CONICET | Buscador de Institutos y Recursos Humanos

During the Oxfordian coral-reefs flourished at mid-palaeolatitude on the Neuquen epicontinental shelf. The reefal facies (bioherms) of the La Manga Formation at Portada Covunco have been studied to identify and characterize different types of Late Jurassic reefs. Sedimentological and paleoecological observation lead to the reconstruction of a coral reefal tract in a shallowing-upward succession evidenced by the associated microfacies. Seven generic reef types are recognized in the patch-framestones. These are: I) platy microsolenids (Microsolena) with growth entirely lateral, developed within clean limestone facies; II) reefal thickets dominated by tall dense phaceloid colonies (Calamophylliopsis ?) developed in pure carbonate muds; III) mixed coral-siliceous sponge ( hexactinellids and lithistids) reef with echinoids in marly facies; IV) branching ramose coral (reef developed in marly facies; V) microbial crusts-coral reef dominated by diverse massive colonies (thamnastero-meandroide), ramose corals (Actinastrea) and domal, brain corals (Australoseris) and some small siliceous sponges; VI) platy- corals associated with diverse bioclastic material (cidarid echinoids, bivalves, gastropods, brachiopods, coralline sponges, bryozoans, serpulids, Tubiphytes; VII) tall dense phaceloid colonies developind among sand-shoal and coral debris channels. Such succession is repetitive. The generation of coral reefs and their compositional types were probably controlled by allogenic factors, such as the variations in oxygen and nutrient content, terrigenous input, climatic changes, water depth and accumulation rate. This reefal succesion can be correlated with the global carbonate reef event, which occurred widespread within the epicontinental seas bordering the northern Tethyan ocean and the marginal basins of the young North Atlantic ocean.