O. Isik Ece

Diagenetic transformation of magnesite pebbles and cobbles to sepiolite (Meerschaum) in the Miocene Eskisehir lacustrine basin, Turkey

Magnesite pebbles in Miocene lacustrine conglomerates in northwest Turkey have been partially to totally replaced by sepiolite. Only 5% of the magnesite pebbles have been converted to essentially pure sepiolite; the rest represent mixtures of magnesite and sepiolite. This process of sepiolitization is documented by X-ray diffraction (XRD), chemical, scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques. These techniques show that the sepiolitization proceeds from the rim towards the core of the pebbles. The conglomerates, with pebbles of magnesite and ultramafic rocks, were deposited in a near-shore environment on the margin of a large Miocene lake with an ophiolitic substratum. The diagenetic transformation of magnesite to sepiolite is believed to have been caused by the interaction of mixed meteoric and lacustrine waters, which were undersaturated with respect to magnesite. The sepiolitization occurred during the highstands of the lake, when the near-shore conglomerates were flooded by the silica-rich lake waters. The pH of the water during the sepiolitization was probably on the order of 10.5–11.5. The sedimentary magnesite beds in the center of the Miocene basin show no sepiolitization, which is explained by the presence of pore water saturated with respect to magnesite.Magnesite pebbles in Miocene lacustrine conglomerates in northwest Turkey have been partially to totally replaced by sepiolite. Only 5% of the magnesite pebbles have been converted to essentially pure sepiolite; the rest represent mixtures of magnesite and sepiolite. This process of sepiolitization is documented by X-ray diffraction (XRD), chemical, scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) techniques. These techniques show that the sepiolitization proceeds from the rim towards the core of the pebbles. The conglomerates, with pebbles of magnesite and ultramafic rocks, were deposited in a near-shore environment on the margin of a large Miocene lake with an ophiolitic substratum. The diagenetic transformation of magnesite to sepiolite is believed to have been caused by the interaction of mixed meteoric and lacustrine waters, which were undersaturated with respect to magnesite. The sepiolitization occurred during the highstands of the lake, when the near-shore conglomerates were flooded by the silica-rich lake waters. The pH of the water during the sepiolitization was probably on the order of 10.5–11.5. The sedimentary magnesite beds in the center of the Miocene basin show no sepiolitization, which is explained by the presence of pore water saturated with respect to magnesite.The magnesite-sepiolite replacement process is chemically modeled as a 4-stage process from dimerization to polymerization.

Effect of the adsorption of non-ionic polymer poly(vinyl)pyrolidone on the rheological properties of Na-activated bentonite

Rheological properties of Na-activated bentonite were studied after adding poly(vinyl)pyrolidone (PVP). The experimental results have been discussed considering bentonite types and concentrations of additives PVP. In the use of the bentonite clay sludges in industry, the addition of PVP polymer is recommended if an increase in viscosity is desired.

ALTERATION OF VOLCANIC ROCKS AND GENESIS OF KAOLIN DEPOSITS IN THE ŞILE REGION, NORTHERN ISTANBUL, TURKEY. I: CLAY MINERALOGY

The Şile Region contains discontinuous, cyclic, thin coal beds and industrial clay deposits that were accumulated in lacustrine basins which received extensive volcanoclastic sediments due to transport of highly weathered calc-alkaline volcanic rocks. The Sülüklü area has the largest kaolin deposit in this region. Cyclic kaolinization depended on the degree of leaching of Si and alkalis in cyclic swamp environments and, therefore, kaolinite contents vary in each discontinuous lens-shaped clay bed and underclay within the basin. The kaolins comprise disordered kaolinite, illite, smectite, gibbsite, quartz, pyrite, anatase, K-feldspar and goethite. Depth-related changes in the distribution of clay minerals, associated with coal beds, are indicative of organic acid-mineral reactions. Kaolinite crystallization initiated at the edges of sericitic mica sheets in the form of composite kaolinite stacks. The small size (<1 µm), morphology and poor crystallinity of kaolinite crystals suggest that kaolinization post dated transportation. Primary or secondary origins of particles can be determined from the stacking sequences of kaolinite particles using high-resolution transmission electron microscopy images. Kaolinite stacks always contain a small amount of illite, but smectite is only present in the middle and upper levels. Gibbsite is a main constituent of refractory bauxitic clays locally found as discontinuous lenses and exploited from the lower level of the basin.Genesis of kaolin deposits took place in two stages: first, there was in situ weathering of the oldest andesitic agglomerates, tuffs and ashes at the base of the lacustrine basin coupled with discharge of shallow thermal waters which were initiated by local hydrothermal alteration; second, surface weathering enhanced transportation of altered rocks from the surrounding hills into the lacustrine basin. Kaolinization took place in cyclic swamp environments, as indicated by the presence of cyclic thin- to thick-bedded coals that provided necessary humic and fulvic acids for the post-depositional alteration of altered volcanic rocks to kaolin in dysaerobic, relatively low-pH conditions in saturated groundwater zones.

