bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deformation processes in accretionary wedges—examples from the SW margin of the Southern Uplands, Scotland
Authors: Knipe R. J. , Needham D. T. 
Published: April 2008

Summary
The deformation which accompanies the evolution of accretionary complexes at active margins is discussed using examples from the Southern Uplands of Scotland. The area was part of a northward-dipping subduction complex during Ordovician and Silurian times before the final closure of the Iapetus Ocean in the Early Devonian. The structures present in the SW margin of the Southern Uplands may be assigned to four different processes typical of accretionary-prism evolution. These are (a) downslope gravity-driven movement, (b) accretion-related folding and thrusting, (c) late accretion or collision processes, and (d) post-collision adjustments. The problems of recognizing and separating these processes in the Southern Uplands are discussed as well as the similarities which occur between overthrusting processes in foreland thrust-and-fold belts and the underthrusting processes taking place in accretionary complexes. In addition an attempt is made to assess the effects of the changes in deformation behaviour occurring during lithification which accompanies accretion. A model is presented here which relates the evolution of folds and thrusts to the changing material properties of sediments during accretion, and emphasizes the importance of the deformation behaviour of the hanging wall to accreting packages in these processes.
Geochemical characteristics of collision-zone magmatism
Authors: Harris Nigel B. W. , Pearce Julian A. , Tindle Andrew G. 
Published: April 2008

Summary
This paper reports the results of a systematic geochemical study of intermediate and acid intrusive rocks from a number of continent-continent collision zones of Phanerozoic age. Four groups of intrusions can be recognized, each associated with a particular stage in the tectonic evolution of a collision zone.

Pre-collision calc-alkaline (volcanic-arc) intrusions
which are mostly derived from mantle
modified by a subduction component and which are characterized by selective enrichments in
LIL elements.

Syn-collision peraluminous intrusions (leucogranites)
which may be derived from the
hydrated bases of continental thrust sheets and which are characterized by high Rb/Zr and
Ta/Nb and low K/Rb ratios.

Late or post-collision calc-alkaline intrusions
which may be derived from a mantle source
but undergo extensive crustal contamination and can only be distinguished from volcanic-arc
intrusions by their higher ratios of Ta/Hf and Ta/Zr.

Post-collision alkaline intrusions
which may be derived from mantle lithosphere beneath
the collision zones and which carry high concentrations of both LIL and HFS elements.

The geochemical evolution of crustal melts within groups (ii) and (iii) can be viewed in terms of the dehydration reactions, volatile transfer and transient geothermal gradients that result from thrust tectonics in the zone of collision.
Geochemical and tectonic evolution of the Damara Belt, Namibia
Authors: Hawkesworth C. J. , Menzies M. A. , van Calsteren P. 
Published: April 2008

Summary

The Damara is a high-grade, apparently intracratonic, Pan-African Orogenic Belt which has been the subject of unusually detailed geochemical and petrological studies. Basement inliers (2.0–1.0 Ga) underlie predominantly continental sediments, deposited in the period 1.0–0.7 Ga, and these are overlain unconformably by molasse-type deposits at least 580 Ma old. Basic volcanic rocks are rare, but the centre of the Damara Belt is characterized by large volumes of syn- and post-tectonic granitic rocks intruded between 750 and 450 Ma. Many were derived from the pre-existing crust as indicated by their initial
87
Sr/
86
Sr = 0.705–0.76, ɛ
Nd
= 0 to −17, δ
18
O = +7.1 to +15.2‰. Moreover, combined Nd- and Sr-isotope studies on sediments, granites and basement rocks suggest that at 500 Ma, in the centre of the belt, 2.0 Ga basement was sandwiched between rocks with younger model ages above and below. Metamorphic temperatures and pressures reached ∼620°C and 7–8 kb in the S where the Rb/Sr biotite ages are 500–480 Ma and ∼660°C and 3–4 kb in the centre of the belt where the biotite ages are 460–440 Ma. Prograde metamorphism (and partial melting) in the central part of the belt continued after the closure of the biotite ages along the margins and since the former is a zone of domal uplift structures, the crustal melting and diachronous metamorphism are attributed to differential uplift in an area of thickened continental crust. There is good evidence that the evolution of the Damara was intimately linked with that of the N-S trending belt now exposed in South America, although in detail the relationship between metamorphism and the inferred tectonic movements is still poorly understood. Nonetheless, since preliminary data indicate that the N-S belt may have formed along a destructive plate margin, it is speculated that for at least some of its history, the Damara evolved in an extensional intracontinental basin behind a zone of active subduction.
Collision and Cordilleran orogenesis: an Andean perspective
Authors: Dalziel I. W. D. 
Published: April 2008

