Nilgün Okay

An active, deep marine strike‐slip basin along the North Anatolian fault in Turkey

The Tekirdag depression within the Marmara Sea in the Mediterranean region is an active, rhomb-shaped strike-slip basin along the North Anatolian fault with a basin floor at a water depth of −1150 m. New multichannel seismic reflection data and on-land geological studies indicate that the basin is forming along a releasing bend of the strike-slip fault and is filled with syntransform sediments of Pliocene-Quaternary age. The basin is bounded on one side by the North Anatolian fault and on the other side by a subparallel normal fault, which forms the steep submarine slope. In cross section the basin is strongly asymmetric with the thickness of the syntransform strata increasing from a few tens of meters on the submarine slope to over 2.5 km adjacent to the North Anatolian fault. Seismic sections also show that the slope-forming normal fault connects at depth to the North Anatolian fault, implying that the basin is completely detached from its substratum. The whole structure can be envisaged as a huge, rather flat, negative flower structure. The releasing bend of the North Anatolian fault, responsible for the formation of the basin, is flanked by a constraining bend. Along the constraining bend, the syntransform strata are being underthrust, implying a recent change in the direction of the regional displacement vector. This thrusting is responsible for the uplift of the submarine slope to a height of 924 m, possibly by a mechanism of elastic rebound. Regional geology suggests that most of the syntransform strata are lacustrine with only the topmost few hundred meters consisting of deep marine clays. The anomalous present depth of the Tekirdag depression is due to reduced Quaternary sedimentation coupled with high rates of displacement along the North Anatolian fault, which amounts to 20 mm/yr in the Marmara Sea region.

Sinistral transport along the Trans-European Suture Zone: detrital zircon–rutile geochronology and sandstone petrography from the Carboniferous flysch of the Pontides

The Lower Carboniferous flysch of the Istanbul Zone in Turkey is an over 1500 m thick turbiditic sandstone–shale sequence marking the onset of the Variscan deformation in the Pontides. It overlies Lower Carboniferous black cherts and is unconformably overlain by Lower Triassic continental sandstones and conglomerates. The petrography of the Carboniferous sandstones and the geochronology and geochemistry of the detrital zircons and rutiles were studied to establish the provenance of the clastic rocks. The sandstones are feldspathic to lithic greywackes and subgreywackes with approximately equal amounts of quartz, feldspar and lithic clasts. The amount of quartz and lithic fragments decreases upwards in the sequence at the expense of feldspar. The lithic fragments are dominated by intermediate volcanic rocks, followed by metamorphic and sedimentary rock fragments. Coarse lithic fragments are generally granitoidic. In the discrimination diagrams, sandstone samples lie mainly in the field of dissected arc. A total of 218 detrital zircons and 35 detrital rutiles from four sandstone samples were analysed with laser ablation ICP-MS. The detrital zircons show a predominantly bimodal age distribution with Late Devonian to Early Carboniferous (390 to 335 Ma) and Cambrian–Neoproterozoic (640 to 520 Ma) ages. The remaining 9 % of the analysed zircons are in the 1700–2750 Ma range; zircons of the 700–1700 Ma age range are absent. The REE patterns and Th/U ratios of the zircons are consistent with a magmatic origin. With one exception (Neoproterozoic), the rutile ages are Late Devonian–Early Carboniferous and their geochemistry indicates that they were derived from amphibolite-facies metamorphic rocks. Sandstone petrography and detrital zircon–rutile ages suggest one dominant source for the Lower Carboniferous sandstones: a Late Devonian to Early Carboniferous magmatic and metamorphic province with overprinted Neoproterozoic basement. Late Devonian–Early Carboniferous magmatic and metamorphic rocks are unknown from the Eastern Mediterranean region. They are, however, widespread in central Europe. The Istanbul Zone is commonly correlated with the Avalonian terrranes in central Europe, which collided with the Armorican terranes during Carboniferous times, resulting in the Variscan orogeny. The Carboniferous flysch of the Istanbul Zone must have been derived from a colliding Armorican terrane, as indicated by the absence of 700–1700 Ma zircons and by Late Devonian–Early Carboniferous magmatism, typical features of the Armorican terranes. This suggests that during Carboniferous times the Istanbul terrane was located close to the Bohemian Massif and has been translated by strike-slip along the Trans-European Suture Zone to its Cretaceous position north of the Black Sea.

Exploring submarine earthquake geology in the Marmara Sea

The disastrous 1999 earthquakes in Turkey have spurred the international community to study the geometry and behavior of the North Anatolian Fault (NAF) beneath the Marmara Sea. While the area is considered mature for a large earthquake, the detailed fault geometry below the Marmara Sea is uncertain, and this prevents a realistic assessment of seismic hazards in the highly-populated region close to Istanbul. Two geological/geophysical surveys were recently conducted in the Marmara Sea: the first in November 2000 with the R/V Odin Finder, and the second in June 2001 with the R/V CNR-Urania. Both were sponsored and organized by the Institute of Marine Geology of the Italian National Research Council (CNR), in cooperation with the Turkish Council for Scientific and Technical Research (TUBITAK) and the Lamont-Doherty Earth Observatory of Columbia University Multi-beam bathymetry, multi-channel seismic reflection profiling, magnetometry high-resolution CHIRP sub-bottom profiling, and bottom imaging were carried out with a remotely operated vehicle (ROV). Over 60 gravity and piston cores were collected.

