bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Northern Igneous Complex of Guernsey, Channel Islands
Authors: Topley C. G. , Brown M. , D’Lemos R. S. , Power G. M. , Roach R. A. 
Published: April 2008

Abstract
The Northern Igneous Complex of Guernsey consists of four intrusive bodies, the St Peter Port Gabbro, the Bordeaux Diorite Complex, the Cobo Granite and the L’Ancresse Granodiorite. Although these bodies can be shown to be emplaced in the order given, evidence suggests that a small time span separated the intrusive events, which occurred around 500 Ma ago. The geochemistry of the complex is calc-alkaline, compositions from olivine gabbro to granite being represented. The granitic rocks have compositions typical of volcanic arc granites. The St Peter Port Gabbro is a layered body, with layering present on three different scales. The layering and the geochemical variation can be explained by invoking magmatic processes. The Bordeaux Diorite Complex consists of a range of lithologies from meladiorite to granodiorite, the magmas of which are shown to have been contemporaneously mobile, although magma mingling as opposed to mixing has occurred. Despite their contemporaneity, the different magmas of the Bordeaux Diorite Complex are not related directly to each other by fractionation. The Cobo Granite is homogenous but has complex relationships with the Diorite Complex. At the northern margin of the Granite a zone of granite/diorite magma mixing occurs. Details of the process involve local chilling, breaking of the chilled carapace followed by comingling and partial mixing. Geochemistry reflects the mixing process. The L’Ancresse Granodiorite is lithologically and geochemically homogeneous. Its western contact with the Diorite Complex is faulted, but the eastern contact again shows a variety of granodioritic and dioritic lithologies which have led others to invoke processes of magma mixing and metasomatism. It is argued here, however, that these lithologies are part of the variation inherent in the Bordeaux Diorites, rather than having been produced during the emplacement of the Granodiorite.
The post-tectonic Cadomian plutonic complex of La Hague, Manche, N. France
Authors: Power G. M. , Brewer T. S. , D’Lemos R. S. 
Published: April 2008

Abstract
In the La Hague region, NW of Cherbourg, France, the post-tectonic Cadomian Northern Granites Complex consists of seven rock units which range in composition from diorites to trondhjemite and K-feldspar granite. With the notable exception of the Ecuty Granite, the units tend to become mineralogically more evolved with decreasing age. They are calc-alkaline and have the characteristics of the products of volcanic arc magmatism. In detail, their geochemical differences support magma formation from several different sources.
The Ecuty Granite gives a Rb-Sr whole rock isochron age of 527 ± 4 Ma, the St Germain Granite, 515 ± 12 Ma and the Cap de la Hague Granodiorite, 477 ± 8 Ma. Thus this igneous activity spanned at least 50 Ma of Cambro-Ordovician time. This, together with evidence of plutonic sequences of similar character and age in Guernsey and Jersey supports the view that post-tectonic Cadomian activity continued well into lower Palaeozoic times in the northern part of the Armorican Massif.
The geochemical character of late Cadomian extensional magmatism in Jersey, Channel Islands
Authors: Lees G. J. 
Published: April 2008

Abstract
An episode of magmatism, which may represent the last igneous phase attributable to the Cadomian orogenic cycle, is found in southern Jersey, Channel Islands. A zone, some 3 km wide, of intensive dyke injection, the Jersey Main Dyke Swarm, cuts across post-orogenic calc-alkaline plutons, though showing a close temporal link with their emplacement.
The nature of the dyke swarm magmatism is dominantly but not exclusively basic. A clear acid—basic bimodality is present with very little intermediate material. Although subjected to varying degrees of alteration under low-grade metamorphic conditions, the primary nature of the rocks is often preserved. All those having a basaltic composition are olivine-normative, but show a high-K calc-alkaline character. Fairly high LREE enrichments are present. MORB-normalized spidergrams confirm that the magmatism was of a mature calc-alkaline type, similar to that generated at active continental margins such as the Andes.
The presence of the swarm indicates a period of late post-orogenic crustal extension sub-parallel to the NE-SW strike of the proposed Cadomian active continental margin in the Armorican Massif. It could represent injection of the last remnants of magma from an already decayed subduction zone system into a newly cratonized environment.
Basement-cover relationships of a reactivated Cadomian mylonite zone: Rosslare Complex, SE Ireland
Authors: Murphy F. C. 
Published: April 2008

