bluuebunny/crossref_metadata_2025 huggingface dataset:
Transport and emplacement mechanisms of mass-flow deposits on Monte Vulture volcano, Basilicata, southern Italy
Authors: Duncan A. M. , Cole P. D. , Guest J. E. , Chester D. K.
Published: April 2008

The Lahar Facies of Mt Vulture, which forms a broad apron around the base of the cone, is composed predominantly of mass-flow deposits. There is a spectrum of lithological types ranging from monolithologic units which may be of a primary pyroclastic flow origin and are composed entirely of juvenile material, to polylithologic deposits, containing a range of clast types, interpreted to be cold debris-flow deposits. Some debrisflow deposits show evidence of being hot on emplacement. Debris-flow deposits are interbedded with lapilli-fall layers and lava flows suggesting formation contemporaneous with eruptive activity. Some debris-flow deposits travelled no more than 3 km from their source. Many flows were apparently non-erosive, although there is one example where a debris-flow eroded clasts from the top of a lava flow. The presence of fractured ‘jigsaw’ blocks and large fragile blocks of pyroclastic material rules out turbulent flow and high shear for much of the transport prior to emplacement. Multiple grading and abundant development of reverse grading with large lava blocks rafted on, or protruding through, the upper surface of flow units implies that the lahars were high-concentration, high-strength flows in which differential shearing produced discontinuous multiple grading. Locally, individual debris-flow deposits have convex upper surface profiles with internal grading paralleling the surface, strongly supporting a conclusion that these debris-flow deposits were emplaced en masse.
Destructive mass movements associated with Quaternary volcanoes in Hokkaido, Japan
Authors: Yamagishi Hiromitsu
Published: April 2008

Hokkaido, the northern island of Japan, is situated on the North American Plate between the Pacific Plate and the Eurasian Plate; it is set on an island arc subducted by the two latter plates. Hence, Hokkaido has many Quaternary volcanoes. Most of these volcanoes have the andesitic to dacitic composition diagnostic of island arcs. They are remarkably unstable due to steepness of the upper slopes, structural fragility, and post-hydrothermal alteration. Consequently, in Hokkaido, many destructive mass movements occur from the Quaternary volcanoes. They are represented by debris avalanches from stratovolcano or lava dome collapses, hydrologic mass flows due to rainfalls, and slides associated with caldera formation.
Turbidites from slope failure on Hawaiian volcanoes
Authors: Garcia Michael O.
Published: April 2008

Turbidites are common in the sediments surrounding the Hawaiian Islands. Cores were taken during leg 136 of the Ocean Drilling Program 320 km west of the island of Hawaii on the outer side of the arch that surrounds the southern end of the Hawaiian chain. They contain Pleistocene to late Oligocene graded volcanic sand layers with fresh glass (or its alteration products) and mineral fragments (olivine, plagioclase, and clinopyroxene). Some layers have mixed assemblages of Pleistocene to Eocene radiolarians or Eocene and Cretaceous ichthyoliths. The glass fragments are weakly vesicular and blocky to platy in shape. The glass fragments from individual Pleistocene to Pliocene layers have large compositional ranges (i.e. larger than expected for a single eruption). These features indicate that the turbidites probably were deposited from turbidity currents that originated on the flanks of Hawaiian volcanoes. The low to moderate sulfur content of the sand glasses indicates that they were derived from partially degassed lavas that were erupted under shallow marine to subaerial conditions. The turbidity currents ran over the
c.
500 m high Hawaiian Arch, which indicates that the currents were at least 325 m thick. Similar turbidite deposits are located 930 km south of the Hawaiian Islands. Thus, debris avalanche from Hawaiian volcanoes can generate enormous turbidity currents that transport sediments long distances from their source. This phenomenon is an alternative explanation to Antarctic bottom waters for generating mixed assemblages of Pleistocene and Eocene radiolarians in deep-sea sediments.
Spectral analysis of volcanic tremor associated with the 1993 paroxysmal events at Stromboli
Authors: Carniel Roberto , Casolo Siro , Iacop Franco
Published: April 2008

The year 1993 was characterized by three paroxysmal phases at Stromboli: two (February and October) consisted of a series of violent explosions, the third (May) of strong Strombolian activity, accompanied by a small lava flow. Here we investigate the characteristics of the tremor before, during and after these paroxysmal phases. One evident feature is that the three phases analysed are significant expressions of the Strombolian activity. In fact, they mark a considerable change in the dynamics of the volcano. The energy content, both in terms of volcanic tremor and of number of events drops to very low values after the periods of intense activity. Concerning the evolution of the spectral content of the tremor before the paroxysmal phases, there seems to be a concentration of energy in the low frequency range (below 5 Hz for the crisis in May; below 3 Hz for the February and October events), with clearly identifiable peaks in some cases, while after the crisis the spectrum becomes again much more scattered. This transition, especially in the case of the strong explosions of February and October, happens abruptly. A continuous monitoring of the spectral content of volcanic tremor on Stromboli can therefore be a useful tool to identify the beginning of an instability which may lead to a paroxysmal phase.
Tonalite-trondhjemite-granodiorite magmatism and the genesis of Lewisian crust during the Archaean
Authors: Rollinson H. R.
Published: April 2008

This paper reviews the major and trace element and isotopic geochemistry of the Lewisian tonalite-trondhjemite-grandiorite/granite (TTG) gneisses from the mainland Lewisian. The main crust-forming event in the Lewisian was at
c.
3.0 Ga, although some supracrustal rocks preserve evidence for an earlier history. The granulites of the Central Region of the Lewisian preserve evidence of a younger episode of crust generation and a model is proposed for these rocks in which new crust generated at
c.
2.6 Ga is contaminated with
c.
3.0 Ga crust. It is proposed that the ‘depletion’ in the elements U, Th, K & Rb in the Central Region TTG granulites is original, i.e. related to the process of crust generation rather than of granulite facies metamorphism as previously supposed.