Summary

The Andean Cordillera is the result of interaction between oceanic lithosphere, forming the floor of the Pacific Ocean Basin, and S American lithosphere during the Mesozoic and Cenozoic. Break up of Gondwanaland was accompanied by widespread extensional tectonics in its S American segment during the Early to Mid-Mesozoic. The trend, dimensions and nature of the resulting basins were to a considerable extent controlled by the structure of the pre-Jurassic basement. Elongate basins formed along virtually the length (
c
. 7,500 km) of the Pacific margin from Northern Peru (5°S) to the Northern Scotia Ridge (56°S). These basins developed within, or immediately behind, a magmatic arc.

Mid-Cretaceous uplift and compression, contemporaneous with the global increase in seafloor spreading rates, took place along the length of this Pacific margin composite back-arc trough. Horizontal shortening accompanied the uplift, but only S of lat. 50°S did extensive penetrative fabrics develop in the basin called the Magellan Geosyncline by Aubouin (1965) because of its partially ophiolitic floor (the ‘Rocas Verdes’) and infilling of deep-marine volcaniclastic turbidites. This Mid-Cretaceous event may have been critical in initiating the process of Cordilleran orogenesis. Subsequently part or all of the Late Cretaceous batholiths were intruded into the uplifted back-arc trough as the locus of magmatic activity moved eastwards to its present location and dominantly E-verging fold-and-thrust belts developed along the eastern flank of the Cordillera.
Thus in the development of the present Andean Cordillera, S of 5°S, ‘collision’ was confined to the re-welding of a zone of failure between an ensialic magmatic arc and its parent continent. For the most part this involved little horizontal displacement and reflects, therefore, what might be described as ‘accordian tectonics’, a curtailed version of the Wilson cycle. Only in the very far S, in Tierra del Fuego and S Georgia, does crust appear to have been consumed in the arc-continent ‘collision’.
Arenig and Llanvirn graptolite biostratigraphy, Canadian Cordillera
Authors: Lenz A. C. , Jackson D. E. 
Published: April 2008

Summary

Lower Ordovician graptolites of the Canadian Cordillera (southeastern British Columbia to northern Yukon) are strongly allied to those of the Victorian sequences of Australia and the nearly identical succession of New Zealand, consequently the Stage classification of Victoria is adopted with only minor modifications. Biostratigraphic zones recognized herein, and their Victorian correlatives, are
Tetragraptus approximatus
(upper Lancefieldian),
T. fruticosus
(Bendigonian),
Didymograptus protobifidus
(Chewtonian),
Isograptus victoriae lunatus
(very poorly known) and
I. v. maximodivergens
(lower and upper Castlemanian, respectively),
Oncograptus
possibly with lower and upper divisions (Yapeenian),
Paraglossograptus tentaculatus
divisible into a lower unit equivalent to Dariwillian 1 and 2, and an upper unit correlative with about Dariwillian 3 and characterized by the appearance of
Sinograptus
, and
Diplograptus decoratus
Dariwillian 4 and higher).

