AYBE- Katı Yer Bilimleri Lisansüstü Programı

Bu topluluk için Kalıcı Uri

http://hdl.handle.net/11527/262
Çalışma Konuları: • Paleo-Tektonik / Paleotectonics • Neo-Tektonik / Neotectonics • Bölgesel Jeoloji / Regional Geology • Metamorfik Petroloji / Metamorphic Petrology • Tetis Jeolojisi / Geology of Tethys • Morfotektonik / Morphotectonics • Volkanoloji / Volcanology • Sedimantoloji / Sedimantology • Deniz Jeolojisi / Marine Geology • Magmatik Petroloji / Magmatic Petrology • Yapısal Jeoloji / Structural Geology • Paleontoloji / Paleontology • Stratigrafi /Stratigraphy • Kuvaterner Jeolojisi / Quaternary Geology • Topics in Micropaleontology

Gözat

Konu "Çoklu-proksiyon yöntemi, Kızılırmak Nehri" ile AYBE- Katı Yer Bilimleri Lisansüstü Programı'a göz atma
  • Öge
    A multi-proxy study of the Kızılırmak river terraces andits delta, northern turkey: Implications for tectonics,sedimentation, sea level and environmental changes
    (Eurasia Institute of Earth Sciences, 2019-03-20) Berndt, Christopher ; Çiner, Atilla ; 602142002 ; Solid Earth Sciences ; Katı Yer Bilimleri
    River deltas as one end feature of a river are affected by a number of factors determining their shape, presence and longevity. At present, those landforms give space for large human populations as well as agricultural farmland. Aside, plenty of species, including several threatened and rare ones, inhabit the delta's wetlands creating valuable ecosystems of international importance. Nevertheless, delta plains are highly variable environments reacting quickly to changes in sediment influx from the river as well as wave, tides and current activity. The sediment transport of a river to the delta is highly depending on external and internal environmental factors. These sediments contain data about the evolution of past climate, sea level and geodynamics on local over regional to global scales. On the other hand, several river deltas worldwide are distinctly affected by human activities such as river dams which reduce the sediment transportation downstream to the delta. Those impacts lead to artificially-induced changes in their morphology, i.e., shoreline retreats. The lower stream of the Kızılırmak River in northern Anatolia comprises of ecologically rich wetlands on the present delta plain as well as elevated fluvial and delta terraces. The Kızılırmak River delta is located at the border between the Central Anatolian Plateau and the Black Sea. The Central Anatolian Plateau is a major feature of the Alpidic orogeny in Anatolia and uplifted slowly during Quaternary. The North Anatolian Fault Zone, forming a broad restraining bend in the central section of the Pontide Mountains, tectonically impacts the northern margin of the plateau. This northward progressing deformation is suggested to accelerate the uplift of the northern margin of the Central Anatolian Plateau until the southern coast of the Black Sea. The dating of fluvial and marine terraces has now been established to temporally constrain and reconstruct active tectonics impacting this delta during Quaternary. On the other hand, the Black Sea is the largest semi-enclosed sea with a globally unique fauna due to its repeated disconnection from the world ocean. It was disconnected during the Last Glacial Maximum (ca. 20 ka) until it became reconnected to the Mediterranean Sea in early Holocene. Ostracod faunal assemblages are well established proxies for marine, as well as limnic, palaeoenvironmental reconstructions due to the high preservation potential of their valves in sediments. Those characteristics create the opportunity to apply quantified statistical analyses of their faunal assemblages to identify principal influencing factors. Cyprideis torosa (Jones) is a brackish water ostracod that lives mainly in marginal environments, but can withstand a wide variety of conditions. This species forms phenotypic adaptations of its carapace to cope with environmental changes with up to severe hypersaline conditions. Recent studies started to use those morphological variations to create transfer functions determining palaeoenvironmental variables, i.e. salinity. The aim of this thesis is the reconstruction of the Quaternary evolution of the lower stream and delta of the Kızılırmak River. This goal will be achieved by identifying the geodynamics at the northern margin of the Central Anatolian Plateau combined with the influence of the North Anatolian Fault Zone, which creates several fluvial terrace levels along the lower course of the Kızılırmak River; and unraveling the Holocene palaeoenvironmental evolution of the delta with its dependencies to the Anatolian climate and Black Sea sea level changes, based on ostracod faunal assemblages. In addition, we analyse how the environmental conditions modify in turn the size and shell thickness variation of Cyprideis torosa (Jones) as phenotypic morphological adaptations for a future improved characterization of marginal marine