bluuebunny/crossref_metadata_2025_split huggingface dataset:
The mineralogy and metamorphic geology of low-grade metasediments, Northern Range, Trinidad
Authors: FREY M. , SAUNDERS J. , SCHWANDER H. 
Published: December 2007

Forty-one low-grade metasediments from the Northern Range of Trinidad and from the neighbouring island of Tobago, West Indies, were investigated by microscopic, X-ray powder diffraction, Guinier camera technique and electron microprobe methods. The following minerals were encountered (in order of decreasing abundance): quartz, muscovite, chlorite, paragonite/muscovite mixed-layer, paragonite, organic material, calcite, pyrophyllite, dolomite, albite, hematite, chloritoid, pyrite, rutile, titanite, rectorite, stilpnomelane.
The chemical composition of muscovite is dependent on the mineral assemblage, with Si = 6.1–6.2 per formula unit in two high alumina assemblages, versus Si = 6.6 in a low alumina assemblage. Microprobe analyses indicate that muscovite, paragonite and pyrophyllite are sometimes intergrown on a micrometre scale. Chlorite composition estimated from X-ray data shows good correspondence with microprobe data for two Al-poor samples but is less satisfactory for an Al-rich sample.
Observed mineral assemblages in AKNa are indicative of the pyrophyllite-paragonite-albite fades. For the first time, chemical data for coexisting pyrophyllite, chlorite (M = MgO/(MgO+ FeO) = 0.377) and chloritoid (M = 0.110) are given. This assemblage is indicative of the low or medium pressure range of the lower greenschist facies.

Pressure conditions during metamorphism are not well constrained but a minimum pressure of 2 kbar, corresponding to 5–6 km of overburden, can be estimated from the Na
M4
content of actinolite. Temperatures derived from the calcite-dolomite geothermometer range between 300 and 350°C and are consistent with the presence of the assemblage pyrophyllite + calcite + quartz.
Sealed microcracks in the Lewisian of NW Scotland: a record of 2 billion years of fluid circulation
Authors: HAY S. J. , HALL J. , SIMMONS G. , RUSSELL M. J. 
Published: December 2007

Examination of a suite of Lewisian gneisses from NW Scotland has revealed the sequential development of microcrack networks sealed by minerals deposited from fluids passing along them. The sealants were deposited during periods of both localized and regional fluid permeation through the gneisses. The study has shown that both microcracks and shear zones may remain open as permeable pathways over several fluid permeation phases; and that an open porosity within crystalline rock may be maintained, between permeation events, by partially sealed microcracks. The separate microcrack sets, identified by their mineral sealing phases have widespread regional distributions.
Several magnetite sealing events, specific to lithologies and structures, occurred during pre-Torridonian times associated with the Scourian and Laxfordian metamorphic cycles.
Four main post-Laxfordian regional sealing events have been identified, characterized by the mineral suites calcite + K-feldspar; prehnite + albite + calcite; pumpellyite + quartz + calcite; and stilpnomelane, respectively. Of these, calcite + K-feldspar is pre-, or earliest, Torridonian. Prehnite + albite + calcite, and pumpellyite + quartz + calcite are associated with Torridonian events: a model of a downward permeating hydrothermal system involving non-marine ground water is envisaged to account for their formation at about 1000–800 Ma, before the deposition of the Applecross Formation Later stilpnomelane, along with less well developed K-feldspar; barite; and pyrite, may either be a result of this system or perhaps a later one associated with the Cambrian marine transgression of the craton at about 600 Ma.
A geophysical investigation of post-Alpine granites and Tertiary sedimentary basins in northern Greece
Authors: MALTEZOU F. , BROOKS M. 
Published: December 2007

