The Algerian Margin : A Case Study of Interaction between Plio-Quaternary Sedimentation and Tectonics

Domzig, Anne ¹; Deverchere, Jacques ²; Strzerzynski, Pierre ²; Yelles, Karim ³; Babonneau, Nathalie ²; Cattaneo, Antonio ⁴; Mercier de Lepinay, Bernard ⁵; Graindorge, David ²; Bracene, Rabah ⁶; Kherroubi, Abdelaziz ³; Gaullier, Virginie ^7
1 Midland Valley Exploration, Glasgow, United Kingdom.
² UMR6538 Domaines Oceaniques, UBO-IUEM, Plouzane, France.
³ CRAAG, Algiers, Algeria.
⁴ Geosciences marines, Ifremer, Plouzane, France.
⁵ Geosciences Azur, Valbonne, France.
⁶ Sonatrach, Boumerdes, Algeria.
⁷ Laboratoire IMAGES, Universite de Perpignan, Perpignan, France.

Offshore Algeria is a key area to study the reactivation in compression of a Cenozoic passive margin. This region is often affected by Mw=6-7.5 earthquakes: for example the 2003 Boumerdes event (Mw=6.8) which occurred on a previously unknown offshore reverse fault. This earthquake was associated with mass-transport deposits like debris flows and turbidites that lead to cable ruptures further in the basin. Here we summarize the multi-scale structures observed in the offshore Algerian margin based on the MARADJA'03 and MARADJA2/SAMRA'05 cruises data (multibeam bathymetry, seismic-reflection, side-scan sonar, backscattering, CHIRP).

The morphology of the margin and the structure of the Neogene sediments on the slope and in the basin, particularly the Plio-Quaternary sediments, are shaped by recent fault-related folds and near-surface faults distributed across the margin and also found far on land. Morphological and structural interpretation of the available data along the ~1000 km of the margin leads us to characterize several fault segments with a variable length and position. In Central Algeria (Algiers region), the main contractional structures are active blind thrusts (Plio-Quaternary) generally located near the ocean-continent transition and verging to the north (opposite to pre-existing features). They form generally large asymmetrical folds sub-perpendicular to the present-day convergence direction, which are often arranged in en echelon segments at different scales. Offshore Boumerdes (east of Algiers), we show that the faults have typically a flat-and-ramp geometry creating a succession of perched basins from the mid-slope down to the deep basin, and prograding towards the basin. Although the Messinian salt tectonics and the sedimentary fluxes at the outlets of canyons play a significant role, the sediment deposition as well as the morpho-structure of the margin appear to be controlled at first order by these slow-rate tectonic movements, indicating a clear interaction between crustal-scale tectonics and sedimentation. We discuss the implications of these results in terms of seismic hazard and sedimentary architecture (turbidites) in deep environments.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009