Ömer Feyzi Gürer

Progressive development of the Büyük Menderes Graben based on new data, western Turkey

Oblique and normal fault systems exposed in the Buyuk Menderes Graben (BMG) region record two successive and independent complex tectonic events. The first group tectonic event is defined by an E–W extension related to N–S contraction and transpression. This group is responsible for the development of NW- and NE-trending conjugate pairs of oblique faults which controlled Early–Middle Miocene basin formation. Between the Early–Middle Miocene and Plio-Quaternary strata exists an unconformity, indicating a period of folding, uplift and severe erosion associated with N–S shortening. The second group of events was the change in tectonic regime from E–W extension to N–S extension which controlled the formation of the Buyuk Menderes Graben by three progressive pulses of deformation. The first pulse of extensional deformation was initially recorded in the region by the exhumation of the deep part of the Menderes Massif (MM) with the development of the E-trending Buyuk Menderes Detachment Fault (BMDF). The minimum age of this pulse is constrained by the older Plio-Quaternary fluviatile deposits of the Buyuk Menderes Graben that range in age from the Plio-Pleistocene boundary interval to Late Pleistocene. The second pulse, which is marked by the rapid deposition of alluvial deposits, initiated the formation of approximately E–W-trending high-angle normal faults synthetic and antithetic to the Buyuk Menderes Detachment Fault, on the northern margin during Holocene times. These faults are interpreted as secondary steeper listric faults that merge with the main Buyuk Menderes Detachment Fault at depth. The third pulse was the migration of the Buyuk Menderes Graben depocentre to the present day position by diachronous activity of secondary steeper listric faults. These steeper faults are the most seismically active tectonic elements in western Turkey. According to the stratigraphic and structural data, the N–S extension in the Buyuk Menderes Graben region produced a progressive deformation phase with different pulses during its Plio-Quaternary evolution, with migration of deformation from the master fault to the hangingwall. The formation of diachronous secondary synthetic and antithetic steeper faults on the upper plate of the Buyuk Menderes Detachment Fault, hence the southward migration of the deformation and of the Buyuk Menderes Graben depocentre, should be related to the evolution of detachment in the region. The presence of the seismically active splays of secondary faults implies an active detachment system in the region. This young Plio-Quaternary N–S extension in the Buyuk Menderes Graben may be attributed to the combined effects of the two continuing processes in Aegean region. The first process is back-arc spreading or probably the roll-back of African slab below the south Aegean Arc, which seems to be responsible for the change in the stress tensor from E–W extension to N–S extension. The second and later event is the southwestward escape of the Anatolian block along its boundary fault, that is, the North Anatolian fault (NAF).

Late Miocene transcurrent tectonics in NW Turkey: evidence from palaeomagnetism and 40Ar–39Ar dating of alkaline volcanic rocks

A number of intra-continental alkaline volcanic sequences in NW Turkey were emplaced along localized extensional gaps within dextral strike-slip fault zones prior to the initiation of the North Anatolian Fault Zone. This study presents new palaeomagnetic and 40 Ar- 39 Ar geochronological results from the lava flows of NW Turkey as a contribution towards understanding the Neogene- Quaternary tectonic evolution of the region and possible roles of block rotations in the kinematic history of the region. 40 Ar- 39 Ar analyses of basalt groundmass indicate that the major volume of alkaline lavas of NW Turkey spans about 4 million years of episodic volcanic activity. Palaeomagnetic results reveal clockwise rotations as high as 73 ◦ in Thrace and 33 ◦ anticlockwise rotations in the Biga Peninsula. Movement of some of the faults delimiting the areas of lava flows and the timing of volcanic eruptions are both older than the initiation age of the North Anatolian Fault Zone, implying that the region experienced transcurrent tectonics during Late Miocene to Pliocene times and that some of the presently active faults in the region are reactivated pre-existing structures.

