bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural and metamorphic history of a segment of the Sesia-Lanzo zone, and its bearing on the kinematics of Alpine deformation in the western Alps
Authors: Ridley J. 
Published: April 2008

Summary
The Sesia-Lanzo zone of the western Alps is a zone of heterogeneous crystalline basement that was reworked and remobilised during the Alpine orogeny, partly under eclogite-facies metamorphic conditions. Reworking took place in three separable phases of deformation, each under different metamorphic conditions and each localised predominantly within a particular zone in the crust. The structures and fabrics produced by the phase of deformation post-dating the early eclogite-facies event, and associated with glaucophane-albite parageneses, suggest a strike-slip tectonic setting. Within the Sesia-Lanzo zone, up to a few tens of kilometres of N-S strike-slip movement is inferred for the late Cretaceous-early Tertiary. Movement within a strike-slip system may have been responsible for much of the uplift of the eclogitic rocks from 60 km depth.
On the age of deep crustal extensional faulting in the Ivrea zone, northern Italy
Authors: Brodie K. H. , Rutter E. H. , Rex D. 
Published: April 2008

Summary

High temperature fault zones in the Valle d’Ossola region of the Ivrea zone in northern Italy appear to accommodate extension of the deep crustal section.
40
Ar-
39
Ar age spectra indicate that this extensional event occurred prior to 280 Ma, and initiated a period of crustal thinning and cooling. Interpretation of the closure temperature in this system is dependent on grain size and cooling rate.
Kinematics of the western Mediterranean
Authors: Dewey J. F. , Helman M. L. , Knott S. D. , Turco E. , Hutton D. H. W. 
Published: April 2008

SummaryThe kinematic understanding of the relationship between relative plate motion and the structure of orogenic belts depends upon a knowledge of relative plate motion across the plate boundary system, the relative motion of small blocks and flakes within the system, an evaluation of orogenic body forces, and an understanding of the thermomechanical evolution of the upper part of the orogenic lithosphere in determining strength and detachment levels. We have built a preliminary model for the Cenozoic kinematic evolution of the western Mediterranean oceanic basins and their peripheral orogens that integrates (1) the motion of Africa relative to Europe based upon a new study of Atlantic fracture zones using SEASAT data and the Lamont-Doherty magnetic anomaly database, (2) a new interpretation of the rotation of Corsica/Sardinia and the opening of the Balearic and Tyrrhenian oceanic basins, (3) sedimentary facies sequences in the Apennines, Calabria, and Sicily, and (4) Apennine/Calabrian structure and structural sequence.
Alpine thermal evolution in the central and the western Alps
Authors: Hunziker J. C. , Desmons J. , Martinotti G. 
Published: April 2008

Summary
In the western and central Alps, high-pressure assemblages dated as Eoalpine are distributed in the Pennine, Piemonte and Austro-Alpine units. The starting point of metamorphism must have been at low temperatures as both pre-Alpine metamorphic basement and Mesozoic sediments have been involved. In those parts of the Sesia-Lanzo zone where no later Tertiary high temperature overprint modified or obliterated the early Alpine history, the Eoalpine peak of metamorphic pressure was reached at about 110 Ma, the temperature peak at 85 Ma and a cooling down to 300°C at 60 Ma. The radiometric evidence gives insight into the Cretaceous orogenic events which also include penetrative deformation, nappe thrusting and uplift. The Pennine and Austro-Alpine units are both considered to have been located south of the Jurassic oceanic gap and to have formed parts of the fragmented northern margin of Gondwana.
The Tertiary Mesoalpine and Neoalpine metamorphic events in the western Alps are separated in time by 32–30 Ma magmatic intrusions. In the central Alps both events are distinguished on the basis of an additional schistosity connected with the second event. The Neoalpine ages are considered as resulting from the Mesoalpine thermal conditions outlasting the Mesoalpine time and, in the Simplon region, as recrystallization ages related to late mylonitization.
The convergence rates during the Cretaceous orogenesis were one order of magnitude greater than during the Tertiary orogenesis. Sedimentation in some Pennine units continued through Eoalpine times until Palaeogene; this is interpreted as resulting from the imbrication of blocks of different evolution in Tertiary times.
Unravelling the thermo-tectonic evolution of the Alps: a contribution from fission track analysis and mica dating
Authors: Hurford A. J. , Flisch M. , Jäger E. 
Published: April 2008

