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Distinguishing Natural and Archaeological Deposits: Stratigraphy, Taxonomy, and Taphonomy of Holocene Shell-Rich Accumulations from the Louisiana Chenier Plain

¹ Department of Geology and Geophysics, Louisiana Sate University, Baton Rouge, LA 70803
² Department of Sociology and Anthropology, University of Louisiana at Lafayette, Lafayette, LA 70504

Shell-rich deposits of the Louisiana chenier plain (LCP) include three types: (1) cheniers, Holocene relict shorelines of 10–100 km in length that typically are composed of laterally continuous, planar beds primarily containing poorly sorted bivalves in a sandy matrix; (2) mounds, 3–5 m high, 10 m across, anthropogenic structures composed of redeposited sediment that have been formed primarily through depositing basket-loads of nearby chenier sediment; and (3) middens, thin, unstratified lenses that are typically1–3 m long,, although they can be up to 100 m across, often lacking topographic expression, and composed primarily of large Rangia cuneata in a black clay matrix. Middens are deposited on cheniers by humans as refuse. LCP mounds often are recognizable using criteria such as topographic expression, and both middens and mounds often are identifiable through faunal composition and the presence of artifacts. However, efforts to record the cultural history of southwestern Louisiana have been hampered because many LCP mounds are now remnants (mounds that have been excavated for road fill and have lost their original diagnostic topographic expression from mound construction). Further, these archaeological deposits contain many of the same species found in cheniers, may be composed primarily of chenier sediment, and directly overlie cheniers. But, LCP cheniers, middens, and mounds have different depositional histories and it may be possible to develop additional stratigraphic, taxonomic, and taphonomic criteria to distinguish them. Preliminary tests indicate that the following criteria can be used to distinguish among these deposits. LCP cheniers typically are composed of alternating coarse- to fine beds of shell and fine- to medium sand. LCP middens examined are small lenses mainly of one molluscan species and black clay. The LCP mounds examined have a complex stratigraphy of mainly unlayered redeposited chenier sediment. Both mounds and middens exhibit somewhat greater taphonomic alteration (particularly chemical) than cheniers and contain evidence of human occupation, such as pottery fragments, vertebrate remains, and charcoal.