Muhsin Eren

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.

Kilop Cretaceous Hardground (Kale, Gümüshane, NE Turkey):description and origin

Abstract A hardground surface is well exposed in the Kilop area of Kale (Gumushane, NE Turkey) which forms part of the Eastern Pontides. Here, the hardground is underlain by shallow water Lower Cretaceous limestones, and overlain by Upper Cretaceous red limestones/marls which contains a planktonic microfauna including Globotruncanidae. In the field, the recognition of the hardground is based on the presence of extensive burrows (especially vertical burrows), the encrusting rudistid bivalve Requienia , neptunian-dykes with infills of pelagic sediments and synsedimentary faults. Skolithos and Thalassinoides -type burrows are present. Some burrow walls show iron hydroxide-staining. The extensive burrowing occurred prior to lithification. On the other hand, the neptunian-dykes and synsedimentary faults, which cut the hard ground, occurred after the lithification. These features indicate the progressive hardening of the substrate. The burrowed limestone consists of an intrabioclastic peloidal grainstone which was deposited in an intertidal to shallow, subtidal, moderate to relatively high energy environment. The peloidal limestone shows little or no evidence of submarine cementation, characterized by only scarce relics of isopachous cement rims of bladed calcite spar. The grainstone cement is composed predominantly of blocky calcite and overgrowth calcite cements on the echinoid-fragments. The origin of this cement is controversial. Biostratigraphic analysis of the limestones demonstrates that there is a marked stratigraphic gap (hiatus), spanning the Aptian to the Santonian, in the Cretaceous of the Kilop area. The formation of the Kilop Hardground is related to the break-up and subsidence of the Eastern Pontides carbonate platform during the formation of the Black Sea backarc basin. Hardground development was initiated in a shallow marine environment of slow sedimentation and with moderate to high energy indicating slow subsidence. Later, the hardground subsided abruptly, as shown by the deposition of pelagic sediments on the hardground surface. During drowning, the Kilop area was converted to a bypass-margin where currents were effective. The formation of the hardground may also have been associated with an eustatic rise in sea-level.

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.

Genesis of tepees in the quaternary hardpan calcretes, Mersin, S Turkey

In the Mersin area, the calcretes are widespread and occur in a variety of forms. The upper surface of the hard laminated crust (hardpan calcrete) represents a distinctive surface morphology of dome-like or slightly elongated dome-like and rarely ridge-like morphologies. These antiformal surface morphologies are interpreted as calcrete-tepee structures. Their cross-sections appear as an upward buckled crust or surface undulation. Troughs are present between the dome-like morphologies, and rarely associated with vertical and subvertical fractures. Petrographic and stable isotope data suggest formation in a vadose zone under subaerial conditions. Semi-arid climatic conditions of Mediterranean type are favourable for calcrete development and furthermore for tepee formation in hardpan calcretes. Thermal and moisture related expansion and contraction seem to be the most likely mechanisms in formation of the calcrete tepees.

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.

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.

MINERALOGY, GEOCHEMISTRY, AND GENESIS OF SEPIOLITE AND PALYGORSKITE IN NEOGENE LACUSTRINE SEDIMENTS, ESKİŞEHİR PROVINCE, WEST CENTRAL ANATOLIA, TURKEY