Summary
Fission track analysis of apatite and zircon, and K-Ar and Rb-Sr dating of white mica and biotite provide time and temperature constraints for direct dating of deformation phases and in establishing cooling and uplift rates and patterns. In the western Alps, timing of the Sesia-Lanzo zone Eoalpine metamorphic temperature peak is confirmed between 110 and 85 Ma, possibly preceded by the pressure maximum. The slowly cooling Sesia zone reached 200–250°C by ∼33 Ma and ∼100°C by ∼25 Ma, with fast uplift during the late Oligocene to Miocene Insubric phase; cooling in the adjacent Gran Paradiso Massif occurred slightly later, with fission track zircon and apatite ages of 30±2 and ∼22 Ma respectively. No evidence to support an inverted metamorphism of the Gran Paradiso was found. In the Silvretta nappe (E Alps) three different uplift styles and periods are distinguished: uparching between 110 and 35 Ma, homogeneous uplift during 35 and 2 Ma and recent eastward tilting. The data imply that updoming of the Engadine Window occurred before ∼31 Ma. In the central Lepontine Alps, a uniform late Neogene to recent mean uplift rate of ∼0.5 mm/a succeeded early Miocene uplift at ∼2.2 mm/a in the southern steep belt (root zone), the latter resulting from a major phase of backthrusting of the central Alps along the Insubric Line. Clear-cut time-temperature paths are not found for the Suretta Nappe (central Alps): fission track data delimit the Miocene cooling, but speculative interpretation of phengite-mica and K-Ar amphibole ages suggests that the main deformation (possibly Ferrera phase) occurred between 55 and 36 Ma. Schematic models are advanced to describe the asynchronous thermal evolution of different parts of the central Lepontine Alps.
Time and place in Alpine orogenesis — the Fermor Lecture
Authors: Hsü K. J. 
Published: April 2008

Summary
Alpine geologists have suggested that the main structures of the Alps have been formed by a late Eocene event, which lasted at most a few million years. Data on earlier and later deformations have been interpreted as the evidence of Eoalpine and Neoalpine phases. The supposedly episodic nature of the Alpine orogenesis has been considered to be a fundamental contradiction of the seafloor spreading which predicts slow and gradual movement.
The purpose of this contemplation on time and place in Alpine orogenesis is to point out that the paradox is man-made: the interpretation of the episodic nature of orogeny is a relic of the defunct catastrophic theory of orogeny of Elie de Beaumont (1831). Divorced from that discredited assumption, the orogenic data in the Alps are consistent with a postulate of continuous orogenic deformation since the early Cretaceous.
The Alps is a collision-type of orogen. Using the late Eocene collision-event as a time marker, we can recognize two major stages of deformation: the Eoalpine subduction, and the Neoalpine post-collisional. The geological evidence is consistent with the postulate of a gradual build-up of the Alpine edifice, consequent upon the approach between two continental blocks since the early Cretaceous and continuing deformation after the late Eocene collision.

The Eoalpine subduction should have started 130 Ma ago, some 50 Ma before the approach of the African and European Plates. This and other geological evidence necessitates an assumption of relative movements among 3 plates to explain the Alpine orogenesis; the middle Mediterranean Plate (M-plate) had movements independent of Africa since 130 Ma
bp
. The kinematics of plate displacements in the Alpine-Mediterranean region have been reconstructed, using the data on Atlantic magnetic lineations to fix the positions of Africa and Europe, and geological evidence to guide the movement of the M-Plate. This kinematic analysis, harmonized with geological data, indicates that the Alpine Orogenesis resulted from the relative movement between the European- and M-Plates at rates of about 1 centimetre per year. There is no contradiction between Alpine geology and the plate-tectonic theory.
Phanerozoic ironstones: an introduction and review
Authors: Young T. P. 
Published: April 2008

