İstanbul ili, Sazlıbosna (Arnavutköy) - Kayabaşı (Başakşehir) civarının jeolojisi ve yapısal evrimi
Geology of iİstanbul, Sazlıbosna (Arnavutköy) - Kayabaşı 
(Başakşehi̇r) area and structural evolution
Yazar: MERT BALAMİR
Danışman: PROF. DR. SERDAR AKYÜZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Jeoloji Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: Jeoloji Mühendisliği = Geological Engineering

Özet:
İstanbul ilinin batısında yer alan Sazlıbosna-Kayabaşı civarında ayrıntılı jeolojik incelemelerle bölgedeki formasyonların litolojik, stratigrafik ve yapısal özellikleri araştırılmıştır. Bu araştırma kapsamında 1/25000 ölçeğinde jeoloji haritası ve kesitleri hazırlanmıştır. Bölgede Alt Karbonifer yaşlı Trakya Formasyonu, Eosen yaşlı Hamamdere, Soğucak ve Ceylan Formasyonları ve Miyosen yaşlı Çukurçeşme Formasyonları yer almaktadır.
Alt Karbonifer yaşlı, kumtaşı-şeyllerden meydana gelen Trakya Formasyonu sahanın temelini oluşturur. Üzerine Orta-Üst Eosen yaşlı, birbiriyle yanal ve düşey geçişli Hamamdere, Soğucak ve Ceylan Formasyonları açılı uyumsuz olarak gelir. Üst Miyosen yaşlı Çukurçeşme Formasyonu ise bu birimleri örter. Hamamdere Formasyonu sığ denizel-şelf ortamında çökelmiş çamurtaşları ile başlar ve üste doğru resiften taşınan, ince kireçtaşı aratabakalarıyla devam eder. Soğucak Formasyonu, resifal kireçtaşlarından meydana gelir. Şelfe (Hamamdere Formasyonu) ve açık deniz-havzaya doğru ince tabakalar halinde izlenir. Ceylan Formasyonu açık deniz-havza ortamında çökelmiş, kırıntılı kireçtaşı aratabakalı marn ve çamurtaşlarından oluşur. Çukurçeşme Formasyonu akarsu ortamında oluşmuştur ve inceleme alanında yer yer kil bantlı kum ve çakıllar şeklinde izlenmektedir.
Tabaka ölçümleri, kıvrımlar ve faylar incelendiğinde sahanın etkilendiği 4 ayrı deformasyon dönemi ve gerilme yönü tespit edilmiştir. Trakya Formasyonu'nu etkileyen 1. deformasyon evresinin Karbonifer sonrasında, Hersiniyen Orojenezi etkisiyle, D-B yönlü sıkışarak, 2. deformasyon döneminin ise Triyas sonrasında, Kimmeriyen Orojenezi döneminde K20B yönlü sıkışarak geliştiği düşünülmektedir. Trakya Formasyonu'nu etkileyen 3. deformasyon dönemi ise Alpin Orojenez döneminde meydana gelen K15D yönlü bir sıkışma ile gelişmiştir. İnceleme alanında tespit edilen 4. deformasyon ürünü ise Eosen çökelleri içinde izlenmiştir. Hafif şiddetli bu deformasyon, Eosen sonrası, Üst Miyosen öncesinde K45B yönlü bir sıkışma ile gelişmiştir.

Abstract:
Lithological, stratigraphic and structural properties of formations in the area have been investigated in the Sazlibosna-Kayabasi vicinity placed west of İstanbul. A 1/25.000 scale geological map and cross sections were prepared. Lower Carboniferious aged Trakya Formation, Eocene aged Hamamdere, Sogucak and Ceylan Formations, and Miocene aged Cukurcesme Formation were seen in the area.
The Lower Carboniferous age Trakya Formation with a dominant lithology of sandstone and shale forms the base of the field. On the top of the Trakya Formation, the Upper-Middle Eocene aged Hamamdere, Sogucak and Ceylan Formation lie unconformably. Eocene formations show lateral and vertical transitions with each other. The Upper Miocene Cukurcesme Formation covers these lithologies. Alluvium sediments occasionally cover these formations.
The field of investigation is dominated by parallel laminated shales which are, green-yellowish and green-brown-grey-bluish on color and thin-medium layered.Cleavage progression can be seen in the shales within the formation. The formation structure is very fractured, folded, and faulted.There are parallel and small scale, cross sediments within the sand stones and lower sediment layers are sharp and eroded.Ripples are observed on the upper surface of the sandstones were interpreted to be formed by turbuditial flows.The petrographic research that was carried out on the thin sections of the sansdstone samples within the formation revealed that the grains are scattered randomly.The grains can be mostly classified as angular – semi round and of metamorphic quartz origin. Fillate type, metamorphic originated rocks (usually mica fillate), muscovite, and occasional feldspar (usually plagioclase) are also observed.
The Hamamdere Formation starts with mudstone depositions in a marine-shelf environment and builds up with thin intermediate layers of limestone carried upwards from the reef. The formation developed primarily in three facies, namely: backreef (biomicrit), (Folk, 1962) reef (biolithite), and forereef. These facies generally change lateral and horizontal to one another. Petyrographical observation reveals that the limestones are generally composed of coral and red algae colonies of variable size.  The age of the formation is determined as Bartonian, by Özcan and Less (2011), via the determination of fossils within.
Sogucak Formation is formed by reef limestones. It is observed as thin layers through the shelf (Hamamdere Formation) and the deeper basin. The unit starts with carbonate enriched mudstones. This varying thickness stratigraphy changes first to thin and scarce, then to medium and common, yellowish grey colored carstic and transported coral reef substratas at the top of the formation. 
 