The geology of the Rhodope region of northern Greece consists of crystalline basement rocks of the Rhodope Massif in which Tertiary extensional basins and granitic intrusions of Oligocene age occur widely.
Geophysical modelling has highlighted the close spatial relationship of the Tertiary sedimentary basins and post-tectonic granites of closely similar age. Geochemical data for selected granites are used to support the suggestion that there is a close genetic relationship between the episode of granite intrusion and the tectonic development of extensional basins.
Palaeomagnetism of Permo-Triassic rocks in the Iberian Cordillera, Spain: acquisition of Secondary and characteristic remanence
Authors: TURNER P. , TURNER A. , RAMOS A. , SOPEÑA A. 
Published: December 2007

Magnetostratigraphy is widely used as a tool for stratigraphical correlation but there are problems in its application to rocks which have suffered complex diagenesis, particularly sandy, continental red beds. In such cases the complete magnetic record should be studied in relation to its depositional, diagenetic and structural history. To this end a detailed palaeomagnetic study has been made of Permian and Triassic rocks in the northern Iberian Cordillera, Spain. Four stratigraphical units comprising the Autunian, 'Saxonian', Buntsandstein and Muschelkalk have been studied in a single section near Molina de Aragon which is well-documented sedimentologically. Autunian rocks have a characteristic remanence which is exclusively reversed and corresponds to the Kiaman Interval of Lower Permian age. A pole position (49 N, 167 W) is consistent with previous studies which indicate the rotation of Iberia in post-Triassic times relative to the stable European plate. The Saxonian facies show complex, multicomponent magnetizations; no polarity zonation can be resolved but individual components were acquired prior to the rotation of Iberia.
The Buntsandstein is remarkable in that much of it is completely remagnetized in a direction similar to the present local geomagnetic direction. This secondary remanence is carried by fine grained hematite which has been formed as a result of carbonate dissolution and other diagenetic reactions. Initially, these iron oxides were probably superparamagnetic and remanence was only blocked-in by structural inversion of the Iberian Cordillera in Tertiary times and after rotation of the Iberian plate. Some of the primary remanence is preserved in some fine grained lithologies of the Buntsandstein, indicating that normal and reversed zones of magnetization were originally present. The magnetization of the Muschelkalk carbonates is also complex; secondary components similar to those of the Buntsandstein are present but there is evidence that primary components were mainly normal during Karnian times.
Some ecological implications of palaeoatmospheric variations
Authors: MOORE P. D. 
Published: December 2007

The past composition of the atmosphere is gradually being elucidated with increasing precision. But advances in the understanding of the ecological and evolutionary implications of atmospheric changes are not keeping pace. A graphic model is presented here to indicate the complexity of interacting forces resulting from a change in atmospheric carbon dioxide level, and it can be seen that any resultant ecological outcome will be influenced by a series of (sometimes opposing) factors. This is particularly true of the hydrological consequences of atmospheric change and hydrology will undoubtedly prove a major influence on vegetation.
Changes in the levels of both atmospheric carbon dioxide and oxygen have had profound effects on the evolution of plant life by modifying the selective pressures favouring alternative systems of carbon assimilation. These photosynthetic strategies are also closely related to local hydrology. More ecological and physiological information is clearly needed before the biological consequences of Variations in the atmosphere of the past can be appreciated.
Diagenesis of the Kimmeridge Clay Formation, onshore UK
Authors: SCOTCHMAN I. C. 
Published: December 2007

Study of sedimentology, carbonate geochemistry and clay mineralogy of four laterally continuous beds from the outcrop of the Kimmeridge Clay Formation indicates strong lateral variations in the depositional and early diagenetic processes, reflecting the basin and swell topography of the depositional basin.
The mudstones from the swell environment with low sedimentation and subsidence rates are shelly and carbonate–rich with thin, poorly developed oil shales. They were deposited under dysaerobic conditions with consequent poor organic-matter preservation. Early diagenetic processes were limited to the sulphate reduction and methanogenesis zones with the formation of discrete horizons of concretions. The shallow burial depths attained are reflected by the immaturity of the organic matter in the mudstones although ordered illite-smectites are present.
Sediments from other locations comprise black, organic-rich mudstones, the thick beds and good organic-matter preservation indicating deposition under high sedimentation and subsidence rates with anoxic bottom waters in a basinal environment. These indurated mudstones contain a few shell fragments and much pyrite, indicating intense reaction in the sulphate reduction zone. Carbonates were precipitated in the methanogenesis and decarboxylation zones as ferroan calcites and dolomites. The much greater burial depths are indicated by the higher maturity of the organic matter and by the ordered nature of the illite–smectites and the loss of kaolinite.
A decade of phosphorite research and development
Authors: NOTHOLT A. J. G. , JARVIS I. 
Published: December 2007

