Quartz and silica as guide to provenance in sediments and sedimentary rocks
Quartz is the most abundant and widespread detrital mineral in sedimentary rocks due to its wide occurrence in crystalline source rocks and to its relative resistance during transport and sedimentation. It occurs as a detrital component in conglomerates, sandstones and other siliciclastic rocks. In the presented contribution quartz is considered as guide to provenance analysis in sedimentary basins but also for provenance evaluation of other geological, archeological and industrial materials.
In order to reconstruct the provenance of quartz various properties and parameters are commonly in use: colour, shape, internal structure, type of inclusions, geochemical parameters and cathodoluminescence. The analytical methods used can differ in preparation procedures, equipments used, time of analysis, etc. resulting in a wide spectrum of methods.
The grain shape of quartz can be inherited from the source rock and/or acquired during transport, but is difficult to recognize in older sediments strongly affected by diagenetic overprint. Internal structures of crystallographic origin such as type and size of primary grain intergrowth, undulatory extinction and other features, which are difficult to interpret, are often preferred as provenance criteria. The inclusions can be classified according to size, shape and mineralogy, appearance and chemical as well as isotopic composition and microthermometry of fluid inclusions.
Although the "classical" methods of provenance analysis are still in use, modern analytical methods brought a lot of new mineralogical and geochemical data concerning the origin of quartz, especially those allowing single-grain analysis or spatially resolved analyses of the specific parameters (e. g., trace elements, oxygen isotopes, cathodoluminescence). Thus, complex investigations by a combination of classical and modern methods will have the greatest potential for a successful provenance interpretation.
On the other hand, the quartz investigations should be complemented by sedimentological and geochemical studies (e.g., heavy-mineral analysis, bulk-rock geochemistry, etc.), which can help in obtaining a subtle characterisation of the sample material. Best results will be obtained if background data of potential source areas and possible parent rocks, respectively, exist.