The STRATAGEM project: Stratigraphic development of the glaciated European margin

The EC-funded STRATAGEM project ran from 2000 to 2003 and was a study of the Neogene evolution of the glaciated northeast Atlantic margin from Lofoten to Porcupine, an area extending over nearly 20 degrees of latitude. An extensive seismic, borehole and sample database has been used, much of it supplied by the oil industry. The main products of STRATAGEM have been an integrated, unified stratigraphic framework in the form of an atlas documenting and illustrating the detailed stratigraphy of the entire margin, and a detailed evolution model for this margin. A brief summary of the background to, and organisation of, the project is presented, together with an outline of the main objectives, the physiographic setting of the area and the database.     

Pleistocene glacial history of the NW European continental margin

In this paper new and previously published data on the Pleistocene glacial impact on the NW European margin from Ireland to Svalbard (between c. 48°N–80°N) are compiled. The morphology of the glaciated part of the European margin strongly reflects repeated occurrence of fast-moving ice streams, creating numerous glacial troughs/channels that are separated by shallow bank areas. End-moraines have been identified at several locations on the shelf, suggesting shelf-edge glaciation along the major part of the margin during the Last Glacial Maximum. Deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55°N and northwards, whereas the margin to the south of this is characterised by the presence of submarine canyons. Glaciation curves, based primarily on information from the glacial fed fan systems, that depict the Pleistocene trends in extent of glaciations along the margin have been compiled. These curves suggest that extensive shelf glaciations started around Svalbard at 1.6–1.3 Ma, while repeated periods of shelf-edge glaciations on the UK margin started with MIS 12 (c. 0.45 Ma). The available evidence for MIS 2 suggest that shelf-edge glaciation for the whole margin was reached between c. 28 and 22 ¹⁴C ka BP and maximum positions after this were more limited in some regions (North Sea and Lofoten). The last glacial advance on the margin has been dated to 15–13.5 ¹⁴C ka BP, and by c. 13 ¹⁴C ka BP the shelf areas were completely deglaciated. The Younger Dryas (Loch Lomond) advance reached the coastal areas in only a few regions.     

Submarine mass movements on glaciated and non-glaciated European continental margins: A review of triggering mechanisms and preconditions to failure

In this paper we present an overview of the major triggering mechanisms and preconditions for slope failure on the European continental margins, a vast area in which the dominant factors on sedimentation and erosional processes vary both spatially and temporally. Therefore, we have collated and integrated new as well as published data for both the formerly glaciated and non-glaciated areas of this highly dynamic margin for a time period mainly from the Last Glacial Maximum (LGM) to the present. Mass transport type is predominantly translational sliding on the high-latitude continental margins (north of 52°N), whereas turbidites dominate on lower latitudes. This is partly related to the average slope of the respective continental margin segments and differences in both sediment types and soil properties. Additionally, on low latitudes, submarine slope failures mainly occurred during glacial conditions with low sea level, whereas on high latitudes, they occur during the relatively fast transition from glacial to interglacial conditions (i.e. during periods of sea level rise). The largest submarine slides (e.g. Storegga, Trænadjupet, Andøya) on the glaciated Norwegian margin occurred during the Holocene, a time of rapid ice sheet decay, continental uplift and increased seismic activity, one of the most important triggering mechanisms for large failures during deglaciation processes. Preconditioning factors such as weak layers related to contourite drifts and rapid loading by glacial sediments may enhance strain localization and creep processes on the slope.     

Neogene stratigraphy and the sedimentary and oceanographic development of the NW European Atlantic margin

