bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐contact tonometry: optometrists’ current practice in England and Wales
Authors: Tuck Maurice W. , Crick Ronald P.
Published: December 2007

A survey of 133 optometrists who used a non‐contact tonometer indicates that in only a half of patients tested were more than two readings per eye taken. Most optometrists made the number of readings conditional on the intraocular pressure (IOP) shown by the initial readings. About 1% of patients aged over 40 years were called back for a second IOP test. In a follow‐up questionnaire with 90 respondents, only 24 (27%) stated that they had rechecked any patient by Goldmann applanation tonometry during the previous 6 months. Of these 90 optometrists. 20 (22%) had not had their tonometer serviced within the previous 24 months. It was concluded that, whilst non‐contact tonometry makes a major contribution to glaucoma detection, improvements could be made in current practice which require little extra lime.
Non‐compliance in contact lens wear
Authors: Claydon Bridget E. , Efron Nathan
Published: December 2007

Non‐compliance is emerging as a critical issue in the contact lens field. This problem has been studied at depth in general health care situations and is seen as the responsibility of both practitioner and patient (client) working in a health care partnership. The contact lens practitioner and patient present a specific case for the study of non‐compliance in areas such as hygiene, solution use, appointment attendance and wearing limes. From 40 to 91% of contact lens patients have been reported as non‐compliant in the use of recommended care and maintenance regimens and many of these are confused or ignorant about their behaviour. In order to arrive at a general set of conclusions from the studies published to date, it is important to understand the methodology of each study, its purpose, the definition of non‐compliance used and the way the results were analyzed and described. This review summarizes the research into non‐compliance in the contact tens field to date. A set of general conclusions is drawn and a model for compliance in the context of contact tens practice is proposed.
Double‐masked placebo‐controlled trial of precision spectral filters in children who use coloured overlays
Authors: Wilkins A. J. , Evans B. J. W. , Brown J. A. , Busby A. E. , Wingfield A. E. , Jeanes R. J. , Bald J.
Published: December 2007

We selected 68 children who reported benefit from individually chosen sheets of coloured plastic placed upon the page when reading, and who used these regularly without prompting. These children viewed text illuminated by coloured light in an apparatus that allowed the separate manipulation of hue (colour) and saturation (depth of colour), at constant luminance. Many of the children reported improvements in perception when the light had a chromaticity within a limited range, which was different for each individual. A pair of plastic spectacle lenses (‘experimental’ lenses) was dyed so as to provide the appropriate chromaticity under conventional while (F3) fluorescent light. An additional pair was prepared having very similar colour but with a chromaticity outside the range in which perception was reported to improve (‘control’ lenses). Each pair was provided for 1 month in random order. The children kept diaries (36 completed) recording symptoms of eye‐strain and headache. The children and those responsible for their assessment were unable reliably to distinguish ‘experimental’ from ‘control’ lenses. Nevertheless, symptoms were less frequent on days when the ‘experimental’ lenses were worn (P < 0.003).
Ophthalmic, health and social profile of guide dog owners in Northern Ireland
Authors: Jackson A. J. , Murphy P. J. , Dusoir T. , Dusoir H. , Murdock A. , Morrison E.
Published: December 2007

Only 96 out of an estimated 28 000 registerable visually impaired persons, resident in Northern Ireland, currently make use of guide dogs for the blind. Results from this study indicate that guide dog owners represent a young, healthy and highly motivated subgroup of blind persons who have been profoundly visually impaired for prolonged periods of time. The implications of future ophthalmological developments, and of the educational and employment requirements of the visually impaired, are discussed.
Hybrid diffractive–refractive achromatic spectacle lenses
Authors: Charman W. N.
Published: December 2007

The possible utility of high‐power hybrid achromatic spectacle lenses, each consisting of a contact combination of refractive and diffractive components, is considered. It is shown that such a combination can, in principle, minimize blur due to transverse chromatic aberration in high‐power prescriptions such as those for uphakes and high myopes. The combination has essentially the same thickness and weight as a conventional singlet lens. Some practical problems relating to hybrid designs are discussed.
Direction of gaze and comfort: discovering the relation for the ergonomic optimization of visual tasks
Authors: Menozzi M. , Buol A. v. , Krueger H. , Miège Ch.
Published: December 2007

Perceived exertion caused by the extraocular muscles was assessed as a function of the direction of gaze and recorded in 114 subjects using a psychometric method. The results confirm statements in the literature that maximum comfort is achieved when gaze is aimed downwards. We found mi correlations between perceived exertion and age or viewing distance. The relationship is relevant to ergonomics, for example in tens lining and workplace layout.
Occupational testing of near vision
Authors: Vos Johannes J. , Padmos Pieter , Boogaard Jan
Published: December 2007

The quality of near vision depends on distance visual acuity, accommodation capability and near vision correction, and cannot therefore be expressed in acuity values. Most near vision tests do not recognize this, and the lack in standardization should lie mainly attributed to this fundamental shortcoming. A new lest, the Priegel lest, with a basically different conceptual basis is introduced. Its characteristics are discussed and a comparison with existing near vision tests is made. Consequences for legal testing are drawn.
New range of stand magnifiers based on standardized image position
Authors: Rumney Nicholas J.
Published: December 2007

