FN Archimer Export Format PT J TI Sedimentary structures offshore Ortona, Adriatic Sea - Deformation or sediment waves? BT AF BERNDT, Christian CATTANEO, Antonio SZUMAN, Magdalena TRINCARDI, Fabio MASSON, Doug AS 1:1;2:2;3:1;4:3;5:1; FF 1:;2:PDG-DOP-DCB-GM-LES;3:;4:;5:; C1 Natl Oceanog Ctr, Southampton SO14 3ZH, Hants, England. IFREMER, Ctr Brest, Plouzane, France. CNR, ISMAR, I-40126 Bologna, Italy. C2 NOC, UK IFREMER, FRANCE CNR, ITALY SI BREST SE PDG-DOP-DCB-GM-LES IN WOS Ifremer jusqu'en 2018 copubli-europe IF 2.029 TC 28 UR https://archimer.ifremer.fr/doc/2006/publication-2280.pdf LA English DT Article DE ;Adriatic Sea;Seismic amplitudes;Submarine creep;Sediment waves AB The late Holocene mud wedge on the Adriatic shelf offshore Ortona, Italy, shows undulating sub-parallel seismic reflector sequences which extend several kilometres along strike and 100–200 m down-dip in water depth between 20 and 80 m. The amplitude of such undulations is up to 5 m and the undulations continue as stacked sediment packages downwards throughout the 35 m thick mud wedge. The undulations are separated by 4° to 5° dipping boundary zones and at first glance these sediment undulations resemble the seafloor sedimentary structures visible in the Humboldt Feature offshore California. There is an ongoing debate whether seafloor undulations are the result of deformation processes or sediment deposition and/or reworking due to submarine shelf currents. A dense net of recently reprocessed and digitally interpreted high-resolution Chirp seismic data on the Adriatic shelf favours an interpretation that these undulations developed, in the upper part of the stratigraphic section through sediment reworking rather than through deformation. There are three lines of evidence for this: (1) the spatial extent of the undulations coincides with higher seabed reflector amplitudes than found both on the shelf and in the distal part of the shelf. If the features were solely caused by slope failure there should be no change of amplitudes, (2) the seabed reflector amplitude is generally higher on the gently dipping or flat upslope limbs than on the steeper downslope limbs, supporting a current origin that causes preferred deposition of sediments with higher acoustic impedance on the top, (3) the boundaries between the undulations are dipping at angles that are much lower than the angle of internal friction of these sediments excluding that a simple model like the Mohr–Coulomb under gravitational loading could describe the undulations as sediment deformation and failures. PY 2006 PD DEC SO Marine Geology SN 0025-3227 PU Elsevier VL 234 IS 1-4 UT 000243253100016 BP 261 EP 270 DI 10.1016/j.margeo.2006.09.016 ID 2280 ER EF