The great Santonian fire: implications for the regional geology and petroleum exploration

Abstract

This paper presents the new idea of a great fire that occurred in the Santonian, in the region that corresponds nowadays to southeast Brazil. This conclu-sion derives from palynological analyses, which have often reported palynofacies with predominant carbonized terrestrial organic matter in the Santonian of Campos and Santos basins. The most curious aspect of the Santonian palynofacies from the basins of the Brazilian southeastern continental margin is the fact that well preserved palynomorphs coexist with carbonized terrestrial organic matter. In former times it was believed that this feature was due to a mixing of materials coming from different stratigraphic levels, since early observations were based on cutting samples. Recently, however, new data coming from core and sidewall samples confirm the presence of organic matter with different carbonization levels in a same stratum. In order to explain this intriguing palynofacies association, we present the hypothesis that most organic matter comprised by this stratigraphic level was affected by an extensive forest fire. The main evidence to support this assumption is the fact that marine palynomorphs (dinocysts) associated to the carbonized organic matter are never burned. Incendiary volcanic activities, accompanied by pyroclastic flows are suspected to be the main cause for the aforesaid fires in the studied area.