Combined Optical Industries Ltd. Of Slough, UK, have released a new range of illuminated stand magnifiers These have been designed with u uniform emerging vergence and art1 specified in terms of equivalent power according to the new standards. This paper describes these magnifiers in terms of their measured optical and ergonomic properties. The expected enlargement ratios achieved with typical presbyopic additions are tabulated.
Investigation of accommodative and binocular function in dyslexia
Authors: Evans Bruce J. W. , Drasdo Neville , Richards Ian L.
Published: December 2007

The visual correlates of dyslexia are the subject of controversy, and much evidence suggests that they may include some aspects of binocular and accommodative function. These factors were investigated in 43 control and 39 dyslexic children, who were matched for age, sex and performance intelligence quotient. The dyslexic group exhibited significantly lower positive and negative vergence reserves, and vergence instability when the eyes were dissociated at near. Their amplitudes of accommodation also were significantly reduced. However, other measures including dissociated and associated heterophoria and accommodative lag and facility were similar in both groups. The stability of motor ocular dominance, as assessed with a modified Dunlop test, was similar in both groups. The results of a simulated reading visual search task suggested that the vergence and accommodative dysfunction were not a major cause of the dyslexia. Further analyses, using reading‐age matched groups, suggested that these ocular motor correlates were not attributable to the better reading performance in the control group. The most likely remaining explanation is that they are, in most cases, non‐causal correlates of the dyslexia.
Spatial summation of the differential light threshold as a function of visual field location and age
Authors: Latham Keziah , Whitakerxy David , Wild John M.
Published: December 2007

Static differential light thresholds were measured as a function of stimulus size (Goldmann sizes I‐V) along four visual field meridia (75, 165, 255 and 345°) with the Humphrey Field Analyzer 640. Data were obtained for both young ( n= 10, age 23.6 ± 2.9 years) and elderly ( n= 10. age 72.0 ± 5.2 years) normal subjects. The resulting peripheral spatial summation curves could be equated to the foveal data simply by a change in size scale, which increased linearly with eccentricity. E2, values, expressing the eccentricity at which stimulus size must double for performance to remain comparable to the fovea, were in the order of 3–9°. Whilst the rate of scale change is approximately the same for both young and elderly observers, differences in performance can be explained by a combination of lower sensitivity and a bias in sensitivity towards larger stimulus sizes with increasing age.
Pursuit eye movements in chronic schizophrenics: relationship between increased saccades and negative symptoms
Authors: Ciuffreda K. J. , Alpert M. , Blackstone T. , Fudge R. , Thaler J.
Published: December 2007

Smooth pursuit eye movements of chronic schizophrenics (n= 16) and controls (n= 10) were recorded while subjects tracked a sinusoidally‐moving target. Negative symptoms in schizophrenics were rated using the Schedule for the Assessment of Negative Symptoms. An increased frequency of smooth pursuit eye movement abnormalities was found in the schizophrenic group, including greater variability of gain and more frequent and larger saccades. Frequency of saccades was positively correlated with the Negative Symptoms scales for attentional impairment and alogia. The results confirm findings of eye movement dysfunction in schizophrenics and provide new evidence that the motor and cognitive dysfunctions of schizophrenia may be related.
Mass and centroid of rigid lenses
Authors: Burek Henry , Douthwaite W. A.
Published: December 2007

By subdividing a lens design into simpler units it is possible to evaluate its mass and locate its centre of mass (the centroid). The constituent subcomponents form plane sections of the sphere, or, in the case of aspheric lenses, sections of a conicoid. The theory of lens analysis in terms of the conicoidal (and spherical) frustrum is discussed and a BASIC computer program is presented to perform the calculations for spherical multicurve contact lenses.
Eye drop container delivery: a source of response variation?
Authors: German Emma J. , Hurst Mark A. , Wood Diana
Published: December 2007

Variations in response to topically applied ocular drugs (e.g. mydriatics and cycloplegics) and their possible aetiology have been studied previously. It appears that individual patient differences, external influencing factors and the characteristics of the particular drug may all govern the response. One factor worthy of note in this regard is the possibility of variation in the drug volume instilled. Single‐use eye drop containers known as Minims® are commonly used during ophthalmic diagnostic procedures. However, in this study the drop volume was shown to vary considerably, depending upon the angle at which the Minims® container was held, the particular drug and the number of drops previously expelled from the unit.
Use of contact lenses by firefighters: Part 2. Clinical evaluation
Authors: Owen Christopher G. , Margrain Thomas H. , Woodward E. Geoffrey
Published: December 2007

Contact lenses can be worn in a variety of environmental conditions and do not increase the wearers risk of injury. In many situations they offer significant corneal protection. Currently firefighters are prohibited from using contact lenses. To evaluate whether contact lenses are a safe form of visual correction 50 firefighters were fitted, and examined after 1, 4 and 10 months of contact lens wear. Twenty‐nine were fitted with soft contact lenses, and 21 with rigid gas permeable contact lenses. Statistically significant increase in lid sulcus hyperaemia was found in both the SCL and RGPCL groups (P<0.01, P=0.02. respectively), as well as an increase in hyperaemia of the vertical quadrant of the bulbar conjunctivae (P= 0.01, P= 0.02. respectively) In addition the RGPCL group showed a statistically significant increase in hyperaemia of the lateral portion of the bulbar conjunctivae (P<0.01), consistent with exposure epitheliopathy. The SCL group showed statistically significant increase in corneal staining in the vertical quadrant for all visits (P=0.02, P=0.01, P=0.02 for all visits, respectively), indicative of lens dehydration. These findings although clinically significant are not unique to firefighting, and are found within a “normal” population of contact lens wearers. In conjunction with questionnaire data (Owen et al., 1996) we conclude that soft contact lenses can be worn safely by firefighters without additional risk.
Vision and driving ‐ a literature review and commentary
Authors: Charman W. N.
Published: December 2007

