Abstract Over the last 50 years, the North Sea and the Atlantic Margin and, more recently the Barents Sea, represented key study areas for academic and professionals interested in the exploration for and production of hydrocarbon from the Earth's subsurface. Nowadays, these areas may play a major role in the so-called ‘energy transition’, with the energy industry now seeking to reduce emissions related to hydrocarbon consumption, and leading the development of carbon capture and storage activities, such as the Northern Light project ( https://northernlightsccs.com ). Consequently, there is an increasing interest in advancing our knowledge regarding the stratigraphy, sedimentology and tectonic development of the North Sea, Atlantic Margin and Barents Sea with a cross-border approach.

Abstract Permo-Triassic rift basins offer important hydrocarbon targets along the Atlantic margins. Their fill is dominated by continental red beds, comprising braided fluvial, alluvial fan, aeolian, floodplain and lacustrine facies. These relatively lightly explored basins span both the Atlantic and Tethyan domains and developed above a complex basement with inherited structural fabrics. Sparse data in offshore regions constrain understanding of depositional geometries and sedimentary architecture, further impeded by their deep burial beneath younger strata, combined with the effects of later deformation during continental breakup. This paper provides results from a multidisciplinary analysis of basins along the Atlantic margin. Regional seismic and well data, combined with geochemical provenance analysis from the European North Atlantic margins, are integrated with detailed outcrop studies in Morocco and Nova Scotia. The research provides new insights into regional basin tectonostratigraphic evolution, sediment fill, and reservoir distribution, architecture and quality at a range of scales. Regional seismic profiles, supported by key well data, indicate the presence of post-orogenic collapse basins, focused narrow rifts and low-magnitude multiple extensional depocentres. Significantly, Permo-Triassic basin geometries are different and more varied than the overlying Jurassic and younger basins. Provenance analysis using Pb isotopic composition of detrital K-feldspar yields new and robust controls on the sediment dispersal patterns of Triassic sandstones in the NE Atlantic margin. The evolving sedimentary architecture is characterized by detailed sedimentological studies of key outcrops of age equivalent Permian–Triassic rifts in Morocco and Nova Scotia. The interplay of tectonics and climate is observed to influence sedimentation, which has significant implications for reservoir distribution in analogue basins. New digital outcrop techniques are providing improved reservoir models, and identification of key marker horizons and sequence boundaries offers a potential subsurface correlation tool. Future work will address source and seal distribution within the potentially petroliferous basins.

No abstract available.

The seafloor off greater Los Angeles, California, has been extensively studied for the past century. Terrain analysis of recently compiled multibeam bathymetry reveals the detailed seafloor morphology along the Los Angeles Margin and San Pedro Basin. The terrain analysis uses the multibeam bathymetry to calculate two seafloor indices, a seafloor slope, and a Topographic Position Index. The derived grids along with depth are analyzed in a hierarchical, decision-tree classification to delineate six seafloor provinces—high-relief shelf, low-relief shelf, steep-basin slope, gentle-basin slope, gullies and canyons, and basins. Rock outcrops protrude in places above the generally smooth continental shelf. Gullies incise the steep-basin slopes, and some submarine canyons extend from the coastline to the basin floor. San Pedro Basin is separated from the Santa Monica Basin to the north by a ridge consisting of the Redondo Knoll and the Redondo Submarine Canyon delta. An 865-m-deep sill separates the two basins. Water depths of San Pedro Basin are ~100 m deeper than those in the San Diego Trough to the south, and three passes breach a ridge that separates the San Pedro Basin from the San Diego Trough. Information gained from this study can be used as base maps for such future studies as tectonic reconstructions, identifying sedimentary processes, tracking pollution transport, and defining benthic habitats.

High-resolution sonar data are necessary to map bottom substrate for habitat studies but are lacking over much of the continental shelf. With such data, areas covered by sediment can be distinguished from bedrock areas with an accuracy of ~90%. Without these data, the extent of sediment as thick as 10 m cannot be resolved, and estimates of the extent of rocky seafloor are exaggerated. A study area north of Anacapa Island in Southern California interpreted as a large rocky area after mapping with low-resolution seismic systems was found to have exposed rocky bottom in only 10% of the area when mapped with high-resolution, side-scan sonar. The area of rock was estimated using video-supervised, sonar-image classification of textural derivatives of the data calculated from gray-level co-occurrence matrices. The classification of soft bottom was found to be ~90% accurate using an independent data set, derived from seafloor sampling records. Two general types of rock exposure are observed—sparse linear outcrops of layered sedimentary rocks and more massive, rounded outcrop areas of volcanic rocks. The percentage of exposed rock in volcanic areas exceeded that in sedimentary rock areas by a factor of 5 in the study area north of Anacapa Island. South of Point Arguello, 80% of the shelf seafloor is underlain by sedimentary rock units. The percentage of area that is exposed, rocky-reef habitat may be greater in other areas of coastal seafloor if the bedrock is predominantly volcanic.

