Sarah J. Boulton

The Neogene–Recent Hatay Graben, South Central Turkey: graben formation in a setting of oblique extension (transtension) related to post-collisional tectonic escape

Structural data and a regional tectonic interpretation are given for the NE–SW-trending Hatay Graben, southern Turkey, within the collision zone of the African (Arabian) and Eurasian (Anatolian) plates. Regional GPS and seismicity data are used to shed light on the recent tectonic development of the Hatay Graben. Faults within Upper Cretaceous to Quaternary sediments are categorized as of first-, second- and third-order type, depending on their scale, location and character. Normal, oblique and strike-slip faults predominate throughout the area. The flanks of the graben are dominated by normal faults, mainly striking parallel to the graben, that is, 045–225°. In contrast, the graben axis exhibits strike-slip faults, trending 100–200°, together with normal faults striking 040–060° and 150–190° (a subset strikes 110–130°). Similarly orientated normal faults occur throughout Upper Cretaceous to Pliocene sediments, whereas strike-slip faults are mostly within Pliocene sediments near the graben axis. Stress inversion of slickenline data from mostly Pliocene sediments at ten suitable locations (all near the graben axis) show that σ 3 directions (minimum stress axis ≈ extension direction) are uniform in the northeast of the graben but orientated at a high angle to the graben margins. More variable σ 3 directions in the southwest may reflect local block rotations. During Miocene times, the Arabian and Anatolian plates collided, forming a foreland basin associated with flexurally controlled normal faulting. During the Late Miocene there was a transition from extension to transtension (oblique extension). The neotectonic Hatay Graben formed during the Plio-Quaternary in a transtensional setting. In the light of modern and ancient comparisons, it is suggested that contemporaneous strain was compartmentalized into large-scale normal faults on the graben margins and mainly small-scale strike-slip faults near the graben axis. Overall, the graben reflects Plio-Quaternary westward tectonic escape from a collision zone towards the east to a pre- or syn-collisional zone to the west in the Mediterranean Sea.

Tectonic and sedimentary evolution of the Cenozoic Hatay Graben, Southern Turkey: a two-phase model for graben formation

Abstract New structural and sedimentary studies form the basis of a new interpretation for the Neogene Hatay Graben. Fault analysis reveals three contemporaneous trends of fault orientation (000°–180°, 045°–225° and 150°–350°) suggesting that the graben is transtensional in nature. Sedimentary studies show that, following shallow-marine deposition from the Late Cretaceous to the Eocene, a hiatus ensued until Early Miocene fluvial sedimentation. After a Mid-Miocene marine transgression, water depths increased until the Messinian salinity crisis, followed by a regression from the Pliocene to the present day. The basin initially developed as the distal margin of a foreland basin of the Tauride allochthon to the north, developing a classic sedimentary sequence during Mid-Late Miocene. Stresses caused by loading of the crust created a flexural forebulge to the south that supplied sediment mainly northwards. During the Plio-Quaternary, transtensional graben development took place, primarily influenced by the westward tectonic escape of Anatolia along the East Anatolia Fault Zone and left-lateral offset along the northward extension of the Dead Sea Transform Fault. This area is, thus, an excellent example of a foreland basin reactivated in a strike-slip setting. Our new two-phase model: foreland basin, then transtensional basin for the Hatay Graben, is in contrast to previous models, in which it was generally assumed that the Plio-Quaternary Hatay Graben represents a direct extension of the Dead Sea Fault Zone or the East Anatolian Fault Zone.

Geomorphic and geological constraints on the active normal faulting of the Gediz (Alaşehir) Graben, Western Turkey

The Gediz (Alaşehir) Graben is located in the highly tectonically active region of Western Turkey. Extension owing to regional geodynamic controls has resulted in a broadly two-phase evolution of the graben; first, low-angle normal faulting relating to the exhumation of the Menderes Massif metamorphic core complex took place between 16 and 2.6 Ma; second, high-angle normal faulting initiated c. 2 Ma forming the Gediz and other east–west-trending graben in the region. Here we quantify the throw rate along the fault array over the last 2.6, 2 and 0.7 myr using structural and geological constraints, along with analysis of topographic relief as a proxy for footwall uplift. We derive, for the first time, time-averaged rates of fault motion from 0.4 to 1.3 mm a−1 along the strike of the Gediz Graben, with variation in throw rate associated with the geometry of single fault strands. Patterns in throw rate along-strike of the graben-bounding fault array also suggest that the fault segments have become linked during the last 2.6–2 myr, possibly at 0.8–0.7 Ma. Furthermore, these data suggest that an earthquake occurring along the graben-bounding fault could have a maximum predicted Mw of 6.3–7.6.

