Gelibolu yarımadası, Gökçeada ve Bozcaada arasındaki deniz alanının geç pleyistosen-güncel sismik stratigrafisi ve paleocoğrafik evrimi
Late pleistocene-present seismic stratigraphy and paleogeographic evolution of the marine area between Gelibolu peninsula, Gökçeada and Bozcaada
Yazar: DERYA İPEK GÜLTEKİN KARAKOÇ
Danışman: PROF. DR. CENK YALTIRAK
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Jeoloji Mühendisliği Ana Bilim Dalı / Jeoloji Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2022
Konu: Jeoloji Mühendisliği = Geological Engineering
Dizin: Deniz jeolojisi = Marine geology ; Gelibolu Yarımadası = Gallipoli Peninsula ; Paleocoğrafya = Paleogeography ; Sismik stratigrafi = Seismic stratigraphy ; Çanakkale-Bozcaada = Çanakkale-Bozcaada ; Çanakkale-Gökçeada = Çanakkale-Gökçeada

Özet:
Bu çalışmada, Kuzey Ege Denizi'nde, Gökçeada, Bozcaada ve Gelibolu Yarımadası arasında kalan alanda, sığ sismik veriler kullanılarak bölgenin Geç Pleyistosen-Güncel sismik stratigrafisi ve paleocoğrafik evrimi araştırılmıştır. Çalışmada, 2005 yılında Türk Deniz Kuvvetlerine bağlı Seyir Hidrografi ve Oşinografi Dairesi tarafından yürütülen TCG Çubuklu ve TCG Çeşme adlı araştırma gemilerinden toplanan çok ışınlı batimetri haritaları ile 1995, 1996 yıllarında TCG Çubuklu ve 1997 yılında Arar R/V araştırma gemileri tarafından toplanan yaklaşık 590 km uzunluğunda sismik veri kullanılmıştır. Batimetri verileri kıyıya kadar anonim sonar verileri ile tamamlanmış ve yanlış okumalar düzeltilmiştir. Çok ışınlı derinlik verileri bölgenin morfolojik unsurlarının tanımlanmasında kullanılmıştır. Kâğıda baskı sismik veriler bilgisayar ortamına aktarılarak sayısallaştırılmıştır. Çalışma alanının Geç Kuvaterner stratigrafisinin araştırılmasında küresel deniz seviyesi değişimleri esas alınarak sekans stratigrafik yöntem analizleri kullanılmıştır. Schlumberger şirketine ait Petrel programı kullanılarak, sismik kesitler üzerinde yüksek yansıma genliğine sahip yüzeyler belirlenerek, birimler arası uyumsuzluk yüzeyleri belirlenmiştir. Tanımlanan yüzeyler 3 boyutta birleştirilerek her bir birimin taban yüzeyi oluşturulmuştur. Oluşturulan bu yüzeyler arasındaki farklar alınarak birimlerin kalınlık dağılım haritaları elde edilmiş olup bu veriler küresel deniz seviyesi değişim eğrisine göre yorumlanmıştır. Elde edilen taban topografyaları ve kalınlık dağılım haritaları ile deniz seviyesi değişimleri ve birimlerin bulunma konumlarına göre tektonik çökme hızı hesaplanmıştır.
Bu çalışmalar sonucunda, sismik verilerde gözlenen kıvrımlı akustik temel birim üzerindeki paket içerisinde deniz tabanından aşağıya doğru sıralanan birimler tanımlanmıştır. Deniz seviyesi düşmesi esnasında erozyon ve depolanma arasında oluşan minör yükselmelerde havza kenarında aşmalı plaj ve delta çökelleri ile tanımlanan bu birimler sırasıyla Birim 1, Birim 2, Birim 3 ve Birim 4 olarak adlandırılmıştır. Bu çalışmalar sonucunda, Gökçeada-Limni sırtı ile Biga Yarımadası arasında 136-12 bin yıl öncesine kadar hep bir körfez olduğu zaman zaman göl ortamına dönüştüğü anlaşılmış ve bu çalışmada Aksu Baseni olarak adlandırılmıştır. Ayrıca, Çanakkale Boğazı ekseninden deniz seviyesi düşmesine bağlı olarak oluşan derin kanyonun daima Saroz körfezine uzandığı doğal olarak Çanakkale Boğazı ve uzantısı olan Anafartalar kanyonunun eski boğazı oluşturduğu anlaşılmaktadır.

Abstract:
In this study, the Late Pleistocene-Present stratigraphy and paleogeographic evolution of the area between Gökçeaada, Bozcaada and Gallipoli Peninsula in the North Aegean Sea were investigated using shallow seismic data. Multi-beam bathymetry maps collected from the research ships TCG Çubuklu and TCG Çeşme conducted by the Turkish Naval Navigational Hydrography and Oceanography Department in 2005 and approximately 590 km long seismic data collected by the research ships TCG Çubuklu in 1995, 1996 and Arar R/V in 1997 is used. Bathymetry data were completed with anonymous sonar data up to the shore and some spikes were corrected. Multi-beam depth data were used to define the morphological features of the region. The seismic data printed on the paper were transferred to the computer environment and digitized. Sequence stratigraphic method analyzes based on global sea level changes were used to investigate the Late Quaternary stratigraphy of the study area. By using the Petrel program of Schlumberger company, surfaces with high reflection amplitudes were determined on seismic sections, and unconformity surfaces between units were determined. The defined surfaces were combined in 3 dimensions to form the base surface of each unit. The thickness distribution maps of the units were obtained by taking the differences between these surfaces, and these data were interpreted according to the global sea level change curve. The tectonic collapse rate was calculated according to the base topographies and thickness distribution maps obtained, sea level changes and the location of the units.
