Shell mounds as environmental proxies on the southern coast of Brazil

Despite the multiple constraints of using shell mounds for building relative-sea-level (RSL) curves, one of the premises behind this use is still valid in modern archaeological research. This refers to the sites being continuously built near bodies of water rich in fish species and mollusk beds. Studies that combine the evolution of settlement patterns with the geological evolution of coastal areas in Brazil reach analogous results: the distribution of shell mounds in time and space follows the landscape transformations induced by RSL variations through the Holocene. Although shell mounds are not precise indicators of RSL, they provide evidences of the paleo-geographical changes during the Holocene, of which RSL is one of the many control variables. By collecting and transporting mollusks to the shell mounds, humans inevitably carry sediments from the substrate where mollusks live, for example, the beaches and lagoons near the sites. In this work, the geoarchaeological study of three shell mounds located in the southern coast of Santa Catarina State, combined with mollusk taxa identification, show the direct association of shell mound content with the changing landscape. The predominance of Ostrea sp. versus Anomalocardia brasiliana, the presence of colluvial versus lagoonal sediments, and the occurrence of echinoid spines versus muddy aggregates with diatoms, gastropods, and glauconitic clay characterize the distinction between sites built before and after the maximum Holocene transgression, respectively. This attests the potential of geoarchaeological analyses in shell mounds as a complementary proxy for paleo-environmental reconstructions.