Iapetus in the late Silurian and produced the Scandian orogeny; early Devonian northward accretion of a Gondwana-derived terrane induced sinistral transpression across the British slate belts and segmented the Scottish Highlands by sinistral strike-slip.
Mid-Devonian to mid-Permian floral and faunal regions and provinces
Authors: Allen K. C. , Dineley D. L.
Published: September 2007

The middle to late Palaeozoic biota in seas adjacent to the Caledonide-Appalachian orogen included an abundant generally cosmopolitan benthos in both carbonate and clastic environments. Where low clastic sediment input permitted, organic reefs and build-ups were characteristic of this tropical area. Early Devonian biogeographic provinces did not persist into later times. The pelagic fauna, dominated by ammonoidea, bivalvia, conodonts and vertebrates, was rich, rapidly evolving and, again, cosmopolitan. Vertebrates and conodonts in particular were wide ranging.

Among the land plants heterospory and arborescence evolved during the middle and late Devonian in a number of classes, particularly the Lycopsida and Progymnospermopsida. Genera were largely cosmopolitan during this time, and only one floristic region can be recognized worldwide, although there is some evidence for slight provincial floral variation outside Laurussia.

During the early Carboniferous arborescent Lycopsida were abundant. Three floristic regions can be identified worldwide, of which one is the Circum-Tethyan Region including Laurussia, Kazakhstania and China. Two floral provinces are recognized within the Laurussian part of this region.

In late Carboniferous and early Permian times, when gymnosperms replaced the pteridophytes as the dominant forms, there is a more clear-cut separation of floral regions, and by early Permian two floral regions are recognized within Laurussia which are clearly different from those away from this land mass.

Non-marine bivalvia and vertebrates were highly cosmopolitan from mid-Devonian time onwards, with amphibia appearing in Greenland in the late Devonian and reptiles appearing in eastern Canada and western Europe in Westphalian A time.
Mid-Devonian to early Permian volcanism: Old World
Authors: Francis E. H.
Published: September 2007

Three major episodes of activity are distinguished in each of three volcanotectonic provinces. The provinces are represented by a craton to the N and the Moldanubian zone (including central Iberia) in the S separated by the orogen which combines the inner Saxothuringian-Ossa Morena zone with the outer Rhenohercynian-S Portuguese zone. During the first episode (380–325 Ma) activity did not begin on the craton until early Carboniferous and was then continental, alkaline and mainly basaltic; in the orogen, however, bimodal mainly tholeiitic activity assumed to be back-arc in character continued from early in the Devonian, while the southern province was experiencing calc-alkaline volcanism probably related to northwards subduction of the proto-Tethys ocean crust. The second episode saw the alkaline activity of the craton becoming volumetrically reduced and largely more phreatic, while the orogen became volcanologically inactive and calc-alkaline activity probably continued in the S, although the evidence (distal ash-fall farther N) is indirect. In the third episode the orogen, now accreted to the northern craton, experienced, with the craton, renewed and more silica-undersaturated alkaline activity related to newly formed fracture patterns, while in the southern province there was a resurgence of calcalkaline activity.
Post-Acadian metamorphism in the Appalachians
Authors: Murray Daniel P.
Published: September 2007

Well-documented post-Acadian metamorphism occurs at three locales along the eastern flank of the Appalachians, where it has affected Avalonian basement and/or Carboniferous cover. Carboniferous rocks of coastal New Brunswick display a greenschist-facies metamorphism of Pennsylvanian to Permian age which largely post-dates associated Alleghanian ductile deformation. In southeastern New England sedimentary rocks of late Pennsylvanian age have undergone an amphibolite-facies Barrovian metamorphic event (275–290Ma) that is syn- to post-ductile deformation and is truncated by peraluminous granite. Considerations of patterns of metamorphism in surrounding crystalline rocks implies that at least two distinct late Palaeozoic tectonothermal events have affected New England. In the Piedmont of Virginia and the Carolinas amphibolite-facies metamorphism (roughly 260–310 Ma) is synchronous with the emplacement of syn-kinematic granitoids. In all three areas isogradic patterns, where determinable, are complex, reflecting the effects of later faulting and fault-controlled retrograde metamorphism.

