bluuebunny/crossref_metadata_2025 huggingface dataset:
OKN asymmetries and binocular function in amblyopia
Authors: Westall Carol A. , Woodhouse J. Margaret , Brown Valerie A.
Published: December 2007

Asymmetrical optokinetic nystagmus (OKN) means that OKN has a lower gain (slow‐phase eye velocity/stimulus velocity) for monocular temporalward than nasalward visual field motion. OKN tends to be asymmetric in amblyopia, leading to suggestions of a link between OKN asymmetry and binocularity in the literature. The present study measured OKN in 13 amblyopes and five normal subjects. In an attempt to identify those binocular cells used in the OKN response, the degree of OKN asymmetry was compared with binocularity assessed by two different techniques: (1) stereopsis and (2) interocular transfer of threshold elevation (IOT). Horizontal monocular OKN was recorded for three different stimulus velocities in each subject. All the amblyopes were found to be stereoblind, although three amblyopes showed OKN asymmetries close to those found for the normal group. More association was seen between interocular transfer of the threshold elevation and OKN asymmetry; not all amblyopes demonstrated reduced IOT, but those amblyopes with no IOT all had OKN asymmetries more than 125% of the mean of the normal group. However, no association was seen between the amount of OKN asymmetry and the degree of IOT. The results are discussed in terms of the role of different groups of binocular neurones for OKN and the effect of the sensitive periods of development on these binocular neurones.
Myopia in optometry students: family history, age of onset and personality
Authors: Bullimore Mark A. , Conway Roisin , Nakash Adam
Published: December 2007

The relationship between refractive error and family history, age of onset and personality was investigated in 189 optometry students. Subjects completed a questionnaire requesting details of their refractive history, type of correction and their family history. Subjects also completed an Eysenck Personality Inventory (EPI). Subjects were categorized as hyperopes, emmetropes or myopes on the basis of their questionnaire responses. No significant relationship was found between refractive group and the prevalence of myopia in parents. Myopic subjects, however, showed a significantly higher prevalence of myopic siblings. Furthermore, late‐onset myopes showed a higher prevalence of myopic siblings than early‐onset myopes. No significant personality differences were found between the refractive groups.
Effect of a scotoma on eye movements during visual search
Authors: Murphy K.St.J. , Foley‐Fisher J.A.
Published: December 2007

Eye movements have been recorded during a free visual search task both with and without an artificial foveal scotoma. Results of the eye movement measurements show that neither fixation durations nor mean saccade amplitudes are significantly modified by the loss of foveal vision.
Low vision aids (evaluation of 185 patients)
Authors: Temel Ahmet
Published: December 2007

One hundred and eighty‐five referred patients with various eye pathologies were evaluated retrospectively after they had undergone an examination and issued with a prescription for low vision. The majority of patients (77%) benefited from the prescribing of low vision aids (LVA). Spectacle‐mounted magnifiers, high reading additions and telescopes were used as LVAs. Visual acuity, age and magnification are important factors in the assessment of an LVA.
Do visibility and colour recognition isopters relate to the distribution of Pα and Pβ ganglion cells of the human retina?
Authors: Drasdo N. , Thompson C. M.
Published: December 2007

Early perimetrists recognized that the threshold stimulus diameters for visibility and colour recognition differ markedly in peripheral vision. However, we observed that these diameters are identical at the fixation point. This means that these threshold diameters, when plotted against eccentric visual angle, have unequal slopes, perhaps related to recently reported data on estimated magnocellular and parvocellular neural sampling intervals. We therefore collected perimetric data on eleven normal observers, using red stimuli on the Zeiss Jena Type 1 Bowl Perimeter. It was found that the slopes were steeper than those for supposedly corresponding neural data. This could be explained by taking into consideration that (a) the slow rate of stimulus movement allowed parvocellular contribution to visibility; and (b) the possibility of an enhanced foveal representation in the cortical colour processing areas. The clinical significance of these findings is briefly discussed.
Eye‐tracking infra‐red optometer
Authors: Okuyama F. , Tokoro T. , Fujieda M.
Published: December 2007

An eye‐tracking infra‐red optometer has been developed to measure dynamic refractive power during slow horizontal eye movement. It consists of two instruments: an optometer to measure the refractive power of the human eye, and an eye tracker. When measuring refractive power, the eye tracker is used to maintain automatically the optical axis of the optometer coincident with the visual axis of the human eye. The measurement range of the optometer is approximately ‐10 to + 10 D; refractive power is measured with an accuracy of about 0.4 D and with a precision of 0.05 D over an eye movement range of 60 degrees. The maximum trackable eye movement velocity is over 100 degs‐1, with a time delay of about 0.13 s. Furthermore it was confirmed that eye refraction measurement during vergence is possible using this eye‐tracking infra‐red optometer.
Anthrax of the eyelid
Authors: Barnard N. A. Simon
Published: December 2007

Anthrax is a rare infection that is transmitted to humans from animals or animal products. In its cutaneous form it may produce lesions of the eyelids which can lead to cicatricization and ectropion. Exophthalmos, optic atrophy and panophthalmitis have also been reported. A case of anthrax affecting the eyelid of a patient seen by the author in Kabul, Afghanistan, is presented.
Visual fitness to drive after stroke or head injury
Authors: Shute Rosalyn H. , Woodhouse J. Margaret
Published: December 2007

