Age of radiolarian-chert blocks from the Senonian Ophiolitic Mélange (Ankara, Turkey)

Abstract The Senonian Ophiolitic Mélange of the Ankara Mélange Supergroup includes numerous blocks of radiolarian cherts. These blocks contain various radiolarian assemblages from the Albian to the Turonian ( Pseudodictyomitra pseudomacrocephala, Thanarla tieneta) , the Lower Cretaceous ( Thanarla conica, Alievium helenae, Pseudodictyomitra carpatica) , the Kimmeridgian-Tithonian ( Ristola altissima, Sethocapsa cetia, Podocapsa umphitreptera) and the lower Jurassic ( Parahsuum simplum). Upper Norian radiolarians were obtained from two of these blocks. The assemblage is represented by Betraccium deweveri Pessagno and Blome, Ferresium triquetrum Carter, Pylostephanidium ankaraense n. sp. (Genus Pylostephanidizi was formerly unknown in the upper Triassic) and other taxa. Thus, upper Norian fauna of Turkey exhibits close similarity to the radiolarian assemblages of western North America, Eastern Russia, Japan and the Philippines. This provides further evidence for the correlation of Mediterranean and Pacific Triassic sequences. These data allow for the conclusion that the sedimentation of radiolarian cherts was common in this part of Tethys during the Late Triassic and the Jurassic.     

Modeling stream flow and sediment yield using the SWAT model: a case study of Ankara River basin,Turkey

The Soil and Water Assessment Tool (SWAT) was tested for prediction of stream flow and sediment yield in the Ankara basin, Turkey. The overall objective of this study was to evaluate the performance and applicability of the SWAT and generate a soil erosion map. Thirteen years of daily/monthly flow and monthly sediment data were used for calibration and validation. Model performance was evaluated using statistical measures to assess the applicability of the model in simulating stream flow and sediment yield during calibration (1989–1996) and validation (1982–1984) periods. Nash Sutcliffe efficiency (NSE), relative error (RE), and R² (coefficient of determination) for daily flow were computed as 0.61, ?0.55, and 0.78, respectively; and as 0.79, ?0.58, and 0.89 for monthly flow during the calibration. Statistical comparisons of sediment yield produced values for NSE, RE, and R² of 0.81, ?1.55, and 0.93, respectively, during the calibration. The resulting map suggests that significant portions of urbanized and highly cultivated areas in the vicinity of stream channels are particularly vulnerable to soil erosion. SWAT satisfactorily simulated hydrology and sediment yield and can be used as a tool in decision-making for water resources planning in a basin with similar characteristics.     

Finger prints of the formation of geothermal springs on the granitoids: Beypazarı–Ankara, Turkey

The Beypazarı granitoid in central Anatolia was emplaced during the Late Cretaceous and it is partly covered with Early Miocene–Quaternary sedimentary and volcanic units. Compression and tension regimes of the Beypazarı granitoid emplacing along the Sakarya River were evaluated considering the kinematical characteristics of discontinuities on granitoids, petrographic/geochemical works, formation of geothermal spring and irregularities in topographic structure. It was determined that the Beypazarı granitoid was witnessed with NE–SW compressional stress and NW–SE extensional stress which resulted in the formation of the Kapullu normal fault with N55–72°E, 78°SE crossing the Kapullu spring site. There are also several other probable normal faults around this fault in the Sakarya River basin. The results of the geochemical studies reveal that SiO₂, Na₂O, Al₂O_3, CaO and K₂O as a major oxide and As, Rb, Sr, Th and U as trace elements are decreased away from the Kapullu bath spring. On the other hand, the ratio of Fe₂O₃ and MgO as major oxide and Y as a trace element with the lost on ignition (LOI) are increased away from the Kapullu fault. Regard as the regional plate tectonism, there is a consistency between the direction of compression in the Beypazarı granitoid and that developed by the southwesterly movement of the Anatolian plate.     

Effect of weathering on the geomechanical properties of andesite, Ankara – Turkey

Andesite exposed in different parts of Ankara has different weathering categories varying from fresh to residual soil. The geomechanical properties of the andesite are significantly affected by weathering. Buildings constructed especially in completely weathered and residual soil levels of the andesite have some geotechnical problems. In this study, the variation of the geomechanical properties of the andesite due to weathering is investigated in three selected sites of Ankara, through optical microscope, X-ray diffraction analyses, major element analyses, pressuremeter tests, physicomechanical tests, and seismic refraction method. The data gathered from the field and laboratory studies were used to assess the characteristics of the weathering zones. Based on the data obtained from this study, an idealized weathering profile is assessed. No bearing capacity and consolidation settlement problems exist in the area. However, care should be taken for immediate settlement of the buildings. Slopes with heights less than 8 m are not expected to cause any significant problems for buildings. There exists a ground amplification problem in the study area. The natural period of the building should not match that of the weathered rock. The ground response analyses reveal that the buildings with four to seven stories may be adversely affected from earthquakes due to resonance phenomenon. Therefore, this has to be taken into account when designing new buildings.     

