Contractional salt deformation in a recently inverted basin: Miocene to current salt deformation within the central Algerian basin

Abstract

Field analogues illustrating the early stage of deformation of shortening structures in salt-bearing orogenic fold-and-thrust belts are not yet well illustrated in literature. The relatively young Messinian salt of the Algerian basin could represent a good case example of such systems. The Algerian Basin is a deep-water Miocene back-arc basin including a layer of mobile Messinian evaporites up to 2 km thick. The Messinian salt was deposited in an already inverted basin, after its extensive stage. Its inversion initiated in the Tortonian, with a N-NW shortening induced by the north-westward motion of the African plate. In this study, we use new 2D multichannel seismic data to identify, classify and map salt structures throughout the central Algerian Basin and re-assess its structural style. We interpret contractional salt tectonic structures, such as buckle folds, squeezed diapirs and related salt sheets as evidence of regional thickskinned shortening episodes. We conclude that horizontal displacement loading has driven salt deformation within the basin since its deposition. We also show spatial variations in the structural style of the central Algerian Basin, both along-and down-dip. We demonstrate that the initial shortening-related salt deformation in the late Messinian was focussed along the Algerian margin and later shifted outward toward the Balearic margin in the Plio-Quaternary. The shifting of the deformation front is interpreted to be a result of the thickening and strengthening of the overburden. The second peak of deformation may have reactivated faults along the Emile-Baudot escarpment with thick-skinned deformation. We also observe a variation in the intensity of the salt deformation along the margin from SW to NE, which may be due to variable tectonic loading applied along the Algerian margin or the pre-shortening distribution of salt.

Salt Tectonics in the Provençal Basin, Western Mediterranean Sea

“…Early deformation (since the first phase of salt deposition) has been discussed in the Western Mediterranean by several authors (e.g. Gaullier et al 2014;Soto et al 2022;Blondel et al 2022). Since the deformation started in the flat, horizontal deep basin and the listric faults are only active later (since the Lower Pliocene), we exclude that the gravitational gliding is the main trigger cause of the onset of salt deformation.…”

“…Nevertheless, an almost imperceptible difference in UU thickness could trigger the formation of passive diapirism as long as the sedimentation rate is not great enough to inhibit the process (see for instance Rowan andGiles, 2021 andBlondel et al 2022). The first phase of deformation is clearly observed only in the transitional crust domain.…”

A submarine morphotectonic analysis combining GIS-based methods and virtual reality: Case study of the low-rate active thrust faulting off Boumerdès (Algeria)

“…They show that 1) geodetic velocity vectors relative to Eurasia strike roughly NW-SE and decrease progressively in length from west (~3.0 mm/yr) to east (~.5 mm/ yr) along the coast of Algeria, and 2) the horizontal shortening rate in the offshore domain is of about 1.5 mm/yr at the longitude of Boumerdès. Therefore, the long-term horizontal slip rate on the Boumerdès fault is necessarily less than this value since there is evidence for some continuous deformation (likely lower than 20%) by buckling of the oceanic lithosphere (Leffondré et al, 2021) and because some NW-SE shortening is also taking place at the toe of the Balearic margin (Camerlenghi et al, 2009;Maillard and Mauffret, 2013;Blondel et al, 2022).…”