bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Subcutaneous Interleukin‐2 Therapy on Phenotype and Function of Peripheral Blood Mononuclear Cells in Human Immunodeficiency Virus Infected Patients
Authors: Aladdin  , Larsen  , Møller  , Ullum  , Buhl  , Gerstoft  , Skinhøj  , Pedersen
Published: March 2003

In the context of clinical therapy with recombinant human interleukin‐2 (IL‐2), we monitored immunological alteration in 10 human immunodeficiency virus type‐1 (HIV‐1)‐infected individuals, on stable antiretroviral therapy, who had a CD4+ cell count between 200 and 500 cells/mm3. Subcutaneous IL‐2 was prescribed thrice weekly (at a dose of 3 × 106 IU) for 24 weeks and the patients were followed‐up for 32 weeks. IL‐2 treatment induced an increase in the CD4+ percentage (P < 0.001) and CD4+ cell count (P < 0.009). Furthermore, natural killer (NK) cell activity was increased (P < 0.001) at week 8 of treatment, whereas lymphokine‐activated killer (LAK) cell activity showed a transient, nonsignificant increase at week 8 and was reduced (P < 0.001) at 32 weeks. However, the cytotoxic T‐lymphocyte (CTL) activity decreased against HIV antigens, and the proliferative response to Candida, IL‐2 and phytohaemagglutinin (PHA) declined during the first 8 weeks (P < 0.05) and returned to baseline levels after 32 weeks. The HIV RNA level did not change during IL‐2 therapy; however, after 8 weeks of follow‐up a significant increase (P < 0.001) in viral load was observed. In conclusion, continuous IL‐2 treatment to HIV‐infected individuals enhanced the CD4 count, but the in vitro lymphocyte function was impaired and an increase in viral replication occurred after treatment.
Anti‐SSA/Ro Antibody Determination by Enzyme‐Linked Immunosorbent Assay as a Supplement to Standard Immunofluorescence in Antinuclear Antibody Screening
Authors: Blomberg  , Ronnblom  , Wallgren  , Nilsson  , Karlsson‐Parra
Published: March 2003

The aim of this study was to investigate the frequency and possible clinical relevance of SSA/Ro antibodies, as determined by enzyme‐linked immunosorbent assay (ELISA), in patient sera not exhibiting a concomitant positive reaction by the standard immunofluorescence (IF) test using HEP‐2 cells as substrate. SSA/Ro reactivity, as shown by ELISA, was found in 285 (7%) of 4025 serum samples consecutively remitted for antinuclear antibody (ANA) screening. Seventy‐five of these serum samples (26%), derived from 64 patients, were negative by the IF‐ANA screening test. Serum samples from all 64 patients exhibiting SSA/Ro reactivity by ELISA without concomitant positivity by IF‐ANA were further investigated by IF using transfected HEP‐2 cells hyperexpressing the 60,000 MW SSA/Ro antigen (HEP‐2000®) and by immunodiffusion (ID) and Western blot. In 55 of these 64 patients, SSA/Ro reactivity could be verified by one or more of the other techniques investigated. Twelve of these patients fulfilled four or more American College of Rheumatology (ACR) criteria for systemic lupus erythematosus (SLE) and another five patients exhibited a histologically confirmed cutaneous lupus erythematosus (LE). In four of the 12 IF‐ANA‐negative patients with a diagnosis of SLE, the SSA/Ro reactivity was only detectable by ELISA and Western blot. In conclusion, the use of a sensitive ELISA assay could provide a clinically important supplement to the routine ANA screening by IF, which does not detect certain anti‐SSA/Ro‐containing sera among patients with relevant autoimmune diagnoses. Detection of anti‐SSA/Ro antibodies, however, does not alone signify cutaneous LE or SLE but adds weight to these diagnoses that should rely heavily on other clinical information.
A Soluble Mannose Receptor Immunoadhesin Enhances Phagocytosis of Pneumocystis carinii by Human Polymorphonuclear Leukocytes In Vitro
Authors: Stehle  , Rogers  , Harmsen  , Ezekowitz
Published: March 2003

Pneumocystis carinii is an opportunistic pathogen that causes pneumonia in immunocompromised hosts. In the normal host, P. carinii is susceptible to an array of first line host defense mechanisms that are operative in the lung. Alveolar macrophages play a central role in the clearance of inhaled organisms. The macrophage mannose receptor (MR) appears to be sufficient for P. carinii phagocytosis. In individuals infected with the human immunodeficiency virus, MR expression on alveolar macrophages and P. carinii phagocytosis are decreased, however, Fc‐receptor mediated phagocytosis remains intact. In this study, we demonstrate that a recombinant soluble MR immunoadhesin, consisting of the essential carbohydrate binding MR ectodomain and the Fc‐region of human immunoglobulin (Ig)G1, binds P. carinii and leads to an 8.2‐fold increased uptake of P. carinii by phagocytic cells. Our results suggest that the soluble MR immunoadhesin may have therapeutic potential in the treatment of P. carinii infections.
Tamoxifen Decreases Renal Inflammation and Alleviates Disease Severity in Autoimmune NZB/W F1 Mice
Authors: Wu W.‐M. , Lin B.‐F. , Su Y.‐C. , Suen J.‐L. , Chiang B.‐L.
Published: March 2003

