Turbidite chronostratigraphy off Algiers, central Algerian margin: A key for reconstructing Holocene paleo-earthquake cycles
|Author(s)||Babonneau Nathalie1, Cattaneo Antonio2, Ratzov Gueorgui3, Deverchere Jacques1, Yelles-Chaouche Abdelkarim4, Lateb Tassadit4, Bachir Roza Si4|
|Affiliation(s)||1 : Univ Brest, IUEM, CNRS UMR Domaines Ocean 6538, Pl N Copernic, F-29280 Plouzane, France.
2 : IFREMER, Geosci Marines, BP 70, F-29280 Plouzane, France.
3 : Univ Nice Sophia Antipolis, Geoazur, CNRS, Observ Cote Azur, 250 Rue Albert Einstein, F-06560 Valbonne, France.
4 : Ctr Rech Astron Astrophys & Geophys, BP 63,Route Observ, Algiers 16340, Algeria.
|Source||Marine Geology (0025-3227) (Elsevier Science Bv), 2017-02 , Vol. 384 , P. 63-80|
|WOS© Times Cited||4|
|Keyword(s)||Algerian margin, Marine paleoseismology, Turbidite, Holocene|
|Abstract||Northern Algeria is threatened by moderate to large magnitude earthquakes resulting from the slow convergence between the African and European plates. Main active faults are located offshore along the Algerian coast, as exemplified by the 2003 Mw 6.9 Boumerdès earthquake. This event triggered numerous and widespread turbidity currents over ∼ 150 km along strike in the Algerian basin (reaching 2800 m of water depth) and demonstrates the multi-source and multi-path characteristics of earthquake-triggered turbidity flows along this margin segment.We rely on the sedimentological analysis of five cores located at the toe of the Algiers margin, close to the 2003 cable break sites, to explore the potential for Holocene turbidite paleoseismology. Radiocarbon measurements provide age models for hemipelagic sediments. Based on sedimentary facies identification, analysis of depositional sequences (stacking pattern) and a stratigraphic framework established by age models, a first correlation of turbidites between the 5 cores is attempted. The number of turbidites is constant at the base of the continental slope and decreases seawards (over 80 km away from the coast). From turbidite correlations, 36 synchronous events are identified along the Algiers margin segment over the last 9 kyr, and are tentatively interpreted as seismically triggered, providing a 250 yr long mean recurrence interval.The main historical earthquakes in the Algiers area (2003, 1716 and 1365 AD) reasonably correlate with three out of the four last turbidites, strengthening the hypothesis that turbidites are suitable markers for Holocene paleoseismology. Recurrence intervals of turbidites range between 50 and 900 yr, defining quiescence periods exceeding 450 yr. Three quiescence periods lasting about 800, 1400 and 500 yr (7–6.2 ka BP, 5.4–4 ka BP, and 1.5–1 ka BP, respectively) support irregular earthquake cycling. Earthquake-triggered turbidites are more frequent in the study area than in the western adjacent margin segment (offshore El Asnam). This higher frequency could arise from the location of the seismogenic faults beneath the continental slope, whereas they are located several tenths of kilometers onland in the El Asnam area, implying less instabilities of the submarine slope.|