Kuzey Anadolu Fay Sistemi Güney Kolunun Geyve-Gemlik arasındaki kesiminin tektonostratigrafik evrimi

Abstract

Strands of the North Anatolian Fault System (NAFS) in the Marmara Region were re-named within the content of this Ph. D. thesis. This fault system has been defined as horse-tail splitting into three strands as the Northern Strand of the North Anatolian Fault System (NAFSNS), Southern Strand of the North Anatolian Fault System (NAFSSS) and Southern-a Strand of the North Anatolian Fault System (NAFSSS-a). Lithostratigraphy, morphotectonic features, structural geology, basin models and historical earthquakes of the region were studied by this study for the Geyve-Pamukova and İznik basins located between Geyve (Sakarya), Mekece (Sakarya), İznik (Bursa) and Gemlik (Bursa) on the NAFSSS and bordered by the Armutlu-Ovacık Zone in north and the Sakarya Zone in south. Six main faults (Sarıgazi, Mekece, Dırazali, Gürle, Orhangazi, Umurbey) and three fault zones developed by the secondary segments related to the six main faults were mapped as the NAFSSS in the region. The Sarıgazi main fault in the east of the study area and in the Geyve-Pamukova basin and the Geyve Fault Zone (GFZ) were created by the secondary segments. Deposits of the Geyve-Pamukova basin were mapped based on the lithostratigraphic facies. The units from the bottom to the top of the basin were classified into four formations as Geyve (Qg), Pınarlı (Qp), Çardak (Qc) and Hocaköy (Qh). The Geyve formation was divided into Kollu pebblestone (Qgk) and Beylik clastic (Qgb) members and Çardak formation was sub-divided into Ayvalık (Qga) and Yanıkorman (Qcy) clastic members. The Kollu pebblestone member deposited at the base of the Geyve-Pamukova basin is a debris-flow deposit. The source for this member is Sakarya River and its small tributaries.Beylik clastic member of the Kollu pebblestone defines channel and set-point enviroments of the same river. The present deposition of these units in the southern edge of the basin is directly related to the deformation caused by the right lateral displacements by the Sarıgazi fault in Sakarya River. Alluvial fan Hocaköy formation overlies these basal units with uplifting of southern block by the Sarıgazi fault. The southern edge of the basin is formed by the right lateral fault. However, flood-plain sediments of the Pınarlı formation are deposited on the northern edge, where the deformation effect is less. The youngest unit is the Çardak formation located in the middle of the basin. This formation resembles to the Geyve formation. Architecture of the Iznik Basin along the NAFSSS developed when the step-over of the northwesterly striking Dirazali fault to Gurle fault triggered westerly step-over of the Gurle fault to east-westerly striking Umurbey fault due to simple dextral shear kinematics and north-nortwesterly, south-southwesterly transtensional deformation. This basin architecture was also supported by the southerly dipping, dextral oblique Orhangazi fault that is identified at the northern edge of the Iznik fault. The vertical displacement of southern edge of the basin by the right lateral faulting caused disconnections to the sea level. As a result, the İznik formation was deposited in a brackish water environment. After the sedimentation phase in the basin, the dominant right lateral oblique movement of the Gurle fault located between the Umurbey and Dırazali faults elevated the İznik formation approximately 60 m from the basin surface. Additionally, the Orhangazi fault which has the same charter as the Gurle fault controlled the İznik and Hocaköy formations located in the western section of northern edge of the basin. The slickenlines pointing out a right lateral oblique normal faulting indicate a rotation with simple shearing and transtension for the right lateral fault system. The basin was formed as lazy S shaped pull-apart basin that was created by the right lateral faulting and NNE-SSW dilatation. This neo-tectonics shows that the İznik basin is a pull-apart basin developed with a transtensional right lateral faulting. Almost all of the structural features of the right lateral simple shearing strain elipsoid were developed during the all stages of the basin opening. Keywords: Southern Strand of the North Anatolian Fault System, Tectonostratigraphy, Lazy S shaped pull-apart basin.Kuzey Anadolu Fay Sistemi güney kolu üzerinde neotektonik dönemde oluşan düzlük alanlar birbirine Mekece-İznik koridoru ile bağlanan Geyve-Pamukova ve İznik Havza’larıdır. Geyve-Pamukova Havza’sının litostratigrafisi alttan üste doğru; yanal geçişli Geyve-Pınarlı, Hocaköy ve Çardak formasyonlarını içerir. Hocaköy formasyonu güney bloktan gelen drenajın, Geyve formasyonu ise Sakarya Nehri’nin desteği ile oluşmuştur. Bunun yanında Sakarya Nehri’nin havza açılımından günümüze değin uğradığı sağ yanal atımlı deformasyon Geyve formasyonunun gelişmesinde birincil etkendir. İznik Havza’sında ise Erken Khazarian’dan günümüze alttan üste doğru İznik, Hocaköy ve Solöz formasyonları çökelmiştir. Geyve-Pamukova Havzası güney kenarındaki KD-GB doğrultulu sağ yanal atımlı Sarıgazi Fayının açılmalı dönmesi sonucunda gelişmiş gevşek S biçimli çek-ayır havza şeklinde oluşmuştur. İznik Havzası ise güney kenarındaki KD-GB doğrultulu sağ yanal atımlı Dırazali fayının, BKB-DGD doğrultulu sağ yanal oblik bir normal fay olan Gürle fayına sıçraması ile birlikte oluşmaya başlamıştır. Havzanın kuzey kenarındaki KB-GD doğrultulu sağ yanal oblik normal fay karakterli Orhangazi fayı ise havzanın Geyve-Pamukova Havzasına göre daha simetrik açılmasına destek olmuştur. İnceleme alanının bütününe hakim olan sağ yanal basit makaslamalı sistem İznik Havza’sının ise daha geniş ölçekli çek-ayır havza şeklinde açılmasını sağlamıştır. Anahtar Kelimeler: Kuzey Anadolu Fay Sistemi Güney Kolu, Tektonostratigrafi, Gevşek S biçimli çek-ayır havza.&nbsp