Late Episodes Research Articles

Competence-based Early Professional Development: first impressions of the Northern Ireland programme

This article records beginning teacher (BT) experience of the Early Professional Development (EPD) programme introduced in Northern Ireland in 1998. It reviews the integrated, partnership and competencebased teacher education programme of which EPD is the latest episode. Samples of BTs currently in the programme were interviewed and surveyed by questionnaire. Key programme features were scrutinised: extent of BT involvement in EPD; the nature of development activity; the influence of support and accreditation facilities; use of a competence-based Career Entry Profile (CEP). Results indicate hesitant BT involvement and varied experiences. Quality and extent of involvement were influenced by quality of school support, availability of continuous employment, the introduction of compulsion, and the varying demands of planning, teaching and assessment following first appointment. School priorities and personal interests were major determinants of focus for EPD activity. Formally profiled assessments of personal competence (CEPs) were little used

The structure of a major suture zone in the SW Iberian Massif: the Ossa-Morena/Central Iberian contact

We have investigated the stratigraphy, structure and metamorphism of the boundary between the Ossa Morena Zone (OMZ) and the Central Iberian Zone (CIZ), two significant continental portions of the Variscan Iberian Massif. The OMZ/CIZ contact is marked by a strongly deformed and metamorphosed NW–SE trending narrow band, namely, the Central Unit, in which partially retrogressed eclogites are included. During the Middle-Late Devonian the CIZ overthrust the OMZ, and in the footwall km-scale recumbent folds and thrusts developed with decoupling and underplating of the lower crust. At the same time, in the hanging wall there took place intense though localized back-folding and back-shearing. In the Early Carboniferous a transtensional tectonic regime sank the overthrust block resulting in the exhumation of eclogites. These eclogites probably came from the underthrust OMZ lower crust, and they are at present included in the suture zone (Central Unit) of this continental collision. The extension is responsible for the origin of a basin and bimodal magmatism on the southern border of the CIZ. A late episode of folding and fracturing significantly contributed to the final complex picture of this suture boundary.

Chronic allograft nephropathy categorised in chronic interstitial and vascular rejection

Chronic rejection in renal transplantation is an alloantigen-dependent immune process ultimately leading to graft failure. We reviewed the literature on the basis of the case history of a patient who lost her renal allograft apparently from chronic interstitial rejection. Chronic rejection presents clinically as chronic transplant dysfunction starting at various intervals after transplantation. The histopathologic features consist of chronic allograft nephropathy with or without transplant vasculopathy or glomerulopathy. Chronic rejection should be differentiated from chronic toxicity of calcineurin inhibitors, de novo or recurrent glomerulonephritis, polyoma (BK) virus nephropathy, transplant renal artery stenosis, and nephrosclerosis. Young recipient age, black race, presensitization, histoincompatibility, and acute, especially vascular, and late acute rejection episodes are dominant risk factors, compatible with immunologic mechanisms. Cellular and humoral responses resulting from indirect recognition of alloantigens with subsequent fibrotic sequelae play a central role in the pathogenesis. Circulating donor-specific antibodies and staining for C4d can detect humoral chronic rejection. The prognosis depends on alloreactivity and the presence of progression factors such as old donor age, renal dysfunction, proteinuria, hyperlipidemia, and smoking. A multifactorial approach directed to the risk and progression factors is needed to prevent premature graft loss from chronic rejection.

Genetic and Biological Variation in Equine Infectious Anemia Virus Rev Correlates with Variable Stages of Clinical Disease in an Experimentally Infected Pony

Genetic and biological variation in the regulatory protein Rev of equine infectious anemia virus (EIAV) were examined throughout a clinically dynamic disease course of an experimentally infected pony. Following infection with the virulent EIAVWyo, the pony underwent a variable disease course, including an acute fever episode at 12 days postinfection (DPI), multiple recurrent fever episodes until 135 DPI, a prolonged subclinical period, and two late fever episodes. Viral RNA was isolated from the inoculum and sequential sera samples, and the rev exon 2/gp45 overlapping ORFs were amplified, cloned, and sequenced. Novel variants were found throughout infection, and genetic analyses indicated that both the Rev and gp45 ORFs were under selective pressure. The Rev variant predominant in the inoculum, R1, remained predominant during the early periods following infection (until 35 DPI); however, R1 was replaced by new predominant variants during the recurrent fever period (67–135 DPI). R1 reemerged as the predominant variant during the afebrile period, but a new predominant variant, R93, was associated with the late fever episodes. Rev variants predominant during recurrent febrile and late-febrile periods had significantly higher Rev-mediated nuclear export activity than the variants predominant during the acute and afebrile periods. Statistical correlation was found between Rev activity and different stages of clinical disease. Together, these results suggest that genetic and biological variation in rev may be a contributing factor in EIAV disease progression.

