Fluid escape structures in the north Sicily continental margin

High resolution and multichannel seismic profiles coupled with multibeam echosounder (seafloor relief) data, acquired along the northern Sicily continental margin (southern Tyrrhenian Sea), document the occurrence of mound and pockmark features, revealing fluid escape processes. Along this margin, morphology of the high-gradient continental slope is irregular due to the presence of structural highs, slope failures and canyons, and is interrupted by flat areas at a mean depth of 1500 m.Seismostratigraphic analysis tools and methods were used to identify fluid escape structures and to work out a classification on the basis of their morpho-acoustic characteristics. The detailed 3D bathymetric chart was used to define the top view morphologic features and their areal distribution. With the aim to evaluate the geochemical content of fluids, we collected a 2.3 m long sediment core in correspondence of a pockmark at a depth of 414 m. Pore waters were sampled every 10 cm and analysed in relation to their conductivity (EC) and composition (δ¹⁸O, δD, Li, Na, K, Mg, F, Cl, Br, NO₃, SO₄).The new data show the occurrence of different types of structures with highly contrasting seismic and morphologic signatures, both dome-type and concave-upward structures. The latter have a characteristic circular shape and are known as pockmarks. Morphobathymetric, stratigraphic and structural data suggest that these structures occur along fault planes, mainly associated with diagenetic carbonates and fluid venting activity. Pockmarks could be the result of both fault and landslide structures, as they appear aligned along a straight direction and occur in proximity of the slope, and are associated with slope instabilities. The structural features are possibly associated with the recent tectonics mapped on-land as well as the widespread seismicity of the margin.Geochemical features reveal that pore water is slightly enriched in heavy isotopes with respect to Mediterranean seawater, while the distribution profiles of EC, ion concentration (Cl, SO₄, Na, K, Mg, Ca), ion/Chloride ratios (Na/Cl, K/Cl, Ca/Cl, Mg/Cl and Alk/Cl) seem to indicate the existence of an external source of fluids and the occurrence of sediment-fluids interaction processes. A possible mechanism causing pore water freshening could be the destabilisation of gas hydrates.     

Sedimentary and structural patterns on the Iberian continental margin: an alternative view of continental margin sedimentation

A long-range side-scan sonar (GLORIA) survey of the entire West Iberian slope and rise has provided the first overview of the interrelationship between structure and sedimentation patterns on a continental margin. The results emphasize the importance of slope-following contour currents as a depositional mechanism in fashioning this continental rise. Terrigenous sediments transported down-canyon by-pass the rise which does not consist of a series of coalescing fans. The sedimentation patterns identified on the sonographs can be interpreted in terms of facies models and caution must be exercised against over-emphasis of downslope processes in models for the construction of lower slopes and rises.     

Seismic and sequence stratigraphy of the central western continental margin of India: late-Quaternary evolution

Seismic and sequence stratigraphic architecture of the central western continental margin of India (between Coondapur and south of Mangalore) has been investigated with shallow seismic data. Seismic stratigraphic analysis defined nine seismic units, that are configured in a major type-1 depositional sequence possibly related to fourth-order eustatic sea-level changes, comprising regressive, lowstand, transgressive and highstand systems tracts. The late-Quaternary evolution of the continental margin took place under the influence of an asymmetric relative fourth-order sea-level cycle punctuated by higher frequency cycles. These cycles of minor order were characterised by rapid sea-level rises and gradual sea-level falls that generated depositional sequences spanning different time scales. During the regressive periods, dipping strata were developed, while erosional surfaces and incised valleys were formed during the lowstands of sea level. Terraces, v-shaped depressions, lagoon-like structures observed on the outer continental shelf are the result of the transgressive period. In the study area we have recognised a complex erosional surface that records a long time span during the relative sea-level fall (regressive period) and the following sea-level lowstand and has been reworked during the last transgression. We also infer that sedimentation processes changed from siliciclastic sedimentation to carbonate sedimentation and again to siliciclastic sedimentation, marking an important phase in the late-Quaternary evolution of the western continental shelf of India. We attribute this to an abrupt climate change at the end of the oxygen isotope stage 2, between the Last Glacial Maximum and the Bølling-Allerod event (14?000 yr BP). This sensitive climate change (warming) favoured the formation of reefs at various depths on the shelf, besides the development of Fifty Fathom Flat, a carbonate platform on the outer shelf off Bombay developed prior to 8300 yr BP. The highstand systems tracts were deposited after the sea level reached its present position.     

