bluuebunny/crossref_metadata_2025_split huggingface dataset:
Grade and time of metamorphism in the Caledonide Orogen of Britain and Ireland
Authors: Fettes D. J. , Long C. B. , Bevins R. E. , Max M. D. , Oliver G. J. H. , Primmer T. J. , Thomas L. J. , Yardley B. W. D. 
Published: April 2008

Abstract
Plate 3 depicts three major belts distinguished by their style and age of metamorphism: the orthotectonic and paratec-tonic zones of the Caledonides and the Hercynides. Age of metamorphism, shown on the inset map (Plate 3), in part reflects the areal distribution of these zones and refers to the timing of the main phase or peak of metamorphism. The orthotectonic zone is, therefore, shown to be metamorphosed during the earliest Ordovician although recrystaHization was almost certainly taking place from the late or even mid-Cambrian to the Silurian. In the paratec-tonic belt the main metamorphism is shown as occurring in the period Lower Ordovician-to-Silurian although recrystahization may well have continued into the Lower Devonian. The Lower Devonian rocks within the central and southern Caledonides have suffered folding and weak metamorphism normally before Middle Devonian times and have been differentiated on the map.
The southern limit of significant Caledonian deformation is normally taken as the northern edge of the Midland Block (F. W. Dunning, pers. comm.). However, it is believed that weak Caledonian metamorphism affected rocks south of this line. Similarly, recrystaHization associated with the Hercynian extended well to the north of the so-called Hercynian front, the northern limit of strong deformation (F. W. Dunning, pers. comm.). There is, therefore, some doubt as to whether the main recrystaHization in pre-Carboniferous rocks of South Wales and the English Midlands relates to the late-Caledonian or to the Hercynian.
Palaeomagnetic constraints on the position of Gondwana during Ordovician to Devonian times
Authors: Bachtadse V. , Briden J. C. 
Published: April 2008

Abstract

The currently available palaeomagnetic data base for Gondwana is reviewed and using revised rotation parameters for the fit of the southern continents an attempt has been made to construct an apparent polar wander path for Gondwana during Ordovician to Permo-Carboniferous times using a cubic spline fitting technique. Although the density of the data set is still rather sparse and the quality of the data is variable, our approach seems to be justified when tying the apparent polar wander path to selected palaeopoles of high quality. The palaeogeographic scenario based on our results is rather complex. Rapid northward shift of Gondwana during the Ordovician to the Early Silurian and subsequent collision with Laurentia is followed by divergence and the formation of a wide intervening ocean during the Devonian. The final closure of this ocean did not begin before the Late Devonian and was completed by the Late Carboniferous. If the apparent polar wander path presented in this paper is correct, then extremely high drift rates of about 23 cm a
-1
have to be postulated for Gondwana during the Late Ordovician-Silurian.
Palaeozoic palaeogeography from palaeomagnetism of the Atlantic-bordering continents
Authors: Kent Dennis V. , Van Der Voo Robert 
Published: April 2008

Abstract
Revised palaeogeographic reconstructions of the Atlantic-bordering continents and intervening terranes are presented for the Siluro-Devonian boundary, Early Devonian, and Late Devonian, based on incorporation of new palaeomagnetic results that have become available from Laurentia and Gondwana. The key features of the palaeogeographic model are the transpressive collision between the eastern margin of Laurentia and the northwest South American margin of Gondwana in the Siluro-Devonian, and the subsequent Devonian retreat of the north African margin and the development of a wide ocean between Africa and Europe by the Late Devonian. Although rather complex and involving rapid motions especially of Gondwana, the revised Devonian plate tectonic evolution as indicated by palaeomagnetism is not inconsistent with biogeographic and palaeoclimatological evidence.
Palaeoclimatic constraints for palaeozoic Palaeolatitudes of Laurentia and Euramerica
Authors: Witzke Brian J. 
Published: April 2008