Summary
Ironstones, particularly ooidal ironstones, have long fascinated sedimentary geologists and have generated an enormous variety of interpretations, but have remained poorly understood. A recent upsurge in interest in this group of rocks has generated much new information derived from many different disciplines within the earth sciences.
The first part of this introduction examines recent advances, and attempts to produce a synthesis of them, with particular reference to the genesis of marine ooidal ironstones. Current models for the formation of marine oolitic ironstone-formations are discussed, and a working model based on various lines of recent research is proposed. This model invokes the intrasedimentary formation of berthierine ooids in marine environments during post-oxic diagenesis. The ooids may be mechanically modified and mineralogically transformed by reworking, as well as by later diagenesis. Goethite ooids may be oxidized berthierine ooids, reworked lateritic ooids or primary grains. The formation of oolitic ironstone-formations is favoured by a break in clastic sediment supply, continued supply of iron and physical reworking. Many sedimentary environments may supply these parameters, but changes in sea level leading to the flooding of land masses and the reworking of suitable terrestrial soils may be both an important source for the iron and provide a break in clastic sediment supply.

In the second part of this introduction the terminology and classification are discussed, and conventions proposed. The term
berthieroid
is introduced as a non-specific term for material of undetermined berthierine or chamosite composition. The term
ironstone
is proposed as a petrological term and as an informal lithostratigraphic term. A deposit composed of
ironstones
may be termed an
ironstone-formation
. It is recommended that a ‘Dunham’ style of classification is employed petrographically, with -
ironstone
replacing the -
stone
of the original carbonate classification. The nomenclature of allochems in ironstones is also discussed. A glossary of ironstone terminology is provided.
Aspects of iron incorporation into sediments with special reference to the Yorkshire Ironstones
Authors: Spears D. A. 
Published: April 2008

Summary
Ironstones of former economic value occur in both Coal Measures and Jurassic sequences in Yorkshire. The distribution of pyrite and siderite in the Coal Measures sediments is explained by the stability relationships between the two minerals and the controls on the rate of pyrite formation, particularly the sulphate availability, but also involving the amount and quality of metabolizable organic matter and the iron availability. In marine black shales early diagenetic pyrite formation may have immobilized much of the available iron, whereas in non-marine sediments iron was available over much longer diagenetic periods to form siderite in the mudrocks and pyrite in the coals. The qualitatively more important siderite forms clay ironstones by a process of diagenetic redistribution and concentration of original iron. In the marine Jurassic sediments pyrite and siderite again show a cyclic distribution. The same explanation holds for pyrite in the marine black shales, but in the grey shales loss of metabolizable organic matter under oxic conditions mainly allows post-oxic reactions, which includes reduction of iron but little sulphate reduction. In the oolitic ironstones efficient loss of organic matter in an important oxic zone is seen as a key factor. The oolitic ironstones do represent an original enrichment of iron in contrast to the other ironstones considered. Post-oxic reactions are thought to be important and produced berthierine and siderite. The possibility of some diagenetic enrichment of iron in the oolitic ironstones should be recognized.
Temporal patterns among Phanerozoic oolitic ironstones and oceanic anoxia
Authors: Van Houten F. B. , Arthur M. A. 
Published: April 2008

