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The present paper investigates the outcrop-scale architecture of submarine gravity flow deposits in both moderately to highly confined settings. A significant dataset was gathered on the sand-rich, confined, siliciclastic turbidite system of the Annot Sandstone Formation (SE France). We focused on thick sedimentary bodies formed by depletive gravity flows, in relatively distal settings (sand-rich lobes). The purpose was to investigate the architectural variability of their small scale components (beds and bedsets) and consequently to evaluate the associated heterogeneities (facies changes, grain size, sedimentary features, sediment thickness, etc.). Therefore, we provide a set of detailed descriptions on well-exposed outcrops, through very high-resolution correlation panels built thanks to multiple vertical logs. These turbidite system end-members have rarely been described in such details and have often been considered as laterally continuous and homogeneous. On the basis of the hierarchical subdivisions of turbidite lobes, results show a high complexity in internal architecture from lobe bed to lobe scale whereas large scale (scenery-seismic scale) is characterized by apparently homogeneous tabular and very extensive sandbodies (thus corresponding to the classical definition of “sheet-sands”). This complexity implies heterogeneities not only in terms of sediment thickness changes (abrupt pinch-outs and variable scale compensation features), but also in terms of facies and associated sedimentary features distributions (tractive structures, internal scours with associated by-pass, freezed mudclast-rich layers, etc.). This facies variability is controlled by the interplay between internal erosive bedforms (i.e. large scours) and constructive bedforms, such as dome-shaped or laterally stacked bedsets that are related to local topographic controls and compensation processes. Variability then appears both laterally and vertically. Besides, results also showed small scale evidences of interactions between turbidite flows and basin floor, only expressed at lobe bed to lobe element scale, especially on the basin sides where paleoslope is subject to erosion and remobilisation and where flows can undergo significant changes. Concerning both seismic and reservoir implications, although those deposits are characterized by a sheet-like geometry, this high internal variability necessarily implies heterogeneities in terms of petrophysical characteristics (porosity, permeability) that may have a significant impact on fluid circulation. These elements lead us to reconsider both sedimentary processes involved in their building and also reservoir models that can be established on field analogues.

International audience; The Lauzanier area represents the northernmost extension of the Annot Sandstone series and contains deposits between 650 and 900 m-thick. This basin was active from upper Bartonian or lower Priabonian to early Rupelian. It is composed of two superposed units separated by a major unconformity. The sediment supply is due to channelled flows coming from the south. Flow processes include mass flow to turbidity currents. The size of the particles and the absence of fine-grained sediment suggest a transport over a short distance. The Lower Unit is made of coarse-grained tabular beds interpreted as non-channelled lobe deposits. The Upper Unit is made of massive conglomerates interpreted as the channelled part of lobes. These lobe deposits settle in a tectonically confined basin according to topographic compensation that occurs from bed scale to unit scale. The abrupt progradation between the lower and the upper unit seems related to a major tectonic uplift in the area. This uplift is also suggested by a change in the petrographic nature of the source and an abrupt coarsening of the transported clasts. This field example allows providing high resolution analysis for depositional sedimentary sequences of terminal lobe deposits in a coarse-grained turbidite system. The outcrop analysis shows the lateral evolution of deposits and the system progradation allows a longitudinal analysis of facies evolution by superposing on the same outcrops the channelled lobe system and the non-channelled lobe system. These results of high-resolution outcrop analysis can be extrapolated to results obtained on sedimentary lobes in recent deep-sea turbidite system that are either restricted to cores, or with a lesser resolution (seismic).

The margin of the Gulf of Cadiz is swept by an intermediate current the Mediterranean Outflow Water (MOW) flowing from the Mediterranean to the Atlantic. On the northern margin of the Gulf (Algarve Margin, South Portugal) the MOW intensity is low, and fine-grained contourite drifts are built up with an alongslope alignment. Recent sedimentological studies emphasize the presence of complex process interactions resulting in the formation of a unique depositional architecture. Alongslope processes related to contour currents generate contourite drift, while downslope processes form canyons and channels aligned on deep faults. This paper uses a combined oceanographic and geological dataset to simulate the different types of interactions between gravity processes and contour currents, which were evidenced on this margin. An extrapolation of the contour current intensity has been used based on the present day velocity field and sea-level fluctuations over the simulated geological time-scale. According to our model results, the construction of the contourite drift is closely linked to contour current velocities and directions, the types of sediments transported and the existing topography. Using modern sedimentological understanding of the area, we have correlated gravity flow's strongest activity to sea level lowstand periods mainly due to a closer connection between canyon's mouth and river or deltaic systems. The simulated gravity flows are initialized at different locations and times on the margin depending on the preserved lobes retrieved from seismic analysis. Their resulting morphological features are identified as perched-lobes with volumes and forms close to the ones observed on Portimao and Lagos Drifts. This study provides a process-based understanding of the construction of contourite system and a physical evaluation of the interactions between gravity flows perpendicular to the slope, and alongslope processes. In addition, it shows the influence of autocyclic factors in the construction of contourite sedimentation, which is important to consider in future sedimentary paleo-reconstruction interpretations.