Early Jurassic coral reef development outside Tethys: an example from western Argentina

Abstract

Coral-reefs suffered during the end-Triassic extinction event, being scarce during the Early Jurassic. This paper deals with an Early Pliensbachian reef from Puesto Araya, southern Mendoza, Argentina. Five sections were logged ensuring lateral and vertical coverage across the reef outcrop. All determinable associated faunal elements of the reef were recorded. The reef structure was generated by phaceloid and cerioid coralla, and at least two, most likely three, developmental phases were recognized. The first of these shows an early demise, the second a neat vertical succession. The third phase may show the main successional stages or, less likely, may represent a progradation of the previous phase. Phaceloid coralla dominate the colonization stage, and cerioid ones the domination stage; in the diversification stage cerioid morphologies prevail or else; both morphologies occur in similar proportion. All the structural guilds were identified in the Puesto Araya reef, particularly during the diversification stage. Suspension feeders dominate the trophic guilds, though deposit-feeders, herbivores, and carnivores were also present, and cerioid corals might have been zooxanthellate. Although developing some relief over the surrounding sea floor (a true bioherm), the coral growth was constratal. Unlike other coral-reefs, the microfossil assemblage is dominated by nodosarid foraminifers, being most diverse during the diversification stage of the third phase. This reefal structure shares many features with the Sinemurian coral-reefs from the East Pacific realm, but the dominance of cerioid coralla in later seral stages is a novelty of the Puesto Araya reef.