ALBERT

Description: Records of organic matter accumulation, organic carbon isotopic composition and iron content covering the last 1.7 Ma are presented for the Congo Fan Ocean Drilling Program (ODP) Site 1075, and are compared with their counterparts from ODP Site 663 in the equatorial upwelling region. They are discussed with regard to variations in African precipitation and Congo River discharge and in the context of changes in trade-wind-driven marine productivity for the tropical Atlantic at periodicities typical of Milankovitch forcing. On the Congo Fan, elevated total organic carbon mass accumulation rates (TOC MAR) and Fe intensities occur predominantly during interglacial periods when the African monsoon was most intense. Band-pass filtering applied to TOC MAR shows distinct precessional variations, indicating that the African climate was largely controlled by low-latitude insolation changes. Only for the last 0.6 Ma, an interval of enhanced glacial-interglacial climate changes, is the precessional TOC MAR signal superimposed by a strong 100 ka oscillation. In contrast, variations in terrestrial iron input to the Congo Fan indicate pronounced 100 ka variance already well before global glacial-interglacial cycles increased in amplitude between 0.9 and 0.6 Ma. Obliquity cycles in the Fe signal are strongly expressed for the last 0.9 Ma. The highest amplitudes in the precessional variance of fluvial Fe input occur when amplitudes in the 100 ka oscillation were at intermediate levels and reveal a 800 ka cycle in phase shift with respect to precessional forcing. Together with a pronounced 800 ka signal in the 100 ka amplitude variations during the last 1.7 Ma, the Congo Fan iron record therefore suggests that eccentricity modulation of the low-latitude insolation directly influenced the equatorial African monsoon system and probably the weathering conditions on land. It further suggests that low-latitude precessional forcing and monsoonal response in the tropics might have played an important role for 100 ka cycles in global climate well before huge continental ice sheets existed.

Description: A late Early Pleistocene pollen record was obtained from a coastal site in Auckland, New Zealand. A combination of isothermal plateau fission track ages on interbedded tephras, palaeomagnetism, palynostratigraphy and orbital tuning to the marine oxygen isotope record of Ocean Drilling Program Site 677 constrained the age of the topmost 28 m of sediments to c. 1.4-1.0 Ma (Marine Isotope Stages (MIS) 45-28). For this interval a diverse pollen record consisting of mostly extant pollen types shows multiple compositional shifts from a Nothofagus-dominated to conifer-dominated regional vegetation. These shifts are broadly correlated to changes in the marine oxygen isotope record. The inferred climate was moist, temperate, stable, and cooler than at present, but never as cool as the last glacial maximum. A permanent increase in Nothofagus forest in the region after MIS 35 seems to be related to a long-term palaeoclimatic shift that probably included greater temperature extremes between warm and cool stages and decreases in humidity and increased seasonality during cool stages. Although the Patiki pollen record predates the mid-Pleistocene revolution by c. 100 ka, the nature of climate change itself was already in transition, and becoming more similar to the climate regime experienced in northern New Zealand in the Late Pleistocene.

Description: During the strong 1999 Izmit (Kocaeli) earthquake, 100 km long east-west-striking (N80{degrees}-100{degrees}), right-lateral, fault traces were formed. In the epicentral area the seismic ruptures did not follow any known or mapped fault traces, but morphology and tectonostratigraphic evidence from trenches reveal pre-existing earthquake-related features, e.g. elongated valleys, shutter ridges, high-angle slopes, scarplets and stream offsets. In the Golcuk Peninsula a characteristic NW-SE-trending extensional fault segment emerged at the surface with a 1.5-2 m maximum vertical displacement and a 0.30 m right-lateral component. The resulting coseismic fault scarp was mapped in detail, and two trenches were excavated at the Deniz Evler site. The 1999 displacement at this site was 1.50 m, whereas the penultimate event displaced the same sediments by 0.70 m, and a previous event by 0.20 m. Displacement is not characteristic, as fault-associated soft (recent) deltaic deposits, and the fault itself, are typically not coseismic, but rather a secondary accommodation structure in geometric consistency with the right-lateral main displacement zone. The data were compared with similar results from the A[s]ag[i] Yuvacik, Kular Yaylacik and Acisu sites between Izmit and Sapanca Lake. The same fault segment seems to have been activated and produced surface ruptures including during the earthquakes of AD 1509, AD 989 and AD 554, plus two prehistoric events. The palaeoseismological results provide clear evidence for repeated reactivation of the same fault or fault segments during historical seismic events.

