Slope‐to‐basin stratigraphic evolution of the northwestern Great Bahama Bank (Bahamas) during the Neogene to Quaternary: interactions between downslope and bottom currents deposits

Multichannel high‐resolution seismic data along the northwestern margin of the Great Bahama Bank (GBB), Bahamas, detail the internal geometry and depositional history of a Neogene‐Quaternary carbonate slope‐to‐basin area. The stratigraphic architecture through this period evolves from (i) a mud‐dominated slope apron during the Miocene, (ii) a debris‐dominated base‐of‐slope apron during the Late Pliocene and then (iii) return to a slope apron with very short prograding clinoformal aprons during the Pleistocene. This geometric evolution was broadly constrained by the development of the Santaren Drift by bottom current since the Langhian. The drift expands along the northwestern GBB slope, forming a continuous correlative massive feature that shows successive phases of growth and retreat and influenced the downslope sediments distribution. Indeed, Late Pliocene deposits are confined into the moat, forming a strike‐continuous coarse debrites belt along the mid‐slope, preventing their free expansion into the basin. The occurrence of basinal drift that operated since 15 Ma showed a significant upslope growth around 3.6 Ma and is interpreted as resulting from the closure of the Central American Seaway which also coincides with a global oceanographic re‐organization and climate changes in the Northern Hemisphere.     

Seismic stratigraphy and paleogeographic evolution of Fairway Basin,Northern Zealandia,Southwest Pacific: from Cretaceous Gondwana breakup to Cenozoic Tonga–Kermadec subduction

We present the first comprehensive seismic‐stratigraphic analysis of Fairway Basin, which is situated on the rifted continent of Zealandia in the Tasman Sea, southwest Pacific, between Australia and New Caledonia. The basin is 700 km long, 150 km wide, and has water depths of 500–3000 m. We describe depositional architecture and paleogeographic evolution of this basin. Basin formation was concurrent with two tectonic events: (i) Cretaceous rifting during eastern Gondwana breakup and (ii) initiation and Cenozoic evolution of Tonga–Kermadec subduction system to the east of the basin. To interpret the basin history we compiled and interpreted 2D seismic‐reflection profiles and make correlations with DSDP boreholes and the geology of New Caledonia. Five seismic‐stratigraphic units were defined. The deepest and oldest unit, FW3, folded and faulted can be correlated with volcaniclastic sediments and magmatic rocks in New Caledonia that are associated with Mesozoic Gondwana margin subduction. Alternatively, given the basin location 200–300 km west of New Caledonia and inboard of the ancient plate boundary, the unit could have formed as Gondwana intra‐continental basin with no known correlative. The overlying unit FW2b records syn‐rift deposition, probably associated with Cretaceous Gondwana breakup. Subaerial erosion supplied terrigenous sediment into the deltas in the northern part of the basin, as suggested by the truncation surfaces on the basement highs and sigmoid reflector geometries within unit FW2b respectively. Above, unit FW2a records post‐rift sedimentation and passive subsidence as the Tasman Sea opened and the Fairway Basin drifted away from Australia. Subsidence led to the flooding of the basement highs and burial of wave‐cut surfaces. Eocene compressive deformation resulted in minor folding and tilting within the Fairway Basin and was associated with the formation of many diapiric structures. The top of unit FW2 is an extensive unconformity that is associated with erosion and truncation on surrounding ridges. Above this unconformity, unit FW1b is interpreted as a turbidite system sourced from topography created during the Eocene tectonic event, which we interpret as being related to Tonga–Kermadec subduction initiation. Pelagic carbonate sedimentation is now prevalent. Unit FW1a has progressively draped the basin during Oligocene to Pleistocene subsidence. Many small volcanic cones were erupted during this final phase of subsidence, either as a delayed consequence of subduction initiation, or related to Tasmantid and Lord Howe hotspot trails. The northern Fairway Ridge remains close to sea level and its reef system continues to supply carbonate detrital sediments into the basin, most likely during sea‐level lowstands. Fairway Basin contains a nearly continuous record of tectonic and paleoclimatic events in the southwest Pacific since Cretaceous time. Its paleogeographic history is a key piece in the puzzle for understanding patterns of regional biodiversity in the southwest Pacific.     

