A Review of the Morphology, Structure and Depositional Pattern of the Western and Central Algerian Margin

Jacques Deverchere, Abdelkrim Yelles-Chaouche, and Rabah Bracene

The Western and central Algerian margin has undergone a complex tectonic evolution during the Cenozoic. After recalling the main conflicting kinematic scenarii proposed to explain the birth of the Algerian and Alboran basins, we examine the different witnesses of this recent tectonic and magmatic evolution from the coast down to the deep basin using a set of marine seismic data acquired in the last years and some published data on land and at sea. The overall morphology of the margin as well as the structures of the basement and Cenozoic sediments indicate clearly strong changes of the margin from west to east: they appear likely related to a large wrench faulting episode which has guided the opening of the West Algerian basin, following (or partly overlapping in time) a collisional stage of the Internal Zones of the Rif and Kabylies. Sedimentary deposits up to the Messinian testify for this contrasting evolution along strike, although volcanics and mobility of Messinian salt have often obscured this pattern. More recently, Quaternary sediments deposited in the deep basin depict large ridges shaped by inherited structures of the basement and by the recent tectonic reactivation of the margin. This tectonic activity is occurring at a slow rate and is recorded both offshore and near the coastline by faults, folding, growth strata and uplift of marine terraces. The most recent deposits cored along different parts in the deep basin offer the possibility to identify series of paleoturbidites that are tentatively correlated through space and time in order to identify the role of paleoearthquakes in their triggering. Off the Mostaganem-El Marsa segment of the margin, 10 to 25 turbidites deposited over the last ~8ka that are partly correlated with the paleoseismic record of the El Asnam fault. This paleoseismic catalog shows a recurrence interval of 300-700 years for most events, but also a great interval of >1200 years without any major earthquake, suggesting that the level of static stress may have drastically dropped as a result of three main events occurring within the 800 years prior the quiescence period. This approach offer new perspectives for better assessing the seismic hazards in the Alboran and Algerian domains.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013