bluuebunny/crossref_metadata_2025 huggingface dataset:
Petrology of Lower Cretaceous carbonate mud mounds (Albian, N. Spain): insights into organomineralic deposits of the geological record
Authors: Neuweiler Fritz , Gautret Pascale , Thiel Volker , Lange Robert , Michaelis Walter , Reitner Joachim
Published: March 2003

The process of organomineralization is increasingly well understood with respect to modern carbonate sediments accumulating adjacent to tropical reef atolls and reef caves. Mineralization related to non‐living organic substrates results in autochthonous micrite production (‘automicrites’). ‘Automicrites’ are the main constructive element of Lower Cretaceous (Albian) carbonate mud mounds in northern Spain. These slope mud mounds occur within transgressive and early highstand system tracts encompassing several macrobenthic ecological zones. They are clearly separated from the biocalcifying carbonate factory (Urgonian carbonate platforms), in both space and time. Within these build‐ups, most ‘automicrites’ were initially indurated and accreted to form a medium‐relief growth framework. ‘Automicrites’ have a uniform, presumably high‐Mg‐calcite precursor mineralogy. They show an inorganic stable‐isotope signature (∂13C around +3·3‰) within the range of early marine cements, and skeletal compounds lacking major vital effects. Epifluorescence microscopy shows that they have facies‐specific fluorescence, which is similar to skeletal compounds of Acanthochaetetes, but clearly different from allomicritic sediment and cements, which are mostly non‐fluorescent. The EDTA‐soluble intracrystalline organic fraction (SIOF) of Albian automicrites shows an amino acid spectrum that is similar to shallow subsurface samples from their modern counterparts. Gel electrophoresis of the SIOF demonstrates an exclusively acidic character, and a mean molecular size range between 20 and 30 kDa. Experiments in vitro (inhibition tests) indicate that the SIOF has a significant Ca2+‐binding capacity. Fluorescence and chemical characteristics of SIOF point to a main substance class, such as humic and fulvic acids, compounds that form from pristine organic matter during early diagenesis. Biomarker analyses provide evidence for the crucial role of biodegradation by heterotrophic microorganisms, but no biomarker for cyanobacteria has been found. Primary sources of organic material should have been manifold, including major contributions by metazoans such as sponges. It is concluded that many carbonate mud mounds are essentially organomineralic in origin and that the resulting fabric of polygenetic muds (‘polymuds’) may represent ancestral metazoan reef ecosystems, which possibly originated during the Neoproterozoic.
Flow pattern within a Permian submarine slump recorded by oblique folds and deformed fossils, Ulladulla, south‐eastern Australia
Authors: Smith John V.
Published: March 2003

The flow pattern within a slump in Permian marine rocks of the southern Sydney Basin, Australia, is recorded by folds and deformed fossils. Abundant brachiopod and bryzoan fossils in the slumped rocks are relatively undeformed, but fossil crinoid stems have been deformed by relative rotation of individual ossicles. Measurement of the strain indicates that the deformation of the crinoids is consistent with flexural flow folding within the slump. Previous models assume that curved slump fold axes remain parallel to the enveloping bedding surface of a slump sheet. Detailed measurements of the orientation of slump folds in this study found fold axes to be oblique to bedding, which is interpreted as a result of folds plunging downward towards the flanks of the slump or slump lobes. In the present model, fold axes are not generally parallel to the strike of the fold axial surface, and this can explain differences between the orientations of slump fold axes and axial surfaces when these are used as directional indicators of slump movement.
The hydrodynamic and sedimentary setting of nearshore coral reefs, central Great Barrier Reef shelf, Australia: Paluma Shoals, a case study
Authors: Larcombe Piers , Costen Andrew , Woolfe Ken J.
Published: March 2003

The Great Barrier Reef (GBR) shelf contains a range of coral reefs on the highly turbid shallow inner shelf, where interaction occurs with terrigenous sediments. The modern hydrodynamic and sedimentation regimes at Paluma Shoals, a shore‐attached ‘turbid‐zone’ coral reef, and at Phillips Reef, a fringing reef located 20 km offshore, have been studied to document the mechanisms controlling turbidity. At each reef, waves, currents and near‐bed turbidity were measured for a period of ≈1 month. Bed sediments were sampled at 135 sites. On the inner shelf, muddy sands are widespread, with admixed terrigenous and carbonate gravel components close to the reefs and islands, except on their relatively sheltered SW side, where sandy silty clays occur. At Paluma Shoals, the coral assemblage is characteristic of inner‐shelf or sheltered habitats on the GBR shelf (dominated by Galaxea fascicularis, up to >50% coral cover) and is broadly similar to that at Phillips Reef, further offshore and in deeper water. The sediments of the Paluma Shoals reef flats consist of mixed terrigenous and calcareous gravels and sands, with intermixed silts and clays, whereas the reef slope is dominated by gravelly quartz sands. The main turbidity‐generating process is wave‐driven resuspension, and turbidity ranges up to 175 nephelometric turbidity units (NTU). In contrast, at Phillips Reef, turbidity is <15 NTU and varies little. At Paluma Shoals, turbidity of >40 NTU probably occurs for a total of >40 days each year, and relatively little time is spent at intermediate turbidities (15–50 NTU). The extended time spent at either low or high turbidities is consistent with the biological response of some species of corals to adopt two alternative mechanisms of functioning (autotrophy and heterotrophy) in response to different levels of turbidity. Sedimentation rates over periods of hours may reach the equivalent of 10 000 times the mean global background terrigenous flux (BTF) of sediment to the sea floor, i.e. 10 000 BTF, over three orders of magnitude greater than the Holocene average for Halifax Bay of <3 BTF. As elsewhere along the nearshore zone of the central GBR, dry‐season hydrodynamic conditions form a primary control upon turbidity and the distribution of bed sediments. The location of modern nearshore coral reefs is controlled by the presence of suitable substrates, which in Halifax Bay are Pleistocene and early Holocene coarse‐grained (and relatively stable) alluvial deposits.
The final phase of dead‐ice moraine development: processes and sediment architecture, Kötlujökull, Iceland
Authors: Kjær Kurt H. , Krüger Johannes
Published: March 2003

