bluuebunny/crossref_metadata_2025 huggingface dataset:
Cathodoluminescence petrography and isotope geochemistry of KT impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize
Authors: Fouke Bruce W. , Zerkle Aubrey L. , Alvarez Walter , Pope Kevin O. , OcampO Adriana C. , Wachtman Richard J. , Grajales Nishimura Jose Manuel , Claeys Phillipe , Fischer Alfred G.
Published: March 2003

The depositional and diagenetic history of Cretaceous–Tertiary (KT) impact ejecta deposited 360 km from the Chicxulub crater, at Albion Island, Belize, has been investigated using integrated cathodoluminescence and isotopic analyses. A quarry exposes 26 m of Upper Cretaceous Barton Creek Formation dolomitized marine limestone overlain by 16 m of dolomitized Albion Formation impact ejecta. The Albion Formation consists of a lower fine‐grained ≈1‐m‐thick spheroid bed and an upper 15‐m‐thick coarse conglomeratic diamictite bed. A 14‐event paragenetic sequence has been documented and used as a temporal framework to interpret chemostratigraphic trends in bulk rock δ18O, δ13C and 87Sr/86Sr. The uppermost surface of the Barton Creek Formation was subaerially exposed before the KT impact, as indicated by a brecciated palaeosol that caps upsection decreases in δ13C and δ18O. Small 1‐cm‐diameter spheroids in the spheroid bed exhibit vermicular crystalline textures but lack the concentric zonations common to accretionary lapilli. These spheroids are hypothesized originally to have been impact glass or reactive Ca and Mg oxide dusts that adhered to water vapour particles condensing from the cooling impact vapour cloud. The spheroids were dolomitized soon after deposition. The earliest dolomitization in the matrix sediments of the Albion Formation was also post‐depositional, replacing clays formed by devitrification of impact glass. Dolomite and clay 87Sr/86Sr exhibit a distinct symmetrical distribution in the spheroid bed ranging from 0·707745 to 0·707872. Although unproven, this may represent primary changes in the chemical composition of the impact glass. The limestone clasts in the diamictite bed were dolomitized before the KT impact and exhibit upsection decreases in bulk rock 87Sr/86Sr. This suggests that the clasts were excavated from strata equivalent in age or older than the Barton Creek Formation at locations closer to, or in, the Chicxulub crater.
A phylogenetic reconstruction of the Ichneumonoidea (Hymenoptera) based on the D2 variable region of 28S ribosomal RNA
Authors: BELSHAW ROBERT , FITTON MIKE , HERNIOU ELISABETH , GIMENO CARMEN , QUICKE DONALD L. J.
Published: March 2003

The D2 variable region of 28S rRNA was sequenced in a wide range of Ichneumonoidea to provide the first comprehensive phylogenetic reconstruction of this superfamily. The two constituent families (Braconidae and Ichneumonidae) were each found to contain a single well‐supported clade dominated by the more plesiomorphic life history strategies (idiobiosis, ectoparasitism and attacking endoephytic hosts). In the Braconidae this clade corresponds to the morphologically‐defined group called the cyclostomes. In the Ichneumonidae the clade unites for the first time the pimpliformes (sensu Wahl) with most of the phygadeuontoid subfamilies and several small taxa including Adelognathus and Euceros. Relationships among the remaining, more biologically‐derived, subfamilies were less well resolved, but included among the Braconidae a well‐supported microgastroid clade and strong evidence for a sister group relationship between the Agathidinae and Sigalphinae.
Revised concept of Chrysoperla mediterranea (Hölzel), a green lacewing associated with conifers: courtship songs across 2800 kilometres of Europe (Neuroptera: Chrysopidae)
Authors: Henry Charles S. , Brooks Stephen J. , Johnson James B. , Duelli Peter
Published: March 2003

The Holarctic carnea‐group of Chrysoperla green lacewings consists of numerous cryptic, sibling species, distinguished principally by vibrational courtship songs. A European member of this species‐group, C. mediterranea (Hölzel), was originally diagnosed by its dark green coloration, red band across the front of the head, narrow wings, minute basal dilation of the pretarsus and ecological association with pines. Here we describe its courtship and mating song, which uniquely distinguishes the species from all other members of the carnea‐group in Europe. Males and females both produce a single type of song, characterized by a long train of short, closely spaced volleys and nearly constant carrier frequency. Measured song features are nearly invariant across a large geographical range that extends well outside that previously known for C. mediterranea. Principal components analysis confirms the uniqueness of the mediterranea song in comparison with five other sympatric song species of the carnea‐group. Populations which show the mediterranea song phenotype do not necessarily retain all of the traditional morphological features of the species, particularly in eastern parts of the range. Specifically, the green coloration may be less intense, the wings broader and the pretarsal basal dilation larger, resulting in significant morphological overlap with other song species. Larval morphology and ecophysiology also fail to distinguish C. mediterranea from other song species. Based on unique song phenotype, however, we conclude that C. mediterranea is a valid biological species, which can also be recognized in museum collections when a suite of physical attributes is used.
Macrosiphum on ferns: taxonomy, biology and evolution, including the description of three new species (Hemiptera: Aphididae)
Authors: Jensen Andrew S. , Holman Jaroslav
Published: March 2003

