AYBE- İklim ve Deniz Bilimleri Lisansüstü Programı - Doktora
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Sustainable Development Goal "none" ile AYBE- İklim ve Deniz Bilimleri Lisansüstü Programı - Doktora'a göz atma
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ÖgeQuaternary tectonic and climatic interactions in central pontides, Turkey; inferences from osl and cosmogenic applications on fluvial deposits(Lisansüstü Eğitim Enstitüsü, 2021) Mcclain, Kevin Patrick ; Yıldırım, Cengiz ; Çiner, Tahsin Attila ; 672551 ; İklim ve Deniz BilimleriThe fluvial incisional response to Cenozoic uplift has been widely studied, yielding insights on timing, patterns, and/or rates of rock uplift. Absolute dating of Quaternary landforms in actively uplifting regions can provide accurate rock uplift rates that after careful interpretation can be used to explain the processes that developed the landscape. The Mediterranean region, or western half of the Alpine-Himalayan orogenic belt, is comprised of complex environments resulting from the convergence of the African and Arabian plates with Eurasia, subsequent trench retreats, and mantle processes (Wortel and Spakman, 2000). One of these environments is the Central Anatolian Plateau, which is an orogenic plateau between the contractional Eastern Anatolian Plateau and the Western Anatolian Extensional Province. While the uplift of the southern margin of the plateau has complex relationships with the lithospheric mantle and subduction along the Cyprus Trench, the northern margin is suggested to be decoupled from mantle processes of the plateau interior and southern margin. Instead, its uplift and lateral growth are mostly attributed to the development of the broad restraining bend of the North Anatolian Fault, a transform fault between the Anatolian microplate and Eurasian Plate. The environment between the restraining bend and Black Sea is also referred to as the Central Pontides and has been interpreted as a growing orogenic wedge with a positive flower structure geometry. However, the faults north of the restraining bend show weak modern seismicity, and their Quaternary activity is not fully understood at this time. Over the last decade marine terraces, delta terraces, and fluvial terraces have been used to calculate rock uplift rates in the eastern and central flanks of the Central Pontides, revealing a possible uplift rate increase with proximity to the North Anatolian Fault restraining bend. Marine terraces as far north as the Sinop Peninsula and a Mw 6.6 earthquake offshore on the western flank show a compressional tectonic regime extending into the Black Sea shelf. On the western flank of the Central Pontides there are several main rivers incising the topography of the plateau margin en route to the Black Sea. The Filyos River is the largest of these and has the best known fluvial terrace record preserved, including a strath terrace staircase of seven levels on the hanging wall block of the Karabük Fault, a reverse fault verging towards the restraining bend. Here, the Filyos River incises through the Karabük Range, creating ~1700 m of relief in the Filyos River Gorge. The first part of the thesis focused on calculating rock uplift rates at this terrace staircase using the OSL method to date the deposition age of fluvial terraces. The bedrock incision rates revealed a glimpse of the highest uplift rates recorded in the Central Pontides, with uplift rates of 1.15 mm/a before 366 ± 19 ka. However, the younger terraces revealed a suspiciously low bedrock incision rate of just 0.12 mm/a during the last 366 ka. The high incision rate period experienced two lateral channel migrations and an epigenetic gorge formation, suggesting the Filyos River is capable of eroding and transporting thick local aggradation. This means something other than local coseismic landslides would be required to prevent the river from reaching equilibrium and incising bedrock for long periods. In the second part of the thesis, the environment downstream from the Filyos River Gorge was investigated. The areas with clastic bedrock tend to laterally erode enough to accommodate more aggradation and form fluvial terraces. With the exception of the terraces staircase upstream, the Filyos River Gorge has lithologies that restrict lateral mobility of the channel. Clastic lithologies reappear on the windward side of the Karabük Range, downstream from the Filyos River Gorge. Here, the remnants of three fill terrace levels are preserved, but mostly with poor conditions for OSL sampling. Luckily, at a main river-tributary junction stronger alluvial fan layers overly the lowest fill terrace level, helping to preserve it. OSL dating of a longitudinal bar layer revealed a fill terrace age of 275 ± 12.8 ka. Three well-rooted limestone boulders were sampled on the surface of the landform, revealing a maximum abandonment age of 39.5 ± 3.5 ka. Geomorphic interpretations of the main river valley and tributary catchments identified a large, previously unmapped landslide upstream from a limestone tributary canyon that the tributary incises through in its final kilometers. This landslide would have provided a sudden influx of sediment into the tributary, resulting in transport through the canyon and onto the main valley. This was confirmed in the alluvial fan layers on the opposite side of the valley. There is evidence of outburst floods in elevated fluvial ~35 m above the tributary channel between the landslide and tributary canyon. The most recent fill terrace level at 275 ka formed during a hiatus of fluvial terrace formation upstream. Therefore, it is assumed that the aggragation during that period was not local to this valley segment and is instead the result of conditions in the larger catchment. The Filyos River may not have the ability to efficiently remove such catchment-wide aggradation, especially in cooler climatic periods when precipitation rates are reduced. With the local environment occurring in the more landslide-prone windward side of the Central Pontides, it is also possible that new base levels form due to fill terrace formation, disturbing preventing continuous bedrock incision upstream. The main river-tributary junction fan would have formed such a base level but is less likely to interrupt incision on significant scales. Therefore, the results show the importance of comparing rock uplift rates of fluvial terraces to rates and interpretations of downstream fill terraces. Upstream in the Filyos River Valley strath terrace staircase, the lower 0.12 mm/a bedrock incision rates since 366 ± 19 most likely significantly underestimate the rock uplift rates, meaning the rock uplift rates of the Karabük Range are on the order of 1.15 mm/a. Collectively, the results show that the strain directed at the western flank of the Central Pontides by the North Anatolian Fault restraining bend produces the highest measured Central Pontides rock uplift rates. These first rock uplift rates on the western flank support the model of a growing orogenic wedge with a positive flower structure. The results also show the sensitivity of the hillslopes to fail and produce catastrophic landslides that form landslide dams, alluvial fans at river junctions, and cause channels to migrate to new positions through the formation of epigenetic gorges. This could have consequences for populations living near the Filyos River and other main rivers incising clastic bedrock.