Recognition of tectonic events in undeformed regions: contrasting results from the Midland Platform and East Midlands Shelf, Central England

Apatite fission-track and vitrinite reflectance data from Central England demonstrate how these techniques can reveal otherwise unrecognized tectonic and/or palaeothermal episodes in apparently tectonically stable areas. The results document the transition from an inverted basinal region in the north (East Midlands Shelf), to a tectonically stable platform in the south (Midland Platform). AFTA data from the region reveal two discrete cooling episodes, in the Early and Late Tertiary. Maximum palaeotemperatures from AFTA and VR data in outcrop samples define a consistent increase from ≤50°C in Lower Cretaceous and Upper Jurassic units in the SE to around 80–90°C in Triassic and older units in the NW. These Early Tertiary palaeotemperatures reflect a combination of deeper burial and elevated basal heat flow. Results from the Rufford-1 well define an Early Tertiary palaeogeothermal gradient of 40.5°C km −1 (32–50°C km −1 at ±95% confidence limits), corresponding to deeper burial by 1450 m of additional section (1.1–2.2 km at ±95% confidence limits), subsequently removed by Tertiary erosion. In contrast, geological considerations suggest a maximum overburden of 800–900 m above the base of the Lower Jurassic in the vicinity of Rugby where palaeotemperatures at outcrop are similar to those near the Rufford-1 location. The discrepancy between stratigraphic and palaeo-thermal reconstruction of former burial depths, often noted in earlier studies, remains unresolved. The Late Tertiary episode is much less well-constrained, but results from Rufford- 1 may require between 910 and 1650 m of eroded section. Thus much of the total amount of removed overburden may have been removed during the Late Tertiary. Results from the Apley Barn Borehole (Oxfordshire) reveal a Late Tertiary palaeothermal episode characterized by a highly non-linear palaeotemperature profile which probably reflects local heating due to passage of hot fluids. Despite stratigraphic evidence for some Early Tertiary erosion results from this borehole show no evidence of Early Tertiary effects. Major Early and Late Tertiary exhumation was limited to regions underlain by older Palaeozoic basins while regions overlying Palaeozoic basement were more stable, experiencing significantly less exhumation. We suggest this reflects the preferential reactivation of the weaker basinal regions as a result of compressional events at plate margins. Our results emphasize the importance of incorporating results from both ‘inverted’ and ‘non-inverted’ areas in understanding the causal mechanisms of uplift and inversion, and highlight the importance of testing apparent stability using palaeo-thermal methods.

Pervasive Pan-African reactivation of the Grenvillian crust and large igneous intrusions in central Dronning Maud Land, East Antarctica

Abstract The geological history of central Dronning Maud Land (cDML) is described on the basis of age data, recent observations, and published data. The ages of both the protoliths of the metamorphic rocks of cDML and their primary metamorphism are Grenvillian (1200 to 1000 Ma). Following a long hiatus for which geochronological data are lacking, the Grenvillian crust of cDML was intruded by abundant Pan-African partly charnockitic granitoids and anorthosites of the Dronning Maud Land igneous province. These intrusions occurred predominantly in two Pan-African igneous episodes. The early igneous episode (about 600 Ma), in which the Grubergebirge anorthosite intruded, was followed by Pan-African high-grade metamorphism, intense ductile deformation and then medium-grade retrogression during later Pan-African events (570 to 520 Ma). The Grenvillian structures and metamorphic signature were pervasively overprinted or completely eradicated. The Pan-African metamorphism and tectonism were completed prior to the late Pan-African igneous episode (500 Ma), in which predominantly post-kinematic granitoids, as well as a small anorthosite, intruded. Thus, the present tectonic structure of the crust in cDML was formed during Pan-African events by overprinting of Grenvillian basement and intrusion of granitoids/syenites and anorthosites.

