LATE HOLOCENE PALEOHYDROLOGY IN CENTRAL WESTERN TURKEY

Marmara Gölü is a broad, shallow lake situated in the Gediz River valley in central western Turkey. The lake’s shallow depth (~6 m max) versus its large area (~13 x 5 km) makes it very sensitive to changes in moisture balance in the region. Large fluctuations in lake level during historical times have resulted in kilometer-scale changes in shoreline position given the subtle bathymetry, but the lake has never gone completely dry in recent memory. To understand past hydrologic and environmental variability in the region, a series of sediment cores were taken in two transects from the edges towards the center of the basin. The sediment cores have undergone a suite of basic sedimentary analyses (magnetic susceptibility, bulk density, and loss-on-ignition) at very high resolution (1 cm) to characterize their physical sedimentology. The stratigraphy records a preexisting floodplain that was succeeded by a shallow lacustrine system. The shallow lacustrine system experienced an abrupt desiccation event during which the basin went completely dry, and then a return to lacustrine conditions, which have persisted to the present day. The abrupt desiccation event is clearly indicated by a classic sequence, which includes an erosional unconformity at the top of the lower, shallow lacustrine deposit, followed by a basal conglomerate (lag deposit) of sedimentary intraclasts, and other subaerial indicators such as debris flows, and incipient pedogenic development. Two AMS radiocarbon dates obtained on macroscopic organic matter right below the erosional unconformity suggest that the desiccation event occurred at some point after the first half of the 5th century AD. This is coincident with several regional paleo records that indicate a strong period of aridity at this time, and that may be linked to variability of the North Atlantic and Indian Monsoon systems. Study of the upper lacustrine deposit via high resolution grain size analyses is currently underway to identify other potential episodes of aridity that did not result in complete desiccation of the basin.