Mound Construction and Site Selection in the Lafourche Subdelta of the Mississippi River Delta, Louisiana, USA

Abstract

Sediment coring and trench excavation, radiocarbon dating, LiDAR data, and indigenous material culture are used to evaluate the cultural affiliation of the Grand Caillou earthen mound site and to place this site within its broader geographic context. This prehistoric Native American complex is located within the Lafourche subdelta, an abandoned portion of the Mississippi River Delta that was active from AD 400 to 1400. Interdisciplinary approaches inform the cultural affiliations of prehistoric inhabitants and document how deltaic processes influenced site selection and timing of occupation relative to newly published optically stimulated luminescence ages for Lafourche subdelta evolution. We find that the Grand Caillou site is situated on the natural levee of a major Lafourche distributary, at its junction with a relict crevasse channel. This location provided geographical advantages including access to major and minor waterways and relatively high topography. Mound construction occurred in stages of alternating lithologies, demonstrating geotechnical knowledge. Ceramic analyses assign affiliation to the Barataria phase of the Plaquemine culture (AD 1000 to 1450). Radiocarbon ages for the mound abruptly truncate at 0.6 ka, coincident with abandonment of the Lafourche subdelta. These data demonstrate highly complex, intertwined relationships between humans and river deltas, a timeless phenomenon documented worldwide.