Ömer Bozkaya

Sepiolite-palygorskite from the Hekimhan region (Turkey)

Upper Cretaceous-Tertiary marine clayey-calcareous rocks of the Hekimhan basin contain fibrous clay minerals in significant amounts. Ophiolitic rocks in the provenance area have contributed the elements to form the clay minerals. XRD, SEM, major, trace and REE analyses were applied to samples taken from several stratigraphic sections. Diagenetic minerals such as smectite, dolomite, calcite, gypsum, celestite and quartz/chalcedony are associated with sepiolite-palygorskite group clays. Trace and rare earth elements (REE) are more abundant in palygorskite than sepiolite. REE abundances in the sepiolite-palygorskite are characterized by negative Eu and positive Nd anomalies when normalized with respect to chondrite and shale. Sepiolites with sharp XRD peaks are formed by diagenetic replacement of dolomite and diagenetic transformation of palygorskite, or by direct crystallization from solution. The average structural formula of the sepiolite is:(Mg7.15Al0.13Fe0.31Cr0.06Ni0.04)(Si11.98Al0.02)O30(OH)4(OH2)4Cao0.03Na0.02K0.02.8H2OPalygorskite appears to be authigenic by direct precipitation from solution. It exists in both monoclinic and orthorhombic forms with the mean structural formula given below(Mg2.22Al1.00Ti0.04Fe0.77Cr0.01Ni0.02)(Si7.68Al0.32)O20(OH)2(OH2)4Cao0.07Na0.05K0.10.4H2O

The pioneer work of Bernard Kübler and Martin Frey in very low-grade metamorphic terranes: paleo-geothermal potential of variation in Kübler-Index/organic matter reflectance correlations. A review

Low-temperature metamorphic petrology occupies the P–T field between sedimentary and metamorphic petrology. Two important pillars of low-temperature metamorphism are coal petrology and clay mineralogy. When low temperature petrology was established bridging a hiatus between the two classical geological disciplines of sedimentary geology and metamorphic petrology, geologists faced a need for the usage of different terminology tenets. Martin Frey and Bernard Kübler were two pioneers in low-grade metamorphic petrology. They focused their research on clarifying the relationships of clay mineralogy and organic petrology to metamorphic pressure (P) and temperature (T) conditions. The ultimate aim of M. Frey and B. Kübler was to establish a correlation between clay indices and organic parameters for different geodynamic setting and therefore for various pressure–temperature (P–T) conditions occurring in low grade metamorphic terranes. For this purpose, a special attention was addressed to the correlation between the Kübler-Index (KI) and vitrinite reflectance (VR). All these efforts are dedicated to estimate the P–T conditions and thus to gain insight into the geodynamic evolution of low-grade metamorphic terranes. B. Kübler and M. Frey honored here concentrated their studies to the Helvetic Central Alps area. The very low-grade Helvetic domain is therefore of basic interest of this paper. Ensuing the extensive compilation of data from the Helvetic domain, a reinterpretation of Kübler and Frey’s research is presented in the light of last decade’s scientific progress. A comprehensive dataset available enables to discriminate many factors influencing the Kübler-Index and organic-matter reflectance alongside to time, temperature and pressure. The correlation is restricted to the KI and organic matter reflectance (mostly VR) because most of the studies used both methods. Organic matter reflectance (OMR) includes data from vitrinite reflectance and bituminite reflectance measurements. Geodynamics has important control on the KI/VR (OMR) correlation. Tectonic units having a similar geodynamic evolution are featured by the comparable KI/OMR trends, related to the particular paleo-geothermal conditions. Obviously the KI/OMR correlations provide a mean to characterise geothermal gradients and metamorphic very-low-grade pressure–temperature conditions. In terranes where high deformations rates are reported, exceeding the high anchizone conditions, strain promotes the kinetic effects of temperature and pressure on the KI versus OMR ratio.

