Türkiye Jeoloji Bülteni

Abstract: The Neogene sequence around Sazak and Biçer (NE Sivrihisar) which deposited in  two different depositionalsystems as the Sakarya and Porsuk formations, has been studied by being divided in 7 facies. The firstdepositional system is the Miocene Sakarya formation, which is characterized by andesitic-basaltic volcanics(Lower-Middle Miocene), detritic and carbonate facies(Upper Miocene). The Pliocene Porsuk formation, whichis the second depositional system of the lithological units, rests on this lithological group at a low angularunconformity. The main facies of the Porsuk formation are characterized by conglomerate-sandstone, greencoloured mudstone-claystone, carbonate and grey-beige coloured gypsiferous mudstone-claystone.In the field, the claystones of the Porsuk formation are characterized by different colours (brown, creambeige, white, green) and different lithology (clayey limestone, dolomitic claystone, gypsiferous claystone). In thewhole basin area, clay paragenesis is represented by sepiolite, palygorskite, smectite, chlorite and illite. In thesouthern part of the basin, sepiolite is the dominant clay mineral in the dark brown and cream-beige colouredclaystones-limestones. In the whole basin area, green coloured claystone, gypsiferous claystone, mudstone andmarl are characterized by palygorskite, smectite, chlorite and illite paragenesis. In scanning electron microscopyexaminations, sepiolite minerals have been observed as ballshaped fiber bunches, palygorskite has been observedas parallel fibers, and smectite mineral is formed of flat leafs with a honeycomb texture in the form of frequentwavy leaves being detected.According to field and laboratory data, sepiolite, palygorskite and smectite minerals must have been formedby in-situ deposition and independently of each other. During the mineral formation in the basin, salinity,alkalinity and water controlled these factors and mineral formation. Sepiolites were formed in lake margin swampenvironments and also partially under humid conditions as a result of Mg and Si enrichment. Al, which originatedfrom the detritic materials transported in the lake basin, enabled the formation of palygorskite and smectiteminerals. Evaporitic mud flats served as suitable environments for the precipitation of smectite, palygorskite andchlorite. In addition, these minerals were preferentially deposited in the deep lake environment with greenmudstone and claystones.

Abstract: The gypsum member of the upper Miocene aged Sakarya formation in the Polatli-Sivrihisar Neogene basin isrepresented by five different sub-lithofacies. These are: a) secondary massive gypsums b) primary laminatedanhydrite c) secondary laminated brecciated-nodular gypsum d) clastic gypsum (gypsum arenite) and e) chevronselenitic gypsum. Among these, massive gypsum with iron-manganese bands separated by sparse sulphur crystalsand primary laminated anhydrite with algal stromatolithic structures are important in respect of their formationmechanisms. The geochemical and geostatistical evaluation of different minerallization types from gypsumanhydrite samples of these sub-facies provide evidence of their possible source of origin. For this purpose 24samples of different types including 13 major oxides, 15 trace elements and 13 rare earth elements were analyzedand from these results the correlation coefficient values for couple elements were determined and statisticalgraphics were prepared. After these geostatistical studies, three main groups of elements were identified. Amongthese: Group-I comprised SiO , Al O , K O, Rb, ∑ Fe O , MgO, MnO, As,V, TiO , P O , Zr, Zn, Ni, Co and Cu, 2 2 3 2 2 3 2 2 5Group II comprised Ba, Sr, Mo, Pb, W, F, Au and Na O and Group III comprised CaO and SO combinations. These 2 3combinations commonly show excessive vug-filling diagenetic clay minerals and/or carbonization withinevaporites. On the other hand, the results of geochemical analysis of trace elements show higher values than thechemistry of evaporitic playa lake sedimentary environments. The reasons for these high values are considered tobe: the fact that during the evaporation process the upper Miocene paleolake was under the influence of freshground water input, variation in climatic conditions for a short period of time (like dryness and wetness), limitedreducing environmental conditions in isolated parts of the lake and post depositional hydrothermal dissolutioning.The geochemical and geostatistical evaluation of upper Miocene evaporites of the gypsum member ofSakarya formation have identified that these evaporites were deposited in a playa lake complex with differentdepositing lithologies (siliciclastics and carbonates) which were affected by paleoclimatic conditions, periodicterrestrial volcanism and syn-sedimentary tectonics. 

Abstract: This study investigated the magnesite occurrences which are hosted by Triassic aged serpantinized peridoditelocated south of the Izmir-Ankara Suture Zone. The magnesite indicates two different depositional forms withindividual veins and stokwork type magnesite in fractures and cracks which altered ultramafic rocks. Both types ofmagnesite occurences include magnesite and dolomite, while individual magnesite veins besides this have a littlecalcite. The average contents of the individual magnesite veins in the major-oxides are MgO 43,73%, SiO₂ 2,95%, 2FeO₃ 0,75%, and CaO 3,73% while the stokwork magnesite is MgO 47,04%, SiO₂ 0,39%, FeO₃ 0,55%, CaO 1,15% and a low amount of SiO2 and CaO. The content of the stokwork magnesite is determined to be the better for sintermagnesite. Some trace element contents of both types of this magnesite are correlated with the graphics of traceelement distribution in magnesite given by Möller (1989), and it is found that Cr, Ni, Co, Cu, Fe, Mn, Ba, Hg, Ti, B,Ba distrubution corresponds with magnesite related to ultramafics. Higher Sr contents in individual vein  occurences results from content of calcite. The REE (Rare Earth Element) distribution of both types of magnesiteshows positive La, Eu, Lu anomalies and negative Ce, Sm, Tb, Y anomalies. An oxidizing condition duringdeposition and a lower temperature environment are indicated.

Abstract: The Yuvaköy neigbourhood is an area where Ankara-Çankırı ophiolite crops out. Yuvaköy ophiolite consists ofascending formations of tectonic complex, volcanic-sedimentary sequence, tectonites and cumulates. These unitsare covered byCretaceous and Tertiary sedimentary units. Miocene volcanics are represented by Tekke volcanics.The examined field is a tectonic complex containing heterogenous harzburgite, gabbro, diabase, basalt,radiolarite and limestone blcoks. Tectonites are represented by serpentinized harzburgites. Volcanic andsedimentary sequences comprise basalt, radiolarite, and limestone in chert alternations. The Tekke volcanics arecomprised of andesitic lava, agglomerate and tuffs.Results of chemical analyses showed that the diabase dikes are tholeiitic and the basalts are alkaline incharacter. The andesites of the Tekke volkanics are of intermediate, sub-alkaline character and are andesiticdacitic compositions.Harzburgites underwent serpentinization to an advanced level . Such a transformation results from the factthat the area has been subjected to a low-medium grade metamorphism of greenschist facies conditions. Thisstudydetermined that the basaltic rocks were spilitized due to the effect of metasomatism. Chemichal Alteration Index(CIA) values indicated that the rocks in the area underwent chemical alteration at the beginning stages of themedium zone.The outcrops in the units in the studied are, bear traces of Alpine Orogenic Movements. Deformationstructures occurred during and aftersettlement in the studied area, and these are observed as overthrust faults.