In the USA at least, Alleghanian metamorphism also affected areas well beyond the boundaries of Avalonian terranes
sensu stricto
into the polydeformed crystalline terrane to the W (Inner Piedmont, Merrimack synclinorium). Within these crystalline rocks the Permian thermal overprint appears to be focussed along shear zones. Late Palaeozoic regional metamorphism in the Appalachians probably reflects crustal thickening related to continent-continent or continent-microcontinent collisions characterized by heat transfer along fundamental tectonic boundaries, and not simply proximity to late Palaeozoic igneous activity or subduction-zone tectonics.
Fourth time-slice: mid-Devonian to Permian synthesis
Authors: Rodgers John
Published: September 2007

By some time in the middle Devonian, the Iapetus Ocean between Laurentia and Baltica was entirely closed (Acadian orogeny in the Maritimes and New England) and the Rheic Ocean between Baltica and proto-Gondwana was mostly closed (Devonian orogeny in France), although some relict oceanic basins (
cf.
Black Sea) may have remained. The Theic Ocean between Laurentia and proto-Gondwana (Africa) may well have remained partly open for much longer, but probably contained already consolidated continental blocks of various sizes. Where closing was fairly complete, late Palaeozoic deformation took the form of relatively narrow zones, often rift zones containing pull-apart basins whose sediments were later strongly deformed (sometimes with plutonism and metamorphism), lacing between larger blocks that remained barely affected but moved
en bloc
by strike-slip (Maritimes, Armorica) or large-scale thrust movement (southern Appalachians, Mauritanides). Certain zones however, are former continental passive margins, e.g. the Appalachian Valley and Ridge and the folded belt from southern Ireland to the Rheinische Schiefergebirge. Remaining oceanic areas presumably closed diachronously during the Carboniferous or early Permian, but few are available for inspection (Lizard?). The Theic suture is apparently traceable by geophysics beneath the coastal plains and shelves from southern Portugal to Florida. Deformation in any one area was episodic (Stillean phases), but no consistent episodes can be followed over the whole orogen.
Relative thermobarometry and metamorphic
P-T,
paths
Authors: Spear Frank S.
Published: September 2007

Relative thermobarometry involves the determination of changes in
P
and
T
experienced by a rock through analysis of mineral zoning, inclusion suites and reaction textures. For this purpose, the differential forms of the thermodynamic equations and mass balance constraints are particularly useful because the equations are linear, and direct computation of changes in dependent variables may be made by matrix inversion of the system of equations defining the thermodynamic constraints and multiplication by changes in independent variables. The number of independent variables equals the phase rule variance if only intensive variables are considered and equals two if mass balance constraints are imposed. Isopleth diagrams may be readily constructed for mineral composition, mineral moles or equilibrium constants provided that entropies, volumes and solution models for all phases as well as a reference assemblage equilibrated at a known
P
and
T
are available. An example is presented demonstrating the use of such diagrams in the interpretation of diffusion zoning and retrograde reaction textures in a high-grade gneiss from western New Hampshire, USA.

The
P-T
paths computed from relative thermometry may be sensitive monitors of the tectonic history because errors of ± 5–10% propagate to small errors in the
P-T
path for small changes in
P
and
T
. The
P-T
paths from the lower plates of thrust sheets may reveal isothermal compression culminating at pressures representative of the maximum depth of burial. Subsequent heating or cooling of such rocks reveals how the thermal structure evolves after thrusting and may permit speculation about the pre-thrusting thermal structure.
The link between metamorphism, volcanism and geotectonic setting during the evolution of the Andes
Authors: Aguirre L. , Levi B. , Nyström J. O.
Published: September 2007

A low-grade, non-deformational, regional metamorphism ranging from burial to ocean-floor type characterizes the Andean range. Longitudinal variations exist, coinciding with changes in the chemistry of the volcanic suites involved, both trends being controlled by the geotectonic setting. The study of Cretaceous volcanic rocks in Colombia, Peru and Chile indicates that: (i) ocean-floor metamorphism (high-
T
gradients) correlates with tholeiitic volcanism in marginal basins where the continental crust was eliminated or extremely attenuated; (ii) burial metamorphism (low- to moderate-
T
gradients) correlates with calc-alkaline to shoshonitic volcanism in ensialic, aborted, marginal basins with moderate thinning of the continental crust. The metamorphism in the Andes, which is characterized by a counter-clockwise
P-T-t
path, started during the initial stages of basin formation and preceded the orogenic activity, contrary to the development in compressional geotectonic settings.
The structural evolution of the Brent Province
Authors: Yielding Graham , Badley Michael E. , Roberts Alan M.
Published: September 2007

The structural evolution of the Viking Graben has been the fundamental control on the deposition of the Brent Group and on the development of trapping geometries. Major crustal extension in the early Triassic caused tilting of basement fault blocks, which can still be clearly seen at the basin margins. By the mid-Triassic a post-rift thermal-subsidence basin was established. Local fault control on Brent Group deposition indicates the onset of a second period of crustal extension, although the main control on subsidence at this time was still thermal relaxation following Triassic rifting. Extension during deposition of the Brent was of only
c.
1% magnitude.

