Selahattin Kadir

THE OCCURRENCE AND GENESIS OF CLAY MINERALS ASSOCIATED WITH QUATERNARY CALICHES IN THE MERSIN AREA, SOUTHERN TURKEY

Caliche in various forms, namely powdery, nodule, tube, fracture-infill, laminar crust, hard laminated crust (hardpan), and pisolitic crust, is widespread in the Mersin area in southern Turkey. It generally occurs within and/or over the reddish-brown mudstone of the Kuzgun Formation (Tortonian, Miocene) and alluvial red soils of the Quaternary. The mineralogical distribution along representative caliche profiles was examined by X-ray diffraction, scanning electron microscopy, differential thermal analysis-thermal gravimetry, and chemical techniques. Calcite is the most abundant mineral associated with minor amounts of palygorskite in caliche samples, whereas smectite is prevalent mainly in the reddish-brown mudstone and alluvial red soils of the caliche parent materials and is associated with appreciable amounts of palygorskite. These minerals are also accompanied by trace amount of illite, quartz, feldspar, and a poorly crystalline phase. Palygorskite fibers and fiber bundles were developed authigenically on euhedral or subhedral calcite crystals of the caliche units and at the edges of smectite flakes in the caliche host-rocks or sediments. Intense, continuous evaporation of subsurface soil-water resulted in an increase in pH and the dissolution of detrital smectite within the red mudstones and alluvial red soils that enclose the isolated caliche forms, and caused an increase in the Al+Fe and Mg/Ca ratio, favoring the formation of palygorskite under alkaline conditions. The calcium required for caliche formation may have originated from eolian dust, detrital carbonate minerals, and/or other caliche materials, which are dissolved by carbonic acid.

GEOLOGY, MINERALOGY AND ORIGIN OF CLAY MINERALS OF THE PLIOCENE FLUVIAL-LACUSTRINE DEPOSITS IN THE CAPPADOCIAN VOLCANIC PROVINCE, CENTRAL ANATOLIA, TURKEY

The Güzelöz-İncesu Plateaus are situated in the central and eastern parts of the Cappadocian volcanic province (central Anatolia). This province contains many ignimbrite levels, andesite, basalt intercalated with several paleosols, calcrete, carbonate, fluvial sediments, diatomaceous clayey sediments and pyroclastic sedimentary levels. The presence of mottling, sesquioxide, root traces, rhizoids and burrows in continuous, finely bedded and laminated sediments, paleosols, calcrete, the occurrence of bone- and teeth-bearing reworked pyroclastic materials, and the description of the lithofacies in the study area indicate fluvial and shallow-lake environments. These environments are dominated by smectite and illite, with traces of kaolinite, associated mainly with plagioclase, K-feldspar, quartz, calcite, opal-CT, pyroxene (diopside, rare hypersthene), and locally trace amounts of gypsum and sepiolite. Smectite predominates in paleosols and calcrete units, and generally increases upwards in the profiles, coinciding with a gradual increase in the degree of alteration. Partial to complete alteration of plagioclase, K-feldspar, pyroxene and partial devitrification of glass-shard particles in pyroclastic rocks, development of microsparitic to sparitic cement comprising euhedral rhombic calcite crystals between irregular clay nodules in paleosol and calcrete samples, along with the occurrence of dogtooth-type sparitic crystals in fractures, desiccation cracks and geopetal-type fenestrae, indicate alternating periods of drought and wet, resulting in the development of paleosols and calcretes. Micromorphological development of spongiform smectite on mainly relict feldspar and, locally, on glass shards, indicates an authigenic origin, whereas illite formed either authigenically or by conversion of smectite to illite-smectite.

