CABALERI nora Graciela
congresos y reuniones científicas
Oligocene lacustrine carbonate basin in the NW Extraandean Patagonia (Carinao Formation), Argentina.
CABALERI, NORA; UBALDÓN, MARÍA CECILIA
Congreso; EUG 10; 1999
The Lacustrine Oligocene Carbonate Basin represented by the strata of Carinao Formation is here pesented. Microfacies are described and depositional environment is inferred. The outcrops of the Carinao Formation crop out at the western edge of Sierra de Tecka (43º 10´-43º40´S Lat. and 70º69´W Long.), Chubut Province, NW Extraandean Patagonia. Limestone facies and microfacies of Carinao Formation represent distinct lacustrine environments: bioherms, ponds and fluvial channels. Eight bioherms facies were distinguished: Stromatolites with fenestral fabric, Radial dome microbialite, Microbialite with radial dendrite macrofabric, Microbialite showing fenestral fabric, Pinnacle stromatolites, Laminae microbialite, Microbialite with occasional fenestras and Microbialite mudstone interlayered with intrabioclastic wackestone. The bioherms show different shapes. Some are elongated bars parallel to the paleoshore and resistant to the wave agitation, other are coalescent structures, or are mushroom-shaped. In cross section they show several successive growth phases.The pond microfacies consists of: peloidal grainstone and intraclastic floastone. In this environment the energy differs from moderate to high, with wave agitation. The ponds constitute the boundary of the microbial forms.The fluvial channel microfacies are composed of bioclastic grainstones, biointraclastic grainstone, intraclastic grainstone and floastone. At the northern part of the basin, the very thick fluvial deposits represent channels, which diverge southwards, making up a distributary channel system. On the channel surface current ripples, mud cracks, bird foot prints and casts of sole marks are common.The microfossil association contains Eucypris sp., Limnocythere sp. and Candona sp., characteristic ostracods of fresh water environments and they are frequent in the ponds and fluvial channels facies.