Crustal signature of Late Archaean tectonic episodes in the Yilgarn craton, Western Australia: evidence from deep seismic sounding

Deformation in the greenstone supracrustal rocks of the Eastern Goldfields Province of the Archaean Yilgarn Craton in Western Australia is delaminated from the underlying basement along a regional detachment surface presently at 3–7 km depth. This might suggest that the history of crustal deformation cannot be inferred with any certainty from that of the greenstones. However, seismic images of the crust below the greenstones show structures that can be interpreted in terms of a series of tectonic events similar to those within the greenstones. The upper crust (below and to the west of the greenstones) is largely unreflective, with interpreted west-dipping reverse faults. The middle crust is reflective, with reflector geometry implying thickening by west directed thrust stacking, and the lower crust has a fabric indicative of ductile deformation. These reflection fabrics imply crustal shortening, probably during the Late Archaean regional D2 ENE–WSW shortening event. They were subsequently overprinted and disrupted by structures consistent with regional NNW–SSE strike slip D3 faulting, and probably younger, more localised D4 faulting. The seismic images of the crust therefore show that the crust suffered tectonic events in which both the order and direction of deformation are similar to those of the greenstones. This is evidence that the whole crust deformed when the greenstones deformed. However, the scale and style of deformation vary with depth through the crust, and include thrusting and probably folding in the upper crust, thrust stacking in the middle crust, and ductile deformation in the lower crust. The length scale (wavelength) of structures in the middle and lower crust is greater than that in the greenstones.

Noncompliance in organ transplant recipients: a literature review

The consequences of failing to comply to doctor’s instructions can be damaging and devastating for the individual patient and their family. Noncompliance also leads to waste, as it reduces the potential benefits of therapy, and to the extra cost of treating avoidable consequent morbidity. Life-long immunosuppression is a prerequisite for good graft function, and noncompliance is often associated with late acute rejection episodes, graft loss, and death. It might be assumed that transplant patients constitute a highly motivated group, and that compliance would be high. Unfortunately, this is not the case: overall noncompliance rates vary from 20 to 50%. This overview includes literature on heart, liver, and kidney transplants in adult and pediatric transplant patients. Compliance behavior after transplantation, noncompliance and its relationship to organ loss and death, retransplantation outcome after graft loss due to noncompliance, and reasons for postoperative noncompliance will be addressed.

The episodic nature of air pollution transport from Asia to North America

We employ the Geophysical Fluid Dynamics Laboratory (GFDL) global chemistry transport model (GCTM) to address the episodic nature of trans‐Pacific pollution. The strongest Asian CO episodes over North America (NA), occurring most frequently between February and May, are often associated with disturbances that entrain pollution over eastern Asia and amplify over the western Pacific Ocean. Using 55 ppb of Asian CO as a criterion for major events, we find that during a typical year three to five Asian pollution events analogous to those observed by Jaffe et al. [1999] are expected in the boundary layer all along the U.S. West Coast between February and May. In contrast to CO, Asia currently has a small impact on the magnitude and variability of background ozone arriving over NA from the west. Direct and indirect Asian contributions to episodic O3 events over the western United States are generally in the 3–10 ppbv range. The two largest total O3 events (>60 ppbv), while having trajectories which pass over Asia, show negligible impact from Asian emissions. However, this may change. A future emission scenario in which Asian NOx emissions increase by a factor of 4 from those in 1990 produces late spring ozone episodes at the surface of California with Asian contributions reaching 40 ppb. Such episodic contributions are certain to exacerbate local NA pollution events, especially in elevated areas more frequently exposed to free tropospheric and more heavily Asian‐influenced air.

Clinical risk associated with appointment noncompliance in heart transplant recipients.

This study examined the prevalence of appointment noncompliance in 101 heart transplant recipients and how appointment noncompliance is related to patient profile and clinical risk. Appointment noncompliance was defined as patients not showing up at 1 or more planned clinic appointments (at a minimal frequency of every 3 months) during the previous year. Clinical variables were collected from medical files. Psychosocial variables were measured using established instruments. Medication noncompliance was assessed using electronic event monitoring. Paired t test, Wilcoxon 2-sample test, chi-square test, or Fisher exact test were used for statistical analysis as appropriate. The prevalence of appointment noncompliance was 7%. Appointment noncompliers were significantly younger, were less likely to live in a stable relationship with a partner, were more depressed, perceived their health as poorer, experienced more symptom distress, and had significantly more drug holidays. Fifty-seven percent of the appointment noncompliers experienced 1 or more late acute rejection episodes, compared to 2% of the appointment compliers. Appointment noncompliance is a critical behavioral risk factor in the occurrence of late acute rejection episodes in heart transplant patients. Patient profiles allow the identification of patients at risk for appointment noncompliance.