The visual requirements that currently have to be met by those applying for and holding current UK driving licenses for private motor vehicles are discussed, together with the incidence of road accidents and the general scientific and social problems of setting visual standards for driving. Literature relating to the effectiveness of various visual tests in predicting the accident‐prone‐ness of individual drivers is reviewed. A striking feature of the data on the age‐dependence of accidents and visual performance is that although visual performance by most tests steadily declines after early middle age, older drivers have less accidents than their younger counterparts, whose visual performance is superior. It is concluded that, although correlations between poor vision as assessed by some tests and accident rates can be shown in large samples of drivers, as yet, no single test or combination of tests has been shown to be able to effectively screen out those at risk of accidents without also leading to the disqualification of a substantial number of potentially safe drivers. Thus no change in the present visual requirements is recommended at the present time.
Graphical representation of visual acuity data
Authors: Moseley Merrick J.
Published: December 2007

Accurate graphical depiction of data requires that distances between points map precisely to the quantitative differences they represent. In the case of Snellen visual acuity, consecutive line sizes do not generally correspond to equal increments in visual angle, hence scores plotted against axes marked off in equal intervals provide a false representation of the relation between plotted values. A worked example illustrates the nature of this problem and its solution.
Sheep refraction, correction and vision in Lewis Carroll's Through the looking glass and what Alice found there (1871)
Authors: Piggins David , Phillips Clive
Published: December 2007

The reports and depiction of the vision and refraction of sheep by Lewis Carroll in Through the looking glass and what Alice found there (1871) appear to be at the very least optically ambiguous to the light of our contemporary knowledge of the refraction of the sheep eye with its large pupil and lack of accommodation and pupil closure.
Interconverting the matrix and principal‐meridional representations of dioptric power and reduced vergence
Authors: Harris W. F.
Published: December 2007

Converting the traditional representation of power as sphere, cylinder and axis to the dioptric power matrix F is usually performed by means of Long's equations and the reverse process by means of Keating's equations. It is sometimes useful to be able to convert directly between the matrix and power expressed in terms of principal powers F| and F2 along corresponding principal meridians at angles a and a2. The equations for interconverting F and the principal‐meridional representation expressed as F^{a}F2 are presented here. Equivalent equations allow direct interconversion of the reduced vergence matrix L and the principal‐meridional representation of vergence L{a)L2. Vergence becomes infinite at line and point focuses. Similarly effective power and back‐ and front‐vertex power are infinite for some systems. Nevertheless it is possible unambiguously to represent infinite vergence and vertex power in principal‐meridional form. However, information is usually lost in these infinite cases when the principal‐meridional representation is converted to the matrix representation, and the former is not recoverable from the latter. As a consequence the matrix representation is usually unsatisfactory for vergences and vertex powers that are infinite. On the other hand, the principal‐meridional representation of vergence and power is always satisfactory. If one adopts the position that effective powers and vertex powers are really vergences rather than powers then one concludes that the matrix provides a satisfactory representation for powers of thin systems in general but not for vergences. Implied by a vergence at a point is an interval of Sturm. The equations for characterizing the interval from the reduced vergence are presented.
Pupil photometric efficiency and effective centre
Authors: Atchison David A. , Scott Dion H. , Smith George
Published: December 2007

We use equations to show pupil photometric efficiency and effective pupil centre when the Stiles‐Crawford function is not centred on the pupil of the eye.
Masked Hypertension Definition, Impact, Outcomes: A Critical Review
Authors: Papadopoulos Dimitris P. , Makris Thomas K.
Published: December 2007

The phenomenon of masked hypertension (MH) is defined as a clinical condition in which a patient's office blood pressure (BP) level is <140/90 mm Hg but ambulatory or home BP readings are in the hypertensive range. The prevalence in the population is about the same as that of isolated office hypertension; about 1 in 7 or 8 persons with a normal office BP level may fall into this category. The high prevalence of MH would suggest the necessity for measuring out‐of‐office BP in persons with apparently normal or well‐controlled office BP. Reactivity to daily life stressors and behavioral factors such as smoking, alcohol use, contraceptive use in women, and sedentary habits can selectively influence MH. MH should be searched for in individuals who are at increased risk for cardiovascular complications including patients with kidney disease or diabetes. Individuals with MH have been shown to have a greater‐than‐normal prevalence of organ damage, particularly with an increased prevalence of metabolic risk factors, left ventricular mass index, carotid intima‐media thickness, and impaired large artery distensibility compared with patients with a truly normal BP level in and out of the clinic or office. Also, outcome studies have suggested that MH increases cardiovascular risk, which appears to be close to that of in‐office and out‐of‐office hypertension. The aim of this review was to define the entity of MH, to describe its prevalence in the general population, and to discuss its correlation with cardiovascular events.
Blood Pressure—The Better Biomarker: Delay in Clinical Application
Authors: Giles Thomas D.
Published: December 2007

