Palaeogeographic evolution of the late Miocene Rifian Corridor (Morocco): Reconstructions from surface and subsurface data

Abstract

The Rifian Corridor was one of the Mediterranean-Atlantic seaways that progressively restricted and caused the Messinian Salinity Crisis (MSC). Many key questions concerning the controls on the onset, progression and termination of the MSC remain unanswered mainly because the evolution of these seaways is poorly constrained. Uncertainties about the age of restriction and closure of the Rifian Corridor hamper full understanding of the hydrological exchange through the MSC gateways: required connections to sustain transport of salt into the Mediterranean for the primary-lower gypsum and halite stages. Here we present integrated surface-subsurface palaeogeographic reconstructions of the Rifian Corridor with improved age-control. Information about age and timing of the closure have been derived from high-resolution biostratigraphy, palaeoenvironmental indicators, sediment transport directions, and the analysis of published onshore subsurface (core and seismic) datasets. We applied modern taxonomic concepts to revise the biostratigraphy of the Rifian Corridor and propose astronomically-tuned, minimum-maximum ages for its successions. Finally, we summarise the palaeogeographic evolution in four time slices corresponding to the middle Tortonian (10.57-8.37), late Tortonian (8.37-7.25 Ma), early Messinian (7.25-6.35 Ma), and late Messinian (6.35-5.33 Ma). Several successions record the closure of the corridor via a continuous marine to continental-lacustrine transition. The youngest dated marine sediments represent a good approximation of the age of seaway closure. The closure of the South Rifian Corridor is constrained to 7.1-6.9 Ma; that of the North Rifian Corridor is more uncertain and ranges from 7.35 to ca. 7 Ma. We conclude that the Rifian Corridor was already closed in the early Messinian and did not contribute to the restriction events that resulted in the MSC. Because the Betic Corridor is also closed by the early Messinian, the modern Gibraltar Straits remain the sole option in the Western Mediterranean as last Messinian seaway that was open during the MSC. Our results imply that the Gibraltar Straits could have been established as the exclusive Mediterranean-Atlantic portal already in the late Miocene, and therefore we suggest that future field and drilling campaigns should target the Alboran Sea and the Gibraltar region to investigate water exchange before and during the Messinian Salinity Crisis and its impact on Atlantic circulation and global climate.

New age constraints on the western Betic intramontane basins: A late Tortonian closure of the Guadalhorce Corridor?

“…Models show that the relative gateway depths of the two straits determine whether they both have two‐way exchange, or in‐ and outflow only (De la Vara, Topper, Meijer, & Kouwenhoven, ). Since both gateways show indications of similar depth (100–300 m; Capella et al., ; Martín et al., ), a two‐layer exchange regime in both gateways is the most likely possibility. This suggests a vigorous saline input into the North Atlantic at that time, which might therefore have influenced North Atlantic circulation and overturning (Li, ; Rogerson, Rohling, Bigg, & Ramirez, ).…”

Mantle resistance against Gibraltar slab dragging as a key cause of the Messinian Salinity Crisis

“…In the external Rif, Miocene basin evolution was controlled by thin‐skinned thrusting associated with the westward drift of the Alborán domain which locally created W‐ to SW‐ward transport kinematics (Platt et al, ), and SW‐ward migration of the foredeep (Capella et al, , ; Chalouan et al, ) (Figure ). By the late Miocene, the Rifian Corridor developed as a system of interconnected basins on top of thrust‐sheets and a partly submerged foreland, as either piggy‐back or foredeep depocentres, with the marginal marine incursions dating ~8 Ma (Capella et al, ; Roldán et al, ). Between 8 Ma and the latest Tortonian (~7.25 Ma), a marked switch occurred from basin subsidence to thick‐skinned contraction resulting in fault kinematics orientated N‐S to NE‐SW.…”

“…To the east of the Nekor fault, E‐W to ENE‐WSW extension was recorded since the late Miocene (Galindo‐Zaldívar et al, ). Further south, the Taza‐Guercif Basin (Figure b) experienced basin uplift and regression already during the early Messinian (Capella et al, ; Gomez, Barazangi, & Demnati, ). Some NW‐SE orientated shortening is recorded in the sediments (Bernini, Boccaletti, Moratti, & Papani, ), but caused only minor vertical offsets; the majority of thrust faults is buried and did not break through the upper Miocene sequences (Gomez et al, ), suggesting only moderate crustal deformation since ~8 Ma compared to the Rif west of the Nekor fault.…”

“…After the arrest at ~8 Ma of rapid west‐ward rollback, NNE‐directed slab dragging became the remaining slab motion (Spakman et al, ). The indentation of the Moroccan continental margin, generated by the mantle resistance against NNE slab dragging, initiated the event of regional thick‐skinned tectonics west of the Nekor fault that closed the Rifian Corridor in the early Messinian, at around 7 Ma (Capella et al, , ). This SSW indentation is likely also responsible for the thickened crust contiguous to the slab edge (Gil et al, ) as well as the on average NNE‐SSW contraction observed in the Rif (Capella et al, ; Pedrera et al, ) rather than NW‐SE orientated Africa‐Eurasia convergence, whose direction is compatible only with the minor shortening and folding recorded in the eastern Rif and the western Betics (Bernini et al, ; Jiménez‐Bonilla et al, ) (Figure b).…”

“…Field evidence suggests that by 7 Ma, the Betic and Rifian gateways were shut and uplifted (Capella et al, ; van der Schee et al, ). After 7 Ma, an embryonic Strait of Gibraltar took over the connectivity in an area that was either always submerged or barely emergent on top of the Flysch units (Krijgsman et al, ).…”