FORAMINIFERA FROM THE EXOTIC PERMO-CARBONIFEROUS LIMESTONE BLOCKS IN THE KARAKAYA COMPLEX, NORTHWESTERN TURKEY

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Geology of the Paleotetis units at the northern part of Edremit Bay

İnceleme alanı Kuzeybatı Anadolu’da Biga Yarımadası’nın güneyinde, Edremit Körfezi ve kuzeyinde yer alan Kazdağ ve çevresini kapsar. Kazdağ Grubu, amfbolit-granulit fasiyesinde metamorfik bir istiftir.  Kazdağ Grubu üzerinde, bir sıyrılma fayı dokanağı ile yeşil şist fasiyesinde metamorfik birimlerden oluşan Karakaya Karmaşığı bulunur. Kazdağ Grubu, okyanus kabuğu, üzerinde gelişen okyanus platosu çökel ve volkanikleri, Karakaya Karmaşığı, riftt çökelleri, denizaltı-dağı, denizaltı platosu, hendek çökelleri, dalma-batma gerisi havza çökelleri temsil eden bir eklenir prizmadır. Kazdağ Grubu ve Karakaya Karmaşığı Paleotetis Okyanusu’nun Permo-Karbonifer’de oluşumu ve Triyas’ta kapanmasının hemen hemen tüm aşamalarını temsil eder. Anahtar Kelimeler: Paleotetis, Kazdağ Grubu, Karakaya Karmaşığı, jeodinamik evrim.Study area is located to the south of the Biga Peninsula, NW Anatolia. It includes the Edremit Bay and the Kazdağ Group to the north. The rock groups represent a geological period starting from the Carboniferous to present. On the basement a metamorphic series in amphibolite-granulite facies take place. These series form the Kazdağ Group itself and are made up of the Babadağ Formation, Sarıkız Formation, Kavurmacılar Formation and Altınoluk Formation. A detachment fault and the metamorphic Karakaya complex (green schist facies) take place on the Kazdağ Group. To the east, the Karakaya Complex starts with the Fazlıca, Kınar and Kalabak units, which contain shale, schist, fillate, basalt and marble, on a Palaeozoic granodiorite basement. These units are overlain by the units of Nilüfer, which is made up of tectonically thrusted spilits, and Tepeoba, which is made up of felsic fillate and tuffs, respectively. The unit Hodul passes laterally into the unit Nilüfer and it is made up of arkozic sandstone, rare spilit and chert alternations. On top of these formations, the unit Çal is located with a tectonic contact and it contains Permian-Trias limestone blocks in a size of a mountain. The study area forms the pieces of Palaeotethys ocean dominated between Carboniferous and Triassic. The rocks of the Kazdağ Group form the Laurassia part of the ocean crust while the Karakaya Complex represents the southern environments of the south-dipping oceanic crust. These environments include the sea-mount (Nilüfer unit), accretional prism (Hodul unit), marginal basin (Tepeoba unit) and passive Cimmeria margin of this basin (Fazlıca+Kınar+Kalabak). The Laurassia and Sakarya continents collided during Middle-late Triassic and the units between these continents formed the Karakaya Complex in the form of tectonic slices.Keywords: Paleotethys, Kazdağ Group, Karakaya Complex, geodynamic evolution

Late Cretaceous-Eocene Geological Evolution of the Pontides Based on New Stratigraphic and Palaeontologic Data Between the Black Sea Coast and Bursa (NW Turkey)

