Facies characteristics in a semi-confined basin: from high net:gross channelized sheets to lower net:gross onlap margins. Grand Coyer basin, SE France

Abstract

Common stratigraphic-trap reservoirs in the Gulf of Mexico and along the margins of the Atlantic are found within channelized (e.g., Tahoe) or basin margin settings (e.g., Auger, Mars). These are frequently within small, structurally controlled and topographically complex “fill and spill” minibasins; most often in saltprovinces. High net/gross channel and lower net/gross basin-margin environments occur concurrently in most basins and deciphering the lateral and distal relationships between these environments may be key to understanding reservoir connectivity. The Grand Coyer remnant (Grès d’Annot, southeast France) demonstrates lateral and distal facies changes in a confined basin with complex paleotopography. Within the basin a relatively thin-bedded unit, the Marnes Brunes Inférieures, is interpreted as a distal and lateral equivalent of the thick-bedded and channelized Grès d’Annot (Stanbrook and Clark, 2004). The Marnes Brunes Inférieures represents deposition away from the main axis of flow which is represented by the Grès d’Annot. The finer grained facies of the Marnes Brunes Inférieures is shown to pre-date as well as to intercalate with the higher net/gross sections the Grès d’Annot in both a lateral and distal sense. Also the bedding of the Marnes Brunes Inférieures is shown to onlap the underlying paleotopography, with higher net/gross Grès d’Annot, in turn, onlapping the Marnes Brunes Inférieures; these bedding discordances are often associated with slumping. The intercalation and bedding discordance has implications for hydrocarbon charge, seal and distal connectivity in a lateral sense. Multiple examples of, and the relationships between, these facies are shown.