The visual requirements for driving in Britain are outlined and how they might be compromised following stroke or head injury examined. The role of the optometrist in assessing such patients who wish to resume driving is discussed. Topics discussed include legal considerations, the relationship between visual problems and driving ability and the vision‐testing techniques that are most appropriate for use with the brain injured. An illustrative case history is presented.
Measurement of the posterior corneal radius using slit lamp and Purkinje image techniques
Authors: Royston J. M. , Dunne M. C. M. , Barnes D. A.
Published: December 2007

A method for measuring the radius of the posterior corneal surface using the first and second Purkinje images has recently been developed. Values for the posterior corneal radius in the vertical meridian obtained using this method are compared with those obtained using a more conventional slit lamp method. A good correlation was found between values obtained using the two methods.
Review of ophthalmic factors in dyslexia
Authors: Evans Bruce J. W. , Drasdo Neville
Published: December 2007

Dyslexia and the effect of visual problems on reading ability have long been subjects of controversy. This paper critically reviews the literature on the relationship between reading disability and visual acuity, refractive error, binocular vision anomalies, eye movements, ocular pathology and the transient and sustained visual systems. The limitations of much of the work in this field are described, with particular reference to the problems of subject selection and group matching. Tentative conclusions, with deference to the complex nature of dyslexia, are drawn and suggestions are made for future research.
A new system for the measurement of ocular motility using a personal computer
Authors: Thomson W. David , Desai Nimish , Russell‐Eggitt I.
Published: December 2007

A new system (automated Hess screen, AHS) for the measurement of ocular motility using a personal computer is described. The subject is seated with his/her head restrained at a fixed distance from a colour monitor and views the screen through red/green goggles. A red target is displayed on the screen and the subject is instructed to move a green stimulus (using a joystick control) until the stimulus appears to be centred on the target. A button on the joystick is pressed and the computer registers the relative position of the target and stimulus. This procedure is repeated for a range of target locations (positions of gaze) and the entire routine is then repeated with the other eye fixing, by reversing the colour of the target and stimulus. The oculomotor fields may be displayed on the screen, printed, plotted or saved on a magnetic disc. A prototype system (based on an IBM AT with a 20 in monitor viewed from 25 cm) has been evaluated in a clinical environment on a sample of patients with a wide range of oculomotor problems, and compared with the electronic Hess screen (EHS). In general, the shapes of the oculomotor fields obtained using the two instruments were similar, but the AHS tended to measure a slightly converged displacement of the plots relative to the EHS and to record larger deviations, particularly in patients with incomitant fields. However, the test‐retest reliability and the diagnostic value of the charts obtained were similar for both instruments. There was no significant difference between the durations of the examinations with the EHS and AHS. The AHS is a viable alternative to the EHS.
Presaccadic spike potential with vertical saccades
Authors: Doig H. Ross , Nesfield Catheryn J. , Boylan Christine
Published: December 2007

Presaccadic spike potentials were recorded from four electrodes placed around the eyes for 20 degree vertical saccadic eye movements. Twenty upward and 20 downward saccades were recorded using electro‐oculography and the spike potentials back‐averaged from the start of the eye movement. Separate average waveforms were obtained for upward and downward saccades. The onset of the spike was between 17.3 and 6.8 ms before the start of the saccade with downward saccades having earlier onsets than upward saccades. This difference was only significant in the right eye (P < 0.025). The peak occurred between 3.4 ms before to 5.2 ms after the start of the eye movement and was earlier with downward saccades. This was only significant in the right eye (P < 0.025). The onset to peak amplitude measured between 15.9 and 42.3 μV with no statistical difference between upward and downward saccades. It was found, however, that the electrodes placed below the eyes recorded larger amplitudes for upward saccades than the other electrode‐recording positions (right eye P < 0.05, left eye P < 0.025). A second component to the spike potential waveform was observed in many of the recordings and a possible origin of this component due to eyelid activity is hypothesized.
The experience of a university‐based low vision clinic
Authors: Leat Susan Jennifer , Rumney Nicholas James
Published: December 2007

An open low vision clinic has been in operation at University of Wales College of Cardiff, Department of Optometry for 5 years. This paper describes the demography and visual characteristics of 218 consecutively presenting patients. A detailed survey of the aids prescribed is conducted. A significant proportion of low vision patients required only simple aids (56.8%) and low magnification (71.6%). It is suggested that these patients could be assisted in an optometric practice.