Abstract
Palaeozoic lithic palaeoclimatic data were plotted at the series or stage level for Laurentia (North America) and Euramerica. Their distribution was used to infer the extent of humid and arid climatic belts across the continent for specified time intervals. Climatic data are potentially useful for constraining palaeolatitudes for times when zonal atmospheric circulation remains the dominant pattern. Arid lithic indicators (evaporites, carbonate oolite) and humid indicators (coal, bauxite) were constrained to provide the best fit of these data into a simple zonal climatic pattern delineating subtropical arid belts and equatorial and/or temperate humid belts, respectively. An attempt was made to minimize occurrences of arid indicators in interpreted equatorial regions to maximize a zonal fit. Climatic belts can be arranged in a temporally consistent zonal climatic scheme for much of the Palaeozoic, but monsoonal and orographic effects apparently disrupted the general zonal pattern during portions of the Late Palaeozoic. The interpreted climatic patterns suggest progressive southward movement of Laurentia during the Cambrian through Early Devonian followed by general northward drift of Euramerica during the Middle Devonian through Permian. Lithic palaeoclimatic data provide an independent means to test palaeolatitudes interpreted from palaeomagnetic data. There is general agreement between palaeoclimatic and palaeomagnetic interpretations, but some discrepancies, particularly for the Devonian and Early Carboniferous, warrant further attention.
Biogeography of Ordovician and Silurian faunas
Authors: Cocks L. R. M. , Fortey R. A. 
Published: April 2008

Abstract

The new reconstructions generated for this volume fit well with the majority of Ordovician and Silurian faunal data and are a great improvement on previous attempts. The distribution of selected trilobites, brachiopods and graptolites are plotted on the new maps and confirm the importance of palaeolatitude in controlling the faunal distributions, particularly of the old cratons, which are shown for the Early Ordovician and Late Silurian. Two contrasting patterns of cratonic faunas are (a) disjunct or (b) gradational across a large palaeocontinent, e.g. Gondwana. Marginal and deeper-water biofacies show different patterns, which help to define the edges of palaeocontinents, but which are not so constrained in their palaeolatitudinal distributions. In contrast pelagic trilobites do not help to define palaeocontinents, but were sensitive to palaeo temperature and palaeolatitude. Specific case histories are considered, in particular the closing of Iapetus and the contemporary widening of the Rheic Ocean and the positioning of Avalonia, and the ancestry of the various associated trilobite and brachiopod genera during the later Ordovician. The Ashgill deeper-water
Foliomena
fauna is also plotted.
Biogeography of the Devonian stromatoporoids
Authors: Stock C. W. 
Published: April 2008

Abstract
Stromatoporoids were a common component of shallow carbonate environments of North America, Eurasia, and Australia during the Devonian. They were least abundant during the Early Devonian. After that time abundance increased, and remained high steadily through the Frasnian. At the Frasnian-Famennian boundary the number of stromatoporoids was greatly diminished, but they did not become extinct until the end of the Devonian (at the end of the Strunian). The geographic extent of stromatoporoids expanded and contracted concurrently with increases and decreases in total population size. Provincialism at the genus level prevailed during the Early Devonian, with stromatoporoids inhabiting the Old World and Eastern Americas Realms; none are known from the Eastern Americas during the Siegenian. For the remainder of the Devonian stromatoporoids were cosmopolitan at the genus level. The abundance of stromatoporoids varied directly with eustatic sea level during the Devonian. Variations in depositional conditions apparently controlled the local distribution of genera.
Early and Middle Devonian gastropod biogeography
Authors: Blodgett R. B. , Rohr D. M. , Boucot A. J. 
Published: April 2008

Abstract
Early and Middle Devonian gastropods show biogeographic patterns remarkably similar to those of better studied faunal groups of this same interval, notably articulate brachiopods, rugose corals, and trilobites. Three biogeographic realms are recognized: Old World, Eastern Americas, and Malvinokaffric Realms. Gastropod diversity is highest in the Old World Realm and lowest in the Malvinokaffric Realm. The diversity patterns and the high degree of shell ornamentation suggest that the Old World Realm was generally warmer than the Eastern Americas Realm, and that both were considerably warmer than the cool temperate to cold polar waters of the Malvinokaffric Realm. The utility of gastropods for fine-scale delineation of biogeographic units is illustrated for the Eifelian of western North America. At least two subprovincial units (the Alaska-Yukon and Nevada subprovinces) can be recognized. Eifelian gastropods from interior and southeastern Alaska belong to a single unit (the Alaska-Yukon Subprovince), and are most closely related to coeval faunas of northwestern Canada, suggesting little displacement of most of Alaska's so-called 'suspect' terranes. Plotting the data on the Devonian palaeogeographic maps of Scotese results in several suggested emendations: (1) North America should be moved south by 10-20°; (2) Australia is too far south on the Emsian and Givetian reconstructions, it should be in a more palaeotropical position; and (3) Siberia is too far north, it too should also be placed in a palaeotropical position.
Givetian-Frasnian phytogeography of Euramerica and western Gondwana based on miospore distribution
Authors: Streel Maurice , Fairon-Demaret Muriel , Loboziak Stanislas 
Published: April 2008