Abstract
Recurrent ductile and brittle displacements characterize the steep boundary mylonite zones that enclose Proterozoic gneisses of the Rosslare Complex in SE Ireland. The northern exposed limit of the Complex is a wide displacement zone containing greenschist facies mylonites derived from two protoliths: (a) basement gneisses and (b) supracrustal metasediments. Important sinistral transcurrent movements produced these mylonites probably during the late Precambrian. Docking of the Precambrian ‘Monian’ sediments to the Rosslare basement may indicate remobilization of a basement/cover relationship. The transpression, uplifted and eroded the mylonites into early Palaeozoic (?Cambrian and Arenig) overstep sediments. Renewed dip-slip displacement, possibly during the Ordovician, was distributed through the mylonites and deformed the sedimentary cover rocks. Finally, the initially wide displacement zone along the northern boundary of the Complex narrowed to discrete brittle faults during subsequent Palaeozoic reactivations. Following pre-Arenig ductile sinistral shear along the probable southern margin of the Complex, each bounding fault strand had divergent histories which involved decoupling of an anastomosing transpressive system.
Precambrian successions in SW Iberia: their relationship to ‘Cadomian’ orogenic events
Authors: Quesada Cecilio 
Published: April 2008

Abstract
Despite extensive reworking in Devonian and Carboniferous times, two major deformational events taking place in late Precambrian times may be recognized in the SW Iberian Massif. These have been collectively referred to as ‘Cadomian’ or ‘Pan-African’. The Precambrian successions may be subdivided into pre-orogenic and syn-orogenic groups on the basis of their tectonostratigraphic evolution with respect to the Cadomian orogeny. The pre-orogenic successions (roughly mid-upper Riphean) represent different parts of a miogeoclinal wedge, the basement of which is not known as yet. Polyphase deformation and variable degrees of metamorphism accompanied the first Cadomian event.
The syn-orogenic successions (roughly upper Riphean-Vendian) were laid down during and after the first Cadomian event and were in turn deformed and slightly metamorphosed by the second single-phased deformation. These correspond to two distinct types: calc-alkaline igneous successions and flysch-like deposits, that can be interpreted respectively as an orogenic continental arc suite and a foreland basin fill, on the basis of their geochemical and sedimentological characteristics.
Comparative geology and mineralogy of the southeastern United States and Togo phosphorites
Authors: Van Kauwenbergh S. J. , McClellan G. H 
Published: April 2008

Abstract
The physical and mineralogical characteristics of the southeastern United States and Togo phosphorite deposits are the result of both primary depositional factors and secondary diagenetic processes. The North Carolina phosphorites appear to be ‘unaltered’ or are in the first stages of alteration. Both the Florida and Togo phosphorites have resulted in the removal of mineral species (primarily carbonates), systematic decarbonatization of the carbonate-fluorapatite, the development of iron and aluminium phosphates, and clay mineral alteration profiles.
Microbial mediation in phosphatogenesis: new data from the Cretaceous phosphatic chalks of northern France
Authors: Lamboy Michel 
Published: April 2008

Abstract
Detailed petrographic study of the Upper Cretaceous phosphatic chalks of northern France, particularly by scanning electron microscopy, shows that phosphate occurs predominantly as phosphatized bacterial remains. Shiny phosphatic crusts on hardgrounds and anisotropic phosphate coatings on grains are interpretated as phosphate mineralized microbial (‘microstromatolitic’) structures. Phosphatic remains of ovoid bacteria and of microbial colonies with botryoidal surfaces have been observed in chambers of foraminiferans and bryozoans, and within other bioclasts, and occur as pore linings in peloids, coprolites and lenses of phosphatic chalk incorporated into hardgrounds. The microbial community which formed the crusts and grain coatings developed by surface accretion, whereas the other community grew solely in the intragranular porosity of grains and in the extragranular porosity of semilithified sediments. Analysis of these two types of microbial growth, which have also been documented from other phosphorite deposits, permits a better but as yet incomplete understanding of the mechanisms of phosphatization.
Pebbly phosphate and granular phosphorite (Late Cretaceous, southern Israel) and their bearing on phosphatization processes
Authors: Lewy Zeev 
Published: April 2008

