Sediment undulations on the Llobregat prodelta: Signs of early slope instability or sedimentary bedforms?

Abstract

[1] A field of sediment undulations has been mapped by means of high-resolution multibeam bathymetry and seismic reflection profiles in the Llobregat River prodelta, off the city of Barcelona, Catalonia, Spain. Similar features had previously been recognized in other prodelta environments and interpreted either as downslope sediment deformation or sedimentary structures induced by bottom currents or hyperpycnal flows. Since the study area is undergoing significant offshore development, proper interpretation of such sediment undulations is needed for a correct risk assessment. The occurrence of the sediment undulations is restricted to the prodelta front on slope gradients between 3 and 0.2°. The undulations have developed at the edge and atop an area of gas bearing sediments within the Late Holocene high-stand mud wedge. An evaluation is made of the characteristics of the sediment undulations in order to determine the most likely process for the origin of these structures. Among these characteristics are the continuity of the reflections and lack of diffractions in between different undulations, their size distribution (large to small) both from shallow to deep and with depth in section, the asymmetry (decreasing from proximal to distal), the crest to trough vertical distance on the landward side of the undulations (up to 0.5 m), and the lack of features that could indicate a progressive movement such as growth structures and drag folds. These characteristics indicate that the sediment undulations on the Llobregat River prodelta do not result from sediment deformation but rather from the interaction of bottom currents generated by hyperpycnal flows from the Llobregat River with regional sea water circulation. Their identification as sediment waves implies that such features do not pose a major hazard for further offshore development.

Contourite drift evolution and related coral growth in the eastern Gulf of Mexico and its gateways

“…The MSC characteristics and overall setting are neither consistent with large-scale submarine slides (Lewis 1971;Dingle 1977), nor with submarine landslides studied by means of very high-resolution seismic or hydroacoustic systems (e.g., and Lee 1996;Locat and Lee 2002;Urgeles et al 2007;Sultan et al 2008).…”

“…The differentiation between these processes is generally a challenging task for seismic interpreters and has been addressed in several past and recent studies (e.g., Faugères et al 1999Urgeles et al 2007;Sultan et al 2008).…”

Modeling of submarine cyclic steps: Controls on their formation, migration, and architecture

“…For example, Lee et al (2002) suggested that several features previously reported as submarine-landslide deposits may, in fact, be migrating sediment-wave fi elds, including the "Humboldt slide" on the Eel River margin in northern California, the continental slope in the Gulf of Cadiz, the Adriatic shelf, and the continental shelf off the Malaspina Glacier in the Gulf of Alaska. Some other examples of deposits that are being reconsidered as sediment waves generated by density currents are sedimentary structures offshore Ortona in the Adriatic Sea (Berndt et al, 2006) and the Llobregat prodelta (Urgeles et al, 2007).…”

Multi-proxy analysis in defining sedimentary processes in very recent prodelta deposits: the Northern Phlegraean offshore example (Eastern Tyrrhenian Margin)

“…Trincardi and Normark 1988) or for example by river-sourced storming events or hyperpycnal flows, (e.g. Urgeles et al 2007Urgeles et al , 2011 and references therein).…”

“…Cattaneo et al 2004) or hyperpycnal flows bottom currents and regional sea water circulation (e.g. Urgeles et al 2007) and recently processes in the bottom boundary layers (Urgeles et al 2011).…”