INTRODUCTION

The ultimate object of this thesis was to find an additional correlation tool, particularly for correlating beds in barren sedimentary sequences. This is based on the fact that the hydrocarbon industry is frequently confronted with barren sequences in various formations and stratigraphic ages. The traditional petrophysical-based correlation method often cannot fingerprint apparent uniform successions; consequently this results in poor stratigraphic control and ambiguous correlation. Alternative techniques, such as paleomagnetic and heavy mineral analysis have successfully been applied to enhance correlation. However, these techniques are time-consuming and expensive, as are isotope-age-determining methods.

A more time- and cost effective correlation tool is provided by a geochemical technique, called "chemostratigraphy" (Pearce, 1995). Geochemical-based correlation has been applied in the past. Conventional methodologies and downhole geochemical logging devices were developed (Hertzog et al., 1987), but these applications were costly and not particularly successful. All these previous analysis efforts mostly had in common only including a few major elements, because former analytical equipment had limited multiple analysing techniques.

Recent research has concluded that the major chemical elements have limited value as chemostratigraphic indicators. Primary, because they are associated with major minerals like quartz, feldspars and clay minerals, which are susceptible to transportation, weathering and diagenesis. Many heavy mineral-types, however, demonstrate no modification during these processes (Morton et al., 1983). Most likely, these qualities are the key for successful application of heavy mineral analysis, to aid provenance determination, mapping sediment dispersal patterns and correlating bodies and sequences. According to Füchtbauer (1974), "although heavy minerals make up an accessory mineral component (mostly <1%) of siliciclastic rocks, yet they strongly influence the concentrations of trace- and rare earth elements". For example are the immobile trace element concentrations such as Zr, Nb and Cr controlled primarily by the abundances of the heavy-minerals zircon, rutile and chrome-spinel (Preston, 1998). This fact often generates distinctive geochemical fingerprints and geochemical marker horizons, both of which can be very useful for correlation (Pearce, 1995).

The link between some heavy minerals controlling some immobile elements initiated recent research to rely on immobile elements as geochemical indicators. As a result of the modern analytical equipment availability, major-, trace and rare earth elements can rapidly be analysed in a single analysing-transit. Currently, element analyses are accomplished more time- and cost-effectively compared to previous analysing techniques. Such improvements are implemented by the utilisation of XRF, ICP-AES and ICP-MS. Additional advantages are also demonstrated by higher analytical precision and small sample mass, only requiring 0.2 - 0.6g of one sample unit and consequently qualifying not only cores but also cuttings as sufficient representatives for chemostratigraphic sampling purposes.

This study is testing the feasibility of vertical and lateral, immobile element/mineral-based, chemostratigraphic correlation, by sampling several well-exposed and well-correlative layers in the field. Both heavy mineral- and geochemical analysing methods were used to identify resemblance between two or more immobile elements or minerals, which can demonstrate signatures and trends in individual beds and/or sequences. The outcrops of the Eocene/Oligocene deep-marine siliciclastic Grès d'Annot Formation, in the area of Lauzanier, Department of Alps de Hautes Provence, SE France, were preferred since the outcrop situation is most favourable for sampling purposes.