bluuebunny/crossref_metadata_2025 huggingface dataset:
Longitudinal study of visual functions in young insulin dependent diabetics
Authors: Banford D. , North R. V. , Dolben J. , Butler G. , Owens D. R.
Published: December 2007

The aim of this study was to compare the visual functions of a group of young insulin dependent diabetes mellitus patients (IDDMs), (n= 42) with an age and sex matched control group (n= 24). Examinations were carried out every 3 months for 2 years. There were no significant differences in visual acuity between IDDMs and control subjects. The IDDMs made significantly more errors with the desaturated D15 compared with the control group (P < 0.05). The contrast sensitivity for the IDDMs was lower at each spatial frequency compared with the control group, being significantly different from 3 c/deg and above (P < 0.05). A negative correlation was found between HbA1, and contrast sensitivity at 6 and 12 c/deg; as the HbA1 increased the contrast sensitivity decreased (P < 0.05). As the blood glucose level decreased, the colour vision deteriorated (P < 0.05). There was no significant difference between the visual performance of those IDDMs with retinopathy (n= 5) compared to those without.
Changes in refractive trends and optical components of Hong Kong Chinese aged over 40 years
Authors: Lam Carly S. Y. , Goh Winnie S. H. , Tang Y. K. , Tsui K. K. , Wong W. C. , Man T. C.
Published: December 2007

The age trends of refractive errors, astigmatism and optical components were studied in 220 Chinese subjects aged over 40 years. Myopia did not dominate in this age group. With increasing age, the prevalence of hyperopia increases from 2% at age 40–45 years to 66% at age > 65 years. Against‐the‐rule astigmatism was more prevalent than the other types. Significant correlations were found between age and spherical equivalent power, age and vitreous depth and axial length. Sex differences were found among the optical components but not in the refractive error. Myopia appears to be more prevalent among the younger age groups than the older age groups of the Hong Kong Chinese population, and the importance of genetics in determination of refractive error is called into question by these findings.
Derivation of corneal flattening factor, p‐value
Authors: Lam Andrew K. C. , Douthwaite William A.
Published: December 2007

A mathematical equation was, derived to calculate the corneal p‐value based on the central and peripheral corneal radii and the corresponding semichord diameters. The calculation was simplified by a computer program written using GWBASIC. The accuracy of corneal p‐value generated from this program was checked with Douthwaite's modified keratometer with good correlation. This program could be used lo find out the corneal p‐value and apical radius ro for any topographic keratometer which only provides central and peripheral radii without any information of the p‐value and apical radius.
Facial characteristics in children with Down's syndrome and spectacle fitting
Authors: Woodhouse J. Margaret , Hodge Stuart J. , Earlam Richard A
Published: December 2007

Significant refractive error is very common among children with Down's syndrome so the requirement for spectacles for this group is high. The aim of this study was to measure the facial characteristics of children with Down's syndrome and to compare them with two previous studies which have aided the design of children's spectacle frames. The study was carried out in two schools in South Wales, measuring 20 children between the ages of 3.6 and 14.4 years. The results show that between the ages of 7 and 14 years, facial characteristics of children with Down s syndrome do not change with age and rarely coincide with those of other children, either of a similar age or younger. Thus children with Down's syndrome cannot be fitted satisfactorily with conventional children's frames, and it would be desirable for a specially designed range of frames to be made available.
Postlens tear film morphology, lens movement and symptoms in hydrogel lens wearers
Authors: Little Simon A. , Bruce Adrian S.
Published: December 2007

Postlens tear film morphology, lens movement and symptoms were assessed in 100 subjects wearing hydrogel contact lenses on a daily wear schedule. Postlens tear film appearance in specular reflection was categorized as amorphous, coloured, striated or dynamic (variable with bliniking), and subjects’symptoms were assessed using a questionnaire. Non‐amorphous appearances were present in 25% of subjects and occurred approximateiy equally with HEMA, Acuvue. Igel 55 and other lens types. Patterned appearances were found to be associated with reduced lens movement (Kruskal‐Wallis ANOVA, P < 0.001). The most common symptom (dryness) was not significantly related to postlens tear film appearance. Postlens tear film morphology was shown to be a determinant of lens movement, but may be unrelated to common symptoms.
Spectral sensitivity in patients with dysthyroid eye disease
Authors: Sharanjeet‐Kaur  , Dickinson Chris M. , O'Donoghue Eammon , Murray Ian J.
Published: December 2007

The majority of patients with dysthyroid eye disease have an acquired colour vision defect. However, no psychophysical investigation of selective damage to colour or flicker pathways has been carried out. In order to clarify the nature of the visual pathology, we have used a psychophysical technique (spectral sensitivity) to selectively stimulate the chromatic and achromatic mechanisms. Spectral spots of size 1° presented at a rate of 1 Hz on a bright 1000 td white background are detected by the chromatic mechanism but a rate of 25 Hz reveals the achromatic mechanism. Fifteen patients (28 eyes) between the ages of 50–70 years were tested. The study showed that all patients had reduced spectral sensitivity, either 1 Hz, 25 Hz or both. The patients with reduced 1 Hz or 25 Hz spectral sensitivity only had a shorter systemic and ocular duration of the condition, had no proptosis, normal intraocular pressures in primary gaze, slightly higher intraocular pressures on upgaze, normal visual field plots and FM 100‐Hue error scores higher than the normal age‐matched values. The patients with reduced both 1 Hz and 25 Hz spectral sensitivities had a longer systemic and ocular duration of the condition, had proptosis, normal intraocular pressures in primary position, higher intraocular pressures on upgaze and higher FM 100‐Hue error scores than the age‐matched normals and those in Groups 1 and 2. A total of 50% of patients in Group 3 had defective visual field plots. These data suggest that there is damage of the large achromatic fibres and small chromatic fibres in dysthyroid eye disease. The mechanism of the damage could be one of ischaemic or mechanical or both.
Quantification of prism induced metamorphopsia as a model for clinical retinal (and other) distortions
Authors: Hirose Hiroshi , Enoch Jay M. , Tuan Kuang‐Mon
Published: December 2007

