Tsunami-related scour-and-drape undulations in Middle Pliocene restricted-bay carbonate deposits (Salento, south Italy)

Abstract Middle Pliocene transgressive shelly carbonate deposits in the Pesculuse area (Salento, south Italy) were laid down in a protected bay bounded on the seaward side by a ridge of Cretaceous limestone. Within this setting, a number of palaeocommunities influenced by water energy, turbidity, rate of sedimentation and consistency of substrata have been recognized. Episodically, the low-energy background sedimentation was punctuated by events of exceptional energy, which produced giant wavy scours up to more than 50 m in wavelength, draped by graded and laminated and locally trough cross-bedded calcarenites. There are some descriptions of giant scour-and-drape features of comparable scale in the literature. However, only in rare cases were they interpreted as tsunamiites. Although the physical aspects of the scouring mechanism remain obscure, the large-scale wavy structures are thought to result from the passage of tsunami surges encroaching landwards in relatively protected waters, and then sweeping back offshore. This assumption is based not only on the exceptional scale and regularity of the scours, but also on a number of additional features, such as the evidence of opposite flows directed both landwards and seawards, composition of calcarenites pointing to the mixing of sediments supplied by different sources and bi or tripartition of the beds suggesting that the high-energy events consisted of a number of pulses rapidly following one another. Nearshore low-energy areas are sites where the record of tsunamis may be preserved without loss, because they are efficient sediment traps where subsequent reworking is prevented by the low energy level of the environment.