MINERALOGY, GEOCHEMISTRY, AND ORIGIN OF BENTONITE IN UPPER CRETACEOUS PYROCLASTIC UNITS OF THE TİREBOLU AREA, GİRESUN, NORTHEAST TURKEY

Widespread alteration in the Upper Cretaceous pyroclastic units of the Tirebolu (Giresun) area, NE Turkey, has resulted in significant occurrences of bentonite with economic potential. No detailed geological, mineralogical, or geochemical characterization of these occurrences has been carried out to date. The aim of this study was to describe the geological background, the mineralogical, chemical, and stable-isotope characteristics of the bentonite, and major aspects of their formation, e.g. type and source of low-temperature alteration, mass balance, chemical evolution of the smectites, and geochemistry of major and trace elements. The bentonite contains abundant smectite with occasional kaolinite and mordenite, volcanogenic feldspar, quartz, biotite, hornblende, glass shards, and pumice fragments, along with the diagenetic minerals, opal-CT, and, in some locations, calcite. X-ray diffraction patterns of the clay fractions exhibit characteristics of pure montmorillonite and beidellite-type smectite. Micromorphologically, the smectite exhibits a honeycomb texture, the kaolinite occurs in both vermiform and irregular platy forms, and the mordenite occurs in fibrous form. All of these minerals are edged with devitrified volcanic glass and resorbed feldspar. Chemically, the smectites are Ca-smectite. Geochemical data indicate that alteration of the pyroclastic units took place under suboxic and anoxic environmental conditions during bentonite formation. Field observations and mineralogical, geochemical, oxygen, and hydrogen isotopic data indicate that the alteration of feldspar and volcanic glass in the pyroclastics by mixed meteoric and sea water in a shallow marine environment under alkaline and acidic conditions, respectively, controlled by environmental Al, Ca, and Na concentrations, resulted in the formation of authigenic smectite, mordenite, and kaolinite. A large Ca content in the smectite originated from surrounding units, which resulted in high alkalinity; Mg originated from seawater.

Dolocretes and associated palygorskite occurrences in siliciclastic red mudstones of the Sariyer Formation (Middle Miocene), southeastern side of the Çanakkale strait, Turkey.

The origins of dolocrete and associated palygorskite in the Çanakkale region of Turkey have been little studied, but are of fundamental importance for a more complete understanding of the mineralogy of this region. The present study was undertaken in order to narrow this gap. Siliciclastic red mudstones within alluvial-fan deposits of the Middle Miocene Sariyer Formation locally contain dolocretes in various forms (powdery, nodular, and fracture-filling) and scarce matte-brown, authigenic clay lenses. The mineralogical characteristics of dolocrete and authigenic clay lenses were examined using polarized-light microscopy, X-ray diffraction, differential thermal analysis and thermal gravimetry, scanning-electron microscopy, and infrared spectroscopy, as well as by chemical and isotopic methods. These analyses indicate that the dolocretes are indeed predominantly dolomite, coexisting with variable amounts of palygorskite. The authigenic clay lenses are composed mainly of palygorskite. Dolomite appears as euhedral crystals, whereas palygorskite developed authigenically as interwoven fibers on and between resorbed dolomite crystals, rimming euhedral crystals, and as fiber bundles (where dolomite ± magnesite is absent). The stable-isotope values and some petrographic features, such as alveolar texture and dolomite needles, support a pedogenic origin for the dolocretes. In the initial stage, dolomite formed by replacement of siliciclastic red mudstones and/or by precipitation from percolating soil-derived water in a near-surface setting. Subsequently, palygorskite either precipitated on the dolomite crystals from relatively more evaporative water, replaced the host-rock mudstone in the presence of Al + Fe, or formed directly from solution where the Ca/Mg ratio decreased and the Al + Fe increased. In view of the large Cr and Ni contents of the bulk-rock samples, the elements required for the crystallization of dolomite and palygorskite (namely Mg, Ca, Si, Al, and Fe) may have been supplied by weathering of ophiolitic rocks that crop out in the area.

GEOLOGY AND MINERALOGY OF LATE MIOCENE CLAYEY SEDIMENTS IN THE SOUTHEASTERN PART OF THE CENTRAL ANATOLIAN VOLCANIC PROVINCE, TURKEY

