Abstract Deep-water sedimentation is currently a major focus of both academic research and industrial interest. Recent studies have emphasized the fundamental influence of seafloor topography on the growth and morphology of submarine ‘fans’: in many turbidite systems and turbidite hydrocarbon reservoirs, depositional system development has been moderately to strongly confined by pre-existing bounding slopes. This publication examines aspects of sediment dispersal and accumulation in deepwater systems where basin-floor topography has profoundly affected deposition, and the associated controls on hydrocarbon reservoir architecture and heterogeneity. The papers herein offer a global perspective which is wide-ranging in terms of both approach and location, including contrasting case studies of outcrop, subsurface, modern and experimental systems.

Abstract For over 150 years, the fascinating outcrops of the Grès d'Annot Formation of SE France have attracted the interest of many geologists, from different countries and from academic as well as industrial spheres. As relates in this volume, the initial interest was stratigraphic (identification of contemporaneous formations corresponding to continental to marine settings) and structural: the recognition of large displacements of Alpine nappes led to new concepts of mountain formation. Concerning the sedimentology of deep marine deposits, major advances were made in the late 1950s and early 1960s with the progressive emergence of the turbidite concept and its recognition in the field ( Faure-Muret et al. 1956 ; Kuenen et al. 1957 ; Bouma 1962 ; Lanteaume et al. 1967 ), and the development of the first submarine canyon/fan valley model ( Stanley 1961 ). From that time onwards the Grès d'Annot outcrops were used as a training area in the field, with the organization of numerous meetings and field courses (for example Beaudoin et al. 1975 ; Stanley 1975 ). Renewal of this research activity was stimulated in the 1980s by the upsurge of intensive exploration on continental margins and the emergence of seismic stratigraphy; the Grès d'Annot were studied in order to help seismic interpretation and, at the same time, complementary flume experiments of submarine avalanches were developed for better understanding of turbidity current processes ( Laval et al. 1988 ). The critical field studies in the 1980s led to the first comprehensive

Abstract High-frequency cycles (genetic units or parasequences), with a mean duration of 20000 years, have been identified in the Grè d'Annot turbidite system of the southern Alpine foreland basin (Late Eocene/Early Oligocene). They filled a narrow (2–8 km wide) synsedimentary syncline that formed a confined basin fed upward by a fan-delta located on a narrow shelf. These cycles are 10m thick, and each consists of a basal heterolithic component and an upper sandy homolithic unit, traceable over at least 10 km. They result from the superposition of (1) a progradational phase with an accretionary system (low-angle accretionary bedsets) and a feeder system (by-pass to high preservation oblique laminasets) and (2) an aggradational phase with a ‘spread’ system overlain by a condensed interval. The progradational phase shows very low-angle clinoforms (low-angle accretionary sets, 1–2 m high, a few tens to a few hundreds of metres long) fed by erosional structures (channels or large scours, 0.2–2 m deep, a few metres to a few tens of metres wide). The aggradational phase (subplanar laminasets, ‘scour and fill’ structures) forms a ramp, and drapes the underlying sediments. These progradational geometries may be explained by the narrow sub-basin morphology and by the transition from channelled flow (updip narrow part) to unconfined flow (downdip wider part). These genetic units directly record the variations in sedimentation rate of the feeding fan-delta on the shelf, which are controlled by the 20 000 year cycles of sea-level change.

Abstract The Côte de l’Âne section has been previously interpreted as shallow marine deposits (deltaic system with delta-front to bay head and back-barrier environments). The purpose of this article is (1) to suggest a reinterpretation of these facies of the Grès d'Annot in this area as deep marine deposits and (2) to discuss the effect of an evolving seafloor topography during sedimentation on the stacking pattern of turbiditic deposits. The facies analysis of the sedimentary succession is based on eight measured sedimentological logs and on the visual correlation of identified surfaces. Detailed sedimentological observations permitted the identification of a turbidite facies spectrum, schematized in nine facies associations. Outcrop-scale analysis highlights a downstream thickening of the sedimentary sequence resulting from a strong control by tectonic deformation. This deformation is mainly a flexure with a half-wavelength longer than 500m. Associated normal faults may be related to a gravity slide of unconsolidated sediments accommodated within the flexure. Finally, detailed correlations based on the genetic unit model in the Restefonds-Sanguinière system establish the effect of an evolving seafloor topography during sedimentation on the stacking pattern of turbiditic deposits.