Abstract
The Givetian and Frasnian miospore distributions in western Gondwana and southern Euramerica show a rather uniform vegetation prevailing from palaeo-polar to palaeo-tropical regions. Similar climatic conditions are certainly required to explain this but it is concluded from a discussion on the dispersal of homosporous vegetation that no wide oceans separated these regions at the time. Frasnian northern Euramerica vegetation seems different and might correspond to an equatorial belt. Heckel & Witzke's palaeogeographical reconstruction fits much better with the miospore distribution than other maps.
The Balkhash-Mongolia-Okhotsk region of the Old World Realm (Devonian)
Authors: Hou Hong-Fei , Boucot A. J. 
Published: April 2008

Abstract
Reconsideration of the Emsian brachiopods from parts of central Asia extending from the Lake Balkhash Region easterly through Heilungjiang leads us to conclude that they should be separated as a distinct region, termed the Balkhash--Mongolia--Okhotsk Region, of the Old World Realm. This conclusion was arrived at after considering the high level of endemic genera, plus the significant admixture of genera common with the Eastern Americas and Tasman Realms.
Reconstruction of the Laurasian and Gondwanan segments of Permian Pangaea
Authors: Lottes Ann L. , Rowley David B. 
Published: April 2008

Abstract

A reappraisal of the geological and geometrical constraints on the fits of the continents around the Atlantic, Indian and circum-Antarctic oceans is used as a base upon which to re-examine Early and Late Permian palaeomagnetic data. The palaeomagnetic poles from each of the three main Late Palaeozoic palaeo-continents: Eurasia, North America, and Gondwana define statistically well determined means for the Early and Late Permian. When these poles are reconstructed, the means, and their associated A
95
cones of confidence do not superimpose. The lack of superposition of Late Palaeozoic palaeomagnetic poles on Wegener-style Pangaea reconstructions based on Mesozoic and younger seafloor spreading geometries has been noted for some time. Most solutions to this problem have involved alternative 'tight fits' of the Pangaean continents for the Late Palaeozoic. Solutions invoking the non-dipole behaviour of the magnetic field have also been proposed. We examine the geometric consequences of the 'tight fit' Mesozoic-based Pangaean reconstructions that allow better fit of the palaeomagnetic data and conclude that the magnitudes of overlap (650-950 km) required by these modifications are not compatible with the geological and tectonic evidence from these regions. We prefer to use a 'looser' Pangaea fit that does not necessarily result in the superposition of palaeomagnetic poles. However, when the individual poles from Europe, North America, and Gondwana are combined into a global mean pole, it is observed that both the 'tight' and the 'loose' fit yield virtually indistinguishable mean pole positions. Considering the strong geological and geometrical arguments against the palaeomagnetically derived fits and the lack of a clear statistical difference between the two we use our revised Pangaean reconstruction to determine palaeo-latitudinal framework of the Eurasian, North American, and Gondwanan segments of Pangaea for the Early and Late Permian. The validity of these palaeo-latitudinal reconstructions is tested with climatically sensitive floristic and lithological data by Ziegler, and found to be satisfactory.
Devonian palaeogeography and palaeobiogeography of the Central Andes
Authors: Isaacson P. E. , Sablock P. E. 
Published: April 2008

Abstract

During Devonian time, western Gondwana (northern Chile, Bolivia, and Peru) witnessed a period of thick clastic rock deposition. The sialic Arequipa Massif, apparently a stable terrane since Precambrian time, supplied the bulk of the Bolivian intracratonic basinal sediments. Late Ordovician orogeny in northern Chile-northwestern Argentina included the emplacement of the Puna magmatic arc, with attendant plutonism. The resulting highland supplied coarsegrained sediments to northern Chile. Late Devonian(?) orogenesis deformed Early to Middle Devonian rocks in northern to central Peru. It is suggested that mid-Palaeozoic convergence was 'buffered' by the Arequipa Massif, giving little evidence of orogeny in the Bolivian Devonian-Carboniferous sequence. A highly endemic (Malvinokaffric) shelly fauna, indicative of high palaeolatitudes, occupied the region in Early Devonian (Emsian) time, while allochthonous (Eastern Americas Realm) faunas entered southern Peru. During Middle Devonian time a much lower diversity 'post-Malvinokaffric' fauna (consisting of the brachiopods
Tropidoleptus, Globithyris
, and other taxa) arrived, although a Malvinokaffric stock remained. These taxa arrived via the Amazonas and other eastern basins during a rotation of the region to lower latitudes and presumably warmer waters in Middle Devonian time.
25 years of UK North Sea exploration
Authors: Bowen J. M. 
Published: April 2008

