The Tynemouth Creek Formation (formerly the Tynemouth Creek and McCoy Head Formation) is redefined and detailed stratigraphic and structural sections through representative parts of the formation are presented. The Tynemouth Creek Formation is of Lower Pennsylvanian age and is at least 800 m thick. It is dominantly clastic, shows an overall upward-coarsening from siltstones and sandstones into conglomerates and was deposited in an alluvial fan and piedmont setting. Six sedimentary facies are recognized. (1) Coarse, polymict, clast-supported conglomerates dominate the upper part of the formation.(2) Tabular and channelized pebbly sandstones, up to 8 m thick represent braided channels, the former characterized by unstable banks and laterally migrating channels while the latter may have formed on the upper fan when periodic tectonic movement caused rejuvenation of the streams and resultant channel incision. (3) Erosive-based sandstones up to 30 m thick occur near the base of the formation and are interpreted as point-har deposits of large meandering rivers that existed on the floor of the basin beyond the alluvial fan toe. (4) Thin-bedded sandstones and siltstones were deposited on the banks and in abandoned channels of rivers which locally supported dense growths of CaZamiteA.(5) Red siltstones and sheet sandstones were laid down in interchannel and distal fan areas, the former by low-energy flooding and perhaps wind action; the latter by sheet floods. Paleosols and calcitic nodules are characteristic of this facies. (6) In areas starved of clastic sediment, shallow lakes occasionally formed and accumulated thin bioclastic (ostracode/gastropod/spirorbid) or algal limestones. Palaeocurrents are unimodal with a mean flow towards the north-west. The Tynemouth Creek Formation probably represents a sector of a large alluvial fan that built northward from the southern, fault-bounded margin of the Cumberland Basin. The upward-coarsening of the sequence may record continued tectonic rejuvenation of the source area, causing fan progradation and deposition of coarse, fan-head conglomerates over finer, lower fan sediments. A climate of alternating wet and (?hot) dry seasons is inferred from the sedimentary evidence as a whole. Un groupement unimodal des paleocourants est note, avec un vecteur moyen vers le nord-ouest. La formation de Tynemouth Creek correspond probablement a la portion d'un grand cone de dejection qui s'est edifie en direction nord, a partir de la bordure faillee du Bassin de Cumberland. La granulometrie croissante de la sequence correspond peut etre a un rajeunissement tectonique continuel de la region source, accompagne de la progression du cone ainsi que de la deposition de conglomerats grossiers du cone superieur sur les sediments plus fins de la partie inferieure du cone. Un climat marque par l'alternance entre saison humide et saison seche (chaude?) est deduit a partir des donnees sedimentologiques.