Tracking the last sea-level cycle: seafloor morphology and shallow stratigraphy of the latest Quaternary New Jersey middle continental shelf

Seafloor geomorphology and surficial stratigraphy of the New Jersey middle continental shelf provide a detailed record of sea-level change during the last advance and retreat of the Laurentide ice sheet (120 kyr B.P. to Present). A NW–SE-oriented corridor on the middle shelf between water depths of 40 m (the mid-shelf “paleo-shore”) and 100 m (the Franklin “paleo-shore”) encompasses 500 line-km of 2D Huntec boomer profiles (500–3500 Hz), an embedded 4.6 km² 3D volume, and a 490 km² swath bathymetry map. We use these data to develop a relative stratigraphy. Core samples from published studies also provide some chronological and sedimentological constraints on the upper <5 m of the stratigraphic succession.The following stratigraphic units and surfaces occur (from bottom to top): (1) “R”, a high-amplitude reflection that separates sediment >46.5 kyr old (by AMS ¹⁴C dating) from overlying sediment wedges; (2) the outer shelf wedge, a marine unit up to 50 m thick that onlaps “R”; (3) “Channels”, a reflection sub-parallel to the seafloor that incises “R”, and appears as a dendritic system of channels in map view; (4) “Channels” fill, the upper portion of which is sampled and known to represent deepening-upward marine sediments 12.3 kyr in age; (5) the “T” horizon, a seismically discontinuous surface that caps “Channels” fill; (6) oblique ridge deposits, coarse-grained shelly units comprised of km-scale, shallow shelf bedforms; and (7) ribbon-floored swales, bathymetric depressions parallel to modern shelf currents that truncate the oblique ridges and cut into surficial deposits.We interpret this succession of features in light of a global eustatic sea-level curve and the consequent migration of the coastline across the middle shelf during the last 120 kyr. The morphology of the New Jersey middle shelf shows a discrete sequence of stratigraphic elements, and reflects the pulsed episodicity of the last sea-level cycle. “R” is a complicated marine/non-marine erosional surface formed during the last regression, while the outer shelf wedge represents a shelf wedge emplaced during a minor glacial retreat before maximum Wisconsin lowstand (i.e., marine oxygen isotope stage 3.1). “Channels” is a widespread fluvial subarial erosion surface formed at the late Wisconsin glacial maximum 22 kyr B.P. The shoreline migrated back across the mid-shelf corridor non-uniformly during the period represented by “Channels” fill. Oblique ridges are relict features on the New Jersey middle shelf, while the ribbon-floored swales represent modern shelf erosion. There is no systematic relationship between modern seafloor morphology and the very shallowly buried stratigraphic succession.     

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.     

Seasonal variability of living benthic foraminifera from the outer continental shelf of the Bay of Biscay

