Facies and depositional sequences of the Late Pleistocene Gocu shoreline system, Konya basin, Central Anatolia: Implications for reconstructing lake-level changes

Well-developed coarse-grained palaeo-shoreline deposits are found along the rising margins of the Konya basin, marking the former extent of a now desiccated Late Pleistocene lake. This study evaluates the depositional environments and the sequential evolution of a shoreline system that developed at the northern margin of the Konya palaeolake near Gocu. Several laterally continuous quarry sections provided an excellent opportunity for studying spatial and temporal changes of depositional environments and related lake-level fluctuations. Eight principal sedimentary facies and six major lithostratigaphic units have been identified in these deposits representing progradational and retrogradational episodes of shoreline development. The lowest sequence is an aggradational unit formed by wind-driven currents and waves in a sand-dominant lake bottom above the wave base. It is overlain by a convoluted palaeosol C-14 dated to ca 28,300 sp representing a major lowering of lake levels. Following an unconformity, the next sequence is characterised by large-scale gravelly clinoforms that progressively offapp/downlap onto the underlying sequence, and correspond to progradation of a foreshore resulting from storm-originated oscillating and unidirectional currents, avalanching processes and minor subaqueous debris flows. It is overlain by an areally extensive lensoid body of structureless clays comprising a thin organic layer, abundant rootlets and freshwater mollusc shells, formed from suspension fallout in a quiet, very shallow freshwater lagoonal environment. This phase, representing a more minor lake regression, has been 14C dated to ca. 21,960-20,730 sp. The final sequences include large-scale sand waves and bars, which developed by storm-originated wave surges and strong shoreline currents, and prograding delta foresets. These sequences indicate a renewed lake transgression to higher water levels; before a final regression after 17,500 sp. Lack of tectonic deformation and the overall sedimentary characteristics of the beach system at Gocu clearly suggest that the sedimentary evolution of the system is closely related to lake-level fluctuations resulting from long- and short-term hydro-climatic changes. Successive stages of lake-level rises and large amounts of supply of coarse grained material imply a positive hydrological balance and relatively high rates of sediment discharge from the adjacent hillslopes. (C) 1999 Elsevier Science Ltd. All rights reserved.