Archaeoseismological analysis of the late 4th century CE tsunami event of Baelo Claudia (Gibraltar Arc, South Spain)

Abstract

We report on the tsunami deposits burying the coastal Roman remains of the Baelo Claudia archeologic site and its surroundings up to ca. +8 m above the sea-level. We present new data from 2D ERT profiles (Electric Resistivity Tomography) of the lagoonal zone near the eastern necropolis, adjacent to the city walls, as well as new sedimentologic insights on the paleotsunami deposits inside and outside the city. The tsunami layer has been well documented inside the city in previous works, being archaeologically dated in the late 4th century CE. It is interpreted that the tsunami triggered the latter abandonment of the city. The tsunami layer is a dark cohesive sandy deposit (28 to 52 cm thick) containing fragments of pottery, fish and animal bones, glassware, bricks and large boulders of masonry blocks, and column drums. The layer also contains microfaunal assemblages with a mixture of benthic and planktonic foraminifera, as well as lagoonal brackish-water gastropods, numerous shell debris, and broken reworked foraminifera. Data presented in this work indicate that the paleotsunami layer is mainly composed of well-rounded fine-medium sands originated from the reworking of aeolian and littoral beach deposits of the old roman spit-bar enclosing the ancient embayment. We interpret parts of the tsunami layer as backwash deposits trapped within the ruins of the city after the earthquake destruction, as testified by recent excavations in the funerary monuments of the Eastern necropolis.