TTG genesis in the Lewisian is the product of the dehydration melting of amphibolite at > 18 kb depth and > 800°C. Differences in the levels of U, Th, K & Rb (LILE) between the TTG gneisses of the different regions of the mainland Lewisian is attributed to differences in the partial melting process. LILE-depleted rocks experienced dehydration followed by dehydration melting, whereas LILE-rich rocks are the product of dehydration melting alone.
The evolution of the Grenville Province in eastern Labrador, Canada
Authors: Gower Charles F.
Published: April 2008

Rifting at
c.
1.71 Ga separated the Mealy Mountains terrane from pre-Labradorian Laurentia and resulted in a short-lived (backarc?) basin, followed by southward subduction giving rise to 1.68-1.66 Ga Labradorian calc-alkaline arcs, partly built on older crust in the Mealy Mountains terrane. The arcs and subduction were also short lived, terminating when accretion against the Makkovikian and Eastern Churchill provinces occurred at 1.65 Ga. The Trans-Labrador batholith developed as a result of crustal thickening during suturing of the 1.68-1.66 Ga arc-related rocks to pre-Labradorian Laurentia. Further bimodal magmatism, in response to crustal thickening, continued until
c.
1.62 Ga, followed by waning granitic magmatism until 1.60 Ga.

The Labrador Orogen and older rocks in the Mealy Mountains terrane are flanked to the south by Pinwarian (1.51-1.45 Ga) granitoid rocks, possibly the inboard manifestation of a northward-subducting continental-margin arc at the southern margin of Laurentia. Extension, mostly coincident with the 1.71 Ga zone of weakness, started at
c.
1.45 Ga. Although rifting was successful further west, it is only represented by basaltic magmatism (Michael and Shabogamo gabbros) along a linear zone in Labrador. Similar tectonism characterized the same zone periodically for at least the next 150 million years during which time the 1.27 Ga Harp-Nutak dykes were emplaced and slightly younger rocks of the Seal Lake Group formed north of the Grenville Province.

After
c.
1.23 Ga tectonic conditions changed, partly in response to Elzevirian accretion of arc terranes preserved in the southwest Grenville Province, that are speculated to have once also existed south of the exposed eastern Grenville Province. Alternating compressional and extensional conditions terminated at
c.
1.0 Ga during collisional orogenesis associated with the final stages of development of the Grenville Orogen. Grenvillian deformation in Labrador (1.08-0.97 Ga) resulted in northwesterly thrusting, the effects of which are focused in the Exterior Thrust Belt, and widespread plutonism in the Interior Magmatic Belt. Thrusting in the Exterior Thrust Belt is sited along the zone of 1.71 and 1.43 Ga rifting. Uplift and cooling continued until 0.90 Ga as crustal stability was gradually achieved.
40
Ar/
39
Ar geochronological constraints on the tectonothermal evolution of the Eastern Segment of the Sveconorwegian Orogen, south-central Sweden
Authors: Page Laurence M. , Stephens Michael B. , Wahlgren Carl-Henric
Published: April 2008

A
40
Ar/
39
Ar study to constrain the tectonothermal evolution across the Eastern Segment of the Sveconorwegian Orogen has been initiated in the area north and east of lake Vänern, south-central Sweden. This segment of the orogen is confined by two major deformation zones, the Sveconorwegian Frontal Deformation Zone (SFDZ) in the east and the Mylonite Zone in the west. Previous structural work and the prograde character of the metamorphism within the study area suggest that an older (<
c.
1.57 Ga), regional foliation was formed by ductile shear deformation in a compressional tectonic regime. The orientation of this foliation was subsequently modified by later rotation along younger ductile shear zones in the easternmost, frontal part of the orogen (SFDZ). The
40
Ar/
39
Ar ages for hornblende suggest that the regional foliation is Sveconorwegian. Furthermore, white mica ages demonstrate that the Sveconorwegian tectonothermal overprint continues at least 40 km east of the traditionally accepted limit situated along the ‘Protogine Zone’. These results also provide age constraints for different phases of Sveconorwegian tectonothermal evolution with an older group of ages from 1009–965 Ma and a younger set from 930–905 Ma. The older ages are inferred to constrain a minimum age for crustal thickening during which the regional foliation and metamorphism developed, while the younger are associated with later compressional movement along the SFDZ.
Palaeomagnetism and Sm-Nd ages of the Neoproterozoic diabase dykes in Laanila and Kautokeino, northern Fennoscandia
Authors: Mertanen S. , Pesonen L. J. , Huhma H.
Published: April 2008