Zone by zone diversity studies of Pacific Faunal Province graptolites indicate maximum species’ diversity in the
fruticosus
and
tentaculatus
zones and lowest diversity about the
lunatus
Zone.
Biostratigraphy of the Ordovician
Nemagraptus gracilis
Zone
Authors: Finney Stanley C. , Bergström Stig M. 
Published: April 2008

Summary

The middle Ordovician
Nemagraptus gracilis
Zone has long been used as a prominent, reliable correlation datum, having been recognized on every continent except Africa and Antarctica. However, there is some disagreement today on its definition and its boundaries. A re-examination of the original definition of the zone and evaluation of pertinent graptolite and conodont biostratigraphical data from key sections in Scotland, Wales, Scania, New York, Texas, Alabama and Australia indicate that the first appearance of
N. gracilis
is synchronous worldwide and can thus be used to define the base of the zone. Additional studies, however, are necessary before an internationally recognized upper boundary of the zone can be defined.

The Berrybush Burn section in Scotland is proposed as a general reference section of the
N. gracilis
Zone graptolite assemblage, with the Fågelsång and Albany sections in Scania and New York, respectively, as secondary reference sections. The Fågelsång, Sweden and Calera, Alabama sections are proposed as local reference sections for the lower boundary of the zone in, respectively, Europe and North America.
Cluster analysis of isograptid individuals from Bullengarook, Victoria, Australia
Authors: Schleiger N. W. 
Published: April 2008

Summary

Bullengarook Slate Quarry is a locality high in the Ca3 Zone and less than 100 m below the Castlemaine-Yapeenian boundary. The diversity of isograptids at the quarry is high with juvenile
Pseudisograptus
occasionally occurring with the
Isograptus
species.
The Ordovician graptolite-bearing strata of Xiushui drainage basin, Jiangxi, southern China and their correlation
Authors: Yu Jianhua , Fang Yiting 
Published: April 2008

Summary
The Xiushui drainage basin of Jiangxi is situated on the northern margin of the Jiangnan biogeographical province and adjoins the southern Yangtze province. The Ordovician System in this area is well developed, with a clear base and top, and is rich in fossils. It is one of the best Ordovician sections in China. The stratigraphy, faunal characteristics and correlation of the Ordovician graptolite-bearing strata have been studied. The lower and upper boundaries of the Ordovician System are also discussed.
Graptolite zones of upper Ordovician to middle Silurian age in a continuous section at Ziyang, Shaanxi, China
Authors: Fu Li-pu 
Published: April 2008

Summary

Silurian strata are well developed in Qinling, China where there are many continuous sections (Fu 1980; Lin 1979; Mu 1980). The Bajiaokou section in Ziyang, Shaanxi is described, and is one in which all the international Llandovery graptolitic zones occur. It may be divided into more than twenty graptolite zones from the
Amplexograptus disjunctus yangtzensis
Zone to the
Cyrtograptus centrifugus
Zone.
Graptolite zones in the Ordovician and Silurian of the Gorny Altai
Authors: Obut A.M. , Sennikov N.V. 
Published: April 2008

Summary
The Ordovician and Silurian graptolite zonal scale, based on studies of the stratigraphic distribution of graptolite assemblages in Great Britain, is compared with the problems of using data in other regions where often no stratotypes for zonal subdivisions are presently defined. Assuming such local stratotypes in future we can note that the total graptolite scale, being a sum of sections with biostratigraphic graptolite zones distinguished therein, serves as an instrument for exact determination of geological time; and perhaps this scale does not need the distinction of stratotypes of zonal subdivision having as it does in each case exclusively chronostratigraphic significance.
Zonal graptolite successions distinguished in different regions, and zonal subdivisions of the total graptolite reference scale, often have index species of the same name, and the same chronostratigraphic extent of zonal subdivisions. As a rule, stratotypes for provincial, regional and local graptolite zones are not distinguished, but some investigators offer characteristics of so-called standard sections where the whole successive set of zones with rich graptolite assemblages is given.
According to a recommendation of The Stratigraphic Code of the U.S.S.R. (Stratigraphicheskii Kodeks S.S.S.R., 1977) stratotypes of regional biostratigraphic zones ought to be distinguished. In those cases where the world set of stratotypes is recognized in the same section of graptolite zones for the territory; a local reference section. The standard section necessary both for intra-regional correlations and for inter-regional ones can include either the full set of graptolite zones of a system, series, stages or only a limited number of zones. The Ordovician and Silurian of the Gorny Altai is used as an example of the above principles.
Families of Retiolitida and their phylogenetic relations
Authors: Obut A. M. , Zaslavskaya N. M. 
Published: April 2008

