Karstification in Miocene gypsum: an example from Sivas, Turkey

In this study, karstification developed in the Miocene gypsum which covers a large area around Sivas, Turkey, the relation between regional tectonics and karstification, and hydrogeological features have been investigated. The karstic features in the gypsum have developed conforming to the fault zones and the general strikes of gypsum beds. In the study area, numerous dolines (sinkholes) and ponors (swallow holes) of different sizes are observed. Most of these karstic features are in the different-sized longitudinal depressions (troughs) which conform to the tectonic structures. These karstic features occur NE-SW along bedding planes and about NW-SE and NE-SW along fault zones. At the intersections, high-capacity (yield) karst springs (Göydün and Seyfe springs) are observed. The Göydün and Seyfe springs issue from the karstified gypsum aquifer, with an average discharge of 1.10 m³/s and 0.25 m³/s, respectively. In addition, there are some low-yield (a few l/s) springs in the same drainage area. The surface drainage area of the springs is 64 km², and the precipitation in this area cannot provide the total groundwater discharging from Göydün and Seyfe springs. Water budget calculations indicate that more than 70% of the water discharged by these two springs is provided from the adjacent basins. The Göydün and Seyfe springs are rich in dissolved solids and average electrical conductivities (EC) are about 13?000 μS/cm. The major cations in the waters are Ca and Na; major anions are SO₄ and Cl, and the waters are brackish. Because of these properties, especially in summer and autumn, the springs cause extreme salinization in K?z?l?rmak river.     

Identification of soil erosion and fluvial sediment problems

A computer model has been used to estimate soil loss and sediment yield from irregular field-size units of small watersheds. Input to the model includes spring data (i.e. relating to February through May) for the independent variables of the Universal Soil Loss Equation, and for factors such as surface roughness, an index of overland runoff, and proximity to the stream. Output from the model includes maps of seasonal estimates of potential soil losses, field sediment delivery ratios, and expected sediment yields. On the basis of selected erosion and sediment yield tolerances, the output information has been analysed to identify watershed areas which (1) exhibit both erosion and sediment yield problems; (2) exhibit only erosion problems; (3) exhibit only sediment yield problems; and (4) exhibit neither erosion nor sediment yield problems. The percentage of the watershed area in each category and the percentage of the watershed soil loss and sediment loads contributed by each category are also identified. Application of the procedure for planning remedial control programs for five watersheds is discussed.     

A geohazard reconnaissance study based on geoscientific information for development needs of the western region of Istanbul (Turkey)

The role of geoenvironmental information is becoming increasingly important as legislative changes have forced developers and planning authorities to consider more implications and impact on the environment of large-scale development initiatives. Therefore, integration of surface and subsurface geoscientific information for development needs has prime importance and provides a means of identifying potential problems and opportunities at an early stage in any planned development. However, from the experience of recent natural disasters, it is evident that this was not case the taken into consideration in many countries. In addition to thousands of casualties, many urbanized areas, industrial districts and large-scale engineering structures suffered severe damages from the natural hazards due to many reasons including the lack of preliminary engineering geological maps and zoning maps of the settlement areas. Turkey is one of the countries which is exposed to natural hazards such as earthquakes, landslides and floods. In particular, the devastating 1999 Kocaeli earthquake, which affected the Marmara Region of Turkey, focused the attention on densely urbanized and industrialized metropolitan areas such as Istanbul. The rapid growth of Istanbul, particularly towards west with minimal geoscientific information resulted in an overwhelming pressure on the natural environment. In addition, a large earthquake, which is expected to occur in the Marmara Sea within the next 30 years, also pose a threat to the city and its surroundings. In this study, on the basis of the geological, geomorphological and geophysical reconnaissance study, an integrated geoscientific data were collected from the western region of Istanbul and evaluated for geohazards. The paper focuses on the geological and geomorphological aspects that control the occurrence of some geohazards such as earthquake-induced liquefaction, landslides and flooding. In this context, the geological map of the region was revised and Quaternary deposits were classified into 11 units, in detail. Liquefaction-prone areas were evaluated by using geomorphological criteria based on field investigation, by the examination of the available records from 88 boreholes drilled on recent deposits and by the data from resistivity profiles. The landslides within the region were classified according to their type, relative depth and activity. In addition, fluvial and marine flood-prone areas were also delimited within the region. Finally, a series of maps such as landslide inventory maps, and maps showing liquefaction- and flood-prone areas were produced with the aid of Geographic Information Systems (GIS) to assist in designing further detailed site investigations and to reduce costs by ensuring a more focused approach to strategic planning and site selection.     

