A possible Plio-Pleistocene tsunami deposit, Hornitos, northern Chile

A section equivalent to the Pliocene La Portada Formation exposed in the co astal cliff at Hornitos, northern Chile, contains a ca. 7-10 m thick conglo merate bed. The bed occurs within a succession of shallow marine sandstones and has an erosional contact with underlying strata. The largest boulders of basement (5 m) are angular to very angular and are set within a matrix o f very poorly sorted fine to very coarse grained shell-rich sandstone. Also present are very well rounded granodiorite pebbles and shallow marine sand stone intraclasts (maximum 10 m). The clast size, erosional contact, associ ated facies and bed thickness suggests that the conglomerate bed is a shall ow marine tsunami deposit. The angular clasts indicate limited transport an d no marine reworking prior to deposition. They represent alluvial fan sedi ment incorporated into the bed during tsunami backflow. Intraclasts of shal low marine sandstone are thought to have been ripped up and included in the bed during the seaward passage of the tsunami across the shoreface.