3. 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 Lac du Lauzanier, Department of Alps de Hautes Provence, SE France, were preferred since the outcrop situation is most favourable for sampling purposes. To provide an overview of the Grès d'Annot outcrops in the main study area, the Lac du Lauzanier, a geological mapping was carried out. For advancing the correlation of distinct beds, 5 vertical logs were generated in the field from 3 detached north-south-parallel flanks.

A further aim of this work is an application of provenance to determine source areas of the Grès d'Annot Formation. Thus, besides the Lauzanier sampling area, a provenance focus was combined with sampling of the Grès d'Annot exposures in the areas of the 48km south-southwest sited Annot and in the 64km southeast faced Peira Cava (Figure 3.1). Primarily, this was done to compare the constitutions of sediments from the samples derived from far-distant locations, because their results may indicate if these areas were supplied by the same source area or not. To support the provenance study furthermore in addition to geochemical analysing, direction of sediment paleoflow, sediment composition and sedimentological features were analysed. This sediment focus served as an effort in interpreting the depositional environment of the Grès d'Annot Formation and to contribute to rather different interpretations of depositional environment among other authors.

A final focus in this study was granted to the tectonic setting and the grade of diagenesis the Grès d'Annot Formation had gone through in the three studied localities.

The main study area, Lac du Lauzanier, surrounded by the Grès d'Annot layers, is located between the northwestern part of the Argentera Massif and the Sub-Brianconnais Nappes (Figure 3.2), in the Alps de Hautes Provence Department, 2km west of the French-Italian Border, 18km east of Barcelonnette (Figure 3.1) and 10km south-southeast of Larche, in the northern part of the national park (National Parc du Mercantour) (Appendix 1: Gelolgical Map, UTM coordinates). During the summer monthsit is possible to drive from Larche by car, on the marked path (IGN route number: G.R.5-56), up to the parking place at Pont Rouge 1907m above sea level. This parking place is the northern entrance and border to the Parc du Mercantour (Figure 3.2.1.1). From Pont Rouge (at 1897m) there is a 3.5km, about one and a half-hour walk, to the northern border of the mapping area and to the first outcrops of the Grès d'Annot Formation. Further 1.5km, half an hour walk, is the beginning of the Lac du Lauzanier at 2284m above sea level.

The three areas studied in this work, which are exposing the Grès d'Annot Formation are: the main study area of Lac du Lauzanier and the areas serving for additional geochemical sampling purpose, Annot and Peira Cava (Figure 3.1 and 3.2).

The main study area, Lac du Lauzanier, surrounded by the Grès d'Annot layers, is located between the northwestern part of the Argentera Massif and the Sub-Brianconnais Nappes (Figure 3.2), in the Alps de Hautes Provence Department, 2km west of the French-Italian Border, 18km east of Barcelonnette (Figure 3.1) and 10km south-southeast of Larche, in the northern part of the national park (National Parc du Mercantour) (Appendix 1: Gelolgical Map, UTM coordinates). During the summer months it is possible to drive from Larche by car, on the marked path (IGN route number: G.R.5-56), up to the parking place at Pont Rouge 1907m above sea level. This parking place is the northern entrance and border to the Parc du Mercantour (Figure 3.2.1.1). From Pont Rouge (at 1897m) there is a 3.5km, about one and a half-hour walk, to the northern border of the mapping area and to the first outcrops of the Grès d'Annot Formation. Further 1.5km, half an hour walk, is the beginning of the Lac du Lauzanier at 2284m above sea level.

The Annot area (Figure 3.1, 3.2 and 3.2.1.2) is located in Alps de Hautes Provence, 37km northwest of Grasse and 48km south-southwest of Lac du Lauzanier. The outcrops of the Annot area are situated directly at the east side of the village, stretching northwards, a total outcrop surface of about 32km2 (Figure 3.2.1.2). The altitudes of the Grès d'Annot exposures are ranging from 850 in the west- and up to 1612m in the east.

The Peira Cava area (Figure 3.1, 3.2 and 3.2.1.3) is situated in the Alps Maritimes, 26km north-northeast of Nice and 64km southeast of Lac du Lauzanier. Outcrops of Grès d'Annot Formation are found randomly in the village of Peira Cava, a surface expanding approximately 36km2. Altitudes of the Grès d'Annot outcrops are ranging from 890 - 1787m.

