Alluvial geoarchaeology of a Middle Archaic mound complex in the lower Mississippi valley, U.S.A

The Nolan site (16MA201), ¹⁴C dated 5200-4800 cal yr B.P. and located in the Tensas Basin of northeastern Louisiana, is the only recorded Middle Archaic mound site in the alluvial valley of the Mississippi River. Alluvial deposition has buried the Nolan site under 3-4 m of Holocene sediment, prohibiting traditional excavation of the site. Because data are unattainable by other means, soil coring and subsequent stratigraphic and sedimentological analyses permit reconstruction of the natural and cultural depositional history of the Nolan site. The sedimentary characteristics of basal deposits within cores suggest the presence of an Arkansas River paleochannel immediately adjacent to the site. Chronostratigraphic data show this channel was no longer active by ca. 5200 cal yr B.P. Contrary to existing models, the Arkansas River Meander Belt 4 and the Mississippi River Meander Belt 4 are not the same age. Microartifact and loss-on-ignition analyses of sediment identify natural versus cultural strata and permit the identification of artificial constructions - including four earthen mounds and one earthen ridge - at the Nolan site. Overbank sediments attributed to a mapped Mississippi River Stage 4 meander belt are dated ca. 4800-3800 cal yr B.P. This age is considerably younger than previous estimates and demonstrates the existing chronological models for Mississippi River meander belts must be carefully assessed. Core analyses also reveal flood-related crevasse splays deposited throughout the Tensas Basin after the occupation of the Nolan site. These deposits serve as relative chronological indicators and aid in stratigraphic assessments of the Nolan site. Reconstruction of the earthworks and their stratigraphic context reveals one of the largest and earliest Middle Archaic mound sites in North America.