Report of the eleventh (and final) International Field Workshop and Symposium of Project 156: Phosphorites, organized by A. J. G. Notholt, National Correspondent, 1. Jarvis, and W. C. Burnett (Florida State University) and held at Hertford College, Oxford, England, 5–8 September, 1988. The meeting attracted over 70 delegates and speakers representing 14 countries. It consisted of 41 talks and 2 poster presentations covering a wide range of phosphorite research. A selection of papers will be published by the Geological Society as a Special Publication.
Project 156: Phosphorites is one of the most successful and probably the largest of long-term, interdisciplinary geological research projects supported by the International Geological Correlation Programme (IGCP). It owes its origin to the hypothesis by P. J. Cook, currently of the Bureau of Mineral Resources, Geology and Geophysics, Canberra, that a major Proterozoic-Cambrian phosphogenic province extends through the Asian and Australian region, perhaps comparable in size with the late Cretaceous-Eocene Tethyan province of northern Africa and the Middle East. In his Keynote Address, Dr Cook recalled that although Project 156 was established in 1977 as a research programme on Proterozoic-Cambrian phosphorites of Asia and Australia, such had been the ensuing international interest that three other Working Groups were formed within the Project, devoted respectively to an International Phosphate Resource Data Base; Young Phosphogenic Systems; and Cretaceous-Eocene Phosphorites. All four working groups had generated much research in the Project’s lifetime, a reflection also of the great scientific interest in phosphorites by virtue of their complex petrography and
The structure of the Bracco Ophiolite complex (Ligurian Apennines, Italy): a change from Alpine to Apennine polarity
Authors: HOOGERDUIJN STRATING E. H. , VAN WAMEL W. A. 
Published: December 2007

The Bracco ophiolite complex, exposed in the area studied as the Bracco Subunit of the Melange Nappe, is tectonically intercalated between the underlying Canetolo Nappe and the overlying Lavagna Nappe. Detailed structural analysis and mapping in these units reveals a multi-phase deformation history. In the Bracco Subunit and the Lavagna Nappe, this history is characterized by a change, from SW (i.e. ‘Alpine’) directed folding of the ophiolitic basement and its sedimentary cover, to NE (i.e. ‘Apennine’) directed folds and thrusts. The Canetolo Nappe only shows Apennine vergent structures.
The Alpine vergent structures are considered to be developed during the Late Cretaceous to Palaeocene in an accretionary wedge associated with an east-dipping subduction zone. The first Apennine directed structures are low-angle extensional faults and cascading folds, indicating that the change to Apennine polarity resulted from gravitational collapse of the accretionary wedge during the Palaeocene to Eocene. Gravitational instability is considered to have resulted from a drastic decrease of subduction rate during the Palaeocene, which has led to extension and uplift of the wedge. The rapid decompression under isothermal to slightly decreasing temperature conditions of the high-pressure terrains in the Voltri Massif concurs well with this tectonic scenario.
Shear zones at the Laxford front, NW Scotland and their significance in the interpretation of lower crustal structure
Authors: COWARD M. P. 
Published: December 2007

