SEDIMENT ACCUMULATIONS FROM THE BOCA PAILA CAVE SYSTEM LOCATED IN THE SIAN KA'AN BIOSPHERE OF THE YUCATAN PENINSULA PROVIDE EVIDENCE ON RECENT SEA-LEVEL RISE AND FORMATION OF THE CLASSIC MAYA CANAL SYSTEM

Cave sediments along the eastern coast of the Yucatan Peninsula contain important records of paleoenvironmental change that have not been fully explored. Reconstructing environmental changes in Boca Paila lagoon reveal more details about sea level, flooding of the Sian Ka’an Biosphere, and the timeline of occupation at Muyil, an important Classic Maya maritime trading site. Three sediment cores (BP1, BP2, and BP3) were collected from a cave system beneath Boca Paila lagoon in the Sian Ka’an Biosphere, and elemental (X-Ray Fluorescence Core Scanning) and foraminiferal analyses were performed. The combined results from lithology, radiocarbon dating, elemental concentrations, and microfossils show three distinct phases of coastal evolution. Phase 1 (1157 BCE or earlier), an upland forest, is characterized by organic-rich peat, a relative absence of foraminifera, and low Sr/Ca, Si/Ti, and Ti/K ratios indicating dry conditions at the karst surface. Phase 2 (1157 BCE – 312 CE), a shallow wetland, is marked by an increase in weathering products (Ti/K), diatom productivity (Si/Ti), and marine foraminifera (Ammodiscus sp.) indicating more open water conditions. Phase 3 (>312 CE), a wetland/lagoon environment, is characterized by carbonate-rich marl, a greater diversity of marine foraminifera (including Ammonia tepida, Elphidium sp., Rosalina sp., and Bolivina sp.), and increased Si/Ti and Sr/Ca values indicating input of marine sediment with sea level rise. Sea level curves and climate records support the interpretation of a dry upper karst environment prior to 1157 BCE, with sea-level rise forming shallow (~<50 cm) wetlands by ~312 CE. Previous archeological analysis estimates that the first settlers arrived at Muyil ~350 BCE, but that population expansion and construction of most structures occurred during the Postclassic (1000–1550 CE). Sea-level would have been an important factor in the expansion of coastal settlements and trade routes; continued sea level rise after ~312 CE allowed for the formation of lagoons and channels connecting the coast to Muyil and other inland sites which would likely not have been navigable prior to the Early Classic period. This study highlights the impacts of environment on society, as well as the importance of karst cave systems for obtaining paleoenvironmental records.