Late Miocene clayey sediments were deposited in lake-margin and shallow-lake environments of the southeastern Central Anatolian Volcanic Province (CAVP). Yellow to red mudstone, alternating with thin beds of conglomerate and sandstone in the Mustafapaşa Formation, is overlain by altered white Cemilköy ignimbrite. Grain size fines upward in each sequence (conglomerate, sandstone, and mudstone). The occurrence of reddish coloration upward, ripple marks, desiccation cracks, plant rootlets and remnants, and the development of initial-stage paleosols in association with smectite reveal that the area underwent alternating periods of siliciclastic and volcaniclastic sediment supply (wet) and drying. Micromorphologically, the development of spongy smectite in mudstone of the Mustafapaşa Formation and vermiform kaolinite in the Cemilköy ignimbrite on resorbed detrital feldspar and devitrified glass reveals in situ precipitation driven by dissolution and precipitation mechanisms. In addition, alteration of these sediments may have resulted in the depletion of soluble alkaline elements, such as Ca, Na, and K, from the ignimbrite downward into the Mustafapaşa Formation. Alternatively, the leaching of these elements — due to the hydrologically open system of the lake environment — may have resulted in the enhancement of Al+Fe/Si-favored precipitation of kaolinite in an acidic environmental condition, namely, of the altered Cemilköy ignimbrite at the top of the profile of the Mustafapaşa Formation, and of smectite in an alkaline setting within lower-level sediments where carbonate minerals were lacking. The coexistence of smectite with accessory illite indicates that illitization occurred via release of K and Al during excess desorption of feldspar. Large Ni and Co values in mudstone samples, and Fe oxidized and partly chloritized pyroxene and hornblende, indicate that the basin was also affected by ophiolite-related supply.

MINERALOGICAL AND GEOCHEMICAL CHARACTERISTICS AND GENESIS OF HYDROTHERMAL KAOLINITE DEPOSITS WITHIN NEOGENE VOLCANITES, KÜTAHYA (WESTERN ANATOLIA), TURKEY

The Kütahya kaolinite deposits are the most important source of raw materials for the ceramics industry in Turkey. To date, no detailed mineralogical or geochemical characterizations of these materials have been carried out; the present study aims to fill that gap. The Kütahya kaolinite deposits formed by alteration of dacite and andesite tuffs related to Neogene volcanism whichwas associated withe xtensional tectonics. The kaolinite deposits contain silica and Fe- and Ti-bearing phases (pyrite, goethite, and rutile) in vertical and subvertical veins that diminish and then disappear upward. Mineralogical zonation outward from the main kaolinite deposit is as follows: kaolinite ± smectite + illite + opal-CT + feldspar; feldspar + kaolinite + quartz + smectite + illite; quartz + feldspar + volcanic glass. The veins and mineral distributions demonstrate that hydrothermal alteration was the main process in the development of the kaolinite deposits of the area. The very sharp, intense, diagnostic basal reflections at 7.2 and 3.57 Å, as well as non-basal reflections, well defined pseudohexagonal to hexagonal crystallinity with regular outlines, ideal differential thermal analysis-thermal gravimetric curves, and ideal, sharp, infrared spectral bands indicate well crystallized kaolinite. Micromorphologically, the development of kaolinite plates at the edges of altered feldspar and devitrified volcanic glass indicates an authigenic origin. Lateral increase in (SiO2+Fe2O3+MgO+Na2O+CaO+K2O)/(Al2O3+TiO2) from the center of the kaolinite deposit outward also indicates hydrothermal zonation. Enrichment of Sr in altered and partially altered rocks relative to freshvolca nic-rock samples demonstrates retention of Sr and depletion of Rb, Ba, Ca, and K during hydrothermal alteration of sanidine and plagioclase within the volcanic units. In addition, depletion of heavy rare earth elements (HREE) relative to light rare earth elements (LREE) in the kaolinized materials may be attributed to the alteration of hornblende. The negative Eu anomaly suggests the alteration of feldspar by hydrothermal fluids. The isotopic data from kaolinite and smectite indicate that hydrothermalalteration processes developed at 119.1–186.9°C and 61.8–84.5°C, respectively. Thus, the kaolinite deposits formed by hydrothermal alteration of volcanic glass, feldspar, and hornblende by a dissolutionprecipitation mechanism which operated under acidic conditions within Neogene dacite, andesite, and tuffs.