The Lewisian rocks in the Scourie-Laxford region, NW Scotland, show variations in shear strains and associated structures on the southern (upper) margin of a zone of intense Laxfordian reworking. The Scourian block was thrust a large distance obliquely northwards over the northern Laxfordian gneisses as part of a Laxfordian episode of crustal thickening. This was followed by crustal extension, during which time the Scourian block moved down to the south. Granite sheets were intruded along the main shear zone in a dilational region at the base of a rotational extensional block.
The Laxfordian contractional and extensional deformation occurred under amphibolite facies conditions and analogies can be made with middle crustal structures inferred from deep seismic data. For example, structures produced during late Laxfordian crustal spreading can be compared to those seen on the BIRPS offshore Scottish data, which formed during Devonian basin development following Caledonian crustal thickening.
The Scourie–Laxford structures give an idea of fault kinematics at the brittle-ductile transition in the middle to lower crust. Steep faults pass down into more gently dipping ductile shears and then to a zone of anastomosing shears which accommodate the strains and rotations at the base of the rigid upper crust. The shears may concentrate along a more planar zone of deformation, forming a detachment or decoupling zone, below which the extension may be variable, depending on the mode of lithospheric stretching.
Palaeocomputing: keyboard to the past
Authors: FUNNELL B. M. , OWEN A. W. 
Published: December 2007

The Lyell Meeting ‘Palaeocomputing: Keyboard to the Past’ of
24
February
1988
celebrated the application of computing and, in particular, microcomputers and their associated numerical and graphical methods, to the analysis of problems in palaeontology and stratigraphy. Sir Charles Lyell was one of the earliest geologists to apply numerical and statistical methods deliberately to the resolution of problems in historical geology, so the resurgence of interest in such methods, fuelled by the advent of the new technology of computers, seemed an appropriate topic for a Lyell Meeting. The meeting was also the first to be sponsored by the Joint Committee for Palaeontology (supported jointly by the British Micropalaeonto-logical Society, the Geological Society, the Palaeontographical Society and the Palaeontological Association).

Several speakers contributing to the meeting had recently published or were about to publish the results reported at the meeting, and therefore only two new papers have been contributed to the Journal. This report gives the sources and extended abstracts of the other contributions.
The meeting was organized in three sections: (a) analysis and presentation of data; (b) analysis of shape; (c) reconstructing the past.
(a) Analysis and presentation of data

D. A. T. Harper & P. D. Ryan
commenced the meeting by presenting a paper on ‘The evolution of a statistical system for palaeontologists’ to be published in the
Journal.

They gave an historical review of the increasingly sophisticated use of statistics in palaeontology culminating in modern computer-based approaches. Harper & Ryan emphasized that user-friendly microcomputer software is ideal for
The nature and analysis of the stratigraphic record
Authors: SMITH D. G. 
Published: December 2007

Report of an Ordinary General Meeting of the Geological Society, organized by the Stratigraphy Committee and convened by D. G. Smith, held at Burlington House on 28 September 1988.
The purpose of the meeting was to bring together practitioners of as many as possible of the diverse current approaches to stratigraphic analysis, and to present stratigraphy as a dynamic and rapidly developing discipline central to our understanding of global processes. There has been an increasingly open recognition of the role of models as fundamental to progress in stratigraphy, with consequent diminution of emphasis on objective documentation of the stratigraphic record for its own sake. This more analytical approach is underlined by the greater use of numerical methods and by the linking of stratigraphy, through subsidence analysis at the basin-scale, to global-scale tectonic processes. Along with this, there has been a tendency for increasing divergence of approach between those in institutional research and those in exploration, for whom the predictive power of the model-driven approach is essential to their livelihood. The meeting succeeded, through 15 oral presentations and one poster, in giving a good impression of the variety of current approaches to stratigraphic analysis, from highly theoretical to explicitly field based.

The theme of the incompleteness of the stratigraphic record was introduced by
D. V. Ager,
who argued that the record is not even
representative
of the geological past.
E. A. Hailwood
pointed out the danger of circular reasoning in deducing stratigraphic incompleteness from the biostrati-graphic record, as the latter is
Late Caledonian extensional reactivation of a ductile thrust in NW Scotland
Authors: POWELL DEREK , GLENDINNING N. ROBERT W. 
Published: December 2007

