bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metamorphosed ophiolitic rocks from the Serbo-Macedonian Massif, near Lake Volvi, North-east Greece
Authors: Dixon J. E. , Dimitriadis S. 
Published: April 2008

Summary

The paper describes preliminary results from the 120 sq km Volvi mafic complex within the Greek Serbo-Macedonian Massif. We conclude from published information and isotopic ages that the central and eastern part of the Massif (basement and Triassic/Jurassic cover) were affected by an amphibolite-facies regional metamorphic and deformational event in the Late Jurassic-Early Cretaceous. Delayed uplift from this same event may explain Tertiary ages from Kerdilion migmatites. The Volvi complex may thus be A: pre-Mesozoic ‘basement’, or B: an
in situ
Mesozoic rift complex
or
C: a Mesozoic collisional suture remnant. Field, microprobe and XRF data appear to fit model B best. Though deformed, the complex has recognisable 100% sheeted-dyke tracts and substantial areas of undeformed gabbro at lower structural levels. Deformation began before the end of magmatic activity: late sheets of pegmatic gabbro cut deformed dykes; late dykes cut sheared gabbro. Assemblages are of high-grade amphibolite facies and give garnet-hornblende temperatures of 750°C, significantly higher than inferred for staurolite-garnet schists outside the complex. Geochemically, the basaltic rocks show LIL enrichment and are intermediate between ‘alkalic’ and ‘above-subduction-zone’ in character. The complex may relate to Mesozoic rift-basins identified in E. Serbia, but is not thought to be a Palaeotethyan remnant.
Sapropelic layers in the NW Aegean Sea
Authors: Cramp A. , Collins M. B. , Wakefield S. J. , Banner F. T. 
Published: April 2008

Summary

The present study examines sapropelic layers and associated sediments in the NW Aegean Sea, based upon the analysis of cores collected during the 7/78 cruise of the R.R.S.
Shackleton
.

Preliminary sedimentological analyses of some of the cores, including the use of X-ray techniques, did not at first detect either a sapropel or a sapropelic layer (defined as >2% and 0.5 – 2.0% organic carbon, respectively—Sigl
et al.
1978) in the sediment. Further investigations, including the analysis of organic carbon, on twelve of these cores have demonstrated the presence of horizons relatively rich in organic carbon. These horizons contain up to approximately 1.0% organic carbon and could be regarded as sapropelic layers. The horizons vary between 26 and 33 cm in thickness and are found at depths of 25 to 100 cm below the sediment-water interface, in cores which range from 101 to 240 cm in length.

Organic carbon profiles are presented, together with a discussion of the corresponding X-ray analysis and a preliminary note on the biogenic contributions to these sediments.
Neogene to Quaternary geodynamics of the area of the Ionian Sea and surrounding land masses
Authors: Fabricius Frank H. 
Published: April 2008

Summary
Investigations in the north-eastern and central Ionian Sea document important palaeogeographic and palaeoceanographic changes since Neogene time. These findings support the model of shallow basinal evaporation during Messinian time. On this basis the rate of subsidence of the Ionian Sea is calculated for the last 6 Ma, at about 1 m per 1000 years for basinal settings and half this for marginal settings.
Elevated terraces corresponding to high glacio-eustatic stages in the Quaternary are frequent on Mediterranean coasts at heights up to more than 150 m above present sea level. Together with elevated marine deposits of Pliocene age, they testify to general coastal uplift. These epeirogenic tectonics are interpreted as compensation for the subsidence of Mediterranean basins.
In its present general form the Mediterranean Sea has existed since Pliocene time. The first indications of the foundering of the Ionian basin are Messinian evaporites. The formation of such huge basins is interpreted as the result of the transformation of former continental crust to ‘intermediate’ or ‘oceanized’ crust. The important fast vertical tectonics of the margins of ‘Mediterranean type’ differ considerably from those of the Atlantic or Pacific type.
Clastic facies models and facies analysis
Authors: Anderton R. 
Published: April 2008