In addition, visual acuity, distance or near is not a good indicator of eventual visual performance with an LVA. Therefore, it was concluded that all patients having measurable form vision should receive a low vision assessment.
Effect of preservatives in artificial tear solutions on tear film evaporation *
Authors: Tomlinson Alan , Trees Gerald R.
Published: December 2007

It has been suggested that certain preservatives in artificial tears may affect the stability of the tear film lipid layer. In the present study, tear film evaporation rate (TER) was measured with a modified Servomed Evoporimeter to determine whether preservatives affected tear stability. Two solution combinations were compared in a cross‐over study of eight non‐contact lens wearers. These combinations consisted of identical solutions, one preserved with either benzalkonium chloride (0.004%) or chlorobutanol (0.5%), the other non‐preserved. Grouped data analysis showed no significant difference in TER with either solution combination. Individuals showed differences, but these were not related to the preservative. It is suggested that these concentrations of chlorbutanol and benzalkonium chloride did not affect the stability of the tear film lipid layer as indicated by an altered TER.
The refractive status of Hong Kong Chinese infants
Authors: Edwards Marion
Published: December 2007

One hundred and fifty‐eight full‐term Hong Kong Chinese infants were examined, at the age of approximately 10 weeks, using retinoscopy. Fifty of the subjects were re‐examined at the ages of 20, 30 and 40 weeks. Cyclopentolate 1% was used to produce cycloplegia. Photographic methods were used to assess the straightness of the eyes of 122 infants. While the mean spherical equivalent of the refractive error at 10 weeks was within the limits reported in studies of Caucasian infants, a rapid decrease, not previously reported, occurred between the ages of 10 and 40 weeks. The amounts of astigmatism found were in line with results from Caucasian eyes but the direction was overwhelmingly with‐the‐rule. The prevalence of anisometropia decreased with age and anisometropia was not prevalent at the age of 37 weeks. Two exotropes (1.6%)and no esotropes were identified although this may have been confounded by the use of cyclopentolate.
Colour‐mediated grouping effects in good and disabled readers
Authors: Solman Robert T. , Cho Hae‐Sook , Daint Stephen J.
Published: December 2007

Specific deficits in the processing of transient usual stimuli have been identified in reading disabled children. It has, separately, been suggested that suitably chosen coloured lenses can be used to assist reading disabled children but this is controversial. To assess an hypothesis as 10 how coloured lenses might remediate visual processing, this study compared the visual perceptual grouping effects of eighteen disabled readers with those made by eighteen good readers of the same age. Perceptual grouping effects were obtained for each child under a normal condition and wearing blue, yellow, grey, red and green optical framed lenses. The results replicated previous work in demonstrating a larger grouping effect for the disabled readers, and it was suggested that this finding was consistent with the presence of a transient deficit in these children Comparison of the grouping effects obtained using the coloured lenses showed that although there was no significant impact on the performances of the disabled readers, the blue lens significantly increased the size of the grouping effect for the good readers. The presence of the blue lens decreased the activity initiated by stimulation of the red and green cones relative to the level of activity initiated by blue cone stimulation, As blue cone initiated activity appears (o play little part in the transfer of acuity information, the presence of the blue lens could depress performance in a normal visual system by decreasing the level of acuity information transfer (i.e. the information required for efficient selective attention sorting and minimizing the grouping effect), The absence of a blue lens effect (either negative or positive) in the disabled readers made it difficult for the results to address directly I he question of prescribed coloured filters for the correction of reading problems. However, the results did show that there were reading–dependent colour effects.
Method for identifying amblyopes whose reduced line acuity is caused by defective selection and/or control of gaze
Authors: Regan David , Giaschi Deborah E. , Kraft Stephen P. , Kothe Angela C.
Published: December 2007

Three visual tests were administered to a group of 15 amblyopic children. 15 adult amblyopes and two age‐matched control groups, each of 20 subjects. Test results comprised visual acuity for recognizing high contrast letters presented in line (i.e. Snellen) Formal, isolated‐letter format and repeal‐letter format. The classical Snellen format confounds the effects of gaze control defects with the effects of adjacent contours on a patient's ability to recognize a foveated letter. We designed a repeat‐letter format intended to unconfound these effects. The repeal letter formal is much less sensitive to gaze control defects, and somewhat more sensitive to adjacent contour interactions than is the Snellen format. We report that amblyopic eyes can he subdivided empirically into three repeat‐letter categories: repeat‐letter acuity significantly better than Snellen acuity; repeat letter acuity not significantly, different from Snellen acuity: and repeal letter acuity significantly worse than Snellen acuity. We report that this subdivision cuts across the clinical subclassification of amblyopic and also across the crowding no crowding subclassification. We suggest that, rather than abnormal lateral interactions, defective selection and or control of gaze is an important factor in depressed visual acuity in amblyopic eyes of the first repeal‐letter category but not for the third type, in which abnormal lateral interactions may be important. To test the hypothesis that the response to patching and refractive therapy may be less satisfactory in our first category of amblyopic eyes, we are carrying out a prospective study. If the hypothesis is confirmed, it might then he worthwhile to identify these patients at an early stage and investigate whether therapies designed to improve the control of gaze might be more effective in this group than is patching or refractive therapy.
Twice‐daily use of a chlorobutanol‐preserved artificial tear on rabbit corneal epithelium assessed by scanning electron microscopy *
Authors: Doughty Michael J.
Published: December 2007