Description: The island of Crete represents a horst structure located in the central forearc of the retreating Hellenic subduction zone. The structure and dynamics of the plate boundary in the area of Crete are investigated by receiver function, surface wave and microseismicity using temporary seismic networks. Here the results are summarized and implications for geodynamic models are discussed. The oceanic Moho of the subducted African plate is situated at a depth of about 5060 km beneath Crete. The continental crust of the overriding Aegean lithosphere is about 35 km thick in eastern and central Crete, and typical crustal velocities are observed down to the upper surface of the downgoing slab beneath western Crete. A negative phase at about 4 s in receiver functions occurring in stripes parallel to the trend of the island points to low-velocity slices within the Aegean lithosphere. Interplate seismicity is spread out about 100 km updip from the southern coastline of Crete. To the south of western Crete, this seismically active zone corresponds to the inferred rupture plane of the magnitude 8 earthquake of AD 365. In contrast, interplate motion appears to be largely aseismic beneath the island. The coastline of Crete mimics the shape of a microseismically quiet realm in the Aegean lithosphere at 2040 km depth, suggesting a relation between active processes at this depth range and uplift. The peculiar properties of the lithosphere and the plate interface beneath Crete are tentatively attributed to extrusion of material from a subduction channel, driving differential uplift of the island by several kilometres since about 4 Ma.

Description: The Kerguelen Archipelago is made up of a stack of thick piles of Tertiary flood basalts intruded by transitional to alkaline igneous centres at various times since 30 Ma ago. In the SW, the Rallier-du-Baty Peninsula is mostly occupied by two silicic ring complexes, each with an average diameter of 15 km, comprising dissected calderas cross-cut by subvolcanic cupolas. Previous radiometric determinations yield ages ranging from 15.4 to 7.4 Ma in the southern centre, and 6.2 to 4.9 Ma in the northern one. The felsic ring dykes were injected by coeval mafic magmas, forming, successively, swarms of early mafic enclaves, disrupted synplutonic cone sheets, and late cone-sheets. After the emplacement and subsequent unroofing of the plutonic ring complexes, abundant and thick trachytic pyroclastic flows and falls were emitted from the younger caldera volcanoes, while hawaiite and mugearite lava flows were erupted from marginal maars and cones. Huge trachyte ignimbritic flows filled the glacial valleys in the central Peninsula, and capped lacustrine deposits and older lava flows, while related pumice falls are widespread throughout the archipelago. This powerful plinian eruption took place after the network of glacial valleys was established, but before the Little Ice Age that occurred during the last centuries. In the south of the peninsula, even younger trachytic formations are exposed, and fumarolic vents are still active. The growth mechanisms of a caldera-related ring complex can be explained as a repetitive sequence of two eruptive episodes. The first episode of hydrofracturing, induced by volatile exsolution within the evolving magma chamber, creates a vertical circular fracture zone, along which highly vesiculated magmas are emitted during explosive eruptive events occurring at the surface in a caldera volcano. It is followed by a second episode of cauldron-subsidence of a crustal block down to the degassed magma chamber, induced by pressure release. Downward movement of the crustal block favours the emplacement at shallow depths within the older caldera-filling formations, of discrete magmatic sheets characterized by a 16-km mean diameter and a 1-km mean thickness, corresponding to an average unit volume of 200 km3. Actually, the estimated volumes of the different igneous episodes within the Rallier-du-Baty nested ring complex vary from 60 to 900 km3, and correspond to the production during 15 Ma of about 2800 {+/-} 850 km3 of new materials and a net crustal growth of about 100 {+/-} 30 x 103 m3 per year.

Description: Accelerating seismic strain caused by the generation of intermediate-magnitude preshocks in a broad (critical) region, accompanied by decelerating seismic strain caused by the generation of smaller preshocks in the seismogenic region are systematically observed before strong mainshocks. On the basis of this seismicity pattern a model has been developed that seems promising for intermediate-term earthquake prediction, called the Decelerating in-Accelerating out Seismic Strain Model'. Recent seismological data for the Mediterranean region are used here for backward and forward testing of this model. The selection of the broader Mediterranean region as a test area was motivated not only by the interest of time-dependent seismic hazard assessment in a high-seismicity and highly populated region but also by the fact that the Mediterranean is a natural geophysical and geological laboratory where both complex multi-plate and continuum tectonics are found in a more or less convergent zone. Within this complex geotectonic setting several geological phenomena such as subduction, collision, orogen collapse and back-arc extension take place, leading to the generation of a broad spectrum of mainshocks, reaching MW = 8.0 or greater for subduction-related thrust events and a variety of corresponding seismicity levels and neotectonic activity ranging from very low (e.g. large parts of Iberian peninsula) to very high (broader Aegean area). The backward procedure shows that all six strong (M [≥] 6.8) mainshocks that have occurred in the Mediterranean since 1980 had been preceded by preshock sequences that followed this seismicity pattern and satisfy all model constraints. Application of the model for future mainshocks has led to the identification of nine regions (in the Pyrenees, Calabria, NE Adriatic, Albania, Northern Greece, SE Aegean, NW Anatolia, western Anatolia, NE Anatolia) where current intermediate-magnitude seismicity satisfies the constraints of the model and corresponds to strong (M [≥] 6.2) mainshocks. The magnitudes, epicentres and origin times of these probably ensuing mainshocks, as well as their corresponding uncertainties, are estimated, so that it is possible to evaluate the model potential during the next decade (2006-2015). Furthermore, it is shown that geological observations of surface fault traces can contribute to the accurate location of the foci of future strong mainshocks in the Mediterranean and to an estimation of their sizes. For this purpose, globally valid relations between fault parameters based on geological observations (surface fault length, LS, and fault slip, uS) and measures of mainshock size (mainshock magnitude, subsurface fault length, L, and fault slip, u) are proposed.

