Sedimentological characterization of geological cores from marginal lakes in the Salar de Atacama

Although thought to be high-resolution archives of paleoenvironmental changes, subsurface sediments deposited in saline lakes situated in salar environments have rarely been studied. To address this knowledge gap, sediment cores of varying depths ranging from 0.42 to 2.2 meters were collected from four saline lakes along the eastern margin of the Salar de Atacama, Chile. Characterization included sedimentological descriptions of lithification, sedimentary structures (microbial mats and microbialites), and color, as well as discrete measurements of total organic carbon content. Radiocarbon analysis was conducted on organic matter in the sediments.  The recovered subsurface lithologies were heterogenous in color, stratigraphic features, and age dates, especially when compared between the lakes. Intervals of coarser sediment in the Soncor system lakes Chaxa, Burros Muertos and Barros Negros, appeared to be crystalline and were likely precipitated during periods characterized by higher salinity lake waters. Sediment cores collected from the Soncor system were broadly characterized by low total organic carbon content and punctuated intervals of coarse grained material deeper in the core. In the core collected from Aguas de Quelana, variations in lithology and hardgrounds were commonly observed. In concert, these results suggest that the eastern periphery of the salar was impacted by changes in salinity and water depth as these wetland area experienced changes in extent as a result of changes in wet and dry periods. Radiocarbon dating conducted on organic matter sampled at 4 intervals from each core revealed ages that were significantly older than expected, possibly due to local reservoir effects and subsurface hydrological dynamics. There were five age reversals documented in the transect of cores suggesting that the sources of radiocarbon may have changed over time. Results indicate that the geologic records of saline lake environments are as heterogeneous through time as they are in space.