Fahri Esenli

Genesis of smectite in siliciclastics and pyroclastics of the Eocene İslambeyli Formation in the Lalapaşa region, NW Thrace, Turkey

Abstract The Eocene İslambeyli Formation in the Lalapaşa region (NW Thrace, Turkey) consists predominantly of siliciclastic clayey clastics at the bottom and of claystone, tuff and tuffaceous claystone/ sandstone/limestone in the middle and uppermost parts of this formation. Some tuff-tuffaceous beds of the middle-upper parts of the formation are economically viable bentonite depoits. The İslambeyli Formation exhibits vertical variations in the mineralogy, elemental compositions, and smectite-forming processes. Smectite was formed by weathering and diagenetic processes in the fluvial-shore environments in the lower part and by diagenetic alteration in a shallow-marine environment in the middle-upper parts of the formation. Ca-smectite flakes were formed by two processes: direct precipitation; and by means of a dissolution-precipitation mechanism from feldspar and mica. Dissolution-precipitation was most prevalent in the siliciclastic lower part of the formation. The amounts of Al, Fe, Mg and Ca required to form smectite and accessory illite were supplied mainly from the alteration of feldspars, mica and glass shards. The origin of smectite can also be explained by the inferred solution compositions given the parent phases in this formation, and the devitrification of glass shards in pyroclastic-rich middle-upper parts of the formation. In the upper beds, the observed decrease of K and Fe in the smectite structure coincided with both the increase in the amount of smectite and the increase in solution pH suggesting that precipitation of smectite developed over a prolonged period and under arid conditions.

X-ray diffraction intensity ratios I(111)/I(311) of natural heulandites and clinoptilolites

Heulandite-group zeolites are abundant in the Miocene pyroclastics from Western Anatolia, Turkey. We investigated the relation between the I(111)/I(3¯11) intensity ratios measured by X-ray diffraction (XRD) and the content of exchangeable cations for 15 samples of natural heulandite-group minerals gathered from the Gördes and Bigadiç regions of Western Anatolia. The intensity ratios range from 0.77 to 0.94 in natural heulandites and from 1.38 to 1.80 in natural clinoptilolites. The data obtained from Na-, K- and Ca-exchanged forms of a heulandite and clinoptilolite show that the intensity ratio increases with Na-, K- and Ca-exchange in heulandite and also with Na- and K-exchange in clinoptilolite, whereas it decreases with Ca-exchange in clinoptilolite. The intensity ratios were calculated using the known structural data of clinoptilolites to understand the effect of positions, amounts and kinds of exchangeable cations and water molecules. An increase in Na and Ca may increase or decrease the intensity ratio, depending on their sites and occupancies. Potassium causes a significant increase in the intensity ratio and an increase in Mg decreases the intensity ratio. There is a strong correlation between the intensity ratio I(111)/I(3¯11) and (Na + K)/(Ca + Mg) ratio and thermal stability, both of which have been used to characterize heulandite-group minerals.

A study on the characteristics of some opals from Turkey

The mineralogical characteristics of some Turkish opal-CTs collected from West and Middle Anatolia were studied. They are originated from Eocene to Upper Miocene aged volcanic-sedimentary formations. Of the sixteen samples studied, all except one, were found to be optically isotropic. 101-spacings (4 A band) of opal-CTs show differences within the range of 4.086-4.144A. There are proportional relationships between 4 A band, 2.5 A line, density and total weight loss values of opal-CTs. As their structural disorder which is observed in 4 A band values increases, the water content and the density of opal-CTs increase. The structural ordering increases depending on the geological ageing. Opal-CTs of the samples which consist of opal-CT and quartz associations have more ordered structure than those of opal-CTs which are the only component of the samples.

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.