The second period of extension increased in magnitude following Brent deposition and peaked during the late Jurassic, creating the main structural traps for Brent Province oil and gas. Footwalls to major normal faults were uplifted and eroded. The amount of uplift on a given fault-block can be predicted using quantitative models (flexural and domino models). Subsidence in the adjacent half-graben generally outpaced sedimentation, leading to deep-water basins into which footwall material could collapse. On all but the largest fault-blocks it is likely that footwall uplift rates were low compared with erosion rates, and so footwall crests would have been degraded faster than they would have been uplifted above sea-level. Flushing by meteoric water during the late Jurassic is therefore expected only on the largest fault-blocks (e.g. Snorre, Gullfaks).
Brent Group: sequence stratigraphy and regional implications
Authors: Mitchener B. C. , Lawrence D. A. , Partington M. A. , Bowman M. B. J. , Gluyas J.
Published: September 2007

Previous published models for the stratigraphic evolution of the Middle Jurassic (Aalenian—Bathonian) Brent Group and its equivalents rely largely upon lithostratigraphy, with few reliable time lines for correlation across the Northern North Sea basin. To rectify this a new, largely well-based, multi-disciplinary regional study was undertaken, combining detailed biostratigraphic and sedimentological data from more than 450 wells across the whole of the Northern North Sea basin.

A basin-wide sequence stratigraphy for the Middle Jurassic has been developed, comprising two tectono-stratigraphic units (J20, Aalenian—Late Bajocian and J30, latest Bajocian—Middle Callovian), subdivided into five sequences: J22 (Aalenian), J24 (Early Bajocian), J26 (Early—Late Bajocian), J32 (latest Bajocian—Late Bathonian) and J34 (latest Bathonian—Middle Callovian). The tectono-stratigraphic units developed in response to large scale (second order) tectonic processes: pre-rift thermal uplift (J20) and the onset of rifting (J30), whilst sequence development was controlled by a combination of changes in basin subsidence, sediment supply and eustatic sea level.

A series of palaeogeographic and isopach maps outline the basin evolution and sedimentary response for each sequence. They describe a progressive basinward shift of the J22 and J24 depocentres in response to the thermal uplift; by the end of J26, sediment supply could not keep pace with increased basin subsidence caused by the crustal extension. J32 and J34 represent the first periods where active rifting can be clearly identified in the North Sea basin, with the development of tilted fault block geometries in the East Shetland Basin and Bruce—Beryl Embayment. Continued extension and rifting in these areas led to the development of an overall retrogradational system which extends through to the latest Jurassic.

The study provides a model for North Sea basin evolution and a predictive sequence stratigraphic framework within which the local lithostratigraphy can be resolved and basin potential evaluated.
The fate of feldspar in Brent Group reservoirs, North Sea: a regional synthesis of diagenesis in shallow, intermediate, and deep burial environments
Authors: Glasmann J. Reed
Published: September 2007

