A sedimentary model for the Kimmerídgian Tordillo Formation of the Neuquén basin is proposed. Through the measurement of three strati graphic logs, an ephemeral fluvial system associated with continental mud flats is proposed. The proximal areas are characterised by gravelly and sandy-gravelly longitudinal bars formed in a traction-dominated braid-plain. Towards distal areas, sandy lobes composed of small 3D bars and aggrading current ripples formed during sudden non-channelised floods, alternate with mudflat deposits. This ephemeral fluvial system was developed under a generalised phase of arid to semiarid climate. The volcaniclastic nature of the Tordillo deposits and the palaeocurrent trends allow to suggest a positive land located to the south (Dorsal de Huincul). The uplift of this structure was intense and active at the time of deposition of the Tordillo Formation