palaeoenvironments. In the first part of the thesis, the interplay between coastal uplift, sea level change in the Black Sea, and incision of the Kızılırmak River in northern Turkey is analysed. These processes have created multiple co-genetic fluvial and marine terrace sequences that serve as excellent strain markers to assess the ongoing evolution of the Pontide orogenic wedge and the growth of the northern margin of the Central Anatolian Plateau. Newly acquired high-resolution topographic data and OSL ages accompanied by published information on past sea levels were used to analyse the spatiotemporal evolution of these terraces; a regional uplift model for the northwardadvancing orogenic wedge Pontides was derived that supports the notion of laterally variable uplift rates along the flanks of the Pontides. The best-fit uplift model defines a constant long-term uplift rate of 0.28 ± 0.07 m/ka for the last 545 ka. This model explains the evolution of the terrace sequence in light of active tectonic processes and superposed cycles of climate-controlled sea-level change. Those new data reveal regional uplift characteristics that are comparable to the inner sectors of the Central Pontides; accordingly, the rate of uplift diminishes with increasing distance from the main strand of the restraining bend of the North Anatolian Fault Zone (NAFZ). This spatial relationship between the regional impact of the restraining bend of the NAFZ and uplift of the Pontide wedge thus suggests a strong link between the activity of the NAFZ, deformation and uplift in the Pontide orogenic wedge, and the sustained lateral growth of the Central Anatolian Plateau flank. In the second part of the thesis, the analysis of a 14.5-m-long sediment core, drilled into the eastern delta wetlands, is presented. The palaeoenvironmental impact on the delta plain was analysed using palaeoecological ostracod assemblages accompanied by a palaeo-salinity reconstruction based on sieve pore shape variations on the ostracod Cyprideis torosa (Jones). This study depicts the interplay of terrestrial and marine settings forming mesohaline, shallow lagoons and deltaic lakes since ca. 7.9 ka cal BP. Lagoons with α-mesohaline to polyhaline salinities and β-mesohaline to oligohaline lake environments were identified. Reconstructed palaeo-sea level estimations depict a remarkable environmental variability. The lagoon habitats at 7.9 to 7.0 and 5.3 to 4 ka cal BP were dominated by Cyprideis torosa. Marine influence led to ostracod associations with Loxoconcha spp. and Tyrrhenocythere amnicola especially between 7.9 and 7.0 ka cal BP. Riverine influence in the same period, but especially at about 7.7 ka cal BP, caused dominating Amnicythere spp. Assemblages dominated by Cyprideis torosa and Candona neglecta characterise short phases of a mesohaline deltaic lake environments at about 7.7 and 7.0 ka cal BP as well as after 4 ka cal BP. With a subsequent salinity decrease, C. neglecta and (later on) Pseudocandona marchica became dominant with an interruption by another shortterm lagoonal phase that might be associated with a 'megadrought' between 3.7 and 3.0 ka cal BP. In the final part of the thesis, the valve size of adult and penultimate ontogenetic individuals and shell thickness of Cyprideis torosa was measured in relation to the changes in palaeoenvironmental conditions. A good positive correlation between the size of female valves and the prevailing salinity (correlation coefficient: 0.56) can be reported, while such a correlation is lacking for ontogenetic stage A-1. The absence of large individuals is indicated to be a local effect of the Black Sea fauna. No changes of the height/length ratio of the valves were recognizable along the salinity gradient. Shells are significantly thicker under relatively stable, higher saline conditions, but thinner in highly variable and low saline deltaic lakes. Both morphological features, size and shell thickness of C. torosa, are thus potential tools to give palaeoenvironmental information, especially in C. torosa-dominated, low diversity marginal marine environments. In overall, the study shows that the impact of the North Anatolian Fault deforms the northern margin of the Central Anatolian Plateau until the Black Sea coast in the range of the central Pontide Mountains since at least 545 ka. Hence, the southern part of the Kızılırmak Delta becomes uplifted at an accelerated rate. In addition, the Kızılırmak Delta reacts rapidly on changes in Anatolian climate and Black Sea sea levels forming an alternation of lagoonal and deltaic lake environments in its eastern part since Mid-Holocene. While sea level changes predominantly modify the environments during the early Mid-Holocene, the climate changes have a much higher impact during Late Holocene. In turn, those environmental changes leading to salinity variations correlate to phenotypic changes in the morphology of the ostracod Cyprideis torosa (Jones).