Consecutive phases of de‐icing of ice‐cored moraines and the formation of dead‐ice moraine were monitored over a 4‐year period at the terminus of the Kötlujökull glacier, Iceland. Particularly, the transition from partially ice‐cored moraine with isolated dead‐ice blocks to the ice‐free landscape receives attention in this paper in order to link the final melting processes to the architecture of the sedimentary end product. In the current humid sub‐polar climate of south Iceland de‐icing of partially ice‐cored moraines results chiefly from melting along the bottom surface of ice‐cores with an annual average rate of 25 cm. The final de‐icing is associated with an interrelated group of re‐sedimentation processes and surface features. Series of sinkholes evolve at the toe of dead‐ice blocks, which initiate retrogressive rotational sliding or backslumping of the ice‐cored slopes and the formation of distinct edges and fractures in the adjacent basins. Although backslumping is the dominant process in this phase of re‐sedimentation, structures resulting from this process are rarely recognized in the ice‐free landscape. As ice‐cores gradually diminish the effect of the latest re‐sedimentation events will overprint or destroy most existing sedimentary characteristics. Thus, in the ice‐free landscape, structures mainly related to the formation of sinkholes and fractures remain imprinted on the sediment succession. Generally, no inversion of the topography occurs during the final phase of de‐icing. The overall topography recognized in the late phase of the fully ice‐cored terrain is merely lowered and the amplitude of the relief reduced as de‐icing progresses. The sediment architecture of the ice‐free landscape is characterized by heterogeneous and often slumped diamict sediments with variable thickness and lateral distribution; clast orientation is related to the direction of slopes, and boulders are found in isolated groups or in linear arrangements.
Turbidite depositional architecture across three interconnected deep‐water basins on the north‐west African margin
Authors: Wynn Russell B. , Weaver Philip P. E. , Masson Douglas G. , Stow Dorrik A. V.
Published: March 2003

ABSTRACT The Moroccan Turbidite System (MTS) on the north‐west African margin extends 1500 km from the head of the Agadir Canyon to the Madeira Abyssal Plain, making it one of the longest turbidite systems in the world. The MTS consists of three interconnected deep‐water basins, the Seine Abyssal Plain (SAP), the Agadir Basin and the Madeira Abyssal Plain (MAP), connected by a network of distributary channels. Excellent core control has enabled individual turbidites to be correlated between all three basins, giving a detailed insight into the turbidite depositional architecture of a system with multiple source areas and complex morphology. Large‐volume (> 100 km3) turbidites, sourced from the Morocco Shelf, show a relatively simple architecture in the Madeira and Seine Abyssal Plains. Sandy bases form distinct lobes or wedges that thin rapidly away from the basin margin and are overlain by ponded basin‐wide muds. However, in the Agadir Basin, the turbidite fill is more complex owing to a combination of multiple source areas and large variations in turbidite volume. A single, very large turbidity current (200–300 km3 of sediment) deposited most of its sandy load within the Agadir Basin, but still had sufficient energy to carry most of the mud fraction 500 km further downslope to the MAP. Large turbidity currents (100–150 km3 of sediment) deposit most of their sand and mud fraction within the Agadir Basin, but also transport some of their load westwards to the MAP. Small turbidity currents (< 35 km3 of sediment) are wholly confined within the Agadir Basin, and their deposits pinch out on the basin floor. Turbidity currents flowing beyond the Agadir Basin pass through a large distributary channel system. Individual turbidites correlated across this channel system show major variations in the mineralogy of the sand fraction, whereas the geochemistry and micropalaeontology of the mud fraction remain very similar. This is interpreted as evidence for separation of the flow, with a sand‐rich, erosive, basal layer confined within the channel system, overlain by an unconfined layer of suspended mud. Large‐volume turbidites within the MTS were deposited at oxygen isotope stage boundaries, during periods of rapid sea‐level change and do not appear to be specifically connected to sea‐level lowstands or highstands. This contrasts with the classic fan model, which suggests that most turbidites are deposited during lowstands of sea level. In addition, the three largest turbidites on the MAP were deposited during the largest fluctuations in sea level, suggesting a link between the volume of sediment input and the magnitude of sea‐level change.
Spatial variation of overbank aggradation rate and its influence on avulsion frequency
Authors: Törnqvist Torbjörn E. , Bridge John S.
Published: March 2003