The Late Cretaceous-Eocene geological evolution of northwest Turkey between the Black Sea and Bursa was studied through detailed biostratigraphic characterization of eleven stratigraphic sections. The Upper Cretaceous sequence in the region starts with a major marine transgression and lies unconformably on a basement of Palaeozoic and Triassic rocks in the north (Istanbul-type basement) and on metamorphic rocks and Jurassic sedimentary rocks in the south (Sakarya-type basement). Four megasequences have been differentiated in the Late Cretaceous-Eocene interval. The first one, of Turonian to Late Campanian age, is represented by volcanic and volcanoclastic rocks in the north along the Black Sea coast, and by siliciclastic turbidites and intercalated calcarenites in the south, corresponding to magmatic arc basin and fore-arc basin, respectively. A major ridge along the present southern margin of the Kocaeli Peninsula separated these two realms. In the Late Campanian, volcanism and clastic sedimentation gave way to the widespread deposition of the pelagic limestone and marl of the Akveren Formation; only in the extreme south near Bursa are the pelagic micrites of the Akveren Formation replaced by calciturbidites and siliciclastic turbidites. The age of the Akveren Formation ranges from Late Campanian to Late Palaeocene. The third megasequence is a thick flysch wedge of Early Eocene age, which extends from north of Bursa to the Black Sea coast. The base of the Lower Eocene flysch is marked by a major unconformity. The flysch wedge marks the collision between the Pontides and the Anatolide-Tauride Block. The fourth megasequence is a thick volcanic and volcaniclastic series of late Early to Middle Eocene age, which extends from north of Bursa to the northern margin of the Armutlu Peninsula. The coherent Upper Cretaceous-Eocene stratigraphy, the laterally traceable facies belts, absence of ophiolitic slices and high pressure metamorphic rocks in the Upper Cretaceous-Tertiary series in the region between the Black Sea and Bursa indicate pre-Santonian juxtaposition of the Istanbul and Sakarya zones

Thermochronology of the Miocene Arabia-Eurasia collision zone of southeastern Turkey

The Bitlis-Piitiirge collision zone of SE Turkey is the area of maximum indentation along the > 2400-km-long Assyrian-Zagros suture between Arabia and Eurasia. The integration of (1) fission-track analyses on apatites, (ii) (U-Th)/He analyses on zircons, (iii) field observations on stratigraphic and structural relationships, and (iv) preexisting U-Pb and Ar-Ar age determinations on zircons, amphiboles, and micas provides for the first time an overall picture of the thermochronometric evolution of this collisional orogen. The data set points to ubiquitous latest Cretaceous metamorphism of a passive margin sedimentary sequence and its igneous basement not only along the suture zone but across the entire width of the Anatolia-Tauride block north of the suture. During the early Paleogene the basement complex of the Bitlis and Piitiirge massifs along the suture was rapidly exhumed due to extensional tectonics in a back-arc setting and eventually overlain by Eocene shallow-marine sediments. The entire Oligocene is characterized by a rather flat thermochronometric evolution in the Bitlis orogenic wedge, contrary to the widely held belief that this epoch marked the inception of the Arabia-Eurasia collision and was characterized by widespread deformation. Deposition of a thick Oligocene sedimentary succession in the Mu-Hinis basin occurred in a retroarc foreland setting unrelated to continental collision. During the Middle Miocene, the Bitlis-Piitiirge orogenic wedge underwent a significant and discrete phase of rapid growth by both frontal accretion, as shown by cooling/exhumation of the foreland deposits on both sides of the orogenic prism, and underplating, as shown by cooling/exhumation of the central metamorphic core of the orogenic wedge. We conclude that continental collision started in the mid-Miocene, as also shown by coeval thick syntectonic clastic wedges deposited in flexural basins along the Arabian plate northern margin and contractional reactivation of a number of preexisting structures in the European foreland

Almacık Complex-an exhumed lower to middle crust in northwest Anatolia

The Almacık Complex is a tectonic unit of high-grade metamorphic rocks in the Intra-Pontide Suture Zone in northwest Turkey. It consists mainly of amphibolite, metaultramafic rock, and gneiss, which are intruded by numerous pre-, syn-, and posttectonic felsic veins. The Almacık Complex is variously interpreted as a Cretaceous or Neoproterozoic ophiolite, or a Permian mafic-ultramafic complex representing the middle to lower crust of the Sakarya Zone. Herein, new petrological and geochronological data were presented from the Almacık Complex. Two-pyroxene geothermometry in the metawebsterites indicated that the Almacık Complex has undergone upper amphibolite-facies metamorphism at 750 ± 30 °C and 8 ± 4 kbar. U-Pb zircon and Ar-Ar ages from 11 samples indicate the presence of late Neoproterozoic, Permian, and Jurassic thermal events. Most of the Almacık Complex consists of late Neoproterozoic amphibolites and gneisses, representing the basement of the İstanbul Zone. This basement was intruded by voluminous mafic magma during the Late Permian. The basement and the Permian ultramafic-mafic rocks subsequently underwent upper amphibolite-facies metamorphism during the Jurassic, possibly at the base of a magmatic arc