Sepiolite and palygorskite are common as layers and nodules in the Neogene lacustrine sediments of the Eskişehir area. This study aims to determine their mineralogical and geochemical characteristics, plus the distribution of these economically important sepiolite and palygorskite deposits within the lacustrine environment. Using these data the research goes on to discuss the environmental conditions for their formation. Sepiolite and palygorskite layers are associated with dolomite, marlstone, and argillaceous limestone. The sepiolite nodules (meerschaum), which are former magnesite gravels, are observed in the Upper Miocene reddish-brown fluvial deposits derived from the ophiolite and its fractureinfills at the northern margin of the basin. Sepiolite and palygorskite are only sparsely associated with dolomite and accessory magnesite, quartz, feldspar, and amphibole. Sepiolite and palygorskite fibers formed as oriented platy fan, interwoven, and knitted aggregates in the absence of dolomite indicated precipitation from supersaturated solution. Sepiolite and palygorskite fibers edging dolomite crystals postdate dolomite and formed through precipitation in a vadose environment under semi-arid to arid climatic conditions. High values of Mg+Fe+Ni and enrichment of light rare earth elements (LREE) relative to middle rare earth elements (MREE) and heavy rare earth elements (HREE), Sr content, depletion of Rb+Ba and K, and negligible negative Eu anomalies all reflect the derivation from the Paleozoic metamorphic and Upper Cretaceous ophiolitic rocks. Locally, Upper Miocene to Lower Pliocene volcanic, volcanoclastic, and fluvio-lacustrine sedimentary rocks supplied the required Si, Mg, Al, and Fe for precipitation of Al-sepiolite and Mg-palygorskite with average structural formulae of Si11.91Al0.09O30Mg6.60Al0.78Fe0.13 (OH)4Na0.12K0.06(OH2)4·nH2O and Si7.74Al0.26O20Mg2.52Al1.13Fe0.38(OH)2(OH2)4Na0.32K0.14 Ca0.12·nH2O, respectively. In contrast to the layered sepiolites, the absence of Al and high Ni content in sepiolite nodules suggest formation through replacement of magnesite gravels at shallow burial in an alkal ine environment. The calculated meerschaum sepiol ite chemical formula i s: Si12.02O30Mg7.87Fe0.01(OH)4Na0.13K0.03(OH2)4·nH2O.

Origin of stylolite related fractures in Atoka Bank Carbonates, Eddy County, New Mexico, U.S.A.

Stylolite-related fractures are rare diagenetic features (1% in volume) in Atoka (Carboniferous) bank carbonates in Eddy County, New Mexico, U.S.A. The fractures are often wedge- to curvilinear-shaped, vertical to subvertical, and their wider ends terminate at the seams of major stylolites. The associated stylolites are centimeters in size, low to medium amplitude (up to 1.5cm) and some of them are fabric selective forming at matrix-grain and matrix-cement boundaries. Fractures are filled with predominantly saddle dolomite and late calcite cements. Fracture size ranges from microscopic to 1cm, and they have a width less than 1 mm. A close coexistence of fractures with stylolites suggests that fractures have formed synchronously with the stylolites. In Atoka carbonates, stylolites were formed by progressive burial that is evidence by bedding-parallel or subparallel orientation and different mineral associations along stylolites and also at near areas. These minerals are commonly late calcite and saddle dolomite. Soon after initial stylolitization, dissolved material and/or formation water and surface morphology of stylolites caused localized stress differentiation around stylolite. Compaction differences of less soluble parts at the both sides of stylolitic-highs or lows such as column/peak or waveform result in breakage of less soluble parts above or below column/peak or wave-form. Later wedge-shaped fractures are occluded by late cements provided by stylolitization or stylolitic-channels carring cement-generating fluids from an external source such as dewatering of adjacent shales. Stable isotope values of saddle dolomite (δ18O=−3.5 to −4.0‰ PDB; δ13C=+0.04 to +0.67‰ PDB) and late calcite (δ18O=−5.4‰ PDB; δ13C=+0.7‰ PDB) suggest precipitation at paleotemperatures of 52–55°C for dolomite and 42°C for late calcite based on oxygen values. The temperatures correspond to burial depths of approximately 1450–1600m for dolomite and 1000 m for calcite under present-day conditions, assuming a geothermal gradient of 22°C/km and a surface temperature of 20°C (well data).

