Quartz in sedimentary rocks: OH-defects and trace elements for provenance studies

The flysch basins of the North-eastern part of the Adria Plate are represented by several elongated turbiditic sedimentary units, which are filled by carbonatic and siliciclastic material. In this study we focus on the Julian, Brkini, and Kvarner Islands basins (Italy, Slovenia, and Croatia). The carbonatic part is thought to derive by the disassembly of the nearby carbonate platforms, while the provenance of the siliciclastic material is still a matter of debate. To fill this gap in knowledge and identify the possible source of the siliciclastic portion of the filling sediments, this work presents a new quartz analyses dataset. Quartz can incorporate chemical impurities as defects in the crystal lattice (Al, Li, B, 4H), which are coupled to OH groups and form specific IR absorption bands. These so called OH-defects are correlated to petrogenetic conditions during crystal growth, and they may be used as a provenance tool. The amount of Al-related defects can be used to discriminate between a igneous (> 5ppm) and a non-igneous source (< 5ppm). In this study, FTIR spectroscopy of quartz has been used to investigate the sample set, with interest to its OH defect speciation and content. Julian Basin’s quartz show differences in the supply source within the succession: the oldest ones (JB5 and JB1) show an almost 1:1 ratio between igneous and non-igneous origin; samples JB10 and JB17 show a change with a predominantly igneous source; the youngest samples (JB23 and JB26) have a neat predominance of a non-igneous source. Brkini samples show again a difference in the source with the older BK41 having a more igneous source than the younger BKNV. Samples from the Kvarner Islands Basin indicate a predominantly non-igneous source (DOB) while in RAB1 the non-igneous source seems to be clearly prevalent, even if only few clear spectra were obtained. Trace elements such as Al, Li, B, Ge, Ti, and others have been analysed and quantified by LA-ICP-MS on the same grains. Regarding the Al trace content, it is important to notice that it follows the Al-related OH defects’ trend, demonstrating the possible existence of a correlation between the two analytical methods. Other classifications based on trace elements demonstrate different behaviour within the quartz set, confirming the trend displayed by the OH-defects method.