Any attempt to summarize 25 years of exploration for petroleum in the UK sector of the North Sea must be a daunting task. The outcome, in terms of the oil and gas fields discovered, is the subject of this volume. This introduction will attempt to outline, very briefly, some of the ups and downs of the exploration history which has led the industry to where it stands today, 25 years on (Fig. 1).
When the author was at university in the early 1950s the very idea the the United Kingdom would be likely to become a significant, let alone major world producer of petroleum would have been viewed as utterly ridiculous
It is true that oil and gas indications had been encountered in wells and mines in such disparate areas as sussex, the west Midlands and the Midland Valley of Scotland and as seepages in Dorset, Lancashire and West Lothian, but these had been thoroughly investigated without the discovery of any economically significant oil or gas fields. Indeed, the only economic production at that time came from BP's small east Midlands fields based on Eakring where the first discovery had been made in 1939
The first Serious attempt to explore for oil in the United Kingdom was initiated in 1918 for strategic reasons, when 11 relatively shallow wells were drilled on anticlinal features in various parts of the country. of these only one, Hardstoft-1 in Derbyshire, discovered producible oil, but attempts to follow up the discovery were unsuccessful.
Exploration then
The Alwyn North Field, Blocks 3/9a, 3/4a, UK North Sea
Authors: Inglis I. , Gerard J. 
Published: April 2008

Abstract
Abstract: Situated in the southeastern part of the East Shetland Basin, the Alwyn North Field produces oil and gas from Brent Group reservoirs and gas and condensate from the Statfjord Formation. The structural style is of tilted and eroded fault blocks dipping to the west and aligned north-south conforming to the principal normal fault trend. NE-SW cross elements further separate the hydrocarbon accumulations. The hydrocarbon columns are restricted to the Tarbert and upper part of the Ness Formation of the Brent Group, in sediments associated with the retreat of the Brent delta. The Statfjord Formation was deposited in an alluvial, fan-delta setting with increasing marine influence towards the top of the formation.
The Cormorant Field, Blocks 211/21a, 211/26a, UK North Sea
Authors: Taylor D. J. , Dietvorst J. P. A. 
Published: April 2008

Abstract
The Cormorant Oilfield is located approximately 150 km northeast of the Shetland Islands in Blocks 211/2la and 211/ 26a of the UK sector of the North Sea, in water depths of 500-550 ft. The field was discovered in 1972 by exploration well 211/ 26-1 and consists of four discrete accumulations spread along a major, north-south trending fault terrace. Hydrocarbons are produced from Middle Jurassic (Bajocian) sands of the Brent Group, which was deposited in a wave-dominated delta system. The reservoir has a typical gross thickness of 250-300 ft, locally increasing to 550 ft over faults active during sedimentation. Reservoir porosity varies from 16-28%, with average permeabilities ranging from tens of md to 1300md. The accumulation contains under-saturated 34-36° API oil which was initially overpressured by some 1000-1270 psi. The stock tank oil initially in place and ultimate recovery are estimated at 1568 MMBBL and 623 MMBBL, respectively, reflecting a recovery factor of 39%. The reserves are produced through crestally-located wells supported by down-dip water injectors, and exported via two fixed platforms and an underwater manifold centre. To date, 59 wells have been drilled and 324 MMBBL (52%) of the estimated reserves have been produced.
The Arbroath and Montrose Fields, Blocks 22/17, 18, UK North Sea
Authors: Crawford R. , Littlefair R. W. , Affleck L. G. 
Published: April 2008