The results of palaeomagnetic, rock magnetic and isotope data on the NE-SW trending Neoproterozoic Laanila-Ristijärvi (Finland) and Kautokeino (Norway) dyke swarms, northern Fennoscandia, are reported. Positive baked contact tests in both dyke sets indicate that the characteristic remanence is primary thermoremanence. Rock magnetic and petrological properties show similarity between the two dyke swarms. All the dykes except one (where the dominant carrier is Ti-rich titanomagnetite) have mixed multidomain and single-domain or pseudosingle-domain magnetic carriers of Ti-poor magnetite. From its remanence directions, petrography and rock magnetic properties, the easternmost of the three Laanila dykes represents a deeper crustal level than the other two dykes studied. Palaeomagnetic and aeromagnetic data suggest that the Palaeoproterozoic granulite block containing the easternmost Laanila dyke was uplifted after the dykes were emplaced.

The Sm-Nd isotopic age determinations yield an age of 1042 ± 50 Ma for the Laanila dykes, 1013 ± 32 Ma for the Ristijärvi dykes and 1066 ± 34 Ma for the Kautokeino dykes indicating that the dyke swarms are of similar age within error limits. However, palaeomagnetic pole of the Laanila-Ristijärvi dykes (P
lat
= 2.1 °S, P
long
= 212.2 °E, dp = 12.7°, dm = 21.1°,
N
= 3 dykes) differs significantly from the pole of the Kautokeino dykes (Plat = 35.2 °S, P
long
= 236.8 °E,
N
= 2 dykes). The isotope and palaeomagnetic ages of the Laanila-Ristijärvi dykes are considered agreeable, but on the basis of younger precisely dated Sveconorwegian palaeopoles, a magnetization age of
c.
900 Ma for the Kautokeino dykes is inferred. Three explanations for the discrepancy are suggested: (i) local tectonic movements, (ii) delayed magnetization of the Kautokeino dykes with respect to that of the Laanila-Ristijärvi dykes, (iii) the isotope ages and palaeomagnetic ages are compatible but the Fennoscandian APWP should be revised.
Provenance of late Proterozoic Dalradian tillite clasts, Inner Hebrides, Scotland
Authors: Fitches W. R. , Pearce N. J. G. , Evans J. A. , Muir R. J.
Published: April 2008

A geochemical and isotopic study was made of granitoid clasts taken from the
c.
660 Ma Dalradian tillites of Islay and the Garvellach Islands. Objectives were to investigate tillite provenance as a means of helping to characterize the ages, compositions and distributions of basement rocks near and beneath the Dalradian Supergroup. Most clasts have closely similar trace element and REE compositions, implying that they were derived from source rocks produced in similar, but not necessarily coeval, geotectonic settings. Most samples have geochemical traits of Within-Plate Granites. Nd isotopic model ages of
c.
2.0 Ga were obtained from several clasts. One sample gave a Rb-Sr mica whole-rock age of
c.
1.57 Ga, which is probably close to the age of igneous crystallization.

The clasts are petrographically similar to the syenites of the Rhinns Complex, the
c.
1.8 Ga alkalic igneous suite exposed locally in the Hebridean region SE of the Great Glen Fault. Most clasts, however, are geochemically distinct from the Volcanic Arc-type Rhinns Complex. The isotopic model ages of the clasts overlap those of the Rhinns Complex, but the
c.
1.57 Ga age of one clast is substantially younger. Although most clasts were not eroded from the Rhinns Complex of the type presently exposed, it is possible that they were derived from plutonic rocks closely associated in space and time with the Rhinns Complex. The source plutons and the Rhinns Complex were probably components of the early to Proterozoic Sveccofennian-Ketilidian-Labradorian-Makkovikian mobile belt which contains voluminous plutonic rocks with diverse ages and compositions.
The role of geochemistry in environmental and epidemiological studies in developing countries: a review
Authors: Plant J. A. , Baldock J. W. , Smith B.
Published: April 2008

Concern over the effects of chemicals in the environment on the health of man and animals is growing as rapid economic and population growth extends such problems as land degradation, pollution and urbanization from industrialized nations to the developing world.

In this paper we review the principal socio-economic and environmental pressures on developing countries before discussing the role of geochemistry in: (1) preparing high resolution baseline data to identify potential hazards; (2) understanding the pathways of chemical elements from rocks and soils to man and animals; and (3) developing amelioration strategies to reduce the impacts of inappropriate land use, power generation and mining. The particular geochemical problems of tropical terrains are discussed and some case histories from the international work of the British Geological Survey (BGS), funded by the Overseas Development Administration, are described.

It is recommended that developing nations prepare modern geochemical maps, ideally to the standards set out in International Geological Correlation Programme Project 360 World Geochemical Baseline, and that aid agencies should fund integrated environmental geochemical surveys as being of primary importance, especially for health studies and land use planning; particular attention should be paid to the environmental impact of urbanization. Further understanding of chemical and mineralogical speciation is required to improve the interpretation of geochemical data for environmental purposes.

