engleski

Sedimentology and Geochemistry of the Tufa Deposits and associated Spring Waters emerging along a normal Fault Zone, Honaz, Denizli, SW Turkey

The Denizli basin in the extensional province of western Turkey is well known by its travertine and tufa occurances. The southeast margin of the basin was bounded the by the active Honaz normal fault. In this study, sedimentology and geochemistry of the tufa deposits and associated spring waters were investigated at the Honaz area. The site is located to the western end of the Honaz fault trending east-west direction. The tufa deposits were exposed on the hangingwall of the fault. The studied area is consisted of Kayaaltı , Değ irmenler and Colossae sites. The first two sites are adjacent to each other, whereas the third one is about 5 km to the northeast near the Colossae ancient city in the Aksu streem valley. The tufa mass of the Kayaaltı -Değ irmenler sites was developed as a steep tufa cliff in the north-northeast direction and pinches out in both sides. The upper part of the tufa cliff has been formed in waterfall facies, on the other hand, the lower part represented distal slope was typified by horizontally bedded and detrital tufas. The Kayaaltı tufa deposits are covered by a flat surface at the top. This landscape indicates a perched springline tufa morphology reached up in maturity stage. Most of the deposits are passive apart from the northeast corner of the tufa body at the Değ irmenler site which is the former water mills area. The Pı narbaşı karstic spring waters have been emerging from an altitude of 492 m in the Honaz fault zone. The aquifer rocks are mainly composed of Mesozoic carbonates in the catchment area on the footwall of the fault to the south. The tufa-precipitating waters today run to the Değ irmenler active tufa site in a distance of 1395 m from the spring area by a concrete channel. The waters of spring and accompanying two wells have a flow rate of about 1200 l/s. The water chemistry of the karstic spring is quite different relative to some well-known tufa sites. The waters are certainly enriched in Ca, Mg, HCO3 and SO4. It was classified as Ca-HCO3-SO4 water and supersaturated with respect to CaCO3. The water temperatures of the spring and associated two wells are 18.6, 20.0 and 23.9º C, respectively. The pH values range from 6.6 at the spring to 8.2 at the Değ irmenler active site. The SO4: 122-239 and HCO3: 236-443 in ppm. The chemical and isotopic composition of the tufa deposits as follows: The Sr content is considerably higher with a range from 729.8 to 2780 ppm. The 14C activities are lower (min.: 7.5, mean: 20.0 and max.: 39.5 pMC). The δ 13C values are between -0.40 to +3.45 (VPDB ‰ ), while the δ 18O values are from +20.55 and +22.92 (VSMOW ‰ ). The positive values of the carbon isotopes indicate predominantly mineral origin of carbon. Consequently, studied tufa deposits have a position close boundary between tufa and travertine in geochemical and isotopic composition. Although the spring carbonates investigated were precipitated from the deeply circulated waters with a certain meteoric contribution along the fault zone. However, they were regarded as tufa rather than travertine based on their depositional morphology and field scale features.

tufa; Turkey; isotope analyses; geochemistry

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