Summary
The stratigraphic distribution of Phanerozoic oolitic ironstones corresponds to temporal patterns recorded in common detrital deposits. These patterns, in which ironstones share significant associations with black shales, comprise successively smaller-scale sequences, each defined mainly by major transgressions and regressions, changing rates of erosion and sedimentation, and inter-regional unconformities.
Two 300 Ma episodes of continental dispersal and Pangaeic assemblage of cratons encompassed the maximum rise and fall of sea level. Deposition of ironstones and black shales was essentially limited to 150–170 Ma phases (Ordovician-Devonian; Jurassic-Palaeogene) marked by extensive epicontinental seas and ineffective oxygenation of deep-water masses.
Smaller-scale tectonically distinct phases of cratonic submergence, several to many tens of Ma long, were separated by briefer erosional intervals, or by longer episodes of oscillating conditions during which several interregional unconformities developed. Widespread submergence generally favoured major production of ironstones and black shales. Within this framework both were especially common during the Ordovician and Jurassic periods. A hypothetical quasiperiodic (c. 32 Ma) pattern of global climate change was accompanied by recurring relatively high sea level and expansion of oxygen-depleted water masses. Many of these phases led to widespread development of both ironstones and black shales.
Episodes of fluctuating coastal onlap one to several Ma long reflect variations in sea level, sediment supply, and/or subsidence. Major successions of ironstones repeated on a similar time scale were limited to ten tectonic provinces comprising foreland basins, cratonic margins and unstable cratons, and intracratonic basins. During the favourable phases black shales and ironstones were deposited alternately in some successions.
In many of the major successions an ironstone developed between each of several repeated small-scale sequences in a cadence of several hundred thousand years. Ironstones in these asymmetric units record a long lapse in normal sedimentation during the initial stage of renewed transgressions that commonly spread organic-rich mud across the shelf. The repeated association of ironstones and black shales with sequences of common sedimentary rocks helps constrain speculation about conditions controlling their origin, and suggests that ironstones reflect the more local development of productive conditions.
Eustatically controlled ooidal ironstone deposition: facies relationships of the Ordovician open-shelf ironstones of Western Europe
Authors: Young T. P. 
Published: April 2008

Summary
Ooidal ironstones are a characteristic feature of the Ordovician successions of south-west Europe and adjacent areas. They occur in shallow marine clastic sequences deposited on a broad low-topography shelf. Three stratigraphic intervals have a particularly widespread development of ironstones: the early Llanvirn, the early Caradoc and the early Ashgill. These intervals, corresponding to periods of major global eustatic sea-level rise, are marked by the development of thin, but persistent, ooidal ironstones even in relatively offshore areas. The ironstones produced by these three events have been studied in the previously contiguous areas of central Portugal and Armorica.
The development of the ironstones, and the nature of the successions within which they occur, show remarkable similarities among the three horizons; this recurrence of similar sedimentary facies defines a cyclicity. In each of these ‘first-order’ cycles the upper part is characterised by the occurrence of a second order of cyclicity, represented by asymmetric coarsening— and thickening—upwards sequences of siltstone and sandstone tempestites, commonly capped by phosphatic conglomerates. The latest ‘second-order’ cycle in each case is characterized by a more distal sequence of dark mudstones with graptolites. The chamositic ooidal ironstones lie disconformably above these upper mudstone-dominated cycles, and are interpreted as forming during ‘second-order’ transgressions late in major global transgressive events. Both ‘first-’ and ‘second-order’ sedimentary cyclicity is attributed to eustatic variation. The ‘first-order’ eustatic cycles have a period of 10–15 Ma, and largely correspond to the international stratigraphic series, while the period of the ‘second-order’ cycles is estimated as 0.2–0.5 Ma.
Stratigraphic and environmental patterns of ironstone deposits
Authors: Bayer Ulf 
Published: April 2008

Summary
Evaluation of the accumulation of Minette- and Clinton-type ironstones in terms of stratigraphic successions and regional facies patterns provides a sequence of types from condensed ‘iron shot’ muddy carbonates over barrier bars to distal tempestite deposits. A lagoonal origin of iron-oolites is derived and discussed. Biogenetic carbonate production and a biogenic contribution to iron-oolite formation, as well as replacement patterns of carbonate by iron-minerals indicate that (1) ironstone formation is related to environmental changes in the course of transgressive-regressive cycles and (2) formation of iron-ooids occured in environments with short term fluctuations between oxidizing and reducing conditions. Adopting this dynamic viewpoint allows dissolution and precipitation of iron ‘side-by-side’ without contradicting classical models.
The application of analytical transmission electron microscopy to the study of oolitic ironstones: a preliminary study
Authors: Hughes C. R. 
Published: April 2008