The phytophagous insect fauna of ferns has often been described as depauperate, and some have pointed to the paucity of evidence for adaptive radiation of insect groups feeding specifically on ferns. This paper examines the world's species of fern‐specific Macrosiphum aphids and attempts to determine whether fern‐feeding is a monophyletically derived trait in Macrosiphum. All sixteen species reported to feed on ferns, including three new species, were included in a cladistic analysis, along with fifteen other Macrosiphum species selected to represent the diversity of the genus, Papulaphis sleesmani (Pepper), because of its similarity to fern‐feeding Macrosiphum, and Sitobion avenae (Fabricius), which was used as outgroup. The results gave good support for the monophyly of fifteen of the sixteen fern‐feeders, and also supported a clade consisting of these fifteen fern‐feeders plus Macrosiphum equiseti (Holman), an Equisetum‐specific aphid. One species, Macrosiphum lapponicum Shaposhnikov, from northern Russia, was concluded to be unrelated to other fern‐feeding Macrosiphum. Whether this species truly feeds on a fern requires confirmation. Taxonomic and biological notes are provided for all fern‐feeding Macrosiphum of the world. These include one new combination, Macrosiphum cyatheae (Holman) comb.n., and three new species: Macrosiphum longirostratum sp.n. on Woodsia mollis and Woodsia sp. from Mexico (Michoacán), Macrosiphum miho sp.n. on ‘Aspidium’ sp. from the U.S.A. (Illinois) and Macrosiphum rebecae sp.n. on Adiantum sp. from Mexico (Michoacán). Keys to apterous and alate viviparae of Macrosiphum living on ferns are given.
Phylogeny and taxonomy of the damselfly genus Enallagma and related taxa (Odonata: Zygoptera: Coenagrionidae)
Authors: May Michael L.
Published: March 2003

Abstract The zygopteran genus Enallagma has been the subject of numerous behavioural and ecological studies, but phylogenetic relationships among species have been examined only within eastern North America, and even the composition and diagnosis of the genus are unclear on a world‐wide basis. Most authorities currently recognize about seventy species within Enallagma, comprising two major radiations, in North America and Africa. This study, using morphological data, demonstrates that the North American and a few related Palaearctic species form a monophyletic group that is quite distinct from the African species. The latter are themselves divided into at least three, and probably four, separate clades, one of which may be related to E. parvum of India. Consequently, three of Kennedy's long disused genera, Africallagma, Amphiallagma and Proischnura (Kennedy, 1920) are resurrected and two new genera, Azuragrion gen.n. and Pinheyagrion gen.n. are established for the remaining African taxa. Finally, Enallagma is divided into two subgenera, Enallagma s.s., the typical ‘bluets’, including many North American, Holarctic and Palaearctic species, and Chromatallagma subgen.n., comprising a group of species of more variable colour that is confined to North America, the Caribbean and northernmost South America.
Sedimentological interpretation of high‐resolution seismic facies in the Lower Freshwater Molasse (Chattian, western Switzerland)
Authors: Morend  , Pugin  , Gorin
Published: March 2003

Two shallow high‐resolution seismic reflection profiles acquired across part of the western Molasse Basin near Geneva have been processed and interpreted. Three seismic facies have been identified in the Chattian Lower Freshwater Molasse. They are associated with depositional environments in a sand‐bed meandering river setting. A distal floodplain environment, characterized by alternations of thick shales and thin sandstones and by palustrine‐lacustrine limestones, is represented by a poorly reflective seismic facies with discontinuous reflections. Thick sand‐filled channels generate a highly reflective facies with continuous reflections. Highly re‐flective and continuous reflections characterize the third facies, which is generated by shales and thick proximal clastic deposits, indicative of a proximal floodplain environment. This scientific approach leads to applications in subsurface lithological predictions associated with geotechnical and environmental assessments in the densely populated Swiss Plateau where Molasse sediments form a large part of the substrate.
Surface Rupture of the 1857 Southern Italian Earthquake?
Authors: Benedetti L. , Tapponnier P. , King G.C.P. , Piccardi L.
Published: March 2003

In October 1862, Robert Mallet published an extensive study of a large earthquake that occurred on 16 December 1857, 150 km south‐east of Naples. This event is one of the most destructive ever recorded in Italy. Although continental earthquakes of similar size are almost invariably associated with surface faulting, Mallet did not identify any surface rupture and subsequent workers have also failed to find surface traces. Using satellite images and aerial photographs as a guide, we examined two prominent Quaternary normal fault systems in the field. Flanking the Val d’Agri and the Val di Diano, both trend NW–SE and dip to the SW. The distribution of damage suggests that one or both moved in 1857. On one fault segment in Val d’Agri, we found a 2.5‐m high scarp whose youthfulness and height suggest it is due to the 1857 earthquake. Comparison of the observed slip with rates derived from geomorphic evidence suggests a recurrence time for 1857 type events of about 3000 years. While the new data we provide are consistent with the event having a magnitude of Ms≈ 7.0, there are also grounds for supposing it might have been bigger.
Extensive volcaniclastic deposits at the Mid‐Atlantic Ridge axis: results of deep‐water basaltic explosive volcanic activity?
Authors: Fouquet  , Eissen  , Ondréas  , Barriga  , Batiza  , Danyushevsky
Published: March 2003