Summary
The term facies is used either descriptively, for a certain volume of sediment, or interpretatively for the inferred depositional environment of that sediment. Facies models are intellectual aids to the understanding of sedimentary environments and the origin of ancient sedimentary rocks. Many different models can be constructed to explain a given set of data, depending on which aspect of the facies requires the most illumination and on the types of techniques used in the analysis.
When dealing with ancient rocks, facies modelling is the last stage in the process of facies analysis which consists of the detailed description of exposed or cored sediments, their classification into objectively defined facies, the compilation of the characteristics of each facies, the deduction of the processes of deposition of each facies, the examination of the spatial relationships between facies and the recognition of facies associations, the interpretation of the overall depositional environment of the association and the detailed interpretation and modelling of individual facies. Short cuts can lead to fallacious interpretations. Reliable facies models cannot be produced without careful facies analysis. A facies model may be plausible, yet totally inapplicable to the facies from which it was supposedly derived.
Mechanics of tectogenesis in plate collision zones
Authors: Murrell S. A. F. 
Published: April 2008

Summary
Although continental parts of tectonic plates can be stretched, fractured and rifted, it appears that orogenic belts only form on continental margins or in previously stretched and thinned regions of continents and cratons. This is because continental crust and lithosphere is much weaker under the action of extensional forces than it is under contractional forces. The stretching and shortening of crust and lithosphere is discussed using McKenzie’s (1978) approach and the processes by which thinned or thickened lithosphere is restored to normal thickness are discussed in some detail. It is shown that the expressions for the initial and final changes of surface elevation are the same, apart from a difference in sign, for the cases of stretching and shortening when no material is added, or removed (by erosion). It is also shown that there is a critical value of the initial crustal thickness (∼ 17 km in McKenzie’s (1978) model) which must be exceeded if stretching is to cause crustal subsidence and shortening is to cause crustal elevation. Thinner crust, when shortened, will subside. This may be important in shortening processes at continental margins, where the thicker continental crust will rise and oceanward, the thinner crust will subside. The thermal and metamorphic changes associated with stretching (and thinning) and shortening (and thickening) are discussed. In the deeper parts of shortened and thickened crust prograde metamorphism will occur, possibly leading to anatexis. The strength and deformation mechanisms of crust and lithosphere are summarized. Finally, a collision tectonics model is presented based on the concept of shortening (with concomitant thickening) of the colliding passive and active margins, in which the important role of differential elevation changes across strike is emphasized. In the heart of the orogen will be a thickened crust consisting of thickened basement, a thick deformed sediment pile and nappes thrust from the margin. On a time scale of some tens of Ma, a thick metamorphosed and granitized lower crust will form after sufficient shortening has taken place.
A possible new pattern of cortical deposit in Tremadoc dendroid graptolites from chert nodules
Authors: Urbanek Adam , Mierzejewski Piotr 
Published: April 2008

Summary
Rhabdosome fragments of dendroids from upper Tremadoc chert nodules, studied with TEM, show an unusual pattern of cortical tissue. In contrast to previously studied tissues it consists of an irregular meshwork of wavy, branching and interconnecting fibrils. Differentiated in size and thickness, the fibrous material includes thick, strongly branched fibres. Their presence is a characteristic feature of the cortex in the dendroids examined. The observed pattern of ultrastructure is tentatively described as ‘reticulate fabric’. Its nature remains obscure. It may represent a primary feature, thus being an unusual state of aggregation of fibrous material, but its secondary origin due to preservational degradation of normal dendroid cortex seems more plausible.
Stratigraphic significance of
Glyptograptus persculptus
group graptolites in central Nevada, U.S.A.
Authors: Berry William B.N. 
Published: April 2008