Pre-eruptive conditions revealed by mega- and pheno-cryst compositions from the Quaternary Erzincan Volcanics, Eastern Turkey: Insights into the magma processes

Quaternary Erzincan Volcanics (QEVs) from the Erzincan Basin consist of mega- and pheno-cryst-bearing high-K calc-alkaline dome lavas. Fourteen nearly phenocrystic domes, with a range of basaltic-andesite, andesite, dacite and rhyolite compositions, were emplaced in the North Anatolian Fault Zone. The emplacement ages yielded by the unspiked K–Ar technique range from 102 to 140 ka. The andesitic domes (each less than 3 km in diameter) contain amphibole megacrysts. Amphibole compositions show a linear variation from ferro-edenite, edenite to pargasite from rhyolite to andesite. Pargasitic amphibole megacrysts scattered into the groundmass are very similar in composition to the microlites. All plagioclases are 53 mol%. Oscillation types are An₃₂₋₅₀ whose variations range from 10 to 16 mol% An and have 10–150 μm in thickness. Pre-eruptive conditions, calculated from mega- and pheno-cryst composition, using pyroxene and two oxide thermometers and the Al-in-hornblende barometer, ranged from 918 to 837 °C and 6.6 to 4.3 kbar for andesitic magma, 824–755 °C and 4.6–4.2 kbar for dacitic magma to 803–692 °C and 4.3–3.9 kbar for rhyolitic magma, which correspond to a depth of >10 km for storage region of the crust. The fO₂ values vary from −14.25 to −15.35 log units which are plotted just below nickel–nickel oxide (NNO) buffers. The systematic decrease in thermobarometric results from andesite to rhyolite is consistent with a single magma reservoir moving upward through the crust followed by fractional crystallization. Textural and compositional relationships of mega- and pheno-crystic phases suggest that magma mixing, fluid input to the reservoir and fractional crystallization processes, with a small amount crustal contamination play key role in evolution of the QEVs.     

Mineral phase compositions in silica-undersaturated ‘leucite’ lamproites from the Bucak area, Isparta, SW Turkey

Ultrapotassic rocks in the Bucak area of Isparta Angle, SW Turkey, show unusually low SiO₂ (46.8–49.2 wt.%) and high MgO (10.4–11.6 wt.%) contents, and lamproitic affinity (K/Na, > 2.5; Mg#, 73–75; Al₂O₃, 9.2–11 wt.%, CaO 7.4–10.6 wt.%, Cr, 525–675 ppm; Ni, 442–615 ppm). They are made up by phlogopite (30–40 vol.%), leucite (25–30 vol.%), olivine (5–20 vol.%), which rarely contain Cr-spinel, clinopyroxene (5–10 vol.%), sanidine (5 vol.%) and richterite, with accessory apatite, magnetite and ilmenite. One sample also include negligible sodalite in groundmass, which is unusual mineral in lamproites. Mineral phase variation and textures record discrete phases of pre-eruptive crystallization: (1) early appearance of (Cr-spinel-bearing) olivine, Ti poor phlogopite ± apatite at pressures of ca. 1.0–2.0 GPa, at or close to the lithospheric Mechanical Boundary Layer (MBL), and (2) later appearance of Ti rich phlogopite, clinopyroxene, richterite, leucite, sanidine, and other minor phases, at pressures of ca. 0.1–1.0 GPa, indicating discrete, pressure-specific fractionation events. The Bucak silica poor ‘leucite’ lamproites were probably generated by partial melting of phlogopite-bearing, refractory peridotite at pressures of ca. 1.5–2 GPa, higher than those proposed for SiO₂-saturated ‘phlogopite’ lamproites (ca. 1–1.5 GPa) from Afyon, to the North. The depth (total pressure) of melt segregation probably dominates over volatile partial pressures (e.g. of CO₂, F, H₂O) in determining the SiO₂-undersaturated character of Bucak magmas.     

The identification of an active fault by a multidisciplinary study at the archaeological site of Sagalassos (SW Turkey)

The archaeological site of Sagalassos (SW Turkey) is located in a region characterized by the absence of any significant recent seismic activity, contrary to adjacent regions. However, the assessment of earthquake-related damage at the site suggests that the earthquakes that have been demonstrated to have struck this Pisidian city in ca. AD 500 and in the middle or second half of the 7th century AD are characterized by an MSK intensity of at least VIII and occurred on a fault very close to the city. Different investigation techniques (archaeoseismology, remote sensing and geomorphology, surface geology and structural data, 2D resistivity imaging and palaeoseismological trenching) have been applied at the archaeological site and its direct surroundings in search for the causative fault of these earthquakes. This multidisciplinary approach shows that each of the different approaches independently provides only partial, non-conclusive information with respect to the fault identification. Integration is imperative to give a conclusive answer in the search for the causative fault. This study has, indeed, revealed the existence of a to date unknown active normal fault system passing underneath ancient Sagalassos, i.e. the Sagalassos fault. A historical coseismic surface rupture event on this fault could be identified. This event possibly corresponds to the devastating Sagalassos earthquakes of ca. AD 500 and the middle or second half of the 7th century AD. Finally, this study demonstrates that in the particular geodynamic setting of SW Turkey archaeological sites with extensive earthquake-related damage form an important tool in any attempt to asses the seismic hazard.