Chronic allograft failure in human renal transplantation: a multivariate risk factor analysis.

To identify potential risk factors for the development of chronic renal allograft failure. Chronic allograft failure (CAF) is the leading cause of late graft loss in renal transplantation. The authors studied the risk factors for the development of CAF in a single center during a period in which a consistent baseline immunosuppression regimen (cyclosporine, azathioprine, and prednisolone) was used. Data from the Oxford Transplant Center Database were assessed on 862 renal allografts during a 10-year period. Risk factors were identified using multivariate logistic regression analysis. Biopsy-proven CAF occurred in 77 patients (9.2%) in the entire group. Multivariate risk factor analysis revealed that early and late acute rejection episodes, proteinuria, and serum triglycerides were significant factors. Acute rejection after 3 months was more important than early acute rejection. Serum triglyceride level and proteinuria at 1 year were both elevated in the CAF group. Male sex provided a protective effect. Serum creatinine levels at 6 months after the transplant were not predictive of the risk of developing CAF. These results from the largest single-center review to date suggest that both antigen-dependent and -independent factors are involved in the pathogenesis of CAF. Acute rejection at all time points has a significant impact on the development of CAF.

COMPOSITIONAL VARIATION OF ARSENOPYRITE AND FLUID EVOLUTION AT THE ULSAN DEPOSIT, SOUTHEASTERN KOREA: A LOW-SULFIDATION PORPHYRY SYSTEM

The Ulsan Fe–W mine is located within the Cretaceous Gyeongsang volcano-sedimentary basin at the southeastern edge of the Korean Peninsula. Distinct hydrothermal events resulted in calcic skarn and vein deposits in recrystallized limestone near a Tertiary epizonal granite stock. The deposits of the Ulsan mine present a unique opportunity to document geochemically the complex evolution of a skarn–vein system that is related genetically to a low-sulfidation system. Isochemical contact metamorphism of an early skarn stage (stage I) is displayed by the presence of anhydrous Ca–Al–Mg skarn minerals at the contact between granite and recrystallized limestone. Following magnetite deposition in the main prograde skarn (stage II), the first deposition of arsenopyrite occurs intergrown with rammelsbergite – niccolite – gersdorffite – lollingite – native bismuth – bismuthinite –hexagonal pyrrhotite. These common sulfide assemblages are characterized by an overall low-sulfidation state during the main skarn stage. Retrograde skarn (stage III) is characterized by minor impregnations of scheelite in calcite and quartz, with actinolite and chlorite. During the latest part of stage III, Cu–Zn and polymetallic sulfide mineralization was introduced. The latest episode in the hydrothermal system (stage IV) is characterized by Zn–Pb–Ag mineralization in siderite–quartz veins. Decreasing As contents in arsenopyrite from stages II to IV indicate a decrease in temperature or sulfur fugacity (or both) with time. The various skarn-forming events and ore minerals from various stages are interpreted to have resulted from an evolutionary trend from hypersaline magmatic fluids during prograde skarn formation associated with Fe–As(–Ni) mineralization to low-salinity and low-temperature fluids during the retrograde skarn formation, associated with W–Cu–Zn mineralization. As the influence of magma-derived fluids waned, surficial fluids descended to deeper levels along fractures, resulting in siderite–quartz deposition associated with Zn–Pb–Ag mineralization. These results demonstrate that the Ulsan deposit is likely a skarn deposit that is genetically related to a low-sulfidation porphyry system.

Living unrelated donors in kidney transplants: better long-term results than with non-HLA-identical living related donors?

