HOLOCENE SEA LEVEL AND PALEO-EVAPORATION RECORD FROM THE MARITIME MAYA PORT CITY OF VISTA ALEGRE, YUCATAN PENINSULA

The Maya archeological site of Vista Alegre is located on the north coast of the Yucatan Peninsula in a spatially heterogeneous mangrove environment with a strong seasonality of water chemistry. The ~2 m global sea level rise over the last 2,500 years would have shifted the relative coastline position 100’s of m on this low gradient shelf.

Three sediment push cores 100 – 164 cm long were taken from shallow aquatic sub-environments of Vista Alegre in May 2011 and analyzed for lithology, loss on ignition carbonate and organic matter content, and δ¹⁸O_carb and δ¹³C_carbof bulk carbonate. Age chronologies were constructed using radiocarbon dates of peat and shell material. Physico-chemical water characteristics were mapped during late dry season (May 2011) and end of the rainy season (December 2011).

These proxies reveal four onlapping parasequences representing an overall transgression of the coastline. Relative shifts in paleo-salinity and maximum paleo-evaporation rates are calculated based on δ¹⁸O_carb and Dansgaard based model. The δ¹⁸O_carb varied over 3 – 10 ‰ in the cores, with a calculated average paleo-evaporation of 10%, and a point maximum value of 28%. The calculated paleo-evaporation rates are consistent with modern water chemistry; field observations include salinity as high as 65 psu and evaporation rates up to 53% at the end of the dry season (typically December-May) and salinity as low as 3.3 psu just beyond the end of the rainy season (typically June-November). Good spatial correlation was found between the modern water salinity and the distribution of the isotopic salinity record between the three cores. It is inferred that the spatial distribution of the hydrologic regime has been largely consistent, even though typical salinity rose at a given location with marine transgression over the last 2,500 years. The past distribution and seasonality of available fresh water resources at this coastal Maya trading site would control site occupation and population.