Metamorphopsia (all causes) results in perceived distortions in the visual field. A simple technique utilizing hyperacuity judgments was developed in this laboratory some years ago to allow quantification of such distortions. We ask here, how good is this assessment method at detecting a distortion? To control better investigations of metamorphopsia, a model providing constant optical distortions and resultant perceptual metamorphopsia was devised using plane prisms of 8Δ and 15Δ. The instrument includes a beam splitter and a CRT display controlled by an IBM PC computer and a‘mouse’. In this study, three short vertical lines (perpendicular to the prism base‐apex line) were used to assess image distortion in the central retinal area. Positions of individual lines of this pattern were varied in order to determine perceived distortions induced by a prism. Normal observers were tested on multiple occasions. It is possible to measure accurately prism‐induced directional biases (mean locations) using this method. We separated personal setting biases from the prism‐related distortions. The test method devised mimics modest clinical metamorphopsia. Prism magnitude affected settings. We were able to make judgements to less than ±2% error.
Measuring contrast sensitivity with inappropriate optical correction*
Authors: Woods Russell L. , Strang Niall C. , Atchison David A.
Published: December 2007

Spatial frequency‐selective minima (notches) in the contrast sensitivity function (CSF) because of defocus can mimic those that occur with ocular disease. We examined the influence of measurement conditions on CSF shape in simulated clinical testing. CSF notches occurred with almost all levels of defocus for all subjects. Multiple notches were found under some conditions. Notches were found with defocus as small as 0.50 D. Effects of induced astigmatism depended on the orientation of the target. Notches were apparent in defocus conditions after stimulus size and room illuminance were modified and when subjects had insufficient accommodation to compensate for hypermetropic defocus. The equivalent of notches was not noted with the Pelli‐Robson chart. As defocus‐induced CSF notches may be mistaken for functional loss, careful refractive correction should be conducted prior to clinical or experimental CSF measurement, even at low spatial frequencies.
Optometric glaucoma referrals – measures of effectiveness and implications for screening strategy
Authors: Gilchrist Jim
Published: December 2007

The effectiveness of disease screening is conventionally evaluated using the epidemiological indices of sensitivity and specificity, which measure the association between screening test results and final diagnoses of all the patients screened. The effectiveness of optometric glaucoma referrals cannot be measured using such indices because diagnoses are obtained only on patients who are referred, while the true disease status of those not referred remains unknown. Instead, glaucoma referral effectiveness has been evaluated using measures of ‘detection rate’– the proportion of those screened who are correctly referred, and ‘referral accuracy’— the proportion of those referred who are correctly referred occurrence.

Examination of these operational measures shows that their obtainable values and, hence, their interpretation are influenced by the total proportions of diseased and referred patients, one or both of which will generally be unavailable in evaluating samples of referrals. On the other hand, if valid estimates of these proportions can be obtained from other sources, it is possible to rescale detection rate and referral accuracy to take account of them. This rescaling produces a pair of weighted kappa coefficients, chance‐corrected measures of association between referral and diagnosis, which provide a better indication of true referral effectiveness than other measures.

An important consequence of this approach is that it provides a clear quantitative illustration of the need for a dual strategy to improve the overall quality of optometric glaucoma screening; widespread adoption of more comprehensive modes of screening to improve accuracy, together with a significant increase in the total numbers of patients screened to improve detection. In order for detection rates to reach desirable levels, the total number of referrals in any sub‐population of patients must match or exceed the number of patients with disease. This analysis confirms quantitatively that which is intuitively obvious; not only that glaucoma awareness and uptake of screening opportunities must be encouraged in all patients over 40 years of age, but also that the older and/or more at risk patients are, the greater is their need to take advantage of glaucoma screening.
Deflectometric measurement of mechanical spectacle lens deformation
Authors: Peral Assumpta , Alonso José , Sanz Joán Canos , Bernabeu Eusebio
Published: December 2007

The warpage of a set of six hard resin spherical lenses was measured when they were compressed by means of the tangential force exerted by a metal frame. The technique employed to measure the lenses improves over previous work both because greater precision is achieved, and because radii of curvature are measured in two perpendicular meridians. In this work, a representative sample of lenses has been used in order to test the way in which deformation depends on lens power and base. It is found that the induced warpage is enough to move the tested lenses between different base families, spoiling the initial design of the manufacturer.
Soft contact lens wear in Hong Kong‐Chinese: predicting success*
Authors: Chui Wan Sang , Cho Pauline , Brown Brian
Published: December 2007

