Abstract The Chandeleur Submarine Landslide Complex occurs on the upper Mississippi Fan of the Gulf of Mexico in approximately 1100 m of water, 200 km SE of New Orleans, Louisiana. This part of the Mississippi Fan received high sedimentation throughout the Pleistocene, causing high pore fluid pressure and abundant slope failures, though few as large as the Chandeleur. Given its large size, proximity to major coastal cities and seafloor infrastructures, we examine the Chandeleur Slide to understand what led to the initial slope failure and decipher its post-failure transport behaviour using 2D and 3D multichannel seismic surveys, high-resolution bathymetric data, and well logs. We find a large sediment mass with a translational-rotational behaviour that was displaced to the south/SE up to 40 km from the source area. The Chandeleur Slide includes extensional faulting in the headscarp area and compressional structures in the toe where confined by a natural ramp-like structure. Beneath the Chandeleur Slide, we identify a regional sand-rich unit (called the Blue Unit) that is known to be overpressured. Beneath the Blue Unit we observe an upward-migrating salt diapir. We suggest one possible scenario for the origin of the Chandeleur Slide is the combined effects of an upward-migrating salt diapir impinging on an already overpressured Blue Unit, leading to the initial failure. The initial failure was followed by retrogressive headwall retreat northward, which created the prominent scarp on the seafloor. In total, the Chandeleur Slide complex covers an area of about 1000 km 2 and contains about 300 km 3 of sediment.

Abstract Since the last Special Publication on seismic geomorphology, the application of seismic data has grown substantially, revolutionizing our understanding of basin evolution in the process. The papers presented here provide an insight into the direction of travel for seismic geomorphological analyses and how the science has evolved since 2007. New methods of data collection, new methods of processing and visualization, and the integration of new types of complementary data, all have played a role in maximizing the potential palaeo-environmental insights that can be derived from such studies. The submissions range across different geological settings, consisting of glacial, fluvial, volcanic, deltaic and slope settings. Many of these studies integrate different methods, showing what can be achieved by combining multiple datasets to understand the subsurface. As more legacy datasets become available, the observed acceleration in seismic data availability and the associated publications will likely continue. Newer methods and greater knowledge of the subsurface are yielding a greater understanding of not just the palaeoenvironments, but also what generates seismic reflectivity in the subsurface. The study of seismic geomorphology remains in its infancy, and much exciting research potential is yet to be realized.

Abstract Deltas are discrete shoreline protuberances formed where a river enters a standing body of water and supplies sediments more rapidly than they can be redistributed by basinal processes, such as tides and waves. In that sense, all deltas are river-dominated and deltas are fundamentally regressive in nature. The morphology and facies architecture of a delta is controlled by the proportion of wave, tide, and river processes; the salinity contrast between inflowing water and the standing body of water, the sediment discharge and sediment caliber, and the water depth into which the river flows. The geometry of the receiving basin (and proximity to a shelf edge) may also have an influence. The simple classification into river-, wave-, and tide-dominated end members must be used with caution because the number of parameters that control deltas is more numerous. Other depositional environments, such as wave-formed shorefaces or barrier-lagoons can form significant components of larger wave-influenced deltas, but conversely smaller bayhead or lagoonal deltas can form within larger barrier-island or estuarine systems. As deltas are abandoned and transgressed they may also be transformed into another depositional systems (e.g., transgressive barrier-lagoon system or estuary). Delta plains also contain distributary river channels and their associated floodplains and bays, which can equally be classified as both fluvial and deltaic environments. Sharp-based blocky sandstones, tens of meters up to about a hundred meters thick, within many ancient mid-continent deltas have routinely been interpreted in the rock record as distributary channels, although many of these examples are now reinterpreted as incised fluvial valleys. Distributary channels may show several orders of sizes and shapes as they bifurcate downstream around distributary-mouth bars. Bifurcation is inhibited in strongly wave-influenced deltas, resulting in relatively few terminal distributary channels and mouth bars flanked by extensive wave-formed sandy barriers or strandplain deposits. In shallow-water river-dominated deltas, tens to hundreds of shallow, narrow and ephemeral terminal distributary channels can form intimately associated with mouth bars that form larger depositional lobes. Tides appear to stabilize distributary channels for hundred to thousands of years, inhibiting avulsion and delta switching. As deltas prograde they form upward-coarsening facies successions, as sandy mouth bars and delta-front sediments build over muddy deeper-water prodelta facies. Deltas display a distinct down-dip clinoform cross-sectional architecture. Many large muddy deltas show separate clinoforms, the first at the active sandy delta front and the second on the muddy shelf. Along-strike facies relationships may be less predictable and depositional surfaces may dip in different directions. Overlapping delta lobes typically result in lens-shaped stratigraphic units that exhibit a mounded appearance. All modern deltas grade updip from marine into non marine environments, and Walther’s Law predicts that deltas should show a marine to nonmarine transition as they prograde. However, in many low-accommodation settings, topset alluvial or delta-plain facies can be removed or reworked by wave or tidal erosion during transgression, resulting in top-eroded deltas. Historically, some of these top-eroded deltas have been interpreted as distal shelf deposits, not related to shoreline processes. Sequence stratigraphic concepts, however, allow facies observations to be placed within a larger context of controlling allocyclic mechanisms which allow the correct interpretation of larger delta systems of which only small remnants may be preserved.