Erdogan Tekin

A prelimennary study: Celestite-bearing gypsum in the Tertiary Sivas basin, central-eastern Turkey

Celestite-bearing evaporite mineralization is common in the Tertiary evaporitic units of Ulas-Sivas basin, East-Central Turkey.The first occurrence of gypsum which is “laminated in character” (Balatino gypsum) took place in the shallow inner-lagoon or depressions during regression in the upper Eocene. Thick gypsum and overlying beds composed of the bedded, nodular gypsum and sandstone alternations were formed in a coastal sabkha and abandoned channels within the meandered rivers through the Oligocene time. The last occurrence of evaporitic units, represented by massive and bedded gypsum alternating with sandstones and fossiliferous limestones resulted from limited marine transgression in the early Miocene along the southern margin of the Sivas Tertiary basin.The celestite mineralization preferentially took place within the Miocene evaporites and subordinate amount in the shallow marine limestones and terrestrial siliciclastics ranging from late Eocene to Oligocene in age. Celestite shows different depositional characters such as stratabound, massive, fracture and cave filling. According to microscopic studies, three petrographic types have been determined in these different beds of celestite. They are prismatic and bar-like; sub-idiotopic and tabular; fibrous-radial.The source of the celestite in the Sivas Tertiary basin has been debated. There is little evidence for suggesting sedimentary-syngenetic origin. Many geologists believe that it formed during late diagenesis or epigenetic stages, but this interpretation reflects a lack of a comprehensive study and only depends on field observations. This paper includes both field and laboratory studies (light, ore and electron microscopes, microprobe,87/86Sr isotopes) and obtained initial results which have inclined to the diagenetic-epigenetic origin.

Modern ooids of Cleopatra Beach, Gokova (South Aegean Sea) Turkey: Results from petrographyand scanning electron microscopy

AbstractModern ooids from the Cleopatra Beach on Island in the Gökova Bay, South Aegean Sea, resemble ooids formed on the Bahamian platform. The concentric coatings of the ooids consist of two or more laminae around a carbonate- or non-carbonate nucleus. The oolite cortex is transparent, whereas the non-transparent portions seem to be the dark fields on the oolitic surfaces. The ooids are mixed with molluscan skeletal debris displaying micritic envelopes. Weakly consolidated ooids have been cemented by calcite in the form of meniscus cement.According to electron-microscope studies, three kinds of crystal shapes have been distinguished, as follows:1-Micronodules attributed to microboring organisms such as cyanobacteria or coccoids;2-Tablet-shaped crusts of hemispheres; likely produced by bacterial activity,3-Acicular- or elongate crystals precipitated directly from sea water in vacated holes of the microborings or as of the tangentially orientated parts of the ooids. Algal- and bacterial processes are thought to have been main sources of the carbonate that was precipitated to form the ooids.

Epigenetic origin of celestite deposits in the Tertiary Sivas Basin: new mineralogical and geochemical evidence

