Türkiye Jeoloji Bülteni

Abstract: There are two different types of basements in investigated area. To the east of Daday-İnebolu line, basement is composed of phyllites, slates and metaophiolites which are Triassic to Lower Jurassicin age. These are Paleotethyan deposits which were crossed by intrusions and extrusions in the earlyDogger age. Precambrian and Paleozoic units crop out around Karadere stream to the west part ofDaday-inebolu line. In the Karadere Stream, rocks of Upper Cambrian and Lower Ordovician overliethe units of Precambrian age with primary stratig raphic contact. Paleozoic units form Cambrian toCarboniferous show two regressive sequences. Per mo-triassic sediments which was deposited in a continental environment overlie older sediments with an angular unconformity. The collision betweenGondwana and Laurasia continents caused overth rusting. So, Paleozoic assemblages that belong toGondwana cantinent overthrusted the Paleotethys deposits such as slightly metamorphosed flysch faciesand metaophiolites, form S-SW to N-NE in Dogger. Tectonic features which are caused by this collisioncan be distinguished in the investigated area. Sediments which are younger than Upper Liassic, covered all these tectonic features and older units, tra nsgressively. Transgression progresses continuouslyuntil Upper Paleocene. Island arc volcanic activity which belongs to north dipping Neotethyan subduction zone beneath the Pontides, started in pre-Aibian times. Eocene sediments which were deposited onthe older units with an angular unconformity show different facies in the investigated area. Variousterrestrial deposits are developed during Neogene. These are followed by young alluvium. 

Abstract: A thermal spring of 55°-58° C is found at 2.50 m depth within the marine area, inside thebreakwater at Yıldızburnu of-Ilıca Bay (Çeşme-İzmir). From the points of quantity and species, Foraminifera living in close proximity to the spring exhibit significant differences then the ones living in normalmarina! conditions outside the thermally influenced area. 

Abstract: This study is intended to provide some critical sedimentological and petrological data frompreviously poorly known seqences on the northern flank of the Haymana anticline. Information has beenprovided on the paleocurrents, thin section petrography, heavy minerals and clay minerals of the Upper Cretaceous-Eocene rocks in this region. The sue cessions of the eastern and western parts of the Haymana area consist of deep marine sediments, such as resedimented conglomerates associated with bioolastic and epiclastic sandy turbidites. The general sequ- ence starts with a sandy turbidite formation (HaymanaFormation-Maestrichtian) including conglomerates (wh ich are more abundant in the western area) and continues upwards with the olistolith bearing bioclastic limestone Yeşilyurt Formation. (Montian-Thanetian)which is followed by coarse grained sandstones with conglomerates of the Ilgmlıkdere Formation (Ilerdian). This is overlain by thiribedded sandstones and marls of the Eskipolatlı Formation (Ilerdian-Cuisian)succeeded by the Yamak Formation. In the western area the Yamak Formation consists of amalgamatedsandstones, marls and conglomerates, while in the east the same time interval is represented by theÇayraz Formation (Cuisian-Lutetian) consisting of alternating nummulitic limestones and shales. Paleocurrent directions derived from abundant primary sedimentary structures indicate consistent sedimenttransport from NNW. The composition of the silici lastic sediments demostrates that this northern source of the terrigeneous detritus in the lower formations consisted mainly of magmatic rocks, with metamorphic associates. However, in the upper formations (Eskipolath and Yamak/Çayraz) metamorphicsources became dominant, although magmatic detri tuc was still being supplied. The ill sorted greywacketype sandstones plot in the area of the «subduction complex» on the compositional triangular diagramsof Dickinson (1982), but the overall fields tend to overlap with the fore-arc basin area.

Abstract: The fluorite and barite mineralization are observed within the Cambrien limestones inKatlar ridge locality, 1,5 km. east of Akkaya village in the Eastern Taurus Region.The paragenesis consists of calcite, barite and quartz for the barite veins; and of calcite, whiteviolet fluorite, barite and quartz for the fluorite viens which trends NW-SE. Fluid inclusion studies onthe fluorites have shown a homogenous spread, on single phase, primary and secondary inclusions andit has been concluded that the mineralization can not be of, hydrothermal origin. In addition, lanthanid spectrums of fluorites suggest that the mineralization can not be derived from the hydrothermalsolutions but it may be derived from the carbonate environments.From the study of the data obtained both from field and laboratory, it may be suggested that thefluorite-barite mineralization formed epigenetically, in fracture systems directly from formation watersor by the remobilisation of dispersed elements arfec ted by groundwater. 