The tear stability and tear volume of 55 asymptomatic Hong Kong‐Chinese were assessed before soft contact lens (Hydron Zero 6) wear and repeated on three visits over 28 weeks of lens wear. Soft lens wear caused a significant initial transient decrease in the non‐invasive tear break‐up time (NITBUT), but no change in tear volume as assessed by the self‐prepared cotton thread test (SP‐CTT) and phenol red thread (PRT) test. After 28 weeks, the subjects were classified according to the length of time they could wear their lenses without dry eye related signs and symptoms. The NITBUT and PRT tests were unable to predict the success of soft contact lens wear. However, the SP‐CTT gave a sensitivity and specificity of 88.5 and 52.4%, respectively, in the prediction of subjects most likely to be successful wearers. The positive and negative predictive values at the chosen cut‐off point were 69.7 and 78.6%, respectively. Wetting values, that is, combinations of NITBUT and SP‐CTT values or NITBUT and PRT values, did not predict success in soft contact lens wear.
Step‐along vergence procedures in stigmatic and astigmatic systems
Authors: Harris W. F.
Published: December 2007

The traditional step‐along vergence procedure applies to stigmatic systems, that is, systems that are not astigmatic. Computation is disrupted when a focus coincides with a thin lens or refracting surface. A small change to the procedure results in a modified procedure which overcomes the computational problems. The modified procedure is easier to execute than the traditional procedure and allows one to write down useful equations directly. Among the formulae are those for back‐vertex power. A step‐along vergence procedure also exists for astigmatic systems. It makes use of the dioptric power matrix and the reduced vergence matrix. Computational problems arise when a point or line focus coincides with a thin lens or refracting surface; however they are not overcome by an analogous modification to the procedure. Nevertheless the modified procedure has some advantages including the fact that, as for stigmatic systems, it allows one to write down useful formulae directly. Stepwise calculations of vergence are sometimes performed backward through a system; the advantages and disadvantages described for step‐along procedures holds for such step‐back procedures as well.
The Relationship Between Nighttime Dipping in Blood Pressure and Cerebral Hemodynamics in Nonstroke Patients
Authors: Hajjar Ihab , Selim Magdy , Novak Peter , Novak Vera
Published: December 2007

Inadequate dipping in nighttime blood pressure (BP) is associated with cerebrovascular disease. The authors aimed to determine whether inadequate nocturnal dipping was associated with abnormalities in cerebrovascular hemodynamics in individuals without stroke. Participants in this study underwent 24‐hour ambulatory BP monitoring followed by morning transcranial Doppler measurements of blood flow velocities (BFVs) in the middle cerebral artery during supine rest, head‐up tilt, hypocapnia, and hypercapnia. Nighttime BP decline by <10% was considered nondipping. Of the 102 nonstroke participants (mean age, 53.6 years), 35 (34%) were dippers. Although nondippers had similar BFV and cerebrovascular resistance (CVR) while supine, they had a lower BFV (P=.04) and greater CVR (P=.02) during head‐up tilt compared with dippers. Moreover, greater nighttime dipping in both systolic BP (P=.006) and diastolic BP (P=.03) were associated with higher daytime BFV and lower CVR (P=.01 for systolic BP; P=.02 for diastolic BP). Inadequate nocturnal BP dipping is associated with lower daytime cerebral blood flow, especially during head‐up tilt.
Control of Blood Pressure: Does It Matter Which Agent You Use?
Authors: Moser Marvin , Cushman William C. , Kaplan Norman M.
Published: December 2007

A panel was convened to discuss the question, “Is blood pressure lowering the sole determinant of outcome, or do specific drugs make a difference?” The panel was moderated by Marvin Moser, MD, Clinical Professor of Medicine at the Yale University School of Medicine, New Haven, CT. Panelists included Norman Kaplan, MD, Clinical Professor of Medicine at the University of Texas Southwestern Medical Center at Dallas, TX, and William Cushman, MD, Professor of Medicine at the University of Tennessee in Memphis, TN. The discussion was supported by Boehringer Ingelheim, and each author received an honorarium from Boehringer Ingelheim for time and effort spent participating in the discussion or reviewing the transcript for intellectual content before publication. The authors maintained full control of the discussion and the resulting content of this article.
The Efficacy and Safety of Initial Use of Irbesartan/Hydrochlorothiazide Fixed‐Dose Combination in Hypertensive Patients With and Without High Cardiovascular Risk
Authors: Weir Matthew R. , Neutel Joel M. , Bhaumik Amitabha , Obaldia Maria Elena De , Lapuerta Pablo
Published: December 2007

A post hoc pooled analysis of 2 multicenter, randomized, double‐blind, active‐controlled force‐titration studies assessed the antihypertensive efficacy and tolerability of 7 to 8 weeks' once‐daily fixed‐dose irbesartan/hydrochlorothiazide (HCTZ) 300/25 mg in 796 stage 1 or 2 hypertensive patients according to age (65 years or older or younger than 65) (n=121 or 675) and presence or absence of obesity (n=378 or 414), type 2 diabetes (n=99 or 697), and high World Health Organization‐defined cardiovascular risk (n=593 or 202). Systolic/diastolic blood pressure reductions (27–31/16–22 mm Hg) were similar regardless of age, obesity, and type 2 diabetes status and were greater in high‐ vs low‐risk patients. Dizziness (2.0%–3.7%), hypotension (0%–0.7%), and syncope (0%) were rare and not centered in any subgroup. There was no hypotension in the elderly or in type 2 diabetics. Irbesartan/HCTZ provided consistent blood pressure lowering and tolerability regardless of age, obesity, and type 2 diabetes and greater efficacy in patients with high cardiovascular risk.
Emerging Insights in the First‐Step Use of Antihypertensive Combination Therapy
Authors: Norris Keith , Neutel Joel M.
Published: December 2007