Abstract River avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges, and the associated increase in cross‐valley slope relative to either the down‐channel slope or the down‐valley slope (the latter is termed the slope ratio in the present paper). Therefore, spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion‐dominated models of alluvial architecture. Detailed evidence on centennial‐ to millennial‐scale floodplain deposition has, to date, been largely unavailable. New data on such long‐term overbank aggradation rates from the Rhine–Meuse and Mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto, and can be similar to observations for single overbank floods. This leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios, potentially resulting in increased avulsion frequencies. A revised input parameter for overbank aggradation rate was used in a three‐dimensional model of alluvial architecture to study its effect on avulsion frequency. Realistic patterns of avulsion and interavulsion periods (≈1000 years) were simulated with input data from the Holocene Rhine River, with avulsions occurring when the slope ratio is in the range 3–5. However, caution should be practised with respect to uncritical use of these numbers in different settings. Evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value, irrespective of whether critical slope ratios are used, as in the present study, or superelevation as has been proposed by other investigators.
Sedimentation in a fluvially infilling, barrier‐bound estuary on a wave‐dominated, microtidal coast: the Ouémé River estuary, Benin, west Africa
Authors: Anthony Edward J. , Oyédé Lucien M. , Lang Jacques
Published: March 2003

The Ouémé River estuary is located on the seasonally humid tropical coast of Benin, west Africa. A striking feature of this microtidal estuary is the presence of a large sand barrier bounding a 120 km2 circular central basin, Lake Nokoué, that is being infilled by heterogeneous fluvial deposits supplied by a relatively large catchment (50 000 km2). Borehole cores from the lower estuary show basal Pleistocene lowstand alluvial sediments overlain by Holocene transgressive–highstand lagoonal mud and by transgressive to probably early highstand tidal inlet and flood‐tidal delta sand deposited in association with non‐preserved transgressive sand barriers. The change in estuary‐mouth sedimentation from a transgressive barrier‐inlet system to a regressive highstand barrier reflects regional modifications in marine sand supply and in the cross‐barrier tidal flux associated with barrier‐inlet systems. As barrier formation west of the Ouémé River led to an increasingly rectilinear shoreline, the longshore drift cell matured, ensuring voluminous eastward transport of sand from the Volta Delta in Ghana, the major purveyor of sand, to the Ouémé embayment, 200 km east. Concomitantly, the number of tidal inlets, and the tidal flux associated with a hitherto interlinked lagoonal system on this coast, diminished. Complete sealing of Lake Nokoué has produced a large, permanently closed estuary, where tidal intrusion is assured through the interconnected coastal lagoon via an inlet located 60 km east. Since 1885, tides have entered the estuary directly through an artificial outlet cut across the sand barrier. Although precluding the seaward loss of fluvial sediments, permanent estuary‐mouth closure has especially deprived the highstand estuary of marine sand, a potentially important component in estuarine infill on wave‐dominated coasts. In spite of a significant fluvial sediment supply, estuarine infill has been moderate, because of the size of the central basin. Estuarine closure has resulted in two co‐existing highstand sediment suites, with limited admixture, the marine‐derived, estuary‐mouth barrier and upland‐derived back‐barrier sediments. This situation differs from that of mature barrier estuaries characterized by active fluvial‐marine sediment mixing and facies interfingering.
Lower Miocene gypsum palaeokarst in the Madrid Basin (central Spain): dissolution diagenesis, morphological relics and karst end‐products
Authors: Rodríguez‐Aranda Juan P. , Calvo José P. , Sanz‐Montero M. Esther
Published: March 2003

Abstract The Miocene sedimentary record of the Madrid Basin displays several examples of palaeokarstic surfaces sculpted within evaporite formations. One of these palaeokarstic surfaces represents the boundary between two main lithostratigraphic units, the Miocene Lower and Intermediate units of the Madrid Basin. The palaeokarst formed in lacustrine gypsum deposits of Aragonian age and corresponds to a surface palaeokarst (epikarst), further buried by terrigenous deposits of the overlying unit. Karst features are recognized up to 5·5 m beneath the gypsum surface. Exokarst and endokarst zones are distinguished by the spatial distribution of solution features, i.e. karren, dolines, pits, conduits and caves, and collapse breccias, sedimentary fills and alteration of the original gypsum across the karst profiles. The development of the gypsum palaeokarst began after drying out of a saline lake basin, as supported by recognition of root tubes, later converted to cylindrical and funnel‐shaped pits, at the top of the karstic profiles. The existence of a shallow water table along with low hydraulic gradients was the main factor controlling the karst evolution, and explains the limited depth reached by both exokarst and endokarst features. Synsedimentary fill of the karst system by roughly laminated to massive clay mudstone with subordinate carbonate and clastic gypsum reflects a punctuated sedimentation regime probably related to episodic heavy rainfalls typical of arid to semi‐arid climates. Duration of karstification is of the order of several thousands of years, which is consistent with previous statements that gypsum karstification can develop rapidly over geologically short time periods.
The cladistics and higher classification of the Pimpliformes (Hymenoptera: Ichneumonidae)
Authors: WAHL DAVID , GAULD IAN
Published: March 2003

