Architecture of deep-marine confined sandstone bodies, Eocene-Oligocene Gres d'Annot formation, SE France.
2015-11-19T09:05:30Z (GMT) by
The Tertiary upper Eocene-lower Oligocene Gres d'Annot Formation of southeast France essentially is a sand-rich deep-marine turbidite system deposited in a foreland basin with a structurally complex basin-floor topography, where local basinal highs exceeded 400 m over 8 km. Overall, the Gres d'Annot Formation lacks features typical of submarine fans. Deposition of turbidite sandstones and other sediment gravity flow deposits first occurred within basinal topographic lows as a passive fill which progressively buried these features. Within the southern part of the Gres d'Annot Formation outcrops two separate basin-floor systems are identified on the basis of palaeocurrent dispersal patterns and sandstone onlaps against the basin floor topography. These two systems are the eastern basin-floor system, and the western basin-floor system. The eastern basin-floor system includes the Gres d'Annot Formation outcrops from Peira Cava, Contes and Menton. The oldest part of the sandstone succession in the eastern system is located at Peira Cava where deposition took place at the base of a local submarine slope as relatively sand-rich deposits which tend to shale out into the more distal parts of the basin. The sandstone succession in the Contes and Menton areas show an upsection change from amalgamated and non-amalgamated sandstone packets to essentially amalgamated sandstones. The western basin-floor system includes the St Antonin, Entrevaux, Annot and Grand Coyer outcrops of the Gres d'Annot Fonnation. The St Antonin section comprises three members, each showing an upsection change from thin-bedded to thick bedded turbidites to debris-flow conglomerates, to thin bedded sandstones interpreted as distal shelf/upper-slope storm deposits. The Entrevaux succession shows an upsection change from thin-bedded fine-grained to thicker bedded and coarser grained turbidites. The Annot sandstone succession shows an upsection change from essentially non-amalgamated sandstones to amalgamated sandstone packets and interbedded thin-bedded relatively fine-grained turbidites. The Grand Coyer succession comprises amalgamated turbidite sandstone packets with interbedded sandstone and mudstone packets with small-scale channel development within some of the sandstone/mudstone packets. The western basin-floor system is interpreted as an overall progradation and aggradation of a sand-rich submarine ramp/delta slope into the deeper parts of the western basin floor system. Comparisons of the Gres d'Annot Formation with the deep-marine sandstone reservoirs of the Palaeogene of the northern North Sea, show a similarity of confinement of sandstones and sandstone lobes and may provide a useful comparative system.