Living benthic foraminiferal faunas of six stations from the continental shelf of the Bay of Biscay have been investigated during three successive seasons (spring, summer and autumn 2002). For the three investigated stations, bottom water oxygen concentration, oxygen penetration into the sediment and sediment organic carbon contents are all relatively similar. Therefore, we think that the density and the composition of the foraminiferal faunas is mainly controlled by the quantity and quality of organic input resulting from a succession of phytoplankton bloom events, occurring from late February to early September. The earliest blooms are positioned at the shelf break, late spring and early summer blooms occur off Brittany, whereas in late summer and early autumn, only coastal blooms appear, often in the vicinity of river outlets. In spring, the benthic foraminiferal faunas of central (B, C and D) and outer (E) continental shelf stations are characterised by strong dominance in the first area and strong presence in the second area of Nonionella iridea. In fact, station E does not serve as a major depocenter for the remains of phytoplankton blooms. If station E is not considered, the densities of this taxon show a clear gradient from the shelf-break, where the species dominates the assemblages, to the coast, where it attains very low densities. We explain this gradient as a response to the presence, in early spring, of an important phytoplankton bloom, mainly composed of coccolithophorids, over the shelf break. This observation is supported by the maximum particles flux values at stations close to the shelf break (18.5 g m^− 2 h^− 1) and lower values in a station closer to the coast (6.8 g m^− 2 h^− 1). In summer, the faunal density is maximum at station A, relatively close to more varied phytoplancton blooms that occur off Brittany until early June. We suggest that the dominant species, Nonion fabum, Cassidulina carinata and Bolivina ex. gr. dilatata respond to phytodetritus input from these blooms. In autumn, the rich faunas of inner shelf station G are dominated by N. fabum, B. ex. gr. dilatata, Hyalinea balthica and Nonionella turgida. These taxa seem to be correlated with the presence of coastal blooms phenomena, in front of river outlets. They may be favoured by an organic input with a significant contribution of terrestrial, rather low quality organic matter.     

Architecture of turbidite channel systems on the continental slope: Patterns and predictions

The study of many slope channel systems has led to the development of rules in the form of observations, measurements, and hypotheses. For example, we hypothesize that high abandonment relief can strongly influence the location of the subsequent channel element and will result in an organized channel stacking pattern in which the path of the younger channel element approximates the path of the former element. The rules were developed with the objective of constructing forward models of petroleum reservoirs that are internally consistent, reproducible, and quantifiable. Channelized turbidite deposits can be interpreted to be the product of multiple cycles of waxing-waning flow energy at multiple scales. Systematic changes in the volume and caliber of turbidity flows through time trigger a fall of the equilibrium profile, which drives erosion and sediment bypass across the slope, followed by a rise of the equilibrium profile, which allows deposition on the slope of increasingly mud-rich sediments through time. In most turbidite successions, at least three scales of waxing-waning cyclicity can be interpreted: element, complex set, and sequence. The stacking pattern of channel elements within a complex set-scale cycle tends to be sequential: (1) erosion and sediment bypass; (2) amalgamation of channel elements associated with a low rate of aggradation; (3) a disorganized stacking pattern of channel elements associated with a moderate rate of aggradation; and (4) an organized stacking pattern of channel elements associated with a high rate of aggradation. Stages 1 and 2 may be absent or minor in mud-rich systems but prominent in sand-rich systems. Conversely, stage 4 may be prominent in mud-rich systems but absent in sand-rich systems. Event-based forward modeling, utilizing rules, can produce realistic architectures, such as the four stages described above. Multiple realizations and multiple alternative models can be constructed to quantitatively examine the probability of specific parameters of interest such as pore volume and connectivity.     

Living macromolluscs from a paleo-reef region on the northeastern Venezuelan continental shelf

Drowned reefs, fossil reefs or paleo-reefs, are important ecologically as areas of high biodiversity, foraging, shelter environment, and as areas supporting the spawning aggregations of economically important reef fish species. This is particularly significant when the structures are situated in a wide soft-bottom continental shelf. The presence of limestone structures, fossil reefs and pinnacles dating from circa 8 to 9 ka, to the north of the Paria Peninsula in north-eastern Venezuela, has been known to local fishermen for decades. Using echograms obtained during acoustic fisheries evaluations and the scarce previously available information, an improved location map of hard-bottom structures was made. Benthic samples to study macromolluscs were taken at depths between 54 and 93 m using an unmodified 2-m beam trawl. Four trawl samples were located over fossil reef areas while another four were situated in soft-bottom valleys between limestone structures. Fossil reefs in the area showed a highly patchy distribution. A total of 91 species from 43 Bivalvia, Gastropoda and Scaphopoda families were found, Gastropoda being the dominant class with 49 species. Paleo-reef-covered areas showed higher species richness and only 21% of the species found were common to both substrates. Gastropods Tonna maculosa and Polystira albida were the most abundant species and occurred in both substrate types. Bivalve life habits, a mixture of organism–substrate relationships, shell fixation, mobility and feeding type, differed significantly according to bottom type. Six species are recorded for the first time for eastern Venezuelan waters. Bottom heterogeneity plays an important role in marine ecosystems, providing shelter to fish populations and may be significant as breeding and nursery areas. Its presence in a region with biogeographical interest, situated in the confluence of three major provinces and with oceanographic conditions varying seasonally from upwelling dominated to Orinoco River discharges, makes this the area of interest and it should be evaluated as a possible Marine Protected Area.     