A recent mapping survey followed by submersible diving investigations revealed the existence of extensive volcaniclastic deposits on three adjoining, progressively deeper, segments of the Mid‐Atlantic Ridge, south‐west of the Azores. The maximum water depth at which subaqueous magmatic and hydro‐magmatic explosive processes can occur is controversial. This discovery provides fundamental constraints on the dynamics of deep subaqueous volcanic eruptions. Using multibeam bathymetry, sonar image interpretations, submersible observations, volcaniclastic sample descriptions and chemical analysis, evidence of extensive deep water (up to –1700 m) magmatic explosive activity of basalt at the axis of a spreading Mid‐Ocean Ridge is documented for the first time.
1822 earthquake‐triggered homogenite in Lake Le Bourget (NW Alps)
Authors: Chapron E. , Beck C. , Pourchet M. , Deconinck J‐F.
Published: March 2003

High‐resolution textural signatures of an earthquake‐induced historical ‘homogenite’ layer are presented, as well as its 3D distribution. This homogeneous deposit is correlated with the AD 1822 event (VII–VIII MSK intensity), the main historical earthquake of the French outer Alps, using 210Pb dating and historical chronicles. During this earthquake a violent lake water oscillation was reported (seiche effect). In the present study we discuss the influence of lake water oscillations during earthquake‐induced subaqueous slide, through a pluridisciplinary analysis of subbottom sediments including high‐resolution seismic, sidescan sonar and short gravity coring.
Mélange formation by subduction erosion: the case of the Osa mélange in southern Costa Rica
Authors: Meschede  , Zweigel  , Frisch  , Völker
Published: March 2003

The convergent plate margin off the Osa peninsula in southern Costa Rica is characterized by the indentation of the Cocos ridge at 4–5 Ma. The indentation causes the uplift of the Osa mélange which we interpret to represent an exhumed major channel for the transport of tectonically eroded material down into the subduction zone. We present evidence that, similar to the Nicoya segment of the Costa Rica convergent margin, subduction erosion rather than accretion has been the dominant process along the plate boundary. The composition of the Osa mélange is dominated by tectonized material of the upper‐plate Nicoya ophiolite complex (basalt, radiolarite, limestone). Strong deformation is concentrated in numerous discrete shear zones and produced the layered fabric of large rock volumes, which partly experienced temperatures > 200°C. We thus interpret the Osa mélange to be a product of subduction erosion at the base of the outer arc wedge structure.
Active faults in the Sea of Marmara, western Turkey, imaged by seismic reflection profiles
Authors: Parke  , Minshull  , Anderson  , White  , McKenzie  , Kuşçu  , Bull  , Görür  , Şengör
Published: March 2003

Turkey is moving westward relative to Eurasia, thereby accommodating the collision between Arabia and Eurasia. This motion is mostly taken up by strike‐slip deformation along the North and East Anatolian Faults. The Sea of Marmara lies over the direct westward continuation of the North Anatolian Fault zone. Just east of the Sea of Marmara, the North Anatolian Fault splits into three strands, two of which continue into the sea. While the locations of the faults are well constrained on land, it has not yet been determined how the deformation is transferred across the Sea of Marmara, onto the faults on the west coast of Turkey. We present results from a seismic reflection survey undertaken to map the faults as they continue through the three deep Marmara Sea basins of Çlnarclk, Central Marmara and Tekirdag, in order to determine how the deformation is distributed across the Sea of Marmara, and how it is taken up on the western side of the sea. The data show active dipping faults with associated tilting of sedimentary layers, connecting the North Anatolian Fault to strike‐slip faults that cut the Biga and Gallipoli Peninsulas.
Exhumation of the Central Alps: evidence from 40Ar/39Ar laserprobe dating of detrital white micas from the Swiss Molasse Basin
Authors: Von Eynatten H. , Schlunegger F. , Gaupp R. , Wijbrans J.R.
Published: March 2003

40Ar/39Ar single‐grain laserprobe dating of detrital white micas from early Oligocene to middle Miocene (31–14 Ma) sedimentary rocks of the central Swiss Molasse basin reveals three distinct clusters of cooling ages for the hinterland. Two Palaeozoic age clusters reflect cooling after the Variscan orogeny with only limited reheating during the Alpine orogeny. The third Tertiary age cluster reflecting late Alpine cooling is restricted to sediments younger than 20 Myr old. Micas with cooling ages < 30 Myr are interpreted to originate from the footwall of the Simplon detachment fault, thus representing formerly exposed upper levels of the present‐day Lepontine metamorphic dome. Erosion of these levels is reflected by an increase of low‐grade metamorphic lithic grains in the sandstones. This interpretation puts constraints on the timing of exhumation as well as on the evolution of the drainage pattern of the Central Alps.
The marine osmium isotope record
Authors: Peucker‐Ehrenbrink B. , Ravizza G.
Published: March 2003

Over the past decade the marine osmium isotope record has been developed into a new tracer in palaeoceanographic research. Several analytical developments, particularly in the past few years, have significantly increased our ability to study the behaviour of osmium in the surficial environment. The 187Os/188Os and osmium concentration of seawater, river water, rain, and hydrothermal vent fluids have been measured directly. Recently, the behaviour of osmium in estuaries–critical for estimating the marine residence time of osmium–has been studied. Our knowledge of the surficial osmium cycle has thus significantly improved. In addition, reconstructions of past variations in the marine 187Os/188Os recently have been extended back into the Mesozoic. This review attempts to summarize our current understanding of the marine osmium system–present and past.