Mineralogy and geochemistry of paleocene ultramafic- and sedimentary-hosted talc deposits in the southern part of the sivas basin, Turkey

Talc deposits, located mainly in three areas of north-central Turkey, are present in the ophiolitic series of the Cretaceous and in siliciclastic rocks of the Paleocene. Talc deposits related to ophiolites are between tectonite and cumulate occurring as beds and/or lenses and 0.1–3 cm thick fracture fillings within a 5 m brecciated zone with a vein-type bedding. Sedimentary-hosted talc beds and semi-rounded to angular talc grains (0.1–2 cm) range in thickness from 0.1 to 30 cm within marls and conglomerates. Talc veins form lenses (a few meters long) and spheroidal and/or ellipsoidal nodules (1–10 cm). Calcite, dolomite, serpentine and/or mixed-layered illite-smectite (I-S) minerals are encountered in the talc samples. Serpentine with positive U and Hf anomalies, and talc with positive Nb and Zr anomalies, and negative Ta and Ce anomalies are typically depleted in P and Ti, based on chondrite-normalized trace element patterns. The light rare earth element content of sedimentary-hosted talc with a negative Gd anomaly is richer than those of ultramafic-hosted talc with a negative anomaly for Eu as well as serpentine. Significantly, talc with a uniquely sedimentary origin tends to be the principal source of Nb, Hf, Zr, La, Ce, Pr and Nd with respect to serpentine. δ18O and δD values for talc range from +13.8 to +17.5‰ and −60 to −36‰, and those of serpentine are +9.4 and −88‰, indicating supergene conditions for sedimentary-hosted talc and hypogene for ultramafic-hosted talc. When compared with seawater, δ18O data indicate temperatures of 68°C and 80–98°C for the sedimentary- and ultramafic-hosted talc formations, respectively, and 100°C for serpentine, suggesting that talcification and serpentinization of ultramafic rocks both occurred at nearly the same time with various stages. All data show that the talc occurrences are divided into two types based on their mode of formation. The first corresponds to a serpentinization stage within the ophiolites. The others are the neoformation products of sedimentary deposition, diagenetic and post-diagenetic processes, respectively. Sedimentary-hosted talc also seems to have inherited trace element and isotopic compositions from the parent ultramafic rocks.

Sepiolite–Palygorskite Occurrences in Turkey

Abstract Sepiolite–palygorskite occurrences and deposits in Turkey can be classified as sedimentary (marine and lacustrine), hydrothermal and pedogenic types based on their geological settings and mineralogical features. Marine types are formed within the evaporative clayey–sandy-carbonate rocks of Upper Cretaceous–Lower Miocene in the shallow-coastal lagoonal environment. Lacustrine types of Neogene age occur in nodules and beds containing either exclusively clays and/or carbonates. Vein sepiolite occurrences are developed within the serpentinites or volcanites, and are mostly regarded as hydrothermal in origin. Pedogenic palygorskites are the in situ minerals found in the modern soil, palaeosol, caliche (calcrete) and crusts. In all the cases, the genesis of sepiolite–palygorskite can be explained by two principal processes as mainly sedimentary neoformation (direct crystallization from solutions) and partly diagenetic transformation of other Mg-rich phyllosilicate and carbonate minerals (mainly saponite, dolomite and magnesite), rather than detrital inheritance. Concerning loughlinites, they are derived from volcanic glass as a result of diagenetic neoformation. The commercial deposits of sepiolite and palygorskite so-called special clays are commonly present in Turkey and estimated to be around a few million tons, but only sepiolitic clay is produced as thousand tons in small operations and used in a narrow range of industrial applications.