Taxon‐related diversity patterns from the continental shelf to the slope: a case study on nematodes from the Western Indian Ocean

A study was carried out across the continental shelf and slope in the Western Indian Ocean along the Kenyan margin to unravel depth‐related species diversity patterns portrayed by different nematode families. Sediment samples were collected along four bathymetric transects at 20, 50, 200, 500, 1000 and 2000 m. Three nematode families were selected for species analysis, based on their general occurrence with relatively high numbers and diversity from shelf to slope. All three families exhibited a distinctly different shelf and slope nematode species community. However, all three families also had a significant proportion of species that displayed a eurybathic distribution. Coincidentally, Microlaimidae, the least species‐rich family had the most eurybathic species (75%) compared to Comesomatidae (39%) and Chromadoridae (32%). Total number of species per depth zone along the sampled area (gamma diversity) was three to four times the average number of species (alpha) per station. The difference was more pronounced at the slope than at the shelf. The species turnover was also higher at the slope than at the shelf stations. Each of the three families had a different diversity pattern: Comesomatidae showed a peak at mid‐depth, Chromadoridae increased with depth, and Microlaimidae showed no prominent change with depth. When the three families were combined, the shelf maintained a lower diversity compared to the slope (both local and regional). There was no consistency between genus and species diversity patterns with depth, indicating that genus diversity data may not be a proxy for species diversity. At the lowest taxonomic level (species), the slope showed a higher diversity than the shelf, whereas at higher (genus) taxonomic level the diversity was comparable between the slope and the shelf. The number of species encountered increased with the number of samples analysed and did not reach asymptote, meaning that the area was still under‐sampled. This situation points to the possibility of an even higher regional diversity.     

Particulate barium fluxes on the continental margin: a study from the Alboran Sea (Western Mediterranean)

Particulate biogenic barium (bio-Ba) fluxes obtained from three instrumented arrays moored in the Alboran Sea, the westernmost basin in the Mediterranean Sea, are presented in this study. The mooring lines were deployed over almost 1 year, from July 1997 to May 1998, and were equipped with sediment traps at 500–700 m depth, 1000–1200 m depth and 30 m above the seafloor (1000–2200 m). The results obtained support the growing body of evidence that the relationship between particulate bio-Ba and Corg throughout the water column in margin systems is clearly different from this relation in the open ocean. In the Alboran Sea, the annual averaged bio-Ba fluxes range from 0.39 to 1.07 μmol m⁻² day⁻¹, with mean concentrations of 1.31–1.69 μmol g⁻¹ and bio-Ba/Corg ratios lower than in the open ocean. The low bio-Ba values obtained also indicate that calculating bio-Ba is extremely sensitive to the detrital Ba/Al ratio of each sample. The lithogenic Ba fraction in the Alboran Sea continental margin area contributes between 24% and 85% of the total Ba. Increased bio-Ba export efficiency was observed after periods of high primary productivity and suggests that the processes limiting the bio-Ba formation in the study area relate to settling dynamics of organic matter aggregates. Furthermore, the ballasting effect of the abundant lithogenic and carbonate particles may limit decomposition of organic matter aggregates and enhance the transfer of particles rich in Corg and relatively poor in bio-Ba to the deep seafloor. Lateral input of freshly sedimented biogenic material, including particulate bio-Ba, has been observed on the lower continental slope in the western Alboran Sea. These observations emphasize that the use of the bio-Ba as a proxy of export productivity from the surface ocean must be used cautiously in highly dynamic environments such as those in the Alboran Sea.     