Abstract
The Arbroath Field was discovered by the Amoco operated group comprising Amoco (UK) Exploration Company, Gas Council (Exploration), Amerada Hess Ltd and Texas Eastern (UK) Ltd with the 22/18-1 well in May 1969 and was the first commercial oil field to be discovered in any sector of the northern North Sea. Two years later in 1971, the adjacent Montrose Field was discovered. Both Arbroath and Montrose are located 130 miles east of Aberdeen towards the northern end of the Central Graben area. The two fields have simple non-faulted, anticlinal structures separated by a structural saddle with only 15 ft of relief. The structures are a product of Alpine tectonism combined with differential compaction of the reservoir section. The hydrocarbons have a Kimmeridge Clay source and occur wholly within the Forties Sandstone interval. The oil is trapped by mudstones of the Sele Formation. The reservoir sandstones were deposited in a prograding submarine fan complex and have maintained an average porosity of 23% and a permeability of 80 md.
To date only the Montrose Field has been produced. The main recovery mechanism is natural bottom water drive supplemented by water injection. First oil was produced in 1976 via a tanker mooring system, replaced by a dedicated pipeline in 1984. The Arbroath Field is under development and first oil was produced in April 1990.
The Argyll, Duncan and Innes Fields, Block 30/24 and 30/25a, UK North Sea
Authors: Robson D. 
Published: April 2008

abstract
The Argyll, Duncan and Innes Fields are situated in the UK Central Graben in Blocks 30/24 and 30/25a. They produce oil from Devonian, Rotliegendes, Zechstein and Jurassic reservoirs through a common floating production facility, the Deepsea Pioneer.
Argyll was the first UK North Sea oil field to come on stream, with first oil produced in June 1975. Duncan and Innes were added later and the estimated STOIIP for the three fields is approximately 270 MMBBL. To date over 90 MMBBL have been recovered, and the fields are now on decline.
The Auk Field, Block 30/16, UK North Sea
Authors: Trewin Nigel H. , Bramwell Mark G. 
Published: April 2008

Abstract
The Auk field is located in Block 30/16 at the western margin of the Central Graben. Oil is contained in a combination stratigraphic and structural trap which is sealed by Cretaceous chalk and Tertiary claystones. An oil column of up to 400 ft is contained within Rotliegend sandstones, Zechstein dolomites, Lower Cretaceous breccia and Upper Cretaceous chalk. Production has taken place since 1975 with 80% coming from the Zechstein, in which the best reservoir lithology is a vuggy fractured dolomite where porosity is entirely secondary due to the dolomitization process and leaching of evaporites. Both Rotliegend dune slipface sandstones, and the Lower Cretaceous breccia comprising porous Zechstein clasts in a sandy matrix, also contribute to production. Poor seismic definition of the reservoir results in reliance on well control for detailed reservoir definition. The field has an estimated ultimate recovery of 93 MMBBL with 13 MMBBL remaining at the end of 1988.
The Auk field is situated in Block 30/16 of the Central North Sea about 270 km ESE from Aberdeen in 240-270 ft of water (Fig. 1). The field covers an area of about 65 km2 and is a combination of tilted horst blocks and stratigraphic traps, located at the western margin of the South West Central Graben. The Auk horst is about 20 km long and 6-8 km wide, with a NNW-SSE trend. It is bounded on the west by a series of faults with throws of up to 1000 ft, and the eastern boundary fault has a throw of 5000 ft in the north reducing to zero in the south (Fig. 2). The horst is a westward tilted fault block in the north which grades into a faulted anticline in the south. The Auk accumulation is largely contained within Zechstein dolomites and is ultimately sealed by Cretaceous chalk which overlies the base Cretaceous erosion surface. An E-W cross-section of the field is illustrated by Fig. 3. Auk was the first of the alphabetical sequence of North Sea sea-bird names used for Shell/ Esso fields.
The Buchan Field, Blocks 20/5a and 21/1a, UK North Sea
Authors: Edwards C. W. 
Published: April 2008

Abstract
The Buchan Oilfield is located in Blocks 21/la and 20/5a of the UK North Sea, on the southern side of the Witch Ground Graben. The Buchan structure is a complex tilted and dissected fault block formed during Jurassic extension and rifting. The Upper Devonian-Carboniferous reservoir is composed of fluvial Old Red Sandstone facies sandstones sealed by Lower Cretaceous mudstones and contains a 585m (1919 ft) thick oil column. Poor matrix porosities and permeabilities are enhanced by a pervasive fracture system, although faulting in the reservoir restricts communication between several of the nine producing wells. Hydrocarbon migration has occurred from a mature Upper Jurassic source rock north of the field into the structure across the flank faults. Production of the highly under-saturated oil is by depletion drive with some aquifer sweep to a floating production facility and onward transmission to the Forties Field by pipeline. Production commenced in 1981 and original recoverable reserves are estimated at 90 MMBBL of which 71.5 MMBBL have already been produced.