Reliable AMS ages for Mayan Caches at Copán, Honduras based on spondylus sp. marine shells

Copán, located in western Honduras, is one of the most well-known of all ancient Mayan cities. Over a century of intensive archaeological research has revealed the development of Copán from its origins as a small agricultural village, to a major city state, followed by its decline or ‘collapse’ after AD 800. Copán’s chronology relies heavily on changes in ceramics dated by association with hieroglyphic dates on monuments. There are surprisingly few radiocarbon dates available for a site with such a long-term history of study and researchers have expressed a general reluctance to use radiocarbon dating (mainly on charcoal) at Copán because radiocarbon ages are often too old compared to associated hieroglyphic dates. Dating marine shell offers an alternative approach for radiocarbon-based chronology building at Copán. Spondylus sp. or spiny oyster shell is found in offering caches throughout the Copán valley. Caches are commonly associated with the dedication of buildings, altars and stelae. We have dated cached Spondylus sp. shells and compared their ages with calendrical dates derived from Maya hieroglyphs to obtain new information about Classic Maya caching behaviours and the chronology of contact with exchange partners in coastal areas from where the shell was sourced. A total of 17 Spondylus sp. shells collected from 9 independently dated contexts were analysed for 14C with AMS to high precision (0.30-0.35%) using the facilities at ANSTO and Waikato. Most of our AMS dates agreed well with structural/hieroglyphic dates indicating that Spondylus sp. can be reliably used for dating contexts. The results also showed there was very little time between death of the shellfish and placement within caches suggesting that shells may have been acquired for specific caching/dedication events rather than stored for long periods