No abstract available.

The sources of sediment to the Southern California Bight were investigated with new calculations and published records of sediment fluxes, both natural and anthropogenic. We find that rivers are by far the largest source of sediment, producing over 10 × 10 6 t/yr on average, or over 80% of the sediment input to the Bight. This river flux is variable, however, over both space and time. The rivers draining the Transverse Ranges produce sediment at rates approximately an order of magnitude greater than the Peninsular Ranges (600–1500 t/km 2 /yr versus <90 t/km 2 /yr, respectively). Although the Transverse Range rivers represent only 23% of the total Southern California watershed drainage area, they are responsible for over 75% of the total sediment flux. River sediment flux is ephemeral and highly pulsed due to the semiarid climate and the influence of infrequent large storms. For more than 90% of the time, negligible amounts of sediment are discharged from the region's rivers, and over half of the post-1900 sediment load has been discharged during events with recurrence intervals greater than 10 yr. These rare, yet important, events are related to the El Niño–Southern Oscillation (ENSO), and the majority of sediment flux occurs during ENSO periods. Temporal trends in sediment discharge due to land-use changes and river damming are also observed. We estimate that there has been a 45% reduction in suspended-sediment flux due to the construction of dams. However, pre-dam sediment loads were likely artificially high due to the massive land-use changes of coastal California to rangeland during the nineteenth century. This increase in sediment production is observed in estuarine deposits throughout coastal California, which reveal that sedimentation rates were two to ten times higher during the nineteenth and twentieth centuries than during pre-European colonization.

The rivers of Southern California deliver episodic pulses of water, sediment, nutrients, and pollutants to the region's coastal waters. Although river-sediment dispersal is observed in positively buoyant (hypopycnal) turbid plumes extending tens of kilometers from river mouths, very little of the river sediment is found in these plumes. Rather, river sediment settles quickly from hypopycnal plumes to the seabed, where transport is controlled by bottom-boundary layer processes, presumably including fluid-mud (hyperpycnal) gravity currents. Here we investigate the geographical patterns of river-sediment dispersal processes by examining suspended-sediment concentrations and loads and the continental shelf morphology offshore river mouths. Throughout Southern California, river sediment is discharged at concentrations adequately high to induce enhanced sediment settling, including negative buoyancy. The rivers draining the Western Transverse Range produce suspended-sediment concentrations that are orders of magnitude greater than those in the urbanized region and Peninsular Range to the south, largely due to differences in sediment yield. The majority of sediment discharge from the Santa Clara River and Calleguas Creek occurs above the theoretical negative buoyancy concentration (>40 g/l). These rivers also produce event sediment loading as great as the Eel River, where fluid-mud gravity currents are observed. The continental shelf of Southern California has variable morphology, which influences the ability to transport via gravity currents. Over half of the rivers examined are adjacent to shelf slopes greater than 0.01, which are adequately steep to sustain auto-suspending gravity currents across the shelf, and have little (<10 m) Holocene sediment accumulation. Shelf settings of the Ventura, Santa Clara, and Tijuana Rivers are very broad and low sloped (less than 0.004), which suggests that fluid-mud gravity currents could transport across these shelves, albeit slowly (~10 cm/s) and only with adequate wave-generated shear stress and sediment loading. Calleguas Creek is unique in that it discharges directly into a steep-sloped canyon (greater than 0.1) that should allow for violent auto-suspending gravity currents. In light of this, only one shelf setting—the Santa Clara and Ventura—has considerable Holocene sediment accumulation (exceeding 60 m), and here we show that the morphology of this shelf is very similar to an equilibrium shape predicted by gravity-current sediment transport. Thus, we conclude that a wide distribution of river-shelf settings occur in the Southern California Bight, which will directly influence sediment dispersal processes—both dilute suspended and gravity-current transport—and sediment-accumulation patterns.