Abstract
Phosphate nodules, including common mineralized internal moulds of macrofauna, are found only at certain levels in the chalky, locally bituminous Ghareb Formation (uppermost Campanian-Maastrichtian) of southern Israel. The microstructure of these nodules suggests that they consist of marine sediment cemented by a microbially-mediated apatite, precipitated locally in protected microenvironments, e.g., within partly closed burrows and shells, or within the upper sediment layer. The globular microstructures commonly recognized in the phosphate cements of the pebbly phosphates are regarded as mineralized cells of endobenthic micro-organisms. The global occurrence of pebbly phosphate in diverse lithofacies throughout the geological column indicates the tolerance of these globular micro-organisms to a wide range of ecological conditions.
The grains in the Upper Cretaceous phosphorites of the Negev (southern Israel) consist of bone fragments, phosphatized faecal pellets and ovular grains of different types. The commonest variety of ovular grain consists of microcrystalline phosphate (microphosphate) containing relics of globular microstructures, either forming the whole grain, coating a foraminifera or bone fragment, or cementing small clasts. The latter types resemble the pebbly phosphates and can be regarded as micronodules. The matrix of these granular phosphorites is mainly micritic, and in places argillaceous. In some Negev phosphorites the ovular grains and their matrix consist mainly of loosely packed tubules. These tubular microstructures resemble mineralized filaments of microphytes which form microbial mats on modern shallow seafloors lying within the photic zone. The origin of these granular phosphorites is discussed, and a comparison with the pebbly phosphates indicates that different ecological controls and microbial mediators resulted in the different kinds of phosphate bodies.
Since most of the phosphate matter can be related to microbial activity, it is doubtful whether direct replacement of solid carbonate by phosphate contributes significantly to phosphogenesis in sediments. It is suggested, however, that in many deposits phosphate-precipitating micro-organisms have penetrated and mineralized the borings of algae and other endolithic groups, or have filled dissolution cavities within lithified carbonates.
Geological significance of carbonate substitution in apatites: Israeli phosphorites as an example
Authors: Nathan Y. , Soudry D. , Avigour A. 
Published: April 2008

Abstract

The extent of carbonate for phosphate substitution in francolite (carbonate-fluorapatite) was measured in 177 selected phosphorite samples of Santonian to Eocene age from Israel. The results show that unaltered apatites from different stratigraphic positions have different CO
2
concentrations while those from the same stratigraphic level have a relatively narrow range of concentrations. As a rule phosphorite samples from rocks with a low P
2
O
5
content have a higher carbonate substitution than those from rocks with a high P
2
O
5
content. Apatites from the carbonate-rich Santonian-Campanian Menuha Formation contain on average 5.5% CO
2
, while the average content of the apatites from the phosphatic Campanian-Maastrichtian Mishash Formation is 3.7%. These changes are probably a reflection of the early diagenetic environment and, more specifically, are a function of the varying composition of the interstitial waters.

Epigenesis and/or weathering bring about a significant decrease in the CO
2
concentrations causing an overprint which masks the above picture. Therefore, it is possible to use a CO
2
value for geological interpretation only after making a petrographic analysis, in order to distinguish between early diagenesis and late epigenetic processes.
Depositional sequences of the Duwi, Sibâîya and Phosphate Formations, Egypt: phosphogenesis and glauconitization in a Late Cretaceous epeiric sea
Authors: Glenn Craig R. 
Published: April 2008

