Sedimentological and geochemical characterization of a varved sediment record from the northern Neotropics

Annually resolved sedimentological records (including annual varves) can be used to develop precise chronologies for key climatic and tectonic events. Varved records, however, are most common in high latitude lakes, resulting in a spatial bias with respect to annually resolved records in tropical regions. Here we report on the sedimentology of two sediment cores from Lake Izabal, eastern Guatemala, that contain a well-preserved thinly laminated section spanning ca. 2200 years of the mid-Holocene. We integrate radiocarbon age-depth modeling, sedimentological observations, laminae counting, µX-ray fluorescence scanning, and multivariate statistical analyses to constrain the nature and chronology of the laminations. Our sedimentological and geochemical results suggest that the alternating clastic (dark) and biogenic (light) laminae couplets were deposited annually. Dark laminae are characterized by an abundance of detrital grains, organic detritus, total organic carbon, and terrigenic elements, and most likely formed during times of increased discharge during the rainy season. In contrast, light laminae are characterized by a decrease in detrital grains and total organic carbon, and an increase in biogenic silica constituents, and were likely deposited at times of increased lake productivity during the dry season. We compare a floating varve chronology that spans ca. 2200 years with three radiocarbon-based age-depth models. Consistency between the varve chronology and one of the models partially supports the annual character of the laminated section in Lake Izabal. This laminated section, one of the first annually resolved sedimentological records from Central America, can help explore mid-Holocene hydroclimate variability and regional tectonic processes in this understudied region.