İsmail Ömer Yılmaz

Use of Sedimentary Structures in the Recognition of Sequence Boundaries in Upper Jurassic–Upper Cretaceous Peritidal Carbonates of the Western Taurides, Turkey

Subtidal, intertidal, and supratidal carbonate facies are recognized in the Upper Jurassic (Kimmeridgian)-Upper Cretaceous (Cenomanian) peritidal carbonates of the Fele area (Western Taurides, Turkey). Vertical stacking patterns of these facies are of a cyclical character; shallowing upward is the trend of the cyclicity in these carbonate facies. In-situ karstic breccias, collapse breccias, caliche (laminar calcrete), “Microcodium” accretion, and root casts are structures commonly indicative of third-order sequence boundaries. However, mud cracks, solution pores or vugs, sheet cracks, loferites, and birds-eye structures are commonly delineated by parasequence boundaries. In-situ or collapse breccias can be genetically derived from sheet cracks, mud cracks, solution pores or vugs, and birds-eye structures with increasing exposure time. The use of such sedimentary structures in the recognition of sequence boundaries is highly practical in the ancient carbonate platforms of the world, inasmuch as the sequence boundaries, as demonstrated in this study, correlate with the eustatic sea level curves.

A 2800-year multi-proxy sedimentary record of climate change from Lake Çubuk (Göynük, Bolu, NW Anatolia)

The sediment of Lake Çubuk in NW Anatolia, which is situated very close to the climate boundary between the dry Central Anatolia and the wet Marmara region, is regarded as a suitable climate archive to test inward and outward movements of this boundary in accordance with past climate variations. Herein, we study the stratigraphic record of the last 2800 years of this landslide-dammed lake at 1030 m elevation, using multi-proxy tools (sedimentology, major and trace element geochemistry, stable isotopes, pollen, diatoms and ostracods) and compare the results with other contemporaneous Anatolian climatic records. Our findings indicate that Lake Çubuk recorded seven distinct climatic periods in the last 2800 years that have been previously revealed elsewhere in Anatolia. The most arid period occurred at the end of the Near-East Aridification Phase at approximately 200 BC when the δ18O shifted to very negative values, and the planktonic diatom ratio considerably decreased. The Dark Ages and the late Byzantine periods between AD 670 and 1070 are characterized by more positive δ18O values, increasingly higher lake levels and the most extensive arboreal cover of the entire record. The ‘Little Ice Age’ appeared suddenly, within 40 years, at AD 1350 and is reflected in all of the proxies, including a positive shift in δ18O, a sharp decrease in pollen of shrub and herb to the benefit of pine trees and a rapid increase in benthic diatom abundance indicating a lake level shallowing. In many parts of the record, a close match between the stable isotopes and the pollen assemblage zones in the last 2800 years demonstrates that climate rather than human activity was the primary driver of vegetation cover in this mid-altitude mountain of NW Anatolia.

Geological features and geochemical characteristics of Late Devonian–Early Carboniferous K-bentonites from northwestern Turkey

Abstract Newly discovered K-bentonite beds, interstratified with limestones/dolomitic limestones of the Upper Devonian-Lower Carboniferous Yılanlı Formation, are exposed in the northwestern Black Sea region of Turkey, around Zonguldak and Bartın. K-bentonite samples collected from four different locations: the Gavurpınarı and Yılanlı Burnu quarries from the Bartın area, the Çimşir Çukurları quarry from the Şapça area, and the Güdüllü and Gökgöl highway tunnel section near Zonguldak city were investigated using optical microscopy,X-ray diffraction and inductively coupled plasma mass spectrometry in order to reveal their mineralogical and geochemical characteristics and understand their origin and evolution. The K-bentonites occur at different levels in the Yılanlı Formation as 2-40 cm-thick, greenish to yellowish beds cropping out several hundred metres along strike. Preliminary biostratigraphic data suggest that the protoliths of the Bartın (Gavurpınarı and Yılanlı Burnu) and Güdüllü K-bentonites were deposited at around the boundary between the Frasnian and Famennian, whereas those in the Şapça and Gökgöl sections are slightly younger (Devonian-Carboniferous boundary interval). The lithofacies types of the host carbonate rocks suggest an ‘epeiric’ shallow carbonate platform environment. Illite and mixed-layer illite-smectite were the major clay minerals in the K-bentonites. The K-bentonites from the Bartın area display a high degree of illitization and consist mainly of illite indicating high-grade diagenesis, whereas illite-smectite-rich samples from the Şapca and Gökgöl tunnel locations reflect relatively lower diagenetic conditions. According to their geochemical compositions, two groups of K-bentonites were distinguished, one with alkali basalt (Bartın area and Güdüllü locations) and one with trachyte affinities (Gökgöl tunnel and Şapça locations). Geochemical fingerprinting of K-bentonites by trace and rare earth element (REE) data suggest that tephras with alkali basalt composition have been derived by a source formed in a ‘continental back-arc’ setting, whereas the source of K-bentonites with trachytic precursors is related to ‘continental within-plate rifting’. An evaluation of the global Late Devonian and Devonian-Carboniferous volcanism suggests that the bentonite precursors may be related to late-Variscan magmatism in Laurussia.