Abstract: Although Turkey lies along an impor tant earthquake belt, research activities concerningthe minimization of earthquake hazards are not carried out at adequate levels.The object of this study is to construct a seis mic zonation map in the Bolu region showing theintensity distribution and accelaration rate of the possible future large earthquakes and to help theimplementation of various aspects of minimization of Earthquake hazard.The expected magnitude of the possible large earthquakes along this section of the North Anatolian Fault zone was computed to be 7.3 or higher. It is proposed that the epicenters of such earthquakes can be located on every point within the active fault zone.It is suggested that, the zones defined as very violent and violent should be used for forestry andagricultural purposes.

Abstract: In the core of Amanos anticline, in sout hern Turkey, there is a Paleozoic sequence that runsthrough Precambrian and Cambrian in the Devonian.In this study, we have investigated the depositional environments and paleogeographic evolutionof the sedimentary rocks, at the lowest part of which there exists the Precambrian Eğribucak formation. This unit consist of alternating graywacke and lami nated shale and contains scour marks, tool marksand trace-fossils as horizontal burrows. The Eğribu cak formation was formed in a deep marine environment where turbidite cycles could develop.The Cambrian Eğrek formation consists of qu artzarenites that unconformably overlies the Eğribucak formation. The Eğrek formation settled in a shal low shelf environment where waves and storms werepredominant.The Koruk formation consist of dolomicrite, int ramicrite, intrasparite, micrite and dolomite. ThisCambrian formation, which involves certain oolites, stromatolites and bird`s-eye structures, was deposites in a low energy stable shelf and in its near shore environments.Pink, nodular and thin-bedded tnderesi formati on which consists of micritewas probably deposites in the slope environment of the shelf.cortaining trilobites,The Middle-Upper Cambrian Tiyek formation which contains shale, litharenite and graywacke, restsupon Middle-Cambrian tnderesi formation. It was deposited in the open shelf-basin environments.The Ordovician Bahçe formation comprises quartzarenite and shale alternation,shallow shelf-shore deposit where storms and waves were predominant.It is a typical,The Upper Ordovician-Lower Silurian Kızlaç formation is represented by shales, litharenites andsublitharenites. The sedimentary structures and the sequence of the formation indicate that the lowerpart of the unit was formed in an open shelf environment; whereas, the upper part of the same unitwas accumulated in a delta and bay environments.Pink-purple Dedeler formation is composed of litharenite and shale alternation. Distinct marks ofa meandering river could be observed in this formation.The Ayran formation is formed by sublithareni te, quartzarenite and shale alternation. It is depo*sited in a beach shelf environments which gradually passed in deeper water.There transgressions and two regression are, thus, apparent in the Amanos Paleozoic rocks.All of these sedimentary rocks were developed in the platform of the Nubian-Arabian shield thatextends in Turkey and in certain parts which were transformed in basins and continental environments of the same platform.According to paleocurrent data, the sediments were supplied roughly from the east-southeast regionduring the paleozoic period.

Discussion: Yılmaz (1984), yazısında İşler (1982)`nin çalışması ile ilgili olarak farklı görüşler ileri sürmüştür. Bu görüşler üç şık halinde toparlanmış olup yazar bu görüşlere karşı kendini savunmuştur.

Reply: Yılmaz (1984), aynı yörede yapılan İşlerin (1982)incelemesinde irdeleyerek, iki çalışma arasındaki bazı farklılıkları ve bu farklılıkların olasılı sonuçları üzerine düşüncelerini belirtmiştir. Bu yazıda Fikret İşler`in önerdiği tartışma düzenine uygun olarak yanıt da üç madde halinde özetlenmiştir.

