Tectonostratigraphic evolution of the eastern Algerian margin and basin from seismic data and onshore-offshore correlation

Abstract

International audienceThe eastern Algerian basin, part of theWestern Mediterranean domain, is a back-arc basin resulting fromthe SE drift of the Lesser Kabylia block gave rise to continental extension and birth of a new oceanicdomain. We aim here to define the structure and tectonostratigraphic evolution of this basin and theadjoining continental margin. Indeed, the absence of wells and the lack of published MCS data kept thisarea mostly unknown. The crustal architecture (down to the Moho) and seismo-stratigraphy of thesedimentary infill are detailed, emphasizing particularly the pre-Messinian series, by combining a newset of offshore deep penetrating seismic, conventional MCS sections, and wide angle seismic data.Because no well exist offshore we realized new field descriptions of the Late Oligocene and Miocenedeposits on land and propose onshore-offshore extrapolation and age correlations. The pre-Messinianseries display four main units (PMSU1 to 4) above which Messinian units are consistent with stratigraphicmodels already proposed for the Mediterranean basin, the deep basin displays units as old as theOMK (“Oligo-Miocene Kabyle”) series on land. The basement is shaped by conjugate transcurrent faultsstriking N120- N40, forming a series of rhombic troughs resulting from transtensional tectonics. Thecoeval E-W extension and NW-SE stretching of the continental crust suggest a radial opening of theAlgerian basin during Late Oligocene- Lower Miocene, followed by a progressive uplift of the uppermargin after the collision of Lesser Kabylia with Africa. Besides, steep slope of the eastern Algerianmargin, downward flexure of the oceanic basin near the margin toe and growth of S-dipping thrustswithin the margin evidence a significant Quaternary stress inversion. Overall, this study highlights thecomplex stress evolution of the East Algerian margin since Oligocene times, as evidenced by significantupward/downward vertical motions and crustal extensional/compressional successions. We summarizethis evolution into three main stages: (1) rifting (including sea-floor spreading) at Late Oligocene-Burdigalian in the context of back-arc, (2) collision between AlKaPeCa blocks and Africa at 17 Ma, andpost-rift sag basin infill, till Late Tortonian to Messinian, and (3) inversion of the margin and developmentof flexural basins at Quaternary times