Summary

Isolated material of retiolitid graptolites from boreholes in the Russian and Siberian platforms is described and has enabled a reassessment of the classification and phylogeny of this large group of graptolites to be made. The Order Retiolitida (Mikhaylova 1970) is considered to consist of the following families: Archiretiolitidae (Bulman 1955); Pseudoretiolitidae (Obut & Zasalavskaya 1974); Retiolitidae (Lapworth 1873); and Plectograptidae (Bouček & Münch 1952). The new subfamilies Pseudoplegmatograptinae (Retiolitidae) and Gothograptinae (Plectograptidae) are proposed and the taxa
Agastograptus robustus
gen. and sp. nov. and
Pseudoplectograptus
gen. nov., both assigned to the Plectograptinae, are erected.

All material used is deposited in the Institute of Geology and Geophysics of the Siberian Branch of the Academy of Sciences of the U.S.S.R., Novosibirsk.
Mode of secretion of graptolite periderm, in normal and retiolite graptolites
Authors: Bates D. E. B. , Kirk N. H. 
Published: April 2008

Summary
The construction of graptolite periderm is discussed with particular reference to the rival extra-thecal tissue (secretion) and pterobranch (mortaring) models, and it is concluded that only the former model fits the observed structures. Evidence from a number of retiolite graptoloids demonstrates that they also have a continuous periderm, and were constructed in a similar manner.
Assemblages of Silurian graptolites in various facies of the East Baltic region
Authors: Paškevičius J. 
Published: April 2008

Summary

All the facies beginning with black clay to carbonate mud in a complete and continuous geological section with graptolites (from the
cyphus
Zone to the
lochkovensis
Zone) can be distinguished in the Lithuanian Silurian. The assemblages of graptolites were determined, and an attempt was made to analyse dependence of the graptolites on various facies. During this work it was ascertained that the most numerous general species and individuals in the assemblages are found at the junctions of clayey and carbonate facies. These assemblages must have been developed on the continental slope of the Silurian sea. The number of species in general slightly decreases in the direction of the past open sea (black-clay facies), to say nothing of the shelf zone (the carbonate facies), where graptolites are especially scarce. Here one can trace a certain analogy between the distribution of zooplankton of the present-day seas and that of the graptolites, which composed the macrozooplankton of the seas of the geological past.

Thus the graptolites being a pelagic group of the zooplankton of the past, lived, developed and were widespread in the deeper part (probably in mezopelagic) of the open sea, mostly beginning at the continental slope.
Modern pterobranchs: observations on their behaviour and tube building
Authors: Dilly P. N. 
Published: April 2008

Summary
There is a considerable difference in the ultrastructure of fusellar tissue between fossil graptolites and modern pterobranchs. The phylogenetic significance of these differences is uncertain. It was thought that the ultrastructure of the earliest, and therefore probably the simplest, stage of formation of the pterobranch prosiculum might provide additional relevant clues. The larva escapes from the original dome-shaped seal by producing a hole, and immediately produces a series of fuselli around the aperture. The zooid uses the cephalic shield to construct the tube. The size of the original fuselli is very variable, but soon achieves adult size. The fuselli are very similar to those of adult erect tubes, and have oblique sutures. There is much extraneous material incorporated into the wall. It is proposed that the fibrils of the stroma of the coenecium somehow mature after they have been secreted. Histochemical tests suggest that the stroma contains a considerable amount of acid and sulphated mucopolysaccharides. Tests for chitin and keratin have been uniformly negative. Similar positive histochemical reactions have been achieved on the cephalic shield. Adult tube building and repair are reported for the first time.
Late Weichselian transgression, erosion and sedimentation at Gullfaks, northern North Sea
Authors: Carlsen Randi , Løken Tor , Roaldset Elen 
Published: April 2008

