Browsing by Author "Hashemi, K"

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    Defining denudation rate of carbonate rocks using cosmogenic 36Cl in the Taurus Mountain, S-SW Turkey
    (Copernicus GmbH, 2021-04-19) Hashemi, K; Sarikaya, MA; Wilcken, KM
    Denudation of carbonate terrains occurs by the contribution of both chemical and mechanical weathering. In-situ cosmogenic 36Cl is a robust proxy to quantify the long-term total denudation rate of carbonate rocks. In this study, we defined the steady-state denudation rate of carbonate bedrock using 36Cl for 105-106 years under the temperate Mediterranean to semi-arid climate in and around the Taurus Mountain Range, S-SW Turkey. We collected 13 samples from different lithological units; Jurassic-Cretaceous neritic limestone in the temperate western Taurus, Miocene neritic limestone in the semi-arid Central Taurus, and Mesozoic marbles in the continental part of Central Taurus. The calculated denudation rates range from 28.9 ± 1.4 mm/ka in the Mediterranean coastal range to 1.6 ± 0.1 mm/ka towards northern continental/rain shadow. We compared the denudation rates with a range of parameters such as topographic, climatic, lithologic and mechanical properties of rocks. For almost all samples denudation rate increases with elevation, with two exceptions with the highest rates despite their lower elevations. This high denudation rates could be due to their proximity to the sea. Our results showed that denudation rates decrease with increasing distance from the coast. All denudation rates showed a positive correlation with mean annual precipitation (MAP ~ 400-760 mm) as suggested by other studies worldwide. Annual temperatures (MAT ~ 6-16 °C), however, has a negative correlation with the denudation rates, i.e. the highest denudations occur in the low temperatures (MAT ~ 6-8 °C). The mechanical strength of the rocks was measured with a Schmidt hammer in the field. The high rebound values of Schmidt hammer, indicating the high mechanical strength, correlate with low denudation rates. Nevertheless, the mechanical strength of the carbonate bedrock is not as effective as precipitation or available moisture on denudation rates. This could be shown by two samples close to the Mediterranean which both have high mechanical strength nonetheless show the highest denudation rates. In conclusion, our study suggests that carbonate bedrock denudation in Taurus Mountain correlates with high elevation (~ 1900-2250 m), high precipitation (~ 700-800 mm), low temperatures (~ 6-8 °C) and short distances from the Mediterranean coast.
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    The Namaras rock avalanche: evidence of mid-to-late Holocene paraglacial activity in the Central Taurus Mountains, SW Turkey
    (Elsevier B. V., 2022-07-01) Hashemi, K; Sarıkaya, MA; Görüm, T; Wilcken, KM; Çiner, A; Žebre, M; Stepišnik, U; Yıldırım, C
    The Namaras rock avalanche (NRA) deposit originated from the northern flank of the glaciokarstic Geyikdağ Mountain in the Central Taurus Range, SW Turkey. The deposit has an area of ~0.430 km2 and an estimated average thickness of 10 m, corresponding to 4.3 million m3 volume. The fan-shaped deposit area consists of house-sized Jurassic-Cretaceous neritic limestone boulders that overlie lateral and hummocky moraines down into the valley. We used geomorphological mapping and 36Cl surface exposure dating to obtain six boulder ages which unravelled the NRA age, the number of events and their geometric features. Our results indicate that the NRA consists of two successive mid-to-late Holocene events; the first high magnitude main event with a weighted average age of 4.59 ± 0.25 ka followed by a second low magnitude event with a weighted average age of 3.77 ± 0.20 ka. 36Cl exposure dating of the lateral moraine covered by the rock avalanche deposit yielded approximately an age of ~12.30 ± 1.20 ka. The older event with a maximum runout distance of 1550 m and 600 m elevation loss yielded in a travel angle of 21°. Similarly, the younger event with 1720 m maximum runout length and 640 m vertical elevation loss resulted in a travel angle of 20°. The bedded limestone with cross-joints in the glacial cirque preconditioned the NRA slope failure. The significant lag time between deglaciation and the rock avalanche indicates that the glacial erosion and debuttressing acted as preparatory factors. Based on the low seismic activity in the Central Taurus Range and the synchronicity of the rock avalanche with mid-to-late Holocene climatic transitions, we propose that climatic factors may have triggered the NRA failure. The age of the older main event coincides with the warm drought period of the mid-Holocene associated with torrential rainfalls in the Taurus Mountains, while the age of the younger event correlates with the long wet period in the late Holocene. Thus, the main NRA event may have been triggered by the influence of warm temperatures and intense rainfall, while the second event may have been triggered by prolonged period of high precipitation. The two events of the NRA are coeval with the enhanced rock slope failures dating back to 5–3 ka in the Alps. © 2022 Elsevier B.V.