Female pigmented rabbits received two drops of a chlorobutanol 0.5%‐preserved, polyvinyl alcohol‐based artificial tear at 21.00 h and 09.00 h for 1, 2, 3, 6 or 12 consecutive days. The animals were killed at 15.00, 6 h after the last treatment. Scanning electron microscopy of the corneal epithelial surface at × 200 magnification revealed only occasional cell exfoliation averaging <8% of the surface analysed at central. mid‐peripheral and peripheral sites, showing minimal cytotoxic effects. The level of exfoliation was maximal after 2 to 3 days treatment and then returned to close to zero, so the eye adapts to repealed use of the artificial tears. Evaluation of the surface microplicae of the cells at × 15000 indicated subtle, but distinct, changes in what might be the mucus material associated with the cell surface, especially after 2 and 3 days treatment.
Clinical contrast sensitivity chart evaluation
Authors: Elliott David B. , Whitaker David
Published: December 2007

Three different types of contrast sensitivity chart were used on normal patients by six optometrists in clinical practice. The charts were the Vistech, the Pelli ‐Robson and the Cambridge low‐contrast gratings test. We examine the data in terms of the differences between optometrists and the variation of contrast sensitivity with the age of the patient. There was a highly significant difference between the scores from different optometrists for all three charts. We attribute this to variability in measurement technique. There was also a highly significant effect of age for all three charts, with older observers tending to exhibit lower contrast sensitivity. On the Vistech chart, this sensitivity deficit was most pronounced at higher spatial frequencies. The level of redundant information in the tests is discussed.
Effect of induced fixation disparity on binocular visual acuity
Authors: Jenkins T. C. A. , Pickwell L. D. , Abd‐Manan F.
Published: December 2007

Fixation disparities were artificially created for distance vision by prisms, and the monocular and binocular visual acuities were measured. The normal approximate 10% improvement in binocular visual acuity compared to monocular visual acuity, deteriorated in proportion to the amount of fixation disparity created by the prisms. This was true in both eso‐ and exo‐disparity. although not to the same extent.
Population distribution of stereoscopic ability
Authors: Coutant Ben E. , Westheimer Gerald
Published: December 2007

Of 188 unselected biology students participating in one or both of two tests measuring stereoscopic depth detection ability. 183 (97.3%) were able to see a depth difference at horizontal disparities of 2.3 min arc or smaller. At least 80% could detect depth differences at 30 sec arc disparity. These findings indicate the most people are able to take advantage of the increasing utilization of stereoscopic displays.
Reading performance with low vision aids: relationship with contrast sensitivity
Authors: Leat Susan J. , Woodhouse J. Margaret
Published: December 2007

Reading performance and contrast sensitivity were measured in 30 subjects with low vision due to a variety of pathologies. The Pepper test was used to quantify reading rate and accuracy with the subject's own prescribed optical reading low vision aid. It was found that both reading rate and accuracy were repeatable measures. Reading rates were found to he correlated with contrast sensitivity at 0.5c/deg (r= 0.62). Multiple regression analysis also showed that the best predictor of reading rate was contrast sensitivity at 0.5c/dcg and that no other components of the contrast sensitivity function helped to explain more of the variance. This indicates that primarily low spatial frequencies are necessary for reading with optical low vision aids, as has been found previously for reading with a close circuit TV system.
Mathematical description of isogyre formation in refracting structures
Authors: Pierscionek Barbara K. , Chan Derek D. Y. C.
Published: December 2007

The cross pattern (isogyres) formed by certain crystals when they are placed between crossed polarizers and illuminated with convergent light results from birefringent properties of the medium. A similar image is seen in refracting structures which exhibit little or no birefringence, such as the eye lens. This paper provides a mathematical explanation of the formation of isogyres by refraction.
Accommodation and chromatic aberration: effect of spatial frequency
Authors: Stone Debra , Mathews Steven , Kruger Philip B.
Published: December 2007

When subjects view an edge in while light, a colour fringe, produced by longitudinal chromatic aberration (LCA) of the eye, is formed at the edge. The colour fringe changes with changes in focus, and serves as a complex colour‐coded cue for reflex accommodation. Fincham found that 60% of his subjects failed to accommodate appropriately when the colour fringe was removed with an achromatizing lens or by the use of monochromatic light. Our experiment sought to determine the spatial frequencies al which LCA is most effective. We monitored accommodation in 10 subjects while they viewed sinusoidally moving sine‐wave gratings (1–3 D at 0.2 Hz; l–10.5c/deg) in a Badal optometer. The targets were “while” gratings with LCA normal, doubled, neutralized or reversed. Doubling the aberration has minimal effect, removing the aberration reduces gain and increases phase‐lag, and reversing the aberration severely disrupts accommodation. Sensitivity to these chromatic cues exists at all spatial frequencies tested, but is most prominent between 3 and 5 c/deg. These results support the view that the system monitors focus by comparing contrast in red‐green and perhaps blue‐yellow colour‐opponent mechanisms.
Colour and flicker thresholds for high frequency increments
Authors: Schwartz Steven H.
Published: December 2007

Previous investigators have elicited spectral sensitivity functions for the chromatic and achromatic systems by manipulating the stimulus spatiotemporal parameters. An alternative strategy for obtaining these two functions is to use a single set of stimulus parameters and vary the threshold criterion. This can he accomplished by determining colour and flicker thresholds for a high frequency train of increments. In the current study, spectral sensitivity functions, based on colour and dicker thresholds, were determined for increments presented at 25 Hz. The colour and dicker threshold functions are similar in form to those previously published for the chromatic and achromatic systems. The existence of distinct threshold functions for colour and flicker are interpreted in the context of parvo and magno pathways. Potential clinical applications of this model arc discussed.
Maximizing the dynamic range of the Humphrey Field Analyzer for blue‐on‐yellow perimetry
Authors: Hudson Chris , Wild John M. , Archer‐Hall John
Published: December 2007