Abstract The deep marine Grès d'Annot Formation is one of the best exposed analogues to sand-rich turbidite sub-surface systems. Provenance and reservoir heterogeneities have been investigated through a geochemical study of different areas and facies in this formation. Most compositions may be described as mixtures between carbonate and three clastic end-members, i.e. clay, framework grains and a subset of the heavy minerals (zircon, Tioxide, apatite, monazite). These end-members have a nearly uniform chemistry over the studied area and a granite-dominated provenance consistent with a Corsica-Sardinia source hypothesis. This rather uniform provenance makes the Annot Formation a favourable case for exploring the relationships between facies and geochemistry. Not only do different facies differ in average composition, but chemical variations at the bed scale fingerprint the depositional mechanism: archetypal (graded) turbidites and traction-dominated (over-bank) deposits display contrasting variation trends in geochemical plots. The local-scale variation patterns and the general relationship between grain size and chemistry are tentatively integrated in a single differentiation model, providing a rationale for the use of geochemistry in provenance studies, and a possible way to characterize sedimentary facies.

Abstract Onlap terminations of deep-marine sandstones in the Grès d'Annot, SE France, exhibit a range of styles, from abrupt onlap to feathering ‘aggradational onlap’ geometries. These are well exhibited in the large exposure of southward onlap terminations at Montagne de Chalufy, on the southern end of the Trois Evêchés Massif (Alpes de Haute Provence). These stratal architectures are here simulated by geometrical models that are governed simply by bounding slope gradients and the ratio of coeval slope to basinal aggradation rates. In cases of no coeval deposition on bounding slopes, pure onlap results. In cases of high slope aggradation rates relative to basinal aggradation rates, a feathered geometry results with successive sandstone beds onlapping against successively younger slope drapes. The cyclicity of alternating sand-rich and sand-poor packets seen at Chalufy results in a stepped climbing trajectory of successive slope base positions, with climb angle equal to bounding slope angle when mud-poor sandy flows deposited sandstone bodies with abrupt onlap, and climbing more steeply when slope drapes are deposited. An implication of this result is that any zones of facies change and palaeocurrent swing that are related to distance from bounding slope will exhibit a comparable vertical trajectory through time. The two end member termination types can be compared with the convergent-baselapping and convergent-thinning seismic facies used in the Gulf of Mexico subsurface and elsewhere. The convergent-baselapping seismic facies may include both abrupt onlap and intervals of feathering aggradational onlap if the presence of slope drapes is not resolvable by the frequency content of the available seismic data.

Abstract The increasing use of three-dimensional seismic data for reservoir characterization justifies the need for an accurate and fast seismic modelling tool. Synthetic seismic data sets, where the geological model is controlled at each location, provide crucial information for the understanding of the seismic response in connection with various geological features. The method used here involves a wave equation approximation based on ray tracing and Born formalism in the context of a one-dimensional background, thereby providing economic computation of a very useful subset of geological models. The software enables a high level of flexibility to be applied to a range of realistic experiments. In particular the software provides pre-stack multi-component seismic response of a three-dimensional heterogeneous reservoir, including both reflected and converted waves, at the level of the target. In order to analyse and reconstruct the architecture of deep-water gravity deposits, we present a realistic synthetic seismic experiment of one Grès d'Annot outcrop. A geological interpretation of the outcrop has been based on photo panoramas calibrated with vertical sedimentological sections. The internal distribution of facies has been interpolated using geostatistical simulation, with one of the stochastic realizations of the reservoir architecture serving as the three-dimensional cube of lithofacies corresponding to the reservoir model. These lithofacies were assigned elastic parameters of an analogue Brazilian field. The reservoir model is then buried within a smooth background model, and a seismic model generated. The purpose of generating three-dimensional seismic models is to analyse the seismic signature of the different sedimentary architectures, in order to provide guidelines for the seismic interpretation of comparable subsurface reservoirs. Compared with convolution results, the computed synthetic data are more realistic and closer to the actual seismic data. This is mainly due to the fact that the method takes into account the lateral heterogeneity included in the vicinity of each reflecting point.

