Abstract Submarine landslides triggered by earthquakes can generate turbidity currents. Recently, several studies have reported that the remobilization of surface sediment triggered by earthquakes can also generate turbidity currents. Such sedimentary processes may be influenced by sediment characteristics, seafloor morphology and seismic motions. Here, we verify surface sediment remobilization using sedimentary records from the Nankai forearc region, SW Japan. We collected multi-core and piston core samples from a small confined basin, mainly composed of silty clay or very fine sand. Radiocaesium measurements of the multi-core show consistently high values in the upper 17 cm and low values below this depth. Rapid sediment deposition after 1950 is assumed, and the most likely cause is the 2004 off the Kii Peninsula earthquake. Based on calculations using bathymetric maps and palaeocurrent data, settlement of the upper 17 cm can be explained by redeposition of the surface ( c. 1 cm) slope sediment around the basin. Muddy turbidites are also identified in the piston core. The gap in radiocarbon age observed around 2.0 m bsf (metres below seafloor) implies similar sedimentary processes. Our study represents the first examination of surficial remobilization from sedimentary cores in the Nankai forearc region.

Abstract A M w 7.2 earthquake centred beneath the upper Laurentian Fan of the SW Newfoundland continental slope triggered a damaging turbidity current and tsunami on 18 November 1929. The turbidity current broke telecommunication cables, and the tsunami killed 28 people and caused major infrastructure damage along the south coast of Newfoundland. Both events are believed to have been derived from sediment mass failure as a result of the earthquake. This study aims to identify the volume and kinematics of the 1929 slope failure in order to understand the geohazard potential of this style of sediment failure. Ultra-high-resolution seismic reflection and multibeam swath bathymetry data are used to determine: (1) the dimension of the failure area; (2) the thickness and volume of failed sediment; (3) fault patterns and displacements; and (4) styles of sediment failure. The total failure area at St Pierre Slope is estimated to be 5200 km 2 , recognized by escarpments, debris fields and eroded zones on the seafloor. Escarpments are typically 20–100 m high, suggesting failed sediment consisted of this uppermost portion of the sediment column. Landslide deposits consist mostly of debris flows with evidence of translational, retrogressive sliding in deeper water (>1700 m) and evidence of instantaneous sediment failure along fault scarps in shallower water (730–1300 m). Two failure mechanisms therefore seem to be involved in the 1929 submarine landslide: faulting and translation. The main surficial sediment failure concentrated along the deep-water escarpments consisted of widely distributed, translational, retrogressive failure that liquefied to become a debris flow and rapidly evolved into a massive channelized turbidity current. Although most of the surficial failures occurred at these deeper head scarps, their deep-water location and retrogressive nature make them an unlikely main contributor to the tsunami generation. The localized fault scarps in shallower water are a more likely candidate for the generation of the tsunami, but further research is needed in order to address the characteristics of these fault scarps.

Abstract We construct a Paleogene North America-Gulf of Mexico sediment budget, accounting for sources and sinks, to constrain the temporal and spatial distribution of sediment. Sediment supply is derived from empirical geomorphic relationships, as well as an integrated, source-to-sink numerical model of landscape evolution for denudation linked to fluvial and deltaic sediment transport and deposition. Knowledge of sediment supply from source areas informs predictions of unaccounted deposits of the deep-water Wilcox Formation by assuming budget closure. These first-order predictions can be coupled with high-resolution, probabilistic geomorphic and stratigraphic scaling relationships to provide long-range trends in depositional facies and architecture that link to oil and gas reservoir modeling.

Abstract We illustrate how sediment budgets can be used to understand the relationships between tectonics and sedimentation and to estimate the partitioning of sediment in shelf, slope, and basin-floor fan compartments within ancient shelf-margin strata. The studied Lewis-Fox Hills shelf margin represents the early Maastrichtian infill of the Laramide-type Washakie-Great Divide basin of southern Wyoming. The shelf margin shows an evolution in two stages. In Stage 1, the shelf margin is characterized by rising shelf-edge trajectory associated with increasing clinothem volumes, widening marine topsets, and increasing clinoform heights; a relatively large fraction of the sediment budget is stored on the shelf compartment through Stage 1. In Stage 2, the shelf-edge trajectory becomes more progradational and is associated with decreasing clinothem volumes, wide coastal-plain topsets, and stable to decreasing clinoform heights; a larger fraction of the sediment budget is stored within deep-water compartments. We interpret that the evolution from Stage 1 to Stage 2 is driven chiefly by tectonic uplift of the adjacent mountains and associated basin subsidence: increasing in Stage 1 and stable to possibly decreasing in Stage 2. Sediment budget calculations suggests that average sediment supply to the basin was 4-16 × 10 6 ton/y, yield was within 200-2000 ton/km 2 /y, and hinterland maximum relief was 1000-3000 m. Integration of sediment budget estimates within source-to-sink evolution represents a powerful tool to build improved tectono-stratigraphic models, and develop predictive models for sediment storage across shelf-margin compartments.

Abstract The concept of “passive” river restoration after dam removal is to allow the river to restore itself, within constraints such as localized bank erosion defense where infrastructure or property boundaries are at risk. This restoration strategy encounters difficulties in an urban environment where virtually the entire stream corridor is spatially constrained, and stream-bank protection is widely required. This raises the question of the meaning of river restoration in urbanized settings. In such cases, the sedimentary record can document paleohydrologic or paleogeomorphic evolution of the river system to better understand long-term response to the removal of the dam. Secor Dam was a low-head weir on the Ottawa River flowing through the City of Toledo, Ohio, and its outlying suburbs. The dam was constructed in 1928 and removed in 2007 to enhance aquatic ecosystems, improve water quality, and avoid liability concerns. Predam removal feasibility studies predicted the hydrological and sedimentological responses for the dam removal and determined that reservoir sediments were not significantly contaminated. Postdam removal studies included trenching, sediment coring, geochronology, and surveying. The buried, pre-1928 channel was located and showed that watershed urbanization resulted in channel armoring. Incision in the former reservoir exhumed a woody peat layer that was subsequently shown to be a presettlement hydromorphic paleosol currently buried beneath 1.7 m of legacy sediments, mostly deposited since ca. 1959. Today, the river flows through an incised channel between fill terraces composed of legacy sediments. Additional coring and survey work documented that the channel lateral migration rates averaged 0.32 m/yr over the past ∼80 yr, and that the meander wavelength is increasing in response to dam removal. Using sediment budget concepts, significant channel bank erosion and lateral channel migration should be expected until this river system reworks and removes accumulated legacy sediments currently in floodplain storage. In this dam removal project, “active” restoration practices, such as riparian wetland restoration, would have been more in accord with scientific understandings. That did not happen in this case because of disagreements among different constituencies and because of limitations of funding mechanisms.