Seasonal dating and the valve-pairing technique in shell-midden analysis

Three-dimensional excavation of 23 artifact fragments and 4382 shells was carried out in the shell layer of an abandoned dwelling pit. Principal component analysis using three locational variables was used for drawing the central axes and the regression plane of the shell layer. Valve-pairing carried out on the clam Meretrix lusoria indicated that 380 pairs could be established among a total of 2089 unbroken valves. Preservation of shells was estimated at 70% by comparing the number of shells found in the shell layer with the clam population size which was in turn calculated by a probability formula using paired valves among samples. In addition to these data, the distance separating pairs gave some idea of the movement of shells. Seasonal dating by daily growth line counting showed that the shell layer could be subdivided into at least three main seasonal layers and that the period of accumulation was approximately 500 days.