It has been documented that sex hormone may play a role in the pathogenesis of murine lupus. To determine the effect of tamoxifen (TAM) on NZB/W F1 female mice, a total dose of 800 μg (22 mg/kg body weight) of TAM was administered subcutaneously every 2 weeks. The control mice were injected with peanut oil only. After treatment with TAM for 5 months, the mice were killed and immunological parameters were evaluated. The results suggest that NZB/W F1 mice treated with TAM had less severe proteinuria and increased survival rate compared to controls. Flow cytometric analysis of splenocytes revealed a significantly lower percentage of B cells and CD5+ B cells in the TAM‐treated group. There was a significantly lower serum level of soluble tumour necrosis factor (TNF) receptor I and II molecules in the TAM‐treated mice. Immunohistological study showed that control mice had severe immune complex deposition in the kidney. In contrast, TAM‐treated mice had much less pathological change. In summary, this study demonstrated that TAM treatment might be able to alleviate the symptoms of lupus nephritis, influence B‐cell count, modulate the expression of cytokine receptors and thereby subsequently affect immune function. Further studies to determine the cellular mechanisms in lupus nephritis may increase our understanding of this complex disease and provide additional targets for therapeutic intervention.
Isolation of Human Anti‐idiotypes Broadly Cross Reactive with Anti‐dsDNA Antibodies from Patients with Systemic Lupus Erythematosus
Authors: Zhang W. , Winkler T. , Kalden J. R. , Reichlin M.
Published: March 2003

Antibodies to double stranded (ds)DNA play a central role in clinical diagnosis and disease expression in Systemic lupus erythematosus (SLE). This paper describes the isolation of anti‐idiotype reagents (anti/antidsDNA) from four SLE sera and the demonstration of broad and quantitatively similar cross reactivity to both polyclonal and monoclonal anti‐dsDNA antibodies isolated from SLE patients. Seven affinity‐purified polyclonal and three monoclonal human anti‐dsDNA preparations reacted preferentially with anti‐idiotype F(ab′)2 coated plates compared to normal immunoglobulin (Ig)G F(ab′)2 coated plates in elisa. In contrast, autoantibodies of other specificities (anti‐Ro/SSA, anti‐La/SSB, and anti‐U1RNP) reacted equally with anti/anti‐dsDNA F(ab′)2 and normal IgG F(ab′)2 coated plates. Such anti‐idiotypic antibodies could play a significant role in the regulation of anti‐dsDNA antibody levels in SLE.
Maturation of Dendritic Cells by Recombinant Human CD40L‐Trimer Leads to a Homogeneous Cell Population with Enhanced Surface Marker Expression and Increased Cytokine Production
Authors: Würtzen P. A. , Nissen M. H. , Claesson M. H.
Published: March 2003

Dendritic cells (DC) have been shown to be potent inducers of specific cytotoxic T‐cell responses both in vivo and in vitro. Furthermore, exposure to cytokines such as tumour necrosis factor (TNF)‐α or CD40 triggering changes DC phenotype and cytokine production and may enhance the T‐cell activating capacity of the DC. We studied DC phenotype and cytokine production as well as the T‐cell proliferation and cytotoxic T lympocyte (CTL) activation induced by DC generated in vitro. In addition, the effect of exposure to recombinant human CD40L‐trimer (huCD40LT) on these parameters was investigated. Effective differentiation of monocytes derived from freshly isolated peripheral blood mononuclear cells (PBMC) was obtained with granulocyte macrophage‐colony stimulating factor (GM‐CSF) and interleukin (IL)‐4. The DC expression of human leucocyte antigen (HLA) molecules, CD80, CD83, and CD86 was markedly enhanced by exposure to huCD40LT even compared to TNF‐α exposure. Only a moderate cytokine production was observed initially, while TNF‐α addition or CD40 triggering, especially, induced enhanced production of IL‐6 and IL‐12 p40. Surprisingly, comparable induction of T‐cell proliferation by a DC allostimulus or through the presentation of PPD, and influenza M1‐peptide specific CTL activity was obtained with nonmaturated (CD83−) and maturated (CD83+) DC. In conclusion, a final maturation of monocyte‐derived DC through huCD40LT resulted in a highly homogeneous cell population with enhanced surface marker expression and high production of pro‐inflammatory cytokines. In addition, the induction of responses to allo or recall antigens presented by huCD40LT maturated DC was comparable to the responses obtained with the DC maturated through TNF‐α exposure.
Long‐Term Donor Chimerism after MHC (RT1) Mismatched Bone Marrow Transplantation in the Rat: the Role of Host Alloreactive NK Cells
Authors: Engh E. , Strøm‐Gundersen I. , Benestad H. B. , Rolstad B.
Published: March 2003

We have investigated the role of major histocompatibility complex (MHC) (RT1) disparities in the engraftment of bone marrow (BM) cells after whole body irradiation of rats. Mononuclear BM cells from PVG.RT7.2 (RT1c) rats were injected i.v. into sublethally (10Gy) whole body irradiated PVG (RT1c) rats and RT1 congenic and recombinant PVG rats. Repopulation of the BM, spleen, and blood with donor cells was assessed by FACS analysis of cells labelled with the fluorescein isothiocyanate (FITC)‐labelled HIS41 monoclonal antibody (MoAb) against the RT7.2 marker. In RT1 matched (PVG.RT7.2 → PVG) and RT1‐mismatched combinations (PVG.RT7.2 → PVG.1AV1), where radioresistant host natural killer (NK) cells could not recognize the BM inoculum as foreign, a donor chimerism close to 100% was observed after 6–8 weeks. However, in rat strain combinations where host NK cells could recognize an RT1 mismatch, almost no donor cells survived, and the rats were repopulated with leukocytes of host origin. In intra‐MHC recombinant rat strains the element determining rejection or acceptance of the allograft mapped to the RT1‐B/D‐C/E/M region in PVG.R8 and PVG.R23 rats, in accordance with the patterns of NK alloreactivity in these strain combinations. NK cells may therefore be a primary obstacle to successful allogeneic BM engraftment in this model.
Significantly Depressed Percentage of CD27+ (Memory) B Cells among Peripheral Blood B Cells in Patients with Primary Sjögren's Syndrome
Authors: Bohnhorst J. Ø. , Thoen J. E. , Natvig J. B. , Thompson K. M.
Published: March 2003