Given the severe organ shortage and the documented superior results obtained with living (vs. cadaver) donor kidney transplants, we have adopted a very aggressive policy for the use of living donors. Currently, we make thorough attempts to locate a living related donor (LRD) or a living unrelated donor (LURD) before proceeding with a cadaver transplant. We compared the results of our LURD versus LRD transplants to determine any significant difference in outcome. Between 1/1/84 and 6/30/98, we performed 711 adult kidney transplants with non-HLA-identical living donors. Of these, 595 procedures used LRDs and 116 used LURDs. Immunosuppression for both groups was cyclosporine-based, although LURD recipients received 5-7 days of induction therapy (antilymphocyte globulin or antithymocyte globulin), whereas LRD recipients did not. LURD recipients tended to be older, to have inferior HLA matching, and to have older donors than did the LRD recipients (all factors potentially associated with decreased graft survival). Short-term results, including initial graft function and incidence of acute rejection, were similar in the two groups. LURD recipients had a slightly higher incidence of cytomegalovirus disease (P=NS). We found no difference in patient and graft survival rates. However, the incidence of biopsy-proven chronic rejection was significantly lower among LURD recipients (16.7% for LRD recipients and 10.0% for LURD recipients at 5 years posttransplant; P=0.05). LRD recipients also had a greater incidence of late (>6 months posttransplant) acute rejection episodes than did the LURD recipients (8.6% vs. 2.6%, P=0.04). The exact reason for these findings is unknown. Although LURD recipients have poorer HLA matching and older donors, their patient and graft survival rates are equivalent to those of non-HLA-identical LRD recipients. The incidence of biopsy-proven chronic rejection is lower in LURD transplants. Given this finding and the superior results of living donor (vs. cadaver) transplants, a thorough search should be made for a living donor-LRD or LURD-before proceeding with a cadaver transplant.

Plate interactions control middle–late Miocene, proto-Gulf and Basin and Range extension in the southern Basin and Range

Middle–late Miocene (proto-Gulf; ∼12–6 Ma) extension around the Gulf of California (Gulf Extensional Province) is commonly interpreted as resulting from partitioning of oblique Pacific–North American plate motion into strike–slip displacement along the margin and east–northeast extension perpendicular to the margin within the North American plate. We propose that this mechanism also applies to kinematically similar, predominantly east–northeast extension that occurred at the same time throughout the southern Basin and Range province, from southern Arizona and New Mexico to the Trans-Mexican Volcanic Belt. New field and 40Ar/ 39Ar data in Sinaloa and Durango confirm that this episode of extension occurred on the mainland side of the Gulf and in the Basin and Range east of the Sierra Madre Occidental, which is generally considered the eastern margin of the Gulf Extensional Province. Published data indicate the middle–late Miocene episode also occurred across the northern and southern ends of the Sierra Madre where the Gulf Extensional Province connects with the Basin and Range: (1) from central Sonora into southern Arizona and New Mexico, and (2) from Nayarit into central Mexico north of the Trans-Mexican Volcanic Belt. This episode appears to have affected an area that continues to the eastern edge of the Basin and Range province in Texas and San Luis Potosi. Recognition that this episode of extension affected the entire southern Basin and Range resolves the discrepancy between the amount of extension calculated based on plate reconstructions and that based on field data within the Gulf Extensional Province alone. Published plate reconstructions require 160 to 110 km of east–northeast extension between ∼12 and 6 Ma. If taken up solely within the Gulf Extensional Province, this would have generated 66 to 78% extension, which is much greater than observed. Spread across the entire southern Basin and Range it requires only ∼20% total extension, which is more consistent with observations of cumulative extension between 12 and 6 Ma. Extension was partitioned into the Gulf Extensional Province because (1) it lies between two stable batholith belts (Mesozoic Peninsular Ranges on the west and mid-Tertiary Sierra Madre Occidental on the east) that resisted extension and (2) the Gulf was thermally weakened by immediately preceding arc magmatism. Extension in the main Basin and Range province in part probably avoided the relatively strong, batholithic crust of the Sierra Madre Occidental.

A genetic model for a mesothermal Au deposit: evidence from fluid inclusions and stable isotopic studies at El Sid Gold Mine, Eastern Desert, Egypt