A regional correlation of Neogene stratigraphy has been attempted along and across the NW European Atlantic continental margin, between Mid-Norway and SW Ireland. Two unconformity-bounded successions are recognised. These are referred to as the lower and upper Neogene successions, and have been dated as Miocene–early Pliocene and early Pliocene–Holocene, respectively, in age. Their development is interpreted to reflect plate-wide, tectonically driven changes in the sedimentary, oceanographic and latterly climatic evolution of the NE Atlantic region. The lower Neogene succession mainly preserves a record of deep-water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities, within this succession, on both sides of the eastern Greenland–Scotland Ridge from the mid-Miocene. This is interpreted to record enhanced deep-water exchange through the Faroe Conduit (deepest part of the Southern Gateway), and can be linked to compressive inversion of the Wyville–Thomson Ridge Complex. Thus, a pervasive, interconnected Arctic–North Atlantic deep-water circulation system is a Neogene phenomenon. The upper Neogene succession records a regional change, at about 4 Ma, in the patterns of contourite sedimentation (submarine erosion, new depocentres) coeval with the onset of rapid seaward-progradation of the continental margin by up to 100 km. This build-out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin. Associated changes in deep-water circulation may be part of an Atlantic-wide reorganisation of ocean bottom currents. Glacial sediments form a major component of the prograding shelf margin (shelf-slope) sediment wedges, but stratigraphic data indicate that the onset of progradation pre-dates significant high-latitude glaciation by at least 1 Ma, and expansive Northern Hemisphere glaciation by at least 3 Ma.     

Thermal evolution of the western Svalbard margin

The northern Norwegian-Greenland Sea opened up as the Knipovich Ridge propagated from the south into the ancient continental Spitsbergen Shear Zone. Heat flow data suggest that magma was first intruded at a latitude of 75° N around 60 m.y.b.p. By 40–50 m.y.b.p. oceanic crust was forming at a latitude of 78° N. At 12 m.y.b.p. the Hovgård Transform Fault was deactivated during a northwards propagation of the Knipovich Ridge. Spreading is now in its nascent stages along the Molloy Ridge within the trough of the Spitsbergen Fracture Zone. Spreading rates are slower in the north than the south. For the Knipovich Ridge at 78° N they range from 1.5–2.3 mm yr^-1 on the eastern flank to 1.9–3.1 mm yr^-1 on the western flank. At a latitude of 75° N spreading rates increase to 4.3–4.9 mm yr^-1.Thermal profiles reveal regions of off-axial high heat flow. They are located at ages of 14 m.y. west and 13 m.y. east of the northern Knipovich Ridge, and at 36 m.y. on the eastern flank of the southern Knipovich Ridge. These may correspond to episodes of increased magmatic activity; which may be related to times of rapid north-wards rise axis propagation.The fact that the Norwegian-Greenland Sea is almost void of magnetic anomalies may be caused by the chaotic extrusion of basalts from a spreading center trapped within the confines of an ancient continental shear zone. The oblique impact of the propagating rift with the ancient shear zone may have created an unstable state of stress in the region. If so, extension took place preferentially to the northwest, while compression occurred to the southeast between the opening, leaking shear zone and the Svalbard margin. This caused faster spreading rates to the northwest than to the southeast.     

Rifting and early evolution of ancient ocean basins: the record of the Mesozoic Tethys and of the Galicia-Newfoundland margins

Although of different age, the undeformed Cretaceous Iberia/Newfoundland margins and the relics of the Jurassic Briançonnais/Adriatic margins preserved in the Alps document a similar spatial and temporal evolution of rifting suggesting that the evolution of both pairs of margins was controlled by the same processes. Rifting appears to depend strongly on the thermal history of the lithosphere, which controls the rheology and consequently also the structural evolution of the margin. The tectonic evolution of non-volcanic margins appears to be distinctly different from that of volcanic ones.     

Episodic Cenozoic tectonism and the development of the NW European ‘passive’ continental margin