The conditions employed for blue‐on‐yellow perimetry (i.e. a blue stimulus filter and a high luminance yellow background) are in conflict with those that allow a maximum dynamic range. A modification is described for increasing the dynamic range of the Humphrey Field Analyzer (HFA) for blue‐on‐yellow perimetry. The position of the HFA stimulus bulb was lowered by reducing the length of both terminals. A concave mirror with a 28 mm radius of curvature was positioned behind the lowered stimulus bulb to give a filament image partly above and partly overlapping the original filament profile within the confines of the size V stimulus patch diameter. The modification achieved a 60% increase in the light output on the default 0 dB value of 10000 apostilbs and, therefore, a useable dynamic range for blue‐on‐yellow perimetry of 2.94 log units. The effective increase in voltage supply to the stimulus Kilb permitted a filament life of 260 operating hours. Furthermore, the modification ensured the correct calibration of the instrument.
Arabic visual acuity chart for low vision examination
Authors: Al‐Khattabi Sultan , Oduntan Alabi O.
Published: December 2007

An Arabic visual acuity chart has been designed for low vision examination, using ten Arabic letters constructed on a 5 × 5 framework. The chart contains seven pages with acuity values ranging from 20/600 to 20/80, corresponding to letter sizes of 26.5–3.5 cm. Interletter spaces were made one‐fifth the size of each letter in a row while inter‐row spaces were made equal to the height of the letters in the row below. The chart will be useful to eye care practitioners who may wish to use Arabic charts in low vision evaluation.
Risk of accidents among elderly car drivers with visual acuity equal to 6/12 or 6/15 and lack of binocular vision
Authors: Gresset Jacques A. , Meyer Francois M.
Published: December 2007

To document the risk of road accidents associated with minimal visual acuity (equal to 6/12 or 6/15) and lack of binocularity (stereoacuity = 200 sec arc), 1400 drivers who had had an accident during their 70th year were compared with 2636 controls randomly selected from the 30 000 70–year–old drivers who had had no accident during the same time. Information on visual characteristics and demerit points was obtained for all subjects from the Quebec Automobile Insurance Board. Mileage and prevailing driving conditions were documented through a mail questionnaire. The relative risks of accidents were estimated while controlling for traffic convictions, mileage, time spent and frequency of driving during rush hours. Drivers with minimal visual acuity alone had the same risk of road accidents as other drivers (OR= 0.97 Cl 95%: 0.68–1.38). The risk of accidents among drivers with both minimal visual acuity and lack of binocularity was moderately higher than among other drivers (OR= 1.23, CI 95%: 0.88–1.72).
Glassblowers' ocular health and safety: optical radiation hazards and eye protection assessment
Authors: Oriowo Olanrewaju M. , Chou B. Ralph , Cullen Anthony P.
Published: December 2007

The arms of this study were to investigate the levels of optical radiation exposure in glassblowing and to determine type(s) of protective eyewear commonly used. Radiometric measurements of radiant emissions from different molten glass materials and heating systems were carried out in six installations. Spectral transmittance curves of available protective lenses used at the locations were obtained. Significant variation (P= 0.0001) in ocular irradiation was obtained. All operations produced irradiances higher than the threshold limit values (TLVs for the visible spectrum (400 to 700 nm). In craft glassblowing which employs furnace systems, irradiance levels exceeding the TLVs for near infrared (760 to 1100nm) were obtained. Molten soda‐lime and quartz glasses emitted substantial subthreshold near UV radiation. This study shows that variation exists in glassblowing ocular radiation exposure due to different glass materials and heating systems, therefore selection of appropriate eye protector should be on an individual basis.
24‐Hour Blood Pressure Monitoring in the Evaluation of Supine Hypertension and Orthostatic Hypotension
Authors: Ejaz A. Ahsan , Kazory Amir , Heinig Marcelo E.
Published: December 2007

The presence of orthostatic hypotension has been shown to be a significant, independent predictor of all‐cause mortality. Systolic and diastolic orthostatic hypotension, reversal of the circadian pattern, and postprandial hypotension are some of the hemodynamic factors that may contribute to the increased mortality seen in patients with orthostatic hypotension. The high variability of blood pressure in orthostatic hypotension cannot usually be adequately assessed by a one‐time measurement. In this group of patients, 24‐hour ambulatory blood pressure monitoring may be more useful.
TECTONIC CONTROL OF OFFSHORE SEDIMENTARY BASINS TO THE NORTH AND WEST OF IRELAND
Authors: Max M. D.
Published: December 2007

A newly compiled tectonic map of Ireland and part of the offshore area can be used to show that a pattern of rejuvenated Caledonian structures was superseded by newly imposed structures at about the time of the opening of the northern North Atlantic Ocean. There are three distinct patterns of structural control: 1. Older Caledonian structures, 2. Younger Caledonian structures and 3. ‘Oceanic’ structures. Younger structural patterns are each superimposed on older, so that locally interference patterns are developed. Each of the structural regimes has controlled sedimentation in particular zones, and where superimpostion has occurred, mixed shelf‐continental and ‘oceanic’ sedimentation can be expected at different structural levels.