Discussion: Fosilli düzeylerin gerçekten yazarın belirttiği gibi Üst Ordovisiyen yaşlı olabileceğini düşünelim. Budurumda Üst Ordovisiyen tabakaları içindeki Orta Ordovisiyen fosillerinin varlığım ancak bu fosillerin taşınarak daha genç çökeller içinde yeniden gömülmüş olabilecekleri olasılığı ile açıklayabiliriz ki bu olasılığı da yazar paleoekolojik yorumunda «fosillerde sürüklenme izlerinin bulunmadığı, organizmaların yaşadıkları ortamlarda fosilleştiği «sonuca varımıyla geçersiz kılmaktadır. Bu durumda, fosiller farklı iki düzeyden (Orta Ordovisiyen fosillerini içeren düzey ve Üst Ordovisiyen fosillerini içeren düzey) derlendiği halde aynı örnek torbasına konarak laboratuvarda bu örnek torbası içindeki brakiyopod topluluğuna yüzde oranı hesaplarıyla mı yaş verilmiştir? Verilen yaş ve zon adı böyle bir yöntem uygulandığını göstermektedir ki yazıda sık sık tekrarlandığı gibi «arazi gözlemleri, laboratuvar çalışmaları ve sayısal değerlerin sonuçları» birbirleriyle uyumlu değil aksine çok açık olarak birbirleriyle çelişkilidir.

Reply: Topluluğun sayısal değerlendirilmesi: Burada fauna analizi tüm paleontolojik çalışmalar (tayinler, korelasyon, stratigrafik yayılış vs. gibi) sonuçlandıktan sonra ele alınmıştır. Sonuçlar uzun yazılar yerine şematik diyagramlarla gösterilmiştir. Cins ve türlerin sıklık miktarı karşılaştırma amacıyla daha önceden belirlenen stratigrafik yayılış tablosu üzerinde verilmiştir (Çizelge 2), Pek çok türü Üst Ordovisiyen (Üst Karadosiyen - Aşgiliyen tipi olarak gözlenen bu toplulukta örneklere ait, veri eksikliğinden kaynaklanan daha genç veya daha yaşlı birkaç örneğin bulunması o topluluğun belirli lokalitede stratigrafik konumda da uyum gösteren jeolojik yaşım değiştirmeye yeterli değildir.

Tartışma: Halil Baş (1986) tarafından sunulan "Sinop Volkanitlerinin petroiojisi ve jeokimyası" adlı makaledeki ayrıntılı petrolojik ve petrokimyasal sonuçlar daha önceki çalışmalarla (Peccerıllo ve Taylor., 1975; Gedik ve diğerleri 1984) tam bir uyum içindedir. Hatta Volkanıtlerin jeokimyasal analizleri bölgenin Üst Kretase magmatik zonalitesini ortaya çıkaracak nitelikte ayrıntıya sahiptir. Jeokimyasal veriler rejyonal jeolojik verilerle birlikte değerlendirildiğinde ancak anlamlı ve doğru sonuç verebilir. Nitekim sadece jeokimyasal analizleri değerlendirecek "KA-A (Şosonitik) kayaçların Pontidlerin en kuzey bölgeleri içinde bulunması nedeniyle Sinop Volkanizmasının veren yitim kuşağının güneyde yerleşmiş olabileceği görüşü" kanımızca yanlıştır. Çünkü Sinop ve çevresi coğrafik olarak kuzeyde kalmasına rağmen bulundurduğu KA-A volkanizması ile jeotektonik ortam olarak Pontidlerin güneyini yani ark gerisi bölgelerini temsil eder (Bektaş, 1984; Bektaş ve diğerleri, 1984) başka deyişle sözü edilen volkanizma kuzeyde yerleşmiş bir yitim zonu ile ilişkili olmalıdır.

Yanıt: Bektaş ve Gedik, Baş (1986) tarafından sunulan «Sinop volkanitlerinin petrolojisi ve jeokimyası» adlı makalede öne sürülen, Pontitlerde Üst Kretase-Eosen aralığında kuzeye yönelik bir yitimin varlığı görünüşüne karşı çıkarak güneye yönelik bir yitimi savunmuşlardır. Bu arada diğer bazı verilerle birlikte Baş (1986)m adı geçen makaledeki verilerini kendi görüşlerini destekleyen kanıtlar olarak yorumlamışlardır.