Türkiye Jeoloji Bülteni

Abstract: The results of the petropraphic and petrochemical investigation of the Middle-Upper Miocene agedigneous rocks which have covered large areas in Bodrum peninsula in Southeast Anatolia were presented, and theirregional distribution were investigated and their genetic implications according to plate tectonics were discussed. Inthe investigated area, the magmatism has started as mon zonitic plutons in the Middle Miocene at different locationsAfter the monzonitic plutons, which have hybrid magma tic origin and probably have calc-alkaline character, a violent volcanism affected the investigated area at the of the Middle Miocene, and widespread tuff-agglomerate depositsand calc-alkaline volcanic rocks such as andesite-dacite rhyodacite-rhyolite were formed- The calc-alkaline magmawhich have been originated by the anatexis of the continental crust and which have given those high potassiccalc-alkaline first stage volcanics have started to blend with alkaline primary magma of the mantle. The first stagevolcanism has ended with shoshonotic lavas of latitic and trachyandesitic composition. The second volcanic stagehas started during Upper Miocene. It had shoshonotic features at the beginning and had continued to form shoshonotic basaltic lavas- The primary magma which entirely had originated from mantle had been active in the latterstage. Totally alkaline trachybasalt-trachyte-comenditic trachyte and the alkaline rhyolite (comendite) which was thelast product of the alkaline series had formed as dykes. We conclude that the volcanicsm had originated as theproduct of the continental rifting because of the tension regime which had been dominant in Western Anatolia.

Abstract: Twenty brachiopod species and thirty five genera belonging mainly to superfamilles of Lingulacea,Orthacea, Enteletacea, Plectambonitacea, Strophomenacea, Atrypacea are identified from two different localities onthe eastern side of the Bosphorus. These fossils show different faunal associations.One locality is near Çengelköy and yields conulariids and brachiopods in chamozitic beds («Çengelköy Chamosite»), the type locality within so-called «Laminated Shales». These fossil associations belong to the Exoconulariaistanbulensis-Aegiromena Zone and are of Middle Ordovician (Late Llandeilo-Early Caradoc) age.The second locality is 1,5 km north of Pendik, east of Istanbul. The studied horizons correspond to younger bedsin the «Laminated Shales» and are termed «Bryozoan Shales» These were formerly thought to be Upper Silurianor Early Devonian (Gedinnian) age. In this study, the new collections show that the «Bryozoan Shales» whichcontain mostly Orthida, are of Upper Ordovician (Late Caradoc-Ashgill) age. They include Orthambonites calligramma, Orthambonites humilidorsatus, Nicolella actoniae, Hesperorthis cf- eraigensis, Glytorthis aff. maritima, Saukrodictya hibernica, Drabovia sp., Leptestiina prantli, Anizop leurella tricostellata, Strophomena aff. planumbona, Christiania sp-, Catazyga sp. and together with the ostracod genera Uhakiella sp., Pseudoulrichia sp-, and the bryozoansDicranopora sp. and Atactotoechus sp.These Upper Ordovician (Upper Caradoc-Ashgill) brachiopod assemblages show close affinity to those of Bohemia, Great Britain, France, Spain, Sweden, North Africa, Ireland and North America- Therefore the content of shellyfauna indicates the cosmopolitan nature of the Mediterranean and the North European Provinces.

Abstract: The investigated area is located in an approximately east-west trended ophiolitic melange belt betweenDumanlı Dağı (Tokat) and Çeltek Dağı (Sivas). The Boztepe Formation of Upper Campanian to Paleocene age lieswith a local unconformity over the ophiolitic melange, forming the basement- This formation has been subdividedinto four members grading in one another- From bottom toward top, these are-. Yakaboyu Member which consistsof clastic rocks interbedded with pelagic limestone- Maden Member composed mostly of pelagic limestone; Yakupoğlan Member which is composed of sandstone, clay stone and rarely conglomerate and contains neritic fossils; ÇaltılıMember which is made up mostly of neritic carbonates. Olistostromes whose components have been derived fromthe underlying ophiolitic melange are abundant in the lower members in general. Lutetian elastics overlie theUpper Cretaceous rock assemblage with a regional angular unconformity.

Abstract: Lacustrine deposits of Upper Eocene that crop out near Kmik village, NW Ankara, consist of algal bioherms and various geometric forms of stromatolites- Small algal bioherms contain two types of carbonates-, tufa andcarbonate cones. Tufa is an organic carbonate mass made up of green algae which were rapidly encrusted by micritewhile alive. Rapid micritization is probably in response to photosynthetic release of GO2- The other bioherm groups(digitate-columnar carbonate cones) are also represented by radial growth of blue-green algae.The bioherms are covered and partly surrounded by bedded pellet-intraclasts and bioclastic grainstones-packestonesdeposited during the temporal fall and rise in lake level. A thin laminated crust formed under subaerial conditions,cover the grainstone-packestone layers and the bioherms.In the studied area, stromatolites generally overlie the algal bioherms. These are different kinds of organo-sedimentarystructures formed by trapping and binding actions of the blue-green algae in lacustrine environment. Despite the factthat the stromatolites were built only by blue-green algae genus «Schizotrix», increasing water energy and availablesediment led to different geometric forms. These forms can be grouped as LLH-lateral linked hemispheroids, SH-stacked hemispheroids and SS-oncoidal stromatolites.Organic and inorganic CaCO3 precipitation caused rapid calcification and cementation in bioherms. Mat actions ofthe blue-green algae and other biochemical events are the main effects on the cementation and configuration ofthe porosity of stromatolites.

Abstract: Turhal antimony deposits are the richest antimony deposits of Turkey. The mineralisation area iscovered by metamorphic rocks of Pre-Upper Jurassic age that are composed of alternations of phyllite and quartzitewith carbonates, and contain interlayers of metabasites and marble blocks. The metamorphic rocks are successivelyoverlain by Upper Jurassic-Lower Cretaceous limestones and sedimentary rocks of Eocene age.The antimony deposits occur as four different depositional types- In addition; first, second and third types of mineralisations are subdivided in a and b subtypes- Stibnite is found as the only ore mineral and quartz and calciteas the gangue minerals in the deposits. The stibnite crystals are mostly oxidised at surface.It is proposed that the la and possibly 2a subtype deposits have been formed in the depositional environment bysynsedimentary processes, prior to metamorphism; whereas the other types have been formed by transportation ofantimony from the la and lb subtypes of deposits and the metamorphic rocks.

Abstract: This study covers the homogenization and freezing studies on fluid inclusions of the lead-zinc deposits of Akdağmadeni.The freezing studies reveal that salinity of the hydrothermal solutions was high during the early stages of skarnisation (20 % NaCl equivalent during the magnetite-garnet-pyroxene and epidote-amphibole stages) and graduallydecreased during the following stages (10 % NaCl equivalent during the epidote-chlorite-sulphide stage and 3-4 %NaCl equivalent during the kaolinite-muscovite stage). In addition, the freezing studies show a pressure of formationranging from 300 to 500 bars.The homogenization studies indicate formation temperatures for the magnetite-garnet-pyroxene, epidote-amphibole,epidote-chlorite-sulphide and kaolinite-muscovite stages as >500°C, 460-490°C, 390-430°C and <320°C respectively.All the findings of this study are in good agreement with the results from other geobarometry and geothermometrymethods applied to these deposits.