Multidisciplinary studies, involving epidemiologists, biochemists and nutritional specialists, are essential if natural and anthropogenic impacts are to be properly assessed and practical amelioration measures implemented.
Formation of cave salts and utilization by elephants in the Mount Elgon region, Kenya
Authors: Bowell R. J. , Warren A. , Redmond I.
Published: April 2008

Herbivores such as the African elephant receive most of their nutrient uptake through digested vegetation or water. When these nutrient sources do not fulfil dietary requirements, eating and digestion of soil and rock can be a common phenomenon. In the Mount Elgon National Park on the Kenya-Uganda border, elephants have taken this activity one step further. Deposits of calcium-sodium-rich alkaline rocks show evidence of quarrying by elephants on the surface, but most of the activity takes place underground in caves. The Na-Ca-Mg-rich rocks are leached by groundwater which reacts with animal excreta in the humid environment of the cave floor to form a series of secondary carbonate, sulphate, halide, nitrate and phosphate minerals by evaporation. Additionally some salts are precipitated on the cave walls by direct evaporation of the cave waters. Inside the caves, elephants tusk and ingest the salt-enriched rock fragments. In an area like Mount Elgon, where supergene processes leach chemical elements essential for dietary requirements from the surface ecosystem, the secondary salts in the caves are potentially an important mineral supplement for wildlife nutrition. Although elephants are the principal exploiters, other wildlife species and humans (for livestock) also utilize the cave salts and surface diggings.
Groundwater geochemistry and health: an overview
Authors: Edmunds W. M. , Smedley P. L.
Published: April 2008

The natural geological and geochemical environment, in addition to providing beneficial mineral content and bioessential elements to groundwaters, may also give rise to undesirable or toxic properties through a deficiency or an excess of various elements. In this paper the controls on the release of toxic elements are considered together with the geochemical conditions that give rise to excess and deficiency. Many studies have pointed towards an inverse correlation between water hardness and cardiovascular disease and the associated mobility of metals in soft waters may also be a contributory factor. Under acidic conditions Al and Be as well as other metals may be released, whilst changes in redox conditions as well as pH will affect the mobility of Fe, Mn and As in particular. Some potentially toxic elements such as Ba and F are usually held at acceptable concentrations in groundwaters by the respective solubility controls of barite and fluorite; quality problems arise from these elements when groundwaters contain respectively low sulphate or low calcium concentrations. Deficiencies of Se and I (as well as F) in groundwater are related to the low geochemical abundance of these elements in certain environments. In the context of groundwater pollution it is important first to define the natural baseline concentrations of key elements of health importance.
Water quality and dental health in the Dry Zone of Sri Lanka
Authors: Dissanayake C. B.
Published: April 2008

The Dry Zone of Sri Lanka has mostly poor rural folk, who live in very close association with the immediate physical environment, depending on it for their living. Many of these people have lived in such a confined environment throughout their lives and it is reasonable to assume that at least some aspects of their health could be correlated with the geochemistry of their immediate environment.

Hydrogeochemical investigations of surface well water and deep well water in parts of the Dry Zone notably in the North Central Province, have shown that the fluoride concentrations often reach anomalously high levels, of the order of 10 mg
−1
in some instances. As a result of this, dental fluorosis is increasing in its prevalence among school children. With over 13 000 tube wells with hand pumps, mostly in the Dry Zone, the problem of dental fluorosis will assume serious proportions in the future unless methods of defluoridating household water supplies are developed.

An attempt has been made to implement a programme of defluoridating water supplies with a defluoridator using charcoal and charred bone meal. However, a major awareness programme is needed to educate the villagers of the dangers of excessive fluoride in drinking water and the need for community participation in maintaining household defluoridators.
Geochemistry of iodine in relation to iodine deficiency diseases
Authors: Fuge Ron
Published: April 2008

Seawater is the most important reservoir for terrestrial iodine (mean concentration 58 µgl
−1
I); this is a major influence on iodine distribution in the secondary environment. Volatilization of iodine from the oceans, possibly as elemental iodine or as an organically-bound species, is the main source of the element in the environment. The distribution of iodine in the secondary environment is, therefore, largely controlled by proximity to the oceans, with rainwater and surface run-off relatively enriched in iodine in near-coastal regions. Soil iodine content is also strongly influenced with coastal soils being much enriched and central continental soils being depleted. Topography has a marked influence with soils in rain shadow areas being relatively depleted in iodine. While iodine input is a major controlling influence on its geographical distribution in soils, the soil’s ability to retain iodine is also an important factor. Organic matter together with iron and aluminium oxides and clays are the important sinks of soil iodine.

An additional factor in the distribution of iodine in the secondary environment, and its subsequent availability to the biosphere, relates to its speciation in soils. In acid oxidizing conditions iodine is likely to be present as the I
−
ion and as such liable to be volatilized as I
2
. In near-neutral or alkaline conditions iodine is likely to be present as the IO
3
−
ion which is not volatilized. Soils in limestone areas, with pH values of 7 and above, have thus been found to be much enriched in iodine compared to acidic soils in neighbouring areas.