One of the major control structures in and immediately off NW Ireland is the Great Glen Fault system, which has been repeatedly rejuvenated since its development in Caledonian times. Other major control structures are associated with the Porcupine Seabight, which probably developed during the initiation of the immediately adjacent North Atlantic Ocean basin. Where these structural systems intersect at the head of the Seabight, sedimentational provinces can be defined.

A poorly defined E‐W structural line at about 53° 25′ across the northern part of the Seabight may reflect deep wrench faulting related to a subjacent transform. Major structures along this line would have influenced sedimentation and consequent growth structures. This line may be an eastward analogue of the Gibbs Fracture Zone against which the axial zone of ‘quasi‐oceanic’ or attenuated continental crust in the Porcupine Seabight could terminate.
THE EMERGENT HORMUZ SALT PLUGS OF SOUTHERN IRAN
Authors: Kent P. E.
Published: December 2007

The extrusive salt plugs in the “gently folded zone”of the Zagros mountain belt are almost exclusively composed of Hormuz evaporites carrying exotic blocks, originating at depth of 3–5 km below surface, dated as mainly late Precambrian.

In recent years, there have been considerable advances in the understanding of the history of emplacement, on the stratigraphy of the very large exotic blocks of bedded Infra‐Cambrian sediments, on the stratigraphy of the very large exotic blocks of bedded Infra‐ Cambrian sediments on the entrained volcanic and intrusive igneous rocks and on the mineral occurrences. The charactreistic and controversial feature are described, with the minearl occurrences. The characteristic and controversial fetures are described, with emphasis on the newer information and on the relationships of the plugs to normal folds, thrusts and transverrse fracture zones.

The absences at surface of the many cubic kms of country rock displaced from the neck of each plug has hitheto presented an unsoloved probelm; prevoious explanation fail to fit availabel facts. It is now postulated that in most cases initial extrusion took place at higher stratigraphic levels, and that the original vent material has been eroded along with the sediments lost following uplift of the mountain belt.

The concept that pre‐orogenic plug movement was not exceptinal but normal, so that the plugs penetrated an essentially flat‐lying sedimentary blanket, resolves also the contrast between their regular distribution in the southeastern Zagros and their random reltion to the Pliocene fold trends, as well as the tendency for inflexions of fold axes to be located where they encounter the weak points provided by the salt intrusions.
ON THE THEORY OF GROWTH FAULTING*: A GEOMECHANICAL DELTA MODEL BASED ON GRAVITY SLIDING
Authors: Crans W. , Mandl G. , Haremboure J.
Published: December 2007

A geomechanical delta model is presented that explains and permits quantitative reproduction of the main features associated with growth faulting. The model is based on a soil‐plasticity analysis of gravity sliding of overpressured clays and silts on very gentle delta slopes. In this analysis, the packets involved in gravity sliding —called ‘units’—are well quantified. The delta body may behave as a stack of such units (‘multi‐unit’ delta model), which can behave differently depending on such parameters as sedimentation rates, changes in lithology and compactional behaviour. Two prominent and essentially different structural expressions of the model are discussed: (a) the regularly spaced growth‐fault pattern, without recognisable toe regions; (b) the complete slide structure with a well‐developed toe region. The shapes of the roll‐over structures (particularly the positions of the crests), the thickening of the layers near the growth faults, antithetic faulting and horsetailing of growth faults can be derived from the model without the need to invoke any deeper seated mechanism in the substratum. The basic assumptions of this geomechanical model are supported by observations in Ireland and examples from literature. It may contribute to the reconstruction of the hydrocarbon migration history in a delta by accounting for the synsedimentary development of stresses and fault structures that may control hydrocarbon migration. Recently, geomechanical aspects came in focus again for the assessment of seismic amplitude anomalies in the search for hydrocarbons (Crans and Berkhout, 1979).
TIME, TEMPERATURE AND ORGANIC MATURATION‐the evolution of rank within a sedimentary pile
Authors: Wright N. J. R.
Published: December 2007

Throught using the current published literature and attempting to gain insights into the maturation history of sedimentary basins, in particular the time of potential oil generation, the author has become aware of certain problems associated with the diagrammatic representation of burial histories and rank evolution. This note does not represent the product of any new experimental work or any rthinking of the thermodynamics of the complex organic reactions involved in maturation of kerogen; I have simply taken published “models” of organic maturation and attempted to apply them to a simple and, I think, intuitively understandable pictorial representation of the progressive evolution of rank within a sedimentary colume.
SOME HOLOCENE GEOMORPHOLOGICAL AND SEDIMENTOLOGICAL OBSERVATIONS FROM OMAN AND THEIR PALAEOGEOLOGICAL IMPLICATIONS
Authors: Beydoun Z. R.
Published: December 2007

