engleski

Glauconitic materials from Lower Miocene Macelj Formation (NW Croatia) – new data

The Macelj formation, situated in the northwestern part of Croatia, in the Hrvatsko Zagorje region, as well as in the adjacent eastern Slovenia is composed of Vučji Jarek, Čemernica, Lipni Vrh and Vrbno members. The Vučji Jarek is the lowermost member of the Macelj formation laid transgressively on an erosional unconformity over Eggerian sediments. The Vučji Jarek sediments were deposited within a marine, nearshore environment under tidal influence. The sediments are characterized by horizontal-bedded and cross-bedded glaucony sandstones and tuffs. The Čemernica member succeeds the Vučji Jarek member. It consists of clayey and silty sediments affected by intensive bioturbation, and silty marls rich on ichnofossils. The deposits were formed in the offshore-transition zone between shoreface and offshore. The Macelj formation deposits were formed in Eggenburgian and in the lower part of Ottnangian time. The formation builds up an elongated syncline, plunging towards the east. Glauconitic materials from Macelj-sandstones have been already investigated in detail but during recent investigations glauconitic materials belonging to different members, Vučji Jarek and Čemernica, of the formation were investigated. Two samples of glauconitic materials were separated per member and investigated by X-ray powder diffraction (XRPD), infrared (IR) and Mössbauer spectroscopy, and by chemical methods. Performed analyses revealed that investigated glauconitic materials from two members differ significantly. XRPD patterns showed that no impurities were present in investigated materials. Diffraction pattern of Čemernica samples have broader diffraction maxima, this is best seen for 001 peak, indicating higher expandable layer content. The observed d(060) for these samples of 1.510 Å ; ; ; in comparison to 1.516 Å ; ; ; for Vučji Jarek samples indicates higher Al content in them. In spite of the fact that IR spectra of all samples are characterized by poorly resolved broadened bends, they differ in the appearance of the OH-stretching region. Those from Čemernica member samples have more pronounced band at 3603 cm-1, which can be ascribed to Al-Mg cationic environment of the OH groups in addition to bands at 3557 (Mg-Fe3+ and Al-Fe2+) and 3530 cm-1 (Fe3+-Fe2+) that are practicaly the only visible in Vučji Jarek samples. In two samples from Vučji Jarek sediments potassium content (7.75 and 8.03 wt% K2O) was higher than in two samples from Čemernica member having 5.58 and 6.24 wt% K2O respectively, what is in accordance with observed differences in XRPD patterns. The content of expandable layers in Vučji Jarek and Čemernica samples is approximately 5 and 20% respectively. Mössbauer spectra recorded at room temperature, fitted with four doublets with Lorentzian line shape, show differences in site populations for samples belonging to different members.

glauconitic materials; XRD; IR; Mössbauer spectroscopy

nije evidentirano