The North Atlantic margins are archetypally passive, yet they have experienced post-rift vertical movements of up to kilometre scale. The Cenozoic history of such movements along the NW European margin, from Ireland to mid-Norway, is examined by integrating published analyses of uplift and subsidence with higher resolution tectono-stratigraphic indicators of relative movements (including results from the STRATAGEM project). Three episodes of epeirogenic movement are identified, in the early, mid- and late Cenozoic, distinct from at least one phase of compressive tectonism. Two forms of epeirogenic movement are recognised, referred to as tilting (coeval subsidence and uplift, rotations <1° over distances of 100s of Kilometres) and sagging (strongly differential subsidence, rotations up to 4° over distances <100 km). Each epeirogenic episode involved relatively rapid (<10 Ma) km-scale tectonic movements that drove major changes in patterns of sedimentation to find expression in regional unconformity-bounded stratigraphic units. Early Cenozoic tilting (late Paleocene to early Eocene, c. 60–50 Ma) caused the basinward progradation of shelf-slope wedges from elongate uplifts along the inner continental margin and from offshore highs. Mid-Cenozoic sagging (late Eocene to early Oligocene, c. 35–25 Ma) ended wedge progradation and caused the onset of contourite deposition in deep-water basins. Late Cenozoic tilting (early Pliocene to present, <4±0.5 Ma) again caused the basinward progradation of shelf-slope wedges, from uplifts along the inner margin (including broad dome-like features) and from offshore highs. The early, mid- and late Cenozoic epeirogenic episodes coincided with Atlantic plate reorganisations, but the observed km-scale tectonic movements are too large to be accounted for as flexural deflections due to intra-plate stress variations. Mantle–lithosphere interactions are implied, but the succession of epeirogenic episodes, of differing form, are difficult to reconcile with the various syn-to post-rift mechanisms of permanent and/or transient movements proposed in the hypothetical context of a plume beneath Iceland. The epeirogenic movements can be explained as dynamic topographic responses to changing forms of small-scale convective flow in the upper mantle: tilting as coeval upwelling and downwelling above an edge-driven convection cell, sagging as a loss of dynamic support above a former upwelling. The inferred Cenozoic succession of epeirogenic tilting, sagging and tilting is proposed to record the episodic evolution of upper mantle convection during ocean opening, a process that may also be the underlying cause of plate reorganisations. The postulated episodes of flow reorganisation in the NE Atlantic region have testable implications for epeirogenic movements along the adjacent oceanic spreading ridge and conjugate continental margin, as well as on other Atlantic-type ‘passive’ margins.     

Late Cenozoic prograding wedges on the NW European continental margin: their formation and relationship to tectonics and climate

During late Pliocene to Pleistocene times, prominent prograding wedges were deposited along the continental margin of NW Europe, resulting in seaward shelf break migration of up to 150 km. Much of the sediment accumulation occurred marginal to the former mid- to high-latitude ice sheets. The geographical distribution, and stratigraphical and chronological data may suggest that the instigation of the wedges was variously related to tectonic uplift as well as a response to the late Pliocene to Pleistocene climate deterioration and onset of major northern hemisphere glaciations. The onset of wedge growth on the NW UK and Irish margins was initiated at about 4 Ma in response to tectonic tilting of the margin in that region. However, glacially derived sediments here comprise a significant proportion of the wedges, especially since 0.44 Ma. For the Faroe margin, no detailed chronology is available; however, it may be inferred that onset of glacigenic wedge growth here did not post-date that observed on the NW UK and Irish margins. Offshore Norway, wedge growth has largely occurred since ca. 2.7 Ma in response to northern hemisphere glaciations, also recording a major change in sediments transport routes at 0.8–1.1 Ma (reflecting larger Fennoscandian Ice Sheets). Presently, it is uncertain whether the glacigenic wedge growth was preceded by a fluvial phase (in response to uplift) in this area. In the western Barents Sea, an early phase of wedge growth was (glacio) fluvial in character. Off western Spitsbergen, the development was similar to that of the Barents Sea although the glacigenic wedge-growth phase may have started somewhat earlier.The wedges commonly display gently inclined seaward prograding clinoforms, and transparent to chaotic internal acoustic facies. Sampling of their sediments reveals that they are mainly composed of glacigenic diamicton interbedded with marine and glaciomarine sediments that, to various extents, have been affected by bottom-current action. The clinoforms of these wedges vary in geometry from oblique to sigmoidal, and they also show varying degrees of aggradation throughout their development. The resulting stratal stacking pattern can be attributed to a combination of variations in sediment supply, sedimentary processes, and accommodation space, the latter being a function of tectonic movements and/or loading induced subsidence as well as eustatic sea-level fluctuations.     