Observed exhumed Pleistocene river channel conglomerates now standing as ridges, and inland sabkha sedimentological structural phenomena from Oman, are discussed. Their significance as tools in the interpretation of similar palaeogeological environments is considered. Correlation with similar channel fills elsewhere in Arabia and Iran indicates aggradation as having occurred between 35,000–7,000 yrs BP and suggests that this was principally by sustained flow during pluvial phases accompanying the last global glaciation, (at least in this part of the Middle East). Elevations of the now inverted channels above their deflated desert surroundings are used for calculating deflation rates, and reservoir porosity‐permeability characteristics of similar ancient deposits are considered. Additional and new data on halite crust structures from the Umm‐as‐Samim inland sabkha are presented mainly in photographs backed by factual data which are commented upon; sabkha formation probably commenced about 4,500 yrs BP. The preservation of similar origin halite deposits in the stratigraphic record is briefly discussed.

This note is intended to augment data on desert environments that appear to have either had passing mention, or simply recording without assessment of their significance as tools or indicators in the interpretation of similar palaeogeological environments. It is the hope that the observations recorded here will stimulate further work on these and other Holocene phenomena in the region concerned and also elsewhere, together with dissemination of results, so that implications to various aspects of applied geology can be better evaluated and understood.
PRIMARY PETROLEUM MIGRATION BY MOLECULAR SOLUTION: CONSIDERATION OF NEW DATA
Authors: Price Leigh C.
Published: December 2007

Previous criticisms of primary petroleum migration by molecular solution have been: (1) the large compositional and molecular weight differences between hydrocarbons most readily dissolved in water and those found in crude oils, and (2) previously‐measured aqueous petroleum solubilities were not high enough to account for petroleum deposits using reasonable geologic assumptions. New crude oil aqueous solubility data remove both of these criticisms. Above 275° C, with both increasing gas content and temperature, the solute hydrocarbons become compositionally more and more similar to, and eventually exactly match, the starting material. Mass balance calculations, using experimentally‐measured crude oil solubilities, show that between 275° and 375° C, under realistic geologic assumptions, crude oil aqueous solubility is high enough to account for petroleum deposits. These new data also show that molecular solution is not a viable agent of primary petroleum migration below 275° C.

Although the new data remove these two criticisms, three others are immediately raised: (1) there is inadequate water in sediments at temperatures between 275° to 375° C for migration by molecular solution, (2) sediment hydrocarbons will be thermally destroyed by these temperatures, and (3) these high temperatures are not present in most petroleum basins. Consideration of existing data suggests these criticisms can be satisfactorily answered. It is therefore concluded that a deep‐hot origin of petroleum and its migration by solution could fall within the restraints of the natural system.

It is possible much or most of the world's oil has undergone primary migration by molecular solution; however two other mechanisms may also be viable: gaseous solution, and in the case of extremely rich source rocks, some form of a bulk phase migration.
THE PANGAEAN PARADOX: WHERE IS IT?
Authors: Crawford A. R.
Published: December 2007

The postulation of a Precambrian (about 1,300 Ma) expansion of the Earth by Embleton et al. (1981) and Schmidt and Embleton (1981) to explain paradoxical results from palaeomagnetism, by creating a Pangaea asymmetrically disposed on the Earth, produces more problems than it solves. It is preferable to infer that the present pattern of continent and ocean, which appears to be normal (and is probably non‐random) derives from a Pangaea which covered the Earth completely or almost completely in the Precambrian and dispersed during the Mesozoic‐Cenozoic at a critical stage of persistent, exponentially‐increasing and perhaps mildly‐pulsatory expansion. In this orderly dispersal, the geometrical relations between the continents were maintained. Data from palaeomagnetism for the period 1,000–200 Ma, although amenable to a consistent orthodox interpretation, may nevertheless be illusory and indicative not of any different continental pattern (in terms of geocentric angles) but of some inner disturbance perhaps related to (or at least concurrent with) large‐scale obliquity changes. An earlier critical stage, represented by the ‘Pan‐African event’ over the period 750‐450 Ma, was the time of the first development of future continental outlines.

This exponentially‐increasing expansion permitted retention of continental meridionality from the Precambrian, except for Asia, and preservation in their original orientations of imprints of a global fracture pattern on the continents.

Major Mesozoic‐Cenozoic expansion avoids the need for a ‘Tethys Ocean’ (as distinct from an epicontinental Tethys Sea). Precambrian expansion would create such an ocean as an extension of a great and equally artefactual ‘Panthalassa’.
LOWER CRETACEOUS LITHOSTRATIGRAPHY NE OF THE SOLE PIT AREA IN THE UK SOUTHERN NORTH SEA
Authors: Crittenden S.
Published: December 2007

Seven boreholes from block 49, UK sector have been divided lithostratigraphically to illustrate the degree of comparison between the Dutch and British lithostratigraphical schemes for the Lower Cretaceous of the southern North Sea.

The two schemes differ in scope and finesse, with the Dutch scheme offering more subdivisions. Both are applicable to boreholes in the British as well as the Dutch sectors of the southern North Sea. Borehole 49/25‐1 (Shell/Esso) is designated as the reference borehole in the British sector to illustrate the Dutch scheme.