The monophyly of the ichneumonid clade Pimpliformes is established and the phylogenetic relationships of the eight component subfamilies are resolved. The clade (Acaenitinae + (Diacritinae + (Cylloceriinae + (Diplazontinae + Orthocentrinae)))) is the sister‐lineage to the clade (Pimplinae + (Rhyssinae + Poemeniinae)). The Nearctic genus Cressonia Dasch is transferred to the Diacritinae from the Orthocentrinae. Tribes are not recognized in the Acaenitinae as the Coleocentrini (sensu Townes, 1971) is paraphyletic with respect to the Acaenitini. The Cylloceriinae is recognized as comprising three genera, Cylloceria Schiødte, Allomacrus Förster and Sweaterella gen.n. The Orthocentrinae, including the Helictinae of authors, is shown to be monophyletic, but the latter is clearly shown to be paraphyletic if the Orthocentrus genus‐group is excluded. The Pimplinae comprises four monophyletic tribes: the Delomeristini, consisting of Delomerista Förster and Atractogaster Kriechbaumer; the Perithoini trib.n., which includes only Perithous Holmgren (= Hybomischos Baltazar syn.n.); the Pimplini, which includes the Theronia genus‐group as well as the Pimpla genus‐group; and the Ephialtini, which includes the Polysphinctini syn.n., a monophyletic group that previously rendered the restricted Ephialtini paraphyletic. The tribe Delomeristini is the sister‐group to the clade (Ephialtini + (Perithoini + Pimplini)). The subfamily Poemeniinae is recognized as comprising three tribes: the Pseudorhyssini (trib.n.) which includes the single Holarctic genus Pseudorhyssa Merrill; the Rodrigamini (trib.n.) which includes only the Costa Rican genus Rodrigama Gauld; and the Poemeniini. The tribe Pseudorhyssini is the sister‐group to the clade (Rodrigamini + Poemeniini). The phylogenetic inter‐relationships of the genera of Poemeniini are resolved. A new genus from South Africa, Guptella (gen.n.) is described, and Achorocephalus Kriechbaumer is shown to be a synonym of Eugalta Cameron (syn.n.). The evolution of biological traits within the Pimpliformes is discussed with reference to the elucidated phylogeny, and zoogeographic patterns are outlined.
Bela oceanic lithosphere assemblage and its relation to the Réunion hotspot
Authors: Gnos  , Khan  , Mahmood  , Khan  , Khan  , Villa
Published: March 2003

The Bela ophiolite of Pakistan contains a complete ophiolite‐accretionary wedge‐trench sequence emplaced onto the Indian continental margin during the northward drift of India‐Seychelles over the active Réunion hotspot. A structurally higher ophiolite overlies an accretionary prism, which is thrust over a foreland basin. Shear‐sense determinations in peridotite mylonites in the ophiolite footwall and imbrication structures in the underlying accretionary wedge indicate an ESE emplacement. Sedimentary rocks in the accretionary wedge indicate Aptian‐Albian pillow lavas, initially deep water conditions, and increasing influence from the continent until the Maastrichtian. The ophiolite emplacement was predated and accompanied by Fe‐tholeiitic and alkaline magmatism related to the Réunion hotspot and continuous incorporation of trench sediments into the accretionary wedge. 39Ar/40Ar dating shows that the ophiolite formed around 70 Ma. Intraoceanic subduction initiated between 70 and 65 Ma, obduction onto the Indian passive margin occurred during the formation of the Deccan traps at ≈ 66 Ma, and final thrusting onto the continental margin ended in the early Eocene (≈ 50 Ma). The ophiolite emplacement occurred during the counterclockwise separation of Madagascar and India‐Seychelles which caused shortening and consumption of oceanic lithosphere between the African‐Arabian and the Indian‐Seychelles plates.
Evolutionary model for Alpine Corsica: mechanism for ophiolite emplacement and exhumation of high‐pressure rocks
Authors: Malavieille  , Chemenda  , Larroque
Published: March 2003

A tectonic model of Alpine Corsica is proposed based on geological studies. Its evolution starts after the Jurassic with intraoceanic subduction, followed by mid‐Cretaceous subduction of the European continental margin under the oceanic segment of the Adriatic plate. After subduction of the continental crust to a depth of ≈ 150 km, slices of crustal material are buoyantly uplifted together with high‐pressure oceanic rocks (ophiolites and ‘schistes lustrés’). High pressure–low temperature continental gneiss units overthrust the outer segments of the European crust, while producing a normal sense motion along the upper surface of the rising crustal body. During the Eocene, the closure of the remnant Ligurian oceanic basin separating the proto Corsican belt and Adria, resulted in a second orogenic phase with the emplacement of unmetamorphosed ophiolitic nappes which overthrust the previously exhumed and eroded HP belt. This Corsican model suggests an original evolutionary path for orogenic belts when continental collision is preceded by intraoceanic subduction.
Thermo‐mechanical approach to validation of deep crustal and lithospheric structures inferred from multidisciplinary data: application to the Western and Northern Alps
Authors: Burov E. , Podladchkov Y. , Grandjean G. , Burg J.P.
Published: March 2003

Current multidisciplinary studies confront the difficult problem of validation and verification of internal compatibility of geophysical and geological data of different nature, quality and origin. Our ‘geodynamic’ approach exploits the natural interdependence between the data related to different physical properties of geological structures (density, rheology, temperature, stress). Using the latter as input for a thermo‐mechanical finite‐element model, we can verify whether the inferred properties and geometries (i) are mechanically stable, (ii) require rheologically consistent stresses, strains, realistic thermal conditions, etc., and (3) will evolve in a geologically realistic way in the future. This ‘mechanically balanced’ approach is tested on the Alpine orogen (ECORS and NFP20 profiles) in the framework of the GeoFrance 3D programme. The results suggest a number of corrections and adjustments that can be made to existing seismically‐and gravity‐predicted geometries of structures such as the Ivrea body and those of the depleted subducted crust.
Determination of metamorphic grade in siliceous muscovite‐bearing rocks in Madagascar using reflectance spectroscopy
Authors: Longhi  , Mazzoli  , Sgavetti
Published: March 2003

