Türkiye Jeoloji Bülteni

Abstract: The formation of island arc (800-625 Ma.) on the northern part of the Gondwana land (Supercontinent) is accepted to be the begining phase in the geological evolution of Turkey. The rifting of the supercontinent and its breaking apart (625-555 Ma.) gave riseto the separation of the basement of the Pan African fragment-accepted to be the naclcous of the Anatolian microcontinent-from the northern part of the Gondwana land. Synorogenic sedimentation in the marginal basins (back-arc basin) (550-500 Ma.), orogenicmet amorphism (-500 Ma.), rise of the Anatolian microcontinent (500-470 Ma.) and intrusion of the collisional granitoids (470-450Ma.) are the most important phases in the geological evolution. Other important events at the end of Early Paleozoic can be cited asglaciation of the Gondwana land (450 Ma.). Toridya rise (440 Ma.), formation of glacial conglomerates and post glacial transgression (440-420 Ma.) and passage to the Anatolian carbonate platform (400 Ma.). 

Abstract: Two types of deposits can be differentiated in the Gümüşler area: 1) veins ofSb±llg±W and associated replacement type Ba-Sb mineralization, 2) disseminations and vein lets of IIg±Sb in brecciated zones. The vein deposits are localised along E-W trending and N-dipping faults mainly in marbles, and along marble-gneiss contacts. Replacement type Ba-Sb mineralization occurs in fracturesand along NE-dipping faults in marble and marble-gneiss contacts, and are structurally above the associated Sb±IIg±W veins.The Gümüşler deposits have a diverse mineralogy including scheelite, barite, stibnite, cinnabar, Sb-sulphosalts and gold. Goldis associated with cinnabar deposition stage, and is locally enriched in near surface zones with concentrations as high as 37.3 ppmat the Mehmetler Yurdu Sivrisi Tepe prospect, but is not economically viable. Silicification is the dominant wall rock alteration atthe mineralized locations of the Gümüşler area but dolomitisation, kaolinisation, sericitisation, cloritisation, tourmalinisation and epidotisation also occur at the periphery of the mineralization.There is a spatial relationship between the Rasih-lhsan deposit and the felsic dykes of Cenomanian age some of which are hydrothermally altered and cut by the Sb±llg±W veins. This indicates a post-Senomaman age for mineralization in the Gümüşler area. A similar relationship is also observed at the Mehmetler Yurdu Sivrisi Tepe prospect. In `this prospect, high gold concentrations are spatially associated with brecciated felsic dykes. This close relationship between mineralization and felsic dykes present inboth occurrences may indicate that mineralization in the Gümüşler area is genetically related to post-magmatic fluids associated with the granitic magmatism.

Abstract: Average labile forms of iron from the bottom sedimans of the Marmara Sea is 50% of the total iron and dominant ion is Fe².Fe² is the dominant species of the labile forms at the shallow areas; whereas Fe³ is dominant at the deeper part of the basin. Thelabile form distribution of iron indicate that oxidation state of the Marmara Sea sediments is reverse of that of the Black Sea: i.eanoxic sediments are round at the shallow levels and generally oxic sediments are recovered at the depth of 480 m. The dominance of Fe² near coastal areas is related to high sedimentation rates and reduction processes in the bottom sediments. These reduction processes could be related to decomposition of organic matter which is generated either by primary biological productivity of thesea by terrestrial input. The increase in the amount of Fef3towards the deeper part could be explained by low sedimentation ratesand long term bottom current activity of Aegean Sea in the study area. Bottom sediments of the Marmara Sea could be oxidised bythis long term ventilation processes and associated sea water-sediment interactions under the low sedimentation conditions.The oxidic level of the deeper part of the Marmara Sea (110-480 m.) which is mainly composed of Fe³constitutes favorable conditions which allows the trapping of the heavy metals within sediments; where as reducing conditions at the shallow water areasgive rise to the dissolution of heavy metals from the sediments and then migration in the sea water.Weak positive correlation between labile forms of iron and organic matter implies technogenic iron input. The increasing values of Pb, Zn, Ni, Cu on the upper levels of sediments is related to both diagenetic migration and technogenic-antropogenic contamination. Fe21 Fe³ values of the northern coast are higher than those of the southern coast. This difference may be due to effect of the bottom water current pattern of Aegean Sea in the study area, which causes oxidasition of deep sediments particularly in the south.