Laboratory characterization of the porosity and permeability of gas shales using the crushed shale method: Insights from experiments and numerical modelling

Gas production from shale resource plays has transformed the USA energy market. Despite the knowledge gained from the analysis of large amounts of shale core, appraisal of shale gas resource plays requires a large number of wells to be drilled and tested. Ideally, core analysis results would provide an indication of both the gas filled porosity and permeability of shale resource plays, which could then be used to reduce the number of wells needed during appraisal. A combination of laboratory experiments, numerical modelling and a round-robin test have been conducted to assess the validity of the crushed shale method (CSM), which has been widely used in industry to assess the porosity and permeability of shale. The results suggest that the CSM can provide reasonably precise estimates of porosity measured at ambient stress if a standard sample cleaning method is adopted; although a reliable method to correct these values to subsurface conditions needs to be developed. The CSM does not, however, appear to provide useful information on shale permeability. A round-robin test shows that differences of up to four orders of magnitude in permeability were provided by different laboratories when analysing the same sample. These huge differences seem to occur due to a combination of errors in calculating permeabilities from pressure transients, differences in the way that permeability is calculated as well as uncertainties regarding the effective size of crushed shale particles. However, even if standardized, the CSM may not be particularly useful for characterizing the flow capacity of shale because it is insensitive to the presence of high permeability zones that would control flow in the subsurface.     

Spatial patterns and environmental drivers of benthic infaunal community structure and ecosystem function on the New Zealand continental margin

To investigate regional drivers of spatial patterns in macro- and meio-faunal community structure (abundance, biomass and taxonomic diversity) and ecosystem function (sediment community oxygen consumption [SCOC]), we sampled two regions in close proximity on New Zealand's continental margin—the Chatham Rise and the Challenger Plateau. Sites (n = 15) were selected in water depths ranging from 266–1212 m to generate a gradient in sedimentary properties and, in particular, surface pelagic productivity. Both macro- and meio-fauna abundance and biomass was 2–3.5 times higher on the Chatham Rise than on the Challenger Plateau, reflecting regional differences in pelagic primary production. We also found significant inter- and intra-regional differences in macro-fauna taxonomic diversity with two distinctive site groupings in each region. Univariate and multivariate measures of macro-fauna community attributes were most strongly correlated with sediment photosynthetic pigment (explaining 24%–59% of the variation). Sediment pigment content was as equally important in explaining meio-fauna community structure (36%–7%). Unlike community structure, SCOC was most strongly correlated with depth (44%), most likely reflecting temperature effects on benthic metabolism. Our results highlight the importance of a benthic labile food supply in structuring infaunal communities on continental margins and emphasise a tight coupling between pelagic and benthic habitats.     

Oblique rifting in the Havre Trough and its propagation into the continental margin of New Zealand: Comparison with analogue experiments

The Havre Trough is opening by oblique back-arc rifting which is propagating into the continental margin of New Zealand at the Taupo Volcanic Zone. Variations of deformational style along the rift axis have been investigated by comparison with analogue experiments which incorporate brittle and ductile rheologies and are scaled for gravity. Based on the results of the analogue experiments, we present a tectonic model for oblique rifting in the Havre Trough, which involves the rheological contrast between oceanic and continental lithosphere and the oblique geometry of the continental margin of New Zealand with respect to the regional rift trend. The model shows that the continental margin, which is weaker than both oceanic and continental lithosphere, cannot support large shear stresses. The two lithospheres can be decoupled during extensional events along the marginal shear and, depending on the continental margin orientation, this shear can modify the regional stress field. A heterogeneous stress field will rotate normal stresses to be perpendicular or parallel to the margin. As the two lithospheres decouple during extension, the rift grabens and internal faults of the oblique rift system propagate normal to the marginal shear. This model explains the oblique trend of the Havre Trough's tectonic fabric and its relationships to the Vening Meinesz Fracture Zone which represents the oceanic/continental lithospheric boundary.As the Havre Trough rift propagates into the continental margin, rheological differences between oceanic and continental lithosphere result in variations in distribution of strain along the rift axis. Extension of oceanic sub-arc lithosphere is localized into a single rift graben. At the transition into continental rifting, the zone of extension widens into a number of rift grabens forming complex indentations into the margin. This change in deformation style is consistent with analogue experiments as well as other natural examples and results from the contrast in lithospheric rheology and its influence on the process of strain localization.     