“The truly great advances in our understanding of nature originated in a way almost diametrically opposed to induction. The intuitive grasp of the essentials of a large complex of facts leads the scientist to the postulation of a hypothetical law or laws. From these laws, he derives his conclusion.”—Albert Einstein, “Induction and Deduction in Physics,” Berliner Tageblatt, December 25, 1919, CPAE 7:28.
Is Heart Failure More Prevalent in Patients With Peripheral Arterial Disease? A Meta‐Analysis
Authors: Anand Rishi G. , Ventura Hector O. , Mehra Mandeep R.
Published: December 2007

Because risk factors for heart failure (HF) cluster in persons with peripheral artery disease (PAD), the authors conducted a meta‐analysis to examine the prevalence of HF in individuals with PAD. MEDLINE searches were performed to review all PAD clinical trials (1966–2003). Expected control population prevalence rates for HF were derived from the National Health and Nutrition Examination Survey (NHANES) database. In total, 11,304 patients were evaluated. The average age of the patients was 67±5 years. The prevalence of HF in patients with PAD was 7.9% (range, 5.3%–13.9%) compared with an expected prevalence of 4.1%(range, 3.7–4.5%). The relative risk for increased HF prevalence among those with PAD was 1.9 (range, 1.35–3.10; P<.001). Thirteen (range, 7–19) PAD patients needed to be screened to detect 1 case of HF. The presence of PAD is associated with a 2‐fold increase in the prevalence of HF. The use of PAD as a risk marker for underlying HF may enhance the effectiveness of screening criteria for HF detection.
PERMIAN TO TERTIARY FAUNAS AND PALEOGEOGRAPHY: SOMALIA, KENYA, TANZANIA, MOZAMBIQUE, MADAGASCAR, SOUTH AFRICA
Authors: Kamen‐Kaye Maurice
Published: December 2007

Permian to Tertiary faunas along the eastern margin of Africa, and on Madagascar, are presented, described, and discussed. Presentation of the faunas is made in four charts: Permo‐Triassic, Jurassic, Cretaceous, and Tertiary. A correlation chart provides tentative time‐rock units. Paleogeography northeast and east of Africa is derived from the writer's analysis of marine invertebrate fauna, and is delineated in sketches for Late Permian, Jurassic, and Cretaceous times. Limitations exist on the conclusions that can be drawn from fauna alone. Pelagic waters can be indicated, but their extent cannot be specified, and lack of diversification in some of the pelagic genera results in unavoidable ambiguities of interpretation. Nothing in the faunal evidence so far available, however, disproves unequivocally the existence of an ancestral Indian Ocean from Late Permian onward. Even if such an ancestral ocean did not exist the pattern of pelagic waters that can be inferred from marine invertebrate fauna constitutes an impediment to models that suture Australia or India to Africa or Madagascar. Peninsular India, on readings of its own geology across the foreland‐orogen boundary, may have occupied its present position through the whole of geologic time.
SOURCE ROCKS AND THE ORIGIN OF NATURAL GAS IN THE FAR EAST
Authors: Grunau Hans R. , Gruner Ueli
Published: December 2007

Most source rocks of the Far East (Figs. 2 and 6) have a strong humic component, and, therefore, a large gas‐generating capacity. This is an obvious reason why the Far East as an entity is largely a gas province. In particular, the following statements can be made:

(i) Mixed or humic type source rocks in combination with temperature gradients exceeding 3.5°C and minimal burial depths of 3,000m generate predominantly gas (e. g. Gippsland basin, SE Australia; Kapuni gas field, New Zealand).

(ii) Mixed or humic type source rocks in combination with average or slightly below average temperature gradients and burial depths exceeding 3,200‐4,000m generate predominantly gas and condensate (e. g. Dampier sub‐basin, Western Australia; Arun gas field, North Sumatra).

(iii) Mixed and/or humic type source rocks generate gas in the vicinity of magmatic intrusive or extrusive bodies provided magmatic activity post‐dates source rock deposition.

(iv) Most source rocks of the Far East are Paleocene to Miocene age, and source rock maturity and post‐maturity was in many cases reached in Neogene to Recent times.

(v) Mesozoic source rocks of partly humic or mixed type are known from Afghanistan and Australia, Paleozoic source rocks from Australia.

(vi) Retention of the gas phase may have been inadequate in areas of strong Neogene folding (e. g. Sumatra, East Kalimantan and Burma Tertiary basins).

(vii) At the present state of knowledge the question as to which part of natural gas is thermally degraded oil and which part stems from a gas source rock, cannot be satisfactorily solved.
EARLY DIAGENESIS AND THE PRESERVATION OF POROSITY IN JURASSIC LIMESTONES
Authors: Purser Bruce H.
Published: December 2007

The study of Quaternary sediments has shown that carbonates are susceptible to early lithification, or to dissolution, in many different environments. Most of these surface effects, although reducing primary porosity, rarely destroy it completely. Although similar diagenetic phenomena also occur in ancient rocks, the great majority of limestones do not exhibit early diagenetic fabrics; much sparitic cement is possibly related to carbonate liberated by pressure‐solution within the limestone mass.

