Paleo Slide Set: Climate and the Classic Maya Civilization
Gypsum crystals (CaSO4) found within the littoral zone of Lake Chichancanab

Because the water of Chichancanab is nearly saturated with CaSO4, gypsum crystals 
can be found in the littoral zone encrusting aquatic macrophytes. However, gypsum 
is not precipitating in the open lake today. This image illustrates gypsum crystals 
found at depth in the sediment core taken in 6.9 m of water. The presence of gypsum 
in the littoral zone indicates times in the past when the climate was drier, the lake 
volume was reduced, and gypsum was precipitating from lake water. We can therefore use 
the sulfur content of the lake sediments, which reflects gypsum content (CaSO4), as an 
indicator of dry climatic conditions. 

Photo Credits:
David A. Hodell 
Department of Geology, University of Florida