南海西南次海盆两侧陆缘新生代构造沉降特征及演化过程

构造沉降史分析有助于认识盆地的形成演化过程,是盆地分析的重要基础。为对比分析南海西南次海盆两侧陆缘新生代构造演化特征,本文选取了横穿南海西南次海盆两侧陆缘的多道地震剖面测线,其中NH973-3测线横跨西南次海盆北侧陆缘中-西沙地块,NH973-1+SO27-04联合剖面跨越西南次海盆南侧陆缘南沙地块,在地震地层解释的基础上,采用回剥法和平衡剖面技术分析了西南次海盆两侧陆缘构造沉降特征及伸展过程。分析结果表明：（1）西南次海盆两侧陆缘的构造沉降曲线特征表现为裂陷初始期曲线斜率平缓,裂陷强烈期和末期曲线斜率较陡,断-拗转换期和拗陷期曲线斜率又回归相对平缓的反“S”形多段式特征;（2）两侧陆缘的构造沉降具有一定的延迟滞后性,造成此现象的原因可能与西南次海盆两侧陆缘岩石圈的分层差异伸展及南海西缘断裂的右旋走滑活动有关,且南海西缘断裂的右旋走滑活动造成两侧陆缘的构造沉降中心向南迁移;（3）两侧陆缘盆地主要形成于晚渐新世,北侧陆缘因受晚渐新世南海西缘断裂右旋走滑活动的改造影响而形成伸展-走滑相关的沉积盆地,南侧陆缘在早中新世因受到挤压碰撞的改造影响而形成伸展-挠曲复合型沉积盆地。这些研究成果可为南海西南次海盆两侧陆缘沉积盆地的油气和天然气水合物的勘探开发提供重要的科学背景支持。     

Unexpected fast rate of morphological evolution of geologically-active continental margins during Quaternary: Examples from selected areas in the Italian seas

In the last few decades, seafloor imagery systems have drastically changed our vision of a mostly regular and depositional marine landscape, evidencing how erosive and mass-wasting processes are widespread in the marine environments, with particular reference to geologically-active areas. Most of the previous studies have focused on the characterization of these features, whereas a very few ones have tried to estimate what is the extent and order of magnitude of erosion rates in these areas. In this paper, we show several examples from some of the most geologically-active margins off Southern Italy aimed to a) quantify the spatial extent of such processes, b) better understand the role of submarine erosion in the morphogenesis of the coastal sector, and c) try to roughly estimate the order of magnitude of erosion rates in these areas. The results are impressive, with mass-wasting features widespread from coast down to −2600, affecting from the 52% up to 97% of the whole continental slope. Because of the narrow or totally lacking shelves in these areas, mass-wasting processes often occur close to the coast and match embayment of the coast, so indicating a key role in the morphogenesis of coastal sector, with significant implication on the related geohazard. Finally, based on a morphological approach integrated by available stratigraphic constraints we have roughly estimated average erosion rates in these areas, ranging from (at least) some mm/year to a few cm/year, i.e., some hundreds of meters up to kilometers eroded in each eustatic cycle. Despite the large uncertainties of these estimates as well as their spatial and temporal variability in response to regional and local factors, the obtained values are very high and they should be considered for future model of margin evolution, source-to-sink computation and marine/coastal geohazard assessment.     

Eocene post-rift tectonostratigraphy of the Rockall Plateau, Atlantic margin of NW Britain: Linking early spreading tectonics and passive margin response

A regional study of the Eocene succession in the UK sector of the Rockall Plateau has yielded new insights into the early opening history of the NE Atlantic continental margin. Data acquired from British Geological Survey borehole 94/3, on the Rockall High, provides a high-resolution record of post-rift, Early to Mid-Eocene, subaqueous fan-delta development and sporadic volcanic activity, represented by pillow lavas, tuffs and subaerial lavas. This sequence correlates with the East Rockall Wedge, which is one of several prograding sediment wedges identified across the Rockall Plateau whose development was largely terminated in the mid-Lutetian. Linking the biostratigraphical data with the magnetic anomaly pattern in the adjacent ocean basin indicates that this switch-off in fan-delta sedimentation and volcanism was coincident with the change from a segmented/transform margin to a continuously spreading margin during chron C21. However, late-stage easterly prograding sediment wedges developed on the Hatton High during late Mid- to Late Eocene times; these can only have been sourced from the Hatton High, which was developing as an anticline during this interval. This deformation occurred in response to Mid- to Late Eocene compression along the ocean margin, possibly associated with the reorganisation to oblique spreading in the Iceland Basin, which culminated at the end of the Eocene with the formation of the North Hatton Anticline, and the deformation (tilting) of these wedges. A series of intra-Eocene unconformities, of which the mid-Lutetian unconformity is the best example, has been traced from the Rockall Plateau to the Faroe-Shetland region and onto the Greenland conjugate margin bordering the early ocean basin. Whilst there appears to be some correlation with 3rd order changes in eustatic sea level, it is clear from this study that tectonomagmatic processes related to changes in spreading directions between Greenland and Eurasia, and/or mantle thermal perturbations cannot be discounted.     

