• Lagoonal-peritidal facies (cycles) with abundant bivalves including megalodontids, and gastropods, alternated with decimetric corals horizons and nodular marls, probably deposited on a broad carbonate platform.

• The Luning Formation crops out in a wide area of Western Nevada and is part of the Luning Allochthon, a series of nappes composed of Triassic and Jurassic sedimentary rocks and Permian to Triassic volcanic rocks (Oldow 1981). The thickest succession of the Luning Formation is located north of the Pilot Mountain (Tab. 1) where it shows a total thickness exceeding 2000 m (Sandy & Stanley 1993), divided in three members: Lower, Middle and Upper. The Lower Member is an alternation of shales and coral and sponge biostromes, while the middle member is fully terrigenous, showing alternation of shales, sandstones and conglomerates. The Upper (algae-bearing) Member shows a regular alternation of lagoonal-peritidal facies, with abundant bivalves, gastropods and megalodonts, alternated with decimeter-thick coral horizons and nodular marls. Muller & eFrguson (1936) had already evidenced the abundance of fossils in the Upper Member of the Luning Formation. Preliminary conodont results indicate a middle Norian age for this portion of the formation.

•The presence of a thick terrigenous member, around 600 m (Sandy & Stanley 1993) plus the occurrence of marls with variable percentage of clay minerals, might suggest that the Luning Formation was probably deposited close to the American continental margin and not in the middle of Panthalassa.