Visible short‐wave infrared laboratory reflectance spectra of quartzites and micaschists from the Precambrian basement of central‐western Madagascar are dominated by the muscovite spectrum. The spectra were measured from rock samples collected along an E–W traverse across a metamorphic sequence recording progressively higher metamorphic grades. The wavelength of the Al–OH band around 2200 nm decreased westward and was inversely correlated with AlVI content of muscovite in rocks showing the same nonlimiting assemblage. This shift is correlated also with an increase of band intensity, which is attributed to the progressive increase of metamorphic grade. All of these variations in rock spectral properties can be detected by the high spectral resolution MIVIS and AVIRIS sensors, as well as by the lower resolution TM sensor.
Age and provenance of early Precambrian metasedimentary rocks in the Lapland–Kola Belt, Russia: evidence from Pb and Nd isotopic data
Authors: Bridgwater D. , Scott D. J. , Balagansky V. V. , Timmerman M. J. , Marker M. , Bushmin S. A. , Alexeyev N. L. , Daly J. S.
Published: March 2003

207Pb/206Pb ages are presented for detrital zircons (Laser Ablation Microprobe ICP‐MS) and whole‐rock Nd isotopic determinations (TIMS) from samples of Neoarchean and Palaeoproterozoic metasedimentary rocks from the Umba granulite terrane and the Keivy domain of the Central Kola composite terrane, Kola Peninsula, north‐western Russia. Three are samples of rocks from the Umba granulite terrane that were deposited ≈ 2.20–1.90 Ga; they contain Archaean detritus, much of it older than 3.0 Gyr, as well as abundant 2.20–1.95‐Gyr‐old material. Deposition may have occurred on the margin of an Archaean craton with an exposed Palaeoproterozoic magmatic arc source, possibly during orogenesis. Two samples from the Keivy domain have remarkably similar, dominantly Archaean detrital zircon age spectra. One was deposited pre‐2.4 Ga, whereas the other was probably deposited post‐2.01 Ga. Both had similar sources, compatible with the proximal country rocks, and possible shallow‐water (?) cratonic margin depositional settings.
Apatite fission‐track analysis of Neogene exhumation in northern Corsica (France)
Authors: Cavazza W. , Zattin M. , Ventura B. , Zuffa G. G.
Published: March 2003

Apatite fission‐track analyses along a W–E‐orientated transect across northern Corsica indicate an important episode of crustal exhumation in late early Miocene time. Samples taken from the Alpine orogenic wedge, from the adjacent foreland basin and from the crystalline basement complex flooring the basin are completely reset. This implies that a ≥ 2.0–2.3‐km‐thick crustal section made of thrust sheets and/or autochthonous foreland deposits has been removed by erosion since early Miocene time. A geometric projection of this lost cover towards the west indicates that all of northern Corsica was covered either by Alpine nappes or middle Eocene foreland deposits. Fission‐track ages are the same across the main boundary fault system separating the Alpine orogenic wedge and the foreland, indicating the absence of significant differential vertical displacement between upper and lower plates during Neogene unroofing.
Significance of earthquake‐related anomalies in fluids of Val D’Agri (southern Italy)
Authors: Italiano F. , Martelli M. , Martinelli G. , Nuccio P. M. , Paternoster M.
Published: March 2003

Geochemical investigations carried out at the Campano–Lucano Apennine (Southern Italy) revealed the presence of fluids composed of a mixing between components of shallow and deep origin, where mantle‐derived helium is also detectable. For the gas phase, the deep component is represented by both CH4 and CO2‐rich gases, while the shallow one is N2‐dominated. Coinciding with the 3 April 1996 ML=4.9 earthquake, the CH4‐rich component mixed with the shallow, N2‐dominated one at the Tramutola well (Val d’Agri), displaying wide variations in mixing proportions. In contrast, no significant modifications occurred in relation to the 1998 ML=5.5 event. According to the collected data, an earthquake‐related transient modification of local crustal permeability is suggested for the 1996 event. The different crustal response to the two events may be related to different stress distributions around the epicentres or may suggest a different tectonic connection between the Val d’Agri and the two earthquake locations.
How hydrofractures become arrested
Authors: Gudmundsson Agust , Brenner Sonja L.
Published: March 2003

Fluids in the earth's crust are commonly transported by hydrofractures, such as dykes and mineral veins, many of which become arrested at various crustal depths. Hydrofractures are commonly arrested – some showing blunt tips – at contacts between soft (low Young's modulus) and stiff (high Young's modulus) layers. For example, many dyke tips are arrested at contacts between soft pyroclastic rocks and stiff basaltic lava flows, and vein tips at contacts between soft marl and stiff limestone. Theoretical models indicate that overpressured, buoyant hydrofractures in homogeneous, isotropic host rocks should normally reach the surface. In layered host rocks, however, abrupt changes in Young's moduli, horizontal discontinuities, and layers with unusually high fracture‐perpendicular stresses encourage hydrofracture arrest. It is proposed that for layer‐parallel loading, stiff layers favour hydrofracture arrest during active compression but soft layers during extension. It is concluded that for hydrofracture propagation to occur, the stress field along its potential pathway must be essentially homogenous.
Superimposed tectonic and hydrothermal events during the late‐orogenic extension in the Western French Massif Central: a structural and 40Ar/39Ar study
Authors: Roig Jean‐Yves , Faure Michel , Maluski Henri
Published: March 2003