GEOCHEMISTRY OF MIXED-LAYER ILLITE-SMECTITES FROM AN EXTENSIONAL BASIN, ANTALYA UNIT, SOUTHWESTERN TURKEY

The Antalya Unit, one of the allochthonous units of the Tauride belt, is of critical, regional tectonic importance because of the presence of rifting remnants related to the break-up of the northern margin of Gondwana during Triassic time. Paleozoic — Mesozoic sedimentary rocks of the Antalya Unit consist mainly of calcite, dolomite, quartz, feldspar, and phyllosilicate (illite-smectite, smectite, kaolinite, chlorite, illite, chlorite-smectite, and chlorite-vermiculite) minerals. Illite-smectite (I-S) was found in all of the sequences from Cambrian to Cretaceous, but smectite was only identified in Late Triassic-Cretaceous sediments. R0 I-S occurs exclusively in early-diagenetic Triassic—Cretaceous units of the Alakırçay Nappe (rift sediments), whereas R3 I-S is present in late-diagenetic to low-anchimetamorphic Cambrian—Early Triassic units of the Tahtalıdag Nappe (pre-riftsediments). Kubler Index (KI) values and the illite content of I-S reflect increasing diagenetic grades along with increasing depth. Major-element, trace-element, rare-earth-element (REE), and stable-isotope (O and H) compositions were investigated in dioctahedral and trioctahedral smectites and I-S samples from the pre-rift and rift-related formations. Both total layer charge and interlayer K increase, whereas tetrahedral Si and interlayer Ca decrease from smectite to R3 I-S. Trace-element and REE concentrations of the I-S are greater in pre-rift sediments than in rift sediments, except for P, Eu, Ni, Cu, Zn, and Bi. On the basis of North American Shale Composite (NASC)-normalized values, the REE patterns of I-S in the pre-rift and rift sediments are clearly separate and distinct. Oxygen (δ18O) and hydrogen (δD) values relative to SMOW (Standard Mean Oceanic Water) of smectite and I-S reflect supergene conditions, with decreasing δ18O but increasing δD values with increasing diagenetic grade. Lower dD values for these I-S samples are characteristic of rift sediments, and pre-rift sediments have greater values. On the basis of isotopic data from these I-S samples, the diagenesis of the Antalya Unit possibly occurred under a high geothermal gradient (>35ºC/km), perhaps originating under typical extensional-basin conditions with high heat flow. The geochemical findings from I-S and smectites were controlled by diagenetic grade and can be used as an additional tool for understanding the basin maturity along with mineralogical data.

New Mineralogic Data and Implications for the Tectonometamorphic Evolution of the Alanya Nappes, Central Tauride Belt, Turkey

The Alanya Unit, consisting of three nappes, crops out in the Demirtas-Anamur area of the Tauride Belt and is related to the Alpine orogeny. The Mahmutlar nappe of Permian and pre-Permian age progressively evolved as indicated by 2M1 white K-mica, Mg-chlorite, and 1M biotite which are related to increasing metamorphism from its upper (phyllite, metasiltstone) to lower parts (biotite schist, staurolite-kyanite-garnet-mica schist). The b values of the white K-micas are characterized by a facies series of medium- to high-pressure metamorphism. The Sugözü nappe comprises garnet-mica schist with metabasite (eclogite, glaucophane schist) interbands and/or lenses composed of muscovite, chlorite, and rarely paragonite and illite-smectite. The crystallinity and b values of phengitic micas in the metapelites represent epizonal and medium-pressure facies conditions. The Yumrudag nappe of Pre-Permian-Triassic age is characterized by index minerals, such as chloritoid, paragonite, kaolinite/dickite, 1Tc pyrophyllite, and margarite. Epizonal 2M1 white K-micas with low b values indicate lower-pressure metamorphism. The mineralogic and geochemical signatures of these metasedimentary rocks indicate that the nappes were predominantly derived from different sources. The Mahmutlar nappe developed under a Barrovian-type, regional dynamothermal progressive metamorphism. The Sugözü nappe records an earlier high-pressure/low-temperature metamorphism that has been overprinted—together with the structurally overlying Mahmutlar nappe—by a later Barrovian metamorphic event. The Yumrudag nappe, on the other hand, is characterized by a metamorphic evolution with a typical counterclockwise P-T-t path in an extensional basin, such as those of the northern allochthonous Tauride units, indicating that its southward emplacement onto the other nappes was relatively late.

Very Low Grade Metamorphism of Upper Paleozoic–Lower Mesozoic Sedimentary Rocks Related to Burial and Thrusting in the Central Taurus Belt, Konya, Turkey

Metasedimentary and sedimentary rocks that represent the allochthonous Bolkardagi Unit crop out in the Central Taurus Belt. Devonian units include mainly slate, metadolomite, metadolomitic limestone, and metasandstone. Slates with slaty cleavage and chlorite-mica stacks are characterized by phyllosilicate, quartz, calcite, dolomite, feldspar, and goethite. Phyllosilicates consist of 2M1 and lesser amounts of 1M muscovite, IIb chlorite, pyrophyllite, paragonite. PM, C-V, C-S. rectorite, and dickite, and reflect conditions of the low epizone-anchizone. In the Carboniferous-Triassic units, limestone, clayey limestone, dolomitic limestone, marl, shale, and sandstone retaining primary textures are composed of calcite, dolomite, quartz,1Md illite, chlorite, and I-S, and locally smaller quantities of 2M1 muscovite, PM, paragonite, pyrophyllite, and rectorite. In contrast, the Triassic formation is made up of calcite, 1Md illite, I-S, kaolinite, smectite, chlorite, C-S, C-V, dolomite, and quartz. Textural and mineralogical data indicate that development of the diagenetic-metamorphic grade in the Central Taurus was related to sedimentary burial and thrusting; moreover, the metasedimentary rocks were metamorphosed in a typical anticlockwise P-T-t pathway in an extensional setting.