Sediment discharged into the portion of the Southern California Bight extending from Santa Barbara to Dana Point enters a complex system of semi-isolated coastal cells, narrow continental shelves, submarine canyons, and offshore basins. On both the Santa Monica and San Pedro margins, 210 Pb accumulation rates decrease in an offshore direction (from ~0.5 g cm −2 yr −1 to 0.02 g cm −2 yr −1 ), in concert with a fining in sediment grain size (from 4.5φ to 8.5φ), suggesting that offshore transport of wave-resuspended material occurs as relatively dilute nepheloid layers and that hemiplegic sedimentation dominates the supply of sediment to the outer shelf, slope, and basins. Together, these areas are effectively sequestering up to 100% of the annual fluvial input. In contrast to the Santa Monica margin, which does not display evidence of mass wasting as an important process of sediment delivery and redistribution, the San Pedro margin does provide numerous examples of failures and mass wasting, suggesting that intraslope sediment redistribution may play a more important role there. Basin deposits in both areas exhibit evidence of turbidites tentatively associated with both major floods and earthquakes, sourced from either the Redondo Canyon (San Pedro Basin) or Dume Canyon (Santa Monica Basin). On the Palos Verdes shelf, sediment-accumulation rates decrease along and across the shelf away from the White's Point outfall, which has been a major source of contaminants to the shelf deposits. Accumulation rates prior to the construction of the outfall were ~0.2 g cm −2 yr −1 and increased 1.5–3.7 times during peak discharges from the outfall in 1971. The distal rate of accumulation has decreased by ~50%, from 0.63 g cm −2 yr −1 during the period 1971–1992 to 0.29 g cm −2 yr −1 during the period 1992–2003. The proximal rate of accumulation, however, has only decreased ~10%, from 0.83 g cm −2 yr −1 during the period 1971–1992 to 0.73 g cm −2 yr −1 during the period 1992–2003. Effluent-affected sediment layers on the Palos Verdes shelf can be identified in seabed profiles of naturally occurring 238 U, which is sequestered in reducing sediments. The Santa Clara River shelf, just north and west of the Santa Monica and San Pedro margins, is fine-grained and flood-dominated. Core profiles of excess 210 Pb from sites covering the extent of documented major flood deposition exhibit evidence of rapidly deposited sediment up to 25 cm thick. These beds are developing in an active depocenter in water depths of 30–50 m at an average rate of 0.72 g cm −2 yr −1 . Budget calculations for annual and 50-yr timescale sediment storage on this shelf shows that 20%–30% of the sediment discharge is retained on the shelf, leaving 70%–80% to be redistributed to the outer shelf, slope, Santa Barbara Basin, and Santa Monica Basin.

Sedimentary strata on the Southern California shelf and slope (Point Conception to Dana Point) display patterns and rates of sediment accumulation that convey information on sea-level inundation, sediment supply, and oceanic transport processes following the Last Glacial Maximum. In Santa Monica Bay and San Pedro Bay, postglacial transgression is recorded in shelf deposits by wave-ravinement surfaces dated at 13–11 ka and an upsection transition from coastal to shallow-marine sediment facies. Depositional conditions analogous to the modern environment were established in the bays by 8–9 ka. On the continental slope, transgression is evidenced in places by an increase in sediment grain size and accumulation rate ca. 15–10 ka, a consequence of coastal ravinement and downslope resedimentation, perhaps in conjunction with climatic increases in fluvial sediment delivery. Grain sizes and accumulation rates then decreased after 12–10 ka when the shelf flooded and backfilled under rising sea level. The Santa Barbara coastal cell contains the largest mass of postglacial sediment at 32–42 × 10 9 metric tons, most of which occurs between offshore Santa Barbara and Hueneme Canyon. The San Pedro cell contains the second largest quantity of sediment, 8–11 × 10 9 metric tons, much of which is present on the eastern Palos Verdes and outer San Pedro shelves. By comparison, the mass of sediment sequestered within the Santa Monica cell is smaller at ~6–8 × 10 9 metric tons. The postglacial sediment mass distribution among coastal cells reflects the size of local fluvial sediment sources, whereas intracell accumulation patterns reflect antecedent bathymetric features conducive for sediment bypass or trapping.