INSTITUTO ARGENTINO DE NIVOLOGIA, GLACIOLOGIA Y CIENCIAS AMBIENTALES
Unidad Ejecutora - UE
Coral patch reef system and associated facies from southwestern Gondwana: paleoenvironmental evolution of the Oxfordian shallow‑marine carbonate platform at Portada Covunco, Neuquén Basin, Argentina
CABALERI, NORA G.; BERESI, MATILDE; ARMELLA, CLAUDIA; LOSER, HANNES
Lugar: Berlin; Año: 2016 vol. 63 p. 2 - 2
During the Middle Oxfordian, the epicontinentalshelf of the Neuquén Basin was a site of major corallineevolution and reef building. This work expounds the studiesperformed on the La Manga patch reefs at Portada Covuncolocality, near Zapala city, Neuquén province. Basedon the results of 12 facies/microfacies types and the verticalsuccession of coral morphotypes a shallowing-upwardtrend ranging from a shallow subtidal-lagoon- to intertidalsettings is inferred. The microfacies model suggests anooidal shoal area in the highest energy zone and variouspatch reefs on the shallow carbonate platform. Autochthonousreefal facies comprise a low diversity of platy coraland mixed coral-siliceous sponge framestone, ramosecoral bafflestone, and microbial bindstone. Non-reefalfacies are composed of ooidal packstone, bedded bioclasticwackestone-packstone, and marl levels. Several shallowing-upward episodes are evidenced by local erosionalsurfaces (main exposure surface-MES). The succession ofplaty corals (exclusively Australoseris) followed by ramosecorals (Etallonasteria, Stelidioseris, and Stephanastrea rollieri)probably reflects local environmental changes. Theupward change in reefal composition is best interpreted inresponse to extrinsic physical parameters (local relativelyminor sea-level fluctuations). Siliceous sponges occur in low percentages. The La Manga reefal succession couldbe correlated with the ?global carbonate reef event?. Thisevent occurred in most basins associated with the Tethyanoceanic belt and the North Atlantic Ocean, in low paleolatitude.The Portada Covunco reefs grew at higher paleolatitudes(nearly 39° south), within an embayment of theNeuquén Basin, with open circulation to the paleo-PacificOcean on the southwestern margin of the Gondwana realm.