The 187Os/188Os of seawater during the Cenozoic to first order mimics the marine 87Sr/86Sr record. It is therefore tempting to interpret both records as reflecting increased input of radiogenic osmium and strontium resulting from enhanced continental weathering regulated by climatic/tectonic processes. However, the marine osmium isotope system differs fundamentally from the marine strontium isotope system. This review emphasizes three important differences. First, large impacts are capable of resetting the 187Os/188Os to unradiogenic values without significantly affecting the marine strontium system. Second, organic‐rich sediments are characterized by high 187Re/188Os; resulting 187Os/188Os ingrowth‐trajectories are similar to the average slope of the Cenozoic 187Os/188Os seawater record. Trends towards more radiogenic 187Os/188Os seawater therefore can be caused by weathering of organic‐rich sediments at a constant rate. Third, the marine residence time of osmium is sufficiently short to capture short‐periodic (glacial‐interglacial) fluctuations that are inaccessible to the buffered marine strontium isotope system. This offers the opportunity to discriminate between high‐frequency (climatic) and low‐frequency (tectonic) forcing.
Chemostratigraphy of Neoproterozoic carbonates: implications for ‘blind dating’
Authors: Melezhik Victor A. , Gorokhov Igor M. , Kuznetsov Anton B. , Fallick Anthony E.
Published: March 2003

The δ13Ccarb and 87Sr/86Sr secular variations in Neoproteozoic seawater have been used for the purpose of ‘isotope stratigraphy’ but there are a number of problems that can preclude its routine use. In particular, it cannot be used with confidence for ‘blind dating’. The compilation of isotopic data on carbonate rocks reveals a high level of inconsistency between various carbon isotope age curves constructed for Neoproteozoic seawater, caused by a relatively high frequency of both global and local δ13Ccarb fluctuations combined with few reliable age determinations. Further complication is caused by the unresolved problem as to whether two or four glaciations, and associated negative δ13Ccarb excursions, can be reliably documented. Carbon isotope stratigraphy cannot be used alone for geological correlation and ‘blind dating’. Strontium isotope stratigraphy is a more reliable and precise tool for stratigraphic correlations and indirect age determinations. Combining strontium and carbon isotope stratigraphy, several discrete ages within the 590–544 Myr interval, and two age‐groups at 660–610 and 740–690 Myr can be resolved.
The northern Patagonia Somuncura plateau basalts: a product of slab‐induced, shallow asthenospheric upwelling?
Authors: De Ignacio Cristina , López Ivan , Oyarzun Roberto , Márquez Alvaro
Published: March 2003

The Meseta de Somuncura forms the largest basaltic plateau (20 000 km2) of southern Argentina (extra‐Andean domain). Most of these tholeiitic to alkaline rocks were extruded at ˜ 25 Ma (late Oligocene). The absence of rifting–thinning processes, plume activity, or slab‐window phenomena leaves only one major possibility for the generation of Somuncura: asthenospheric (‘OIB‐like’) corner flow leading to a transient thermal anomaly above the subducting plate. It is suggested herein that the intake of hot asthenosphere was forced into a favourable topography (concave‐up) of the subducting plate, when a major plate reorganization event (Farallon to Nazca) was taking place in late Oligocene to early Miocene time. The fast and vigorous intake of asthenosphere would have been induced by slab roll‐back, leading to decoupling of the subducting plate. The Somuncura volcanic episode can be regarded as a marker of the passage from the extremely oblique subduction of Farallon, to the birth of the Nazca plate and roughly perpendicular convergence between South America and Nazca.
A Holocene coastal aeolian system, Vejers, Denmark: landscape evolution and sequence stratigraphy
Authors: Clemmensen L. B. , Andreasen F. , Heinemeier J. , Murray A.
Published: March 2003

Stratigraphical studies of Holocene aeolian strata formed at the inner margin of the Vejers dunefield on the west coast of Jutland have contributed to an understanding of aeolian landscape evolution in a storm‐influenced temperate climate belt. The aeolian system was characterized by alternating periods of activity and stabilization. Intense inland sand transport occurred just after 4000 BC, 2300 BC, 600 BC and AD 300–500. Periods of sand movement were apparently initiated during climatic shifts towards more stormy conditions, and they may be linked to a millennial‐scale cycle in North Atlantic Holocene climate. Preservation of the accumulated aeolian sand records a long‐term rise in ground‐water level. Water table behaviour was initially controlled by sea level, but after about 2300 BC water table rise was linked to coastal outbuilding and to an overall change towards a more humid climate.
No major thermal event on the mid‐Cretaceous Côte d’Ivoire–Ghana Transform Margin
Authors: Wagner T. , Pletsch T.
Published: March 2003

Transient mid‐Cretaceous thermal uplift induced by lateral heating from passing oceanic lithosphere is often invoked as a mechanism for the formation of the Côte d’Ivoire–Ghana basement ridge in the Equatorial Atlantic. This heating event should have affected mid‐Cretaceous sedimentary rocks along the ridge. However, organic maturity and clay mineral data on the thermal evolution of these rocks suggest that burial temperatures did not exceed 80 °C and that palaeo–geothermal gradients are not anomalous. Optical petrography and the stratigraphic pattern of temperature‐sensitive parameters indicate that higher palaeotemperature estimates are related to admixtures of preheated, detrital organic and inorganic matter. Erosion brought the sediments to their present shallow burial depths. Lack of evidence for significant thermal alteration implies that either thermal exchange between oceanic and continental lithosphere along the Côte d’Ivoire–Ghana Transform Margin was negligible, or that lateral heating by oceanic lithosphere was not strong enough to affect the sedimentary cover of the basement ridge.
A coupled petrological–tectonic model for sedimentary basin evolution: the influence of metamorphic reactions on basin subsidence
Authors: Petrini K. , Connolly J. A. D. , Podladchikov Yu. Yu.
Published: March 2003

