Caught Between a Rock and a Soft Place: Using Optical Dating to Date Ancient Clam gardens on the Pacific Northwest

Summary

Rock-walled archaeological features are notoriously hard to date, largely because of the absence of organic material for radiocarbon dating. This study demonstrates the efficacy of dating clam garden walls using optical dating, and uses optical ages to determine how sedimentation rates in the intertidal zone are affected by their construction. Clam gardens are rock-walled, intertidal terraces that were constructed and maintained by coastal First Nation peoples to increase bivalve habitat and productivity. These features are evidence of ancient shellfish mariculture on the Pacific Northwest and, based on radiocarbon dating, date to at least the late Holocene. Optical dating exploits the luminescence signals of quartz or feldspar minerals to determine the last time the minerals were exposed to sunlight (i.e., their burial age), and thus does not require the presence of organic material. Our optical ages suggest that clam garden walls on Quadra Island, British Columbia, were built incrementally within the last two millennia, and increased sedimentation rates in the intertidal zone by up to fourfold. The dating of rock-walled marine management features such as clam gardens and fish traps can lead to significant advances in our understanding of the intimate relationships that Indigenous peoples worldwide developed with their seascapes.

This Resource is Part of the Following Collections

• Society for American Archaeology 82nd Annual Meeting, Vancouver, BC (2017)

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Record Identifiers

Abstract Id(s): 17318