It is suggested that iodine from oceanic sources migrates in a series of ‘steps’ across landmasses by deposition followed by revolatilization. High pH soils and organic-rich soils then act as a migration barrier for iodine. In addition, it is suggested that volatilized iodine is bioavailable and any geochemical barrier to such volatilization deprives the biosphere of a major source. In this context it is interesting to note that several goitre endemias occurred in areas with limestone bedrock.
Preliminary studies of acid and gas contamination at Poas volcano, Costa Rica
Authors: Nicholson R. A. , Roberts P. D. , Baxter P. J.
Published: April 2008

Primary volcanic phenomena are potentially catastrophic, whilst those of a secondary nature may be merely considered as background activity but may be of sufficient intensity to cause long-term suffering to indigenous populations. The latter is the case at Poas volcano in Costa Rica, where a change in the quiescent state of the volcano has been shown by increasing activity during the last decade. Acid gases are apparently now being emitted more intensely than before, particularly during the dry season, to the detriment of the health of people and domestic livestock living in the surrounding countryside. Damage to crops and farm buildings is also evident.

A pilot geochemical study has been undertaken at Poas volcano to determine the principal constituents of the gas emissions, the form in which they are most likely to be transported and the extent of the area within which they can be easily measured.

The results obtained indicate that emissions of mixed volatile acids contribute to the problems encountered, and that, as might be expected, seasonal changes and distance from the source also exert control. Rainfall effectively scrubs the acid gases during the wet season, thereby considerably ameliorating the immediate effects of the emissions.
A re-evaluation of Middle and Upper Jurassic stratigraphy and the flooding history of the Moray Firth Rift System, North Sea
Authors: Davies Richard J. , Stephen Kevin J. , Underhill John R. , Davies Richard J. , Stephen Kevin J.
Published: April 2008

The application of a sequence stratigraphic approach to the study of the Middle and Upper Jurassic of the Moray Firth has enabled the stratigraphy of disparate onshore and offshore successions to be linked and clarified. The results allow for the construction of regional correlation panels, chronostratigraphic diagrams and palaeogeographic maps which illustrate the tectono-stratigraphic evolution of the basin and importantly show a new flooding history for this arm of the North Sea rift system. It is now demonstrable that the Inner Moray Firth (IMF) and Outer Moray Firth (OMF) were separated by a topographic high centred around the Ross Granite area (UKCS blocks 13/28 and 13/29) from the Bajocian until the latest mid-Oxfordian. New biostratigraphic results demonstrate that the first marine influx into the Buchan Trough area of the OMF was Callovian in age (significantly earlier than previous models) and probably marked connection with the South Viking and/or North Central Grabens. Similar marine depositional systems are envisaged to have developed in the geographically isolated IMF basin and Buchan Trough area of the OMF basin during the Callovian, early and mid-Oxfordian. The unification of these marine basins occurred during the latest mid-Oxfordian via the South Halibut Trough, with a subsequent early Kimmeridgian connection via the Halibut Platform. The new flooding model suggests that the drowning of the rift arm was more rapid than previously believed and that within the rift itself any relief associated with a Mid-Jurassic doming episode, which created ‘the Mid-Cimmerian Unconformity’ had effectively diminished by this time. Although the deflation of a triple junction-centred dome remained an important process in the basin’s Mid-Jurassic evolution it was not the sole causal control on rift-arm stratigraphy. Instead the complexities of the Mid- and Late Jurassic flooding of the Moray Firth are interpreted to be the result of both short- and long-term regional sea-level changes superimposed upon a complex evolving rift topography.
The role of trace fossil (ichnofabric) analysis in the development of depositional models for the Upper Jurassic Fulmar Formation of the Kittiwake Field (Quadrant 21 UKCS)
Authors: Martin M. A. , Pollard J. E. , Martin M. A.
Published: April 2008

The sedimentology and sequence stratigraphy of the Upper Jurassic (Upper Oxfordian — Middle Kimmeridgian) Fulmar Formation of the Kittiwake Field, Western Platform of the north Central Graben are investigated through an integrated study of core material and wireline logs. The Fulmar Formation, in this area, comprises largely finegrained sandstones which are intensely bioturbated such that the use of primary sedimentary structures for the identification of depositional environments is impractical. By using the approach of ichnofabric analysis presented here, the information provided by trace fossils can be fully utilized in the formulation of a depositional model for the Fulmar Formation.

A depth and substrate-related succession of ichnofabrics was determined for the Fulmar Formation from more complete and progradational successions. This attached shoreface succession extends from a
Chondrites
ichnofabric (offshore), through
Anconichnus
(upper offshore),
Anconichnus
and spreiten burrows and ‘
Teichichnus zigzag
’ (upper offshore-offshore transition zone), bivalve tube ichnofabric (offshore transition zone to lower shoreface),
Ophiomorpha irregulaire
(lower shoreface),
Ophiomorpha nodosa
(middle shoreface) to a burrow mottling ichnofabric and associated high-energy laminated sandstones (upper shoreface). Anomalies in this succession form the basis for the identification of bounding surfaces, particularly omission surfaces (
Thalassinoides
and
Diplocraterion habichi
ichnofabrics) and sequence boundaries.