The lithosphere is subject to fluctuations in temperature and pressure during the formation of sedimentary basins. These fluctuations cause metamorphic reactions that change the density of the lithosphere, which, in turn, influences basin subsidence. This contribution develops a model for sedimentary basin formation to assess the importance of this coupling. The model shows that basin subsidence is significantly affected by metamorphic densification. Compared to results obtained with cruder density models, metamorphic densification accelerates subsidence in the initial post‐rifting stages as garnet becomes stable over an increasing depth interval within the mantle, an effect that amplifies the crust–mantle density contrast. For models with an extraordinarily cold lithosphere, uplift is generated as a late stage of basin evolution. In general, subsidence is not smooth but occurs instead in small steps reflecting periods of accelerated/decelerated subsidence. For typical crustal thicknesses, subsidence is controlled largely by reactions in the mantle, and particularly those determining garnet stability.
Tracking abrupt climate change in the Southern Hemisphere: a seismic stratigraphic study of Lago Cardiel, Argentina (49°S)
Authors: Gilli Adrian , Anselmetti Flavio S. , Ariztegui Daniel , Bradbury J. Platt , Kelts Kerry R. , Markgraf Vera , McKenzie Judith A.
Published: March 2003

Lake sediments from a closed basin in southern Patagonia (Argentina) provide a continental archive with which to reconstruct climate change and to test the interhemispheric synchroneity of abrupt events. High‐resolution sub‐bottom seismic profiles of Lago Cardiel indicate substantial lake‐level changes since the late Pleistocene, which were identified and dated in a series of long piston cores. These data allow the reconstruction of the regional water balance at 49="PSFT−BC"202S since the late glacial. The seismic stratigraphy reveals a dry late glacial climate with a desiccation of the basin around 11 220 yr BP (14C). Lake level rapidly increased by 135 m at the Holocene transition. Following the early Holocene highstand at + 55 m, lake level never dropped significantly below modern level. The palaeoclimate changes implied by the Lago Cardiel record are out‐of‐phase with those implied by records from tropical South America and demonstrate considerable latitudinal asynchroneity in the climate evolution of this continent.
Quartz silt in mudrocks as a key to sequence stratigraphy (Kimmeridge Clay Formation, Late Jurassic, Wessex Basin, UK)
Authors: Williams Carolyn J. , Hesselbo Stephen P. , Jenkyns Hugh C. , Morgans‐Bell Helen S.
Published: March 2003

Sequence‐stratigraphic interpretation of mudrocks is often carried out using proxy indicators for grain size or by consideration of other aspects of lithology thought to relate to sea‐level change, such as organic‐matter content. An alternative stratigraphic analysis, based on direct estimation of quartz‐silt content, was carried out on a major Late Jurassic mudrock (and oil source rock), the Kimmeridge Clay Formation of the Wessex Basin, Dorset, UK. The new data, generated by backscatter SEM, X‐ray and image analysis, show decametre‐scale stratigraphic patterns that are incompatible with many previous sequence‐stratigraphic interpretations based on gamma‐ray logs or visual lithofacies and biofacies description. Correlation with a basin‐margin section in the Boulonnais, northern France, indicates that silt‐rich intervals in basinal facies are coeval, within the limits of biostratigraphic resolution, with shallow‐water sand‐rich packages on the margin. Variation in silt content in the Kimmeridge Clay therefore appears to be a record of relative sea‐level change of at least regional extent. It is suggested that analysis of silt content offers the most reliable basis for generation of a regional sequence stratigraphy in basinal mudrocks. A revised relative sea‐level curve for the Wessex Basin Kimmeridgian and early Tithonian is presented based on this premise.
A refreshing 3D view of an ancient sediment collapse and slope failure
Authors: Huvenne Veerle A. I. , Croker Peter F. , Henriet Jean‐Pierre
Published: March 2003

The combined analysis of high‐resolution 2D seismics and an industrial 3D seismic data volume from the western Porcupine Basin, offshore SW Ireland, revealed an unusual picture of a buried sediment collapse and slope failure. A proportionally thin (≤ 85 m) but vast (> 750 km2) slab of consolidated sediments started to slide downslope, in the meantime breaking into hundreds of vertically undisturbed blocks, up to 500 m in diameter. The most probably overpressured underlying horizon seems to have liquefied and acted as a slide plane until the excess pore pressure had dissipated. Then – still very early in the slide development – the process stopped, freezing the failure at its initial stage.
The snowball Earth hypothesis: testing the limits of global change
Authors: Hoffman Paul F. , Schrag Daniel P.
Published: March 2003

