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Active continental margins are tectonic sites with complex sedimentary processes. Tectono–sedimentary interactions occur over geological time and determine the modern morphology of the margin. However, such interactions have been poorly documented in high‐latitude regions. This study focuses on deep‐water sedimentary systems on the South Shetland convergent margin, which is the only remaining active continental margin in Antarctica. Numerous gullies, 20 canyons and three contourite drifts are identified by interpreting bathymetry, oceanography and reflection seismic data. Heavy mineral contents of a gravity core, located at a downslope elongated mounded drift, show the asynchronous interplay of downslope and alongslope processes. The rest of the margin is dominated by turbidity currents. Variations in the slope gradient control thalweg profiles and sinuosity of canyons. Tectonic‐related morphology restricts the distribution of contourite drifts. Earthquakes triggered by underplating and tectonic compression may induce slope instability at the lower flank of the plastered drift. Tectonic uplift influences the amount of sediments transported by ice sheets and controls the shelf stacking pattern. The mixed turbidite–contourite system transitions to separated canyon and drift systems from passive to active continental margins under the influence of the tectonic‐related morphology. A systematic comparison has been made among several convergent margins with similar tectonic settings. Results suggest that submarine canyons on these shelf‐slope systems have similar morphological features and are comparable in size. Coarse sediment input and steep continental slopes (mean slope 7 to 10°) control the canyon morphology on these margins. Therefore, this research has important implications for furthering the current understanding of sedimentary systems on high‐latitude convergent margins and tectono–sedimentary interactions. [ABSTRACT FROM AUTHOR]

Well‐exposed, vertically dipping, glacially polished outcrops of the Neoproterozoic Windermere Supergroup in the southern Canadian Cordillera include basin‐floor deposits of the Upper Kaza Group overlain by slope channel complexes of the Isaac Formation. Within the 2·5 km thick Kaza and Isaac succession is an up to 360 m thick interval composed of diverse deep‐water stratal elements including scour and interscour deposits, distributary channels, fine‐grained turbidites, terminal splays, mass‐transport deposits, erosional and levéed channels and avulsion splays, which collectively were formed during the development of an ancient passive‐margin channel‐lobe system. The proportion and vertical and lateral arrangement of stratal elements reveal three distinct complexes. The lower complex, consisting mostly of distributary channels and small and large scours, is interpreted to represent the detachment of lobes from an upflow levéed channel, wherein a well‐developed channel‐lobe transition zone was formed by efficient, siliciclastic flows during a period of sustained transport bypass and limited deposition coincident with the onset of falling relative sea level. The middle, comparatively thicker and more sandstone‐rich complex, comprises distributary channel fills, fine‐grained turbidites and lesser terminal splays that are interspersed with small scours, capped by a slope levéed channel filled with coarser‐grained siliciclastic sediment. The abundance of basin‐floor elements suggests negligible separation between the levéed channel and lobe, and therefore a poorly‐developed channel‐lobe transition zone, resulting from inefficient, siliciclastic‐rich depositional flows that became dominant during lowstand and/or ensuing transgression. The stratal makeup of the upper complex resembles the lower detached complex, suggesting a return to efficient flows, and an abrupt change to mixed carbonate–siliciclastic sediments associated with highstand conditions. Accordingly, the stratigraphic architecture and stacking pattern of the Kaza–Isaac interval, which relate to the formation of multiple channel‐lobe transition zones, were controlled by temporal changes in sediment supply and flow characteristics during the long‐term progradation of the Laurentian continental margin. [ABSTRACT FROM AUTHOR]

The Shetland Isles represent an ideal field laboratory for tsunami geoscience research. This is due to the widespread preservation of Holocene tsunami sediments in coastal peat deposits. This study uses published accounts of the Holocene Storegga Slide tsunami to illustrate how two different approaches – mapping of tsunami sediments and numerical modelling – produce radically different run‐up heights. The Storegga Slide is one of the world largest submarine slides and took place ca 8150 cal yr bp on the continental slope west of Norway. The tsunami generated by the landslide deposited locally extensive sheets of marine sand and gravel, as well as redeposited clasts of peat across the contemporary land surface. These sediment accumulations have subsequently been buried by peat growth during the Holocene while exposures of the deposits are locally visible in coastal cliff sections. In several areas, the tsunami sediments can be traced upslope and inland within the peat as tapering sediment wedges up to maximum altitudes of between ca 8·1 m and 11·8 m above present sea level. Since reconstructions of palaeo‐sea level for Shetland for ca 8150 cal yr bp suggest an altitude of 20 m below high tide on the day that the tsunami struck, it has been inferred that the minimum tsunami run‐up was locally between 28·1 m (8·1 + 20 m) and 31·8 m (11·8 + 20 m). However, numerical models of the tsunami for Shetland suggest that the wave height may only have reached a highest altitude in the order of +13 m above sea level on the day the tsunami took place. In this paper a description is given of the sedimentary evidence for tsunami run‐up in the Shetland Isles. This is followed by an evaluation of where the palaeo‐sea level was located when the tsunami occurred. Significant differences are highlighted in tsunami inundation estimates between those based on the observed (geological) data and the theoretically‐modelled calculations. This example from the Shetland Isles may have global significance since it exemplifies how two different approaches to the reconstruction of tsunami inundation at the coast can produce radically different results with modelled wave height at the coast being considerably less than the geological estimates of tsunami run‐up. [ABSTRACT FROM AUTHOR]

