Mapping and assessment-based modeling of soil fertility differences in the central and eastern parts of the Black Sea region using GIS and geostatistical approaches

This study was carried out on arable lands of the central and eastern Black Sea regions including eight provinces (Artvin, Giresun, Gümü?hane, Ordu, Rize, Samsun, Sinop, and Trabzon). The present study aims to generate a soil fertility map for agricultural lands in the central and eastern parts of the Black Sea region. The main objective of this research is to quantify soil fertility by developing a soil fertility index (SFI) model at the regional level. The related objectives were to map the spatial distribution of soil fertility by using auxiliary variables and to model soil fertility within the study region. To accomplish this, a data set for soil fertility differences was collected and a model was developed to predict the spatial distribution of differences across the region. The study area was divided into 2.5 × 2.5-km grid squares. A total of 3400 soil samples were collected from the surface (0–20 cm) of each grid intersection point. The geostatistical method was used to generate the SFI distribution map of the study area for surface soils. Of the total study area, 93.76% had good (S1) or moderately fertile (S2) soil while 6.15% of the area had marginally fertile (S3) soil. Only a very small area (N) had low-fertility soil.     

Visualization of geotechnical data by means of geographic information system: a case study in Eskisehir city (NW Turkey)

Recently, geographic information system Software’s are widely used in engineering geology applications. Such a study was performed in the Eskisehir urban area of about 30 km² via geo-engineering maps, cross-sections and panel-block diagrams, which are formed to predict the properties of foundation soil. In order to determine the engineering geology properties of the region, physical and mechanical characteristics of the soil profile were tested on 1,011 disturbed and 383 undisturbed samples from a total of 170 boreholes. Topographic, lithological and geotechnical data of the region were compiled as a database in computer. Five geological cross-sections were drawn to decipher specifically the alluvial deposits in detail in densely populated areas. Hence, geological characteristics of the area were evaluated in a three-dimensional mode. Five standard penetration test (SPT) cross-sections at the same directions and SPT, uniaxial compressive strength (qu) and soil class Zonation maps were produced at different depths and panel-block diagrams were also created to define the geo-engineering properties of the investigation area. In this respect, the sub-surface of the study area is fully visualized and useful predictor maps, cross-sections and panel-block diagrams are performed to be used in further studies.     

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.     

Adsorption of carbonate and bicarbonate salts at the air–brine interface

Previous research has shown that the flotation of soluble salt is determined by interfacial water structure, thermal stability, and viscosity. These salts include alkali halide and alkali oxyanion salts. Of particular interest are the carbonate salts such as those associated with the great trona deposit of the Green River basin in Wyoming. In this study, we investigated the adsorption of carbonate and bicarbonate salts at the air–brine interface and correlated the adsorption behavior with water structure. Specifically, the equilibrium and dynamic surface tensions of sodium carbonate and sodium bicarbonate salts have been measured as a function of the salt concentration up to saturation and compared with the model prediction using the Gibbs–Langmuir adsorption theory. The results show that the negative adsorption of sodium carbonate leads to a significant increase in surface tension of the brine solution. For sodium bicarbonate, both the negative adsorption and the increase in surface tension are significantly lower when compared with the sodium carbonate case. The negative adsorption is correlated with the water structure making/breaking character of carbonate and bicarbonate solutions. In particular, sodium ions are significantly more hydrated than carbonate and bicarbonate ions, and, therefore, tend to be excluded from the air–brine interface. On the other hand, carbonate and bicarbonate ions are accommodated at the air–brine interface. In any event, the balance between sodium exclusion and carbonate/bicarbonate accommodation results in an increase in the surface tension of these solutions with an increase in salt concentration.     

Petrogenesis of the Neogene alkaline volcanics with implications for post-collisional lithospheric thinning of the Eastern Pontides, NE Turkey

Whole-rock geochemistry, Sr–Nd–Pb isotopes and K–Ar data are reported for alkaline samples collected from the Neogene alkaline volcanics (NAVs) in the Eastern Pontides, northeastern Turkey, in order to investigate their source and petrogenesis and geodynamic evaluation of the region. The NAVs were made of three groups that comprise of basanite–tephrite (feldspar-free; Group A), tephrite–tephriphonolite (feldspar and feldspathoid-bearing; Group B) and alkaline basalt–rhyolite (feldspathoid-free; Group C) series. These rocks cover a broad compositional range from silica-undersaturated to silica-oversaturated types, almost all of which are potassic in character. They show enrichment of LREE and LILE and depletion of HFSE, without a Eu anomaly in most of the mafic samples. Textural features and calculated pressures based on the Cpx-barometer in each series indicate that the alkaline magma equilibrated at shallow crustal depths under a pressure of about 3–4.5 kbar and approximating a crystallization depth of 9–14 km. The NAVs are slightly depleted in isotopic composition, with respect to ⁸⁷Sr/⁸⁶Sr (ranging from 0.705018 to 0.705643) and ¹⁴³Nd/¹⁴⁴Nd (ranging from 0.512662 to 0.512714) that indicate young Nd model ages (0.51–059 Ga). This may indicate that the parent melts tapped a homogeneous and young lithospheric mantle source which was metasomatized by subduction-derived sediments during the Late Mesozoic. Pb isotopic compositions (²⁰⁶Pb/²⁰⁴Pb = 18.85–18.95; ²⁰⁷Pb/²⁰⁴Pb = 15.60–15.74; ²⁰⁸Pb/²⁰⁴Pb = 38.82–39.25) may also be consistent with a model for an enriched subcontinental lithospheric mantle source. Lithospheric thinning and resultant upwelling of asthenosphere induced by lithospheric delamination may have favoured partial melting of chemically enriched, young lithospheric mantle beneath the Eastern Pontides. Then, the melt subsequently underwent a fractional crystallization process along with or without minor amounts of crustal assimilation, generating a wide variety of rock types in a post-collision extensional regime in the Eastern Pontides during the Neogene.     

An Assessment of the Seismicity of the Bursa Region from a Temporary Seismic Network

A temporary earthquake station network of 11 seismological recorders was operated in the Bursa region, south of the Marmara Sea in the northwest of Turkey, which is located at the southern strand of the North Anatolian Fault Zone (NAFZ). We located 384 earthquakes out of a total of 582 recorded events that span the study area between 28.50–30.00°E longitudes and 39.75–40.75°N latitudes. The depth of most events was found to be less than 29 km, and the magnitude interval ranges were between 0.3 ≤ M_L ≤ 5.4, with RMS less than or equal to 0.2. Seismic activities were concentrated southeast of Uludag Mountain (UM), in the Kestel-Igdir area and along the Gemlik Fault (GF). In the study, we computed 10 focal mechanisms from temporary and permanents networks. The predominant feature of the computed focal mechanisms is the relatively widespread near horizontal northwest-southeast (NW–SE) T-axis orientation. These fault planes have been used to obtain the orientation and shape factor (R, magnitude stress ratio) of the principal stress tensors (σ₁, σ₂, σ₃). The resulting stress tensors reveal σ₁ closer to the vertical (oriented NE–SW) and σ₂, σ₃ horizontal with R = 0.5. These results confirm that Bursa and its vicinity could be defined by an extensional regime showing a primarily normal to oblique-slip motion character. It differs from what might be expected from the stress tensor inversion for the NAFZ. Different fault patterns related to structural heterogeneity from the north to the south in the study area caused a change in the stress regime from strike-slip to normal faulting.