The blood pressure (BP) goals set by hypertension management guidelines (<140/90 mm Hg in uncomplicated hypertension; <130/80 mm Hg in type 2 diabetes or kidney disease) are not being achieved in a high proportion of patients, partly because monotherapy is insufficient in many patients. In particular, patients with uncontrolled moderate or severe hypertension and/or associated cardiovascular risk factors remain at high risk for cardiovascular events and hypertensive emergency. In recognition of the urgency of treating moderate and severe hypertension, the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7) advocates the initial use of 2‐drug therapies in patients with systolic BP levels >20 mm Hg above goal or diastolic BP level >10 mm Hg above goal. Regimens should usually include a thiazide diuretic and, for patients with diabetes or kidney disease, an angiotensin‐converting enzyme inhibitor or angiotensin receptor blocker. Recently, clinical trial data have shown that first‐step antihypertensive treatment of moderate and severe hypertension with carefully chosen fixed‐dose combinations provides a high rate of BP goal achievement, a simplified dosing regimen, and superior tolerability compared with monotherapy.
G‐CSF‐Based Stem Cell Therapy for the Heart—Unresolved Issues Part B: Stem Cells, Engraftment, Transdifferentiation, and Bioengineering
Authors: Kurdi Mazen , Booz George W.
Published: December 2007

The authors extend their coverage of recent developments in stem cell‐based therapy for repairing the heart to cover the basic questions of what stem cells should be used and how best to favor their survivability within the injured heart. The authors focus their attention on those adult stem/progenitor cells that have been best investigated in animal studies for repairing the infarcted heart and are the focus of completed or ongoing clinical trials. In addition, they discuss the promise that resident cardiac stem cells offer and the recent identification of specialized architecturally defined niches within the heart to nurse their development. Bioengineering approaches employing off‐the‐shelf mesenchymal stem cell patches may soon provide a way to recreate these niches in the scarred heart. Conceivably, these patches might also be seeded with prescribed mixtures of culturally expanded autologous stem/progenitor cells that would lead to new blood vessel and cardiac myocyte formation. The convergence of bioengineering and molecular biology on stem cell therapy would seem to make what was once unimaginable, cardiac regeneration, a clinical reality in less than one generation.
The Cholesterol Paradox in Heart Failure
Authors: Velavan Periaswamy , Huan Loh Poay , Clark Andrew , Cleland John G. F.
Published: December 2007

Heart failure (HF) is a common and serious condition that is usually due to coronary artery disease (CAD). Hypercholesterolemia is a major risk factor for CAD but, paradoxically, patients with advanced HF often have low cholesterol, which is associated with a poor prognosis. Cholesterol lowering with statins reduces morbidity and mortality in patients with CAD who do not have HF and might also have improved outcome in patients with HF had they not been excluded from the reported trials. The results of large trials such as the Controlled Rosuvastatin Multinational Study in Heart Failure (CORONA) and the Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico‐Insufficienza Cardiaca (GISSI‐HF) study addressing the effects of rosuvastatin in HF are keenly awaited. In addition to cholesterol lowering, statins have other biologic effects that might be responsible for some of their favorable effects. This article examines this cholesterol paradox and possible mechanisms.
USE OF FORELAND MONITORS IN THE CORRELATION AND ANALYSIS OF OROGENIC PULSES
Authors: Wilson H. H.
Published: December 2007

Theories on crustal evolution have been developed from geologic investigations in orogenic belts and in the less deformed foreland or epeirogenic areas. In this paper, it is suggested that, because one global mechanism must govern the evolution of both orogenic and epeirogenic areas, the two must be closely related. Because the interpretation of orogenic belts is complicated so greatly by extreme deformation, metamorphism, and loss of data through erosion, it is logical to seek interpretative leads on their orogenic style and timing by precise observations and analyses of structural “monitors” in the less complex borderlands.

The three foreland monitors considered are: (1) block faulting, (2) salt diapirism, and (3) volcanicity. All three monitors support the concept that tectonic pulses during measurable geologic time have been short lived and synchronous around the globe. They also indicate that the dominant structural stress which triggered these tectonic pulses has been extensional.

If extensional stress also has governed the evolution of orogenic belts, then the interpretations which advocate fundamental vertical tectonics, secondary gravity sliding, and intrusion by mantle diapirism are more acceptable than those which advocate crustal shortening and compression. Moreover, if tensional tectonics has governed both orogenic and epeirogenic areas as well as the ocean‐spreading centers, then the hypothesis of global expansion is more logical and harmonious than the popular and heuristic assumptions on crustal subduction.