Thermal rejuvenation of the Yermak Plateau

The Yermak Plateau, bordering the Arctic Ocean and the Norwegian-Greenland Sea, and adjacent to the continental Svalbard Archipelago, is characterized by high heat flow relative to its surrounding region. South of and parallel to the trend of the plateau lies the formerly active-Spitsbergen Shear Zone (De Geer Zone), which is now occupied by the slowly spreading Knipovich and Molloy Ridges. An analysis of these heat flow data suggest that asymmetric spreading within the Norwegian-Greenland Sea propagated northwards along one of the faults associated with the Spitsbergen Shear Zone. The broad zone of faults, once associated with this paleo-shear zone, extends throughout Svalbard as well as on and to the west of the Knipovich Ridge. This network of faults may comprise a complex system of detachment surfaces along which magma may rise from a deep-seated source and across which simple shear extension may develop. Dike injection into the Yermak Plateau, north of the propagating ridge may have been initiated by the thermal response of the highly fractured lithosphere to this propagating asthenospheric front. We suggest that one of these faults, acting as a secondary detachment to the main fault underlying the Knipovich Ridge, may be dissecting the Yermak Plateau. Based on an analysis of the thermal data, simple shear extension may have been taking place along a broad zone of intrusion. This region has undergone and is probably still undergoing thermal rejuvenation. Multiple zones of intrusion may be a common phenomena along newly rifted continental margins especially when they have been substantially faulted prior to rifting.

Integration of Earth Science Research on the Turkish and Greek 1999 Earthquakes

Preface. In Memoriam: Sirrn Erinc. In Memoriam: Aykut Barka. List of Contributors. Part 1: Turkish 1999 Earthquake. 1. The 17 August 1999 (Golcuk (Kocaeli)-Arifiye (Adapazari) and 12 November 1999 Duzce earthquakes, NW Turkey: their mechanism and tectonic significance E. Gokten, et al. 2. Imaging of the Izmit rupture from the strong motion records M. Bouchon, et al. 3. Tectonic setting of the eastern Marmara Sea B. Alpar, C. Yaltirak. 4. Transition of the North Anatolian Fault Zone (NAZ) in the Sea of Marmara A. Ulugamma, E. Ozel. 5. Western extension of the north Anatolian Fault and associated structures in the Gulf of Saros, NE Aegean Sea M.N. Cagammaatay, et al. 6. Methane in sediments of the deep Marmara Sea and its relation to local tectonic structures P. Halbach, et al. 7. The tsunami threat in the Sea of Marmara, Turkey: A review D.R. Tappin, et al. 8. Earthquakes of the Marmara Sea Basin: Reflections on the need for co-operation between historian and scientist C.F. Finkel. Part 2: Greek 1999 Earthquakes. 9. The Athens earthquake September 7, 1999: Neotectonic regime and geodynamic phenomena I. Mariolakos, I. Fountoulis. 10. Three dimensional P-wave crustal velocity structure beneath Athens region (Greece) using micro-earthquake data G. Drakatos, et al. 11. Earthquake triggering in Greece and the case of the 7 September 1999 Athens Earthquake G.A. Papadopoulos. 12. Destructive earthquake and seismotectonics in the Gulf of Corinth, Central Greece: A Review D. Papanastassiou. 13. Trans-Aegean seismicity, seismic hazard and defences P.W. Burton, G.-A.Tselentis. 14. Methods for imaging earthquake deformation using satellite data and digital elevation models A. Ganas. Subject Index.

Variability of clay-mineral composition on Carolina Slope (NW Atlantic) during marine isotope stages 1–3 and its paleoceanographic significance

Abstract The clay-mineral composition of marine isotope stages 1–3 sediments at the Ocean Drilling program (ODP) Site 1055 on the Carolina Slope consists mainly of illite, kaolinite, chlorite and smectite. Clay-mineral variability is marked by a distinct increase in the relative amounts of kaolinite and smectite during the Holocene and by high illite and to a lesser extent chlorite relative amounts during marine isotopic stages 2 and 3. This grouping of clay minerals as two different assemblages during different isotopic stages suggest their different source affinities. The increase in the ‘kaolinite+smectite’ assemblage in the Holocene is accompanied by a significant increase in the sedimentation rate. The change in the sedimentation regime after the Last Glacial Maximum is interpreted to be related to resuspension and advection of clays and silts by increased deep water activity over the Bermuda Rise, followed by their transport to Site 1055 on the Carolina Slope by shallow elements of the North Atlantic Deep Water. High amplitude variations with high illite amounts characterize marine isotope stage 3 and appear to be related to Heinrich events.