The units lined down from the sea floor are defined in the package on the folded acoustic basement observed in the seismic data. These units, which are defined by the overhanging beach and delta deposits at the basin edge in the minor uplifts formed between deep digging and deposition during the sea level fall, were named as Unit 1, Unit 2, Unit 3 and Unit 4, respectively. Unit 1 is located at the top of the sedimentary collection observed on the folded acoustic basement in seismic profiles. The unit showing reflections parallel to each other and with high reflection continuity. It is a fine sediment covering the older units. It is observed throughout the study area. The uppermost reflection surface of the unit is the current sea floor. The unit deposited at the last sea level rise is defined as the Holocene posttransgression unit. Unit 2 is located below Unit 1 above Unit 3. In the study area, it shows complex reflections observed as fillings in the basins and canal structures in general. In the sections between Gökçeada and Bozcaada, the internal reflection character is usually semi-parallel and chaotic. It shows parallel and semi-parallel reflections in N-S trending seismic sections east of Gökçeada. On the other hand, in the W-E oriented seismic sections taken in the west of the Gallipoli Peninsula, it is observed that the unit consisting of horizontal reflections on a rough topography. Unit 3 is located below Unit 2 and above Unit 4. The unit, which generally shows parallel and semi-parallel reflection characteristics in the deep parts of the study area, shows sigmoidal and complex reflections in the coastal areas. When these reflection differences observed in the lower units of Unit 3 are interpreted, it is understood that the unit consists of marine sediments at the lower levels and deltaic deposits at the upper levels. The unit, which is at the bottom of the sediment collection on the acoustic basement, was deposited on the foundation with an angular unconformity and was named Unit 4. This unit generally shows parallel and semi-parallel reflections. This unit, which is observed as slightly folded in some areas, is well preserved in the Aksu Basin between Gökçeada and Bozcaada. The high amplitude reflection surface observed in the folded structure at the bottom of all seismic lines in the study area has been interpreted as an Acoustic Basement.
The erosion regime formed after the early Pleistocene in the study area shaped the topography in the region. The Late Pleistocene series unconformably overlie the base geological units in the region. In this context, the deposition regimes formed in the region besides the erosion regime are under the influence of sea level changes. Sea level has changed dynamically between -140 and +6 meters in the last 240 thousand years. Unit 4 includes depositional units between +6 m and -90 m depending on sea level changes. This unit was deposited in the period between 136 and 62 thousand years. Unit 3 was deposited between 62-24 thousand years. In this unit, it is seen that the margin facies are constantly displaced and terminate in horizontal reflections in the middle sections and are transitional with Unit 4. There are 4 minimum and 4 maximum sea level changes during the deposition of this unit and these are represented by sigmoidal wedges in margin facies. Unit 2, belongs to the last glacial maximum period and represents between 24-7.6 thousand years. This transgressive unit starts with a channel filling starting from the bottom and spreading towards the edges in the erosion area it has formed starting from -120 m above the sea level, moves towards the edges as the sea level rises, and horizontal reflections begin to be seen in the deepened sections. Unit 1 is a unit that has been deposited from 7.6 thousand years to the present. It generally presents a homogeneous thickness and thickens towards the basin edges due to the coastal dynamics. The maximum and minimum sea levels of each unit were mapped with tectonic subsidence rates calculated according to the sea level change curve based on the base levels and thickness maps of the units. There are two gulfs separated by the Seddülbahir threshold between 136-62 thousand years, a geography that turns into a narrow water passage from time to time, and the island of Lemnos and Gökçeada are connected to each other by land connection. Aksu Basin Bay is in the lagoon environment at the lowest level depending on the sea level. It attains a marine geography when the sea level is at its maximum. Since the Anafartalar Canyon was not separated from the Saros Trough by any threshold during this period, it turns into an estuary when the sea level drops and a wide strait when it rises. While the coast moves towards the land in rising sea levels with tectonic collapse, temporary lakes and gulfs are formed in the area between Bozcaada and Biga Peninsula in falls. The area must have turned into a more marine environment with sea level rise and subsidence between 62-24 thousand years due to tectonic collapse. Unit 3 was highly affected by the dynamics of sea level change between the glacial and interglacial periods of the deposition. Unit 2 represents the maximum sea level fall that occurred 24,000 years ago and the transgressive period that began afterward. Depending on the rise of the sea level, when it exceeds -90 meters (14 thousand years), the sea inflow into Aksu Lake begins, and then when it exceeds - 60 meters (12 thousand years), Anafartalar Bay and Aksu Bay merge. In a period of 11-11.5 thousand years, as a result of rapid sea rise and high-speed flood from the Sea of Marmara, a strong current from the Dardanelles to the Saros Gulf, digging deep in a section up to Arıburnu at the tip of the Gallipoli Peninsula, leaving the sediments it brought towards the Saros Gulf. Depending on the sea level change from 11 thousand years ago, Gökçeada-Limnos island 10 thousand years ago, and Rabbit island 7600 years old Biga peninsula.
As a result of these studies, it was understood that there was always a gulf between Gökçeada-Limni ridge and Biga Peninsula until 136-12 thousand years ago, and it turned into a lake environment from time to time, and it was named Aksu Basin in this study. In addition, it has been understood that the deep canyon formed due to the decrease in sea level from the axis of the Dardanelles always extends to the Saros Gulf, naturally the Dardanelles and its extension Anafartalar Canyon form the old strait.