The distribution and evolution of the essentially retrogradational succession of the Fulmar sandstones is illustrated by analysis of a detailed core log of well 21/18-3, a general cross section through the Kittiwake Field and an Early-Mid-Kimmeridgian time slice facies distribution map.
Facies controls on reservoir quality in the Late Jurassic Fulmar Formation, Quadrant 21, UKCS
Authors: Cannon S. J. C. , Gowland S.
Published: April 2008

Fulmar Formation sandstones have been assessed for reservoir quality in terms of their primary textural and sedimentological characteristics with respect to conventional core analysis data. Some 6000 ft of core were characterized in total using a comprehensive lithofacies scheme and the results integrated with porosity and permeability data to create a statistically valid data set. From this dataset the primary influences affecting reservoir quality have been evaluated for a discrete area of the Central North Sea. Simple cross-plotting techniques indicate general trends in reservoir quality related to lithofacies type and hence depositional energy levels in shoreline/shallow marine shelf environments. Dominant grain size trends are identified that also influence reservoir quality. Broad prograding, aggrading and retrograding sequences are recognized which can be used to sub-divide the reservoir and locally predict reservoir quality.
Upper Jurassic sandstone reservoir quality and distribution on the Fladen Ground Spur
Authors: Freer Geoff , Hurst Andrew , Middleton Paul
Published: April 2008

During the Oxfordian to Early Kimmeridgian much of the Fladen Ground Spur was a positive feature and sourced clastic deposition in the Piper Basin, Witch Ground and South Viking grabens. The
eudoxus
flooding event introduced shallow marine conditions onto the Fladen Ground Spur, and during the continuing transgression, a veneer of clastic sediments was deposited. Three facies units are defined: facies 1 — thin, low-high-energy glauconitic sandstone; facies 2 — medium-high-energy clean, well-sorted medium-grained sandstone; facies 3 — low-energy, fine-grained argillaceous sandstone. Reservoir quality is evaluated using porosity data from neutron porosity and bulk density logs. Porosity-permeability cross-plots provide a workable relationship for permeability prediction in uncored wells. Initial results show that, predictably, facies 2 sandstone has the best poroperm characteristics. Facies 1 sandstone contains locally derived clasts, the diverse nature of which affects reservoir quality. Subcrop is interpreted to be an important, if not causal, factor that controls reservoir quality in facies 1 sandstone.
Reservoir architecture and diagenesis in downthrown fault block plays: the Lowlander Prospect of Block 14/20b, Witch Ground Graben, Outer Moray Firth, UK North Sea
Authors: McCants C. Y. , Burley S. D.
Published: April 2008

The Lowlander Prospect is an Upper Jurassic, downthrown hydrocarbon accumulation, with three-way dip closure and fault seal developed within the Sgiath and Piper formations. The prospect was discovered in 1987 and has since been appraised by more than 900 ft of core from five wells. Detailed core description, conventional core analysis, thin section petrography, fluid inclusion microthermometry, stable isotope analysis and over 2000 ft of wireline petrophysical log interpretation were utilized in constructing an integrated reservoir and diagenetic model for the reservoir units in the prospect.

Piper Formation sandstones form the main reservoir in the Lowlander Prospect. Deposition of Piper Formation sandstones was controlled by three major structural elements which served as separate hinterlands; the Fladen Ground Spur and Piper Ridge to the northeast, Halibut Horst and Platform to the southwest, and regional Toarcian-Aalenian domal uplift to the southeast. Two major coarsening up sequences are present in the Lowlander Piper Formation that represent progradational strandline deposits. Transgressive abandonment sandstones, locally preserved beneath a top Piper Formation unconformity, represent a Volgian transgression and associated reworking of Piper Formation sediments.

Mechanical compaction and diagenetic cementation, the latter including early non-ferroan calcite, kaolin, quartz overgrowths, ankerite, late calcite and barite-sulphide mineralization, have resulted in generally low intergranular porosities in Piper Formation sandstones. However, total porosities are enhanced by the development of late, post-quartz overgrowth feldspar grain dissolution. Microthermometric study of fluid inclusions in quartz overgrowths indicates that precipitation of authigenic quartz took place at temperatures of between 88 and 122°C, concomitant with hydrocarbon migration. Best reservoir quality is developed adjacent to basin centre faults where early carbonate cements and detrital feldspars have been extensively dissolved. Higher depositional energy facies adjacent to the faults were the initial focal point for aggressive fluid ingress into the reservoir. Fluid migration away from the faults resulted in reprecipitation of carbonate cements up-structure towards the graben edges where reservoir quality is now the lowest. Structural highs thus need not be the prime exploration target in downthrown, hanging-wall basin centre plays.
Biomarker maturity profiles in the Inner Moray Firth Basin and implications for inversion estimates
Authors: Pearson Michael J. , Duncan Alasdair D. , Duncan Alasdair D.
Published: April 2008

The thermal stress (maturity) of Oxfordian to Kimmeridgian rocks in 13 Inner Moray Firth wells and at outcrop has been assessed using sterane and hopane isomer ratios. Significant depth profile displacements between the maturity trends for the Beatrice suite, other groups of Inner Moray Firth wells and a Viking Graben calibrant well are considered to be partly due to differences in uplift during Tertiary inversion and partly to varying palaeo-thermal gradients. Present day temperature plots are used to measure cooling from biomarker-derived maximum temperatures and hence to obtain approximate estimates of inversion.