Abstract The Eocene deep-water sand-rich deposits of the Grès d'Annot of southern France have been used as outcrop analogues for offshore Cretaceous reservoirs of Campos Basin, southeastern Brazil. The analogy is chiefly based on the sand-rich, confined nature of the two systems. Such application can be questioned as the contrasting geological settings, i.e. convergent versus passive margin, could produce rather different depositional scenarios. Detailed comparison between the two systems permits, however, recognizing additional similarities, and also some differences, whose recognition is important to ensure the correct application of the Grès d'Annot as an analogue for this and other passive-margin reservoirs. Comparative analysis of channel dimensions, facies continuity, and three-dimensional expression suggests that confined sand-rich systems show many similarities in terms of critical reservoir heterogeneity, providing that palaeotopographic control was similar, regardless of the tectonic environment in which they were formed. In addition, contrasts found among sequences in the same tectonic setting suggest that other factors (such as, for example, sand/shale ratio of the sediment input) play an important role in defining reservoir architecture. These observations further suggest that, once similarities and differences are correctly understood, analogue data, even from quite different tectonic settings, may provide a powerful tool for improving subsurface reservoir models.

Abstract The Eocene-Oligocene Annot Sandstone of South East France is a sand-rich turbiditic system, up to 1000 m thick, which was deposited in several parallel and tectonically controlled sub-basins. For reservoir characterization purposes, three kilometer-scale outcrop areas were studied in detail, resulting in bed-scale, 2D and 3D architecture descriptions. The western Annot-Chalufy confined sub-basin, probably fed from a fan-delta located near Saint Antonin, shows a downstream evolution from very coarse-grained erosive channels (developing lateral terrace deposits) to tabular channelized or depositional lobes separated by thick heterolithic levels acting as major permeability barriers. The eastern Sanguinière narrow sub-basin was probably fed by multiple braided deltas at the border of the Alpine mountain chain to the east. In a ramp setting, coarsening then fining-upward sequences register the increase then decrease in flow energy of coarse-grained amalgamated channelized turbidites that evolve downstream into erosional channels, then finer-grained slope depositional channels and elongated sand tongues. In this framework, the geometrical and geostatistical characteristics of the constitutive architectural elements have been quantified. 3D geocellular reservoir models of the outcrops have been reconstructed and used for synthetic seismic modeling.

Abstract Geostatistical reservoir simulations are now common tools used in intensive exploration and reservoir appraisal; however, at this stage of intensive exploration and appraisal, significant uncertainty still exists due to the limited amount of hard data. A way to better constrain these stochastic simulations could be to integrate information coming from a stratigraphic modeling approach. Stratigraphic models give information about geometry, continuity, location, and dimensions of the main depositional sequences in a study area by using input data such as eustasy, subsidence, and sediment supply; however, geostatistical models aim to generate equiprobable images of the reservoirs inside the main sequences, which honor the well data, and whose variability can be linked to the variability computed from the data. This approach has been validated on an outcrop case study in the Campanian of the San Juan basin in Colorado. The IFP (Institut Français du Pétrole) stratigraphic model Dionisos has been used to introduce quantitative sedimentological knowledge in the stochastic reservoir model heresim. The global trend of the sand:shale ratio evolution in the study area also has been taken into account as an external drift in the geostatistical simulations. For this purpose, the usual algorithm in heresim has been extended for nonstationary (sedimentary trends from continental to marine environments) cases by using the facies proportion blocks instead of one single proportion curve. The coupling of both methodologies allows for more geologically constrained images of the reservoir.