CD27 has been found to be expressed on somatically mutated B cells and is thus a positive marker for memory B cells in peripheral blood (PB). Since abnormal immunogloblin (Ig) production is characteristic of the autoimmune diseases primary Sjögren's syndrome (pSS) and rheumatoid arthritis (RA), we have analyzed in detail the CD27 expression on PB B cell from these patient groups. Staining of PB B cells with monoclonal antibodies (MoAb) specific for CD19 and CD27 revealed a significantly depressed percentage of CD27+ PB B cells in patients with pSS (14.8 ± 1.6%) compared to both healthy donors (31.3 ± 4.7%, P = 0.005) and patients with RA (40.8 ± 4.1%, P = 0.0001). In addition, the percentages of both the IgD+CD27+ and the IgD‐CD27+ B‐cell subpopulations were significantly lower in pSS patients compared to RA patients and healthy donors. However, the relative proportion of IgD‐ and IgD+ cells among the CD27+B cells were almost the same for the three groups. Our data suggest a disturbance in the differentiation of peripheral B cells and possibly a bias towards plasma cell differentiation, resulting in a depressed percentage of CD27+ memory PB B cells in pSS. These results are potentially of pathological significance and of diagnostic value.
Identification of Two Ikaros‐like Transcription Factors in Lamprey
Authors: Mayer W. E. , O'Huigin C. , Tichy H. , Terzic J. , Saraga‐Babic M.
Published: March 2003

The jawless Agnatha (lampreys and hagfishes) represent the phylogenetically oldest order of vertebrates that are believed to lack the adaptive immune system of jawed vertebrates. In order to search for molecular markers specific for cellular components of the adaptive immune system in lampreys, we used the polymerase chain reaction (PCR) to identify genes for transcription factors of the Ikaros family in genomic DNA and cDNA libraries from two species of lampreys, Petromyzon marinus and Lampetra fluviatilis. The mammalian Ikaros‐like family of transcription factors consists of five members, Ikaros, Helios, Aiolos, Eos and Pegasus, of which the first three appear to be essential for lymphocyte development. Two different Ikaros‐like genes, named IKLF1 and IKLF2, were identified in lamprey. They both have the conserved exon–intron structure of seven exons and show alternative splicing like their counterparts in jawed vertebrates. The genes code for predicted proteins of 589 and 513 amino acid residues, respectively. The proteins contain six highly conserved zinc finger motifs that are 83–91% identical to the mammalian members of the Ikaros‐like family. The remaining parts of the sequences are, however, mostly unalignable. Phylogenetic analysis based on the alignable segments of the sequences does not identify the orthologous gene in jawed vertebrates but rather shows equidistance of the lamprey Ikaros‐like factors to each other and to Ikaros, Helios, Aiolos and Eos. Expression studies by reverse transcription (RT)–PCR and in situ hybridization (ISH), however, provide evidence for moderate expression in presumed lymphoid tissues like the gut epithelium and for high levels of expression in the gonads, especially in the ovary.
Testicular‐Associated Immune Deviation: Flushing of the Testicular Lymph Sinusoids Induces Immunosuppression and Inhibits Formation of EAE in SJL Mice
Authors: Veräjänkorva E. , Setälä N. , Teros T. , Salmi A. A. , Pöllänen P.
Published: March 2003

Injection of antigen into the testis has been previously proved to induce systemic tolerance in rats. Testicular‐associated immune deviation (TAID) has thus far been induced and studied only in the rat and the present study was planned to study if TAID could be induced in mice as well. In addition, it was studied if TAID is organ‐specific. Mouse spinal cord homogenate (MSCH), as well as phosphate‐buffered saline (PBS), was injected into the testes of SJL and BALB/c male mice before the induction of experimental allergic encephalomyelitis into the animals. The control animals received MSCH intramuscularly into the hamstring muscles. The animals were followed and graded daily for symptoms attending the next 30 days. In the SJL strain, mice treated with an intratesticular (i.t.) MSCH injection prior to the induction of experimental autoimmune encephalomyelitis (EAE) had the shortest duration of symptoms and the longest time to the onset of the first symptoms. In addition, the mice injected i.t. with PBS had as mild symptoms as those injected with MSCH. There was a statistically significant difference, however, between the groups injected either with MSCH or PBS intratesticularly. In general, mice treated with an intramuscular injection of MSCH got sick first, and had the most severe symptoms for the longest duration of time. In the case of the BALB/c mice, there were no statistical differences between the groups investigated. It is concluded that TAID is a testis‐ and strain‐specific phenomenon in the mouse, and not specific to the rat. In addition, i.t. injection of PBS is just as effective in creating tolerance against EAE as i.t. injection of MSCH in the SJL mice.
Differences in LPS‐Induced Activation of Bronchial Epithelial Cells (BEAS‐2B) and Type II‐Like Pneumocytes (A‐549)
Authors: SCHULZ C. , FARKAS L. , WOLF K. , KRÄTZEL K. , EISSNER G. , PFEIFER M.
Published: March 2003