Feldspar dissolution is an important process affecting the reservoir quality of Brent Group sandstones in the northern North Sea and shows a strong relationship to reservoir temperature and pore water chemistry. In low temperature, brackish, shallow to moderately buried reservoirs (2400–3700 m, reservoir temperature less than 100–120°C) feldspar is generally a major detrital component whose abundance is affected by local variations in facies, extent of early meteoric leaching, and kaolinitization. In deeply buried Brent reservoirs (3700–4700 m) where present burial temperatures exceed 130–140°C detrital K-feldspar is absent and sandstones are characterized by major illitization of early formed kaolinite, precipitation of fibrous illite, extensive quartz cementation, and variable albitization. K-feldspar dissolution apparently supplied elements necessary for illitization, which, according to K-Ar evidence, occurred during early Tertiary burial, associated with initial stages of hydrocarbon accumulation and brine migration. Illite K-Ar ages are unaffected by feldspar contamination in deep reservoirs and the narrow range of measured ages for widely ranging illite size-separates indicates that the major dissolution/illitization reaction was a geologically rapid process. In contrast, illite K-Ar ages from shallow and intermediate-depth reservoirs range from Palaeocene to Early Miocene and often have considerable size dependency due to small amounts of feldspar contamination in coarser fractions. Variable contamination and its effect on measured K-Ar ages often precludes establishing the history of illitization and a well-defined relationship to hydrocarbon accumulation in intermediate-depth reservoirs. Although some feldspar is dissolved during early burial history by low temperature circulation of meteoric water, only deeply buried Brent reservoirs are characterized by the complete diagenetic removal of feldspar; however, the secondary porosity generated by late dissolution is of little benefit to reservoir quality because accompanying cementation results in major loss of permeability.
Open and restricted hydrologies in Brent Group diagenesis: North Sea
Authors: Haszeldine R. Stuart , Brint J. F. , Fallick A. E. , Hamilton P. J. , Brown S.
Published: September 2007

Diagenetic cements in the mid Jurassic Brent Group sandstones of the North Sea have been studied in the Thistle, Murchison, Dunlin and Alwyn South (3/13a-1) oilfields. Volumetrically important cements start with early siderite, kaolinite and calcite, and continue to later kaolinite, ankerite, quartz and illite. The mineralogies of early siderites and calcites are homogeneous in formations with different depositional porewaters. Carbonate concretions nucleated on biotite grains, and their carbon supply was very local and facies controlled. Strontium was derived from dissolution of silicates and shell debris and
87
Sr/
86
Sr rapidly became homogeneous in different formations. Oxygen was derived from meteoric water and was homogeneous throughout, even in marine deposits. These data suggest an open-flow system with uniform meteorically-derived pore fluids and local ion supply throughout the sandstones.

Diagenetically later ankerite formed below 1.1 km and shows mineralogies which are less homogeneous, with
87
Sr/
86
Sr variable. Cement ions could all have been very locally supplied from within the formation. Late kaolinite could also have been formed locally from feldspars within the formation. The exception to this was quartz cement, its large volumes indicating import across formations or from outside the Brent. Fluid inclusions in quartz show abnormally hot temperatures equating to 80–100°C at 2.2 km. These can be interpreted in two ways. First to indicate a large circulation of hot evolved meteoric water within the basin. This would have been induced by tensional fracturing of the crust related to the final phase of North Atlantic rupture in the Palaeocene and Eocene. However, fluid inclusion temperatures within quartz overgrowths show a systematic increase of temperature with present-day burial depth, suggesting that these temperature records could have been reset, and are now too hot. If these temperature data are rejected, a second interpretation is possible. The δ
18
O isotopic signatures show that late diagenetic silicates and carbonates could have grown in meteoric water, unmodified in its δ
18
O value, in a normal geothermal gradient. Illite grew in a slowly flowing fluid, which rapidly evolved to todays δ
18
O values, as individual groups of pores attempted to equilibrate with the rock around them Oil accumulation halted diagenesis and was permitted by buoyant trapping as this porewater system became stagnant.
Coalbed methane in the USA: analogues for worldwide development
Authors: Murray D. Keith
Published: September 2007

Preliminary estimates of coalbed gas in the major coal-bearing basins of the world range from approximately 3000 trillion cubic feet (TCF) to more than 12000 TCF (85-340 trillion cubic metres, TCM). The successful development of this important energy resource will largely depend on the judicious transfer of the coalbed methane (CBM) technology developed in the USA during the past two decades. Innovative field research has been conducted primarily in the San Juan and Black Warrior basins. Projects have involved co-operative efforts between the Gas Research Institute, federal and state geological surveys, academia, both large and small oil companies and private consultants. As a result, significant improvements have been made in many aspects of CBM technology, including: (1) dynamic openhole cavitation completions; (2) advanced hydraulic stimulation procedures; (3) enhanced ultimate coalbed gas recovery using the injection of nitrogen or carbon dioxide into the coalbed reservoir; (4) improved reservoir simulation parametric techniques; and (5) seismic methods to predict areas of optimum reservoir permeability. The appropriate applications of this rapidly developing technology to the complex and varied conditions that exist in other coal-bearing basins throughout the world is expected to lessen significantly the risks inherent in the successful commercialization of coalbed gas in a number of countries.