Summary
Analytical transmission electron microscopy (ATEM) has been used by the author to obtain textural, crystallographic and quantitative chemical information from examples of berthierine-rich and chamosite-rich oolitic ironstones. Individual phases were often found to be too small to have been readily analysed by other techniques. Berthierine laths (of the order of 20 × 500 to 1000 nm) and goethite grains (of the order of 25 nm in diameter) were found to exhibit unorientated microtextures, which were independent of both depositional and oolitic fabrics. Chemical analyses of berthierines revealed fairly uniform compositions regardless of textural association. Chemical data from the chamosite-rich samples appeared analogous to that of the berthierine-rich material, although average crystal sizes were found to be much larger (chamosite laths varied from 0.1 × 1.5 µm to 0.5 × 2 mµ). The compositional data suggest that the chamosite-rich oolitic ironstones are simply the late stage diagenetic (or low grade metamorphic) recrystallized equivalents of berthierine-rich precursors. No direct evidence indicative of the mode of origin for berthierine and goethite ooliths was found. It is suggested that ancient ironstone ooliths were probably formed via similar mechanisms to those which generate modern and ancient carbonate ooliths, although obviously the original sediment and interstitial fluids would have been very different.
Iron-rich ooids, their mineralogy and microfabric: clues to their origin and evolution
Authors: Kearsley A. T. 
Published: April 2008

Summary
The controversy surrounding oolitic ironstone origins has been prolonged by a lack of published discriminatory characters which could be applied to determine the sedimentary processes responsible for the genesis of individual iron-rich ooids. This is in part due to the limitations of optical petrography and has led to confusion between authors as to the nature of the ooids each is describing. A new and simple descriptive system which documents ooid mineralogy and fine structure has been used to distinguish ooids of different origins and a classification of iron-rich ooids into three broad mineralogical categories is proposed in this paper. These Fe-oxide/hydroxide, berthierine/chlorite and siderite dominated groups are further divided by characteristic textural criteria into 15 minor categories. The abundance of ooids which easily fit the three bulk mineralogical categories probably reflects common diagenetic modifications, rather than preservation of discrete primary phases. The wide variety of ooid microfabrics observed by transmitted light microscopy, secondary electron, backscattered electron and X-ray emission imagery reflect differing modes of ooid accretion and early diagenesis, in addition to later diagenetic and weathering processes.
Combined mineralogical and textural classification of individual ooids can indicate the relative importance of individual processes (such as lateritic ooid/pisolith growth, replacement of carbonates by berthierine or primary berthierine precipitation) in the generation of a particular ironstone.
The origin of the Lower Jurassic Cleveland Ironstone Formation of North-East England: evidence from portable gamma-ray spectrometry
Authors: Myers K. J. 
Published: April 2008

Summary
The distribution of K, U and Th in the Cleveland Ironstone Formation, measured by gamma-ray spectrometry, is found to be useful in investigating the origin of oolitic ironstones. The oolitic ironstone seams are enriched in Th and depleted in K relative to the interbedded mudstones which show a close correlation between Th and K. The enrichment of Th in the ironstone seams represents a primary depositional rather than a diagenetic process, and the Th-enriched material must have been transported to the site of ironstone deposition from elsewhere. The values of Th (20–45 ppm) and the Th/K ratios (20–100) recorded in the ironstone seams are consistent with the original Th-enriched material being kaolinitic/bauxitic clay from a lateritic weathering source.
Antarctica’s place within Cambrian to Devonian Gondwana
Authors: Cocks L. R. M. 
Published: April 2008

Abstract
Analysis of various fossil groups, in particular brachiopods, graptolites and trilobites, from Gondwana as a whole, which included much of what is now southern Europe, southern Asia, Africa, South America, Australasia and Antarctica, has determined not only the margins of the Gondwanan palaeocontinent in the early and middle Palaeozoic, but also the relative palaeotemperatures and the probable palaeo-latitudes. The patchy faunal record from Antarctica is reviewed from Cambrian to Devonian times, and this consists of well-dated Early, Middle and Late Cambrian shelly faunas with eastern Gondwanan affinities and deposited under tropical conditions. By contrast, there are no proven Ordovician fossils known and only one disputed Silurian record of two coral specimens from the Beardmore Glacier moraine. In early Devonian times, well-dated Emsian shelly faunas of Malvinokaffric affinity are known from the Horlick Range and there is a diverse Middle Devonian fish fauna from Victoria Land. From these records it can be deduced that, as the large Gondwana plate slid over the contemporary South Pole, the palaeo-latitude of Antarctica slowly increased from tropical to high temperate from Cambrian to Devonian times.