bluuebunny/crossref_metadata_2025 huggingface dataset:
Modulation of CD8 and CD3 by HIV or HIV Antigens
Authors: Jason J. , Inge K. L.
Published: March 2003

To investigate whether human immunodeficiency virus (HIV)‐1 and HIV‐1 antigens modulate surface and cytoplasmic CD8 or CD3, as well as CD4, we used cell permeabilization reagents, surface/cytoplasmic fluorescent staining, multiparameter flow cytometric techniques and an in vitro culture system in which relatively few lymphocytes are actively infected with HIV. Human peripheral blood lymphocytes were: not stimulated, not stimulated but HIV‐inoculated, phytohaemagglutinin (PHA)‐stimulated, PHA/HIV‐inoculated (PHA/HIV), or placed into media with soluble gp120, Rev or Nef. HIV inoculation and Nef had striking modulatory effects on CD8. The cytoplasmic CD8 median fluorescent intensity (MFI) of positive lymphocytes was lower for cells in unstimulated/HIV‐infected cultures than unstimulated cultures (44 versus 62% of ex vivo value, P = 0.032) and lower for cells in PHA/HIV cultures than in PHA cultures (56 versus 100% of ex vivo, P = 0.041). The surface CD8 MFI values for Nef were significantly lower than the ex vivo value (75% of ex vivo, P = 0.006). At days 2–7 of culture, Rev was associated with slight reductions in surface CD4 MFI (58% of ex vivo versus 78% of ex vivo for unstimulated cultures, P = 0.047) and greater effects on cytoplasmic CD3 MFI (131 versus 179% of ex vivo for unstimulated cultures, P = 0.035), and surface CD8 MFI (70% of ex vivo, P = 0.006 versus ex vivo value). The globality of Rev's effects suggests these are related to a shared processing pathway, i.e. not due to direct interaction with CD3, CD4 and CD8; the effects of HIV inoculation and Nef on CD8 expression appear to be more CD8 specific. Because CD8 is essential for cytotoxic T‐cell function, its down‐modulation could inhibit this activity, including anti‐HIV cytotoxicity. Given the critical roles of CD3 and CD8 in T‐lymphocyte signal transduction and antigen responsiveness, the effects of HIV, Rev and Nef on these molecules have clinically significant implications concerning the pathogenesis and treatment of HIV.
Cytokine Levels in Midtrimester Amniotic Fluid in Normal Pregnancy and in the Prediction of Pre‐eclampsia
Authors: Heikkinen J. , Möttönen M. , Pulkki K. , Lassila O. , Alanen A.
Published: March 2003

Midtrimester amniotic fluid cytokines may reflect the function of the maternal immune system in the maternal–fetal interface and thus be predictive of pre‐eclampsia. We determined the concentrations of interleukin (IL)‐6, IL‐8, IL‐10, IL‐11, IL‐12, IL‐15, tumour necrosis factor (TNF)‐α and transforming growth factor (TGF)‐β in amniotic fluid at 14–16 weeks of gestation from women with normal pregnancies and from those who subsequently developed severe pre‐eclampsia. The concentrations of the cytokines in amniotic fluid did not significantly differ between patients and normal controls. The median concentration of IL‐6 was 950 pg/ml in normal pregnant women and 578 pg/ml in the patient group. The median concentration of IL‐8 was 606 pg/ml in normal controls and 294 pg/ml in the patient group. The levels of IL‐6, IL‐8 and TGF‐β correlated positively with each other. TNF‐α concentrations were low and similar in both groups. IL‐10 and IL‐12 were detected at very low levels in 37 and 7% of the samples, respectively. No difference was found in IL‐15 concentrations between the groups. IL‐11 was found only at low levels in both groups. Although none of the cytokines measured was predictive of pre‐eclampsia, this study provides information of cytokines in amniotic fluid during the period when the spiral arteries are remodelled.
Non‐Th2 Regulatory T‐Cell Control of Th1 Autoimmunity
Authors: Bach J.‐F.
Published: March 2003

The Th1/Th2 concept brought an attractive explanation of the active self tolerance which appears to control the onset of pathogenic autoimmunity. New data coming from various independent horizons indicate that self immunoregulation could also depend to a large extent on non‐Th2 cells. Original data derived from the day‐3‐thymectomy model, selective T‐cell lymphocytopenia and nonobese diabetic mice are discussed in an effort to analyze similarities and differences in phenotype (CD25, CD62L and CD45RB) and cytokine pattern (notably interleukin (IL)‐4, IL‐10 and transforming growth factor (TGF)β) of regulatory cells involved in these models. The relationship of these cells with Th3, Tr1 and natural killer (NK) T cells are also discussed. The hypothesis is proposed that CD25 CD62L T cells mediate the physiologic regulation of self regulation whereas Th2 and Th3 cells are essentially induced following sensitization against autoantigens.
Maturation of Thyroidal Dendritic Cells in Graves' Disease
Authors: Quadbeck B. , Eckstein A. K. , Tews S. , Walz M. , Hoermann R. , Mann K. , Gieseler R.
Published: March 2003

