Crustal Strain in the Marmara Pull‐Apart Region Associated With the Propagation Process of the North Anatolian Fault

Abstract

Key Points:• Structural map and geological cross-section of the Ganos-Gelibolu fold system in the Dardanelles region.• Timing, amount of shortening associated to the propagation of the North Anatolian Fault deduced from mapping and critical revision of the stratigraphy.• Reconstruction of the westward propagation of the NAF in the Dardanelles region. AbstractPropagation processes of plate-scale faults through continental lithosphere are poorly documented. The North Anatolian fault (NAF) is a continental right-lateral transform with striking evidence for propagation processes in the Marmara Sea pull-apart region. Earlier work [Armijo et al., 1999] suggests that in the Dardanelles, where the principal, northern branch of that fault (NNAF) enters into the Aegean: (1) a fold-thrust system has progressively developed above the NNAF fault tip, at the WSW corner of the Marmara Sea pull-apart. The main anticline formed there was sheared and its SW half laterally offset by ~70 km to the SW; (2) the timing of structure development appears correlated with sea-level changes associated with the Messinian Salinity Crisis (MSC). Our new description of the Dardanelles (or Ganos-Gelibolu) fold-thrust system is based on structural mapping, field observations and calcareous nannoplankton analyses to date key sedimentary units. Our results provide tight constraints on the main pulse of folding associated with propagation of the tip of the NNAF: it took place in the late Miocene to earliest Pliocene (5.60 to 5.04 Ma), before deposition of undeformed Pliocene marine sediments. The folding is mostly coeval with the MSC and accommodated several kilometers of shortening at the fault tip. After full propagation of the NNAF up to the surface, the folded structure was sheared and right-laterally offset, with an average 14 mm/yr of slip-rate during the past ~5 Myrs. A reconstruction of tectonic evolution suggests a flower structure nucleating and taking root at the tip of the fault.

Evolution of the North Anatolian Fault from a diffuse to a localized shear zone in the North Aegean Sea during the Plio-Pleistocene

“…A second strike-slip system is evidenced at the South Marmara Fault and the Ganos segment, both corresponding to positive flower str uctures for med at a restraining bend (Fig. 2 ; Le Pichon et al 2014 ;Karakas et al 2018 ). These structures record the beginning of the localization of the North Anatolian Shear System in the Pliocene (Armijo et al 1999 ;Le Pichon et al 2014.…”

The myth of the Messinian Dardanelles: Late Miocene stratigraphy and palaeogeography of the ancient Aegean-Black Sea gateway

“…Recently, however, it was claimed that the current strike-slip regime of the entire NAF initiated already in the late Miocene, at an age of 11.4 ± 2.4 Ma, and that east-west propagation may not have taken place (Nuriel et al, 2019). The Pliocene age of NAF initiation in the Dardanelles region is mainly based on the hypothesis that the Formation post-dates the MES (Armijo et al, 1999;Karakas et al, 2018). Here, we have shown that this formation is about 4 Ma older than previously reported, which implies that, if the tectonic reconstructions in the region are correct, the age the NAF initiation in the Dardanelles domain also converges to a late Miocene scenario.…”

“…Recently, the debate revived again by the documentation of the MES in the Seddülbahir and sections, supported this time by the presence of the Pliocene nannofossil Ceratolithus acutus in the Fm (Melinte-Dobrinescu et al, 2009). The presence of this nannofossil led to the hypothesis that the deposits correspond to the marine Zanclean flooding (Karakas et al, 2018), when Atlantic waters cascaded into the largely desiccated Mediterranean basin at the end of the Messinian Salinity Crisis (5.33 Ma). It has, however, been shown that C. acutus is not a reliable marker in Mediterranean and Paratethys environments (Di Stefano and Sturiale, 2010;Van Baak et al, 2016aStoica et al, 2018;Golovina et al, 2019).…”

“…Both play a crucial role in the age debate on the presence or absence of Messinian-Zanclean deposits in the region (Sümengen et al, 1987;Melinte-Dobrinescu et al, 2009). According to the most recent publications, the Seddülbahir section comprises the MES at its base and contains evidence of marine Zanclean fauna in the main outcrop (Melinte-Dobrinescu et al, 2009;Karakas et al, 2018). The Paratethyan fossils of the same section, however, indicate a much older (Tortonian) age (E .…”