Isotopic signatures of organic matter in sediments of the continental shelf facing the Orinoco Delta: Possible contribution of organic carbon from savannas

The ⁸⁷Sr, ¹³C, and ¹⁵N isotopic signatures of organic matter in sediments from the continental shelf facing the Orinoco Delta were measured to determine the contribution of sediments transported from the Amazon River by the coastal Guayana current and the sediments transported by the Orinoco River. Box core samples between 60 and 300 m water depth collected along 4 transects located eastwards to the Orinoco Delta were analyzed. Carbon and nitrogen concentrations decreased with depth under water on the shelf, and were strongly correlated indicating homogeneity of organic matter composition. Phosphorus content was also associated to organic matter in most samples, but some of them revealed deposition of P-enriched sediments. The ⁸⁷Sr/⁸⁶Sr ratios showed a strong continental signature averaging 0.7117, therefore, limiting the possible carbon and nitrogen sources associated with these sediments to C3 trees, C4 grasses, or freshwater phytoplankton. The δ¹³C values were relatively high averaging −21‰, above values reported for sediments on the Amapá shelf and the Amazon River in Brazil. Average δ¹³C values did not differ significantly among transects. High δ¹³C values point to the influence of organic matter transported from the C4-plants dominated savannas in the northern fringe of the Orinoco River. δ¹⁵N values were positive and averaged 5‰, being within the range of values measured in the Marajo island (Amazon River) and the estuary of the Pará River. The δ¹⁵N values differed significantly among transects (4.9–5.2‰), lowest values corresponding to the northernmost transect near the coast of Trinidad, and the highest values corresponding to the transect located at the southernmost position.     

MTD distribution on a ‘passive’ continental margin: The Espírito Santo Basin (SE Brazil) during the Palaeogene

Mass-wasting on the Brazilian margin during the Mid-Eocene/Oligocene resulted in the accumulation of recurrent Mass Transport Deposits (MTDs) offshore Espírito Santo, SE Brazil. In this paper, we use three-dimensional seismic data to characterize a succession with stacked MTDs (Abrolhos Formation), and to assess the distribution of undeformed stratigraphic packages (i.e. turbidites) with reservoir potential separating the interpreted MTDs. High-amplitude strata in less deformed areas of MTDs reflect their internal heterogeneity, as well as possible regions with a higher sand content. Separating MTDs, turbiditic intervals reach 100 ms Two-Way Travel Time (TWTT), with thicker areas coincident with the flanks of growing diapirs and areas of the basin where mass-wasting is less apparent. Turbiditic strata laterally grade into, or are eroded by MTDs, with transitional strata between MTDs and turbidites being also influenced by the presence of diapirs. MTDs show average thickness values ranging from 58 to 82 ms TWTT and constitute over 50% of Eocene-Oligocene strata along the basin slope. Low average accumulations of 58 ms TWTT in areas of high confinement imposed by diapirs suggest sediment accumulation upslope, and/or bypass into downslope areas. This character was induced by the high sediment input into the basin associated with coastal erosion and growth of the Abrolhos volcanic plateau. Our results suggest that significant amounts of sediment derive from the northwest, and were accumulated in the middle-slope region. Interpretations of (palaeo)-slope profiles led to the establishment of a model of margin progradation by deposition of MTDs, contrasting with the retrogressive erosional margins commonly associated with these settings.     