Because thyroidal dendritic cells (t‐DC) may be implicated in the pathogenesis of Graves' disease (GD), we compared t‐DC in thyroid sections of patients with GD (n = 15) and control patients with toxic (TG; n = 12) or non‐toxic goitre (NG; n = 12). Goitres in GD, but not TG or NG, were populated with three discernible t‐DC phenotypes. (i) Immature t‐DC (major histocompatibility complex (MHC) II+/CD40–/CD80–) were located perifollicularly (95% of the patients with GD, but only 55% of TG and 51% of NG patients); numbers of such t‐DC were significantly elevated in GD (P < 0.001). (ii) Partially matured CD80+ t‐DC were present in connective tissue (73% of the patients) and focal interstitial clusters (40% of the patients). In 53% of the patients with GD, single as well as clustered interstitial t‐DC expressed CD40. (iii) However, phenotypically mature t‐DC (MHC II+/CD40+/CD80+/RFD1+) were only present in clusters and colocalized with activated CD4+/MHC class II+ T‐helper (Th) cells. Expression of CD54 and CD83 did not significantly differ among the groups. The phenotype of intrathyroidal DC in GD thus supports their role as potential (co)stimulators of thyroid autoimmunity.
A T‐Cell Functional Phenotype Common among Autoimmune‐Prone Rodent Strains
Authors: Lang J. , Bellgrau D.
Published: March 2003

The genetic basis and familial clustering of autoimmunity suggest that common phenotypic traits predispose individuals to disease. We found a hyporesponsive T‐cell phenotype that was shared by all autoimmune‐prone mouse and rat strains tested, including MRL, nonobese diabetic (NOD), NZB, NZW, NZB/W F1, SJL and SWR mice, as well as DA and BB rats, but was not evident in nonautoimmune‐prone rodents. This T‐cell intrinsic, age‐independent hyporesponsiveness is measured as an increased activation threshold for upregulation of activation markers upon T‐cell receptor (TCR) cross‐linking both in vitro and in vivo. Inefficient deletion of CD4 and CD8 single‐positive, heat stable antigen (HSA)hi medullary thymocytes was also observed in hyporesponsive donors. We interpret these data to suggest that increased TCR‐mediated signalling thresholds in autoimmune‐prone individuals may contribute to the escape of autoreactive thymocytes from negative selection.
Serum Amyloid P Component Does Not Circulate in Complex with C4‐Binding Protein, Fibronectin or Any Other Major Protein Ligand
Authors: Sen J. W. , Heegaard N. H. H.
Published: March 2003

Serum amyloid P component (SAP) is a pentameric plasma protein associated with all known kinds of amyloid. The normal physiological function of the protein has not been fully elucidated but it may be involved in clearance of cellular debris and in innate immunity. An important clue to its normal function is the identity of ligands bound to SAP in the circulation. It has been reported that all SAP is complexed with C4‐binding protein (C4bp) but other studies have not been able to confirm this. We here study this issue by a combination of crossed immunoelectrophoresis (CIE), size exclusion chromatography, and native polyacrylamide electrophoresis and we show that SAP in serum – analysed under native analysis conditions and free of immobilizing antibodies – does not have any major protein ligand. However, when the protein is aggregated by immobilized antibodies, C4bp and fibronectin clearly bind to SAP. If circulating SAP under normal circumstances bind any protein ligand in vivo, our results strongly suggest that this only occurs to a minor extent.
The Cellular Response Associated with Cervical Intraepithelial Neoplasia in HIV+ and HIV– Subjects
Authors: Ahmed S. M. , Al‐Doujaily H. , Reid W. M. N. , Johnson M. A. , Poulter L. W.
Published: March 2003

This study investigates local alterations in T‐cell and macrophage subsets that occur in cervical epithelial neoplasia (CIN), in the presence and absence of human immunodeficiency virus (HIV) infection. Ectocervical biopsies from 10 women with CIN who were infected with HIV, and 10 women with CIN but no HIV infection were studied by immunocytochemistry.

Significantly increased proportions of activated CD8+ T cells were seen in all CIN biopsies, and these proportions were further increased in the presence of HIV infection. Levels of CD8+TIA‐1+ cells were particularly increased in the CIN+HIV+ group. There was a lack of expression of CD28 on the CD8+ cells of the epithelium of CIN+HIV+ samples. A significant reduction in the proportion of epithelial inductive D1+ macrophages and an increase in D1+D7+‐suppressive cells were observed in the CIN+HIV+ cohort.

The lack of expression of CD28 on the CD8+ cells of the epithelium of CIN+HIV+ samples in combination with the reduced CD4+ T‐cell numbers seen in the presence of HIV infection may contribute to the development of higher grade CIN in this susceptible group. This may be aggravated by the reduction in the D1+ epithelial inductive macrophages, which might reflect recruitment of more suppressive D1+D7+ cells. This would further compromise the ability of the local T‐cell system to respond to antigens and thus contribute to the development of neoplasia at this site. These results suggest that the increase in activated CD8+ T cells is a consequence rather than a cause of CIN.
An Established Immune Response against Ovalbumin is Suppressed by a Transferable Serum Factor Produced after Ovalbumin Feeding: A Role of CD25+ Regulatory Cells
Authors: Karlsson M. R. , Kahu H. , Hanson L. Å. , Telemo E. , Dahlgren U. I.
Published: March 2003

We have previously demonstrated that rats fed ovalbumin (OVA) develop a tolerogenic activity in serum, which upon transfer induces tolerance to OVA and suppression of the immune response to a bystander antigen. Here, we have extended these studies and analysed if the tolerogenic activity in serum could suppress an established immune response in the recipients. Rats were immunized with OVA, 4 and 1 week prior to the transfer of serum from either OVA‐fed or control animals.