For the successful resolution of regional tectonic problems, geologists must free themselves of dogmatic constrictions and broad generalisations. As in the exploration for hydrocarbons, what is needed is a scrupulous and patient attention to geologic detail, set within the most precise time framework attainable.
SPHERICAL HARMONIC DEFORMATION
Authors: Challinor A.
Published: December 2007

A radically new method of structural analysis is proposed which relates the deformation of all rocks to a three‐dimensional model of close‐packed spheres and deformation ellipsoids. All rocks exist under variable stress conditions and are deformed, but the principles of three‐dimensional deformation are poorly understood by many geologists and geophysicists. An understanding of rock deformation in three dimensions is a very valuable aid in geological interpretation and in the search for hydrocarbons. The method proposed provides the geologist, geophysicist and associated scientific disciplines with a means of understanding complex, three‐dimensional deformation and attempts to explain all deformational phenomena from mud cracks to plate tectonics. Deformation is a spherical harmonic waveform which, although complex in detail, is intrinsically no more mathematically complicated than the reciprocal of the square root of three. The analysis is illustrated by examples of “compressive” deformation from the Tertiary fold belt of Spitsbergen and the “tensional” or “gravitational” deformation in the Viking Graben of the Northern North Sea.
FLOOD BASALTS: IMPLICATIONS FOR GLOBAL‐TECTONIC HYPOTHESES AND PETROLEUM EXPLORATION
Authors: Kamen‐Kaye Maurice , Meyerhoff A. A.
Published: December 2007

Present geodynamic models treat the continents and ocean basins as separate tectonic domains, whereas the few coordinated attempts to extend continental geology into the deep marine basins, and vice versa, suggest that the two domains may not be so easily distinguished. Flood‐basalt provinces provide one striking example of the great similarity between parts of some continents and the deep‐sea floor. In at least two areas, continental flood basalts can be traced directly into the oceanic realm. Because of this, modern geodynamic models may have to be revised.

Flood basalts also can be associated with petroleum occurrences. Three examples include the discovery of gas beneath Jurassic basalts off north western Australia, of oil beneath Late Jurassic or early Cretaceous basalts off Ghana, and of gas and oil beneath Jurassic to Triassic sills in the Middle and Upper Amazon basins of Brazil.
THE GENESIS OF THE ZOHAR GAS AS DEDUCED FROM ITS CHEMICAL AND CARBON ISOTOPE COMPOSITION
Authors: Amit Ora , Bein Amos
Published: December 2007

The hydrocarbon compositions (C1/ΣC1—C4) = 0.96‐0.98) and the carbon isotopes ratios of methane (—51.4 to—52.1%) studied in the Zohar Gas Field indicate that the generations of the gas was associated with an oil‐generation process. Thus, gas and heavy oils found in the area could have formed simultaneously within one system.

The carbon isotope composition of the CO2 is relatively heavy, with δ13 CO2 value ofabout +7% which is probably the original value of the CO2 generated by biodegradation of the cruded oil.

The dissimilarity in the organochemical characteristics of the Kidod shales, which cap the gas reservoirs and the oils found in the region, as well as the low degree of maturation of the Kidod, shales, negate the accepted hypothesis that these shales are the source rock of the heavy oils and the gas found in the Zohar area. The vitrinite reflectance of the reservoir rocks and of the underlying Jurassic sequences, which is only 0.5%, infers that the gas is not trapped near its site of generation.
DARWIN'S NAVIDAD EMBAYMENT, SANTIAGO REGION, CHILE, AS A MODEL OF THE SOUTHEASTERN PACIFIC SHELF
Authors: Cecioni Giovanni
Published: December 2007

The sedimentary sequence of Darwin's Navidad embayment overlies a Carboniferous metamorphic basement, and was deposited in a NNW‐striking basin, open toward the sea. The sediments formed in a temperate climate and consist of three marine sequences—Cretaceous, Eocene, and Miocene‐Pliocene. They exihibit some potential for oil and gas. The uppermost sediments of the Navidad Group were deposited in a more extensive sea, which was deeper, with lower wave energy. Near the present Pacific coastline, the sediments are tectonically disturbed. Farther east‐and northward, the sediments are not affected by great disturbances. Some good types of stratigraphical traps, such as eolian sand beaches, may be expected.

Key Idea:The model adopted here is considered as one potential basin model for petroleum exploration in the southeastern Pacific shelf, where six or more NNW‐striking open embayments are present.
TECTONIC CONTROL AND PETROLEUM GEOLOGY OF THE PALEOZOIC CLASTICS OF THE MARANHÃTO BASIN, BRAZIL
Authors: Carozzi Albert V.
Published: December 2007

Selected paleoenvironmental maps of the Maranhão Basin from Silurian to Eo‐Carboniferous are analyzed in tercs of their source rock and reservoir potentials. These maps combine petrographic data with the distribution of clay mineral assemblages, palynofacies, trace‐metals, organic carbon and boron. Two depositional models are recognized. The first one, which lasted from Silurian to Eo‐Carboniferous, is model of coalescent deltas in which delta systems (with seven subenvironments) are separated by interdeltaic aras (with five subenvironments). The second model, limited to the Late Devonian, shows a continental ice sheet interfering with a system of coalescent deltas and generating mixed glacio‐deltaic sediments.