MINERALOGY, GEOCHEMISTRY, AND GENESIS OF MUDSTONES IN THE UPPER MIOCENE MUSTAFAPAŞA MEMBER OF THE ÜRGÜP FORMATION IN THE CAPPADOCIA REGION, CENTRAL ANATOLIA, TURKEY

The Upper Miocene Mustafapas-a member of the Ürgüp Formation in the Cappadocia region consists predominantly of mudstones, sandstone, and conglomerate lenses with ignimbrite and basalt intercalations. The mudstones are an important source of raw materials for the ceramics industry in Turkey. A detailed mineralogical, geochemical, and genesis study of these materials has not been performed previously and the present study aims to fill that gap. The characteristics of mudstones of the Mustafapas-a member were examined using X-ray diffraction, scanning and transmission electron microscopy, energy dispersive spectroscopy, and chemical analyses. Weathering products of ophiolitic and pyroclastic rocks were transported into the tectonically subsided zone where they accumulated as fluvial and lacustrine deposits.Weathering in the mudstones is evidenced by smectite flakes associated with relict pyroxene, rod-like amphibole, feldspar, and volcanic glass. The chemical composition of mudstones and their distribution suggest that the depositional basin was supplied with ophiolitic material in the south and ignimbrite material in the north. This interpretation is based on an increase in the quantity of feldspar and opal-A and a decrease in the Fe2O3+MgO/Al2O3+SiO2 ratio from south to north in the study area. The northward increases in Light Rare Earth Elements/Heavy Rare Earth Elements, La/Yb, Zr/Ni and Zr/Co ratios and Nb, Ba, Rb, Sr, and Eu in the mudstones of the Mustafapas-a member with positive Eu anomalies suggest that the Fe, Mg, Al, and Si required to form smectite were supplied mainly through the decomposition of amphiboles, pyroxenes, feldspars, and volcanic glass during weathering processes. After the deposition of mudstones, relative increases in evaporation-controlled Ca, K, and Al in pore water favored the partial dissolution of Ca-bearing minerals and smectite flakes and in situ precipitation of calcite and traces of illite fibers under alkaline micro-environmental conditions during early diagenesis.

Mineralogy, geochemistry and genesis of smectite in pliocene volcaniclastic rocks of the doganbey formation, Beyşehir Basin, Konya, Turkey

Pliocene volcaniclastic lacustrine rocks of the Doğanbey formation in the Beyşehir region (central Anatolia) are composed of organic-matter-bearing claystone, clastic units and dolomite interbeds, suggesting an anaerobic, shallow swampy, lacustrine depositional environment. The depositional environment was subjected to periodic climatic change during which diagenesis occurred, and smectite, and locally palygorskite, were precipitated. Smectite flakes formed authigenically on feldspar and palygorskite fibers between dolomite rhombs and at the edges of smectite flakes. Increases in leaching of Na, K, Sr, Ba and Rb, increasing Al/Si ratios, and Fe with increasing degree of alteration reveal that hydration of volcaniclastic grains (feldspar, glass) by meteoric water — determined from O and H isotopic values — was the main cause of precipitation of beidellite and montmorillonite based on the tetrahedral charge/octahedral charge ratio, with average structural formulae of (Si7.72Al0.28)(Al3.20Fe0.53Mg0.25 Mn0.02Ti0.04), and (Si7.88Al0.13)(Al3.18Fe0.53Mg0.18Mn0.02Ti0.05)(Ca0.11Na0.11K0.09), respectively. Therefore, the Doğanbey-area smectite is presumed to have formed by chemical weathering and dissolution-precipitation from feldspar and glass during diagenesis; palygorskite formed by direct precipitation from Mg-rich solutions during dolomitization, and by transformation from smectite in an alkaline lacustrine environment.

COMPOSITION AND GENESIS OF THE NICKEL-CHROME-BEARING NONTRONITE AND MONTMORILLONITE IN LATERITIZED ULTRAMAFIC ROCKS IN THE MURATDAĞI REGION (UŞAK, WESTERN ANATOLIA), TURKEY

