Understanding the complex geomorphology of a deep sea area affected by continental tectonic indentation: The case of the Gulf of Vera (Western Mediterranean)

N López-González ,Francesco Latino Chiocci ,Jesús Galindo-Zaldı́var ,David Casas,Juán Tomás Vázquez ,Manuel Teixeira,Pilar Mata ,Juan Antonio Rodríguez-García,Ma Carmen Comas ,María Azpiroz-Zabala,Desirée Palomino,Víctor Tendero‐Salmerón ,P Bárcenas ,Silvia Ceramicola,Mariano Yenes,Daniele Casalbore,Ferrán Estrada ,Gemma Ercilla,Belén Alonso,Javier Idárraga-García,José Nespereira,Javier Valencia,Carmen Juan

doi:10.1016/j.geomorph.2022.108126

Abstract

We present a multidisciplinary study of morphology, stratigraphy, sedimentology, tectonic structure, and physical oceanography to report that the complex geomorphology of the Palomares continental margin and adjacent Algerian abyssal plain (i.e., Gulf of Vera, Western Mediterranean), is the result of the sedimentary response to the Aguilas Arc continental tectonic indentation in the Eurasian–Africa plate collision. The indentation is imprinted on the basement of the margin with elongated metamorphic antiforms that are pierced by igneous bodies, and synforms that accommodate the deformation and create a complex physiography. The basement is partially covered by Upper Miocene deposits sealed by the regional Messinian Erosive Surface characterized by palaeocanyons that carve the modern margin. These deposits and outcropping basement highs are then covered and shaped by Plio-Quaternary contourites formed under the action of the Light Intermediate and Dense Deep Mediterranean bottom currents. Even though bottom currents are responsible for the primary sedimentation that shapes the margin, 97% of this region's seafloor is affected by mass-movements that modified contourite sediments by eroding, deforming, faulting, sliding, and depositing sediments. Mass-movement processes have resulted in the formation of recurrent mass-flow deposits, an enlargement of the submarine canyons and gully incisions, and basin-scale gravitational slides spreading above the Messinian Salinity Crisis salt layer. The Polopo, Aguilas and Gata slides are characterized by an extensional upslope domain that shapes the continental margin, and by a downslope contractional domain that shapes the abyssal plain with diapirs piercing (hemi)pelagites/sheet-like turbidites creating a seafloor dotted by numerous crests. The mass movements were mostly triggered by the interplay of the continental tectonic indentation of the Aguilas Arc with sedimentological factors over time. The indentation, which involves the progressively southeastward tectonic tilting of the whole land-sea region, likely generated a quasi-continuous oversteepening of the entire margin, thus reducing the stability of the contourites. In addition, tectonic tilting and subsidence of the abyssal plain favoured the flow of the underlying Messinian Salinity Crisis salt layer, contributing to the gravitational instability of the overlying sediments over large areas of the margin and abyssal plain.

Highlights

Our knowledge of the deep-sea submarine geomorphology has grown substantially in recent years, due to full-coverage multibeam bathymetric maps, their repetition, and the increasing accuracy (e.g., McAdoo et al, 2000; Smith et al, 2007; Chiocci and Ridente, 2011; Ercilla et al, 2011; Ceramicola et al, 2014; Mascle et al, 2014; Kelner et al, 2016)
The main aim of this work is to understand the influence of the different processes that have generated the present-day geomorphology of the tectonically active Palomares continental margin and adjacent northwestern Algerian abyssal plain (Fig. 1A and B)
We propose a new comprehensive model to explain the present-day geomorphology observed along the Gulf of Vera, linking the sedimen tary response to the continental tectonic indentation

Summary

Introduction

Our knowledge of the deep-sea submarine geomorphology has grown substantially in recent years, due to full-coverage multibeam bathymetric maps, their repetition, and the increasing accuracy (e.g., McAdoo et al, 2000; Smith et al, 2007; Chiocci and Ridente, 2011; Ercilla et al, 2011; Ceramicola et al, 2014; Mascle et al, 2014; Kelner et al, 2016). Geomorphological studies should involve the analysis of seismic records and other geophysical data to decipher the deep structures that shape the continental margins and adjacent abyssal plains and their sedimentary architecture Both physiographic domains can be affected by active structures that locally and regionally influence seafloor morphology (Bohoyo et al, 2019; Galindo-Zaldívar et al, 2019; Sakellariou et al, 2019; Lafosse et al, 2020; Tsampouraki-Kraounaki et al, 2021). When studying active geological margins, an integrated view that includes adjacent onshore structures can help us develop a better understanding of deep-sea geomorphic processes (Summerfield, 2005; Mosher et al, 2017). This approach is not a widespread practice amongst marine geologists and should become more frequent (Fig. 1A)

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