The petrographic research that was carried out on the thin sections of the limestone samples within the unit revealed that they were made up of biomicritic limestones transported from the reef.
Ceylan Formation is composed of marl and mudstone deposited in the deep marine-basin environment, intercalated with clastic limestones. The field can be observed above the Hamamdere formation at some levels as a result of trangression. Unconformity over Trace formation is also observed to the west of the Bent river and to the North - Northwest of the field. Microcrystalline carbonate mud has revealed benthic Foraminifera and Nummulit fossils upon the thin section samples of the limestones.
Cukurcesme Formation was deposited fluvial environments and determined to be composed of sand and gravel with occasional clay layers within the field. These lithologies interact as eroded surface related lens structures. It contains unit wedged and galliot type cross strata. Cross stratigriphication scale diminishes towards the surface.
Four different deformation periods and tensional directions were determined as a result of bedding, fold and fault analyses. First deformation period, which effected the Trakya Formation, is considered to be caused by the Hercynian Orogeny in the E-W direction after the Carboniferous; whereas the second deformation period is considered to be caused by the Cimmerian Orogeny in the N20W direction after the Triassic. Third deformation period that effected the Trakya Formation is possibly caused by the Alpine Orogeny in the N15E stress direction. The fourth deformation that is determined in the area of investigation was observed on the Eocene sediments. This deformation was not intensive as much as others and occured between Eosen and Upper Miocene in the N45W stress direction.
Deformations are detected in the Carboniferious Trace formation within the field being observed in different periods; and the Eocine sediments reflect traces of these deformations. When the field data, map remarks, and streographic projection analysis are evaluated together, it is concluded that the first deformation that effected the rocks in the field are developed through EW direction compression (Figure 3.1). While studying the structural geology of the Trace formation, Ketin and Guner (1989) have concluded that the EW direction compression was effected by Hercynian orogeny.
As referenced by the current geographical location, the field is effected by a new deformation period dominated by N20W direction compression (Figure 3.2). The drifting structures (normal faults) which are positioned perpendicular to this compression trend are the products of the same period (Figure 3.7). Even though it is not seen in the field of observation, sedimentation is apparent within the Triassic period and that it is completed by the end of the Triassic period when the stratigrapy of the Istanbul zone is studied. This is a significant proof of the deformation of the Istanbul zone following the Triassic period. The N20W direction compression is considered to be related to the developing Kimmerian orogeny.
The third deformation that effected the Trace formation within the boundries of the field of observation is the N15W direction compression (Figure 3.3) and the North varying structures (Figures 3.5 and 3.6). Upper Cretaceous Volcano sedimentary rocks to the north of both sides of Istanbul and that the Paleozic rocks are pushed and overlapped towards these sediments to the north are well known (Altınlı, Kaya, Ketin and Akyüz). 
 
It is observed that this structure has developed as a result of the same orogeny. It is also known that the Volcano sedimentery structure shows conformity up until the lower Eocene. That is why this orogeny is accepted as developed between lower and middle Eocene and attributed to the Alpine orogeny. Ketin and Guner (1989) indicated that these NW direction compressions are developed effected by the Alpine orogeny.
The fourth and the last deformation period that effected the field of observation is characterized by the NW-SE direction compressions (Figure 3.4) whose Middle-Upper Eocene sediments are slightly folded and the normal faulting that has developed perpendicular to it (Figure 3.8). Since the Upper Miocene aged Çukurçeşme Formation does not show any deformation, this last deformation is interpreted to happen sometime between the Upper Eocene and the Upper Miocene according to the data in the field.