Abstract: Content and fluxes of ice‐transported sand‐sized and gravel‐sized, lithic particles in marine sediment cores are a common tool used to reconstruct glacial variability. Ice‐rafted debris data sets are currently acquired in several different and often time‐consuming ways, and within various grain‐size fractions. This article proposes a novel workflow using an automated method to count ice‐rafted debris to reduce analysis time and subjectivity. The described method is based on the instrument ‘Morphologi G3’ from Malvern Instruments Limited and includes all pre‐processing and post‐processing steps. This particle characterization tool is an automated microscope combined with a proprietary software package. In this study, the analysis was performed on the 150 to 1000 μm fraction. If desired, grain counts can be carried out on the entire sand and silt fractions. However, this would result in a considerably greater turnover time. A total of 350 sediment samples from core MD99‐2283, taken on the upper continental slope at the southern part of the north‐east Atlantic margin, were counted with this automated method. In addition, a total of 161 samples were counted manually as a control on the reliability of the scanning. The comparison of automated versus manually counted biogenic and lithic material shows a convincing correlation between the two methods. The turnover time per automatically counted sample is around 20 min, the method requiring less experience and skills than manual counting. The results yield a promising, time‐saving new technique to achieve high‐resolution ice‐rafted debris counting records with acceptable error margins. [ABSTRACT FROM AUTHOR]

Abstract: Active margin continental slope outcrops from the Eocene Juncal Formation, the Eocene La Jolla Group and the Miocene Capistrano Formation display sedimentary structures and depositional geometries that suggest deposition from Froude supercritical flow, based on comparison to strata produced by flume experiments. These deposits range from boulder‐size soft clasts and cobble‐size hard clasts to silt and mud, and display long‐wavelength and low‐amplitude convex‐up and concave‐up geometries that range from centimetre to hundreds of metres scale, low‐angle foresets and backsets, and common internal and bounding erosion surfaces from centimetres to tens of metres in depth. In places, planar laminations, structureless beds and normally graded beds are laterally or vertically associated with such structures. In other places, consistent backsets or deep and steep‐sided scours occur. This study aimed to discuss the origin of the observed bedforms, contributed to recognition of supercritical flow deposits on continental slopes and expanded the outcrop examples of supercritical flow deposits to silt and mud. This work implies that the erosive and powerful Froude supercritical flow turbidity currents may have a substantial impact on erosional and depositional dynamics on deepwater slopes, especially on active margins due to the steep gradients and high sediment supply. [ABSTRACT FROM AUTHOR]

Depositional slope systems along continental margins contain a record of sediment transfer from shallow-water to deep-water environments and represent an important area for natural resource exploration. However, well-preserved outcrops of large-scale depositional slopes with seismic-scale exposures and tectonically intact stratigraphy are uncommon. Outcrop characterization of smaller-scale depositional slope systems (i.e. < 700 m of undecompacted shelf-to-basin relief) has led to increased understanding of stratigraphic packaging of prograding slopes. Detailed stacking patterns of facies and sedimentary body architecture for larger-scale slope systems, however, remain understudied. The Cretaceous Tres Pasos Formation of the Magallanes Basin, southern Chile, presents a unique opportunity to evaluate the stratigraphic evolution of such a slope system from an outcrop perspective. Inherited tectonic relief from a precursor oceanic basin phase created shelf-to-basin bathymetry comparable with continental margin systems (∼1000 m). Sedimentological and architectural data from the Tres Pasos Formation at Cerro Divisadero reveal a record of continental margin-scale depositional slope progradation and aggradation. Slope progradation is manifested as a vertical pattern exhibiting increasing amounts of sediment bypass upwards, which is interpreted as reflecting increasing gradient conditions. The well-exposed, seismic-scale outcrop is characterized by four 20 to 70 m thick sandstone-rich successions, separated by mudstone-rich intervals of comparable thickness (40 to 90 m). Sedimentary body geometry, facies distribution, internal bedding architecture, sandstone richness and degree of amalgamation were analysed in detail across a continuous 2·5 km long transect parallel to depositional dip. Deposition in the lower section (Units 1 and 2) was dominated by poorly channellized to unconfined sand-laden flows and accumulation of mud-rich mass transport deposits, which is interpreted as representing a base of slope to lower slope setting. Evidence for channellization and indicators of bypass of coarse-grained turbidity currents are more common in the upper part of the > 600 m thick succession (Units 3 and 4), which is interpreted as reflecting increased gradient conditions as the system accreted basinward. [ABSTRACT FROM AUTHOR]

Describes depositional architecture and sedimentary processes of continental slopes. Variation in the area of sea floor covered by individual flows; Average thickness of deposits; Measure of deposit diameter; Upper slope erosional features.