Summary

A prograding sequence of near shore sediments is identified at the border of the northern North Sea plateau (water depth 135 m) and the western slope of the Norwegian Trench. In Late Weichselian time (probably about 15 000 years
bp
) the relative sea level was approximately 180 m lower than today. During this low sea-level stand, the older consolidated glaciomarine sediments in the slope area were exposed to coastal erosion, leading to a prograding unit of sand fining outwards to silt and clay. During rising sea-level the coastal erosion gradually reached a lodgement till deposited at the top of the plateau, resulting in coarser sediments such as stones and gravel, fining outwards to sand down the slope. The plateau area was transgressed shortly after 13 000 years
bp
.
North Atlantic sea-surface temperatures for the last 1.1 million years
Authors: Ruddiman W. F. , Shackleton N. J. , McIntyre A. 
Published: April 2008

Summary
A 1.2 Ma time series of north-east Atlantic sea-surface temperature (SST) has been assembled from the spliced record of piston core K 708-7 (0.68-0 Ma) and hydraulic piston cores taken in nearby DSDP Hole 552A (1.2–0.68 Ma). A no-analogue fauna precludes making credible SST estimates in the interval 1.2–1.1 Ma, but the record above 1.1 Ma is suitable for SST estimates and related time-series analysis.
The amplitude of SST variation is considerably higher in the Brunhes than in the upper Matuyama. This is due both to colder glacial SST minima after 0.85 Ma, and to increasingly warm interglacial SST maxima from 0.7 to 0.4 Ma. The dominant periodicity in the SST signal is centred near 95 000 years; it increases in amplitude by a factor of four from the bottom of the record to the top, with the largest increase occurring between 0.7 and 0.4 Ma. This suggests a relatively gradual evolution of ‘100 000-year’ power over half a million years of the late Quaternary, rather than a single abrupt change at 0.9 Ma.

Significant, but progressively smaller, spectral peaks occur at periods of 54 000, 41 000, 31 000, 23 000 and 19 000 years. Both the 54 000-year and 31 000-year signals may be a response to insolation forcing by minor obliquity terms. Long-term δ
18
O records show small responses by the ice sheets at or near these two periods, indicating the probable initial response of the climate system to these insolation rhythms. In-phase relationships between δ
18
O and SST at these periods suggest that the ice sheets then impose these rhythms on the ocean with no lag. The mechanism by which such small insolation and ice-volume signals become enhanced in the SST record is not clear.
Meltwater influences and palaeocirculation changes in the North Atlantic during the last glacial termination
Authors: Williams Douglas F. , Fillon Richard N. 
Published: April 2008

Summary

Major meltwater plumes during the last glacial termination 13 000 years
bp
are recorded in the δ
18
O anomalies of planktonic foraminifera from North Atlantic and Gulf of Mexico marine sediments. These distinct meltwater plumes represent the discharge of isotopically light freshwater from specific portions of the Northern Hemisphere ice sheets. Plume geometries show that northward incursions of warm, normal saline waters occurred during the last glacial termination, thereby delivering latent and sensible heat to high latitudes of the North Atlantic and enhancing the rate of ice sheet melting.
Gas Prospects in the Variscan Thrust Province of Southern England
Authors: Taylor J. C. M. 
Published: April 2008

Summary
Recently published seismic and other investigations into the Late Carboniferous — Early Permian thrust and fold belts of the Appalachians, the Franco-German border, and to a limited degree so far of southern England, suggest that Variscan deformation is characterised by thin-skinned tectonics. This provides a rationale for recognising flat-lying thrust slices and mapping them in the subsurface. It also implies that the over-ridden rocks may not have been subjected to the excessive burial or the degree of disturbance once assumed. In the Variscan province of southern England the existence of potential source and reservoir rocks can be expected on regional grounds. Consideration of the likely burial and thermal history suggests there may be areas where gas if not liquid hydrocarbons from Palaeozoic source rocks could be preserved. Further geochemical, geophysical and petrophysical investigation seems warranted.