Description: Marine sediments hosting gas hydrates are commonly fine-grained (silts, muds, clays) with very narrow mean pore diameters ([~]0.1 {micro}m). This has led to speculation that capillary phenomena could play an important role in controlling hydrate distribution in the seafloor, and may be in part responsible for discrepancies between observed and predicted (from bulk phase equilibria) hydrate stability zone (HSZ) thicknesses. Numerous recent laboratory studies have confirmed a close relationship between hydrate inhibition and pore size, stability being reduced in narrow pores; however, to date the focus has been hydrate dissociation conditions in porous media, with capillary controls on the equally important process of hydrate growth being largely neglected. Here, we present experimental methane hydrate growth and dissociation conditions for synthetic mesoporous silicas over a range of pressure-temperature (PT) conditions (273-293 K, to 20 MPa) and pore size distributions. Results demonstrate that hydrate formation and decomposition in narrow pore networks is characterized by a distinct hysteresis: solid growth occurs at significantly lower temperatures (or higher pressures) than dissociation. Hysteresis takes the form of repeatable, irreversible closed primary growth and dissociation PT loops, within which various characteristic secondary scanning' curve pathways may be followed. Similar behaviour has recently been observed for ice-water systems in porous media, and is characteristic of liquid-vapour transitions in mesoporous materials. The causes of such hysteresis are still not fully understood; our results suggest pore blocking during hydrate growth as a primary cause.

Description: In high latitudes, recent research has demonstrated that both thermo-erosion and temperature dependence influence sediment release into fluvial systems. An analysis of proglacial suspended sediment concentration (SSC) dynamics is presented for three glacierized basins: cold-based Austre Broggerbreen (Svalbard), polythermal Midre Lovenbreen (Svalbard) and polythermal Glacier B28 (Bylot Island). The temporal variation in processes dominating SSC patterns is assessed using stepwise multivariate regression following the subdivision of the time series. Partitioning of the time series is achieved through principal components and change point analyses. The regression models use discharge and surrogate predictor variables to model SSC, while improvements are made by using air temperature and radiation terms as independent variables. Comparisons are drawn between two sets of models with contrasting subseasonal division. By interpretation of the regression model characteristics, temporal changes in physical processes are implied over the course of the time periods. Numerical analyses suggest there is a trend for changes between fluvial, glacial and periglacial factors forcing responses in SSC. Therefore, it is conjectured that glaciofluvial sediment transfer at high latitudes is influenced by periglacial processes and conditions. This has implications for the predictions of fluvial sediment loads in a changing environment, and the use of sedimentary records for environmental reconstruction.

Description: The first to recognize the complementary shapes of Africa and South America and to suggest that these continents were once joined together was Dutch scientist Ortelius in 1596. He was followed in 1620 by Elizabethan philosopher Sir Francis Bacon, who asserted that the similarity of their shapes could not be accidental. Nearly 200 years later, German naturalist von Humboldt described how the two continents may have fitted together, and in 1860 French geographer Antonio Snyder produced the first map that showed South America and Africa in close contact (e.g., Blankett 1965). By 1915 the German meteorologist Alfred Wegener had amassed enough data to publish a comprehensive scientific argument for the past conjunction of these two continents on the basis of similarities in the Palaeozoic

Description: The idea for a special publication on non-volcanic margins arose during Ocean Drilling Program (ODP) Leg 173 off West Iberia, prompted by ODP's decision to cease publishing the scientific results volumes as hard copy. The Shipboard Scientific Party favoured an open scientific meeting and associated publication. But they did not want to produce a book that was a scientific results volume by another name, but rather contribute to a publication that had a much broader scope than just reporting results obtained off West Iberia. These thoughts, and many scientific discussions during the Leg, were influenced by the presence on board of scientists who also work on Alpine geology: hence the evidence from land and sea' approach that underlies the content of this publication. However, when planning the meeting, we were very conscious of the fact that the West Iberia and Alpine examples might not be typical of other non-volcanic margins. We were keen, therefore, to ensure that margins in other parts of the world were discussed, including a margin that is active today, and that was visited by the JOIDES Resolution not long after Leg 173 took place (Leg 180: Woodlark Basin). We caution, therefore, that it may be premature to use models based on the Iberia and Tethyan margins as the paradigm for all non-volcanic margins. The first paper in this book, by Boillot & Froitzheim, reviews the synergies that have occurred between investigations of the eastern Atlantic non-volcanic margins and remnants of similar Mesozoic margins preserved in the ... This 250-word extract was created in the absence of an abstract.