The geology, mineralogy, geochemistry and technological properties of İslambeyli formation and bentonite occurences in Northwest Thrace basin (Lalapaşa-Pınarhisar)

ABSTRACT Tertiary-Thrace basin is geographically taken parts in SE Bulgaria, NE Greece and NW Turkey and geologically surrounded by the Stradja Massif in the north (Bulgaria and Turkey), the Rhodope Massif in the west (Bulgaria and Greece) and the Menderes Massif in the south (Turkey). İslambeyli Formation; the first group of sediments at the bottom of the Tertiary succession of the Thrace Basin is exposed limitedly as a narrow belt in the border of Paleozoic-Stradja Massif and Tertiary Thrace Basin in the NW Thrace. The main aim of this PhD thesis study was to explain the clay mineralogy of the İslambeyli Formation and technological characteristics of the bentonite levels of the formation. Moreover, geology, general mineralogy-petrography, geochemistry of the İslambeyli Formation and also Stradja Massif and Oligocene formations were studied. In these concept, two study areas were selected: Edirne-Lalapaşa and Kırklareli-Pınarhisar. The study areas were geologically mapped as a scale of 1:25000. The samples were petrographically and mineralogically described by using binocular microscope and polarized-light microscope (Leica) and X-ray diffractometer (Bruker D8 Advance). Modal-mineralogical compositions were estimated on petrographic thin sections for the massif's samples and by XRD-reference intensity ratio method for the İslambeyli Formation's samples. Clay fractions (<2 µm) from the İslambeyli Formation's samples were obtained by sedimentation and centrifuging processes, then analyzed after drying with air, solvating with ethylene-glycol at 60°C for 16 h, and thermally treating at 350 and 550°C for 2 h. The selected samples from the İslambeyli Formation were also studied and analyzed by JEOL JSM-7000F model field emission scanning electron microscope (FE-SEM) and Oxford–Inca model energy dispersive X-ray spectroscopy (EDX). The major oxides and trace-rare earth elements analyses of bulk rock samples from the Stradja massif and İslambeyli Formation and also clay fractions were performed by Bruker S8 Tiger model X-ray fluorescence (XRF) and by Perkin Elmer Elan DRC to 6100 model inductive couple plasma-mass spectroscopy (ICP-MS). Additionally, some technological properties and indexes were explained by detailed tested and analyzed on selected bentonitic samples to correlate technological-mineralogical characteristics of the Ca-bentonites. Tertiary succession unconformably overlay the Stradja Massif in the study areas and it consists of İslambeyli Formation (Eocene), Kırklareli Limestone (Upper Eocene), Pınarhisar and Süloğlu Formations (Oligocene) and the Thrace Formations (Pliocene) in the Edirne-Lalapaşa area. Süloğlu Formation is absent in the Kırklareli-Pınarhisar area. The İslambeyli Formation is conformably overlain by the Kırklareli Limestone deposited in a shallow marine-reef environment. This unit is beige and white colored sandy-clayey limestone composed of mainly micritic-sparitic and rarely recrystallized calcites. Small amounts of quartz, feldspar, muscovite, biotite and pyroclastic fragments increase in the lower part of the Kırklareli Limestone. The Oligocene Pınarhisar and Süloğlu Formations unconformably overlay the Kırklareli Limestone. They consist of conglomerate, sandstone, marl, shale, claystone, oolithic limestone, limestone. The Pliocene-Trakya Formation unconformably overlies the Oligocene formations. They are composed of conglomerates, sandstones, siltstones, and claystones. All of these units are unconformably covered by Quaternary alluvium materials. The lithologies of the Stradja Massif are mainly metagranite and gneiss and rarely schist, amphibolite and serpantinite in the Edirne-Lalapaşa area and only gneiss in the Kırklareli-Pınarhisar area. Petrographically, granoblastic, lepidoblastic, porphiroblastic and mortar textures were observed in thin sections. General mineralogical composition of the massif is defined as quartz, K-feldspar, plagioclase, muscovite, sericite, biotite, chloritized biotite, amphibole (hornblende), garnet, sphene, epidote and opaque mineral. The İslambeyli Formation outcrops around Lalapaşa vicinity and Çömlekakpınar village in the Edirne-Lalapaşa area and around İslambeyli, Akören, Çayırdere and Poyralı villages in the Kırklareli-Pınarhisar area. İslambeyli Formation with a thickness of maximum 70 m consisted of coarse and fine grain clayey clastics at the lower part and claystone, dacitic-rhyodacitic tuff and tuffaceous claystone/sandstone/limestone at the middle-upper parts in the Edirne-Lalapaşa area. The formation with a thickness of maximum 90 m consists of sandstone, clayey sandstone, sandy claystone, carbonate claystone, clayey-sandy limestone and limestone in the Kırklareli-Pınarhisar area. The mineral assemblage of the formation is of mainly dioctahedral Ca-smectite and minor amounts of illite, chlorite and kaolinite as clay minerals and quartz, K-feldspar, plagioclase, muscovite, biotite, calcite, zeolite (heulandite-clinoptilolite) and gypsum as non-clay minerals. Carbonate content increases upwards the formation. Smectite and illite-mica are present in all sections but chlorite-kaolinite is absent in the Cayırdere section. Zeolite and gypsum are found in the middle-upper parts of the formation. Smectite content of the formation