André Poisson

Paleomagnetic reconstruction of the Cenozoic evolution of the Eastern Mediterranean

Abstract A total of 113 paleomagnetic sites were sampled along an Anatolian S–N transect from the Arabian platform, the Hatay region, the Eastern Taurides, the Kirsehir block, the Sivas basin and the Eastern Pontides. Reliable characteristic remanent paleomagnetic directions were retrieved from 37 of these sites, spanning in time from Paleocene to Miocene. In a general way, declinations are westerly deviated and inclinations are shallower than the geocentered dipole value at the present latitudes. When combined with previously published results, these data indicate that a large-scale counterclockwise rotation of Anatolia of some 25° has occurred since the Miocene. Assuming that the pole of rotation of Anatolia with respect to Europe has remained constant in time at the location given by MacClusky et al. [J. Geophys. Res. 105 (2000) 5695] on the basis of the geodetic data, this rotation implies that a large westward displacement (500 km at the average latitude of 40°) has taken place. Assuming that the rotation was initiated by the Arabia/Europe collision about 12 Ma ago, this corresponds to an average displacement of about 40 mm/year. Together with previous results from the western part of the Aegean arc, these results indicate that the main trends of the Cenozoic evolution of the Eastern Mediterranean appear to consist of two post-early Miocene rotations of opposite senses: a clockwise rotation of the western part of the Aegean [Tectonophysics 146 (1988) 183] around a pole situated in northern Albania, and a counterclockwise rotation around the pole given by McClusky et al. [J. Geophys. Res. 105 (2000) 5695]. Comparison with GPS data suggest that both rotations are still active today.

Tectonic Setting and Evolution of the Sivas Basin, Central Anatolia, Turkey

The Sivas Basin is one of several Central Anatolian basins. It developed mainly after the closure of the northern branch of Neotethys. Its location between the Kirsehir Massif and the Taurides impl...

Application of Sr isotope stratigraphy and sedimentary analysis to the origin and evolution of the Neogene basins in the Isparta Angle, southern Turkey

Abstract Four Miocene basins are located within the Isparta Angle in southern Turkey. One of these, the Darioren Basin, is well established as the foreland basin to the adjacent Lycian Nappes which marks the western margin of the Isparta Angle. The tectonic origin of the other three basins (Aksu, Kopru and Manavgat) has remained enigmatic largely because of the difficulties of dating the lowermost part of the succession (continental and shallow-marine conglomerates and limestones). Comparison of carbonate 87 Sr/ 86 Sr with the ocean water Sr isotope record provides a powerful chronological tool for marine sediments. By using Sr isotope ratios in this way, ages of the neritic limestones have been derived despite the absence of age-diagnostic fossils. These data constrain the age of the underlying conglomerates as lower to middle Burdigalian. The timing of deepening and subsidence events suggested by these new dates, taken together with palaeocurrent measurements from conglomerates, suggest that the basin configuration of the Isparta Angle was initiated in the lower Burdigalian and was directly related to movement on north–south-oriented faults. Depocentre development in the north of the Aksu Basin is consistent with a tectonic origin for all three basins by flexurally induced block faulting of the foreland in front of the Lycian Nappes along pre-existing structural weaknesses.

THE NORTH ANATOLIAN FAULT ZONE: DISTRIBUTED NEOGENE DEFORMATION IN ITS NORTHWARD CONVEX PART

Abstract The North Anatolian Fault Zone is composed of two almost rectilinear branches which join in a northward convex bend. In this bent zone, the Pontide-Anatolide collisional system has been cut across by two transpressional belts of fold-and-thrust and wrench faults of lower Neogene age. These structures were reactived during the Neotectonic period, the time of deposition of the Pontus Group. For both of these deformational events, and up to the present, the tectonic regime remained generally transpressional, with a NW-SE direction of compression and a NE-SW direction of extension. It is only recently, during the Upper Pleistocene, that the dextral wrench faults became more localized and more straight than previously. The complexity of the eastern part of the North Anatolian Fault Zone is better understood if one takes into account the role of inherited Miocene-Pliocene transpressional structures.