Consideration of errors in cooling estimates allows the limits of uplift to be constrained. Relative uplift between Inner Moray Firth fault blocks is likely to be subject to fewer estimation errors than absolute uplift (inversion) with respect to the Viking Graben. 12/26-1, the most uplifted well on the Central Ridge, is estimated to have experienced between 400 and 700 m of uplift relative to 12/24-1, the least uplifted in the Smith Bank Graben, although for other wells relative uplift is not always related to present-day structural elevation. Inversion (absolute uplift) of the Smith Bank Graben is probably at least 150 m although the error in this estimate is large. Inversion of well sections in the Beatrice Field is thus estimated to have been around 400 m.
The development of the Ivanhoe, Rob Roy and Hamish Fields, Block 15/21A, UK North Sea
Authors: Currie Susan
Published: April 2008

The Ivanhoe, Rob Roy and Hamish Fields development in southern block 15/21 has been producing oil from Upper Jurassic age sandstones since mid-1989. The two reservoir horizons, historically within the Field models referred to as a ‘Supra Piper’ and a ‘Main Piper’ unit, but now correlated to sandstones in the Piper and Sgiath Formations respectively, comprise shallow marine sandstone facies deposited as part of the progradation of the Piper and Scott delta systems across UKCS quadrant 15. The reservoir has been modelled using a 3D seismic survey shot in 1984 and a sub-regional database of about 20 wells. Through the first five years of field life reservoir performance has been consistently good. In 1985, at Annex B time, the estimate for combined Ivanhoe and Rob Roy Fields STOIIP was 146 × 10
6
bbls. The Annex B total combined reserves figure of 88 × 10
6
bbls for Ivanhoe and Rob Roy was produced by 1994. Both geoscience and reservoir engineering models for the fields have been revised since the Annex B submission. The latest revision resulted in a substantial increase in the estimated initial oil in place figure for the fields. This paper summarizes the initial development of the Fields, subsequent reservoir modelling and the production history during the first five years of field life.
Shale lamination and sedimentary processes
Authors: O’Brien Neal R.
Published: April 2008

Lamination is a common feature of shale and other argillaceous rocks. The type of shale lamination provides an important clue in identifying sedimentary processes when combined with other geological evidence. Presented here is an overview of some common lamination signatures in shale and the sedimentary processes responsible for their formation. Macro-and microfabric and textures of Proterozoic, Palaeozoic, and Mesozoic shales from various sedimentary environments are revealed by X-radiographs, thin-section photomicrographs, and scanning electron microscope micrographs. Characteristic fabrics associated with the following sedimentary processes are presented: (1) bottom flowing currents produce features of fine to thick laminae (approx 0.5–1.0 mm thick) in association with small-scale features of crossbedding, ripple marks, cut and fill and flame structures; (2) deposition from low-density bottom currents and turbidity currents leaves a fabric signature of graded bedding; (3) suspension settling is shown by alternating very fine (<0.5 mm thick) non-graded silt and clay laminae; (4) microbial mats are recognized by wavy lamination.
Tales of 1001 varves: a review of Santa Barbara Basin sediment studies
Authors: Schimmelmann Arndt , Lange Carina B.
Published: April 2008

The varved marine anoxic sediment in the deep centre of the Santa Barbara Basin off California has been studied extensively by sedimentologists, micropalaeontologists and geochemists during the past four decades. The Santa Barbara Basin is the only basin in the California Borderland Province that exhibits laminations for most of the Holocene. These sediments are essential to further our understanding of climate in that they provide a rare oceanic record of climate change with high resolution. In this overview of the complex and multidisciplinary Santa Barbara Basin sediment research, we briefly introduce the reader to the various analytical approaches and present a comprehensive collection of literature references.
Oligocene laminated limestones as a high-resolution correlator of palaeoseismicity, Polish Carpathians
Authors: Haczewski Grzegorz
Published: April 2008

Thin intercalations of laminated coccolith limestones in a series of flysch and black shales define a regional marker horizon in the Oligocene strata of the Outer Carpathians. Distinctive sequences of laminae in the coccolith limestones have been correlated over distances of up to 240 km and across major facies zones. The correlated succession of laminae provided the basis for correlation of intercalated turbidites. The successions of laminae are disturbed at all studied localities by erosional gaps, intercalations of non-laminated limestone and deformation of some intervals of the laminated sequence. The disturbances themselves have been precisely correlated between three major nappes of the Outer Carpathians. The characteristics of the disturbances and their long-distance continuity indicate their seismic origin. The coccolith ooze at the top of the sediment column was firm and its simultaneous disturbance over large areas required earthquakes of magnitudes above 6.5. Laminated pelagic limestones provide a precise chronostratigraphic framework for long-distance correlation of seismic and other events recorded within their sequence.
High-resolution sedimentology and micropalaeontology of laminated diatomaceous sediments from the eastern equatorial Pacific Ocean (Leg 138)
Authors: Pearce R. B. , Kemp A. E. S. , Baldauf J. G. , King S. C.
Published: April 2008