A Comparison Between GEBCO Sheet 5.17 and the International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 1.0

In 1979, the General Bathymetric Chart of the Oceans (GEBCO) published Sheet 5.17 in the Fifth Edition of its series of global bathymetric maps. Sheet 5.17 covered the northern polar region above 64° N, and was for long the authoritative portrayal of Arctic bathymetry. The GEBCO compilation team had access to an extremely sparse sounding database from the central Arctic Ocean, due to the difficulty of mapping in this permanently ice covered region. In the past decade, there has been a substantial increase in the database of central Arctic Ocean bathymetry, due to the declassification of sounding data collected by US and British Navy nuclear submarines, and to the capability of modern icebreakers to measure ocean depths in heavy ice conditions. From these data sets, evidence has mounted to indicate that many of the smaller (and some larger) bathymetric features of Sheet 5.17 were poorly or wrongly defined. Within the framework of the project to construct the International Bathymetric Chart of the Arctic Ocean (IBCAO), all available historic and modern data sets were compiled to create a digital bathymetric model. In this paper, we compare both generally and in detail the contents of GEBCO Sheet 5.17 and version 1.0 of IBCAO, two bathymetric portrayals that were created more than 20 years apart. The results should be helpful in the analysis and assessment of previously published studies that were based on GEBCO Sheet 5.17. Ron Macnab: Retired.     

Seismic structure and response of ocean-continent transition zones – A comparison of an ancient Tethyan and a present-day Iberian site

The tectonic interpretation of basement structures in seismic reflection profiles from ocean-continent transitions (OCT) of magma-poor rifted margins is notoriously difficult due to the scarcity of borehole information. Low-angle intra-basement reflections are frequently interpreted as detachment faults, and in certain locations the drilled top of the basement is interpreted as exhumed detachment fault. The seismic expression of such detachment faults is, however, poorly understood. We address this problem by comparing synthetic seismic data from the Tasna OCT, an exposed remnant of a Tethyan margin, with seismic reflection data from Hobby High, a drilled basement high within the west Iberian margin. Both sites are widely considered as being representative of OCT zones. Their geological similarity and the complementary nature of the data enable us to perform a detailed investigation of the seismic structure and response of these OCT zones. This provides insights into the seismic imaging of OCT zones in general and the tectonic evolution of the associated detachment systems in particular. On the basis of the Tasna OCT models and their seismic responses we have identified some potential characteristics of intra- and top-basement detachments: (i) variable amplitudes and numerous diffractions from the top of exhumed subcontinental mantle, (ii) a continuous and strong reflection imaging the top of exhumed lower crustal rocks, and (iii) a weak and discontinuous reflection of inverse polarity representing a shallow intra-basement crust-mantle detachment. Similar features are consistently observed at geologically equivalent positions in the seismic data from Hobby High and may thus serve as guidelines for interpretation of seismic data from un-drilled OCT zones.     

A review of the equations used to predict the velocity distribution within a ship’s propeller jet

Predicting the velocity within the ship’s propeller jet is the initial step to investigate the scouring made by the propeller jet. Albertson et al. (1950) suggested the investigation of a submerged jet can be undertaken through observation of the plain water jet from an orifice. The plain water jet investigation of Albertson et al. (1950) was based on the axial momentum theory. This has been the basis of all subsequent work with propeller jets. In reality, the velocity characteristic of a ship’s propeller jet is more complicated than a plain water jet. Fuehrer and Römisch (1977), Blaauw and van de Kaa (1978), Berger et al. (1981), Verhey (1983) and Hamill (1987) have carried out investigations using physical model. Current paper reviews the state-of-art of the equations used to predict the time-averaged axial, tangential and radial components of velocity within the zone of flow establishment and the zone of established flow of a ship’s propeller jet.     