Abstract: Arsenic mineralization takes place within the Eocene aged Isparta formation which is Jlyschoid in character. The mineralization occurs as a main vein that is 38 m in length, 1-2 m in thickness with 1-50 cm thick stockwork veinlets developed arround the main vein. It is found along a normal fault zone trending approximately N-S. Realgar-bearing cahile veins have a simple mineral paragenesis which consits of coarse-grained calcite, realgar, barite, pyriteand orpiment. Realgar-bearing calcite veins are epithermal (50-120 C) mineralizations related to Pliocene trachy andesitic-latitic Gölcük volcanism.

Abstract: The basin fill geometries of the Paleocene-Early Eocene units of the Orhaniye-Güvenç region (NW Ankara) is studied using stratigraphic sections. All over the study area, nonfossiliferous Uzunçarşı group overlies with a slight angular unconformity the late Maestrichtian aged Dikmendede formation that passes laterally and vertically to Kuşkonan formation. Uzunçarşı group, which is divided in Lülük, Gökdere and Sarıbeyler formations, plays an important role in the understanding of the Paleocene tectonics and the paleogeograpy of the reg ion.Lülük formation, which is only deposited in the central parts of the studied region, is made-up of the proximal to mid-alluvial fansediments. Gökdere formation sediments, wJiich cover wider areas, show braided river deposits characteristics. This formation is notdeposited in`the NE and S of the area. Sarıbeyler formation is the most extensive formation of the Uzunçarşı group and is composedof lake deposits in the NE and an alternation of lake and fluvial deposits in the SW. Sarıbeyler formation is overlain by a thin butareally extensive unit containing mainly volcanic cobbles, which is overlain by Middle Eocene shallow marine carbonate deposits. Paleocurrent measurements, lithofacies characteristics and distribution of the Uzunçarşı group elastics indicate a closeby S-SE source area. Therefore, Paleocene - Early Eocene sediments of Orhaniye - Güvenç region is not a northward continuation of Tuzgölü basin; but, form the continental fills of a tectonically controlled smaller basin.

Abstract: The Salt Lake water could be classified as Na-Cl type brine with more dilute compositions in the deep zone. Major ion concentrations, in general, exhibit evaporation dependent evolution trends that are further modified by precipitating halite, gypsum, aragonite, and calcite minerals. In the main zone, sediments arc dominant ly composed of gypsum, huntite, magnesite, and polyhalite minerals whereas in the deep zone, Mg-calcite and dolomite minerals are the major constituents in the sediments. Thermodynamic saturation calculations to the lake data suggest that the models based on the specific ion-interaction and the ion-associationformulations could be used to determine the precipitation of evaporate minerals observed in nature. The overall prediction quality ofboth models is similar for the lake water with ionic strengths ranging from 1.35 to 8.5 calculated on t lie molal scale. Moreover, suchmodels are found to be very useful tools for the evaluation of the sediment mineralogy in the light of active precipitation. 

Abstract: The young fluvial sediments exposed at the northern part of the Büyük Menderes Graben have been assigned to latest Plioceneand Pleistocene on the basis of Arvicolidae. These constitute the first mammal findings explaining the age of the sediments at thenorthern part of the Büyük Menderes Graben and the tectonism which controlled the sedimentation. The evolutionary stages of thearvicolids may suggest the presence of four biochronologic units in the time interval between late Villanian and Toringian.

Abstract: This study aims the investigation of disseminated sulphur occurrences in celestite mineralizations at the upper section of Bozbelformation of Eocene age in Sivas basin, located in the Central Eastern Taurid suture belt. The sulphur formations in the study areaare economically insignificant. Electron microscope studies focused on microtexture examination indicate that these elementary sulphur format ions have crystal morphologies in the forms of cloud-like, lobous, spheroidal lace-like and kidney-like structures. Some sulphur crystals are blanketed by other substances. The results of elemental analyses show that the amount of organic matter inthis type ofc/ystals is nearly 1%. These elementary sulphur formations are ofbiogenic origin.The elementary sulphur occurrences in the celestite outcrop at the Bahçeciktepe location were formed by the disintegration ofcelestite crystals through the metabolic activity of sulphate reducing bacteria (most likely by "Desulfovibrio sp.").