The occurrence of celestite in the evaporitic Upper Eocene-Miocene deposits of the Sivas (Ulas) Basin is documented. This paper aims to demonstrate that a group of Tertiary sediment-hosted celestite deposits are epigenetic in origin, rather than syngenetic as has been claimed by a number of previous workers. Thin section petrography, fluid inclusion data, mineral and whole rock geochemistry and isotopic compositions (87/86Sr, 180 and 34/32S) are the main tools employed. The celestite occurs as stratabound, vug-filling, nodular and lenticular types. Petrographic, microtextural (SEM), mineralogical and geochemical analyses indicate that the celestite can be classified as pure, calcareous and gypsiferous varieties. The celestite under polarizing microscope shows xenomorph, pseudomorph and acicular-radial crystal structures. Scanning electron microscope (SEM) analyses reveal abundant zonal structures in single crystals. Ore minerals associated with the celestite mineralization include pyrite (especially bravoite-melnikovite), marcasite, limonite, siderite-ankerite, gold (electrum-nabite), psilomelane, realgar-orpiment, antimony and dedritic chromite. X-ray fluorescense analyses indicate that the celestites contain 53-58 wt.% SrO, 0.05-3.70wt.% BaO, 0.02-3.40b wt.% CaO and 35-44wt.% SO 3 . Average minor element contents are: 0.4 wt.% SiO 2 , 0.9 wt.% Al 2 O 3 , 0.03 wt.% MnO, 0.3 wt.% MgO and 0.3 wt.% Na 2 O. The trace elements recognized are: Mo (1.8 ppm), Pb (18 ppm), W (0.8 ppm), As (2.3ppm), Zn (4ppm) and Cu (7ppm). The homogenization temperatures of fluid inclusions in celestite crystals vary between 210 and 390 °C. Salinity (NaCI equ.) values range from 11 to 23 wt.% NaCl. Fig. 1. A Location of the Tertiary Sivas Basin, Turkey. B Location map of the study area in the Sivas Basin. C Simplified geological map of the study area, showing the location of celestite and celestite-barite (Ba, Sr)SO 4 occurrences. The petrographic, mineralogical, geochemical and isotopic characteristics of the celestite deposits in the Sivas (Ulas) basin are compatible with an epithermalhydrothermal, rather than a sedimentary origin as it was previously proposed. A hydrothermal origin is also supported by the Sr isotope data; since the 8 7 Sr/ 8 6 Sr ratio varries between 0.70590 and 0.70718. Besides, the results of the 1 8 O and 3 4 S/ 3 2 S isotope data are in accordance with the hydrothermal origin.

Microtextural properties of ooids in the middle Jurassic-lower Cretaceous, central taurus carbonate platform, Antalya, Turkey

Ooids occurring in the middle Jurassic-lower Cretaceous carbonate sediments of Akseki, Antalya (Turkey) are of two distinct kinds. Type 1 ooids are small and of irregular shape. They have 1 to 4 cortical laminae with a fine radial structure and patchy micritization. The nucleus of this type is composed of micrite and in places is not visible. In the radial part of this kind of ooid, microporosity and/or microopenings seem to be micro-borings. Type 2 ooids are large and well rounded with vaguely visible nuclei. They display fine concentric micritic laminae which coincide with endolithic microorganisms and microborings of fossils.These ooids accumulated in a subtidal and lagoonal calm-water environment. Cyanobacteria and endolithic algae are thought to have contributed to the formation of these ooids.

EVIDENCE OF MICROBIOLOGIC ACTIVITY IN MODERN TRAVERTINES: SICAKCERMIK GEOTHERMAL FIELD, CENTRAL TURKEY

Modern travertine deposits are observed in the Sicakçermik hot springs located northwest of Sivas, central Anatolia. They are the carbonate deposits of crustal (spongy) and/or alabaster-textured formations controlled by both organic and inorganic processes. The structures formed under the influence of inorganic processes include the accumulations on the fissure and joint ridges. These structures are adjacent to the hot water emergence spots representing the points of rapid hot water flow and sudden release of CO2. The structures developed under the influence of organic processes form in areas at relatively farther distances from the hot water emergence points. These structures were described to be “waterfall or cascade deposits”; “terrace-mound travertines”; and “shallow lake fans” by different researchers. They are recognized in the field by special identifying trails such as manganous-ferrous travertine shrubs resembling ivy, siliceous stromatolites, and ferrous pisoids, 3 to 12 mm in diameter.All the modern travertine samples examined are dominantly formed by subidiomorphic prismatic-tabular calcite crystals. Scanning Electron Microscopy revealed that calcite crystals forming the pisoids are characterized by zonal growth. Stromatolitic formations, on the other hand, bear regular joints developed as a consequence of sudden cooling and some special structures indicative of bacterial activity (in the form of nodule, spheroid, ellipsoid, column, filament and honeycomb or grape bunch structures). In addition, secondary dissolution vugs and pores giving way to the release of CO2 are associated structures with the stromatolitic formations. The data collected from all the utilized techniques suggest that the microbiological formations observed in the travertines of Sicakçermik hot spring were produced by the sulfatereducing, boring-budding bacteria such as Coccoids, Pedomicrobium, Beggiatoa sp., Thiobacillus sp., as well as blue-green algae (Cyanobacteria).The travertine occurrences produced by both organic and inorganic processes have an annual average of 3–5 cm deposition in thickness. The hot water emergence points and their flowpaths manifest seldom-found natural features. These natural monuments are irresponsibly destroyed for several reasons. The authors argue that these formations, significant from the point of view of their occurrence mechanism as well as their final products, must be preserved. If accomplished, a modern natural monument similar to that in Pamukkale (Turkey) and Yellowstone National Park (Wyoming, USA) could develop within a reasonable length of time.