The Upper Holland Marl Member is considered to be equivalent to the Red Chalk formation while the Speeton Formation is divided into the equivalent of the Middle Holland Shale Member, Lower Holland Marl Member and the Vlieland Shale Member of the Dutch sector scheme.
RELATIONSHIP BETWEEN AGES OF SHIELDS, DIPS OF ADJACENT SEDIMENTARY BASEMENTS, AND OCCURRENCE OF OIL AND GAS
Authors: Rogers John J. W.
Published: December 2007

Crystalline shields can become stable at different times. This stability is commonly marked by the end of magmatism and compressive deformation and the beginning of deposition of platformal sedimentary sequences. The margins of the shields are then the basements for undeformed sediments that dip away from the exposed crystalline rocks.

Dips of basements on shield margins directly underlying Phanerozoic sediments have been determined in seven areas in which the margin has not been altered by rifting or other tectonic activity. The adjacent shields have stabilization ages ranging from more than 3,000 m.y. to 600 m.y. The basement dips (tilts) increase progressively from about 3 m/km for older shields to 16 m/km adjacent to the youngest shield (the Nubian‐Arabian shield). These tilts can only approximately be recalculated into uplift rates of the shields or subsidence rates of their margins. The dips are, however, consistent with Phanerozoic uplift rates of Archean cratons of less than 5 m/m.y., or comparable subsidence rates of the margins; such low uplift rates could be caused almost wholly by erosion and isostatic adjustment. Younger shields have undergone some other, as yet unidentified, process that causes more rapid uplift.

The higher dips of basements around younger shields apparently promote the development of thick sections of mildly‐deformed Phanerozoic sediments. Sequences of this type are commonly favorable for accumulation of commercial concentrations of oil and gas. A correlation has been found between age of shield, basement dip, and hydrocarbon occurrence around the western edge of the Canadian shield and the northern edge of Africa. The data show that oil and gas are more abundant in Phanerozoic sediments adjacent to younger shields, which supports the common observation that the world's largest hydrocarbon accumulation (the Arabian Gulf) is adjacent to the world's youngest shield (the Nubian‐Arabian shield).

This criterion for hydrocarbon accumulation may be of some value in exploration of little‐known areas. For example, basements of different ages occur adjacent to the overthrust belt of the northern Rockies, and the generally‐young age of Precambrian basement in the eastern US may indicate considerable thickness of sediment under crystalline thrusts in the Appalachians. Different ages of shields in different parts of China may also have broadly affected sedimentary patterns in that country.
EVIDENCE THAT STABLE CARBON ISOTOPES ARE NOT A RELIABLE CRITERION FOR DISTINGUISHING BIOGENIC FROM NON‐BIOGENIC PETROLEUM
Authors: Giardini A. A. , Melton Charles E.
Published: December 2007

The isotopic abundance of presumably‐pristine primordial carbon has been determined by analyzing carbon dioxide entrapped in a 8.65 carat natural diamond of African origin. The results were 12C = 98.9275% and13C = 1.0725%, which giveδ13C = ‐35.2‰/00. This value is well within the range used to assign a biogenic origin to carbon‐containing compounds, i.e., more negative than ‐18.0‰/00. Similar negative values have been reported for some natural diamonds and carbon‐bearing meteorites. It is concluded, therefore, that stable carbon isotopes can be an unreliable criterion for assigning a biogenic origin to petroleum.
AN APPROACH TO “HALOKINEMATICS” AND INTERPLATE TECTONICS (NORTH‐CENTRAL ALGERIA)
Authors: Assaad Fakhry A.
Published: December 2007

Plate tectonics continues to dominate geological thinking; the main object of this paper is to explain salt movements due to halokinesis in terms of plate kinematics. A term “halokinematics” is proposed by the author to define disturbances ofsaltflo w caused by continuous indirect geologic events which might be a consequence of plate kinematics. Salt rocks constitute the caprock ofdetrital Upper Triassic reservoirs in the NCzone of Algeria whereas eruptive rocks, mainly basalts andspilites, constitute the cap‐rock of the lowermost series to the SE. The absence of Cretaceous formations to the SW of the Pre‐Atlas zone may be mainly attributed to the presence of salt domes.

The study of paleotectonic events on the Epihercynian and African platforms, the wide distribution of spilites in the lowermost series of Triassic detritals and the discovery of flysch facies in the Tellian Atlas may support the existence of two interplates, the Saharan and Atlassic plates. However, detailed geological and geophysical studies would be necessary to confirm this theory.
CHANCO FORMATION, A POTENTIAL CRETACEOUS RESERVOIR, CENTRAL CHILE
Authors: Cecioni Giovanni
Published: December 2007

The Chanco embayment lies 300 km SSW of Santiago, Chile. The sequence within this basin above the metamorphic basement is: Chanco Formation (very clean sandstone), Quiriquina Formation (glauconitic sancistone, rich in organic matter), and Navidad Group (a very good caprock). This section thus contains reservoir, source and caprocks, and is therefore very promising for petroleum investigations. The offshore C‐1 well yielded salt‐water with gas shows, andtwo wells drilled onshore yielded flows of gas. The C‐1 well lies on a gently‐dipping EW‐striking anticlinal structure, the presence of which makes the area very prospective.