The gradual discovery that late Neoproterozoic ice sheets extended to sea level near the equator poses a palaeoenvironmental conundrum. Was the Earth's orbital obliquity > 60° (making the tropics colder than the poles) for 4.0 billion years following the lunar‐forming impact, or did climate cool globally for some reason to the point at which runaway ice‐albedo feedback created a `snowball' Earth? The high‐obliquity hypothesis does not account for major features of the Neoproterozoic glacial record such as the abrupt onsets and terminations of discrete glacial events, their close association with large (> 10‰) negative δ13C shifts in seawater proxies, the deposition of strange carbonate layers (`cap carbonates') globally during post‐glacial sea‐level rise, and the return of large sedimentary iron formations, after a 1.1 billion year hiatus, exclusively during glacial events. A snowball event, on the other hand, should begin and end abruptly, particularly at lower latitudes. It should last for millions of years, because outgassing must amass an intense greenhouse in order to overcome the ice albedo. A largely ice‐covered ocean should become anoxic and reduced iron should be widely transported in solution and precipitated as iron formation wherever oxygenic photosynthesis occurred, or upon deglaciation. The intense greenhouse ensures a transient post‐glacial regime of enhanced carbonate and silicate weathering, which should drive a flux of alkalinity that could quantitatively account for the world‐wide occurrence of cap carbonates. The resulting high rates of carbonate sedimentation, coupled with the kinetic isotope effect of transferring the CO2 burden to the ocean, should drive down the δ13C of seawater, as is observed. If cap carbonates are the `smoke' of a snowball Earth, what was the `gun'? In proposing the original Neoproterozoic snowball Earth hypothesis, Joe Kirschvink postulated that an unusual preponderance of land masses in the middle and low latitudes, consistent with palaeomagnetic evidence, set the stage for snowball events by raising the planetary albedo. Others had pointed out that silicate weathering would most likely be enhanced if many continents were in the tropics, resulting in lower atmospheric CO2 and a colder climate. Negative δ13C shifts of 10–20‰ precede glaciation in many regions, giving rise to speculation that the climate was destabilized by a growing dependency on greenhouse methane, stemming ultimately from the same unusual continental distribution. Given the existing palaeomagnetic, geochemical and geological evidence for late Neoproterozoic climatic shocks without parallel in the Phanerozoic, it seems inevitable that the history of life was impacted, perhaps profoundly so.
Lead isotope systematics of Late Cretaceous – Tertiary Andean arc magmas and associated ores between 8°N and 40°S: evidence for latitudinal mantle heterogeneity beneath the Andes
Authors: Chiaradia Massimo , Fontboté Lluís
Published: March 2003

ABSTRACT Lead isotope variability of magmatic arc rocks and associated mineralization of the Central Andes is usually considered to be the result of mixing between a homogeneous mantle and heterogeneous continental crust. About 230 new lead isotope data on the Northern and Central Andes allow us to compare for the first time lead isotope systematics of the Late Cretaceous – Tertiary arc magmatism and associated mineralization along the Andean chain between 8°N and 40°S. Lead isotope compositions indicate mixing between mantle and upper crustal rocks along the whole Andean chain. Additionally, we have found that mantle end‐members of the Late Cretaceous – Tertiary magmatism are heterogeneous and systematically shifted towards less radiogenic 206Pb/204Pb compositions from north to south along the Andes. This heterogeneity most likely results from mixing between a low radiogenic mantle, possibly carrying a DMM or EM I component, and a more radiogenic mantle, possibly carrying an HIMU component. Thus, our results imply that lead isotope variability of Andean magmas at the continental scale is caused not only by crustal but also by mantle heterogeneity.
The north‐eastern Polish anorthosite massifs: petrological, geochemical and isotopic evidence for a crustal derivation
Authors: Wiszniewska Janina , Claesson Stefan , Stein Holly , Auwera Jacqueline Vander , Duchesne Jean‐Clair
Published: March 2003

ABSTRACT Deeply buried 1.5 Ga Polish anorthosites, accessible only by bore holes, reveal diagnostic features of some massif‐type anorthosites (polybarism, jotunitic parent magma), diapirically emplaced in the mid crust together with the rapakivi granites of the EW‐trending Mazury complex, intruded along a major crustal discontinuity. Geochemical modelling and isotope data corroborate recent experimental work on the basaltic system in dry conditions: the source rock of the parental magma is a gabbronorite, necessarily lying in the lower crust. Since no Archaean crust is known in the region, high initial 188Os/187Os ratios for sulphide‐oxide isochrons and negative εNd values are best accounted for by melting a ∼ 2.0 Ga mafic crust.
Stringent repression and homogeneous de‐repression by tetracycline of a modified CaMV 35S promoter in intact transgenic tobacco plants
Authors: Gatz Christiane , Frohberg Claus , Wendenburg Regina
Published: March 2003

A cauliflower mosaic virus (CaMV) 35S promoter derivative, which is tightly repressed by the Tn 10 encoded Tet repressor in a transient expression system as well as in transgenic plants has been constructed. After treatment of transgenic plants with tetracycline (Tc) the activity of the reporter enzyme β‐glucuronidase (GUS) increased up to 500‐fold in tissue culture as well as under greenhouse conditions. Efficient derepression was achieved by Tc uptake through the roots as well as by Tc treatment of leaves of intact plants. As Tc is not very stable in the plants, this system can also be used for a transient expression of a transgene. This system provides a unique tool for regenerating transgenic plants carrying a repressed transgene and for efficiently de‐repressing its activity by a specific inducer at any time point of further development.
Complementation of Saccharomyces cerevisiae auxotrophic mutants by Arabidopsis thaliana cDNAs
Authors: Minet Michéle , Dufour Marie‐Elisabeth , Lacroute François
Published: March 2003

An Arabidopsis thaliana cDNA bank has been constituted in a Saccharomyces cerevisiae expression vector based on the phosphoglycerate kinase (PGK) promoter and terminator. This bank was used to complement eight S. cerevisiae auxotrophic markers. All of them were corrected. These results confirm the quality of the bank and the feasibility of cloning plant genes by yeast mutant complementation. The cDNA complementing the ura1 yeast mutant was sequenced, analysed and shown to encode a dihydroorotic (DHO) dehydrogenase sequence.
Specific perception of subnanomolar concentrations of chitin fragments by tomato cells: induction of extracellular alkalinization, changes in protein phosphorylation, and establishment of a refractory state
Authors: Felix Georg , Regenass Martin , Boller Thomas
Published: March 2003