Rats that received serum from OVA‐fed donors had significantly lower delayed‐type hypersensitivity (DTH) reaction against OVA 1 week after the serum transfer compared with the controls, and the levels of immunoglobulin (IgG) anti‐OVA antibodies were significantly lower 2 and 4 weeks after serum transfer. Monomeric OVA in amounts corresponding to the OVA transferred with serum did not induce the reduction of DTH response or IgG anti‐OVA antibody levels. In vitro, the proliferation of OVA‐stimulated spleen cells, taken from recipients of tolerogenic serum, was significantly lower compared with spleen cells from the controls. The in vitro suppression seemed to be mediated by a population of CD25+ cells, because the removal of such cells from OVA‐stimulated spleen cell suspensions resulted in increased proliferation in cultures from rats receiving tolerogenic serum. Our results showed that the tolerogenic serum factor can suppress an established immune response in recipient animals, possibly through induction of regulatory CD25+ cells. Whether this capacity might be used to influence chronic inflammatory conditions needs to be investigated.
Bioclastic sediment lobes on a supply dominated Upper Cretaceous carbonate platform margin, Montagna della Maiella, Italy
Authors: VECSEI ADAM
Published: March 2003

A thick bioclastic sediment wedge was deposited on the slope of the Maiella carbonate platform margin in the Late Campanian to Late Maastrichtian. The wedge consists of lobate depositional units (laterally and vertically convex structures). The complex internal geometries of the lobes combine characteristics of unidirectional sandwaves and the alternating point‐sources of deltas. Excellent outcrop permits a detailed documentation and discussion of the depositional processes.

The sediment wedge constitutes a supersequence, which prograded along the platform margin as a result of high sediment supply and forced regression. Within the supersequence, a hierarchy of higher‐order stratigraphic units (sequence sets and sequences) are developed. The individual bioclastic sediment lobes are interpreted as systems tracts and parasequences of the sequences within the sequence sets.
Provenance of the Palaeocene‐Eocene clastic rocks of the Komandorsky Islands
Authors: Rostovtseva  , Shapiro
Published: March 2003

The Palaeocene–Eocene sequence on the Komandorsky Islands is represented by sediments and minor volcanics with a total thickness of more than 3000 m. Sandstone, siltstone, mudstone, siliceous rocks and conglomerate, which have accumulated in the upper and middle parts of a deep‐water fan, prevail. All the debris was delivered from the north‐east, from the side of the contemporary Komandorsky basin in the Bering Sea. Products of volcanic denudation and fresh tephra dominate its composition. However, at some levels the sandstone contains fragments of jasper, quartzite, slate, schist, gabbro and granite as well as non‐volcanic quartz along with a volcanic component. The heavy minerals fraction of the sandstone contains considerable quantities of apatite, zircon, garnet and chromite, as well as pyroxenes, amphiboles and magnetite. The chemical composition of the garnet is specific to metamorphic rocks. A significant admixture of chromite is indicative of denudation from an ophiolite complex. The folded and partly metamorphosed pre‐Palaeogenic rocks were a source of these fragments. Their most likely source terrane was the Shirshov‐Bowers chain (Cretaceous palaeoarc). The Komandorsky block originally was the forearc part of the Aleutian arc where the latter was superimposed on the Shirshov‐Bauers chain. A subsequent north‐west displacement of forearc structures, in response to the transform fault at the boundary between the Pacific and North American plates, could have resulted in the separation of the Komandorsky block from its Early Palaeogene debris source area.
Carbon‐isotope stratigraphy in shallow‐water carbonates: implications for Cretaceous black‐shale deposition
Authors: GRÖTSCH JÜRGEN , BILLING IAN , VAHRENKAMP VOLKER
Published: March 2003

A Barremian to Albian succession on Mount Kanala, part of a Tethyan isolated carbonate platform, was investigated for its δ13C variations. The limestone sequence is composed of a series of peritidal shallowing‐upward cycles with clear petrographic evidence for strong early diagenetic overprinting related to repeated subaerial exposure. Despite significant impact of diagenesis, the observed changes in δ13C can be very well correlated with deep‐water sections from different ocean basins and shallow water carbonate platforms in the Middle East. This lends further support to the applicability of δ13C variations for stratigraphic purposes in shallow‐water limestones. Using the δ13C signal, time resolution in Lower Cretaceous platform carbonates can be significantly increased, independent of bio‐zonations often hampered by ecological variability.

Cyclostratigraphic analysis of the Aptian part of the section shows that strong positive excursions of the cumulative departure from mean cycle thickness of the peritidal shallowing‐upward cycles coincide with global positive δ13C excursions. This, and the fact that positive shifts in the δ13C record are preserved within shallow water limestones, provide evidence that black‐shale accumulation in the ocean basins occurred during sea‐level rise and flooding of platform tops. Integration of carbon‐isotope‐, cyclo‐ and sequence‐stratigraphic results from different carbonate platforms indicate that strong positive global δ13C shifts and concurrent organic‐carbon burial during black‐shale deposition are ultimately caused by rapid rises of eustatic sea level. Hence, the rate of change of eustatic sea level is considered to play a crucial role in black‐shale accumulation in the global ocean basins during the Cretaceous.
An allostratigraphic approach to a non‐marine basin: the north‐western part of Cretaceous Kyongsang Basin, SE Korea
Authors: RHEE  , JO  , CHOUGH
Published: March 2003