Neogene basin development around Söke-Kuşadası (western Anatolia) and its bearing on tectonic development of the Aegean region

Abstract There is a N–S lying narrow strip of Neogene outcrop between the towns of Kusadasi and Soke in western Anatolia. It contains remnants of successive Neogene graben basins. The first graben began to form under the control of a N40–70°E-trending oblique fault system during the Early Miocene. At the initial phase of the opening coarse clastic rocks were deposited in front of the fault-elevated blocks as scree deposits and fanglomerates. Later the graben advanced into a large lake basin. Towards the end of the Middle Miocene the lacustrine sediments of the Early–Middle Miocene age underwent an approximately N–S compressional deformation and elevated above the lake level, and were partly eroded. During the Late Miocene a new graben basin began to form as a consequence of the development of E–W-trending normal faults, formed under the N–S extensional regime. This graben also turned later into a lake environment. The lake extended far beyond the limits of the fault zones, and covered the entire regions stretching from the south of Bafa Lake in the south to Kusadasi and beyond in the north. Micritic clayey limestones were predominantly deposited in the lake. A severe erosional phase followed the termination of the lake basin. This corresponds to the cessation of the N–S extension. When the N–S extension regenerated during the Pliocene(?)–Pleistocene, the Buyuk Menderes graben system began to form. In the western part of the graben, a conjugated pair of oblique faults, the Priene–Sazli fault and the Kusadasi fault, have formed. The faults having important strike-slip components, bounded a tectonic wedge, which began to move westward into the Aegean Sea region. Major morphological features of the region were formed under the effective control of these fault zones.

Neotectonics of the southeast Marmara region, NW Anatolia, Turkey

The North Anatolian Fault Zone (NAFZ) bifurcates into three branches in the Marmara Region, which is a transition zone between the strike– slip tectonics manifested by the NAFZ and the N– S directed extensional regime of western Anatolia. The southern Marmara region is characterized by the middle and the southern branches while the northern branch controls the north Marmara region. The south Marmara region is characterized by approximately E – W trending rhomb-like horst and graben complexes bounded by strike slip-faults with normal component, striking mainly in E – W direction. This study documents the geometry and the structural characteristics of the NAFZ in the southeast Marmara region and discusses the commencement age of the strike– slip tectonics using deformation patterns of Neogene units and information available in the literature. q 2002 Elsevier Science Ltd. All rights reserved.

Origin of the Upper Cretaceous-Tertiary sedimentary basins within the Tauride-Anatolide platform in Turkey

A number of sedimentary basins formed within the Tauride-Anatolide Platform of Anatolia during the Late Cretaceous-Tertiary period. Previous studies have proposed different tectonic and evolutionary models for each basin. Geological characteristics of the basins, however, suggest that all these basins are of the same origin and that they followed a similar evolutionary model to one another. Basin development within the Tauride-Anatolide Platform took place in a post- collisional environment following the northward subduction of the northern Neotethys ocean beneath the Pontides. The closure of the northern Neotethys ocean ended with collision of the Tauride- Anatolide Platform with the Pontide volcanic arc and resulted in large bodies of oceanic remnants thrust over the Tauride-Anatolide Platform as ophiolite nappes. Formation of the sedimentary basins followed the emplacement of the ophiolite nappes as they formed as piggy-back basins on top of the underlying thrust ophiolite basement.

The Geology and Evolution of the Tokat Massif, South-Central Pontides, Turkey

The Tokat Massif is a major metamorphic complex of the south-central Pontides, the origin and development of which have long remained unknown. Recent detailed field-based mapping has revealed the major geological features of this complex. The Tokat Massif appears to be a tectonic mosaic composed of three major components: (1) the Yesilirmak Group; (2) the Turhal Metaophiolite; and (3) the Amasya Group. The Yesilirmak Group, which consists of a coherent lithoiogical sequence involving Paleozoic basement and overlying Triassic units, represents a short-lived basin assemblage. The Turhal Metaophiolite consists of an ophiolitic melange association and slices of a stratigraphically ordered ophiolite. The Amasya Group, the highest-standing tectonic unit, is represented by a lower Paleozoic clastic succession. The different major tectonostratigraphic assemblages of the Tokat Massif record a continent-continent collision between the Laurasian Amasya Group and the Gondwanan Yesilirmak Group. The Turhal Metaophioli...