A comparison of fisheries policy and management in the European Community and Eastern Canada

The fisheries systems which have developed in the European Economic Community (EEC) and Eastern Canada show striking similarities and contrasts. Both show efforts directed at conserving the resource base while setting limits for annual catches and allocating shares in these catches among fishermen. Canada has had less pressure on its resources and has been more successful in restraining over-fishing tendencies; it also has a more fully co-ordinated and effective management system. On the other hand the EEC has greater efficiency in catching, marketing and processing, and in recent times has had less government aid. Better systems would combine Canadian management efficiency with EEC economic efficiency.     

Large-scale variation in macrofaunal communities along the eastern Nordic Seas continental margin: A comparison of four stations with contrasting food supply

A hypothesis-driven approach was used to examine the relative importance of pelagic and advective organic flux as drivers of macrofaunal community structure at mid-slope (900–1400 m) depths along the eastern Nordic Seas margin. Ice-free stations were sampled on the Vøring Plateau (VP, mainly pelagic flux) and Bear Island Fan (BIF, major downslope advection). Seasonally ice-covered stations with episodic inputs of fresh phytodetritus were located on the Svalbard Margin (SM, major current-driven advective input), and Yermak Plateau (YP, low advective input). Macrofaunal biomass was higher at stations with seasonal ice cover, suggesting a greater supply of bioavailable organic matter in the marginal ice zones. At VP, BIF and SM, box corer and multiple corer samples gave broadly consistent community data. Very large infauna in box corer samples from YP indicated the existence of a faunal component absent or not sampled at the other three stations. This faunal component and higher mean body size for 18 out of 23 major taxa at YP relative to VP was consistent with a hypothesis relating body size to interannual variability of sinking flux, but was confounded by a depth difference between the two stations. Consistent with predictions, taxa associated with subsurface ‘caching’ of fresh organic matter were important community elements at stations experiencing episodic pelagic input, but not at the advection-dominated BIF. Current-driven advective flux was associated with high suspension-feeder biomass at BIF, but not at SM. The predicted high representation of subsurface deposit-feeders at BIF was not found. Sipunculans (Nephasoma sp.) known to rapidly subduct fresh organic matter were found at all stations but were most abundant at VP. Comparison with data from the mid-1980s showed a large difference in estimated macrofaunal abundance on the Vøring Plateau, but good agreement in biomass. Community patterns on the Vøring Plateau were generally consistent with earlier data. Standing stock estimates from the Svalbard Margin and Yermak Plateau also agreed well with previous data. Results suggest that large-scale contrasts in organic flux can be used to predict some aspects of bathyal macrofaunal community composition in the Nordic Seas.     

尼日利亚西部大陆边缘海底峡谷下部结构研究

Multi-beam,sub-bottom and multichannel seismic data acquired from the western Nigerian continental margin are analysed and interpreted to examine the architectural characteristics of the lower parts of the submarine canyons on the margin.The presence of four canyons: Avon,Mahin,Benin,and Escravos,are confirmed from the multi-beam data map and identified as cutting across the shelf and slope areas,with morphological features ranging from axial channels,moderate to high sinuosity indices,scarps,terraces and nickpoints which are interpreted as resulting from erosional and depositional activities within and around the canyons.The Avon Canyon,in particular,is characterised by various branches and sub-branches with complex morphologies.The canyons are mostly U-shaped in these lower parts with occasional V-shapes down their courses.Their typical orientation is NE–SW.Sedimentary processes are proposed as being a major controlling factor in these canyons.Sediments appear to have been discharged directly into the canyons by rivers during the late Quaternary low sea level which allows river mouths to extend as far as the shelf edge.The current sediment supply is still primarily sourced from these rivers in the case of the Benin and Escravos Canyons,but indirectly in the case of the Avon and Mahin Canyons where the rivers discharge sediments into the lagoons and the lagoons bring the sediments on to the continental shelf before they are dispersed into the canyon heads.Ancient canyons that have long been buried underneath the Avon Canyon are identified in the multichannel seismic profile across the head of the Avon Canyon,while a number of normal faults around the walls of the Avon and Mahin Canyons are observed in the selected sub-bottom profiles.The occurrence of these faults,especially in the irregular portions of the canyon walls,suggests that they also have some effect on the canyon architecture.The formation of the canyons is attributed to the exposure of the upper marginal area to incisions from erosion during the sea level lowstand of the glacial period.The incisions are widened and lengthened by contouric currents,turbidity currents and slope failures resulting in the canyons.     