The evolution of clastic supplies from Silurian to Eo‐Carboniferous consists of three major episodes of delta progradation strongly influenced by a synsedimentary tectonic control through lineaments of the Precambrian basement. This control concentrated the potential reservoirs in the SE portion of the basin. However, among the three major sandstone systems, the first two (Jaicos and Itaim Formations), which are the coarsest, had their reservoir properties strongly decreased by diagenetic cementation. This leaves the third one (Cabeças Formation) as the best potential target for exploration, particularly since its sandstones under lower deltaic distributaries to delta front facies interfinger with the shales of the Pimenteiras Formation, which at that level display their best developmetn as source‐beds. Further enhancement of these reservoirs is provided where their progradation extends sufficiently westward to be involved in structures along that side of the basin.
PETROLOGY, PROVENANCE, AND DEPOSITIONAL ENVIRONMENTS OF THE RESERVOIR SANDSTONES OF OSSU‐IZOMBE OILFIELD, IMO STATE, NIGERIA
Authors: Adedokun Oluwatele Alabi
Published: December 2007

Upper Eocene immature subarkoses derived from Cretaceous sedimentary rocks, older granites and metamorphic rocks, form the reservoir sandstones of the Ossu‐Izombe oilfield, Imo State, Nigeria. These sandstones accumulated as part of a deltaic deposit. The vertical section of deltaic facies consists, from base to top, of a progradational sequence (prodelta and delta front), an aggradational unit (delta plain, marsh and interdistributary bay), and an overlying transgressive shallow marine interval. This sequence was penetrated by nearly all of the 15 wells drilled in the area. Reservoir sandstones are present within the distributary mouth bars, point bars, braided stream deposits, and the shallow marine interval.

Thin section studies, electric‐log analyses, and data from modern deltas have aided in establishing the environments of deposition of these sandstone bodies. The principal results of this study are: (1) the basal C sandstone represents distributary mouth bar sands deposited at water depths of about 10 m; (2) the intermediate B group consist of point bar and distributary channel sandstone deposits of the lower delta plain; (3) the A‐2 sandstone tops the deltaic cycle as a product of braided streams; and (4) a shallow marine deposit, the A‐1.1 and A‐1 sandstones, occurs at the top of the deltaic cycle.
THE JURASSIC‐CRETACEOUS BOUNDARY IN THE SUBSURFACE OF EASTERN MEXICO
Authors: Chapa A. Cantú
Published: December 2007

The continuous appearance of certain ammonite genera in the cores of some wells were helpful in identifying the Jurassic‐Cretaceous boundary in the subsurface of eastern Mexico. These genera belong to the families Haploceratidae, Berriasellidae, and Protancyloceratinae. The studied wells are located in a large region of the eastern Gulf Coastal Plain of Mexico, the length of which is roughly 1,500 km.

Radioactivity well logging made it possible to locate the exact stratigraphic position of the ammonites in the different wells studied. As a result, it was possible to do both local and regional correlations of the upper beds of the Jurassic.

As a result of the present study, the biostratigraphic subdivision of the upper Tithonian of Mexico can be given as follows:

—a zone of Salinites and Parodontoceras at the top; and

—a zone of Suarites at the base.
SEDIMENTOLOGICAL EVOLUTION AND SEDIMENTOLOGICAL EVOLUTION AND NATURAL RADIOACTIVITY OF TERTIARY SEDIMENTS FROM THE CENTRAL NORTH SEA
Authors: Berstad S. , Dypvik H.
Published: December 2007

In the North Sea well studied in this paper, the radioactive isotopes of U, Th and K are shown to control the variations in the gamma‐log response. Th and K are associated with the clay fraction, while U is enriched in the silt fraction.

In the volcaniclastic Palaeocene and Eocene beds, low gamma activity is due to a high content of volcanic debris poor in U and Th, while higher gamma activity in the younger beds indicates the decrease in volcaniclastic material.
GAS EVOLUTION AND CHANGE OF OIL COMPOSITION DURING STEAM FLOODING OF OIL RESERVOIRS
Authors: Akstinat M. H.
Published: December 2007

The injection of steam into oil reservoirs is a technique commonly used for improving the production of heavy crude oils. Very often, a change in the composition of the oil and gas produced may be observed during steam flooding. In general, corrosive gases, such as H2S and CO2, are produced in increased quantities.

In laboratory experiments on sulphur‐bearing reservoir minerals and crude oils the origin of the change in oil and gas composition was investigated. Temperatures up to 370°C were applied to study temperature‐ and rate‐dependent phenomena. By means of X‐ray fluorescence, gas chromatography and chemical precipitation methods, the change in the sulphur material balance was studied.

It was shown that gas evolution depends strongly on the temperature of the steam injected. Furthermore, it was possible to prove that the gases evolved during steam flooding (such as CO2, H2S etc.) originate from the decomposition of crude oil components. Besides these investigations, a drastic viscosity increase of the residual crude oil was observed after steam injection was applied.

It is concluded that the production of H2S and CO2 may be controlled by temperature adjustment of the steam being injected.
SUBSIDENCE, SEDIMENTATION AND PETROLEUM SYSTEMS
Authors: Perrodon A. , Masse P.
Published: December 2007

Analysis of a number of petroleum provinces has emphasised the importance of sedimentary factors as well as subsidence processes. Subsidence appears to depend on a small number of mechanisms ‐ tectonics, heat flow and gravity. Taking into account thegeodynamic context in which these processes develop, it is possible to compile a classification of subsidence types which is distinct from the usual classifications in terms of basins. The type of subsidence influences the deposition rate, which determines both the potential and the habitat of petroleum. Moreover, existing statistics sho w that the number of “giant”fielako, r thep otential of a petroleum province largely depend on the types of subsidence and subsequent tectonic processes.

However, it is also important to consider the history of a basin in terms of flows: geothermal flows from the mantle and crust; and water and hydrocarbon flows through the sedimentary volume. For these flow transfers, climatic and sedimentary factors, as well as variations in sea level, play a role which is as important as subsidence and uplift in controlling the distribution of non‐deposition areas, unconformities, seals and reservoirs. For example, periods of generalized transgression are favorable to both the development of carbonate platforms, and the formation of impervious horizons, seals and source rocks capable of sealing pre‐existing rifts.

