Sedimentology and 36Cl chronologies of the Late Pleistocene hummocky moraines in Geyikdağ, Central Tauride Mountains, Turkey

We report the sedimentological characteristics and 36Cl chronologies of the largest hummocky moraine field laid down by piedmont glaciers in the Central Tauride Mountains, Turkey. Hummocky moraines are located on the... [ view full abstract ]

We report the sedimentological characteristics and 36Cl chronologies of the largest hummocky moraine field laid down by piedmont glaciers in the Central Tauride Mountains, Turkey. Hummocky moraines are located on the north-facing hill-slopes of the Namaras Valley situated around 2000-2050 m above sea level in Geyikdağ. Hummocky moraine is a descriptive term designating knob-and-kettle (convex and concave) topographies, and is related to ice-disintegration processes of wasting glaciers, which were thickly covered by supraglacial debris. In the study area more or less equally distributed, randomly oriented chaotic mounds and depressions characterize the hummocky moraines. 1-10 m high and 10-30 m wide mounds, with 5-10o upper surface slopes, are separated by 5-30 m wide and a few meters deep irregular depressions. Within the non-stratified and non-sorted sediments that constitute the moraines, few clasts show characteristic flatiron and bullet shapes indicating sub-glacial transport. Occasionally, wide depressions forming mostly ephemeral lakes filled with much finer grained sediments are also present. Hummocky moraines are considered to result by more or less synchronous in situ glacier stagnation in response to marked climatic ameliorations. Alternatively, they were also regarded to result from locally isolated patches of waning glaciers, melting of debris-covered ice in ice-cored moraines, subglacial deformation of coarse debris or reworking of supraglacial debris during uneven ice ablation in front of active glaciers. Twenty-six boulders from hummocky, lateral and terminal moraines from the Namaras Valley and the tributary Susam Valley were dated by cosmogenic 36Cl surface exposure dating. The moraine ages indicate three phases of glacial advances during the Late Pleistocene. The oldest glacial advance occurred in the Namaras Valley at the end of the Last Glacial Maximum (18.0±0.4 ka, ka: thousands years ago) and is recorded entirely by the sequence of hummocky moraines in the mountain. Glaciers retreated towards the Susam Valley (2100-2200 m a.s.l.) and became stagnant during the Late Glacial (14.3±1.3 ka) as observed from hummocky and terminal moraines at the interior and outlet of the valley. Glaciers re-advanced at around 11.5±1.0 ka ago (Younger Dryas) which is represented by several lateral moraines that are at least 50 m higher than the surrounding hummocky moraines in both valleys. Comparable glacial chronologies were obtained from other Turkish mountains and from other Mediterranean mountains. This project is supported by Tübitak project 112Y139.