Thermal Evolution of the Permo−Triassic Karakaya Subduction-accretion Complex Between the Biga Peninsula and the Tokat Massif (Anatolia)

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İzmir‐Ankara suture as a Triassic to Cretaceous plate boundary – data from central Anatolia

The İzmir‐Ankara suture represents part of the boundary between Laurasia and Gondwana along which a wide Tethyan ocean was subducted. In northwest Turkey, it is associated with distinct oceanic subduction‐accretion complexes of Late Triassic, Jurassic and Late Cretaceous ages. The Late Triassic and Jurassic accretion complexes consist predominantly of basalt with lesser amounts of shale, limestone, chert, Permian (274 Ma zircon U‐Pb age) metagabbro and serpentinite, which have undergone greenschist facies metamorphism. Ar‐Ar muscovite ages from the phyllites range from 210 Ma down to 145 Ma with a broad southward younging. The Late Cretaceous subduction‐accretion complex, the ophiolitic mélange, consists of basalt, radiolarian chert, shale and minor amounts of recrystallized limestone, serpentinite and greywacke, showing various degrees of blueschist facies metamorphism and penetrative deformation. Ar‐Ar phengite ages from two blueschist metabasites are ca. 80 Ma (Campanian). The ophiolitic mélange includes large Jurassic peridotite‐gabbro bodies with plagiogranites with ca. 180 Ma U‐Pb zircon ages. Geochronological and geological data show that Permian to Cretaceous oceanic lithosphere was subducted north under the Pontides from the Late Triassic to the Late Cretaceous. This period was characterized generally by subduction‐accretion, except in the Early Cretaceous, when subduction‐erosion took place. In the Sakarya segment all the subduction accretion complexes, as well as the adjacent continental sequences, are unconformably overlain by Lower Eocene red beds. This, along with the stratigraphy of the Sakarya Zone indicate that the hard collision between the Sakarya Zone and the Anatolide‐Tauride Block took place in Paleocene

Multiple Orbitoides d’Orbigny lineages in the Maastrichtian? Data from the Central Sakarya Basin (Turkey) and Arabian Platform successions (Southeastern Turkey and Oman)

The standard reconstruction of species of Orbitoides d'Orbigny into a single lineage during the late Santonian to the end of the Maastrichtian is based upon morphometric data from Western Europe. An irreversible increase in the size of the embryonic apparatus, and the formation of a greater number of epi-embryonic chamberlets (EPC) with time, is regarded as the main evolutionary trends used in species discrimination. However, data from Maastrichtian Orbitoides assemblages from Central Turkey and the Arabian Platform margin (Southeastern Turkey and Oman) are not consistent with this record. The Maastrichtian Besni Formation of the Arabian Platform margin in Southeastern Turkey yields invariably biconvex specimens, with small, tri- to quadrilocular embryons and a small number of EPC, comparable to late Campanian Orbitoides medius (d'Archiac). The upper Maastrichtian Tarakli Formation from the Sakarya Basin of Central Turkey contains two distinct, yet closely associated forms of Orbitoides, easily differentiated by both external and internal features. Flat to biconcave specimens possess a small, tri- to quadrilocular embryonic apparatus of Orbitoides medius-type and a small number of EPC, whereas biconvex specimens possess a large, predominantly bilocular embryonic apparatus, and were assigned to Orbitoides ex. interc. gruenbachensis Papp-apiculatus Schlumberger based on morphometry. The flat to biconcave specimens belong to a long overlooked species Orbitoides pamiri Meric, originally described from the late Maastrichtian of the Tauride Mountains in SW Turkey. This species is herein interpreted to be an offshoot from the main Orbitoides lineage during the Maastrichtian, as are forms that we term Orbitoides 'medius', since they recall this species, yet are younger than normal occurrence with the accepted morphometrically defined lineage. The consistent correlation between the external and internal test features in O. pamiri implies that the shape of the test is not an ecophenotypic variation, but appears to be biologically controlled. We, therefore, postulate that more than one lineage of Orbitoides exists during the Maastrichtian, with a lineage that includes O. 'medius' and O. pamiri displaying retrograde evolutionary features