Climate change impacts on meteorological drought using SPI and SPEI: case study of Ankara,Turkey

ABSTRACT

Using regionally downscaled and adjusted outputs of three global climate models (GCMs), meteorological drought analysis was accomplished across Ankara, the capital city of Turkey. To this end, standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI) were projected under (representative concentration pathway) RCP4.5 and RCP8.5 greenhouse gas scenarios. In general, our results show that Ankara experienced six severe and two extreme drought events during the reference period, 1971–2000. However, the projections indicate fewer drought events for the near-future period of 2016–2040, with no potential extreme drought events. While the RCP4.5 scenario showed that dry spells will be dominant in the second half of the near-future period, the RCP8.5 scenario projected that dry spells will be evenly distributed during the entire near-future period.     

Engineering characteristics of Ankara Greywacke under the foundation of the Beytepe open air theatre,Ankara, Turkey

The construction of a large open air theatre having with an audience capacity of 7,000 is planned at the Beytepe Campus of Hacettepe University located near Ankara, Turkey, in the heart of Anatolia. The foundation of the open air theatre is composed of weak and heavily jointed Ankara Greywacke. An estimation of the strength and deformation of the Ankara Greywacke was required for assessments of short- and long-term stability. Accordingly, rock mass characterization of the Ankara Greywacke was investigated in detail by scan-line surveys and back-analyses of in situ tests performed on the excavated surface of the rock mass. The final version of the Hoek and Brown Criterion (Hoek et al., In: Proceedings of the north American rock mechanics society meeting, Toronto, Canada, pp 1–6, 2002) together with and improvements proposed by Sonmez and Gokceoglu (Int J Rock Mech Min Sci, 43:671–676, 2006) were considered together for the back analyses of small slope benches subjected to plate loading test loaded to failure. In addition, the plate loading test data were used with some well-known empirical equations for predicting of deformation modulus of rock masses to calculate ranges of values of the Geological Strength Index (GSI) The static and pseudostatic slope stabilities of the audience seating structures to be supported by benches excavated into the rock were also analyzed. The stability assessments revealed the unlikelihood of large rock mass failures for the short-term construction stages or for the long-term, as-constructed conditions under static or pseudo-static conditions. Additionally, the analyses showed that there was no need for anchors between the concrete seating structures and greywacke rock mass.     

Jurassic and Cretaceous radiolarian assemblages from the Bornova mélange in northern Karaburun Peninsula (western Turkey) and its connection to the İzmir–Ankara mélanges

Two large blocks of red bedded chert identified within the Late Cretaceous–Paleocene Bornova mélange in northern Karaburun Peninsula yielded Jurassic (late Bathonian–early Oxfordian) and Cretaceous (middle–late Albian) radiolarian assemblages. These new data confirm the correlation of the Bornova mélange with the Bornova Flysch Zone (BFZ) and the ?zmir–Ankara mélanges. A review of all previously obtained ages in chert blocks of the BFZ and the ?zmir–Ankara mélanges is provided in order to strengthen this correlation.     

Fuzzified kinematic analysis of discontinuity-controlled rock slope instabilities

In this study, it is aimed to bring a different approach to kinematic analyses of discontinuity-controlled rock slope instabilities. For this purpose, the data of a detailed discontinuity survey carried out in Ankara, the capital city of Turkey, were updated and reevaluated. Serious discontinuity-controlled instability events were observed in the andesites covering large areas with dense population in the city. Instead of analyzing the effects of the planes belonging only to the major discontinuity sets on the stereographic projection net, all discontinuities were taken into consideration, and kinematic analyses were carried out for planar, wedge, and toppling type failures on pixel basis of the Digital Elevation Model (DEM) of the study area. By doing so, it could be possible to compensate for the deficiency created by neglecting the planes in the lower concentration zones of the stereographic projection. A computer program named FUDIKA (Fuzzified Digital Kinematic Analyses) was written to perform modular kinematic analyses and fuzzy operations, having four modules and operating in three stages. First, Potential Instability Index (PII) was introduced to define instability potential of the rock slopes based on the number of possible instability events for each failure type. Next, the PII values were normalized and fuzzified to obtain PII map of the area. It was seen that when tested on previously occurred instabilities in the area, the PII values obtained through the methodology proposed in the study showed quite a high performance.     

Development of a geotechnical and geophysical database for seismic zonation of the Ankara Basin,Turkey

Engineering geological and geotechnical site characteristics were assessed and seismic hazard studies performed for the Upper Pliocene to Pleistocene fluvial and Quaternary alluvial and terrace deposits for a site west of Ankara, Turkey. Sediment conditions were determined and a soil profile was characterized by surface geophysical methods. These studies were integrated with existing in-situ characterization studies to create a seismic and geotechnical database for the site. A seismic zonation map of the site was then prepared. Site classification systems were assigned to account for site effects in relation to seismic hazard assessments. The consequences of the seismic hazards were investigated and recommendations were presented.