巴丹吉林沙漠南缘高台盐湖记录的中晚全新世气候变化

位于季风边缘区和受西风环流显著影响的巴丹吉林沙漠南缘的高台盐湖提供了中晚全新世亚洲干旱区气候变化的可靠记录。在OSL测年的基础上,通过对高台盐湖剖面CaCO3含量、色度（L*、a*、b*）、粒度端元组分（EM）等环境代用指标的综合分析,重建了我国西北地区中晚全新世的气候变化。结果表明,中晚全新世高台盐湖地区气候变化经历了4个阶段：约7.1～5.3 ka,代表河流作用的EM2占主导,为浅湖/滨湖相沉积环境,气候相对干旱;5.3～1.2 ka期间,代表悬移作用的EM1占主导,指示深湖相沉积环境,CaCO3含量和a*和b*指示流域降水增多,地表侵蚀加强,近源物质输入较多,为中晚全新世以来的最湿润期;1.2～0.2 ka期间,EM2指示沉积环境转为滨湖/浅湖相沉积,气候变干;0.2 ka以来,气候进一步变干,湖泊消亡,演变为现代沙丘堆积。区域古气候替代记录的对比表明,高台地区中晚全新世以来演化过程与中亚干旱区湖泊记录具有一致性,气候变化主要受西风环流与高纬度北大西洋共同影响。     

Salt structures in the Laizhouwan depression, offshore Bohai Bay basin, eastern China: New insights from 3D seismic data

Using the new high-quality 3D seismic data, this paper addresses the salt structures in the KL11 area of the Laizhouwan depression in the southern offshore Bohai Bay basin. In the study area, the salt in the Sha-4 Member of the Paleogene Shahejie Formation thickened, and then formed an S–N trending salt wall, which changes shape regularly along its trend from salt diapir to salt pillow. The change in thickness of the suprasalt layers record five growth phases of the salt wall from the Eocene to the Quaternary: (1) early diapirism, (2) active diapirism, (3) passive diapirism, (4) relative structural quiescence, and (5) arching. The evolution of the salt structures was mostly governed by the multi-phase compression induced by the dextral strike-slip of the Tan–Lu fault, which formed a restraining bend in the study area. There was an original passive stock in the south, which was later tectonically squeezed by E–W compression and became a diapir. As the shortening propagated to the north from the original stock, the salt pillow was created in the north. Relative structural quiescence then followed until the next phase of compression, which arched the thick roof of the salt wall.     

火成岩体在现今陆坡形态调整中的作用：来自南海东沙群岛近海陆坡的启示

对从南海东沙群岛近海陆坡（水深约500-3100m）采集到的二维地震剖面提取地形数据后进行统计学分析,结合地震相研究,发现研究区陆坡形态的变化与火成岩体,以及与火成岩体相关联的沉积过程存在着紧密地联系。共识别出了3种陆坡类型：（a）发育多个火成岩体的粗糙、陡的陆坡（类型1）;（b）发育单个火成岩体的较为光滑、平缓的陆坡（类型2）;（c）无火成岩体发育的光滑并且平缓的陆坡（类型3）。这些火成岩体形成于南海海底扩张之后,具有较为复杂的形态,在地震剖面上多表现为强振幅的杂乱反射。在类型1中,多个火成岩体将陆坡分为上部的两个或者多个次凹和下部的一个主凹,这些凹陷可以同时被沿坡流带来的沉积物充填。然而在类型2中,单个火成岩体将陆坡为一个上部的次凹和一个下部的主凹,只有当上部的次凹被沉积物填满后,沉积物才可以开始充填主凹。类型3为发育斜坡沉积的正常陆坡。研究区现今的陆坡形态是由于火成岩体的侵入和与火成岩体相关的沉积过程所共同导致的陆坡形态调整的结果。三种陆坡类型现今陆坡形态间的差异指示不同的沉积条件和陆坡形态调整。