Lipopolysaccharide (LPS) as a major component of the outer membrane of gram‐negative bacteria stimulates various cells to initiate a signalling cascade which ultimately leads to cell activation and expression of immunoregulatory or inflammatory cytokines. The human respiratory epithelium is an important environmental interface, but differences in LPS‐induced cell activation between bronchial and alveolar epithelial cells have not yet been investigated in detail. First, the expression of Toll‐like receptors (TLRs), as pattern‐recognition receptors, was investigated for the bronchial epithelial cells and type II‐like pneumocytes, demonstrating that they fulfil the prerequisites for LPS signalling. Thereafter, the effects of LPS, soluble CD14 (sCD14) and LPS‐binding protein (LBP) on the release of interleukin‐6 (IL‐6) and IL‐8 were studied. In the presence of LPS, sCD14 induced a significant and concentration‐dependent cytokine release in type II‐like pneumocytes, whereas the response of bronchial epithelial cells to sCD14 stimulation was low, implicating sCD14‐independent activation mechanisms. Furthermore, LBP revealed inhibitory effects on the activation of alveolar epithelial cells, which may represent a novel local defence mechanism during gram‐negative infection. We conclude that distinct pathways exist for LPS‐induced activation of bronchial and alveolar epithelial cells.
T‐ and B‐Cell Epitopes in the Secreted Mycobacterium bovis Antigen MPB70 in Mice
Authors: Tollefsen S. , Pollock J. M. , Lea T. , Harboe M. , Wiker H. G.
Published: March 2003

MPB70 is a soluble secreted protein highly expressed in Mycobacterium bovis and strains of bacille Calmette–Guérin (BCG); as such, it is a candidate for subunit and DNA vaccines against tuberculosis. MPB70 was screened for T‐cell epitopes in four different inbred mouse strains. Major histocompatibility complex (MHC) H‐2b‐expressing mice (C57BL/6) secreted interferon‐γ (IFN‐γ) after stimulation with peptides from the regions 1–20, 41–50, 81–110, 121–150 and 161–193 of the MPB70 sequence. H‐2db mouse (B6D2) splenocytes secreted IFN‐γ after stimulation with some of the same peptides, whereas H‐2d mice (BALB/c and DBA/2) did not secrete IFN‐γ upon stimulation with the peptides. Sera from H‐2db mice immunized with native MPB70 in incomplete Freund's adjuvant (IFA), mpb70 DNA or live BCG Moreau were found to contain antibodies against the native MPB70 antigen. H‐2db mice immunized with native MPB70 in IFA exhibited high titres of peptide‐reactive immunoglobulin G1 (IgG1) antibodies, whereas DNA‐immunized mice reacted with IgG2a antibodies against some of the same peptides. As some of the epitopes recognized by mouse T and B cells have previously been found to stimulate immune responses in humans, cattle and rabbits, we conclude that these epitopes may be good general epitopes for the stimulation of T‐ and B‐cell responses and candidates for a DNA vaccine with a broad applicability.
Origin of polyhalite deposits in the Zechstein (Upper Permian) Zdrada platform (northern Poland)
Authors: PERYT  , PIERRE  , GRYNIV
Published: March 2003

Polyhalite deposits in the Zechstein (Upper Permian) of northern Poland occur in the Lower Werra Anhydrite. In the Zdrada Sulphate Platform, the polyhalite appears to be a very early replacement of anhydrite. The replacement was caused by the halite‐precipitating brines which contained potassium and magnesium ions. The formation of polyhalite was preceded by the syndepositional anhydritization of the original gypsum deposit which has often preserved its primary textures. This anhydritization on the platform and its slopes was a reaction of the precipitated gypsum in a hydrologically open evaporite basin, with brines of salt basins adjacent to the sulphate platform. These brines, when nearly saturated with respect to halite, and potassium and magnesium rich, reacted with anhydrite to precipitate polyhalite along the slopes of the Zdrada Platform. The oxygen and sulphur isotopic compositions of sulphate evaporites indicate that marine solutions were the only source of sulphate ions supplied to the Zechstein basin, and that anhydrite was transformed to polyhalite by reaction with marine brines more concentrated than those that precipitated precursor calcium sulphate minerals.
Downstream changes of large‐scale bedforms in turbidites around the Valencia channel mouth, north‐west Mediterranean: implications for palaeoflow reconstruction
Authors: Morris  , Kenyon  , Limonov  , Alexander
Published: March 2003