Summary

Glyptograptids of the
G. persculptus
group,
Glyptograptus laciniosus
, and climacograptids of the
C. normalis
group (herein described as
C. miserabilis
) occur in the Hanson Creek Interval, or Formation, at Copenhagen Canyon, central Nevada. The graptolites occur in the basal part of an interbedded thin-bedded limestone and chert sequence overlying a quartzsand unit that is recognizable over a wide area in central Nevada and seems to reflect regional shallowing of the seas at the time of its deposition.
Dimorphograptus
sp. cf.
D. confertus
is present in the stratigraphically highest beds of the limestone-chert unit. Conodonts suggesting an early Silurian age are present in the graptolite-bearing sequence. Ashgill (late Ordovician) faunas have been found beneath the quartz-sand unit. Analysis of depositional environments of the Ashgill and early Silurian conodont-bearing beds suggests that deposition was continuous from the late Ordovician into the early Silurian in the area. The
G. persculptus
group glyptograptids display a significant range in variation. Some are relatively narrow and appear to be parallel-sided for much of their length, whereas others are relatively wide and taper noticeably in their proximal regions.
Top Ordovician and lowest Silurian of Dob’s Linn
Authors: Williams S. Henry 
Published: April 2008

Summary

The Upper Hartfell Shale (including Anceps Bands A-E and the Extraordinarius Band) and the lowest Birkhill Shale have been extensively collected at Dob’s Linn revealing many forms previously unrecorded from Britain. The first two Anceps Bands (A and B) contain a distinct fauna from the following three (C-E) and two new subzones are suggested for the
D. anceps
Zone, an earlier
D. complexus
and a later
P. pacificus
Subzone, which should be more widely correlatable units. A major extinction occurred between Anceps Band E and the Extraordinarius Band (
C? extraordinarius
Zone) which contains only a few diplograptid species, as does the basal Birkhill shale (
G. persculptus
Zone). The
O? acuminatus
Zone commences at 1.6 m above the base of the Birkhill Shale with the first occurrence of
A. ascensus
while the monograptid
A. ceryx
appears at 1.9 m. The base of the
O? acuminatus
Zone is considered to be the most suitable horizon for the Ordovician-Silurian boundary.
The Silurian graptolite-bearing strata in China
Authors: Huo Shi-cheng , Shu De-gan 
Published: April 2008

Summary

Details of the Silurian graptolite sequences of China, particularly those of the South China, Kunlun-Qinling and Yangzi provinces, are given and a graptolite zonal sequence proposed for the Silurian of China. The recognition of the upper and lower boundaries of the Silurian in China is discussed and a two-fold division of the Llandovery and a three-fold division of the Wenlock proposed on the basis of graptolite zones. The base of the Silurian is taken at the base of the
Glyptograptus persculptus
Zone; the Silurian/Devonian boundary at the base of the
Monograptus uniformis
Zone. It is shown that close correlations are possible between the proposed zonal scheme for China and those in general use in Eastern and Western Europe.
The monotypic ‘population’ accompanying the lectotype of
Saetograptus varians
(Wood 1900)
Authors: Palmer D. C. 
Published: April 2008

Summary

The lectotype of
Saetograptus varians
(Wood) is accompanied by a monotypic assemblage of graptolites, which is shown to have current orientation and bimodal size distribution. The morphology of the two size classes is compared with that of the lectotype and the development of the nema analysed. This paper is the initial stage in a study of the semispinose Ludlow graptolite
S. varians
and is based on an examination of the lectotype and its accompanying fauna.
Late Mesozoic and Cenozoic sediment flux to the central North Atlantic Ocean
Authors: Thiede Jörn , Ehrmann Werner U. 
Published: April 2008

Summary
A history of Mesozoic and Cenozoic palaeoenvironments of the North Atlantic Ocean has been developed based on a detailed analysis of the temporal and spatial distribution of major pelagic sediment facies, of hiatuses, of bulk sediment accumulation rates, and of concentrations and fluxes of the main deep-sea sediment components. The depositional history of the North Atlantic can be subdivided into three major phases: (a) Late Jurassic and Early Cretaceous phase: clastic terrigenous and biogenic pelagic sediment components accumulated rapidly under highly productive surface water masses over the entire ocean basin; (b) Late Cretaceous to Early Miocene phase: relatively little terrigenous and pelagic biogenic sediment reached the North Atlantic Ocean floor, intensive hiatus formation occurred at variable rates, and wide stretches of the deep-ocean floor were covered by slowly accumulating terrigenous muds; (c) Middle Miocene to Recent phase: accumulation rates of biogenic and terrigenous deep-sea sediment components increased dramatically up to Quaternary times, rates of hiatus formation and the intensity of deep-water circulation inferred from them seem to have decreased. However, accumulation rate patterns of calcareous pelagic sediment components suggest that large scale reworking and displacement of deep-sea sediments occurred at a variable rate over wide areas of the North Atlantic during this period.
Late Neogene submarine erosion events along the north-east Atlantic continental margin
Authors: Stein R. , Sarnthein M. , Suendermann J. 
Published: April 2008