The north‐western part of the Cretaceous Kyongsang Basin, south‐east Korea, comprises alluvial deposits of conglomerate, gravelly sandstone, sandstone and mudstone which can be grouped into four allomembers bounded by stratigraphic discontinuities. The discontinuities trend NW–SE and are marked by distinct facies transitions, abrupt emplacement of conglomerate and thin but persistent mudstone beds. Sedimentary facies and architectural analyses reveal that each allomember formed a depositional system of fluvial channel networks draining toward the south‐east with alluvial fans on the northern margin. Each allomember can be characterized by distinctive architecture of channel‐fills, clast composition of conglomerate and sandstone/mudstone ratio. Successive units show an eastward shift in the locus of deposition, suggesting basinward relocations of alluvial systems. Such variations with time and space are interpreted to reflect changes in accommodation space and sediment supply during basin evolution, probably caused by fault movements. This study shows that detailed mapping, combined with architectural analysis, and the establishment of alluvial allostratigraphy can help assess changes in alluvial systems and structural development of the basin.
Petrography and geochemistry of early‐stage, fine‐ and medium‐crystalline dolomites in the Middle Devonian Presqu’ile Barrier at Pine Point, Canada
Authors: Qing HAIRUO
Published: March 2003

The petrography and geochemistry of fine‐ and medium‐crystalline dolomites of the Middle Devonian Presqu’ile barrier at Pine Point (Western Canada Sedimentary Basin) are different from those of previously published coarse‐crystalline and saddle dolomites that are associated with late‐stage hydrothermal fluids. Fine‐crystalline dolomite consists of subhedral to euhedral crystals, ranging from 5 to 25 μm (mean 8 μm). The dolomite interbedded with evaporitic anhydrites that occur in the back‐barrier facies in the Elk Point Basin. Fine‐crystalline dolomite has δ18Ο values between −1·6 to –3·8‰ PDB and 87Sr/86Sr ratios from 0·7079–0·7081, consistent with derivation from Middle Devonian seawater. Its Sr concentrations (55–225 p.p.m., mean 105 p.p.m.) follow a similar trend to modern Little Bahama seawater dolomites. Its rare earth element (REE) patterns are similar to those of the limestone precursors. These data suggest that this fine‐crystalline dolomite formed from Middle Devonian seawater at or just below the sea floor.

Medium‐crystalline dolomite in the Presqu’ile barrier is composed of anhedral to subhedral crystals (150–250 μm, mean 200 μm), some of which have clear rims toward the pore centres. This dolomite occurs mostly in the southern lower part of the barrier. Medium‐crystalline dolomite has δ18O values between −3·7 to −9·4‰ PDB (mean −5·9‰ PDB) and 87Sr/86Sr ratios from 0·7081–0·7087 (mean 0·7084); Sr concentrations from 30 to 79 p.p.m. (mean 50 p.p.m.) and Mn content from 50 to 253 p.p.m. (mean 161 p.p.m.); and negative Ce anomalies compared with those of marine limestones. The medium‐crystalline dolomite may have formed either (1) during shallow burial at slightly elevated temperatures (35–40 °C) from fluids derived from burial compaction, or, more likely (2) soon after deposition of the precursor sediments by Middle Devonian seawater derived from the Elk Point Basin.

These results indicate that dolomitization in the Middle Devonian Presqu’ile barrier occurred in at least two stages during evolution of the Western Canada Sedimentary Basin. The geochemistry of earlier formed dolomites may have been modified if the earlier formed dolomites were porous and permeable and water/rock ratios were large during neomorphism.
Miocene Gypcretes from the Calama Basin, northern Chile
Authors: Hartley Adrian J. , May Geoffrey
Published: March 2003

Gypcretes of Miocene age are preserved beneath a 9·53 ± 0·36 Ma ignimbrite along the eastern margin of the Oligo‐Pleistocene Calama Basin, northern Chile. They are restricted to a single stratigraphic horizon developed within laterally extensive (>35 km) coalesced alluvial fan deposits, developed along the margin of an endorheic basin. Two types of gypcrete are recognized. Type 1 comprises almost completely gypsum‐cemented sandstones containing alabastrine nodules and columns, sub‐vertical and horizontal veins of fibrous gypsum and ‘v‐shaped’ cracks infilled by clastic material, and are interpreted as surface weathered gypsic crusts. Type 2 gypcretes are composed of massive, reddened poikilitic and mesocrystalline gypsum (up to 80% of the rock) with isolated bedding‐parallel, clast‐rich lenses (200 × 30 cm) and sub‐vertical veins of fibrous gypsum. The massive texture resembles that of well developed B horizons in Quaternary alluvial desert soils. The crystal forms suggest an origin as a subsurface gypsic crust formed by a combination of hydromorphic (poikilitic) and illuvial (mesocrystalline) processes with the fibrous gypsum veins suggestive of periodic surface exposure.

Gypcrete horizons are up to 25 m thick and composed of both gypcrete types. They represent superimposed phases of surface and subsurface gypcrete development. Quaternary gypcretes are developed in arid climatic regimes, but are not considered to develop under hyper‐arid climates. An arid climate is considered to have prevailed in the study area up to 9·5 Ma after which a change to hyper‐aridity favoured gypcrete preservation.
Interaction between aeolian, fluvial and playa environments in the Permian Upper Rotliegend Group, UK southern North Sea
Authors: Sweet
Published: March 2003