In spite of the fact that carbonate sediments frequently have high initial porosities, most of it is destroyed by sparitic cement. The exceptional circumstances favouring the preservation of effective porosity may be related to the presence of an early diagenetic phase. A number of reservoirs exhibit early diagenetic cements, dissolution and dedolomitisation fabrics. It is concluded that early lithification tends to retard or prevent subsequent pressure‐compaction and thus reduces the volume of carbonate available for porosity destruction. The recognition of early diagenetic phenomena in ancient limestones therefore has important economic implications.
DIAGENETICALLY FORMED INTERSTITIAL CLAY MINERALS AS A FACTOR IN ROTLIEGEND SANDSTONE RESERVOIR QUALITY IN THE DUTCH SECTOR OF THE NORTH SEA
Authors: Seemann U.
Published: December 2007

In Permian Rotliegend aeolian sandstones in the Dutch sector of the North Sea, kaolinite dominates over poorly crystallised, pore‐lining illite in areas of shallow burial. Fibrous, bridging illite dominates over kaolinite in the areas of deeper burial.

This distribution of diagenetically formed interstitial clay minerals coincides with a regional permeability trend. Higher permeabilities occur in the area where kaolinite dominates over poorly crystallised, pore‐lining illite; lower permeabilities occur in the area where fibrous, bridging illite dominates over kaolinite.
COMPARATIVE PETROLEUM GEOLOGY OF SOUTHEAST TURKEY AND NORTHEAST SYRIA
Authors: Ala M. A. , Moss B. J.
Published: December 2007

In terms of their regional tectonic setting, SE Turkey and NE Syria belong to the Persian Gulf basin, and the essential structural features of SW Iran and N Iraq are readily discernible here. Large, elongated folds of Alpine (Mio‐Pliocene) age dominate the structure of the region, and the intensity of deformation increases towards the north, in the direction of the Taurus orogenic zone.

Five major depositional cycles have been recognized in the sedimentary record of SE Turkey and NE Syria, and the stratigraphy of the area has been outlined. The depositional cycles are late Precambrian, Cambro‐Devonian, Permo‐Carboniferous to Upper Jurassic, Lower‐Cretaceous to Lower Eocene and Middle Eocene to Recent in age. Important regional unconformities are present at the base of the Permo‐Carboniferous to Upper Jurassic and Lower Cretaceous to Lower Eocene cycles. The effects of the latter unconformity are particularly marked north of the Diyarbakir‐Mardin swell in southeast Turkey, and it has adversely affected the petroleum potential of this region.

Several giant oilfields have been discovered in NE Syria, while in SE Turkey the accumulations are small by Middle East standards and are often only marginally commercial. The difference in size of accumulations is due to more favourable source, reservoir and caprock relationships in the former area. Many of the structures in NE Syria can be regarded as multi‐objective with Tertiary, Upper Cretaceous, Lower Jurassic and Triassic prospects, whereas in SE Turkey the effects of the late Jurassic–early Cretaceous uplift and erosion seem to have restricted the potential pay zones largely to the Upper Cretaceous–Palaeocene section.

Geochemical evidence suggests separate sources for the Tertiary, Cretaceous and Lower Mesozoic crudes of NE Syria, and in SE Turkey much of the currently produced oil is believed to have been generated by late Maestrichtian–Palaeocene basinal shales. However, in both areas there is some evidence that at least part of the oils now trapped in Upper Cretaceous‐Tertiary reservoirs in certain fields may be of deeper origin.
ORGANIC MATTER AS INDICATOR OF THE DEGREE OF METAMORPHISM OF THE CARBONIFEROUS ROCKS IN THE SOUTH WALES COALFIELDS
Authors: Gill W. D. , Khalaf F. I. , Massoud M. S.
Published: December 2007

Isoreflectance maps of vitrinites in coals and phytoclasts (coaly inclusions) in the Coal Measures of S. Wales show a progressive increase in vitrinite reflectance with increase in coal rank and grade of metamorphism towards the anthracite area in the west, without significant variation in reflectances of coals with present depth. Differences between values of vitrinite reflectance in coals and phytoclasts in the same profile are recorded and attributed to variations in depositional environments, and to susceptibility to alteration of the host rocks. Spores in the Coal Measures are progressively carbonized (from golden brown to black) towards the west, and this is not a function of present depth of burial. Reflectance of vitrinites in coals, degree of spore carbonization and coal rank are used in definition of three different diagenetic zones in the coalfield. The Coal Measures could have acted as a source for accumulations of gas in the Permo‐Triassic sequence of the south Irish Sea, if necessary geologic conditions are present. Burial metamorphism (application of Hilt's law) could have caused the coalification of S. Wales coals up to the high and medium volatile bituminous stages (up to the late diagenetic stage). A relationship is established between the lateral variation in coal rank in the coalfield and the regional variation in coal rank in the southern British Isles, where two regions of markedly different geothermal history are recognised. The Diagenetic Zone in the E and S parts of the coalfields marks the final stage in the thermal history of the cold region (the W margin of London Stable Massif), whilst the Anchimetamorphic Zone in the NW part (the anthracite area) represents the final stage in the thermal history of the hot region (the S margin of St. George's Land).