A high-energy solar flare burst complex and the physical properties of its source region

We discuss a solar flare microwave burst complex, which included a major structure consisting of some 13 spikes of 60 ms FWHM each, observed 21 May, 1984 at 90 GHz (3 mm). It was associated with a simultaneous very hard X-ray burst complex. We suggest that the individual spikes of both bursts were caused by the same electron population: the X-bursts by their bremsstrahlung, and the microwave bursts by their gyrosynchrotron emission. This latter conclusion is based on the evidence that the radio turnover frequency was 150 GHz. It follows that the emission sources were characterized by an electron density of about 10¹¹ cm^–3, a temperature of 5 × 10⁸ K and a magnetic field of about 1400–2000 G. They had a size of about 350 km; if the energy release is caused by reconnection the sources of primary instability could have been smaller and in the form of thin sheets with reconnection speed at a fraction of the Alfvén velocity and burst-like energy injections of 10²⁷ erg during about 50 ms each. The energized plasma knots lost their injection energy by saturated convective flux (collisionless conduction) in about 30 ms.     

An overview of the mink study

Highlights of the previous papers in this series are reviewed. Methodology developed for the MINK study has improved the ability of impacts analysis to deal with questions of (1) spatial and temporal variability in climate change; (2) CO₂-enrichment effects; (3) the reactions of complex enterprises (farms and forests) to climate change and their ability to adjust and adapt; and (4) integrated effects on current and, more particularly, on future regional economies. The methodology also provides for systematic study of adjustment and adaptation opportunities and of the inter-industry linkages that determine what the overall impacts on the regional economy might be. The analysis shows that with a 1930s dust bowl climate the region-wide economic impacts would be small, after adjustments in affected sectors. In this final paper we consider whether synergistic effects among sectoral impacts and more severe climate change scenarios might alter this conclusion. The MINK analysis, as is, leads to the conclusion that a strong research capacity will be required to ensure that technologies facilitating adaptation to climate change will be available when needed. The capacity to deal with climate change also requires an open economy allowing for free trade and movement of people and for institutions that protect unpriced environmental values. More severe climate scenarios and negative synergisms can only strengthen these conclusions.     

Radio study of X-ray clusters of galaxies — I. A3528: a pre-merging cluster in the core of the Shapley Supercluster

As part of an extensive radio–IR–optical–X-ray study of ROSAT clusters of galaxies in the Hydra region we have observed the bimodal Abell cluster A3528, located in the core of the Shapley Supercluster ( z  ≃ 0.053), with the Molonglo Observatory Synthesis Telescope at 843 MHz and the Australia Telescope Compact Array at 1.4 and 2.4 GHz. This is part I in a series of papers which looks at the relationship between the radio and X-ray emission in samples of ROSAT selected clusters.   The radio source characteristics — tailed morphologies and steep spectra — are consistent with the effects of a dense intracluster medium and the pre-merging environment of A3528. In particular, we present evidence that the minor member of the radio-loud dumbbell galaxy located at the centre of the northern component of A3528 is on a plunging orbit. We speculate that this orbit may have been induced by the tidal interactions between the merging components of A3528. In addition, the radio source associated with the dominant member of the dumbbell galaxy exhibits many of the characteristics of compact steep spectrum sources. We argue that the radio emission from this source was triggered ∼ 10⁶ yr ago by tidal interactions between the two members of the dumbbell galaxy, strengthening the argument that compact steep spectrum (CSS) sources are young.   Re-analysis of archive pointed Position Sensitive Proportional Counter (PSPC) data using multiresolution filtering suggests the presence of an AGN and/or a cooling flow in the southern component of A3528.     