The Permian Upper Rotliegend Group in offshore UK Quadrants 42, 43, 47 and 48 comprises a sequence of mixed aeolian/fluvial/playa deposits. These deposits are up to 300 m thick and contain a record of the interaction between desert fluvial systems and adjacent aeolian and playa environments. The relative dominance of water vs. wind transport and deposition in this stratigraphic package was a function of fluctuations in the discharge of ephemeral fluvial systems and changes in water table/playa level driven by a combination of climatic change and syndepositional tectonics. The Rotliegend sedimentary record is punctuated by numerous surfaces recording erosion by wind and water. The origin of these surfaces is mostly climatic, with periods of increased runoff resulting in fluvial incision, especially near active faults. During periods of reduced runoff, wind erosion of fluvial deposits occurred, with fluvially derived sand being reworked into expanding aeolian dune fields. Wind erosion also occurred as a rising water table isolated dunes from their sediment supply, resulting in deflation of dunes down to the water table. These surfaces formed in a basin that was subsiding. Thus, even in a background of overall increasing accommodation space, climatically driven falls in the water table allowed for periods of erosion. The occurrence of significant erosion, especially near syndepositional fault zones, resulted in a sedimentary record that shows pronounced lateral as well as vertical facies variations.
Reef margin collapse, gully formation and filling within the Permian Capitan Reef: Carlsbad Caverns, New Mexico, USA
Authors: Harwood Gill M. , Kendall Alan C.
Published: March 2003

An area of reef margin collapse, gully formation and gully fill sedimentation has been identified and mapped within Left Hand Tunnel, Carlsbad Caverns. It demonstrates that the Capitan Reef did not, at all times, form an unbroken border to the Delaware Basin. Geopetally arranged sediments within cavities from sponge–algal framestones of the reef show that the in situ reef today has a 10° basinwards structural dip. Similar dips in adjacent back‐reef sediments, previously considered depositional, probably also have a structural origin. Reoriented geopetal structures have also allowed the identification of a 200‐m‐wide, 25‐m‐deep gully within the reef, which has been filled by large (some  >15 m), randomly orientated and, in places, overturned blocks and boulders, surrounded by finer reef rubble, breccias and grainstones. Block supply continued throughout gully filling, implying that spalling of reef blocks was a longer term process and was not a by‐product of the formation of the gully. Gully initiation was probably the result of a reef front collapse, with a continued instability of the gully bordering reef facies demonstrated by their incipient brecciation and by faults containing synsedimentary fills. Gully filling probably occurred during reef growth, and younger reef has prograded over the gully fill. Blocks contain truncated former aragonite botryoidal cements, indicating early aragonite growth within the in situ reef. In contrast, former high‐magnesian calcite rind cements post‐date sedimentation within the gully. The morphology of cavern passages is controlled by reef facies variation, with narrower passages cut into the in situ reef and wider passages within the gully fill. Gully fills may also constitute more permeable zones in the subsurface.
Architecture of a tide‐influenced river delta in the Frontier Formation of central Wyoming, USA
Authors: Willis  , Bhattacharya  , Gabel  , White
Published: March 2003

The Frewens sandstone is composed of two elongate tide‐influenced sandstone bodies that are positioned directly above and slightly landward of a more wave‐influenced lobate sandstone. The 20‐km‐long, 3‐km‐wide Frewens sandstone bodies coarsen upwards and fine away from their axes, have gradational bases and margins and have eroded tops abruptly overlain by marine shales. These sandstones are superbly exposed in large cliffs on the banks of the South Fork of the Powder River in central Wyoming, USA. The deposits change upwards from thinly interbedded sandstones and mudstones to metre‐thick heterolithic cross‐strata and, finally, to metres‐thick sandstone‐dominated cross‐strata. There is abundant evidence for tidal modulation of depositional flows; however, palaeocurrents were strongly ebb‐dominated and nearly parallel the trend of sandstone‐body elongation. Detailed mapping of stratal geometry and facies across these exposures shows a complex internal architecture. Large‐scale bedding units within sandstone bodies are defined by alternations in facies, bed thickness and the abundance of shales. Such bedsets are inclined (5°–15°) in walls oriented parallel to palaeoflow and gradually decrease in dip over hundreds of metres as they extend from the sandstone‐dominated deposits higher in a sandstone body to muddier deposits lower in the body. Where viewed perpendicular to palaeoflow, bedsets are 100‐metre‐wide lenses that shingle off the sandstone‐body axis towards its margins. The sandstone bodies are interpreted as sand ridge deposits formed on the shoreface of a tide‐influenced river delta. Metres‐thick cross‐strata in the upper parts of sandstone bodies resemble deposits of bars (sandwaves) formed where tidal currents moved across shallows and the tops of tidal ridges. Heterolithic deposits lower in sandstone bodies record fluctuating currents caused by ebb and flood tides and varying river discharge. Erosion surfaces capping sandstone bodies record tidal ravinement. The tidal ridges were abandoned following transgression and covered with marine mud as waters deepened.
Recognition and implications of Eocene tufas and travertines in the Chadron Formation, White River Group, Badlands of South Dakota
Authors: Evans James E.
Published: March 2003

