Cannibalisation of Holocene gravel beach-ridge plains,northern Tierra del Fuego, Argentina

Abstract

Gravel beach-ridge plains form where there is sufficient availability of gravels and wave energy competent to transport the gravel. Even though beach-ridge plains are formed on coasts where sea level has risen during the Holocene, they occur extensively on stable or emergent coasts. Unfortunately, the Holocene evolution of these plains is hard to decipher because of the lack of datable material and their reworked character (minimum age). The rollover of barriers is expected on submerging coasts. On falling sea-level coasts, the beach-ridge plains are in a punctuated process of progradation. Cannibalisation is common in both settings; that is, sediment is eroded to maintain longshore growth. We present morphological and sedimentological data from three gravel beach-ridge plains (San Sebastián, Rı́o Chico and Cabo Peñas) of the northern coast of Tierra del Fuego. These beach complexes occupy embayments that were infilled during the last 5000 yr under different environmental conditions (depth, flooded area, local oceanographic processes and sediment availability). In the evolution of Bahı́a San Sebastián, a strong control was imposed by high waves originating within the bay (due to the strong westerlies). The Rı́o Chico beach-ridge plain evolved during different stages of beach progradation, cannibalisation, spit growth and saltmarsh development. The Cabo Peñas beach-ridge plain evolved in opposite directions due to wave refraction caused by rocky reefs and cannibalisation also took place.