The deposition of the main reservoir unit in the Santos Basin, the fluvial to shallow marine Upper Cretaceous Ilhabela sandstones, took place during a period of active basaltic volcanism. The volcanic rocks have been partly eroded and subsequently deposited in the reservoir. This has been the cause of a complex diagenetic history. The results are locally occurring sandstones with complex lithologies and elastic properties which differ from the basin trend (Klarner et al, 2005). In order to predict and interpret the amplitudes and AVO behaviour of the Ilhabela reservoir it is essential to map the occurrence of the volcanics as well as the transport direction of their erosional products. We make use of the fact that the volcanic related lithologies display a significantly higher Vp/Vs ratio than the embedding clastic sequences. In this paper, an AVO approach is presented which helps to identify volcanic rocks in the section.


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