Side‐scan sonar, seismic and core data are used to identify mega‐flutes, transverse and ‘V’ shaped bedforms in turbidites around the Valencia channel mouth, north‐west Mediterranean. Long‐range side‐scan sonar data reveal a broad, curved, asymmetric, channel, that widens and terminates downfan. The western channel bank near the channel mouth has been partly eroded by turbidity currents that spilled out of the channel. Transverse bedforms on the east of the channel floor are interpreted as antidunes and, if this interpretation is correct, they indicate that the flow was probably supercritical at least locally within the channel. Trains of mega‐flutes, are incised into coarse‐grained sediments of the channel floor near the channel mouth. The association of mega‐flutes and antidunes is thought to be diagnostic of channel–lobe transitions on deep‐sea fans. The mega‐flutes pass downfan into an area of streaks that diverge at up to 45° and indicates flow expansion from the channel mouth. About 75 km downfan from the channel mouth, deep‐towed side‐scan data record transverse bedforms (interpreted as antidunes) passing downfan into an area covered by ‘V’ shaped bedforms with upflow pointing apices (named chevrons here). The chevrons are commonly c. 200 m from limb to limb and c. 2 m in amplitude with flow‐parallel wavelengths of c. 400 m. We propose that chevrons were formed by a strong, probably supercritical (or near critical) turbidity current spreading from the channel mouth and flowing towards the Balearic Abyssal Plain. Thinning of the turbidity current, resulting from flow spreading would allow the Froude number to remain high up to 100 km from the channel mouth and could explain the observed reduction in antidune wavelength.
The grain–fluid interaction as a self‐stabilizing mechanism in fluvial bed load transport
Authors: Mcewan  , Jefcoate  , Willetts
Published: March 2003

A grain‐scale model of fluvial bed load transport is described, with particular emphasis on the equilibrium between the saltating grains and the near bed flow, and its role in determining transport rate. The model calculates, explicitly, the modification of the velocity profile by the moving grains, together with the consequential reduction in surface fluid shear stress. As the surface fluid shear stress is reduced by the moving grains, so the entrainment rate decreases and the model reaches a steady state. The results provide insight into two important questions at a macroscopic level. First, they show that, in the absence of large static roughness, the dynamic roughness caused by the moving grains may be a significant contributor to flow resistance. Secondly, the model indicates the manner in which transport may be limited by a combination of the transport capacity of the flow and the availability of sediment for entrainment. Only in the case of high sediment availability does the fluid shear stress acting at the surface approach the critical entrainment value, reproducing the behaviour suggested by Bagnold (1956) and
Owen (1964). This suggests that prediction formulae based on this assumption only describe the bed load transport system under particular conditions.
Physical and biological controls on the formation of carbonate and siliciclastic bedforms on the north‐east Brazilian shelf
Authors: TESTA VIVIANE , BOSENCE DANIEL W. J.
Published: March 2003

The continental shelf of the State of Rio Grande do Norte, Brazil, is an open shelf area located 5°S and 35°W. It is influenced by strong oceanic and wind‐driven currents, fair weather, 1·5‐m‐high waves and a mesotidal regime. This work focuses on the character and the controls on the development of suites of carbonate and siliciclastic bedforms, based on Landsat TM image analysis and extensive ground‐truth (diving) investigations. Large‐scale bedforms consist of: (i) bioclastic (mainly coralline algae and Halimeda) sand ribbons (5–10 km long, 50–600 m wide) parallel to the shoreline; and (ii) very large transverse siliciclastic dunes (3·4 km long on average, 840 m spacing and 3–8 m high), with troughs that grade rapidly into carbonate sands and gravels. Wave ripples are superposed on all large‐scale bedforms, and indicate an onshore shelf sediment transport normal to the main sediment transport direction. The occurrence of these large‐scale bedforms is primarily determined by the north‐westerly flowing residual oceanic and tidal currents, resulting mainly in coast‐parallel transport. Models of shelf bedform formation predict sand ribbons to occur in higher energy settings rather than in large dunes. However, in the study area, sand ribbons occur in an area of coarse, low‐density and easily transportable bioclastic sands and gravels compared with the very large transverse dunes in an offshore area that is composed of denser medium‐grained siliciclastic sands. It suggests that the availability of different sediment types is likely to exert an influence on the nature of the bedforms generated. The offshore sand supply is time limited and originates from sea floor erosion of sandstones of former sea‐level lowstands. The trough areas of both sand ribbons and very large transverse dunes comprise coarse calcareous algal gravels that support benthic communities of variable maturity. Diverse mature communities result in sediment stabilization through branching algal growth and binding that is thought to modify the morphology of dunes and sand ribbons. The occurrence and the nature of the bedforms is controlled by their hydrodynamic setting, by grain composition that reflects the geological history of the area and by the carbonate‐producing benthic marine communities that inhabit the trough areas.
Silica diagenesis in Eocene shallow‐water platform carbonates, southern Pyrenees
Authors: Giménez‐Montsant Jordi , Calvet Francesc , Tucker Maurice E.
Published: March 2003

Spectacularly developed lower Eocene chert in the Corones platform carbonates of the Spanish Pyrenees is concentrated within a restricted, brackish‐water, laminated ostracod‐rich facies, which also contains abundant sponge spicules. The chert occurs as nodular, bedded and mottled varieties, and four petrographic types of quartz are developed: microquartz; length‐fast (LF) chalcedony; megaquartz; and microspheres. δ18O values of chert range from 29·6‰ to 30·9‰ (SMOW), which correspond to a broad isotope rank common for biogenic and diagenetic replacement cherts. Calcian dolomite crystals with high Fe and Na are disseminated within the microquartz and LF‐chalcedony, but are absent from the megaquartz and host carbonate. The chert is closely associated with desiccation cracks and with interstratal dewatering structures. Load casts are silicified, and laminae rich in sponge spicules are convoluted. Early cracks related to dewatering are filled by microquartz and quartz cements. Ostracod shells within chert are locally fractured; those in the host carbonate are commonly flattened. Late fractures are filled by LF‐chalcedony and megaquartz. There is much evidence for the dissolution of sponge spicules and their calcitization in the carbonate host rock. Silica for the Corones cherts was derived from sponges during early diagenesis and shallow burial. Early mechanical compaction and sediment dewatering played a major role in sponge spicule dissolution, migration of silica‐rich fluids and the consequent precipitation of chert. Quartz cements continued to be precipitated into the burial environment.
Development of a prograding carbonate wedge during sea level fall: Lower Pleistocene of Rhodes, Greece
Authors: Hansen Kim Sten
Published: March 2003