The Lauzanier area and its surroundings are exposed to an alpine climate. After High-Resolution based Rain-Gauge Observations, the average precipitation per year of the region is 2000 - 3000mm/year. The precipitation of the surrounding regions with lower altitudes is seldom more than 500mm/year. Weather changes are abrupt and often unpredictable. This contrast is obviously caused, since this area is a zone where Mediterranean derived warm fronts meets the northern derived cold fronts, resulting higher average precipitation and stronger wind forces than the surrounding areas.
During a personal recognisance of the Lauzanier area on 20 May 97, the area was covered by up to 2m of snow, resulting impossible conditions for fieldwork.
Fieldwork took place from 17 June - 20 August. In the beginning of the period the area was still covered by snow, however the cliffs of the outcrops were predominantly accessible. The maximum temperature at day-time could exceed 20° Celsius and fall below 0° Celsius at night-time. In the beginning of July temperatures fell drastically. Snowfall was even reported at altitudes below 1200m. At altitudes above 2000m snowdrop caused snow depth up till 20cm. At an altitude of 1650m temperatures were as low as 4 - 7°- during the days and droped down to 3 - 5° Celsius below 0° during the night. Mid July temperatures differed extremely from those a couple of weeks earlier. They escalated up to 30° Celsius during the day and felled even below 0° Celsius at night. These extreme differences in temperatures continued throughout all the remaining fieldwork period ending on 20 August.

The area is somewhat funnel-shaped, dipping to the north-northwest, overlain by two roughly north-northwest - south-southeast directed escarpments. These escarpments form three detached north-northwest - south-southeast directed mountain ridges, separated through two equal directed valleys of Vallon du Lauzanier and Vallon du l'Enchastraye (Appendix 1: Geological Map). The morphology of the mountain ridges is controlled by the Grès d'Annot sandstone dips. The significant sharp cuts of the ridges obviously reflects single cycles of the succession, especially seen in the upper part of the succession (Appendix: 3, Panoramic Pictures : 3.1, 3.2, 3.3 and particularly in 3.4). Altitudes are ranging from 1985 - 2955m, giving an average north-northwest dipping slope gradient of 12.6°.
The surface of the study field predominantly exposes solid rock. Scree is regularly covering middle - lower part of the slopes- and even great parts of the valleys. However, a significant zone of the Lauzanier Valley has a few centimetres thick soil and pasture appearance. In contrast, other spots are snow covered all year through. The lake of Lac du Lauzanier is situated in the Lauzanier Valley, while the lake of Lac du l'Enchastraye is located in a valley of a minor escarpment at an altitude of 2702m (Appendix 1: Geological Map).

The dewatering system is controlled by the funnel-shaped morphology, following the two northwards convergent valleys, channelling the Lauzanier- and l'Enchastraye river and gathering at the beginning of the l'Ubayette river in the most northern part of the mapping field in the most southern part of Fourane Valley (Appendix 1: Geological Map). Only the Lauzanier Valley is supplemented with mapping area external water, derived from the southern drainage system of Lac de Derrière la Croix. The l'Enchastraye Valley's water supply is restricted to the study field due to isolation. The middle mountain ridge, between the two valleys, represents the major watershed between the valleys. Additional watershed, preventing drainage of external water are the most eastern and western sited mountain ridges of the study field.

The flora is mostly represented by grass. In water-rich zones, near lakes and streams, the vegetation is dominated by moss. Only one specie of tree is present, restricted to the lower parts of the study area, not existing above altitudes of approximately 2400m. Generally, trees are progressively decreasing up to the timberline level at about 1800m. Above this only few species are represented. The flowers appear in various species, many are endemic such as the Saxifraga Florulenta, which is the symbolic flower of the Parc du Mercantour. Other flowers present are: Anemone Alpina, small-flowered Catchfly, sage-leaved Cistus, Crocus Versicolor, Rock Rose and Star of Bethlehem (information collected from public Parc du Mercantour table at Ponte Rouge parking place).

An overwhelming population of marmots, which also happen to be the Parc du Mercantour mascot (Picture 3.5), particularly represents the Fauna. Further representatives are: moufflons, chamois, ibexes, foxes, and the birds: crows, hawks and eagles. Other reported animals of the region are: weasel; hares and wolves. The wolves were extinct since 1930 in the Parc du Mercantour, however the wolves returned 20 years ago from Italy and repopulated themselves successfully. In the Lac du Lauzanier a significant population of trout is present, yet in lakes above 2400m, they seem to be absent (information collected from public Parc du Mercantour table at Ponte Rouge parking place).