Phytoclasts and spores are recorded for the first time from the Dinantian massive limestones of S. Wales.
THE PROVENANCE AND DISTRIBUTION OF THE PALAEOCENE SANDS OF THE CENTRAL NORTH SEA
Authors: Morton Andrew C.
Published: December 2007

A study of the detrital heavy minerals from Palaeocene sandstones of the central North Sea basins has revealed that variations exist which cannot be explained in terms of varying conditions either during or after deposition, and therefore reflect the influence of distinct source areas. Four sand bodies have been defined on a mineralogical basis, two of which occur in the Central Graben and southern Viking Graben, derived from the E. Shetland Platform, the other two being developed in the Moray Firth area, derived from the Scottish landmass. These sand bodies, when related to the existing lithostratigraphic framework, define four phases of basin subsidence, with the sand depocentre alternating between the Central Graben and the Moray Firth basin. This oscillation in basin subsidence, the association with volcanogenic sediments and the apparent basement control on distribution of sands in the Moray Firth indicate a degree of tectonic control hitherto undescribed for the Palaeocene of the area.

Studies of sandstones in or around the inferred source areas have revealed that the metamorphic basement was the major contributor to the sands of the Moray Firth, rather than the pre‐existing sandstones of Devonian, Permo‐Trias or Jurassic ages which occur on the margins of the Firth. Likewise the Old Red Sandstone or Permo‐Trias sandstones of the East Shetland Platform are not suitable source rocks for the sands of the Central Graben and in this case it has been necessary to postulate the existence, at least until the end of Palaeocene times, of Carboniferous sands on the Platform. Such sands in the central North Sea have been shown to possess a mineralogy not dissimilar from that of the Palaeocene sands in question.
EXPLORATION GEOLOGY OF NORTHEASTERN AFRICA‐SEY CHELLES BASIN
Authors: Kamen‐Kaye Maurice , Barnes Sydney U.
Published: December 2007

The basin of NE Africa‐Seychelles ranks with some of the largest in existence. Dimensions are: length 2,400 km (1,500 mi); average thickness 1.6 km (1.0 mi); and sedimentary volume 2,500,000 km3 (6,00,000 mi3). The early history of the basin in obscure until Late Carboniferous time. Thereafter a major continental cycle of Karroo deposition lasted until the Late Triassic or earliest Jurassic. The cycle that followed, mainly marine, continued with few major breaks until the Pliocene or Quaternary, and witnessed a broadening of the basin seaward of the present coast line. Maximum width of the basin may be related to granitic basement material that crops out on the Seychelles. A description of stratigraphy, thickness, and structure of known strata above basement provides background for an exploration analysis. Among the exploration parameters examined, and found to range from highly favorable to poor, are: sedimentary volume, drilling density, source rocks, reservoir rocks, structure, generation and migration, and hydrocarbon recovery. No commercial production has been established, despite the drilling of nearly 110 wells. This disappointing result could be due to some inherent defect in one or more of the exploration parameters, but also could be due in part to a failure of reflection seismometry to indicate the presence and nature of deep structure. If modern reflection‐seismic techniques can overcome previous inadequacies and provide precise locations, a new round of drilling might define more clearly the potential of the NE Africa‐Seychelles basin for commercial hydrocarbons.
REGIONAL STRUCTURAL ELEMENTS IN NORTHWEST GERMANY
Authors: Pratsch J. ‐C.
Published: December 2007

In the past, the tectonic frame work of NW Germany has been considered to be mainly the result of salt‐tectonic events which formed a system of regional salt walls, salt‐dome fields, and surface structures. The primary cause for salt‐tectonic processes has been considered to be an activation of post‐Variscan (post‐Late Carboniferous) fault blocks, ultimately related to basement fracturing, although the location of such fault blocks has not yet been established. Integration of magnetic, gravity, and published geologic data now leads to the definition of several basement strucural elements in NW Germany that influenced sedimentation and tectonics after Late Carboniferous time, possibly even since early Paleozoic (Caledonian) time. Salt tectonics, however, involves secondary processes. Changes in the present strike of these basement elements from N‐S in the west to NW‐SE in the east are not the result of different phases of basement deformation, but rather the result of movements along pre‐existing basement linears and crustal blocks. mesozoic and Tertiary geologic development in NW Germany follows primarily salt tectonic‐related events. Full recognition of the basic causes underlying geologic processes through time in NW Germany should lead to a better understanding of Geologic processes and their results, and to a logical planning of applied geologic tasks.
THE EVOLUTION OF THE DEAD SEA FLOATING ASPHALT BLOCKS: SIMULATIONS BY PYROLYSIS
Authors: Bein A. , Amit O.
Published: December 2007

The asphalts found as floating blocks on the Dead Sea and deep‐seated in wells differ from all other asphalts of the area, mostly by their more abundand and much better preserved n‐alkance. Since biodegradation was found to be the main alteration process through which crude oil was alterd into aphalts, such well‐preserved n‐alkanes are unexpected. A hypothesis of secondary generation of theise alkanes was tested bny pyrolysis simulations of asphalt at 300d̀C during periods ranging up to 60 days. The abundance and distrubution pattern of the n‐alkanes in the simulated asphalts after 14 days of heating resembles that of the floating asphalt blocks and that found at a depth of 3,500 m. In addiation to saturated hydrocarbons, aromatics and gases were also formed at the expense of resins and asphaltenes. The H/C ratio was balanced by the formation of pyrobitumen and by a gradual decrease of the H/C ratio in the residual resins and asphaltenes. The gas formed contained about 60 to 80% methane with an isotopic composition of‐41 to 42%%. The hydrocarbon content of the simulated asphalt (gas and liquids) increased from about 15% at the stariting material to about 60% after 60 days of heating.