Suspension‐cultured tomato cells respond to yeast cell wall preparations with a rapid, transient alkalinization of the culture medium. Depending on the dose of the stimulus, the pH starts to increase after a lag period of about 0.5–2 min and reaches a transient maximum, up to 0.6 pH units above the initial value, after 2–4 min. Using this alkalinization response as a rapid and convenient assay, a sensitive perception system for small chitin fragments was revealed in the tomato cells. Chitin oligomers with four or more N‐acetylglucosamine residues stimulated the alkalinization response significantly at concentrations below 10 pM and half‐maximally at concentrations of 100 pM. About 10 000‐fold higher concentrations of the trimer, N,N′,N″‐triacetylchitotriose, were required to elicit similar responses. For up to 8 h after a first treatment with 10 nM of the tetramer, N,N′,N″,N‴‐tetraacetyl‐chitotetraose, cells did not respond to a second stimulation with any of the chitin fragments. Throughout this refractory period, however, cells remained fully responsive to preparations of fungal xylanase, another stimulus which induces a more permanent alkalinization after a lag phase of more than 2 min. The alkalinization response to these two qualitatively different stimuli was paralleled by the same characteristic changes in the pattern of protein phosphorylation, detected by in vivo pulse‐labelling with [32P]phosphate for 30 sec. The onset of the alkalinization and of the changes in protein phosphorylation coincided in both cases, and both phenomena were blocked by the protein kinase inhibitor K‐252a. Although the mechanism underlying the extracellular pH increase is unknown, activation of the alkalinization response provides a sensitive and convenient assay to investigate early events in chemoperception of microbial signals by plant cells.
A 330 bp region of the spinach nitrite reductase gene promoter directs nitrate‐inducible tissue‐specific expression in transgenic tobacco
Authors: Rastogi Rajeev , Back Eduard , Schneiderbauer Alois , Bowsher Caroline G. , Moffatt Barbara , Rothstein Steven J.
Published: March 2003

Nitrite reductase is an enzyme in the nitrate assimilatory pathway whose expression is induced upon the addition of nitrate. Furthermore, it is known to be located in chloroplasts in leaves and plastids in roots. A 3.1 kb 5′ upstream region of the spinach nitrite reductase (NiR) gene promoter was shown previously to confer nitrate inducibility on the β‐glucuronidase (GUS) reporter gene expression in both the leaves and the roots of transgenic tobacco plants. In the present study, this 3.1 kb promoter fragment as well as a series of promoter deletion constructs, fused to a GUS gene, were utilized to delineate the region of NiR promoter involved in nitrate regulation of NiR expression by studying the cellular localization of NiR—GUS expression as well as its regulation by nitrate. In plants carrying the longest promoter fragment (−3100 from the transcription start site) and promoter sequences progressively deleted to −330 bp, the expression of GUS was markedly increased in the presence of nitrate, and this expression was found to occur in mesophyll cells in leaves and in the vascular tissues of stem and roots. When nitrate was added to NiR—GUS plants grown in the absence of nitrate, significant levels of GUS activity could be seen in the roots after 2 h and in the leaves after 6 h. Further 5′ deletion of the promoter to −200 bp abolished the nitrate induction of GUS expression, indicating that the 130 bp region of the nitrite reductase promoter located between −330 and −200 is required for full nitrate‐inducible tissue‐specific expression.
Flowering in darkness in Arabidopsis thaliana
Authors: Araki Takashi , Komeda Yoshibumi
Published: March 2003

A modified method for studying the initiation of flowering in darkness (dark flowering, DF) in Arabidopsis thaliana has been developed, and the DF process has been examined with the aid of late‐flowering mutants. A majority of plants developed floral buds by the use of liquid‐shaken cultures in darkness. The late‐flowering phenotype in gi and co mutants and early‐flowering phenotype in a hy2 mutant disappeared in DF. It was found that wild‐type plants grown under DF conditions express light‐regulated genes and develop appropriate leaf architecture, as do the light‐grown plants, without the apparent differentiation of chloroplasts. The shift experiments from darkness to light revealed the critical duration of growth in darkness for the initiation of DF. These results indicate that the DF process to the initiation of flowering is a mode of development distinct from that in light in Arabidopsis.
Analysis of the role of the late‐flowering locus, GI, in the flowering of Arabidopsis thaliana
Authors: Araki Takashi , Komeda Yoshibumi
Published: March 2003

The mutation gigantea (gi) is recessive and belongs to the late‐flowering mutations in Arabidopsis thaliana. The late‐flowering mutations result in a pronounced delay in flowering due to a prolonged phase of vegetative growth, which is manifested by an increased number of primary foliage leaves in the rosette (i.e. vegetative nodes). To examine the nature of the gi mutation, detailed phenotypic analysis was carried out for three representative mutant alleles. The results indicate that gi mutants have a defect in the promotion of the floral induction process by long‐day photoperiods and not in the flowering process per se. Temperature‐shift experiments using a partially conditional allele were employed to determine the timing of the functional requirement for the product of the GI locus. The end of the deduced functional period corresponds to the period at which transition of the apical meristem from the vegetative to the reproductive phase occurs. Such timing is in good agreement with the postulated role of the GI locus. These results demonstrate that the GI locus is involved in the promotion of floral initiation (entrance of the meristem into the transitional stage) by long‐day photoperiods.
Fertile transgenic wheat from microprojectile bombardment of scutellar tissue
Authors: Becker D. , Brettschneider R. , Lörz H.
Published: March 2003