Sedimentology and geochemistry of the middle miocene playa lake evaporites in the Gürün basin (S of Sıvas), central Anatolia, Turkey

The Gürün basin is a half graben filled by alluvial, fluvial and playa-lake deposits of the Gürün Formation accumulated under the N−S direction extensional tectonic regime and volcanic rocks.The Gürün Formation is divided into four members such as the Kavak, Gökpmar, Çayboyu and Terzioğlu members, and the Çayboyu Member has two different evaporitic occurrences such as selenitic and satin spar. During the first phase of evaporite deposition, selenitic gypsum crystals in 5 to 15 cm thick layer within the dolomitic mudstones were formed. The second evaporitic phase consists of four different levels of cavity filling within the sandstones and shale alternation at the upper part of sequence originated as 5 to 10 cm sized satin-spar gypsum crystals with white colored, partly orientated, fibrous-radial shaped. XRF major, minor and some rare elements analyses (La, Ce, Ta, W and U) and low87Sr/86Sr (‰) and δ34S (CDT) values indicate that meteoric and volcanic solution occasionally mixed with the lake water.In addition, low δ18O (SMOW) values in the continental evaporate could be interpreted as mixing of fresh water with the playa lake environment. Selenitic gypsum in the Çayboyu Member of the Gürün Formation was precipitated from ground water-brine water rich in humic acid during periodic desiccations of in the shore-lake plain.

Elemental sulfur of bacterial origin in the lacustrine evaporites of the Polatli-Sivrihisar Neogene Basin (Central Anatolia, Turkey)

This study reports occurrences of disseminated elemental sulfur in gypsum of the late Miocene Sakarya Formation in Polath-Sivrihisar Basin, located in the Central Anatolia Neogene Basins. Thin-section and scanning-electron microscope studies indicate that the sulfur minerals have three main morphologies including lacy, combined spheroidal-lobous, and flabellate-grape-like structures. Studies on the elemental sulfur occurrences suggest that the sulfur was formed by reduction of Sakarya Formation gypsum through the metabolic activities of sulphate-reducing bacteria. This observation is also supported by the trace-element concentrations obtained on both the gypsum and the elemental sulfur samples.

Elemental sulfur formation related to celestine reduction: An example of biomineralization of bacterial origin

This study investigates the disseminated elemental sulfur formation in celestine mineralization in the upper member of the Bozbel Formation (Eocene) in the Sivas basin, Turkey. Optical and scanning electron microscope studies indicate that the sulfur minerals have three main morphologies including lacy, grape-like, and spheroidal — lobous types structures. These sulfur structures are occasionally coated with organic matter. Total organic carbon and infrared spectrometry studies indicate that an average of 1 % organic matter in this sulfur is of biogenic origin. Detailed studies on these elemental sulfur deposits suggest that the sulfur was formed by the reduction of celestine through the metabolic activities of sulfate reducing bacteria. This observation is supported by the trace element values obtained through x-ray fluorescence analyses on both the celestine and the elemental sulfur samples.