In the Western French Massif Central, the Argentat fault is a major structure through which As–Au fluids percolated in the Late Carboniferous along brittle fractures. New petrostructural investigations show that an early ductile normal‐dextral faulting, coeval to leucogranite emplacement took place during the Late Visean syncollisional extension of the belt and was accompanied by a hydrothermal event marked by the growth of muscovites whose 40Ar/39Ar ages cluster around 335 Ma. This early fluid channelling is associated with brittle deformation only in the hangingwall of the Argentat fault, whereas ductile deformation is restricted to the footwall. These results provide new evidence for the upper crust implication during the syncollisional extension in the French Massif Central. This study stresses the interest of a detailed multimethod analysis to characterize hydrothermal processes, especially in basement areas where the tectonic, plutonic and metamorphic evolution is polyphased.
Estimating exhumation rate and relief evolution by spectral analysis of age–elevation datasets
Authors: Braun Jean
Published: March 2003

Extracting independent information on mean exhumation rate and the rate of surface relief change from thermochronometric datasets is essential to improve our understanding of the complex coupling between tectonics and surface erosion, i.e. the time‐scale over which landforms react to changes in uplift rate and/or climate. A new method, based on spectral analysis of age–elevation data collected along one‐dimensional profiles, is presented that provides independent estimates of the mean exhumation rate and the relative change in surface relief. The results are shown to be independent of the assumed geothermal gradient. The method is applied to an existing age dataset from the Sierra Nevada, California, and provides constraints on the evolution of the present‐day relief. The spectral analysis demonstrates how current sampling strategies should be modified to optimize the tectonic and geomorphic information that can be retrieved from a thermochronometric dataset.
Flood and earthquake disturbance of 210Pb geochronology (Lake Anterne, NW Alps)
Authors: Arnaud F. , Lignier V. , Revel M. , Desmet M. , Beck C. , Pourchet M. , Charlet F. , Trentesaux A. , Tribovillard N.
Published: March 2003

Dating recent lake sediment records yielding disturbed 210Pb profiles has been a problem of wide interest in palaeoclimatic and palaeoseismic studies over the last few centuries. When applied to an alpine lake sedimentary record, a high‐resolution sedimentological study reveals that the 210Pb profile is disturbed by the occurrence of single‐event deposits triggered by two different mechanisms: flood events deposits and gravity reworking. Removing disturbed layers from the 210Pb profile yields a logarithmic depth–activity relationship. Using a simple 210Pb decay model (CFCS) provides an assessment of mean accumulation rate of `continuous sedimentation', as opposed to `event‐linked sedimentation'. The correlation of the thickest four gravity‐reworked deposits with historically known earthquakes permits both validation and refinement of the age–depth relationship. This refinement highlights variations in accumulation rate consistent with post‐Little Ice Age climatic variations.
Multiple mantle sources during island arc magmatism: U–Pb and Hf isotopic evidence from the Kohistan arc complex, Pakistan
Authors: Schaltegger Urs , Zeilinger Gerold , Frank Martin , Burg Jean‐Pierre
Published: March 2003

ABSTRACT This paper presents high‐precision U–Pb ages and initial Hf isotopic compositions of zircon from mafic to felsic rocks of the Kohistan Arc Complex, Pakistan. Three magmatic pulses tapping geochemically different reservoirs are distinguished. Partial melting of mantle with MORB‐type isotopic characteristics generated 99–92‐Ma‐old magmas. Plutonism around 85 Ma tapped a more fertile mantle source, most likely consisting of a >600‐Ma‐old metasomatically enriched mantle, or of mantle contaminated by an old sedimentary component; 82‐Ma‐old felsic peraluminous dykes have MORB‐type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc. The isotopic results demonstrate several and rather rapid changes in melt source region during arc development. They also show that there was subordinate continental influence and negligible importance of slab components for the Hf budget during the generation of the Kohistan Arc Complex.
Transition from debris flow to hyperconcentrated flow in a submarine channel (the Cretaceous Cerro Toro Formation, southern Chile)
Authors: Sohn Y. K. , Choe M. Y. , Jo H. R.
Published: March 2003

ABSTRACT It is important to understand the exact process whereby very large amounts of sediment are transported. This paper reports peculiar conglomerate beds reflecting the transition of submarine debris flows into hyperconcentrated flows, something that has been well documented only in subaerial debris‐flow events until now. Voluminous debris flows generated along a Cretaceous submarine channel, southern Chile, transformed immediately into multiphase flows. Their deposits overlie fluted or grooved surfaces and comprise a lower division of clast‐supported and imbricated pebble–cobble conglomerate with basal inverse grading and an upper division of clast‐ to matrix‐supported, disorganized conglomerate with abundant intraformational clasts. The conglomerate beds suggest temporal succession of turbidity current, gravelly hyperconcentrated flow, and mud‐rich debris flow phases. The multiphase flows resulted from progressive dilution of gravelly but cohesive debris flows that could hydroplane, in contrast to the flow transitions in subaerial environments, which involve mostly non‐cohesive debris flows. This finding has significant implications for the definition, classification, and hazard assessment of submarine mass‐movement processes and characterization of submarine reservoir rocks.
Expression of E. coli inorganic pyrophosphatase in transgenic plants alters photoassimilate partitioning
Authors: Sonnewald Uwe
Published: March 2003

Transgenic plants were constructed expressing a novel cytosolic inorganic pyrophosphatase in order to reduce the cytosolic pyrophosphate content. To this end the Escherichia coli gene ppa encoding inorganic pyrophosphatase was cloned between the 35S CaMV promoter and the poly(A) site of the octopine synthase gene and transferred into tobacco and potato plants by Agrobacterium‐mediated gene transfer. Regenerated plants were tested for the expression of the ppa gene by Northern blots and activity gels. Plants expressing active inorganic pyrophosphatase showed a dramatic change in photoassimilate partitioning. In both transgenic tobacco and potato plants the ratio between soluble sugars and starch was increased by about 3–4‐fold in source leaves as compared with the wild‐type. However, whereas source leaves of transgenic tobacco plants accumulated much higher levels of glucose (up to 68‐fold), fructose (up to 24‐fold), sucrose (up to 12‐fold) and starch (up to 8‐fold) this was not observed in potato plants where the change in assimilate partitioning in source leaves was due to an increase of about 2‐fold in sucrose and a reduction in starch content.