Summary
During the last 5 Ma, bottom currents have formed two major hiatuses along the continental margin off north-west Africa. In addition, slumping may have caused hiatuses at Site 397. The hiatuses extend from Gibraltar to the equator between 2800 and 4000 m water depth. At the hiatuses there has been up to 30 m erosion, or reduced sedimentation, at DSDP Sites 544B, 397, 141, and 366. Bio- and magneto-stratigraphy and oxygen-isotope curves relate the hiatuses to cooling events of the North Atlantic Deep Water at about 2.75 and 1 Ma.
A dynamic ocean model of deep-water circulation provides insights into how climate induced changes in the deep-water current regime.
Sediment waves in the eastern equatorial Atlantic: sediment record during Late Glacial and Interglacial times
Authors: Sarnthein M. , Mienert J. 
Published: April 2008

Summary

Standing and migrating sediment waves along the West African continental rise (3000–4500 m water depth) are characterized by a regular spacing of wave length periods that are multiples of 280 m, and by long-term pelagic sediment composition. Interpretations of their origin must account for the following evidence: (1) The wave crests generally run parallel or oblique to the continental rise and also to prevailing (net) currents, as confirmed by SEA BEAM data; (2) Migrating waves along the West African continental margin are directed only upslope, i.e. towards the East. (3) The waves have been accreting for a long time, (>1 Ma). (4) Glacial to interglacial differences in the evolution of sediment accumulation rates on crests and troughs may indicate that the accreting regime was intermittent, and that the waves were more levelled prior to 7500 years
bp
due to increased deposition of siliciclastic matter in the troughs. (5) Absent patterns of grain-size sorting in the fine-grained muds contradict ‘conventional’ models of current-related sediment transport.

A superposition of large tidal components and slow thermohaline net currents (Lonsdale 1978), secondary current processes (Unsöld, pers. comm.), or a superposition of internal waves and thermohaline currents (Kolla
et al.
1980) are regarded as the most probable modes of origin.
Late Pliocene to Recent planktonic foraminifera from the North Atlantic (DSDP Site 552A): quantitative palaeotemperature analysis
Authors: Hooper P. W. P. , Funnell B. M. 
Published: April 2008

Summary
Hydraulic piston cores from Hole 552A (56′02.56′N., 23′13.88′W.), recovered during Leg 81 of the Deep Sea Drilling Project, provide a near-perfect record of the glacial history of the North Atlantic. Oxygen isotope data gathered by Dr N.J. Shackleton were used to select 40 samples representing maxima of glacial and interglacial events, from the initiation of ice-rafting at 2.5 Ma to the present. For each sample the planktonic foraminiferal assemblage was analysed, enabling distinctive warm and cold water assemblages to be identified.

The relative abundance distributions of individual species were compared with the isotope data to assess temperature preferences, including those of two extinct species:
Globorotalia puncticulata
(Deshayes) and
Neogloboquadrina atlantica
(Berggren). A similar correlation for the coiling direction ratio in
Neogloboquadrina pachyderma
(Ehrenberg) gave a coefficient greater than 0.9, showing this to be an especially sensitive indicator of temperature at this latitude.