Influences of Electrolytes, Polymers and a Surfactant on Rheological Properties of Bentonite–Water Systems

Characteristic rheological properties, such as viscosity, shear stress, yield point, gel strength and thixotropy, of natural Ca- bentonite and Na-peptized bentonite were studied after adding LiCl, KCl, CaCl2, MgCl2·6H2O electrolytes; (NaPO3)n, polyvinyl pyrolidone (PVP) polymers and an anionic surfactant (linear alkyl benzene sulphonate, LABS). Changes in flow properties under the influence of various additives at different quantities were investigated in these slurries. The experimental results are discussed in terms of bentonite forms, types and concentrations of additives and influence of exchangeable cations. Bivalent and monovalent cations display entirely different rheological properties in two groups of muds. Furthermore, the difference in the degree of activity of PVP polymer on the viscosity of two mud systems depend on the clay mineral structure. The slurry prepared with Na-bentonite contains a minimum number of tactoids and a maximum number of sheet-bearing clay particles, which reduces the surface area of the clay minerals and increases viscosity by adding PVP polymer.

Influence of Clay Surface Modification on Morphology and Rheology of Polyethylene Glycol/Montmorillonite Nanocomposites

The effects of surface modification of Na-montmorillonite (Na-MMT) on morphology and the rheological properties of polyethylene glycol/ organoclay nanocomposites are investigated. Dodecyltrimethylammonium bromide (DTABr) is used to modify the clay surface. Adsorption of DTABr on Na-MMT is monitored by zeta potential measurements. From zeta potential measurements, three DTABr concentrations, 1 × 10—3, 7.5 × 10— 3, and 5 × 10—2 mol/L, are chosen to fabricate the polyethylene glycol/organoclay composites. The morphology of three sets of organoclays (OMMT1, OMMT2, and OMMT3) is studied by X-ray diffraction (XRD) technique. The increase of basal spacing is found to be 0.2 nm as the DTABr concentration is increased to 7.5 × 10— 3 mol/L. The rheological properties of polyethylene glycol (PEG)/ organoclay nanocomposites are studied for three organoclays at different PEG concentrations. All nanocomposites show Bingham plastic flow behavior. The OMMT3 shows maximum viscoelastic properties in the polymer matrix. The morphology and electrokinetic properties of the PEG/organoclay nanocomposites are also investigated.

Clay mineralogy and occurrence of ferrian smectites between serpentinite saprolites and basalts in Biga Peninsula, Northwest Turkey

The clay mineralogy of an oxisol-saprolite overlying serpentinite and underlying basalt was studied with different techniques to evaluate the clay mineral transformation that occurred and to understand the origin of Fe3+-rich smectite. The saprolite zone of the oxisol, up to 30 m thick, contains smectites of the montmorillonite-beidellite and montmorillonite-nontronite series, as well as illite, chlorite, talc, and goethite or amorphous oxyhydrates. Illite is mainly concentrated in the upper 50 cm thick zone underlying the basalt layer and chlorite-content increases toward altered serpentinite at the base. Minor amounts of nontronite formed mostly toward westward exposures where the hot contact layer between serpentinite and basalt is only 20 cm thick. Greene-Kelly Li-tests revealed that all samples contain montmorillonite, but one sample shows the presence of a minor amount of beidellite.Parent rocks are a mixture of mainly mica schist (the source of beidellite), and minor serpentinite in different percentages and laterally distributed. These rocks were intensely weathered under humid climatic conditions. Silica was concentrated as amorphous transparent (pure silica) cobbles and milky quartz pebbles, and originated from geothermal solutions rising through the Ovaclk thrust fault. The Mg partly formed chlorite. Ferrian smectites in serpentinites were derived obviously from the Mg-rich minerals but Mg is lost much more rapidly than Si during the formation of the clay deposit. The structural formula of the most Fe-rich smectite samples from the study area is (Si6.60−7.10Al1.40−0.90)(Al2.54−1.22Mg0.32−0.92Fe3+1.18−1.68−Ti0.06−0.04)(Ca0.16−0.10Na0.02K0.02−0.12)O20(OH)4. This composition is within the range recorded for the ferrian montmorillonite-beidellite series, with very little vermiculite forming the oxisol-vertisol horizon.