The recognition that asphalts in the Dead Sea basin are secondarily subjected to alteration upon burial might be of economic importance. Asphalts buried to a depth at which maturation conditions are close to that reached in the pyrolysis simulation at 300d̀C after about 60 days may be counted on as source material for hydrocarbons.
QUATERNARY TURBIDITES IN A NERITIC ENVIRONMENT: WELL CNR VE 1, VENICE, ITALY
Authors: Favero V. , Passega R.
Published: December 2007

Turbidites are generally deep‐sea deposits. By contrast, the turbitdites which form a large part of the nearly 1000m Quaternary section, cored in well CNR Venice 1, do not seem to have been deposited at sea depths much greater than 200m. Sea depth, determined mostly by ecological analyses of faraminifera, gradually decreases as the basin was filled with sediments. In the upper part of the well, above 302 m, turbidite sedimentation was replaced by alternating fluvitile and very shallow marine deposition.

In well CNR Venice 1, turbite characteristics vary with the sea depth and the gradient of sea slopes. If near riveer mouths, the slope gradient is sufficient, sediments debouching from rivers readily form turbity currents. The displaced fauna in sand and in shale turbidites is fresh‐water. When gradients decrease, sediments are distributed along the coast and form submarine deltas or coastal shelves. If these shelves are limited by a sandy slope, turbidity currents may originated on this slope. Displaced fauna in the sand turbidites is marine littoral. If sediments of the slope limiting the coastal shelf are silt and clay, muddy turbidity currents can originate provided the gradient is 1% or more.

A critical factor of sedimentation of Venice neritic turbidites is the very fine grain‐size of the sands. Turbidity current suspensions probably were stable as they could be supported by a moderate bottom turbulence. Suspensions therefore were not likely to settle rapidly when the gradient decreased to form fan‐like deposits. They flowed to the bottom of the basin where they spread and made their thickest deposits.

Turbidites similar to Venice Quaternary turbidites may be common in ancient neitic basins, where gradients were sufficiently steep. These turbidites can form good petroleum reservoirs as well as impervious shale beds and permeability barriers.
ON THE THEORY OF GROWTH FAULTING*: GENESIS OF THE “UNIT”
Authors: Crans W. , Mandl G.
Published: December 2007

A detailed and rigorous geomechanical analysis of the stability of overpressured, gently sloping, sediment layers is presented that underlies the Multi‐Unit Delta Model described in Part I (Crans, Mandl and Haremboure, Journ. Petrol. Geol., 2, 3, 1980). That delta model explains and permits quantitative reproduction of main features associated with growth faulting. Starting from the equilibrium equations, the Coulomb‐Mohr yield criterion and the proper initial and boundary conditions, the elastic and plastic stress fields in the sloping, overpressured layer are derived. The plastic stress field is calculated on the grid generated by the “characteristics” of the hyperbolic partial differential equation for the plastic stress state. These characteristics, being called in stress analyses “slip lines”, are potential faults. In the case considered, a parameter equation is derived for one set of slip lines, (potential growth faults), which may simplify into cycloids under special conditions. Once the plastic stress field has been generated, the plastic deformation of the layer can be calculated by introducing the proper boundary conditions to the flow rules or plastic “velocity equations” being discussed extensively. To complete the rheological description, the behavior of the sediment layer is described by attributing also thixotropic properties to the sediment. Although the case discussed is a very specific one, it illustrates how structural geological phenomena can be modeled on the computer in an appropriate geomechanical way. Such a numerical computer model shows the unique relation between plastic stress state and fault pattern, and the non‐unique relation between plastic stress state and deformation pattern, being typical for the theory of plasticity. Generally, the unique relation between stress state and fault pattern is of utmost importance for the seismic interpreter in judging the feasibility of fault patterns. Inversely, one may deduce the stress state in the formation from a convincing fault pattern obtained from structural seismic interpretation which is, among others, important for the evaluation of acoustic properties of the sedimentary sequence used for the probabilistic assessment of seismic amplitude anomalies in the search for hydrocarbons (Crans and Berkhout, 1979, 1980; Crans and Ausburn, 1980).
HYDRODYNAMICS—DOES IT TRAP OIL?*
Authors: Magara Kinji
Published: December 2007

In order for the hydrodynamics of meteoric water to be an important trapping mechanism for hydrocarbon accumulations, it must have existed for a long geologic period extending from the time of secondary hydrocarbon migration and its accumulation to the present time. However, in most interior sedimentary basins, the present hydrodynamic patterns are considered to have been developed only a short while ago (geologically speaking), after the significant uplift and the associated erosional events which caused the present topographical relief. Most petroleum accumulations were probably formed a long time before the development of the present hydrodynamic flow patterns, and hence must be explained by different mechanisms that have been effective for a much longer geologic period.

