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 desi ccated Late Pleistocene lake. This study evaluates the depositional environ ments and the sequential evolution of a shoreline system that developed at the northern margin of the Konya palaeolake near Gocu. Several laterally co ntinuous quarry sections provided an excellent opportunity for studying spa tial and temporal changes of depositional environments and related lake-lev el fluctuations. Eight principal sedimentary facies and six major lithostra tigaphic units have been identified in these deposits representing prograda tional and retrogradational episodes of shoreline development. The lowest s equence is an aggradational unit formed by wind-driven currents and waves i n a sand-dominant lake bottom above the wave base. It is overlain by a conv oluted palaeosol C-14 dated to ca 28,300 sp representing a major lowering o f lake levels. Following an unconformity, the next sequence is characterise d by large-scale gravelly clinoforms that progressively offapp/downlap onto the underlying sequence, and correspond to progradation of a foreshore res ulting from storm-originated oscillating and unidirectional currents, avala nching processes and minor subaqueous debris flows. It is overlain by an ar eally extensive lensoid body of structureless clays comprising a thin organ ic layer, abundant rootlets and freshwater mollusc shells, formed from susp ension fallout in a quiet, very shallow freshwater lagoonal environment. Th is 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 an d bars, which developed by storm-originated wave surges and strong shorelin e currents, and prograding delta foresets. These sequences indicate a renew ed lake transgression to higher water levels; before a final regression aft er 17,500 sp. Lack of tectonic deformation and the overall sedimentary char acteristics of the beach system at Gocu clearly suggest that the sedimentar y evolution of the system is closely related to lake-level fluctuations res ulting 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.