Expression of the cytosolic inorganic pyrophosphatase in tobacco results in stunted growth of vegetatively growing plants due to a reduced internode distance. Upon flowering the transgenic plants increase their growth rate, reaching almost the same height as control plants at the end of the growth period. Old source leaves accumulate up to 100‐fold more soluble sugars than control leaves. This increase in soluble sugars is accompanied by a reduction in chlorophyll content (up to 85%).

Transgenic potato plants showed a less dramatic change in their growth behaviour. Plants were slightly reduced in size, with stems more highly branched. Tuber number increased 2–3‐fold, but tuber weight was lower resulting in no net increase in fresh weight.
Molecular analysis of the avirulence gene avr9 of the fungal tomato pathogen Cladosporium fulvum fully supports the gene‐for‐gene hypothesis
Authors: Van den Ackerveken Guido F.J.M. , Van Kan Jan A.L. , De Wit Pierre J.G.M.
Published: March 2003

The interaction between the fungal pathogen Cladosporium fulvum and tomato is supposed to have a gene‐for‐gene basis. Races of C. fulvum which have ‘overcome’ the resistance gene Cf9 of tomato, lack the avirulence gene avr9 which encodes a race‐specific peptide elicitor. Races avirulent on tomato genotypes carrying the resistance gene Cf9 produce the racespecific peptide elicitor, which induces the hypersensitive response (HR) on those genotypes. The causal relationship between the presence of a functional avr9 gene and avirulence on tomato genotype Cf9 was demonstrated by cloning of the avr9 gene and subsequent transformation of C. fulvum. A race virulent on tomato genotype Cf9 was shown to become avirulent by transformation with the cloned avr9 gene. These results clearly demonstrate that the avr9 gene is responsible for cultivar specificity on tomato genotype Cf9 and fully support the gene‐for‐gene hypothesis. The avr9 gene is the first fungal avirulence gene to be cloned.
Salicylic acid‐inducible binding of a tobacco nuclear protein to a 10 bp sequence which is highly conserved amongst stress‐inducible genes
Authors: Goldsbrough Andrew P. , Albrecht Huguette , Stratford Rebecca
Published: March 2003

A 10 bp sequence motif (TCATCTTCTT) which is repeated several times in the 5′ non‐transcribed region of a barley β‐1,3‐glucanase gene is also present in the non‐translated regions of over 30 different plant genes which are known to be induced by one or more forms of stress. Gel retardation assays and South‐western blotting experiments provide evidence that the motif is the binding site for a tobacco nuclear protein with an apparent molecular weight of 40 kDa. Binding activity is increased when nuclear extracts from salicylic acid‐treated plants are analysed compared with extracts from control plants, indicating that the protein itself is either induced or modified under conditions of stress. These observations suggest roles for the 10 bp motif and its binding protein as cis‐ and trans‐acting regulators of gene expression during response to stress.
Biosynthesis of cutin monomers: involvement of a lipoxygenase/peroxygenase pathway
Authors: Blée Elizabeth , Schuber Francis
Published: March 2003

Cutin is synthesized from oxygenated fatty acids derived preponderantly from oleic acid. The enzymatic pathways involved in the biosynthesis of such cutin monomers have been studied, i.e. 18‐hydroxyoleic acid, 9,10‐epoxy‐18‐hydroxystearic acid (the major constituent) and 9,10,18‐trihydroxystearic acid. This was approached by studying (i) the substrate specificity and stereoselectivity of purified peroxygenase, which epoxidizes unsaturated fatty acids, and fatty acid epoxide hydrolase, i.e. two enzyme activities that have been found recently in higher plants, and (ii) the transformation of oleic acid into cutin monomers by a cell free system, i.e. soybean microsomes. These two enzymes, along with a ω‐hydroxylating activity, can account for the biosynthesis of the oleic acid‐derived cutin monomers and their precursors. A new biosynthetic scheme is proposed, whose pathways take into account the dynamic aspects of the expression of the different enzyme activities involved. Importantly, since peroxygenase, for its activity, is strictly dependent on fatty acid hydroperoxides, which act as co‐substrates, the biosynthesis of cutin monomers is also dependent on the activity of lipoxygenases.
HAT3.1, a novel Arabidopsis homeodomain protein containing a conserved cysteine‐rich region
Authors: Schindler Ulrike , Beckmann Holger , Cashmore Anthony R.
Published: March 2003