A Lower Pleistocene carbonate platform is described from north‐east Rhodes, Greece. It comprises a succession of warm temperate calcarenites (the Cape Arkhangelos calcarenite facies group) developed in a steep‐sided coastal basin. The depositional setting for the sediments is a carbonate wedge developed within a larger‐scale forced regression. Deposition began with aggradation of storm‐dominated lower and upper shoreface deposits. Later, the development of a prograding platform produced giant clinoform foresets. A marked alternation of cross‐bedded and bioturbated clinoforms indicates seasonal transport of carbonate material off the platform. Periodically, the platform edge has been deeply scoured by exceptional storms, after which further deposition repaired the platform margin, and progradation resumed. More than 20 such major storm cycles are preserved. Applying sequence stratigraphy to this succession leads to two different possible interpretations: one with a lowstand systems tract and one with a forced regressive systems tract, depending on the scale of view. The implications of this are discussed. The present example shows clearly that the application of sequence stratigraphic models to real carbonate sequences requires careful consideration of scale and context before interpretations are made.
Origin of spheroidal chert nodules, Drunka Formation (Lower Eocene), Egypt
Authors: McBride  , Abdel‐Wahab Antar , El‐Younsy Ahmed Reda M.
Published: March 2003

Chert nodules of the Drunka Formation (Lower Eocene) are mostly spherical, have diameters from 40 to 120 cm, are quasi‐uniformly spaced 2–3 m apart in the plane of bedding, have concentric internal structure and, except for rare small (<6 cm) solid chert nodules, are less than 85% chertified. Nodules formed after moderate alteration of limestone by meteoric water (δ18Ocalcite = –4 to –8‰) at shallow (<100 m) burial depths; more extensive alteration of limestone (δ18O = –10 to –16‰) by meteoric water followed nodule growth. Chertification was by low‐temperature meteoric water (δ18Oquartz = +18‰ in margins to +22‰ in nuclei) at shallow burial depths. Meteoric water may have invaded the Drunka Formation in association with shelf progradation during the Early Eocene, or during the development of a Middle Eocene unconformity. Replacement of carbonate mud by microcrystalline quartz was the dominant chertification process, but fossils were replaced in part by fine‐grained equant megaquartz, quartzine and chalcedony; the last of these occurs in places as beekite. Opal A‐secreting marine organisms are the inferred source of silica, but none are preserved. There is no compelling evidence of an opal‐CT precursor, so quartz may have formed by direct precipitation. Self‐organization processes of enigmatic character established the spacing pattern of the nodules and also the Liesegang‐banded internal structure of the chert nodules. Nodules grew chiefly by diffusive supply of silica, although one locality has elongate nodules that grew when there was some porewater advection. Chertification patterns and δ18O values of both calcite and quartz indicate that nodule growth was complex and variable. Some nodules probably grew from the centre outwards. Many nodules, however, initially grew simultaneously across the entire nodule, but late‐stage growth was predominantly at the outer margins or at selective internal sites.
Detached mud prism origin of highstand systems tracts from mid‐Pleistocene sequences, Wanganui Basin, New Zealand
Authors: Abbott Stephen T.
Published: March 2003

Marine siltstone successions, 1–20 m thick, form the upper part of sequences in the mid‐Pleistocene Castlecliff section (≈ 0·98–0·35 Ma). The siltstones were deposited within a broad shelf embayment at and about glacioeustatic highstands and are interpreted as highstand systems tracts (HST). Shell‐rich to relatively shell‐poor contacts at the base of Castlecliff HST are interpreted as downlap surfaces, which mark the quenching of transgressive in situ biogenic accumulation (backlap shellbed). Nonetheless, the basal parts of Castlecliff HST successions are enriched in fossil content in the context of the highstand successions as a whole and represent downlap shellbeds. Castlecliff HST are truncated above by sequence‐bounding ravinement surfaces, such that complete sandier‐upward successions and subaerial exposure surfaces associated with sequence boundaries sensu stricto are never preserved. Modern highstand sedimentation in the Taranaki Bight offshore from Castlecliff is characterized by a mid‐shelf mud depocentre and a coastal shore‐connected sand prism, both of which are encroaching upon intervening shell‐rich relict and palimpsest transgressive deposits. The mud depocentre is up to 9 m thick, and deposition is influenced by a gyre caused by bathymetric steering of storm‐driven currents along the embayed coastline. Modern highstand deposition in the Taranaki Bight, in which the mud depocentre is in part detached from the contemporary shore‐connected sand prism, is regarded as an analogue for the deposition of the preserved lower parts of Castlecliff HST. The inferred architecture of Castlecliff HST therefore need not refer to the shore‐connected, progradational geometry predicted by traditional sequence models. The model proposed herein may have application to other shelf palaeo‐embayments in which mid‐shelf focusing of fine‐grained sediment has resulted from coastal steering of currents.
Tsunami‐induced large‐scale scour‐and‐fill structures in Late Albian to Cenomanian deposits of the Grajaú Basin, northern Brazil
Authors: Rossetti Dilce De FÁtima , GÓes Ana Maria , Truckenbrodt Werner , Anaisse JosÉ
Published: March 2003