There are few descriptions of pre‐Quaternary tufa or travertine, yet these deposits have important climatic, hydrological and tectonic implications. In the Badlands of South Dakota, the Late Eocene Chadron Formation contains a variety of tufa (fluvial, lacustrine, paludal and perched springline types), travertine and calcrete (pedogenic and non‐pedogenic types). In fluvial channels, tufas and tufa barrages (oncolites, tufa lithoclast conglomerates and phytoherms) are transitional to travertines (pseudostromatolitic boundstone gravels and small pinnacle resurgences with rimstone edges and pools). Lacustrine tufas formed in small ponds adjacent to other types of tufas and are similar to the ‘low‐energy, bench‐margin facies’ types observed in modern, groundwater‐fed, temperate‐zone hardwater lakes. Paludal tufas are laterally discontinuous sheets of pisoid‐intraclast wackestone that fill palaeotopography. Distal perched springline tufas are mounds of numerous sloping tufa sheets. Concretions and rhizoliths associated with palaeosols are recognized as pedogenic calcretes, whereas non‐pedogenic calcretes are variably cemented, vertically oriented conduits for palaeogroundwater discharge that are located in fault zones. These deposits resulted from palaeogroundwater discharge along faults during the Late Eocene. Coeval unroofing of the Black Hills uplift created a regional groundwater flow system through karsted Palaeozoic limestones exposed in the Black Hills. The Chadron Formation is an avulsion‐dominated, siliciclastic unit, yet important bodies of carbonate accumulated in it as a result of groundwater processes.
Soft‐sediment deformation structures in late Albian to Cenomanian deposits, São Luís Basin, northern Brazil: evidence for palaeoseismicity
Authors: Rossetti Dilce De Fátima
Published: March 2003

Soft‐sediment deformation structures from the Alcântara Formation (late Albian to Cenomanian), São Luís Basin, northern Brazil, consist of (1) contorted structures, which include convolute folds, ball‐and‐pillow structures, concave‐up paths with consolidation lamination, recumbently folded cross‐stratification and irregular convolute stratification that grades into massive beds; (2) intruded structures, which include pillars, dykes, cusps and subsidence lobes; and (3) brittle structures, represented by fractures and faults displaying planes with a delicate, ragged morphology and sharp peaks. These structures result from a complex combination of processes, mostly including reverse density gradients, fluidization and liquefaction. Reverse density gradients, promoted by differential liquefaction associated with different degrees of sediment compaction, led to the genesis of convolute folds. More intense deformation promoted the development of ball‐and‐pillow structures, subsidence lobes and sand rolls, which are attributed to denser, and thus more compacted (less liquefied), portions that sank down into less dense, more liquefied sediments. Irregular convolute stratification that grades into massive beds would have formed at periods of maximum deformation. The subsidence of beds was accompanied by lateral current drag and fluid escape from water‐saturated sands. In addition, the fractures and faults record brittle deformation penecontemporaneous with sediment deposition. All these mechanisms were triggered by a seismic agent, as suggested by a combination of criteria, including (1) the position of the study area at the edge of a major strike‐slip fault zone that was reactivated several times from the Albian to the Holocene; (2) a relative increase in the degree of deformation in sites located closer to the fault zone; (3) continuity of the deformed beds over large distances (several kilometres); (4) restriction of soft‐sediment deformation structures to single stratigraphic intervals bounded by entirely undeformed strata; (5) recurrence through time; and (6) similarities to many other earthquake‐induced deformational structures.
Cyclic sedimentation produced by fluctuations in meltwater discharge, tides and marine productivity in an Alaskan fjord
Authors: Cowan Ellen A. , Seramur Keith C. , Cai Jinkui , Powell Ross D.
Published: March 2003

Glacimarine sediment deposited in the fjord adjacent to Muir Glacier in south‐eastern Alaska consists of rhythmically laminated muds, stratified sandy mud, sand and gravelly mud facies. Cyclicity is recorded by gravelly mud facies deposited during winter by ice‐rafting, black mud laminae formed by spring plankton blooms and variations in tidal rhythmite thickness and texture produced by the interaction of meltwater discharges and tidal currents in the macrotidal fjord. Regular cyclicity in laminae thickness is tested statistically by Fourier transform and can be attributed to a lunar tidal cycle control in the five cores collected up to 6 km from the sediment source. Cores close to the source can have additional laminae as a result of discharge fluctuations, and distal cores may lack full cycles because of variability in the plume path and attenuation with distance. Cyclic variations in sediment texture are recorded in magnetic susceptibility (MS) profiles of the cores. High MS values are produced by turbidite sand beds or by stratified sandy mud deposited by overflow plumes during peak summer meltwater discharge. Low values reflect muddy intervals deposited during periods of low meltwater discharge, such as during autumn and winter. Sediment accumulation rates measured by 210Pb dating range from 82 cm year–1, 2 km from the sediment source at the head of the fjord, to 16 cm year–1, 6 km away. These rates are within the same range as average sediment accumulation rates determined from cyclic seasonal markers within the cores. These data show that, with careful documentation, annual cycles of glacimarine sediment accumulation can be detected within marine cores. Cores collected from the distal portion of the basin were deposited during the transition of Muir Glacier from a tidewater terminus ending in deep water to a terrestrial glacier with an ice‐contact delta deposited in front of the terminus. This transition is recorded by a coarsening‐upward sedimentary sequence formed by turbidite sands originating from the prograding delta above fine‐grained, laminated basin fill deposited by turbid overflow plumes.
Dolomite formation and biogeochemical cycles in the Phanerozoic
Authors: Burns Stephen J. , Mckenzie Judith A. , Vasconcelos Crisogono
Published: March 2003