The El Sid Au mineralisation in the Fawakhir area, Eastern Desert, Egypt, is comprised of hydrothermal quartz veins cutting a Neoproterozoic granitoid pluton. The mineralisation is divided into Au-bearing, transitional and late carbonate vug stages. Pyrite- arsenopyrite and streaky pyrite-sphalerite-galena assemblages characterise the early and late episodes of the Au-bearing stage, respectively. These sulphide minerals sometimes contain Au as inclusions. Fluid inclusions from the Au-bearing stage are H2OCO2 rich fluids (ca 29–62 mole% CO2 and density, ca 0.51-0.66 g cm−3) with moderate to high salinities (ca 12–19 wt% NaCl equiv.). The trapping temperature of the ore occurred between 280 and 350°C, at pressures between 120–170 MPa (∼800–1800 m depth). However, fluid inclusions from the pyrite-arsenopyrite assemblage reflect lower homogenisation temperature measurements (Th) (265–295°C) than those in the streaky pyrite-sphalerite-galena assemblage (330–365°C). The minerals of the transitional and late carbonate vug stages (quartz and calcite) were formed between 180 and 265°C.Oxygen and H isotope data of fluid inclusions hosted in the quartz and calcite from the Au-bearing stage indicate a rather wide range of calculated δ18OH20 and δDH20 (i.e. +3.2 to + 7.8%‰ and −75 to −32‰ , respectively). The data for the streaky pyrite-sphalerite-galena assemblage exhibit higher δ180H20 values (+ 5.3 to + 6.8%‰) and lower δDH20 (−75 to −48‰) relative to that of the pyrite-arsenopyrite assemblage. Calculated isotopic temperatures of quartz-calcite fractionation range from 282 to 353°C and are consistent with the trapping temperatures (280–350°C).The fluid inclusion and stable isotope data imply that Au at the El Sid Gold Mine has been transported as a bisulphide complex. The high salinity and inferred occurrence of CH4 in some fluid inclusions collected from the graphite-rich zone along a serpentinite-granitoid contact suggest that the mineralising solutions gained their metal contents through circulation in the fractured zones and incorporation with a geothermal convective system by wall rock interaction. Deposition of Au sulphides has taken place at shallow crustal levels (∼800–1800 m) as a result of meteoric/magmatic-metamorphic water exchange with wall rocks through H2OCO2 immiscibility during fluid pressure drop and decreasing ligand activity.

Plasma C3a and C4a levels in liver transplant recipients: a longitudinal study.

Liver transplant patients were enrolled in a study designed to investigate correlations between plasma complement C3a or C4a levels and various postoperative complications. Longitudinal EDTA-plasma levels of C3a and C4a were measured by quantitative radioimmunoassay. Acute rejection gave a characteristic and marked increase in blood C3a, C4a and gamma-glutamyl transferase (gammaGT) levels, which rapidly resolved after high dose steroid treatment. Cytomegalovirus (CMV) infections in two of three patients gave an initial small increase only in C3a levels (i.e., alternative pathway activation) followed approximately 6 weeks later by a marked increase in C4a levels (i.e., classical or lectin pathway activation). In a third patient diagnosed for CMV infection, the complement activation profile was complicated by a coincident minor rejection episode. However, a late stage elevation in C4a was also noted. Two patients experiencing biopsy proven recurrent hepatitis C infections following transplantation exhibited increases in both gammaGT and C4a levels, without a significant increase in the level of C3a. Several hepatitis C and one hepatitis B patient had multiple late activation episodes involving marked elevation in both plasma C3a and C4a levels without detectable increases in the liver enzymes conventionally used to monitor organ function. We also showed that ex vivo activation of complement in EDTA plasma from all transplant patients was abnormally high. The classical or lectin pathway is believed to be responsible for this excessive ex vivo complement activation in the plasma of these patients. Therefore, subclinical rejection episodes and/or viral infections may be effectively detected or monitored by measuring C3a and C4a levels in plasma samples from liver transplant patients. Routine measurement of plasma complement products may provide an early non-invasive mode for detecting infections and also serve to monitor chronic or acute changes in the patient's immune system.

Structure and Evolution of the Neogene Guercif Basin at the Junction of the Middle Atlas Mountains and the Rif Thrust Belt, Morocco

The Guercif basin of northern Morocco occupies a 50 ´ 60 km area where the transpressional Middle Atlas mountains terminate and abut the Rif thrust belt. Analysis of over 800 km of 2-D (two-dimensional) seismic reflection profiles and eight exploratory wells, in combination with existing geological data, suggests a late Miocene episode of extension (4%, or 1.7 km, maximum) and a subsequent episode of contraction since the end of the Miocene. Most of the late Miocene deposition was concentrated in a narrow graben (herein referred to as the Guercif graben), which contrasts with the wider physiographic expression of the basin today. Geohistory analysis indicates that tectonic subsidence persisted until the Messinian, and sediment loading continued to drive subsidence even after extension stopped. Timing constraints demonstrate the contemporaneity of the Guercif graben and west-southwest-vergent thrust tectonics of the Rif thrust belt. Similar timing and proximity with the Rif, as well as the graben geometry, suggest that extension in the Guercif basin, in addition to other smaller extensional basins in the northern Middle Atlas region adjacent to the Rif, may represent the distal effects of a broad lateral shear zone bounding the thrust belt.