Late Albian to Cenomanian upper shoreface deposits from the Grajaú Basin, northern Brazil, consist of well‐sorted, very fine‐ to fine‐grained sandstones with swaley, trough, tabular and minor hummocky cross‐stratification. A striking feature of these deposits is the abundance of large‐scale scour‐and‐fill structures, which consist of regularly spaced, repetitive, very shallow swales with either symmetrical or asymmetrical profiles, arranged along an undulose surface or as a succession of superimposed troughs. The sediment filling these scours is characterized by very fine‐grained sandstone with gently undulose, near‐parallel lamination to very low‐angle dipping cross‐stratification intergraded with swaley and hummocky cross‐stratification. The nature of the scours and the sedimentary structures of their fills reveal the action of combined flows, which are hydrodynamically similar to those developed during storms. However, it is speculated that the combined flows responsible for the genesis of these structures were formed by tsunami waves enhanced by tsunami‐induced ebb currents and/or tidal currents. This interpretation is proposed on the basis of several lines of reasoning: (1) palaeogeographic reconstructions of the study area during the late Cretaceous show that it was outside the belt favourable for the development of storms; (2) comparison of the scour‐and‐fill structures with stratigraphically correlatable deposits exposed north of the study area, where similar features occur in association with abundant seismically induced, soft‐sediment deformation structures; and (3) the presence of several styles of soft‐sediment deformation features (i.e. convolute lamination, bed collapse, large‐scale folds, massive bedding, sand‐filled fractures and diastasis cracks) are suggestive of synsedimentary seismic activity in Cretaceous deposits located in and near to the study area. This study proposes that episodic, high‐amplitude tsunami waves, enhanced by tsunami‐induced ebb currents, develop powerful flows capable of producing complex patterns of erosion and sedimentation, which may be represented by scour‐and‐fill structures similar to those described here.
Sedimentology of a Devonian fault‐bounded braidplain and lacustrine fill in the lower part of the Skrinkle Sandstones, Dyfed, Wales
Authors: Marshall John D.
Published: March 2003

The Upper Devonian to Lower Carboniferous Skrinkle Sandstones of the Pembroke Peninsula are predominantly continental deposits from the post‐Caledonian synrift succession at the southern margin of the Upper Palaeozoic Welsh Landmass. The lower part of the Sandstones record deposition in the 30 × 10 km Tenby–Angle fault block, from which a 6‐ to 68‐m‐thick interval is described and interpreted as a lacustrine deposit succeeded by a high‐energy sandy braidplain succession. The lacustrine deposit is dominated by red mudstones and ripple cross‐laminated sandstones. Interbedded quartzose sandstones form a coarsening‐upward sequence from the red mudstones in the basin centre, suggesting a deltaic origin, and a smooth‐fronted braidplain delta model is proposed. The sequence introduces the braidplain succession, composed of groups of horizontal/low‐angle laminated and trough cross‐bedded sandstones. These are compared with recent ephemeral stream and sheetflood sediments and their characteristics used to depict a system of mutually erosive sheetflood and channel bodies, the latter produced during the rising and falling stages of flood events, which alternate to produce a thick multistorey sandstone. Palaeocurrent data indicate an axial drainage system from the north‐west, running parallel to the main faults of the area. This is supported by the maturity and sandy nature of the sediments. Basin closure towards the south and the postulated Bristol Channel Landmass is inferred.
Growth of rigid high‐relief patch reefs, Mid‐Silurian, Gotland, Sweden
Authors: Watts Nigel R. , Riding Robert
Published: March 2003

Patch reefs up to 35 m thick and generally 100–150 m wide, separated by bedded inter‐reef sediment, dominate the Högklint Formation (Lower Wenlock) of north‐west Gotland. The spacing between adjacent patch reefs is variable, but is commonly 150–350 m. The Högklint is a shallowing sequence, and the patch reefs exhibit a well‐developed vertical succession: (1) Axelsro‐type patch reefs developed in the underlying Visby Formation; (2) halysitid tabulates capped by laminar stromatoporoids; (3) domical and bulbous stromatoporoids and red algae; (4) cyanobacterial–algal reef crest. The patch reefs expand upwards from an initial bioherm phase with a small base to a laterally extensive biostrome phase. This gives them a thumb‐tack appearance. In stage 2 of the bioherm phase, rigid framework development and high reef relief resulted in breakage of angular blocks up to 15 m long, which were incorporated into the reefs or fell into adjacent sediments. Poorly sorted talus haloes (Millingsklint Member) also developed adjacent to stage 2 of the bioherm phase. These include angular blocks and exhibit depositional slopes up to 40° away from the reefs. Stage 3 biostrome development was mainly non‐rigid cluster reef, which shed skeletal debris (Domkyrka Member) but few lithified blocks. Stage 4 biostrome development was a reef crest with open to closed frame structure. Storm breakage and overturning produced large blocks with complex cavity fill sequences including double geopetals. Relief during the bioherm phase, indicated by fallen blocks and talus slopes, was up to at least 15 m; during the biostrome phase, it was up to 10 m.
Septarian concretions from the Oxford Clay (Jurassic, England, UK): involvement of original marine and multiple external pore fluids
Authors: Hudson J. D. , Coleman M. L. , Barreiro B. A. , Hollingworth N. T. J.
Published: March 2003