Therefore, a petroleum province can be considered as the final result of an organized set of geological events (in space and in time) that can be called apetroleum system. In such a system, thesequence ofsubsidencemovements and associatedflows isjust asdecisiveas lithological and geometric factors in the formation of a group of pools. This concept of the succession of geodynamics and sedimentary processes which affect petroleum potential is developed, and specific examples of petroleum systems from the North Sea, the Arabian Platform and the Congo Basin are presented.
THE EVOLUTION OF THE SOUTHERN PASSIVE MARGIN OF THE HIMALAYAN TETHYS: MODEL IMPLICATIONS AND CONSTRAINTS ‐ I
Authors: Bhat Mohd. Ismail
Published: December 2007

To outline lthe process of formation of the Tethys Ocean and its developemt from teh Late Carboniferous (Hercynian) epeirogenic phase until teh end of the Cretaceous, (when this ocean started vanishing), an earlier proposed model, involving lithospheric uplift, stretching and developmetn f anastomosing normal faults, which was suggested to explain the thermotectonic evolution of the lKashmir basin, is extended to cover the region from Kashmir to Kempa Dzong (NE Silkkim).

Basement subsidence curves show an overall exponential trend in agreement with teh common behaviour of passive margins. The anomalour Late Jurassic ‐ early Creataceous uplift of the marigin is difficult to explain wiht the available data; however, it seems likely to be related to the very restricted ocean‐floor spreading phase in early Late Creataceous time. The well preserved continental margin suggests a width of <500 km for the Tethys Ocean.

The model and the inferred limited width of the Tethys Ocean have several implications for the evolution of the himalayas. For example: (1) the Main Central Thrust and Main Boundary Thrust are reactivated normal listric faults, which reversed their direction fo move, emt during the closing phase of the Tenthys Ocean; (2) the gravity high along the entire Higher Himalayas is due to the presence of transitional‐zone basic material, intruded during the rift phase; and (3) the limited width fo the Tethys Ocena does not support alleged large‐scale subduction along this belt.

Finally, a few date (known and model‐derived) and conceptual constraints are pointed out. These must be considered in the evolultion of the Himalayas in general, and before in voing subduction in the Himalayas in particular. They include: the time required for passive margins to change to fracture boundaries; the north ward movement of India indicated by paleomagnetic data; th sinistral movement between norhtern and soutehrn continents; the p0osition of the Ladakh batholity within the Indus‐Tsansgpo Suture Zone; the 235+‐13Ma†age of a section fo this batholith; the occurrence of radiolarian chert within underformed beds; the suggested involvement of the Earth's rotational forces in plate‐tectonic driving mechanisms; and the possibility of many changes in teh spin velopcity of the Earth during the lifetime of Tethys.
MIGRATION IN FRACTURE NETWORKS; AN ALTERNATIVE INTERPRETATION OF THE SUPPLY OF THE “GIANT” TAR ACCUMULATIONS IN ALBERTA, CANADA ‐ I†
Authors: du Rouchet J.
Published: December 2007

During secondary migration, the tendency towards a thermodynamic minimization of the hydrocarbon‐water interfacial energy can result in the confinement of petroleum in open fractures and coarser pores, in spite of the repeated conversion of gravitational energy into interfacial energy. A discussion of lithological influences leads to the prediction that migration in granular porosity is likely to end in trapping or dispersal, whereas migration in brittle, compact formations, which are little fractured, can allow the petroleum to reach distant structures.

The source of supply for the “giant” tar accumulations of Alberta is then investigated. Chromatographic analyses strongly support a predominantly Triassic, basinal origin for the Pre‐Mesozoic Unconformity oils and, consequently, of the tars accumulated in the basal Cretaceous sands and Grosmont Paleozoic carbonates. A study of the spatial distribution of the thickness of oil‐stained rocks in the respective formations suggests that migration to the tar accumulations cannot have occured without interruption in the basal, transgressive Cretaceous sandstones, whereas continous migration (from the basin to the shelf) appears to have taken place in the weathered, carbonate Paleozoic sub‐crops.
ORIENTING CONVENTIONAL CORES FOR GEOLOGICAL PURPOSES: A REVIEW OF METHODS
Authors: Davison I. , Haszeldine R. S.
Published: December 2007

A review of four simple techniques used to re‐orient conventional cores back to theri in‐situ position in presented. Cores can be oriented by:

Cutting oriented. cores;

Using dipmeters;

Re‐orienting in highly deviated holes;

Using remanent palaeomagnetism.

The accuracy, costs and limitations of the methods are considered.
THE ORIGIN AND MIGRATION PATHS OF HYDROCARBONS ACCUMULATED IN THE LOWER CRETACEOUS SANDSTONE “GIANT” TAR ACCUMULATIONS OF ALBERTA‐II
Authors: du Rouchet J.
Published: December 2007

The first part of this study was published in the last issue, 7, (4) 381–402, October 1984. The conclusion on p. 103, and references which follow, apply to both papers.
IN SITU FORMATION OF PETROLEUM IN OOLITES‐ II: A CASE STUDY OF THE ARAB FORMATION OOLITE RESERVOIRS
Authors: Ibe A. C.
Published: December 2007

In Part I, (Journ. Petrol. Geol. 7 (3) 267–276) a scheme for the in situ generation and accumulation of hydrocarbons was presented. It was concluded that the indigenous origin of petroleum in oolites, which preculdes a long and wasteful primary migration process, affords another explanation for the exceptionally rich petroleum accumulations which characterise oolite reservoirs. The present paper now tests the validity of that proposal by a selected case study.

