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Cretaceous–Paleogene boundary tsunamite on Adriatic Carbonate Platform and implications on paleogeography of the western Tethys - a review

The Chicxulub asteroid impact triggered a global mass extinction and extraordinary sedimentary perturbations around the Gulf of Mexico region at the Cretaceous–Paleogene (K–Pg) boundary some 66 million years ago (Alvarez et al., 1980 ; Schulte et al., 2010 ; Renne et al., 2013). Moreover, the seismic shock was probably able to trigger giant landslides and submarine failures of the SE continental margins of North America and/or the islands in the Caribbean region, possibly generating a trans-Atlantic mega-tsunami, which propagated to the east. Such a tsunami would certainly affect shallow-marine and coastal sedimentation on continental margins of the SW Europe and NW Africa, presumably also along the margins of the western Tethys Ocean (Korbar et al., 2015, and references therein). The peri-Adriatic area was part of a continental microplate called Adria - a promontory of Africa pointing to the north into the western-central Tethys during the Mesozoic (Channell et al., 1979). The Cretaceous to Paleogene tropical carbonate platform successions in the peri-Adriatic region exhibit a more or less extended hiatus around the K–Pg boundary (e.g., Eberli et al., 1993 ; Bosellini et al., 1999 ; Korbar, 2009). This is probably a supra-regional hiatus since it is recorded also on Panormide platforms (Zarcone et al., 2010), as well as within shallow-water successions of the NW African epicontinental basins opened to the central-eastern Atlantic Ocean (Marzoqi & Pascal, 2000). Thus, there are very few continuous K–Pg boundary shallow-marine successions in the region reported to date: one from Tunisia (Adatte et al., 2002) and two from the SW part of the Adriatic Carbonate Platform (ACP) in the present day Dalmatian archipelago (Adriatic Sea, Croatia - Korbar et al., 2015, 2017a). Both ACP successions include event beds at the K–Pg boundary, which imply sedimentological perturbations related to the Chicxulub impact. Although there is no modern analogue for a broad and isolated tsunamite in a carbonate platform interior (e.g. Shiki et al., 2008), both ACP K–Pg boundary event beds were probably deposited from a major tsunami (Korbar et al., 2017b). Furthermore, in spite of the reported hiatus that include the K–Pg boundary within shallow-marine successions in the NW part of the ACP (Ogorelec et al., 2007), the latest discovery from the Kras (Karst) plateau could confirm a contemporaneous tsunami event also on that remote part of the ACP (Korbar et al., this volume). Reported deep-marine successions in the region lack any disturbance within the K–Pg boundary interval. Both Umbria-Marche (Italy) and Adriatic-Ionian (Albania) basinal K–Pg successions are characterized by many major debrites and slumps above and/or below the K-Pg boundary, but lack any within the narrow boundary interval (Montanari et al., 1989 ; Rubert et al., 2012). Thus, the tsunami must had a source in a more distant region. An unexpected and hypotethical K–Pg boundary seismic shock in north Africa, which would trigger north-directed tsunami, is not probable, since it would affect also the outer shelf deposition of the well-known Tunisian successions (Adatte et al., 2002). Yet, the only reported inner-neritic Tunisian Seldja succession is characterized by a relativelly thick, coarse-grained event bed containing ripped-up clasts of the underlaying terminal Maastrichtian marls, along with abundant and various bioclasts (Adatte et al., 2002), that could be deposited from the same K–Pg boundary intra-Tethyan tsunami. However, the tsunami could be triggered also by an European (Iberian) source. To be consider is that potential key-localities are situated in the eastern African continental margins of Morocco (Marzoqi & Pascal, 2000), facing hypotetical trans-Atlantic tsunami triggered by the Chicxulub impact. If the K–Pg boundary trans-Atlantic tsunami indeed existed, a known general paleogeography of the western Tethys, which is interpretated according to the most relevant geodynamic reconstructions of the Cenozoic Alpine orogenesis in the western Mediterranean (Lowrie & Alvarez, 1974 ; Rosenbaum et al., 2002), would be confirmed. Such a major intercontinental tsunami would imply a wide paleo-Gibraltar strait, and a very broad deep-marine area of the western Tethys without any archipelago acting as a barrier for the proposed trans-Atlantic K–Pg boundary tsunami. If so, the tsunami was finally broken down on the western coasts of the peri-Adriatic carbonate platforms, some 10-20 hours after the Chicxulub asteroid impact, at the end of its almost 10, 000 km destructive run.

K/Pg (K/T) boundary, asteroid impact, distal tsunami, shallow-marine, Adriatic.

The Chicxulub asteroid impact triggered a global mass extinction and extraordinary sedimentary perturbations around the Gulf of Mexico region at the Cretaceous–Paleogene (K–Pg) boundary some 66 million years ago (Alvarez et al., 1980 ; Schulte et al., 2010 ; Renne et al., 2013). Moreover, the seismic shock was probably able to trigger giant landslides and submarine failures of the SE continental margins of North America and/or the islands in the Caribbean region, possibly generating a trans-Atlantic mega-tsunami, which propagated to the east. Such a tsunami would certainly affect shallow-marine and coastal sedimentation on continental margins of the SW Europe and NW Africa, presumably also along the margins of the western Tethys Ocean (Korbar et al., 2015, and references therein).