Evidence is given for ductile extension across a fault zone located on the western seaboard of the Northern Highlands of Scotland. The fault zone lies within the metamorphic Caledonides and extensional movement occurred during the waning stages of Caledonian orogenic activity. An earlier phase of westerly directed overthrusting took place on the same fault zone at higher metamorphic temperatures but after the peak of Caledonian metamorphism. The compression may be broadly coeval with early displacements on the Moine Thrust Zone which probably lies offshore some 10 km to the northwest.
The extensional reactivation could relate to local crustal instability resulting directly from overthrusting; it may have been due to local gravitational collapse following overthickening of the crust. Alternatively the extensional movement may witness the onset of regional gravitational collapse of the orogen during the late Silurian to early Devonian. Reactivation accords with interpretations of the movement histories of similarly eastward dipping offshore faults recognized on seismic reflection profiles.
Disequilibrium trace element partitioning in Jurassic sparry calcite cements: implications for crystal growth mechanisms during diagenesis
Authors: HENDRY J. P. , MARSHALL J. D. 
Published: December 2007

Sparry calcite cements from Middle Jurassic limestones in Central England contain complex non-concentric zoning patterns produced by a combination of sector zonation and a sector-specific, lamellar or polygonal zonation. Electron microprobe analyses of individual zones within crystals document: (1) a sympathetic covariation of Fe, Mg and Sr between two non-equivalent sectors, and (2) episodic further increase of Sr contents coupled with exclusion of Fe, Mg and Mn within the more enriched sectors. Comparison of results from three different localities demonstrates the regional consistency of this pattern, although the magnitude of the differential trace element partitioning varies.
From combined petrographic and geochemical data the trace element variation in the crystals can be shown to bear no simple relationship with either (1) the chemical evolution of the 'bulk' precipitating porefluid, or (2) the relative overall growth rates of the different crystal faces. Previous sector zoning models based on crystal surface configurations and internal structure are unable to account directly for the geochemical patterns observed in this study. Differences between growth mechanisms on the crystal faces of the studied spars are likely to have exerted a significant influence on trace element partitioning. In particular, they offer a plausible explanation for the geometric and compositional characteristics of the sector-specific episodic zoning on the most enriched crystal faces. In general, crystal morphology and composition will be intimately linked by the growth mechanisms operating on different faces and by their response to changes in the diagenetic environment. The validity of diagenetic interpretations from ‘bulk’ geochemical analysis of sparry calcite cements thus rests upon a detailed analysis of any zonation that they contain.
Structural evolution of a subducted continental sliver: the northern Dora Maira massif, Italian Alps
Authors: WHEELER J. 
Published: December 2007

Continental crust of the Dora Maira massif was subducted, in part, to pressures of 30 kbar during early stages of the Alpine orogeny. A new investigation in a transect across the north of the massif has shown that much of the dominant foliation in the upper Dora Maira (Pellice) unit was formed at high pressures of the order of 11 kbar, but at lower pressure than the locally preserved relicts of eclogite-facies metamorphism. This dominant deformation phase produced large recumbent isoclinal folds with intensely flattened limbs in the Pellice unit basement and the overlying Permian–Mesozoic cover (now white augen gneisses and calcschists). The rocks were thus part of the upper crust prior to their subduction, unless an unrealistically large thickness of Mesozoic rocks (now removed) is hypothesized. The Pellice unit was later emplaced over the Chisone unit in greenschist facies conditions.
All shear sense indicators are top-to-west, implying a simple but prolonged history in which high-pressure units were emplaced westwards over lower pressure ones whilst being exhumed. The intense horizontal stretching recorded in the basement gneisses may have helped bring them closer to the surface by thinning. Indirect arguments suggest that such tectonic thinning is not, on its own, sufficient to explain the present setting of the eclogite units. One or more sheets of eclogite material may have been extruded from the Eoalpine subduction zone in addition. Such slabs would be bounded below by west-directed, and above by east-directed, shears. As the Dora Maira massif forms the structurally lowest Eoalpine eclogite unit in the Alps, the observed history is not incompatible with this model. East- or southeast-directed structures in the Alps are commonly identified as backthrusts, but an origin for some as the extensional shears predicted by this model should not be excluded.