estimated by XRD pattern is upper than 50 % in the Edirne-Lalapaşa area and lower than 50% in the Kırklareli-Pınarhisar area in average. The İslambeyli Formation geochemically represents the quartz-rich sedimentary and felsic igneous provenance and active continental margin (ACM) tectonic setting. Addition to the field and petrographic observations, chemical values also indicate the effect of chemical alteration in İslambeyli Formation. Stradja Massif's samples plot on granitic field and are close to fresh feldspar composition while İslambeyli Formation samples are far from the granite and fresh feldspar compositions, and K-feldspar-plagioclase line but close to Al2O3 edge, Al2O3-(FeO*+MgO) line and smectite composition in the ternary diagrams showing alteration degree. The chemical alteration index (CIA) and plagioclase index (PIA) are 55 and 58 for the Stradja Massif, and 69 and 75 for the İslambeyli Formation, respectively. Alteration of the İslambeyli Formation is relatively higher for the samples from the Edirne According to the upper continental crust (UCC), depletions of Ba, K, Sr, P, Ti and enrichments of Th, La, Ce, Nd, Hf, Sm, Tb were found fort the İslambeyli Formation in Edirne-Lalapaşa area. Also, depletions of Cs, Rb, K, Nb, Ta, Hf, Zr, Tm were clear in the samples from Kırklareli-Pınarhisar area. According to the chondrite, light rare earth elements (LREE) enriched, while heavy rare earth elements (HREE) were found close to chondrite value for both study areas. İslambeyli Formation shows negative Eu anomaly. Major oxides such as SiO2, Al2O3, Fe2O3+TiO2 and K2O decrease towards the upper level of the İslambeyli Formation, CaO and MgO increase. In Edirne-Lalapaşa area, Ba, Sr, Rb, Sc, Hf, Nb, Ta, Zr, Y, Mo, Pb, Cu, and ΣREE and the ratios of Th/U, HREE/MREE+LREE and Ce/Ce* increases and Co, Rb, Sr and Eu/Eu* decreases in the pyroclastic-rich and smectite-rich middle-upper levels of the formation. Samples of Stradja Massif (Paleozoic) and İslambeyli Formation (Eocene) indicate mainly active continental margin and partly evolved arc setting in tectonic discriminant diagrams. Smectites of the İslambeyli Formation were defined as montmorillonite-type, dioctahedral Ca-smectite with an average structural formula of [(Si7.80 Al0.20) (Al2.75 Fe0.42 Mg0.93) (Ca0.38 K0.08 Na0.04)]. Smectite in the forms of honeycomb, corn-flake, rose-like and spongy forms was formed by crystallization (dissolution-precipitation) and direct-precipitation processes. Large amounts of Na and K decreased and Mg and Ca increased during the smectite formation in the formation. Primary feldspar and mica were altered to clay minerals after deposition of the İslambeyli Formation addition to the volcanic glass-smectite transition. Feldspar volume and total content of Na2O+K2O in the formation decreased over than 50% relatively to the massif. Smectite formation are generally started within volcanic glassy material and also through the cleavage lines and within pertitic zones of feldspars. Additionally, smectite was transformed at the edges of platy mica minerals. The compositions of solutions and seawater have an effect on the clay alterations. Fe, Mg and Ca were gained and Na, K and Si were lost in the pseudomorphic transformation process of K-feldspar and/or plagioclase and mica to smectite. Mg gained from the seawater probably in a shallow marine environment was largely consumed to smectite formation. On the other hand, the physical-chemical properties should be changed during the deposition, thus the presence of less amount zeolite (heulandite-clinoptilolite) should be resulted by increasing of alkali cations, pH, alkalinity in circulation solutions in middle-upper levels of the formation. Gypsum also occurred in the upper levels of the formation due to some temporal variations in the SO3 -rich circulating fluids when the climate was arid period. Additionally, the middle-upper levels of the İslambeyli Formation is rich in carbonate and also organic matter. The presence of organic matter that may be effective in the gypsum formation. In Edirne-Lalapaşa area, technological parameters are revealed on ten smectite-rich samples selected from bentonite levels of the İslambeyli and Pınarhisar formations. 90% of the particles in the samples are in the range of 35-194 μm size. The pH values range from 7.51 to 8.54 and increase to the upper levels of the formation. The swelling index values are between 2-7 ml/2g and increase depending on the smectite content. The relative filtrate volumes are between 118-352 ml and the highest value is found in the samples from Sinanköy. The plastic viscosity, the apparent viscosity and yield point values range from 0.5-2.5 cp, 1.25-3 cp and 0-2.5 cp, respectively. There is no relationship between viscosity and smectite ratios. Cation exchange capacities (CEC) are in the range of 0.190-0.761 meq/g and increase in direct proportion to the smectite contents of the samples. CEC values of the samples collected from three bentonite quarries are above the limit value accepted for bentonite industry. The water absorption and oil absorption capacities of the samples are; 123-204 %, 0.37-0.67 ml/g, respectively and the precipitation volumes vary between 10-20 %. The zeta potential values of bentonite samples are between -9.5 and -17.4 and the negative zeta potential values increases with increasing Al+3 and decreasing Mg+2 in the octahedral layers of the smectites.