Based on present knowledge of the purely chemical controls on the kinetics of massive dolomite formation, the abundance and distribution of dolomite throughout the Phanerozoic remains an enigma, sometimes referred to as the ‘dolomite problem'. Comparing dolomite abundance to secular variation in seawater chemistry indicates that some changes in seawater chemistry are more likely to have resulted from extensive dolomitization rather than to have caused it. The recently formulated microbial dolomite model provides the opportunity to view the geological history of dolomite formation from a new perspective. A biogeochemical approach to the ‘dolomite problem' reveals a plausible connection between Phanerozoic geochemical cycles and dolomite formation. In particular, periods of more extensive dolomitization broadly correlate with diverse indicators of decreased oxygen levels in the atmosphere and oceans. Lowered oxygen levels would have fostered a more active community of anaerobic microbes, including sulphate‐reducing bacteria, which in turn could have led to more extensive dolomitization of marine carbonates.
Reconstructing the ancestral (Plio‐Pleistocene) Rio Grande in its active tectonic setting, southern Rio Grande rift, New Mexico, USA
Authors: Perez‐Arlucea Marta , Mack Greg , Leeder Mike
Published: March 2003

Deposits of the ancestral Rio Grande (aRG) belonging to the Camp Rice Formation are preserved and exposed in the uplifted southern portion of the Robledo Mountains horst of the southern Rio Grande rift. The sediments are dated palaeomagnetically to the Gauss chron (upper Pliocene). The lower part of the succession lies in a newly discovered palaeocanyon cut into underlying Eocene rocks whose margins are progressively onlapped by the upper part. Detailed sedimentological studies reveal the presence of numerous river channel and floodplain lithofacies, indicative of varied deposition in channel bar complexes of low‐sinuosity, pebbly sandbed channels that traversed generally dryland floodplains and shifted in and out of the study area five times over the 1 Myr or so recorded by the succession. Notable discoveries in the deposits are: (1) complexes of initial avulsion breakout channels at the base of major sandstone storeys; (2) common low‐angle bedsets ascribed to deposition over low‐angle dunes in active channels; (3) palaeocanyon floodplain environments with evidence of fluctuating near‐surface water tables. Sand‐body architecture is generally multistorey, with palaeocurrents indicative of funnelling of initial avulsive and main fluvial discharge from the neighbouring Mesilla basin through a narrow topographic gap into the palaeocanyon and out over the study area. An avulsion node was evidently located at the stationary southern tip to the East Robledo fault during Gauss times, with aRG channels to the north flowing close to the fault and preventing fan progradation. Subsequent Matuyama growth of the fault caused (1) deposition to cease as the whole succession was uplifted in its footwall, (2) development of a thick petrocalcic horizon, and (3) fan progradation into the Mesilla basin. Parameters for the whole aRG fluvial system are estimated as: active single channels 2 m deep and 25 m wide; valley slope 0·24–0·065°; maximum mean aggradation rate 0·05 mm year–1; major channel belt avulsion interval 200 ky; individual channel recurrence interval 100 ky; minimum bankfull mean flow velocity 1·54 m s–1, minimum single‐channel discharge 77 m3 s–1, bed shear stress 22·3 N m–2; and stream power 34·3 W m–2.
Sedimentology and geochemistry of fluvio‐lacustrine tufa deposits controlled by evaporite solution subsidence in the central Ebro Depression, NE Spain
Authors: Arenas  , GutiÉrrez  , OsÁcar  , Sancho
Published: March 2003

The Urrea de Jalón tufa deposits constitute the 20‐ to 50‐m‐thick caprock (0·3 km2) of an isolated mesa. They disconformably overlie horizontal strata of the Tertiary Ebro Basin (NE Spain), which contains a thick succession of lacustrine gypsum and marls, followed by limestones, marls and, locally, fluvial sandstones and mudstones. The tufa deposits show a complex, large‐scale framework of basin‐like structures with centripetal dips that decrease progressively from the base to the top of the tufa succession, and beds that thicken towards the centre of the structure (cumulative wedge‐out systems). These geometries reveal that the tufa deposits were affected by differential synsedimentary subsidence. Distinct onlapping depressions reflect time migration of the subsiding areas. The studied carbonates are composed mostly of low‐Mg calcite, with minor quartz. Some samples have anomalously high contents of Fe, Mn and Ba that may exceed 1% (goethite, haematite and barite are present). Carbonate facies are: (a) macrophyte encrustation deposits; (b) bryophyte build‐ups; (c) oncolite and coated grain rudstones; (d) non‐concentric stromatolite‐like structures; (e) massive or bioturbated biomicrites; and (f) green and grey marls. Facies a and c show a great variety of microbial‐related forms. These facies can be arranged in dm‐ to 2‐m‐thick vertical associations representing: (i) fluvial–paludal sequences with bryophyte growths; (ii) pond‐influenced fluvial sequences; and (iii) lacustrine–palustrine sequences. The Urrea de Jalón tufa deposits formed in a fluvio‐lacustrine environment that received little alluvial sediment supply. Isotope compositions (δ13C and δ18O) reveal meteoric signatures and accord with such a hydrologically open system of fresh waters. The Fe, Mn and Ba contents suggest an additional supply of mineralized waters that could be related to springs. These would have been discharge points in the Ebro Depression of a regional aquifer of the Iberian Ranges. Rising groundwater caused the solution of the underlying evaporites and the synsedimentary subsidence of the tufa deposits.
Bedforms and associated sedimentary structures formed under supercritical water flows over aggrading sand beds
Authors: Alexander J. , Bridge J. S. , Cheel R. J. , Leclair S. F.
Published: March 2003