Neotectonics of the SW Marmara region, NW Anatolia, Turkey

This study reports on the geometric and structural characteristics of the North Anatolian Fault Zone in the southwest Marmara region. The geometric and kinematic features of the faults in the region are described, based on field observations. In addition, the Neogene and Quaternary basin fill which occupies large areas in the region has been determined, and the tectonic regimes controlling these basins are explained. The neotectonic regime is also explained considering different deformation phases affecting the region. The N–S extension and E–W strike-slip have affected the region possibly since the latest Pliocene–Quaternary. Field observations show that these extensional tectonics around the south Marmara region are related to right strike-slip on the E–W North Anatolian fault zone and the N–S Aegean extensional system. The faults in this zone trend approximately E–W in the eastern part of the region and NE–SW towards the west of the region, indicating that they accommodate rotation in addition to differential movement between adjacent blocks.

Complex basin evolution in the Gökova Gulf region: implications on the Late Cenozoic tectonics of southwest Turkey

Southwestern Turkey experienced a transition from crustal shortening to extension during Late Cenozoic, and evidence of this was recorded in four distinct basin types in the Muğla–Gökova Gulf region. During the Oligocene–Early Miocene, the upper slices of the southerly moving Lycian Nappes turned into north-dipping normal faults due to the acceleration of gravity. The Kale–Tavas Basin developed as a piggyback basin along the fault plane on hanging wall blocks of these normal faults. During Middle Miocene, a shift had occurred from local extension to N–S compression/transpression, during which sediments in the Eskihisar–Tınaz Basins were deposited in pull-apart regions of the Menderes Massif cover units, where nappe slices were already eroded. During the Late Miocene–Pliocene, a hiatus occurred from previous compressional/transpressional tectonism along intermountain basins and Yatağan Basin fills were deposited on Menderes Massif, Lycian Nappes, and on top of Oligo–Miocene sediments. Plio-Quaternary marked the activation of N–S extension and the development of the E–W-trending Muğla–Gökova Grabens, co-genetic equivalents of which are common throughout western Anatolia. Thus, the tectonic evolution of the western Anotolia during late Cenozoic was shifting from compressional to extensional with a relaxation period, suggesting a non-uniform evolution.

Development of Evaporites and the Counterclockwise Rotation of Anatolia, Turkey

In western and central Anatolia, numerous basins developed during Tertiary time. The major basins generally are not connected to one another, and cover large areas containing substantial sedimentary deposits. These basins include the following: Thrace, Gediz, Buyuk Menderes, Beypazari, Tuz Golu, Ulukisla, Sivas, Erzincan, Mus, and Adana, as well as others. Two significant differences can clearly be seen in the basin sequences: (1) the age of evaporites—in central Anatolia, evaporites developed during the Oligocene, whereas in western Anatolia they formed during the late Miocene; and (2) the character of the deposition—in central Anatolia, Oligocene redbed molasse deposits are abundant, whereas in western Anatolia they developed in the late Miocene and the beds are thin and not very abundant. Climate is one of the governing factors of deposition, controlled by elevation and latitude. Therefore, the difference in sequences between central and western Anatolia depends on these two parameters. In this study, ...

Late Cenozoic polyphase deformation and basin development, Kütahya region, western Turkey

The Neogene–Quaternary succession in the Kütahya region is of importance in the neotectonic evolution of western Anatolia because the strata contain clear evidence of compression and extension. During the early-middle Miocene, N–S compression/transpression as well as NE–SW- and NW–SE-oriented oblique conjugate faults formed. NE–SW-oriented horsts and grabens developed, controlled by the dominant NE–SW faults. The Seyitömer and Sabuncupınar grabens were filled primarily by terrestrial clastic sedimentary and volcanic rocks. At the end of the middle Miocene, the graben fill was locally folded and reverse faulted, reflecting reactivation of compression. Between the late Miocene and the middle Pliocene, the region underwent erosion and lacustrine sediments accumulated in topographic lows. Between the middle and late Pliocene, compression in the region was again reactivated and basal units were thrust over the pre-upper Pliocene units. The late Plio-Quaternary marked the onset of N–S extension and development of the NW–SE-oriented Kütahya Graben, co-genetic equivalents of which are common throughout western Anatolia. This study indicates that tectonic evolution of western Anatolia involved multiple stages of contraction and extension.