METAMORPHIC-HOSTED PYROPHYLLITE AND DICKITE OCCURRENCES FROM THE HYDROUS Al-SILICATE DEPOSITS OF THE MALATYA-PÜTÜRGE REGION, CENTRAL EASTERN ANATOLIA, TURKEY

Hydrous Al-silicate deposits are found to the south of Pütürge in Malatya city, Turkey. The surrounding rocks consist of mylonitic granitic gneiss overlain by muscovite gneiss with kyanite-bearing metabasic schist lenses on top which are cut by silica veins containing prismatic tourmaline and speculante. Pyrophyllite is found within kyanite gneisses overlying the granitic gneisses. Fibrous, platy pyrophyllite is developed along the edges and cleavage planes of kyanite, whereas platy bunches of dickite occur as replacements of the relict kyanites as well as crack- and pore-fillings. Rocks forming the hydrous Al-silicate deposit contain 2M1 pyrophyllite, alunite, topaz, paragonite, dravite, dumortierite, chlorite and epidote as early hypogene minerals, and 2M1 dickite, diaspore, gibbsite, speculante, goethite and crandallite/goyazite as late hypogene minerals. On the basis of fluid inclusion and stable isotope data, it is estimated alterations to pyrophyllite and kaolinite occurred at temperatures are of 150 and 100°C, respectively, the minerals being formed by meteoric waters interacting with metamorphic rocks. Trace and REE variations are highly distinctive in terms of enrichment of most trace elements in pyrophyllite, whereas REEs are clearly abundant in dickite, indicating different conditions during formation such as early and late hypogene processes. The pyrophyllitic alteration took place in the late Cretaceous (69–71 Ma), whereas kaolinization occurred later.

Metamorphic evolution of the Karakaya Complex in northern Turkey based on phyllosilicate mineralogy

The Triassic Karakaya Complex (KC) of the Sakarya Composite Terrane in northern Turkey is traditionally subdivided into two units. The Lower Karakaya Complex (LKC) consists of a tectonic mélange with blocks of metabasic rocks, metacarbonates, meta-arenites and metapelites that have been affected by high pressure/low temperature metamorphism. It is followed by a low pressure/low temperature metamorphic overprint; the latter is the only metamorphic event in some tectonic slivers of the LKC. The Upper Karakaya Complex (UKC) units are primarily composed of diagenetic to low-grade metamorphic rocks, comprising Late Permian and Triassic cherts and blocks of OIB-type volcanic rocks interfingering with Anisian limestones. LKC slide-blocks of variable sizes are frequently observed within the UKC. Phyllosilicates of LKC and UKC were examined for their abundance, crystallinity, polytype and b cell dimension. Trioctahedral chamositic chlorites have IIb polytype and phengites 2 M1 polytypes in the LKC units and 2 M1 + 1 M + 1Md polytypes of phengitic dioctahedral illites in the UKC units. Kübler index data correspond to the low anchizone and epizone for the LKC units, and to the high diagenesis-low anchizone, and in part to the epizone for the UKC units. The b values of illites are consistent with a high-pressure facies series for the LKC, but only intermediate-pressure facies for the UKC. According to textural features, mineral paragenesis, clay transformations, index minerals, and b values, the lower-middle parts of the LKC represent an accretional tectonic setting, whereas the UKC units reflect pressure temperature conditions of an extensional basin affected by high heat flow.

A New Discovery of the Cretaceous/Tertiary Boundary from the Tethyan Belt, Hekimhan Basin, Turkey: Mineralogical and Geochemical Evidence

A Cretaceous/Tertiary (K/T) boundary location within the Tethyan region (present Mediterranean area) has been discovered in the Hekimhan basin, Malatya, Turkey. The K/T transition in a 1.65-m-thick...