Safety of modern oral contraception: the options for women: lessons to be learned.

The relatively short history of hormonal contraception has been marked by a series of 'pill scares', all of which--after creating panic among users--were proven to be unfounded in terms of public health impact. The latest pill scare, provoked by regulatory action in the United Kingdom and the Federal Republic of Germany in response to the publication of a series of articles indicating a doubling of risk of deep venous thrombosis in users of oral contraceptives containing third-generation progestins, seems finally settled: both the British and the German Drug Regulatory Authorities have now reverted their verdict. The damage unfortunately stays: hundreds of thousands of women have been compelled to abandon the pill of their choice, often deciding to drop contraception altogether, thereby exposing themselves to unwanted pregnancy and--in a number of cases--to pregnancy termination. This latest episode should be turned into something positive: we need to learn that, in the case of drugs in widespread use, before restrictive action is taken--and except for very rare and specific instances--the scientific community must carry out an exhaustive debate on the reality and importance of the observed effects. Although the public should, in each instance, be properly informed, it is only after this process has been completed that restrictive action should be taken. It is hoped that, after this last episode, all concerned have learned this simple principle and will accept being guided by it from now on.

Multiple late Quaternary episodes of exceptional diatom production in the Gulf of Alaska

Hole 887B of the Ocean Drilling Program (ODP) comprises a 44 m (750 kyr) long continuous section recovered from the Patton–Murray Rise, an elevated plateau that is largely isolated from turbidite deposition. The Patton–Murray area is centered under the Alaska Gyre, a region characterized by the domal upwelling of nutrient-rich waters. Marked increases in productivity and rapid settling of biogenic matter are suggested throughout the section by the episodic accumulation of diatomaceous oozes up to ∼1 m thick that are accompanied by barium enrichments. Significant δ 13C org maxima in the major diatomaceous bands suggest that mixed-layer [CO 2(aq)] may have been drawn down significantly during some of the productivity events. The episodes of enhanced productivity at Site 887 occur synchronously with short-lived minima in planktonic foram δ 18O, suggesting a direct link to low salinity, or less likely, warming, events in the Gulf of Alaska. There is no obvious explanation for the events, but they may be related to seasonal incursions of meltwater from Alaska. We speculate that episodic input of meltwater- or dust-borne iron from Asian or Alaskan sources may have promoted the extraordinary diatom production events recorded in the sedimentary record.

Crustal structure beneath the central Oregon convergent margin from potential‐field modeling: Evidence for a buried basement ridge in local contact with a seaward dipping backstop

Models of magnetic and gravity anomalies along two E‐W transects offshore central Oregon, one of which is coincident with a detailed velocity model, provide quantitative limits on the structure of the subducting oceanic crust and the crystalline backstop. The models indicate that the backstop‐forming western edge of the Siletz terrane, an oceanic plateau that was accreted to North America ∼50 million years ago, has a seaward dip of less than 60°3. Seismic, magnetic, and gravity data are compatible with no more than 2 km of subducted sediments between the Siletz terrane and the underlying crystalline crust of the Juan de Fuca plate. The data also suggest the presence of a N‐S trending, 200‐km‐long basaltic ridge buried beneath the accretionary complex from about 43°N to 45°N. Although the height and width of this ridge probably vary along strike, it may be up to 4 km high and several kilometers wide in places and appears to be locally in contact with the Siletz terrane beneath Heceta Bank. Several models for the origin of this ridge are discussed. These include: a sliver of Siletz terrane detached from the main Siletz terrane during a late Eocene episode of strike‐slip faulting; imbrication and thickening of subducted oceanic crust in place; an aseismic ridge rafted in on the subducting oceanic crust during the past 1.2 million years; and a series of ridges and/or seamounts rafted in over a longer period of time and transferred from the subducting plate to the overlying plate. The last model is the most consistent with the complicated history of local uplift, subsidence, and slope instability recorded in the ridges, basins, and banks of this part of the margin. We speculate that the massive seaward dipping western edge of the Siletz terrane in this region inhibits subduction of seamounts and sediments, resulting in fomation of buried ridge as the accumulated flotsam and jetsom of subduction. This process may also be responsible for thickening of lower accretionary complex material, oversteepening of slopes leading to massive slumping, and north‐south extension through strike‐slip faulting in the accretionary complex to the west of the buried ridge. Regardless of its origin, the ridge may currently be acting as an asperity inhibiting subduction.