Scanning electron microscope (SEM)-based analyses of the laminated diatom oozes encountered during Leg 138 reveal three major laminae types. The first lamina type is composed of multiple layers of approximately 20 μm thick diatom mats, which form laminae dominated by assemblages of the pennate diatom, . More than one variety/subspecies of
T. longissima
occurs within these laminae (referred to as the
T. longissima
Group). The second lamina type is composed of a mixed-assemblage of several species of diatoms (centric and pennate varieties), calcareous nannofossils, and subordinate quantities of radiolarians, silicoflagellates and foraminifera. The third lamina type is dominated by an assemblage of nannofossils and minor amounts of those fossil components mentioned above. This last form of lamination is compositionally similar to the background sediment type, foraminifer-nannofossil ooze (F-NO). Two lamina associations occur within the laminated intervals; the first comprises of alternations of
T. longissima
Group and mixed-assemblage laminae (average thickness is approximately 6 mm) and the second is composed of
T. longissima
and nannofossil-rich laminae (average thickness is approximately 3.5 mm). The arrangement of laminae probably originates from the deposition of multiple layers of 20 μm thick mats from one mat-flux episode. The much thinner nannofossil-rich laminae are interpreted to represent periods of more ‘normal’ deposition between mat-flux episodes. The occurrence of several varieties/subspecies of
T. longissima
within individual mat layers is consistent with observations of
Rhizosolenia
diatom mats in the modern world ocean.
Bathymetric segmentation and faulting on the Mid-Atlantic Ridge, 24°00′N to 24°40′N
Authors: Allerton Simon , Searle Roger C. , Murton Bramley J.
Published: April 2008

This investigation of valley-wall faulting and its relationship to bathymetry focuses on the first two segments north of the Kane Fracture Zone. The valley-wall faults imaged by deep-towed sidescan sonar show aspects common to continental normal faults, and a similar erosional pattern, from a fresh fault surface, through eroded, talus covered scarps, to scarps draped with pelagic sediments. The first, southernmost segment is a symmetric graben at the segment centre, and an asymmetric half-graben at the northern end. The second, northern segment is an asymmetric half-graben for its entire length. The gross morphology is reflected in the faulting style, with multiple small faults at the symmetric graben, and one or two large faults on the eastern wall, defining the asymmetic half-graben. This difference in faulting style may reflect differences in depth to the brittle-ductile transition, with asymmetry occurring when the brittle-ductile transition is deep and brittle faults can cross the axial valley, locking faults on the other side. A gross estimate of horizontal strain accommodated by the valley-wall faults correlates well with valley-floor bathymetry, suggesting that bathymetric segmentation is partially due to tectonic thinning at segment ends.
The response of ridge-crest hydrothermal systems to segmented, episodic magma supply
Authors: Haymon Rachel M.
Published: April 2008

Segmented, episodic magma supply and cracking models, advanced to explain ridge-axis discontinuities and along-strike variability, have provoked a recent shift in mid-ocean ridge crest hydrothermal models. Segment-scale and time-series observations of hydrothermal vents and plumes along fast and intermediate spreading centres reveal a close coupling between magma supply and hydrothermal fluxes. Based on the premise that magma supply exerts a primary control on hydrothermal processes, a new paradigm of segmented hydrothermal circulation has arisen featuring independent temporal evolution of hydrothermal systems along individual ridge segments. This paradigm explains observed segment-to-segment variations in the chemical composition of vent fluids and plumes (‘chemical segmentation’). Hydrothermally active segments can be classified, independently of spreading rate, into two types that represent end-members for the coupling of hydrothermal and magmatic processes: magma-rich segments and magma-starved segments. Along magma-rich segments, magma intrudes to shallow depths where water:rock ratios are high. Seafloor vent distribution tends to be magmatically controlled along dyke-induced fissures. Along magma-starved segments, intrusion is at greater depth, and deep cracks (usually faults) are required to transport water to and from the heat source. Water:rock ratios are low and vent locations are influenced by crustal permeability structure, as well as heat source location. Although both segment types can occur at any spreading rate, magma-rich segments are more common at faster spreading rates, and magma-starved segments are more typical at slow spreading rates.
Influence of axial segmentation on hydrothermal circulation at fast-spreading ridges: insights from Hess Deep
Authors: MacLeod C. J. , Manning C. E.
Published: April 2008

The evolution of oceanic hydrothermal systems depends heavily upon the origin, timing and spatial distribution of permeability near the magmatic heat source. At fast-spreading ridges, where permanent magma chambers are inferred, permeability in the plutonic portion of the crust is generated during cooling by time-, strain-rate- and temperature-dependent fracturing, which propagates downwards through the crust as the rocks cool and move off-axis. At major axial discontinuities, however, where magmatism may be intermittent and tectonism plays an important role, the controls on hydrothermal alteration are likely to be more complex.

Gabbros exposed at Hess Deep and sampled by the Ocean Drilling Program during Leg 147 provide the first insights from direct observation into the structural and metamorphic evolution of the lower crust near axial discontinuities. Early amphibolite-facies deformation and alteration are related to cooling, fracturing, and hydrothermal fluid flow within several kilometres of the East Pacific Rise axis. Later, dense fracturing and limited alteration occurred in the greenschist facies as the gabbros were transported into the deformation field at the ‘tectonic tip’ of the westward-propagating Cocos-Nazca ridge.

Although this is only one example of the possible influences of axial segmentation on hydrothermal circulation, and may represent a comparatively simplified view of other natural systems, given the potential variations in strain and strain rate coupled with the possibility of reheating events associated with renewed magmatism, we suggest that the multi-stage structural and metamorphic evolution of the Hess Deep plutonics may be a good analogue for the cooling history of the lower crust at other fast-spreading ridge axial discontinuities.