The sedimentary characteristics of Dagpazari patch reef (Middle Miocene, mut-içel/Turkey)

This study aims to determine facies characteristics of the Dagpazari patch reef (Middle Miocene) located at 13 km north of the Mut (Içel) town. Mut (Içel) and nearby areas are geologically known as Mut Basin situated in the Central Taurides. In the Mut Basin, Middle Miocene time is represented by Mut and Köselerli formations. The Mut Formation comprises reef limestone and interfingers with the Köselerli Formation consisting of claystone, argillaceous limestone and marl.Dagpazari patch reef has a gentle and elongated dome shape. Its elongation extends in NW-SE direction. In the Dagpazari patch reef and its surrounding, five lithofacies and several subfacies have been delineated based mainly on reef geometry and also macro and micro facies features. This patch reef is approximately 15 m thick, 500 m in length and 200 m in width. These are; 1) Base facies (red algal wackestone-packstone, Dunham 1962; biomicrite, Folk 1962); 2) Reef core facies (coral-red algal framestone-bindstone, Embry and Klovan 1971; biolithite, Folk 1962); gastropodpelecypod wackestone-packstone, biomicrite; grainstone, biosparite); 3) Fore reef-flank facies (planktonic foraminiferal-red algal wackestone, biomicrite); 4) Back reef-flank facies (wackestone, biomicrite; local framestone-bindstone, biolithite); 5) Sealing facies (echinoid-intraclast packstone-grainstone, biointramicrite, biointrasparite).Reef core facies is easily separated from other reef facies by: i) presence of frame-building organisms (coral); ii) presence of binding organisms (red algae, bryozoa); and iii) diverse fauna. Reef-flank facies are separated from reef core facies due to their well-bedded appearance. The sealing facies truncates the other reef units with an erosional surface.Facies and frame-building organisms were highly affected by sea-level fluctuation during the Langhian. Grainstone (Dunham 1962) occurred where the environment is close to wave base; planktonic foraminiferal wackestone (Dunham 1962) deposited where the environment was relatively deep. In overall, the Dagpazari patch reef was deposited in shallow environment.

An Approach to Genesis of Sepiolite and Palygorskite In Lacustrine Sediments of the Lower Pliocene Sakarya and Porsuk Formations in the Si˙vrii˙hii˙sar and Yunusemre-bii˙çer Regions (Eskişehii˙r), Turkey

The Lower Pliocene lacustrine sediments of the Sakarya and Porsuk Formations in the Sivrihisar and Yunusemre-Biçer regions consist of claystone, argillaceous carbonate, carbonate, and evaporites. No detailed studies of paleoclimatic conditions have been performed previously. The present study aimed to determine the depositional environment and paleoclimatic conditions for the formation of these economically important sepiolite/palygorskite/carbonate/evaporite deposits based on detailed mineralogical, geochemical, and isotopic studies. Samples from various lacustrine sediments were examined using polarized-light microscopy, X-ray diffraction, canning electron microscopy, and chemical and isotopic analysis methods. Dolomites are predominantly of micrite, which is partly recrystallized to dolomicrosparite/dolosparite close to desiccation fractures. The presence of ostracods and dacycladecean algae in the carbonates reflects a restricted depositional environment. The formation of sepiolite and palygorskite fibers, either as cement between/enclosing dolomite and/or as calcite crystals, reflects occasional changes in physicochemical conditions provided by fluctuations in the lake-water level and influx of groundwater in relation to climatic changes during and after dolomite precipitation. The positive correlations of ΣREE with Al2O3, Nb, high-field-strength elements, and transition elements are due to alteration of feldspar and hornblende in the volcanic units. The high values of Ba and Sr relative to Cr, Co, Ni, and V also indicate that felsic rather than ophiolitic rocks were the parent material. The crossplot of whole-rock SiO2vs. Al2O3+K2O+Na2O and V/Cr ratio suggests deposition of carbonate-dolomitic sepiolite-sepiolitic dolomite under arid climate and oxic conditions, whereas the Ni/Co and V/(V+Ni) ratios of the sediments indicate deposition of organic-bearing sepiolite/palygorskite under anoxic-dysoxic conditions. An enrichment in δ13C and δ18O values of dolomite with respect to calcite is probably due to differences in mineral fractionations. The δ34S and δ18O values and 87Sr/86Sr isotope ratios for gypsum suggest an intensely evaporitic lacustrine environment fed by an older marine evaporitic source. The Si, Al, Mg, Ca, and enhanced TOT/C required for periodic precipitation of organic-rich brown sepiolite/palygorskite characterize deposition in a swampy environment, while dolomitic sepiolite and sepiolitic dolomite formed in ponds by partial drying of the main alkaline lake.