Widespread lateritized ultramafic rocks in the southern part of the Muratdağı region of Turkey constitute a significant source of Ni-Cr-bearing ore with economic potential. However, no mineralogical or geochemical characterizations of these important materials have been performed previously. The aim of the present study was to describe the mineralogy, geochemistry, and genesis of Ni-Cr-bearing smectite in garnierite and ferruginous saprolite associated with the lateritized ophiolite-related ultramafic rocks. The lateritic zones are well developed over serpentinized harzburgitic mantle peridotites. The lateritized units and related bedrocks were examined using polarized-light microscopy, X-ray diffraction, scanning and transmission electron microscopies, and chemical and isotopic methods. The garnierite-containing saprolites are enriched in smectite, Fe-(oxyhydr)oxide phases, and opal-CT. Micromorphological images revealed that flaky smectite and, locally, Fe-rich particles, alunite, gypsum, gibbsite, and sulfur crystals developed along the fractures and dissolution voids. The development of saprolite demonstrates chemical weathering. The presence of silicified and Fe-(oxyhydr)oxide phases associated with gypsum, alunite, and local native sulfur in vertical and/or subvertical fractures and fault infillings are indicative of hydrothermal processes along the extensional, tectonically related fault systems. Chemical weathering and hydrothermal processes, which probably started during the Oligocene and Miocene, led to the formation of nontronite, Fe-bearing montmorillonite, and local Fe-rich kaolinite. Nickel and Cr are concentrated significantly in the saprolite zone and are positively correlated with Fe2O3 content, which is controlled by the formation of nontronite, montmorillonite, and Fe-(oxyhydr)oxide phases. Nickel-Cr-bearing nontronite and montmorillonite precipitated from alkaline water as a result of the increasing (Fe2O3+Al2O3+Cr2O5+Ni+Co)/(MgO+SiO2) ratio under the control of both chemical weathering and hydrothermal processes. The Fe and Mg (associated with Ni and Cr) required for the formation of smectite were supplied by solutions from both chemical weathering and hydrothermal alteration of Ni-Cr-bearing olivine and pyroxene in the harzburgitic bedrock; the Al was supplied by schists, granite, and volcanic units.

MINERALOGICAL AND GEOCHEMICAL CHARACTERISTICS AND GENESIS OF THE GÜZELYURT ALUNITE-BEARING KAOLINITE DEPOSIT WITHIN THE LATE MIOCENE GÖRDELES IGNIMBRITE, CENTRAL ANATOLIA, TURKEY

The Güzelyurt kaolinite deposit is an important source of raw material for the ceramics industry in Turkey. No detailed mineralogical or geochemical characterizations of this deposit have been undertaken previously and these were the goals of the present study. The Güzelyurt alunite-bearing kaolinite occurs along a fault zone in the Late Miocene Gödeles ignimbrite, which consists of dacitic and andesitic tuffs. Horizontal and vertical mineralogical zonations with gradual transitions were observed within the alteration zone. The inner kaolinite, alunite, and 7 Å halloysite zones progress horizontally outward to a smectite zone; and native sulfur- and cinnabar-bearing alunite with 7 Å halloysite and porous silica zones increase as one progresses up through the profile. Fe-(oxyhydr)oxide phases associated with native sulfur and cinnabar demonstrate that multiple hydrothermal-alteration processes resulted in kaolinization and alunitization of the deposit. The kaolinization of feldspar, Fe-(oxyhydr)oxidation of hornblende and mica, the presence of kaolinite as stacked and, locally, book-like forms, and of 7 Å halloysite tubes, and smectite flakes as a blanket on altered volcanic relicts indicate an authigenic origin for this deposit. The leaching of Si + Mg + K and Ba + Rb, the retention of Sr, the enrichment of light rare earth elements relative to the heavy rare earth elements, and the negative Eu anomalies suggest that fractionation of plagioclase and hornblende occurred within the volcanics. The oxygen- and hydrogen-isotopic values of the kaolinite, 7 Å halloysite, smectite, and smectite + kaolinite fractions reflect a steam-heated environment at temperatures in excess of 100°C. An increase in the δD and δ18O values of 7 Å halloysite relative to kaolinite suggests its formation under steam-heated magmatic water, the mixing of steam and meteoric water near the surface, and evaporation. The oxygen- and sulfur-isotopic compositions of alunite suggest the direct influence of steam-derived sulfur. The Güzelyurt alunite-bearing kaolinite deposit is inferred to have formed after an increase in the (Al±Fe)/Si ratio and the leaching of alkali elements, which are driven by the sulfur-bearing low-temperature hydrothermal alteration of feldspar, hornblende, and volcanic glass under acidic conditions within the Neogene dacitic and andesitic tuffs.