Geochemical conclusion of the GdA Fm -
to apply heavy-mineral and XRF for provenance and correlation purposes

Interpretation of the heavy-mineral application

The high-resolution heavy-mineral plots demonstrate homogeneous and uniform distribution and composition of heavy-minerals in the sampled fine - coarse grained arkoses (Diagram 11.2a, b, c, d, e anf f). No matter where in the Lauzanier succession, this is always confirmed by the sample analysis, which includes Grès d'Annot Formation interval of more than 350m (Appendix 2: Log Correlation). This study confirms the heavy-mineral observations of Stanley (1961), which describes the rock composition in a single Bouma-sequence of the Grès d'Annot Formation as differing as much as in the whole succession (Table 8.1.2d). Maybe even the true differing heavy-mineral occurrence in successions are lower than the possible error being made while preparing the heavy-mineral concentrate-slide plus the error of their count. Conclusivly, the heavy mineral application can only confirm that the outcrops of the Grès d'Annot Formation in the Lauzanier area, and also in the southern outcrops (Stanley, 1961), most likely only received sediments from a single source area that probably was sited at the southern Corsica-Sardinia-Esteral-Maures micro-plates assemblage (details, chapter 10.2.1.: Provenance).

Based on the poor fingerprinting in the high-resolution plots, no vertical or lateral correlation was possible to perform with heavy-mineral ratios (Diagram 11.2a, b, c, d, e anf f). Therefore this study may conclude that a local correlation (>3km) with heavy-minerals are not recommendable in sequences, where the mineral content among layers do not differ significant.

However, when focusing on a regional scale (probably <10km), the plots of the heavy-mineral ratios indicate that current is able to transport some heavy-minerals more distant than other (details, chapter 10.2.: Provenance and diagram 11.2a, b and c). Thus this indication suggest that heterogenuous hydraulic properties among stable heavy-minerals are interesting for further studies, since regional quantity comparement in a single bed might reveal direction of paleo-current, the current strength and proximal-distal status.

Interpretation of the XRF application

When considering the shown diagrams, for the aim of identifying lateral or vertical geochemical signatures, this approach was fairly successful. Vertically, the diagrams can roughly categorise the position of the samples in three zones (Diagram 11.3g and h). A further, more detailed determination of the relatively true base - top position of a sample among other samples in the Lauzanier succession, could not be found in any diagram of the immobile element plots (example, diagram 11.3d, e and f). Apparently, it is not possible to record a detailed change of the depositing sediment of the Grès d'Annot basin. Based on the roughly categorised three zones in the diagrams, the basin in the Lauzanier area was initially filled with sediments of low xx, xx and xx contents. Additionally, the diagrams demonstrate an increase of these contents, while deposition was progressing in time. Conclusively, since the diagrams were not able to order the close-spaced vertical samples, the change of immobile element contents were distributing irregularly (example, diagram 11.3d, e and f). This feature implies that the sediments, which most likely derived from the Corsica, Sardinia, Esteral and Maures assemblage of micro-plates (details, chapter 10.2. and 10.2.1.), were supplied by barely changing rock-types during the erosion-period of the source region. The deposition of the sediments, whereas an span of more than 350m were analysed (Appendix 2: Log Correlation), might even have been influenced by an additional source area and causing the slight increase of i.e. the primarily depositing sediments with low xx, xx and xx values (details, chapter 10.2. and 10.2.1.). Another explanation for these rising values might be explained through the ability of the heavy-minerals, which are comprising the high immobile element concentrations, rather tend to settle in a more proximal environment as of the upper super-cycle.

The petrography throughout the analysed part of the Lauzanier succession, and most likely the other successions across the Grès d'Annot basin too, comprise sediments of a nearly constant composition (Chapter 8.1. including the sub-chapters 8.1.1. and 8.1.2., chapter 10.2. and 10.2.1. and chapter 11.2.). The lack of the nearly devoid changes of sediment composition is hindering the approach of identifying vertical fingerprinting in the diagrams. Thus, the area of Lac du Lauzanier is difficult for such an approach. Theoretically, geochemical signatures should be much easier to identify in sequences where the depositing sediments have derived from differing rock-types of more than a single source area, or of varying rock-types of a single source that eroded more selectively.

When studying the geochemical signatures of the bed-to-bed correlation in the plotted diagrams, the immobile elements demonstrate their high sensitiveness. The elements and element ratios predominantly plot obvious fingerprints (Diagram 11.3a, b, i and j). Some samples of individual beds plot well assembled, but a more convincing geochemical fingerprint is the ability of the stable elements to plot aligned, mostly very near a regression line. By all means, this feature cannot be a coincidence, neither can these convincing results be caused by a changing grain-size or sediment homogeneity of the sampled beds. The homogeneity is evidently displayed in the XRF-data table (Table 8.1.2a). If the change of grain-sizes, which is only ranging between an average of 130 - 550µm (Table 8.1.1b), influence or control the plotting is declined by all diagrams (Diagram 11.3a, b, i and j). Hereby, the beds, comprising various grain-sizes, are not plotting any signature at all. The same evidence is featured by the study of the samples of an individual bed, whereby the occurring slight grain-size changes neither are controlling nor plotting signatures in the diagrams.