Bedforms and associated sedimentary structures, formed under supercritical water flow over an aggrading sand bed, were studied in a laboratory flume. Although the geometry and hydraulic characteristics of these bedforms (antidunes, chutes‐and‐pools) are well known, their internal structures are not. The objectives of the study were to: (1) describe the three‐dimensional geometry of the sedimentary structures and examine their mode of origin; (2) develop a relationship between the geometries of the sedimentary structures and the formative bedforms and; (3) identify criteria that distinguish these sedimentary structures from similar types, such as hummocky and swaley cross‐strata. Sedimentary structures associated with antidunes are primarily lenticular laminasets with concave‐upward erosional bases (troughs) in which laminae generally dip upstream or fill the troughs symmetrically. These laminasets are associated with growth and upstream migration of water‐surface waves and antidunes, and with surface‐wave breaking and filling of antidune troughs respectively. In addition, sets of downstream‐dipping laminae are produced by rapid migration of asymmetrical bedwaves immediately after wave breaking. Rare convex‐upward laminae define the shape of antidunes that developed under stationary water‐surface waves. The laminasets and internal laminae extend across the width of the flume, but vary in thickness and inclination, indicating that the antidunes have some degree of three dimensionality. The length and maximum thickness of the lenticular laminasets are approximately half of the length and height of formative antidunes, providing a potentially useful tool for palaeohydraulic reconstructions. The sets of downstream‐dipping laminae formed under antidunes are distinctive and do not occur in hummocky and swaley cross‐strata. Sedimentary structures associated with chutes‐and‐pools are sets of upstream‐dipping laminae and structureless sand.
Septarian concretions: internal cracking caused by synsedimentary earthquakes
Authors: Pratt Brian R.
Published: March 2003

Septarian concretions are abundant in many Phanerozoic marine and marginal‐marine shales and mudstones. They range from a few centimetres to several metres in size and are spherical or ellipsoidal in morphology. In general, formation by localized calcite or siderite cementation in argillaceous sediments began under less than a few metres of burial. Septarian cracks vary widely in shape and configuration: included are networks of wide, vertically, radially and sometimes concentrically oriented, lenticular shrinkage cracks; and narrower, parallel‐sided, straight to irregular tension cracks locally accompanied by brecciation, and plumose and en échelon sigmoidal cracks indicative of shear stresses. Crack types are intergradational; many concretions exhibit multiple cracking events. Enclosed macrofossils and isopachous fibrous calcite cement that lines earlier formed cracks are commonly broken and displaced. In some cases, cracks contain injected lime mud and silt. These features, taken together, testify that cracking involved a spectrum of responses in concretion interiors, from loss of shear strength, dewatering and shrinkage to brittle failure, demonstrating variations in, and contrasts between, the rheological properties of the matrix and enclosed objects. Localization to interiors and outward tapering of lenticular cracks make a case for fracture partitioning and indicate that interiors were softer than exteriors at the time of shrinkage. Parallel‐sided cracks point to greater stiffness, and evolving crack shape in multiply cracked concretions shows that rigidity increased with time. Crack orientations indicate highly variable tensile and shear stress directions within individual concretions. Rupture, brecciation, displacement of fragments, loss of shear strength, liquefaction and injection of unconsolidated granular sediment suggest that deformation events were rapid, if not virtually instantaneous. Previous explanations for the internal cracking, such as gas generation, spontaneous chemical dehydration or localized overpressuring due to compaction, seem either untenable or fail to account for the spectrum of observed features. However, syndepositional earthquake‐induced shaking of cementing bodies of varying rigidity at shallow burial depths seems to be a plausible source for the requisite short‐lived, variable to anisotropic, high‐stress regime inside the concretions. Septarian concretions may thus preserve a signature of basin seismicity as it relates to their cementation history.
Depositional systems and sequence stratigraphy of coarse‐grained deltas in a shallow‐marine, strike‐slip setting: the Bohemian Cretaceous Basin, Czech Republic
Authors: Uličný D.
Published: March 2003

Deposits of coarse‐grained, Gilbert‐type deltas showing varying degrees of reworking of foresets by basinal currents were identified in Middle Turonian to Early Coniacian sandstones of the Bohemian Cretaceous Basin. The progradation of the deltaic packages, earlier interpreted as large‐scale subaqueous dunes, shelf ridges or subaqueous fault‐scarp ‘accumulation terraces’, was controlled by high‐ and low‐frequency, relative sea‐level changes in a relatively slowly subsiding, intracontinental strike‐slip basin. End‐member types of the Bohemian Cretaceous coarse‐grained deltas are deep‐water deltas, characterized by thick (50–80 m) foreset packages with steep (10–30°) foresets, and shallow‐water deltas, which deposited thin (<15 m) packages with foresets typically between 4° and 10°. The differences in thickness and foreset slope angle were controlled predominantly by the accommodation available during progradation. The depositional regime of the deltas was governed by (i) the fluvial input of abundant sand bedload, with a minor proportion of gravel; (ii) gravity flows, most probably caused by liquefaction of the upper part of the unstable foreset slope; and (iii) migration of sandy bedforms on the foreset slopes. The bedform migration was driven by unidirectional currents of possible tidal origin. Individual foreset packages represent systems tracts, or parts of systems tracts, of depositional sequences. A variety of stacking patterns of high‐frequency sequences exists in the basin, caused by low‐frequency relative sea‐level changes as well as by local changes in sediment input. Because of generally low subsidence rates, fluvial or beach topset strata were not preserved in the cases studied. The absence of preserved fluvial facies, which has been one of the main arguments against the fluvio‐deltaic origin of the sandstone bodies, is explained by erosion of the topsets during transgression and their reworking into coarse‐grained lags of regional extent covering ravinement surfaces.