Tectonics of the Sivas Basin: The Neogene Record of the Anatolian Accretion Along the Inner Tauric Suture

The Sivas Basin extends over a major crustal structure underlying the contact zone between the Tauride and Pontide belts. The Kirsehir block, a continental crustal element lying between the main belts, introduces a subordinate suture in front of the Pontides—the Inner Tauride suture. The junction of the two main sutures occurs between Hafikand Imranli. Four structural zones have been considered. The northern basement of the basin, which includes both the Kirsehir continental crust and thrust sheets of ophiolite and pelagic sediments, forms an imbricate stack with an Eocene cover. The Eocene cover shows two distinct sequences: marine neritic and continental basalts overlying the Kirsehir basement, and deltaic and basinal deposits lying to the southeast. Southward tectonic stacking of the entire pile has occurred repeatedly since Oligocene time. The Sivas Basin proper is separated from the Kirsehir basement by the Kizilirmak Basin. This new structural unit consists of nearly undeformed, middle Miocene sands...

A Pattern of Block Rotations in Central Aegea

Paleomagnetic results obtained from Neogene formations on both sides of the Aegean Sea yield of a complex pattern of block rotations in these regions. On the western side, in Evia and Skyros the observed clockwise rotations of various angles are interpreted within the framework of a previously proposed model of distributed deformation by faulting in a zone connecting the north-Anatolian trough to the outer arc. On the eastern side, significant clockwise, counterclockwise and null rotations of coherent blocks have been demonstrated in the island of Lesbos and in western Anatolia. These movements took place during the neotectonic extensional period and their mechanism is not yet fully understood.

Magnetic fabrics and oblique ramp-related folding: A case study from the western Taurus (Turkey)

Abstract An analysis of magnetic fabric has been performed in weakly deformed Paleocene-Eocene limestone adjacent to two subparallel ramp-related folds (Akseki and Ormana folds) from the western Taurus (Turkey). The magnetic fabric of tectonic origin records two trends of well-defined magnetic lineation: N160 ° ± 7 ° and N130 ° ± 14 ° in front of the Akseki and Ormana folds, respectively. The trend of the magnetic lineation is oblique to the Akseki fold, whereas in the Ormana fold, magnetic lineation and fold axis are subparallel. The observed change in the trend of magnetic lineation is probably linked to a change of the shortening direction that occurred during the development of the thrust system. This shows that the two subparallel folds result from two different translation vectors.

Miocene transgression in the central and eastern parts of the Sivas Basin (Central Anatolia, Turkey) and the Cenozoic palaeogeographical evolution

We present here a reappraisal of the tectonic setting, stratigraphy and palaeogeography of the central part of the Sivas Basin from Palaeocene to late Miocene. The Sivas Basin is located in the collision zone between the Pontides (southern Eurasia) and Anatolia (a continental block rifted from Gondwana). The basin overlies ophiolites that were obducted onto Anatolia from Tethys to the north. The Central Anatolian Crystalline Complex (CACC) experienced similar ophiolite obduction during Campanian time, followed by exhumation and thrusting onto previously emplaced units during Maastrichtian time. To the east, crustal extension related to exhumation of the CACC created grabens during the early Tertiary, including the Sivas Basin. The Sivas Basin underwent several tectonic events during Paleogene–Neogene. The basin fill varies, with several sub-basins, each being characterised by a distinctive sequence, especially during Oligocene and Miocene. Evaporite deposition in the central part of the basin during early Oligocene was followed by mid-late Oligocene fluvio-lacustrine deposition. The weight of overlying fluvial sediments triggered salt tectonics and salt diapir formation. Lacustrine layers that are interbedded within the fluviatile sediments have locally yielded charophytes of late Oligocene age. Emergent areas including the pre-existing Sivas Basin and neighbouring areas were then flooded from the east by a shallow sea, giving rise to a range of open-marine sub-basins, coralgal reef barriers and subsiding, restricted-marine sub-basins. Utilising new data from foraminifera, molluscs, corals and nannoplankton, the age of the marine transgression is reassessed as Aquitanian. Specifically, age-diagnostic nannoplankton assemblages of classical type occur at the base of the transgressive sequence. However, classical stratigraphic markers have not been found within the planktic foraminiferal assemblages, even in the open-marine settings. In the restricted-marine sediments, there are rich planktic foraminiferal assemblages of classical type but these are of little use in stratigraphy. In contrast, the gastropod fauna indicate a Burdigalian age. Sediment reworking in the restricted-marine environments precludes stratigraphic determination. In such environments, micro- and nano-organisms experienced atypical developmental conditions. The small benthic foraminifera and associated ostracod assemblages are good indicators of salinity which varied considerably within the restricted-marine sub-basins. Some of the corals within the coralgal reefs barriers are also dated as Aquitanian. A combination of the salt tectonics and the late Miocene north-westward-verging thrusting created the present basin complexity.

