Ichnological characterization of Eocene/Oligocene turbidites from the Grès d'Annot Basin, French Alps, SE France

The ichnology of the Grès d'Annot Basin, SE France, is described in detail for the first time. Deep marine palaeoenvironments from basin slope to basin floor settings are preserved. The Grès d'Annot Formation is a sand-rich, thick-bedded, and coarse-grained turbidite succession. The Marnes Brunes Inférieures Formation is a succession of thin-bedded, fine-grained turbidites interpreted as lateral and distal equivalents of the Grès d'Annot Formation. The siliciclastic basin fill is highly bioturbated and characterized by low diversity, high abundance ichnological assemblages which are described herein. Trace fossil and ichnofabric analysis of the Grès d'Annot Basin is used as a tool for interpreting palaeoenvironmental and depositional changes.Heterolithic successions of thin-bedded turbidite sandstone and inter-turbidite mudstone contain the most diverse trace fossil assemblages found in the Grès d'Annot Basin. Sedimentological and ichnological data suggests that heterolithic facies are found on either relatively quiescent confining slopes as lateral and distal equivalents of larger turbidites or as channel-fill deposits. In these settings trace fossil assemblages are dominated by the deposit feeding activity of vagile, endobenthic organisms (e.g., Ophiomorpha, Phycosiphon, Planolites, and Scolicia).Thick-bedded and channel sandstones contain low diversity trace fossil assemblages dominated by Ophiomorpha. Ophiomorpha in the Grès d'Annot Basin is inferred to have been produced by organisms mostly deposit feeding on buried organic-rich material during inter-turbidite intervals. Ophiomorpha rudis is the most prominent trace fossil found in the Grès d'Annot Basin and dominates the ichnofabrics in all locations within the basin. The deep-burrowing ability of the Ophiomorpha animal is considered to be an adaptation for exploiting buried organic nutrients found in inter-turbidite mudstones.