Investigation of active faults in Morocco using morphometric methods and drainage pattern analysis

A survey has been done of recently active faults in Morocco. In addition to field observations, morphometric methods were applied and an analysis was made of the drainage pattern. In the morphometric analysis, a map of vertical deformation was established from the elevations of summit level surfaces. This enables the recognition of neotectonic discontinuities and lithological contrasts; the actual discrimination of different rock-types can only be achieved by comparison with field observations. The analysis of drainage patterns — including their perturbations and anomalies — can also reveal the presence of features due to neotectonics, structural control or lithological variation. Certain faults can be detected which correspond to structures known from field geology or remote sensing (NE-SW and NW-SE oriented sets). Some new faults are observed which belong to these sets, as well as others which define a new N-S trending set. The present analysis leads to a distinction between ancient faults and currently active faults. The results of this study are shown on a map of recently active faults where the respective vertical displacements are also indicated.

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Zusammenfassung Bei einer Untersuchung der heute aktiven Störungen in Marokko wurden zusätzlich zu Feldbeobachtungen morphometrische Untersuchungen sowie eine Analyse des Entwässerungsnetzes durchgeführt. Bei der morphometrischen Analyse wurde eine Karte der vertikalen Deformationen von Aufragungen aus den Gipfelfluren abgeleitet. Dadurch können neotektonische Diskontinuitäten sowie lithologische Kontraste erkannt werden; die wirkliche Unterscheidung verschiedener Gesteinstypen kann aber nur im Vergleich mit Feldbeobachtungen erreicht werden. Die Analyse des Gewässernetzes — auch seiner Komplikationen und Anomalien — kann gleichfalls Elemente aufdecken, welche neotektonischen Ursprungs bzw. strukturell bedingt oder aber auf lithologische Unterschiede zurückzuführen sind. Bestimmte Störungen korrespondieren mit Strukturen, die aus der Feldgeologie oder der Fernerkundung bekannt sind (NE/ SW- und NW/SE-gerichtete Scharen). Einige neu entdeckte Störungen gehören zu diesen Scharen, während andere ein neues, N/S-streichendes System deutlich machen. Die vorgelegte Analyse erlaubt, zwischen älteren und noch heute aktiven Störungen zu unterscheiden. Unsere Ergebnisse sind in einer Karte der aktiven Störungen zusammengefaßt, in die die vertikalen Versätze gleichfalls eingetragen wurden.

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Résumé Un recensement des failles à jeu récent (néotectonique) a été fait sur l'ensemble du Maroc. Outre les observations de terrain, les méthodes de la morphométrie et celles de l'analyse du réseau hydrographique sont appliquées. En morphométrie, l'établissement d'une carte de la déformation verticale d'après la situation altimétrique de la surface sommitale permet la reconnaisance de structures (discontinuités) néotectoniques et d'alternances lithologiques (la discrimination ne peut être faite que sur le terrain). De même l'analyse du réseau hydrographique, de ses perturbations et de ses anomalies (cf. infra) met en évidence des discontinuités dues à la néotectonique, à la structure des terrains et à la lithologie. Les ensembles morphostructuraux marocains (Meseta, Rif, Atlas), ressortent nettement de la carte de synthèse. On y retrouve les failles connues par la géologie de terrain et par l'analyse des images satellitaires (ensembles de direction NE-SW et NW-SE), de nouvelles failles appartenant à ces deux familles, ainsi qu'un nouvel ensemble de failles de direction N-S. Cette analyse permet de distinguer failles actives et failles anciennes. Les résultats sont portés sur la carte des principales failles à jeu récent avec leurs rejets verticaux respectifs.

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Characterization of multiple functional groups on kaolinite

Multiple proton functional group conditional binding constants (K′_i) and their concentrations (C_i) are determined from detailed acid/base titration data. The C-K′ information is obtained for kaolinite by assuming that the distribution can be approximated by cumulative independent mono protic groups. Linear programming optimization techniques are used to Fit the data. In addition, the electrode calibration is optimized in the data fit. This adjustment is important for high and low pHs. Discrete concentration dependent pXs of about 3.4, 4.5, 6.7 and 9.8 are determined for a reference kaolinite. These correspond reasonably well to designations made by Wehrli et al. (1990, Aquatic Sciences, Vol. 52, pp. 1–31 ) to A10H2 and AlOH proton reactions at edge and surface sites and to silanol exchange. There is an ionic strength effect for one site. Long and short reaction times and reversibility affect the results.