The Cañadón Asfalto Basin as a Surface Analogue of the Offshore Pre-Salt Basins

Authors: Roberto A. Scasso, IGeBA-CONICET-Universidad de Buenos Aires (presenter), Ignacio H. Escapa, Rubén N. Cúneo, CONICET-Museo Paleontológico Egidio Feruglio; Jahandar Ramezani, Massachusetts Institute of Technology

The Cañadón Asfalto Basin, in central Patagonia, shows a 3000 m thick succession of Jurassic and Cretaceous terrestrial sediments subdivided into three megasequences superbly exposed along the Chubut River canyon. The lower J1 megasequence (Hettangian to Late Bajocian) represents the incipient to juvenile stages of an extensional rift basin with high volcaniclastic input in fluvial and lacustrine environments. The seasonally wet, temperate/warm climate favored high productivity and biodiversity. During this stage tectonic relief controlled the accumulation of siliciclastic-dominated sediments in relatively small, fault-bounded depocenters, where later accumulated breccias, agglomerates and ignimbrites associated with an andesitic volcanism centered along the transfer zones. Further subsidence led to formation of microbial limestones capping and fringing upon the high-relief volcanic complexes, with thick, lacustrine limestones and black shales with interbedded basalts, in the deeper part of the depocenters. Different units in Megasequence J1 are separated by erosive or angular unconformities of limited extent, typical of high-relief volcanic settings and lacking of regional significance. The size and shape of the depocenters, the geological succession of depositional and volcanic events as well as the geometry of the sedimentary bodies between the Cañadón Asfalto and Pre-Salt are surprinsingly similar. Furthermore, the composition of the sediments (microbial/silicified limestones, volcaniclastics, black shales) of the J1 Megasequence closely resemble those of the sediments of the Pre-Salt basins and make the Cañadón Asfalto basin a remarkable surface example allowing direct observation of the sedimentary bodies, their lateral changes and complex geometric relations.

Bio:

Roberto A. Scasso, University of Buenos Aires - CONICET

Roberto holds a PhD in Geological Sciences from the University of Buenos Aires. He is Professor of Sedimentology and Head Researcher at the University of Buenos Aires – CONICET, focused on Neuquén and Cañadón Asfalto basins.

Roberto is a member of AGA (Argentine Geological Association), Argentine Association of Sedimentology, IAS and SEPM.