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Sedimentary structures offshore Ortona, Adriatic Sea: deformation or sediment waves?

Sedimentary structures offshore Ortona, Adriatic Sea: deformation or sediment waves?
Sedimentary structures offshore Ortona, Adriatic Sea: deformation or sediment waves?
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.
sediment waves, submarine creep, seismic amplitudes, adriatic sea
0025-3227
261-270
Berndt, Christian
d6db3f62-9891-4e8a-9210-b3aa6a8a4c22
Cattaneo, Antonio
ca00590a-440f-4c59-b9bb-f801f109f66c
Szuman, Magdalena
a9f7806a-fb53-46ec-90f0-49ae4e87d9de
Trincardi, Fabio
d2e18f00-bf92-4c90-a175-a7d0bc0e3d38
Masson, Doug
edd44c8b-38ca-45fb-8d0d-ac8365748a45
Berndt, Christian
d6db3f62-9891-4e8a-9210-b3aa6a8a4c22
Cattaneo, Antonio
ca00590a-440f-4c59-b9bb-f801f109f66c
Szuman, Magdalena
a9f7806a-fb53-46ec-90f0-49ae4e87d9de
Trincardi, Fabio
d2e18f00-bf92-4c90-a175-a7d0bc0e3d38
Masson, Doug
edd44c8b-38ca-45fb-8d0d-ac8365748a45

Berndt, Christian, Cattaneo, Antonio, Szuman, Magdalena, Trincardi, Fabio and Masson, Doug (2006) Sedimentary structures offshore Ortona, Adriatic Sea: deformation or sediment waves? Marine Geology, 234 (1-4), 261-270. (doi:10.1016/j.margeo.2006.09.016).

Record type: Article

Abstract

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.

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More information

Published date: 18 December 2006
Keywords: sediment waves, submarine creep, seismic amplitudes, adriatic sea

Identifiers

Local EPrints ID: 42951
URI: https://eprints.soton.ac.uk/id/eprint/42951
ISSN: 0025-3227
PURE UUID: 053deef4-664d-4ddb-9339-c1fcb109e9d3

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Date deposited: 04 Jan 2007
Last modified: 13 Mar 2019 21:10

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Contributors

Author: Christian Berndt
Author: Antonio Cattaneo
Author: Magdalena Szuman
Author: Fabio Trincardi
Author: Doug Masson

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