From these data a preliminary quantitative palaeotemperature analysis, using a simple transfer function, enabled a sea-surface temperature curve to be calculated for the Late Pliocene and Pleistocene to Recent, which correlates well with both the isotopic data and ecological data for extant species.
Diatom biostratigraphic and palaeoceanographic interpretations for the middle to high latitude North Atlantic Ocean
Authors: Baldauf Jack G. 
Published: April 2008

Summary
Diatoms are useful for biostratigraphic correlation of Neogene sediment sections in the North Atlantic Ocean. The warm-temperate assemblage observed in cores from the middle and high latitude Atlantic enables partial application of the diatom zonations defined in the eastern equatorial Pacific. Sixteen of the equatorial Pacific diatom zones are recognized in cores from the middle latitudes of the North Atlantic.
The diatom assemblage implies that surface waters were warm during the early Miocene in the Rockall Plateau region. A decrease in the quality of diatom preservation, and the occurrence of numerous hiatuses at approximately the early-middle Miocene boundary, suggest a major change in oceanic circulation. An increase in deep water overflow from the Norwegian Sea may have been a contributing factor. Although middle Miocene sediments at both middle and high latitudes are generally enriched with silica, a possible restriction of siliceous sedimentation towards the high latitudes is observed during this time. The interval representing the early late Miocene and earliest Pliocene is generally devoid of diatoms.

Conditions favouring siliceous sedimentation continued at high latitudes and returned to middle latitudes of the North Atlantic during the late Pliocene, maybe in response to increased intensity of the Gulf Stream. The abundance and preservation of diatoms in high latitude Quaternary sediments is partially controlled by climatic fluctuations. The occurrence of the
Denticulopsis seminae
group suggest that cool, low saline waters may have occurred in the North Atlantic between 1.1 and about 0.70 Ma.
Pulsation tectonics as the control of North Atlantic palaeoceanography
Authors: Sheridan Robert E. 
Published: April 2008

Summary
A new theory of pulsation tectonics involving the cyclic eruption of thermal plumes from the D″ layer in the lowermost mantle is proposed as a control of the first-order cycles of palaeocean changes. Plumes carry heat rapidly away from the core/mantle boundary, changing conditions in a way that results in the quiescence of the earth’s magnetic field. The rising plumes, after a phase lag, induce faster plate spreading and widespread intraplate volcanism. Subsequently, colder rock returning to the lower mantle re-establishes the D″ thermal boundary layer and sets up conditions for more turbulent core convection, which in turn allows frequent magnetic reversals. Meanwhile, lower mantle plumes cease erupting, and the plates spread more slowly. The cycles of fast and slow plate spreading and quiet and reversing magnetic field have a period of 60–100 Ma.

Changes in spreading rate on a global scale are probably a major cause of large scale (100–300 m) eustatic sea-level changes. Major global sea-level high-stands in middle to late Jurassic and in middle to late Cretaceous times coincide with fast spreading. Consequential changes in albedo, global temperature, humidity, forestation, atmospheric and oceanic CO
2
, oceanic acidity and oxygenation lead to variations in the preservation of black shales in the oceans, and in the level of the calcite compensation depth (CCD). In the North Atlantic, the climatic factors forced by rising sea-level caused increased black shale preservation and a shallowing of the CCD. With falling sea-levels, less black shale is preserved and the CCD is deeper.
Laboratory Studies into the Generation of Natural Gas from Coals
Authors: Higgs M. D. 
Published: April 2008

Summary
The thermal histories of a Palaeozoic and a Tertiary coal have been investigated by laboratory simulation experiments in which a suite of samples, with natural maturities ranging from 0.4–3.0% vitrinite reflectance (VR), were heated under identical conditions of time and temperature. The cumulative hydrocarbon yield (measured as methane equivalents) was found to be 170 ml/g organic carbon (Org. C) for the Paleoazoic coal and 225 ml/g org. C for the Tertiary coal. Peak hydrocarbon generation was estimated to occur at approximately 1% reflectance for both coals. Carbon dioxide generation for both coals is rapid and can be considered to have ended by 1% reflectance. Nitrogen generation is negligible for both coals over the maturity range investigated.
Geology and Petrophysics of the Victor Field
Authors: Conway A. M. 
Published: April 2008

Summary
The Victor Gas Field is located in the Southern North Sea Gas Province some 140 km east of the Lincolnshire coast. The Lower Permian Leman Sandstone Formation (Rotliegendes Group) forms the reservoir and consists entirely of sandstones with occasional silty shales in the basal section. It rests uncomformably on the Carboniferous, which was uplifted, gently folded and eroded during the Variscan Orogeny.