Septarian concretions occur at several horizons within the Oxford Clay Formation, a marine mudstone containing pristine aragonite and immature biomarker molecules. They record the passage of at least four generations of pore fluids, the first of marine origin and the last still present in cavities. Concretion bodies formed, cracked, and calcite and pyrite precipitated in and around the cracks within the sulphate reduction zone, as demonstrated by C, O, S and Sr isotopic composition (Pore fluid 1). Before major compaction, sandstone dykes were intruded locally, and baryte precipitated, followed by coarse calcite cements with isotopically light oxygen and radiogenic strontium, indicating the introduction of meteoric‐derived water (Pore fluid 2). Later, coarse celestine within concretions has distinct sulphur‐isotopic composition and requires a further, geographically restricted, water source (Pore fluid 3). Celestine‐bearing concretions contain water in tight cavities whose isotopic composition is close to that of modern precipitation. Its chemistry shows that it is equilibrating with pre‐existing minerals implying a relatively recent origin (Pore fluid 4). The mineralogy of the Oxford Clay concretions shows that complex results can follow from a simple burial and uplift history, and that multiple generations of pore fluids can pass through a low‐permeability clay.
Holocene sediment properties of the East Greenland and Iceland continental shelves bordering Denmark Strait (64–68°N), North Atlantic
Authors: Andrews John T. , Kihl R. , Kristjansdottir Greta B. , Smith L. M. , Helgadottir Gudrun , Geirsdottir Aslaug , Jennings Anne E.
Published: March 2003

The oceanographic Polar Front separates the East Greenland and Iceland margins. Surface water temperatures across Denmark Strait vary by 8–12 °C and represent one of the steepest oceanographic gradients on earth. The East Greenland margin is a polar environment, with extensive sea‐ice cover and calving glacier margins; in contrast, the Iceland shelf is much more temperate, and freshwater run‐off is a key component in land–ocean sediment transfers. Average sediment properties from these two contrasting climate and oceanographic continental shelf environments are compared in the spatial domain at 13 sites; the data represent the last 10 000 radiocarbon years of `normal' marine sedimentation for the two regions. The two regions have similar average rates of sediment accumulation (around 43·5 cm kyr−1), so that this key variable is factored out in explaining any differences in sediment properties. Dry sediment density, moisture content, hygroscopic moisture, total organic carbon and carbonate contents, mass magnetic susceptibility and the percentages of sand and silt are compared focusing on: (1) median values for sediment properties; and (2) downcore variability, measured by the coefficient of variation (CV). There are significant differences in all but one (hygroscopic moisture) of the sediment properties between Iceland and East Greenland; in four cases, the sense of the differences was not as predicted. In terms of downcore variation (CV), no difference was found between the two regions, nor between the 13 sites, whereas there are some significant differences between the variables. Carbonate and mass magnetic susceptibility have the largest spreads, and moisture content and dry sediment density are the least variable. Protocols are developed to identify the `type core' in a regional series of sites. The results indicate a need to develop a regional perspective on sediment properties, both as inputs to models of sedimentary processes in different polar/arctic environments, and as an indication of which sediment properties might be best suited for palaeoenvironmental downcore time series.
Estimating the windward slope profile of a barchan dune
Authors: Momiji Hiroshi , Bishop Steven R.
Published: March 2003

A new theoretical scheme is presented to model the shape of a sand dune at equilibrium that does not require iterative calculations of the interaction between the wind flow and topography. The model is constructed by incorporating theory based on aerodynamics into a grain‐scale model that estimates the shear velocity at the dune crest through the calculation of the sand trapping efficiency of the slipface in the lee of the dune. Published field data, collected in southern Peru, California and southern Morocco, show that as a dune becomes higher the windward slope becomes steeper. For the model proposed, the wind flow over a dune was first assumed to be similar to that over a Gaussian hill. By further assuming a fixed shear velocity on the level surface, the windward slope angle and migration speed of dunes in southern Peru can be explained. To comply with all available data, some aspects are still open to further investigation. However the theoretical insight presented herein implies that the upper limit of dune height may be greater in windier environments.
Origin and morphosedimentary evolution of fine‐grained modern continental shelf deposits: the Gironde mud fields (Bay of Biscay, France)
Authors: Lesueur P. , Tastet J. P. , Weber O.
Published: March 2003

Abstract The Gironde mud fields are thin blankets (< 4 m) that extend from the inner to mid‐shelf over a restricted area (600 km2) and overlie palimpsest sands and gravels seaward of the modern Gironde estuary, south‐western France. The bulk of the mud has accumulated over the last two millennia and reflects the complex interactions of: (1) an increasing estuarine supply of suspended particulate matter; (2) resuspension of substrate material by storm events; and (3) biological mixing. The combination of these processes has produced various features within the deposits, related to: (1) the water depth and distance from source of the fine‐grained material, which are manifested as a proximal–distal cross‐shelf trend, from an area of alternating mud sedimentation (temporary after large river flows) with resuspension by storm events to an area of mud accumulation in deeper water where bioturbation predominates; (2) expansions of the mud depocentres over time, such that they become more remote from sources of coarser shelf sediment, resulting in an upward‐fining trend. The lithofacies of the Gironde shelf mud fields exhibit a number of similarities to those of larger scale modern muddy shelves and ancient shallow‐water mudrocks; this work provides a detailed description of a facies model for fine‐grained shelf sediments deposited under relatively constant sea level.