Homeodomain proteins have been shown to play a major role in the development of various organisms. A novel Arabidopsis homeodomain protein has been isolated based on its capability to interact with a DNA motif derived from the light‐induced cab‐E promoter of Nicotiana plumbaginifolia. The homeodomain of this protein, designated HAT3.1, differs substantially from those in other plant homeobox proteins identified so far. Furthermore, HAT3.1 is unique among other Arabidopsis proteins in that it does not contain a leucine zipper motif following the homeodomain. HAT3.1 is further characterized by an N‐terminal region that shares substantial sequence similarity with the maize homeodomain protein Zmhox1a. Within this conserved region, the presence of eight regularly spaced cysteine/histidine residues was observed reminiscent of other metal‐binding domains. Based on the strong evolutionary conservation of this domain, it is proposed that this region represents a novel protein‐motif which is denoted PHD‐finger (plant homeo‐domain‐finger). In vitro DNA binding studies demonstrated that HAT3.1 is capable of interacting with any DNA fragment larger than 100 bp. Interestingly, a deletion of the N‐terminal PHD‐finger domain completely abolished DNA binding, suggesting that this region may play an important functional role in protein—protein or protein—DNA interaction. HAT3.1 mRNA was primarily detected in root tissue, implying a regulatory function of this protein in root development.
Arabidopsis mutants compromised for the control of cellular damage during pathogenesis and aging
Authors: Greenberg Jean T. , Ausubel Frederick M.
Published: March 2003

Mutants of Arabidopsis thaliana which exhibit accelerated cell death in response to pathogens were isolated and characterized to gain insight into how symptom severity and disease resistance are modulated. This paper describes mutants that fall into one of two complementation groups that were identified. A novel feature of these mutants is that they are unable to control the rate and extent of cell death after exposure to a variety of stimuli that induce senescence responses. Thus, accelerated cell death (acd1) mutants show rapid, spreading necrotic responses to both virulent and avirulent Pseudomonas syringae pv. maculicola or pv. tomato pathogens and to ethylene. In addition, they develop necrotic lesions as they age and are sensitive to mechanical stress in a developmentally controlled manner. The acd1 mutants are also susceptible to opportunistic pathogens and show decreased growth inhibition of a heterologous pathogen of bean. The signal for lesion formation is not necessarily due to pathogens or wounding since plants grown aseptically also develop necrotic lesions. The lesions formed under a variety of conditions resemble those produced during a pathogen‐induced rapid cell death response (the hypersensitive response, HR). Analysis of these acd1 mutants may help to explain the molecular basis of the HR and the relationship between this response and the normal process of senescence.
5′ distal and proximal cis‐acting regulator elements are required for developmental control of a rice seed storage protein glutelin gene
Authors: Zheng Zhenwei , Kawagoe Yasushi , Xiao Shouhua , Li Zhijian , Okita Thomas , Hau Toan Lam , Lin Angy , Murai Norimoto
Published: March 2003

Using a homologous transgenic rice system it is demonstrated that 5′ distal and proximal cis‐acting transcriptional regulatory elements are required for developmental control of a rice seed storage protein glutelin gene. Analyses of gene expression of nine progressively truncated 5′ promoter sequences in developing endosperm indicated the existence of at least one major positive element located from the −5.1 to −1.8 kb region. The functional importance of proximal elements in the context of 1.8 kb promoter was demonstrated by single substitution mutations in the TATA box (−28/−23), AACA motif (−73/−61), and protein‐binding boxes I (−103/−86), II (−124/−110), III (−175/−158) and IV (−200/−217). A simultaneous mutation of five protein‐binding sites (−410/−86) essentially eliminated the activity of the 1.8 kb promoter. Although temporal control of the Gt1 gene during endosperm development was retained in plants of constructs from −5.1 kb to −155 bp, spatial control of the glutelin gene was altered when the 5.1 kb promoter was deleted to −507 bp or −154 bp as the reporter gene activities of these constructs were detected in phloem of leaves, and in stems, sheaths and roots of plants.
Tobacco plants transformed with the O‐acetylserine (thiol) lyase gene of wheat are resistant to toxic levels of hydrogen sulphide gas
Authors: Youssefian Shohab , Nakamura Michimi , Sano Hiroshi
Published: March 2003

O‐acetylserine (thiol) lyase (EC4.2.99.8) is the key enzyme in the cysteine biosynthetic pathway of plants and prokaryotes. The gene, cys1, encoding this enzyme was isolated from a wheat (Triticum aestivum L.) cDNA library, and its deduced amino acid sequence found to show 53% sequence identity with the O‐acetyl‐serine (thiol) lyase of Escherichia coli and Salmonella typhimurium. The deduced peptide consists of 325 amino acids (34.1 kDa), contains a conserved motif for the binding of pyridoxal phosphate, a co‐factor required for enzymatic activity, and an N‐terminal region of 37 amino acid residues resembling chloroplast transit peptides. The identity of cys1 was further demonstrated through complementation of an E. coli cysteine auxotroph, which lacks O‐acetylserine (thiol) lyase, by expression of the wheat gene. Northern blot analysis showed that cys1 is highly expressed in green vegetative and reproductive tissues and in the roots of wheat, as well as in the leaves of several plant species. Southern blot analysis demonstrated that the gene exists as a single copy in the wheat genome. Tobacco plants transformed with cys1 in the sense orientation (sense plants) or antisense orientation (antisense plants), under the control of the CaMV 35S promoter, showed high levels of transcripts. The O‐acetylserine (thiol) lyase activity in transgenic plants was determined, and found to be three‐ to fivefold higher in sense plants than in control plants, but unaffected in antisense transformants. Fumigation experiments with toxic levels of hydrogen sulphide (H2S) gas showed that while sense transformants were highly resistant, control and antisense plants were severely damaged by the treatment.