A Compilation of Geophysical Data from the Lazarev Sea and the Riiser-Larsen Sea, Antarctica

On the basis of new geophysical data acquired by the Federal Institute of Geosciences and Natural Resources (BGR) and the Polar Marine Geological Research Expedition (PMGRE) as well as existing data new geophysical maps were compiled for the Lazarev Sea and the Riiser-Larsen Sea between 10°W and 25°E. The new results are: – The drastic change in the strike direction of the volcanic Explora Wedge between longitudes 10°W and 5°W is accompanied with a gradual change from one major wedge, i.e. the Explora Wedge, into at least two wedge-shaped volcanic constructions, each manifested by a sequence of seaward-dipping reflectors in the seismic records. – The southern Lazarev Sea is best described as a continental margin affected by multiple rifting episodes accompanied with transient volcanism. – A distinct N80°E striking basement depression separates the volcanic-prone continental margin of the southern Lazarev Sea from oceanic crust upon which the Maud Rise rests. The southern scarp of the narrow depression was presumably aligned with the eastern scarp of the Mozambique Ridge during the Early Cretaceous. – The Astrid Ridge proper occupies the transition from the volcanic-prone continental margin of the Lazarev Sea to old oceanic crust of the Riiser -Larsen Sea, and it rests upon a large volcanic apron which covers the basement of the southwestern Riiser-Larsen Sea. – No evidence was found that prolific volcanism has affected the early opening of the Riiser-Larsen Sea. – The Lazarev Sea is a sediment-starved region.     

南海东北部陆架边缘第四纪高分辨率层序地层和沉积体系演化及其控制因素

The northeastern shelf margin of the South China Sea(SCS) is characterized by the development of large scale foresets complexes since Quaternary. Based on integral analysis of the seismic, well logging and paleontological data, successions since ～3.0 Ma can be defined as one composite sequence, consist of a set of regional transgressive to regressive sequences. They can be further divided into six 3 rd order sequences(SQ0–SQ5) based on the Exxon sequence stratigraphic model. Since ～1.6 Ma, five sets of deltaic systems characterized by development of wedge-shaped foresets complexes or clinoforms had been identified. High-resolution seismic data and the thick foresets allowed further divided of sub-depositional sequences(4 th order) of regression to transgression, which is basically consistent with published stacked benthic foram O-isotope records. Depositional systems identified in the study area include deltaic deposits(inner-shelf deltas and shelf-edge deltas), incised valleys, and slope slumping massive deposits. Since ～1.6 Ma, clinoforms prograded from the southern Panyu Lower Uplift toward the northern Baiyun Depression, shelf slope break migrated seaward, whereas the shelf edge of SQ0 migrated landward. The development of incised valleys in the continental shelf increased upward,especially intensive on the SB3 and SB2. The slumping massive deposits increased abruptly since SB2, which corresponds to the development of incised valleys. The evolution of depositional systems of continental slope mainly controlled by the combined influence of sea level changes, tectonic movements, sediment supply and climate changes. Since ～3.0 Ma, relative sea level of the northern SCS had been experienced transgression(～3.0 Ma BP) to regression(～1.6 Ma BP). The regional regression and maximum transgressions of the composite sequences were apparently enhanced by uplift or subsidence related to tectono-thermal events. In addition,climatic variations including monsoon intensification and the mid-Pleistocene transition may have enhanced sediment supply by increasing erosion rate and have an indispensable influence on the development of the incised valleys and 5 sets of deltaic systems since ～1.6 Ma.