For an unequivocal discussion of an oolite reservoir productive of petroleum generated in situ, it would be necessary to describe in some detail those formations either underlying, overlying or lateral to the formation of interest which, because of their hydrocarbon content in the general region, might perhaps be supposed to have been the original source of the petroleum now found in the oolites. such an account would be more detailed than space permits. The need arises, therefore, for the selection of an example which allows the least number of alternative possibilities. This was the guiding principle behind the choice of the prolific Arab Formation (Upper Jurassic) of Saudi Arabia as a case study (Fig. 1)
THE PRE‐ZAGROS INTEGRITY OF THE IRANIAN PLATFORM
Authors: Kashfi Mansour S.
Published: December 2007

The Hormoz Formation of InfraCambrian age is the oldest unit recognized in southern Iran. It consists mainly of salt, other evaporites and débris of basement rocks. Some huge blocks of the uppermost PreCambrian and Lower Cambrian layered rocks were lifted to the surface by uprising Hormoz salt.

A detailed field investigation within three major salt diapirs located in the SE segment of the Zagros Fold Belt was carried out. Some lithologic‐stratigraphic correlations between three formations within selected salt domes on the western part of the Zagros crush zone, and the equivalent units on the eastern part, are established.

The Permian transgressive sea deposited basinal clastics unconformably on the Devonian in central Iran, and overstepped the basement rocks in central Arabia. The Pecten species of the Lower Jurassic Neyriz Formation of the Zagros Fold Belt can be correlated with the Nayband Formation of central Iran. The Tertiary evaporites of SSW Iran are correlated with the Tertiary evaporites of central Iran.

Evidence discussed indicates the presence of a single tectonic entity with no geologic break between SW Iran and the plateau of Iran in the NE.
IS THERE A CHICONTEPEC PALLEOCANYON IN THE PALEOGENE OF EASTERN MAXICO?
Authors: Chapa A. cantú
Published: December 2007

The Author studied the sediments in the so‐called Chicontepec paleocanyon of eastern Maxico. With the simultaneous use of planktonic forminifera and electric logs, it was possible to separate the Maastrichtian from the Paleogene, and to subdivide the Paleogene on the basis of paleontologic zones into Paleocene and Lower Eocene. Detailed stratigraphic study made it possible to establish the geographic distribution of the so‐called paleocanyon. The paleocanyon sensu stricto is present only SE of the Poza Rica field. Here, is it present in a plunging synform, in which it has the shape and form of a delta, now at a depth of between 1,800 and 3,600 m below sea‐level.

The erosion which formed the paleocanyon cuts beds that range in age from late Tithonian to Maastrichtian; Paleocene is omnipresent. Hence, the erosion that formed the paleocanyon was pre‐Paleocene.

Many of the stratigraphic criteria which led to the postulation of the paleocanyon are incorrect and are herein revised. Chronostratigraphy, based on the classic succession of foraminiferal zones, correctly applied together with structural‐contour maps selected zones, makes it possible to explain the hydrocarbon distribution.

The high rate of sedimentation during Paleocene and Early Eocene time within the study area is compared with other regions of the world
LITHO‐ AND MICROFACIES OF UPPER JURASSIC CARBONATE ROCKS OUTCROPPING IN CENTRAL SAUDI ARABIA
Authors: Okla Saleh M.
Published: December 2007

A study of surface sections of Upper Jurassic rock units near the city of Riyadh has revealed a total thickness of 500 m. These rock units are the Tuwaiq Mountain Limestone, Hanifa Formation, Jubaila Limestone, Arab Formation and Hith Anhydrite. The characteristic microfacies of Tuwaiq Mountain Limestone include spicular biomicrites in the lower part of the formation, and corals, stromatoporoids and algal biomicrites in the upper part. The characteristic microfacies of the Hanifa, Jubaila and Arab Formations include spicular biomicrites with some argillaceous shales alternating with pelsparities and oosparites. Conglomeratic micrites, dolomites and breccia are found in the upper Jubaila Limestone and the Arab Formation.

The total thickness of these rock units increases in the east to more than 900 m where the Arabian and Gotnia Basins are defined. Central Saudi Arabia is best described as being the site of differential carbonate shelf deposition during Upper Jurassic time. Intra‐shelf basins with euxinic conditions were formed. Over these basins, petroleum source rocks were deposited within each rock unit.
THE ROLE OF GEOTHERMAL GRADIENTS IN HYDROCARBON EXPLORATION IN PAKISTAN
Authors: Khan M. A. , Raza Hilal A.
Published: December 2007

Subsurface geothermal gradients play a significant role in oil exploration. Based on a synthesis of bottom‐hole temperatures recorded in electric logs from 74 exploratory and development wells in various parts of Pakistan, a study of geothermal gradients was undertaken to delineate the temperature regimes and to identify the oil window in various areas. Case‐histories of known accumulations are given to substantiate the results. The first‐ever iso‐geothermal gradient map of Pakistan is presented. A regional correlation of the oil window, superimposed with stratigraphy, is attempted for the first time, providing a unique exploration tool. Several indications, based on geothermal gradients, are given for the regional prospects of oil and gas.