Abstract
Sedimentary facies, depositional environments and stratigraphic relationships of the Upper Cretaceous Duwi, Sibâîya and Phosphate Formations in Egypt are summarized in order to shed light on the origins and interrelationships between phosphorites and their commonly associated facies. The distribution of phosphorites, glauconitic sands, organic carbon-rich shales, cherts and porcelanites, and bioclastic and fine-grained limestones are correlated in both space and time across the central phosphorite provenance of the country. The correlations are linked by means of sequence stratigraphic analysis and are tied to global eustatic sea-level curves.
Two main depositional realms are inferred from the Campanian lithofacies assemblages: (1) a deeper-water hemipelagic environment accompanying maximum transgression dominated by deposition of phosphorites, organic carbon-rich shales and biosiliceous sediments, which, after maximum flooding, shoals upwards into (2) a progradational stage accompanying sea-level fall, during which oyster banks with brackish back-reef sediments (Eastern Desert) and deltaic sediments (upper Quseir Variegated Shale, Nile Valley) dominated eastern portions of the phosphorite belt, while greensands were reworked seaward from earlier inner shelf sediments in the west (Western Desert). These depositional realms encompass (1) transgressive to lower highstand systems tracts and (2) upper highstand to lowstand progradational wedge system tracts, respectively. The reoccurrence of lower Maastrichtian phosphatic shale, marl and associated phosphorite lithofacies at the top of the sequence indicates repetition of the sedimentary cycle.
Both phosphorites and glauconitic greensands appear to be the result of current winnowing and reworking of authigenic grains from previously deposited sediments. The resulting deposits range in scale from thin lag layers, to amalgamated beds, to giant sand waves up to 10 m thick. In the Egyptian setting, the common factors linking massive phosphorite and glauconite occurrences may have been the co-occurrence of humid climate, deep lateritic weathering in hinterlands, anoxic bottom waters on the inner shelf, and high fluvial discharge rates of phosphorus and iron. Superimposed on these factors were influences of cross-shelf currents necessary to concentrate authigenic precipitates, and a sea level change, which acted to markedly reduce the diluting effects of siliciclastic detritus during rapid sea level rise, as well as vertically stack ‘authigenic facies’ during sea level fall.
Clay minerals and phosphorite genesis in the Upper Cretaceous of the northern Siberian Platform
Authors: Zanin Yu. N. , Zverev K. V. , Solotchina E. P. 
Published: April 2008

Abstract
Nodular phosphorites are common in the Turonian to Maastrichtian deposits (sands, silts and clays) of the Yenisei Mouth Depression in the north of the Siberian Platform. Only the silty clays of Campanian age are non-phosphatic. Study of the fine-grained fraction (<2 µm) of these deposits demonstrates that the phosphorite-bearing parts of the succession contain similar clay mineral assemblages. These consist of kaolinite and chlorite, with a small but constant admixture of gibbsite, and in some cases a small amount of montmorillonite. In the non-phosphatic rocks of the Campanian, clay minerals consist only of montmorillonite and chlorite. Kaolinite and gibbsite are completely absent. It is argued that the clay mineralogy and other data suggest that the formation of the phosphorites was linked to the removal of phosphorus from continental areas during periods of intense weathering in a humid subtropical climate.
Phosphogenic events and skeletal preservation across the Precambrian-Cambrian boundary interval
Authors: Brasier M. D. 
Published: April 2008

Abstract
Refined biostratigraphic data from India and new data from Iran confirm that several major phosphogenic events took place within the Precambrian-Cambrian boundary interval across southern and central Asia. The palaeoceanographic setting of these event is briefly reviewed with reference to changes in the biosphere, where it is shown to have coincided with a widespread radiation of skeletons of diverse mineralogy (siliceous, apatitic, aragonitic, calcitic). Although a connection between palaeoceanographic changes and biomineralization cannot yet be demonstrated, the possibility that phosphogenesis enhanced the fossil record at this point is tested.
Preliminary criteria are put forward and illustrated for the recognition of primary phosphatic skeletons, secondarily phosphatized organic remains and secondarily phosphatized carbonate skeletons. This latter category comprises a major proportion of phosphatic small shelly fossils in the Chinese and Iranian sequences. Three kinds of phosphatic taphofacies are then distinguished for early skeletal biotas: residual phosphatic, phosphatized carbonate and phosphatized organic facies (i.e. lägerstatten conditions). In several phosphogenic regions, the skeletal fossil record begins with residual phosphatic assemblages, followed by phosphatized carbonate taphofacies. Such diagenesis played an important role in enhancing the fossil record at this time because the first skeletons were thin (5–40 μm) and vulnerable to neomorphism in dolomitic or clastic facies. Phosphatized organic remains appeared locally during the major phosphogenic events, perhaps associated with more anoxic seafloor conditions that supressed the shelly calcareous benthos.
Sedimentary and sea level changes during glacial cycles and their control on glacimarine facies architecture
Authors: Boulton G. S. 
Published: April 2008