Normal fault growth and linkage in the Gediz (Alaşehir) Graben, Western Turkey, revealed by transient river long-profiles and slope-break knickpoints.

The Gediz (Alasehir) Graben is located in the highly tectonically active and seismogenic region of Western Turkey. The rivers upstream of the normal fault-bounded graben each contain a non-lithologic knickpoint, including those that drain through inferred fault segment boundaries. Knickpoint heights measured vertically from the fault scale with footwall relief and documented fault throw (vertical displacement). Consequently, we deduce these knickpoints were initiated by an increase in slip rate on the basin-bounding fault, driven by linkage of the three main fault segments of the high-angle graben bounding fault array. Fault interaction theory and ratios of channel steepness suggest that the slip rate enhancement factor on linkage was a factor of 3. We combine this information with geomorphic and structural constraints to estimate that linkage took place between 0.6 Ma and 1 Ma. Calculated pre- and post- linkage throw rates are 0.6 and 2 mm/yr respectively. Maximum knickpoint retreat rates upstream of the faults range from 4.5 to 28 mm/yr, faster than for similar catchments upstream of normal faults in the Central Apennines and the Hatay Graben of Turkey, and implying a fluvial landscape response time of 1.6 to 2.7 Myr. We explore the relative controls of drainage area and precipitation on these retreat rates, and conclude that while climate variation and fault throw rate partially explain the variations seen, lithology remains a potentially important but poorly characterised variable. This article is protected by copyright. All rights reserved.

Block and boulder accumulations on the southern coast of Crete (Greece): evidence for the 365 CE tsunami in the Eastern Mediterranean

Abstract The Eastern Mediterranean is one of the most seismically active regions in Europe. Crete, located in the centre of the Eastern Mediterranean, should experience tsunamis resulting from large magnitude earthquakes or volcanic eruptions. At three locations, boulders were observed that may relate to tsunami or storm events. At Lakki, the size of the boulders slightly favours a tsunami origin for deposition. By contrast, at Kommos, boulder size and geomorphology are consistent with storm parameters in the Mediterranean. The most compelling evidence for tsunami transport is found at Diplomo Petris, where a lithologically varied grouping of large boulders (≤690 t) is exposed at sea level. The calculated storm wave heights (15 m) required to transport the observed boulders significantly exceeds winter averages: therefore, these accumulations are interpreted as tsunami deposits. Radiocarbon dating of encrusting biological material was undertaken to constrain periods of boulder motion. Encrustations from Diplomo Petris and Lakki predate the 365 CE earthquake, suggesting that this event transported the largest boulders; the first time that boulder deposits have been identified on Crete from this tsunami. Therefore, these data are important for developing local and regional hazard assessments but also to inform numerical models of tsunami propagation in the Mediterranean.

Tectonic development of the southern Karasu Valley, Turkey: successive structural events during basin formation

Abstract New fault data are presented for the Karasu Valley, southern Turkey. Field measurements concentrate on the Eocene–Miocene (c. 48–7 Ma) sediments exposed on the south-western rift margin, in order to investigate the early development of this basin. Fault data show two trends in orientation NW–SE and NE–SW with a subordinate north–south trend. Stress inversions combined with field relationships indicate at least three phases of faulting. Firstly, an extensional event characterized by NE–SW and NW–SE normal faults, which are interpreted to have formed owing to flexural uplift in the forebulge region to the Bitlis–Zagros collisional front prior to the Middle Miocene. Secondly, north–south normal faults invert to give a stress ratio [R=(σ2 – σ3/σ1 – σ3)] indicative of an extensional stress regime, transitional to strike-slip faulting. The final stress phase (Pliocene–Recent) is of strike-slip faulting and east–west-trending normal faulting. This stress regime is interpreted as the result of the propagation of the Dead Sea Fault or East Anatolian Fault. Previous models of rift formation have invoked either transpressional or transtensional origins for the area; the new data presented here indicate that the southernmost Karasu Valley developed through extension followed by transtension. Supplementary material: The fault data (including location, orientation, kinematic information) used in this study are available at www.geolsoc.org.uk/SUP18532.

Numerical modeling of tidal notch sequences on rocky coasts of the Mediterranean Basin

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