In watery places people prefer to live where they can keep their feet dry, and an elevation of a metre or two can make a difference. The simple distinction between humanly created middens and naturally built features does not easily apply in the Australian tropics, where the natural causes include cyclones, shellfish die-off and the building of mounds by scrub turkeys, and where foragers are not directed in where they choose to camp by concern for the classification by which tidy-minded archaeologists may want to order mounds in the wetlands.
Cheniers are tropical coastal land-forms comprising elongated low ridges of shell, or shelly sand, on coastal wetlands referred to as 'chenier plains'. On active chenier plains the shelly ridges are separated by broad flats of finer-textured sediments, which may be vegetated marshes or mudflats or saline tidal flats.
A common phenomenon in tropical coastal environments is the contiguity in both space and time of prehistoric Aboriginal shell-middens and cheniers. Discriminating between the different types of shell deposit is a difficult task, often compounded by culturally derived shell deposited on the surface of natural shell ridges. In Australia this has resulted both in the mis-identification of prehistoric shell-middens as cheniers (which were then mined for shell grit), and in natural shell deposits having been assigned cultural origins. Recent research in Australia has provided both morphodynamic and temporal models which enable a better understanding of chenier development and the association between cheniers and shell middens. It is essential for both geomorphologists and archaeologists working in tropical coastal landscapes to be aware of the nature and processes of formation of both types of deposit, since failure to distinguish between them can lead to erroneous conclusions and inappropriate management decisions.
Chenier ridge formation
Cheniers, first described from Louisiana in the southern USA (Russell & Howe 1935), are common on tropical depositional coasts. They have been studied extensively in tropical America, for example in Louisiana (Price 1955), Surinam, between the mouths of the Amazon and Orinoco Rivers (Augustinius et al. 1989), and French Guiana (Guyana) (Prost 1989), in tropical Africa in Sierra Leone (Anthony 1989) and in eastern China (Zhao 1989). Australian chenier occurrences have been summarized by Chappell & Grindrod (1984) and Short (1989). Various studies from these areas mention that chenier ridges now act as the focus of human occupation, or are associated with previous occupation. It is reasonable to infer that the better-drained, elevated cheniers have been preferred occupation locations in poorly drained coastal plains. Undoubtedly in low-lying tropical coastal environments archaeological occupation sites tend to be located on elevated landscape elements: on flood-plains and estuaries these are commonly cheniers or beach-ridges (O'Connor & Sullivan in press; P. Hiscock & P. Hughes pers. comm.).
Chenier ridges are considered by some researchers to be distinctive land-forms, and by others to be special, morphodynamically more complex beach-ridges. Beach-ridges (well described in general geomorphic texts, e.g. Bird 1984) are coarse sandy to gravelly deposits formed by episodic, commonly storm-driven wave action at the backs of active beaches. Like cheniers, they may form sequences or clusters, which indicate beach progradation. They also occur as single, low, linear features behind sandy or gravelly beaches, and occasionally as isolated and spectacular large ridges resulting from infrequent high-magnitude events such as tropical cyclones. Unlike cheniers, which occur almost exclusively in seasonally wet tropical locations, beach-ridges form in any climatic regime. Also unlike cheniers, beach-ridge deposits commonly accumulate episodically, and former surfaces are subsequently covered by later deposits. …