Controls on the Composition and Distribution of Holocene Sediment in Lake Junín, Peru

Lake Junín is a high-­elevation intermontane lake in the inner-­tropics of the South American Andes (11° S, 76.1° W) that is highly sensitive to changes in temperature and precipitation, and contains sediments that are well­-suited for multiproxy analysis and can be reliably dated. It is one of the few lakes in the tropical Andes that can provide a continuous record throughout the last glacial cycle and it is ideally situated to record long­-term variations in the South American Summer Monsoon. Lake Junín was drilled in 2015 to recover sediment cores which will provide the longest independently­-dated record of tropical water balance, glacier variability, vegetation history, and paleomagnetic secular variation for the region. We collected six cores across a NE­-SW transect to characterize the controls on sediment composition and distribution prior to drilling. The cores range from 2 to 9 m in length and each contains a complete Holocene section and glacial transition. Interglacial sediments are composed primarily of authigenic carbonates, whereas minerogenic material sourced from nearby glacial outwash fans dominates the late glacial sediment record. All cores exhibit a similar two-­component stratigraphy: an upper section of primarily whitish pink marl with intermittent light brown mud and a lower section of characteristic light gray glacial flour. Magnetic susceptibility data show that the carbonate/clastic contact deepens from NE to SW, and the thickness of the upper carbonate section displays a significant positive correlation with distance from the NE shore. Quantification of Holocene carbonate sediment dynamics in Lake Junín will facilitate more accurate interpretation of their stratigraphic significance in the longer sediment record.