Abstract
In part 1 a simple sedimentation model is presented in which subglacial icecontact, proglacial ice-contact, inner and outer proximal, and distal glacimarine zones are distinguished. In these, facies associations are controlled by: (a) distance from the glacier and the diffusion of glacially-derived water masses and their suspended sedimentary (including berg-transported) debris into nearby oceanic waters; (b) the form and depth of the sea bed, and its position in relation to the continental margin (which help determine water mass character and tidal, wave-driven and geostrophic currents and the stability of sea-bottom sediments).
In part 2 a model of eustatic/isostatic sea level change in the vicinity of a generic ice sheet through a whole glacial cycle is developed. The sedimentation model from part 1 is linked to the sea level model to predict patterns of marine sedimentation near to an ice sheet through a glacial cycle, in inner shelf, outer shelf and continental slope environments.
Comparisons are made between theoretical models and observed patterns of glacimarine facies architecture produced during the last glaciation of Britain, continental Europe and Spitsbergen. The phase relationship between local ice sheet advance and retreat and that of the Laurentide ice sheet, the principal determinant of global eustatic change, is a major determinant of large scale sedimentation patterns.
Modelling rates of sedimentation from icebergs
Authors: Dowdeswell Julian A. , Murray Tavi 
Published: April 2008

Abstract

Icebergs transport debris from ice masses into the glacimarine environment, but iceberg production, debris content and sedimentation rate will vary with glacier dynamics and the nature of marine waters. A model incorporating glaciological and oceanographic parameters calculates the flux of debris calved in icebergs, iceberg melt rates and sedimentation rates with distance from calving tidewater ice fronts. The flux of basal debris calved through a 1 m width of tidewater margin is (
h
d
c
/100)
v
c
, where
h
d
and
c
are basal debris-rich ice thickness and sediment content (%), and
v
c
is iceberg calving rate. Iceberg basal melting for any horizontal interval (d
x
) away from the calving glacier is dy = (
M
b
d
x
)/
v
b
, where
M
b
is iceberg melt rate and
v
b
is horizontal iceberg velocity. Sediment release for any
x
increment depends on iceberg debris concentration and previous berg melt history. Model parameters vary with the nature of climatic conditions, on a continuum from cold polar environments (e.g. High Canadian Arctic, Antarctic Peninsula), through sub-polar environments (e.g. Baffin Island, Svalbard) to more temperate environments (e.g. SE Alaska). These parameters include: glacier flow velocity, glacier thermal regime, basal debris-rich ice thickness, and marine water temperature. Model results suggest that iceberg sedimentation rates are lowest for high polar settings, and most rapid in warm maritime and some sub-polar areas. However, icebergs in cold waters transport debris to significantly greater distances from the parent glacier. The model provides calculations of order of magnitude rates of iceberg sedimentation in varying glacimarine settings.
Fossilization potential of Arctic fjord and continental shelf benthic macrofaunas
Authors: Aitken Alec E. 
Published: April 2008

Abstract

The organic remains of many organisms do not survive the post-mortem period. This study was undertaken to identify patterns of preservation in arctic marine macrofaunas with the goal of aiding Quaternary researchers in the interpretation of fossiliferous marine sediments. The probable fate of 310 genera of marine invertebrates which inhabit the fjords and continental shelf in the eastern Canadian Arctic was investigated. The preservation potential of marine invertebrates was assessed in three ways: by morphology (presence of macroscopic hardparts); by the previous existence of a fossil record (data for genera only taken from the
Treatise on Invertebrate Paleontology
); and by the previous record in Quaternary marine sediments on Baffin Island. Considering the arctic benthos as a whole, up to 860f the genera have not been preserved and are not likely to be preserved.

The fossil record preferentially preserves infaunal suspension feeding and epifaunal browsing organisms. Infaunal suspension feeding bivalves frequently contribute more than 500f the macroscopic hardparts in Quaternary fossil assemblages. The lack of preservation of soft-bodied carnivorous and deposit feeding organisms suggests that little understanding of community trophic dynamics based on the study of trophic group composition is likely to be derived from Quaternary fossil assemblages. Bivalves and gastropods inhabiting fjords and nearshore waters exhibit the greatest preservation potential of all the arctic marine benthos. The excellent preservation potential of arctic marine molluscs offers palaeoecologists the potential to reconstruct ancient marine biocoenoses in glacimarine environments.