Origin and geodynamic evolution of late Cenozoic potassium-rich volcanism in the Isparta area, southwestern Turkey

Post-collisional potassic-rich volcanism of Gölcük Volcano in the Isparta area of southwestern Turkey consists of two groups: (i) extracaldera lavas, corresponding mainly to Pliocene activity; and (ii) intracaldera lavas and pyroclastics (ignimbrite flows and ash/pumice fall deposits) formed during the Quaternary. Extracaldera volcanic rocks mainly comprise lamprophyre (minette), basaltic trachyandesite, trachyandesite, and trachyte. A close relationship exists between the silica content and phenocryst type in the extracaldera volcanics such that trachyte–trachyandesites with SiO2 < 57 wt% and basaltic trachyandesites are characterized mainly by mafic phenocryst phases (e.g. pyroxene, amphibole, biotite–phlogopite). These features suggest suppression of plagioclase crystallization under high H2O pressure conditions. Intracaldera volcanics are composed of tephriphonolitic dikes, remnants of lava flows and domes at the caldera rim, and a trachytic lava dome on the caldera floor. The Gölcük flows and pyroclastics are mainly characterized by strong incompatible element enrichment in large ion lithophile elements (LILEs; e.g. Cs, Ba, U, and Th) relative to K, Rb, and high-field strength elements (e.g. Nb, Ta, and Ti). We conclude that the Gölcük lavas were derived from a metasomatized lithospheric mantle source containing phlogopite–amphibole garnet peridotite; the latter resulted from metasomatism by a hydrous fluid phase related to subducted sediments and oceanic crust. The parental magma for the extracaldera volcanics was lamprophyric, and that for the intracaldera volcanics was basanitic. All the geological and geochemical data show that the alkaline Gölcük lavas display a gradual decrease in silica content with decreasing eruption age, indicating that, in the Isparta volcanic province, the asthenospheric melt component became more important over time. In the extracaldera volcanics, 87Sr/86Sr isotope ratios of the evolved trachyte–trachyandesites range between 0.70366 and 0.70504, whereas these ratios are lower in the less evolved basaltic trachyandesite and lamprophyres, varying in narrow ranges around 0.70365 and between 0.70374 and 0.70453, respectively. The 143Nd/144Nd values lie between 0.51264 and 0.51273 in trachyandesites, 0.51267 and 0.51273 in basaltic trachyandesites, and 0.51270 and 0.51274 in lamprophyres. In the intracaldera lavas, the 87Sr/86Sr isotope ratio is 0.70361 in the tephriphonolite and 0.70388 in the intracaldera trachytic lava dome. The 143Nd/144Nd isotope ratio is 0.51274 in the analysed tephriphonolitic flow and 0.51271 in the intracaldera trachytic lava dome; these values are higher than that of trachyte–trachyandesites of the extracaldera volcanics. The Sr–Pb isotopic signatures indicate that crustal contamination was significant for the evolved extracaldera volcanics, but was negligible for the intracaldera volcanics. The εNd values of the Gölcük volcanics range between 0 and 2.0. The low Sr isotope ratios and positive εNd values are characteristic features of a depleted mantle source. The isotopically depleted and incompatible enriched nature of the Gölcük lavas point to recent enrichment processes prior to partial melting of the mantle source. Conversely, their radiogenic lead isotope compositions (206Pb/204Pb = 19.19–19.54, 207Pb/204Pb = 15.64–15.67, 208Pb/204Pb = 39.12–39.49) indicate an enriched mantle source region.

Tectonostratigraphy of the Southern Sivas Tertiary Basin (Central Turkey) and Comparison with Landsat MSS Imagery

The Sivas Basin is one of the most important sedimentary basins, in terms of tectonics and hydrocarbon potential, in the Central Anatolian region of Turkey. Its development is related mainly to the closure of the northern branch of the Neotethyan ocean, as well as to influences of the closure of the Inner Tauride ocean. This basins complex history is related to several successive orogenic phases during the Cenozoic. Other interesting characteristics of this basin, as in the Central and Eastern Anatolian basins, are the tectonics and lithological features associated with the younger gypsum deposits. The study area comprises two distinct regions, namely the Savcun and Karacaoren areas. The primary stratigraphie relationships between Lutetian turbidites, Oligocene continental gypsum and detritics, and lower to middle Miocene continental deposits of the Savcun area have been elucidated. In this part of the study area, S-verging imbricated thrust systems, mainly located within the gypsum series, developed dur...