Chronology of subduction and collision along the İzmir-Ankara suture in Western Anatolia: records from the Central Sakarya Basin

ABSTRACT Western Anatolia is a complex assemblage of terranes, including the Sakarya Terrane and the Tauride-Anatolide Platform that collided during the late Cretaceous and Palaeogene (80–25 Ma) after the closure of the Izmir-Ankara Ocean. Determining the precise timing at which this ocean closed is particularly important to test kinematic reconstructions and geodynamic models of the Mediterranean region, and the chronology of suturing and its mechanisms remain controversial. Here, we document the Cretaceous-Eocene sedimentary history of the Central Sakarya Basin, along the northern margin of the Neotethys Ocean, via various approaches including biostratigraphy, geochronology, and sedimentology. Two high-resolution sections from the Central Sakarya Basin show that pelagic carbonate sedimentation shifted to rapid siliciclastic deposition in the early Campanian (~ 79.6 Ma), interpreted to be a result of the build-up of the accretionary prism at the southern margin of the Sakarya Terrane. Rapid onset of deltaic progradation and an increase in accumulation rates in the late Danian (~ 61 Ma), as well as a local angular unconformity are attributed to the onset of collision between the Sakarya Terrane and the Tauride-Anatolide Platform. Thus, our results indicate that though deformation of the subduction margin in Western Anatolia started as early as the Campanian, the closure of the İzmir-Ankara Ocean was only achieved by the early Palaeocene.

Devonian to Basal Permian Lithostratigraphy in Southwestern Hakkari: A Perspective from Northern Arabian Mixed Carbonate–Siliciclastic Platform

The Middle Devonian-Lower Carboniferous succession in the Amanos Mountains to the west and in the Hakkari area to the east of the Hazro High are known as the Zap Group, divided into the Yiginli (Middle-Late Devonian) and Köprülü formations (Late Devonian-Early Carboniferous). The Group is overlain by the Late Permian Gomaniibrik Formation. The thickness of the Yiginli Formation, in the HakkariÇukurca area, ranges between 200 and 300 m. The vertebrate and microflora remains indicate a Famennian age for the top of the Yiginli Formation. Brachiopod samples recently collected from the Zap River Valley area allow to establish an Upper Givetian age for the upper middle part of the Yiginli Formation which was until now considered as Famennian on the basis of its micropaleontological contents. In particular, the presence of Atrypids excludes an age younger than Lower Frasnian. Studied brachiopods come from shell concentrations of various clayey-silty levels. The Köprülü Formation represents a variety of marine environments ranging from agitated shallow marine to muddy shelf conditions – below fair weather wave base – and then a return to more restricted shallow marine facies in the upper part. The Köprülü Formation was measured and investigated along the Zap 1 and Zap 2 sections located on the north-east of Köprülü village, 8 km northwest of Cukurca. The Köprülü Formation can be subdivided into three new members. The lower member is composed of dark to grayish limestone and sandy limestone representing the transgressive phase covering the continental deposits of the Yiginli Fomation. The corals described here were collected in this member. The coral assemblage is mainly composed of small non-dissepimented solitary corals belonging to the genera Rotiphyllum, Zaphrentites, cf. Gorizdronia, gen. et sp. indet. and Amplexizaphrentis, including a new species, A. zapense, and the dissepimented coral Caninia aff. cornucopiae. The middle member is composed of thinly laminated dark grey calcareous shales and siltstones; several sandstone layers are also intercalated. The upper part of this middle member is characterized by carbonate concretions embedded in sandy limestone. The fossils, including bivalves are well preserved in this member. The myalinid bivalves, with a few posidonid bivalves have been observed in dark grey calcareous shale horizons. The upper member is dominated by massive grayish sandy/dolomitic limestone with some dark shale intercalations.