A reproducible transformation system for hexaploid wheat was developed based on particle bombardment of scutellar tissue of immature embryos. Particle bombardment was carried out using a PDS 1000/He gun. Plant material was bombarded with the plasmid pDB1 containing the β‐glucuronidase gene (uidA) under the control of the actin‐1 promoter of rice, and the selectable marker gene bar (phosphinothricin acetyltransferase) under the control of the CaMV 35S promoter. Selection was carried out using the herbicide Basta (Glufosinate‐ammonium). From a total number of 1050 bombarded immature embryos, in seven independent transformation experiments, 59 plants could be regenerated. Putative transformants were screened for enzyme activity by the histochemical GUS assay using cut leaf material and by spraying the whole plants with an aqueous solution of the herbicide Basta. Twelve regenerants survived Basta spraying and showed GUS‐activity. Southern‐blot analysis indicated the presence of introduced foreign genes in the genomic DNA of the transformants and both marker genes were present in all plants analysed.

To date, four plants have been grown to maturity and set seed. Histochemically stained pollen grains showed a 1:1 segregation of the uidA gene in all plants tested. A 3:1 segregation of the introduced genes was demonstrated by enzyme activity tests and Southern blot analysis of R1 plants.
Expression of a chimeric uidA gene indicates that polycistronic mRNAs are efficiently translated in tobacco plastids
Authors: Staub Jeffrey M. , Maliga Pal
Published: March 2003

Polycistronic mRNAs are the predominant form of plastid primary transcripts. To determine if there is internal initiation of translation of promoter‐distal open reading frames, a promoterless uidA reporter gene was integrated into the tobacco plastid genome downstream of the rbcL gene. Monocistronic uidA mRNA does not accumulate from the promoterless uidA construct. However, due to inefficient rbcL transcription termination, a polycistronic transcription unit is created that contains the uidA gene as the second cistron. Numerous stop codons in all three reading frames between the rbcL and uidA coding regions ensure that translation of uidA initiates only from the correct start codon. The encoded reporter gene product, β‐glucuronidase (GUS) accumulates to high levels in the transplastomic plants indicating that promoter‐distal cistrons can be efficiently translated in plastids.
Regulation of the Osem gene by abscisic acid and the transcriptional activator VP1: analysis of cis‐acting promoter elements required for regulation by abscisic acid and VP1
Authors: Hattori Tsukaho , Terada Tomoko , Hamasuna Satoshi
Published: March 2003

Osem, a rice gene homologous to the wheat Em gene, which encodes one of the late‐embryogenesis abundant proteins was isolated. The gene was characterized with respect to control of transcription by abscisic acid (ABA) and the transcriptional activator VP1, which is involved in the ABA‐regulated gene expression during late embryo‐genesis. A fusion gene (Osem‐GUS) consisting of the Osem promoter and the bacterial β‐glucuronidase (GUS) gene was constructed and tested in a transient expression system, using protoplasts derived from a suspension‐cultured line of rice cells, for activation by ABA and by co‐transfection with an expression vector (35S‐Osvp1) for the rice VP1 (OSVP1) cDNA. The expression of Osem‐GUS was strongly (40‐ to 150‐fold) activated by externally applied ABA and by over‐expression of (OS)VP1. The Osem promoter has three ACGTG‐containing sequences, motif A, motif B and motif A′, which resemble the abscisic acid‐responsive element (ABRE) that was previously identified in the wheat Em and the rice Rab16. There is also a CATGCATG sequence, which is known as the Sph box and is shown to be essential for the regulation by VP1 of the maize anthocyanin regulatory gene C1. Focusing on these sequence elements, various mutant derivatives of the Osem promoter in the transient expression system were assayed. The analysis revealed that motif A functions not only as an ABRE but also as a sequence element required for the regulation by (OS)VP1.
Alternative RNA products from a rice homeobox gene
Authors: Tamaoki Masanori , Tsugawa Hidehito , Minami Ei‐ichi , Kayano Toshiaki , Yamamoto Naoki , Kano‐Murakami Yuriko , Matsuoka Makoto
Published: March 2003

Three cDNA clones were isolated from rice, OSH42, OSH44 and OSH45, which encode homeodomain sequences in the C‐terminal region. The sequences of these cDNAs differ in the N‐ and C‐termini, but they share an identical homeodomain and an acidic amino acid‐rich region. The transcripts corresponding to these cDNAs are encoded by a single gene on rice chromosome 8. Differential transcription initiation results in a large transcript comprised of exons 1 and 3–7 and a smaller transcript comprised of exons 2–7. The larger transcript is constitutively expressed in all tissues tested, while the smaller transcript is expressed in leaves, stems and rachis but not in roots, flowers, or suspension callus cells. Alternative splicing also occurs at three different acceptor sites in intron 6 in all tissues tested. The GAL4 DNA‐binding domain of yeast was used to study the function of various protein domains. The acidic amino acid‐rich region activates the expression of a reporter gene controlled by the GAL4 target sequence, indicating that it functions as a transactivation domain. The larger transcript encodes a unique alanine and glycinerich region on the N‐terminal side of the acidic region, which is not encoded by the smaller transcript. This region completely suppresses the transactivation activity of the acidic region. This suggests that the product of the larger transcript fails to activate the expression of the target gene(s) while the product of the smaller transcript activates the expression of its target gene(s).