EUROSTRATAFORM Special Issue of Marine Geology

The papers in this Special Issue derive from projects funded by the European Commission (contract number EVK-CT-2002-00079) and the U.S. Office of Naval Research, that were called EUROSTRATAFORM and EuroSTRATAFORM, respectively. Both projects ran concurrently from 2002 to 2005 with a large amount of interaction. The overall goal of these projects was to develop a quantitative understanding of sediment transport routes and mechanisms from river mouth to continental margin and to improve understanding of the resultant stratigraphy. This data will aid prediction of the response of the marine sedimentary system to perturbations, such as climatic and tectonic variability, relative sea-level change, and land-use practices. Given the increasing importance of marine exploitation improved knowledge of the past and better forecasting for the future are essential to manage, and safely exploit the marine environment. The papers in this issue relate to the northwestern Mediterranean, especially the Gulf of Lion and the western Adriatic Sea. The Gulf of Lion, located south of France and east of NE Spain, is a temperate, deltaic margin dissected by numerous canyons. The Gulf of Lion has sedimentary systems ranging from a large season-dominated sedimentary system (Rhône River and its prodelta, at the eastern end of the gulf) to a small event-dominated system (Têt River and its prodelta, near the western end). In the western Adriatic the primary fluvial dispersal system is the Po River (with additional contributions from many smaller Apennine Rivers). Sediment is deposited on the Po delta with some redistribution towards the south along the shelf. The Bari Canyon intercepts this transport pathway and part of the sediment is transferred directly to the deep Adriatic Basin. The first paper by Amblas et al. shows the main seafloor components of the northeast Iberian margin and examines the factors controlling the seascape. These involve a combination of tectonics, long-term fluvial sediment flux to the margin, sediment grain size, basin depth and slope gradient. Papers by Heussner et al. and Palanques et al. examine suspended sediment transport and the flux of particles across the Gulf of Lion. Heussner et al. show that total mass fluxes increase along slope from east to west, indicating an increased shelf export of particulate matter in the western part of the system. In the southwestern part of the Gulf of Lion this is predominantly resuspended sediment with a high seasonal variability. Cold water cascading is the primary mechanism for exchange of particulate matter between the shelf and the slope. Palanques et al. show increases in downcanyon current speeds and sediment transport associated with strong downwelling induced by E–SE storms and to cascading of dense shelf water induced by N and NE winds. A late February storm and cascading event in the Cap de Creus canyon, at the western end of the gulf, was responsible for most of the observed shelf-canyon transfer. Modern sedimentation in more localised areas of the Bourcart canyon and on the Têt inner shelf is examined in papers by Gaudin et al. and Guillen et al, respectively. Gaudin et al. show that dense water cascading is again the main process causing reworking, transport and accumulation of sand within the Bourcart canyon head. They call these deposits “cascadites” and show how they can be distinguished from other deposits such as turbidites and contourites. Guillen et al. present results relating to two storm events on the inner shelf near the Têt river. The effects of the storms were similar offshore but one was associated with a much higher sediment input from the Têt river. During both storms the seabed was eroded to several cm depth and sediment was advected towards the southeast. During the storm with high sediment input, sediment was deposited around the river mouth and this was later eroded by a smaller storm event. Thus a complex pattern of deposition and erosion has emerged in this area. During the last sealevel lowstand much of the Gulf of Lion was subaerial and as sealevel rose retrogressive sand bodies were left at the shelf edge. Jouet et al. show how the sedimentation in this location is cyclical with shoreface deposits and offshore muds deposited during each glacial/interglacial 100 kyr-cycle. They show the evolution of the area through the last sealevel lowstand, identifying intervals of increased fall or slow-down, or even stillstand and the associated development of wave-cut terraces and periods of cementation. Bassetti et al. describe the sand bodies at the shelf edge and show how they have been modified by more recent events such as episodic high-energy events that occur under highstand conditions. Five papers in this volume cover the Rhône sedimentary system at the eastern end of the Gulf of Lion. Papers by Maillet et al. and Miralles et al. relate to the extreme 2003 Rhône flood event. Maillet et al. distinguish areas with considerable erosion from those with considerable deposition and estimate the total volume of sediment deposited, between 0 and 20 m water depth, was 7.8 × 106 m3 t. This is over 15 times the average annual sediment supply from the Rhône. The material was deposited mainly on the delta front with later erosion and redeposition further downslope. The floods also transferred radionuclides that were associated with suspended particulate matter and dumped these in the Gulf of Lion, as discussed in the paper by Miralles et al. Garcia-Garcia et al. show that the areas of highest sediment accumulation from the Rhône outflow are those that have high methane concentrations. This is presumably due to rapid burial of terrigenous organic matter during flood events. A longer-term perspective of sedimentation on the Rhône prodelta is taken by Sabatier et al, who show a strong reduction of sedimentation on the prodeltaic lobe at the main river mouth during the last 150 years, and increased erosion at the minor mouth of the river. These changes are due to reforestation, dam construction and dredging and result in increased erosion of the coastline since the prodeltaic sediment reservoirs are gradually being used up. Moving further offshore, the paper by Dannielou et al. describes a core from the Petit-Rhône neofan levee in which there are multiple turbidite events. The package of turbidites fines upward and a model is proposed showing that this is due to growth of the levee rather than weakening of the turbidity currents with time. The final four papers relate to the Adriatic. Kubo et al. have modelled the prograding Po delta over the last 21,000 years including the late Pleistocene when sediment discharge from the Po was 70% greater than during the Holocene. Palinkas et al. describe sedimentation patterns further south along the Apennine shelf and show that accumulation rates increase towards the south, being greatest near the Gargano Peninsula. Dam construction has reduced sediment supply in recent years but some new sediment is delivered to the shelf during periods of elevated discharge. Berndt et al. examine an area of seafloor undulations off Ortona that could be generated by deformation or bottom-current processes. They present a range of evidence that favours sediment reworking by currents rather than deformation. Finally, the paper by Verdicchio and Trincardi describe bedforms in the South Adriatic basin east of the Gargano Peninsula. Here two bottom-water masses interact to create a complex set of bottom-current deposits and erosional features that appear to be actively developing today. Overall, the integrated research conducted in EUROSTRATAFORM demonstrates that our understanding of European margin systems can be improved when such systems are viewed in a source to sink frame. This Special Issue provides a new view of the northwestern Mediterranean and the Adriatic sedimentary systems combining information on sediment input, current systems and depositional environments. This view shows that these settings are more dynamic, even if of pulsating nature, than previously suspected.