Middle and Late Holocene paleoenvironmental developement of the Curonian Lagoon, Lithuania

The reconstruction of the development of the northern Curonian Lagoon, Lithuania, during the Holocene is based on a wide suite of studies: pollen, diatom and carbonate analyses, measurements of magnetic susceptibility, as well as geochemical data. Recently published data from the Nida-VI borehole show that the age of lacustrine and lagoonal sand spans from Boreal to Sub-Atlantic. Diatom analyses reveal changes in the groups of brackish-fresh and fresh-brackish species and show relatively rapidly changing environmental conditions that could have existed through the ongoing Litorina Sea transgression. The Curonian Spit separated a semi-closed lagoon by the end of Atlantic − beginning of Subboreal, with ”lagoon marl” layer deposited during the Litorina Sea stage. The paleo-lagoon became shallow and freshwater during the Subatlantic. The topmost sediment in the section is nearly devoid of diatom valves likely due to high accumulation rates of sand. Climate shifts and local environmental conditions were distinguished based on carbonate content, with lower values associated with colder periods. The increase in carbonate fraction during the late Atlantic is related mostly to warmer Holocene climate phases. Based on Al/Ti oxide ratio, the Boreal climate was arid and the Early Atlantic largely transitional, whereas the late Atlantic was humid. The absence of negative Ce anomalies, as well as U/Th ratios, suggest that a rather oxic regime prevailed during sedimentation. The origin of several cycles of variation in Zr/Rb may indicate increased weathering. Down core variations in bulk volume magnetic susceptibility closely mirror the textural and compositional trends, with peaks likely reflecting pulses of terrigenous influx during dry periods.