This paper also discusses other possible problems in applying the hydrodynamics concept to understanding the formation of petroleum accumulations, such as the lack of proper water passways and outlets in several basins, the difficulty of moving water through hydrocarbon‐saturated sections of a reservoir, and the difficulty of keeping significant salinity gradients in a reservoir where active water flow has taken place.
A NOTE ON THE SIMULATION OF THE EARLY DIAGENESIS OF RECENT CARBONATE OOIDS
Authors: Ferguson J. , Bush P. R. , Clarke B. A.
Published: December 2007

The following is a short note reporting preliminary experimental work designed to test the feasibility of simulating early diagenetic changes in Recent carbonates. Two experiments are reported; one lasted a period of 3 months and the other for a period of 6 months. In both cases, samples of Recent ooids, split from a single sample taken from the Schooner Cays tidal belt, off Eleuthera Island, Bahamas, were held in a constant temperature/pressure regime in the presence of standard sea water.
PROBABLE GAS HYDRATE IN CONTINENTAL SLOPE EAST OF THE NORTH ISLAND, NEW ZEALAND
Authors: Katz Hans‐Rudolf
Published: December 2007

Anomolous seismic horizons which (1) are strongly reflective, i.e. have a high impedence contrast; (2)cut across bedding planes of sediments;(3)are subparallel with the sea floor; and (4)increase their sub‐bottom depth with increasing depth of sea floor (and thus with decreasing temperature of bottom water) are tentavely identifed as the base of a gas hydrate layer. The anamalous reflections occur below waters 1000‐2500m deep, and along 500km of the continental slope. Some 10–20,000 sq km appear to be underlain by gas hydrates.

The hydrate layer is often associated with structural anomalies(anticlines, tilted faultblocks). These would allow gas to migrate up‐dip into pressure and temperature conditions suitable for hydrate formation. Since the hydrate‐cemented layer itself acts as a barrier to gas migration, free gas will be trapped and accumulated in the sediments beneath it.

It is concluded that huge amounts of hydrocarbon gas, both free gas and solid hydrate, have accumulated in this continental margin. On land, gas and oil generation is widespread, mainly originating from overpressured, Lower Teritiary to Upper Cretaceous shales. From seismic evidence the same formations appear to extend under the shelf and continental slope. The extensive occurence of gas hydrates would confirm that organicrich, terrigenous sediments have extensively been deposited in these areas.
POSSIBLE PRIMARY MIGRATION OF OIL GLOBULES1
Authors: Magara Kinji
Published: December 2007

Difficulty of migrating a large amount of oil in either molecular or micellar solution may lead to an assumption that a continous oil phase or a relatively high (20–30%) concentration of oil in pores of shales is necessary for primary migration to overcome the capillary restrictions against the oil. Movement of small oil globules in shales is believed by many workers to be an extremely difficult process. However, the above assumption is not necessarilly valid in shales which contain a large quantity of structured and semi‐solid water. Such oil globules may defrom by the effect of compacting grains (solid material) and the semi‐solid water, thus reducing the capillary restrictions significantly. This suggests that the small oil globules which are separated from each other can move in the direction of lower stress in the shales: a continous oil phase or relatively high oil concentration is not a necessary requirement for primary oil migration.
EXPLORATION PROSPECTS AND FUTURE PETROLEUM POTENTIAL OF THE CANADIAN ARCTIC ISLANDS
Authors: Rayer F. G.
Published: December 2007

The offshore and onshore area of the Canadian Arctic Archipelago, 1.7 million sq km, is one of the most prospective frontier regions in Canada. The first onshore well was drilled at Winter Harbour in 1961, and the first offshore well was drilled from an ice‐strengthened island at Hecla in 1974. To date, more than 140 wells have been drilled, and 12.0 Tcf of recoverable gas have been discovered as well as a small amount of oil. The gas is largely Lower Jurassic, with smaller amounts in Triassic and Lower Cretaceous strata.

The Canadian Arctic Archipelago is actually underlain by two prospective basins: the older Franklinian geosyncline, or basin, Cambrian through Devonian; and the younger Sverdrup successor basin, Late Mississippian through Middle Eocene. The principal orogenic events to affect the area were the Caledonian uplift (Devonian), the Ellesmerian orogeny, a compressive fold system was produced with décollement of the southern part of the Franklinian on the Ordovician Bay Fiord salt. Vertical uplift, with compression in the east, dominated the Eurekan orogeny.

Objectives in the Franklinian basin include sub‐Bay Fiord (sub‐Ordovician) structures—mainly Lower Paleozoic carbonates and some terrigenous clastics; supra‐salt folds of the Parry Islands fold belt—Ordovician‐Devonian reefs and porous shelf carbonates; other Lower Paleozoic reef bodies; and porous Devonian clastics in the Parry Islands fold belt. Sverdrup basin objectives include mainly terrigenous clastic reservoirs in Pennsylvanian‐Cretaceous rocks, with structural (salt anticlines and diapirs; some folds in the east) and stratigraphic (pinchouts on the flanks of structures, and along the folds) possibilities. The greatest potential in the Sverdrup basin is in the central and western parts. Ultimate recovery of gas is estimated to be at least 125 Tcf.