Fe (super 3+) -rich montmorillonite-beidellite series in Ayvacik bentonite deposit, Biga Peninsula, Northwest Turkey

The Ayvacık bentonites, products of Miocene calc-alkaline volcanic rocks, are composed of smectite of the montmorillonite-beidellite series. Fault-related hydrothermal solutions have altered andesitic rocks to dioctahedral smectites. Differences in the micro-morphology of the two end-members are distinguished by scanning electron microscopy (SEM) studies. The beidellite particles are of delicate ribbons and rosette habits, whereas montmorillonite particles are very thin, curled sheets and flakes. Clay size (<2 µm) fractions contain (in wt. %) 54.90–56.80 SiO2, 19.65–28.54 Al2O3, 0.45–6.28 Fe2O3, 0.10–1.72 CaO, 0.80–4.15 MgO, 0.55–1.88 K2O, and 0.08–1.15 Na2O, which confirm that the beidellites are Fe-rich (5.06–6.28 wt. %), except for one sample (0.45 wt. % Fe2O3). The Greene-Kelly test (Li-saturation and heating) gave very good results for the measurement of the d(001) of the two end-members. Nickel, Ti, and Cr enrichment in smectite is related to the chemical composition of hydrothermal solutions that passed through the ophiolite complex.

Occurrence and properties of natron in the Miocene lacustrine Beypazari basin, Turkey

Natron, Na 2 CO 3 .10H 2 O, is a rarely forming evaporite mineral, which precipitates under the unique physicochemical conditions of Na wt. %, temperature and HCO 3 /CO 3 . Natron is observed in the upper parts of the lower trona level of the Beypazan Neogene volcanosedimentary sequences, where exist two trona beds between 260 m and 285 m depths. In this study, natron and some other soda minerals were examined by detailed geochemical, physicochemical and experimental studies. Euhedral natron crystals were determined sporadically within sedimentary beds. Based on our studies, it is postulated that white, soft and platy-fibrous natron minerals formed in the microenvironments within the rhythmic series of marls and claystones, are precipitated from pore solutions under the conditions of low temperature and high CO 3 /HCO 3 ratio during the end of the first precipitation of the trona deposits. The contents of the trace elements were measured using wet chemical analyses; XRD, DTA and SEM techniques were performed, and the results were evaluated based on the formation conditions of the mineral.

Varying depositional environments of gypsum successions in the Upper Miocene Eskişehir-Sivrihisar lacustrine basin, NW Turkiye

The basement rocks of Eskisehir-Sivrihisar basin are made of Upper Paleozoic metamorphic rocks and Upper Cretaceous ophiolite complex. These rocks are overlain by Middle Miocene sedimentary rocks the base. Upper Miocene-Pliocene stratigraphic succession consists of basal conglomerates, sandstones, claystones, limestones, dolomites and tuffs are thinly interbedded with cyclic evaporites. The main clay mineral assemblage consists of smectite, illite and sepiolite that are enriched in different percentage in different horizons. The Upper Miocene-Pliocene stratigraphic succession consists of alterations of gypsum, clayey carbonates and unconsolidated very soft dolomite beds, which are conformably underlain by sepiolite-bearing clayey carbonates and disconformably overlain by alluvium and conglomerate series of Pleistocene age. The Upper Miocene unit includes three different facies, based on sedimentary properties of gypsum from the base to the top; (I) laminated gypsum beds are thinly interbedded with dolomites and green clays; (2) gypsum rosettes within thin reddish and greenish clays and carbonates; and (3) scattered gypsum mainly within carbonates. Gypsums had been deposited in somewhat different depositional conditions in the same basin where multi-periodic evaporative episodes, ranging from saline to schizohaline environments, had been involved. During these episodes, under high Eh-pH intervals and high salinity conditions, three different types of gypsum formations had been developed in a meromictic-type lake under the influence of varying paleoclimatologic conditions and pore water chemistry of brines. All these gypsum morphologies respectively reflect the different conditions of environments of deposition in a Miocene playa lake basin: (1) subaqueous environments in playa lakes with short evaporation episodes; (2) marginal swamps with cyclic fluctuation of lake level; and (3) extended closed-lake with evaporatic lake water. These different gypsum morphologies are associated with distinctive sedimentary subfacies, which are also primarily related to cyclic climatic changes, alternating semi-arid and evaporite conditions, fluctuation of lake water level and sulphate input in the chemistry of lake water from runoff and hydrothermal source adjacent to basin.