THE HOLOCENE RECORD OF THE LAKE IZABAL BASIN – PEEKING INTO ONE OF THE LONGEST CONTINENTAL RECORDS OF THE NORTHERN NEOTROPICS

The Lake Izabal Basin (LIB) in eastern Guatemala is a pull-apart basin that contains more than 4 km of sediment. Outcrop observations and seismic data interpretation indicate that the sedimentological record spans several million years. Radiocarbon-dated sediment cores from Lake Izabal, which occupies the eastern side of the LIB, have provided a sneak peek into the basin’s infill, revealing an interesting Holocene record that has increased the scientific value of extracting long sediment cores from the basin. Our results indicate that during the early Holocene, Lake Izabal was a shallow freshwater lake with minimal precipitation, as indicated by the presence of organic-rich mud with abundant benthic diatoms, presence of littoral cladocerans and low abundance of terrigenous elements, such as titanium, aluminum, and potassium. At ~8,300 cal yr BP, the abrupt appearance of sub-mm laminations, rapid increase in sediment sulfur, and appearance of diatoms indicative of elevated water salinity reveal that marine waters invaded the low-lying lake. Elevated salinity in the lake persisted for ~3,500 years, as indicated by the continuously high sediment sulfur and the presence of highly dissolved diatoms. During the 3,500-year interval, the abundance of terrigenous elements increased progressively, indicating a change in precipitation from 8,300 to 4,800 cal yr BP. At ~4,800 cal yr BP, the disappearance of sub-mm laminations, increase in bioturbation, and return of the freshwater biota indicates a return to freshwater conditions. Terrigenous elements reached maximum abundance at ~4,800 cal yr BP and remained high until ~1,200 cal yr BP, indicating high precipitation at that time. The Holocene record of Lake Izabal is challenging long-standing hypotheses related to regional precipitation and Caribbean sea-level rise. Investigating the basin’s sedimentological record through deep drilling can provide a temporally-unprecedented record of precipitation, sea-level, and ecosystem function from the northern Neotropics.