Kayın, Sercan; Hisarlı, Z. Mümtaz; İşseven, Turgay; Dokuz, Abdurrahman; Algur, Bahadırhan Sefa

The study area covers a region oriented north-south from the Black Sea coastline in the north to the Kelkit Basin in the south within the eastern Sakarya Zone in northern Türkiye. The objective of this study is to investigate the paleolatitudinal movements of the eastern Sakarya Zone during the Jurassic-Eocene time interval through paleomagnetism. Various volcanic and sedimentary units (e.g., the Şenköy, Berdiga, Mescitli, Çatak, Kızılkaya, and Çağlayan Formations) spanning the time interval from the Early Jurassic to Middle Eocene were identified. A total of 98 locations belonging to Early/Middle Jurassic to Eocene volcanic and sedimentary units were selected for paleomagnetic core sample collection. The samples were subjected to demagnetization through thermal and alternating field methods. Characteristic remanent magnetization directions (ChRM) were obtained. Isothermal remanent magnetization (IRM) and high temperature susceptibility (HTS) measurements were made to identify the minerals responsible for magnetization. To ascertain whether magnetization was acquired through rock formation or as a consequence of subsequent tectonic processes, conglomerate and fold tests were performed. The results showed that magnetization was acquired before folding, i.e., the rocks have primary magnetization. Polarity tests were also conducted using coeval normal and reverse polarity sites. The results indicate that the mean magnetization direction for the Early-Middle Jurassic is 18.1°/55.2° (D/I) and 3.3°/51.5° (D/I) for sedimentary and volcanic rocks, respectively, and 348.7°/46.7° (D/I) for Late Jurassic/Early Cretaceous sedimentary rocks. In the Late Cretaceous period, the mean magnetization direction is 8.0°/49.3° (D/I) and 9.1°/47.0° (D/I) for sedimentary and volcanic rocks, respectively. In the case of the Early/Middle Eocene, the mean magnetization direction is 348.6°/52.7° (D/I) and 5.9°/48.8° (D/I) for sedimentary and volcanic rocks, respectively. In this study, the E/I correction was applied to the Late Jurassic/Early Cretaceous sedimentary rocks, and paleolatitude data obtained from sedimentary rocks were also utilized. Our paleomagnetic results indicate that the eastern Sakarya Zone was situated at latitudes spanning from 27.9° to 35.7° during the Early Jurassic - Middle Eocene time interval. In consequence, the eastern Sakarya Zone constituted a portion of the southern margin of the Eurasian continent during the Late Jurassic and Middle Eocene periods.

Aktaş, Gülten; Hisarlı, Z. Mümtaz; Öksüm, Erdinç

Lake Eğirdir, located within the tectonically complex Isparta Angle of southwestern Türkiye, hosts an actively deforming transtensional basin shaped by multidirectional stresses. Although the surrounding fault systems have been studied previously, the subsurface fault architecture beneath the lake remained largely unresolved. Understanding the lake's subsurface tectonic framework is crucial for regional geological and seismic assessments. This study addresses this gap by applying traditional and advanced edge detection techniques to identify magnetic lineaments and assess their connection with surrounding faults using newly acquired high-resolution magnetic data, corrected for noise and distortions. The distinct magnetic lineaments identified confirm a structural connection on land with the regional fault network around the lake, also showing their continuity under the lake. The results reveal dominant NW-SE and E-W trending magnetic lineaments. The most prominent structure identified within the lake is a NE-SW fault that cuts the NW-SE anomalies and is spatially related to the Yaka Fault on land. Its continuation beneath the lake is confirmed by clustered seismicity and normal fault-type focal mechanisms, indicating active transtensional deformation. These findings highlight active faulting processes that continue to shape the lake basin and contribute to understanding regional seismic hazards. Integration of magnetic, bathymetric, seismic, and geodetic datasets reveals that Lake Eğirdir acts as a dynamic neotectonic transfer zone within the Isparta Angle, facilitating the westward extrusion of the Anatolian Plate.

Aktaş, Gülten; Hisarlı, Z. Mümtaz; Demirel, A. Sinan

The aim of this study was to determine the effects of the main faults and many small-scale faults and submarine structures within Gemlik Bay, on the middle strand of the North Anatolian Fault in the southeast of the Sea of Marmara. In order to produce a fault map for the study area and research tectonic structures, magnetic data were obtained using a cesium vapor magnetometer on a total of 30 profiles (340 km) with N-S and E-W orientation within the bay. Diurnal corrections were applied to obtain the necessary minimization of diurnal variations in the magnetic data. Heading correction and micro-leveling corrections were applied to remove small boat effects, and the reduction to the pole method was applied for greater differentiation of the magnetic data. Magnetic data were analyzed using advanced potential field processing techniques. Euler deconvolution technique was applied to define the extension and depth of the determined lineaments. Boundaries of structures in the region were determined using source edge detection, tilt derivative, the tilt angle of the total horizontal gradient amplitude (TAHG), and a novel edge detector based on the softsign function (SF) techniques. In order to reveal the tectonic evolution of Gemlik Bay, the structures obtained from the analysis results were interpreted and a fault map was produced. The results of the study identified the Armutlu Fault in the north, the Gemlik Fault in the east, the Zeytinbağı Fault and Mudanya Fault in the southwest and the Gençali Fault in the south within Gemlik Bay. These five essential faults significantly affected the region tectonically. These faults correlated well with the location of some previously-known major tectonic structures. Moreover, these important faults following the morphology of the bay indicate that Gemlik Bay was opened by a pull-apart basin mechanism.