Palynostratigraphy of the Ramon and Solimões formations in the Acre Basin, Brazil

Abstract

The Acre Basin has a complex geology that is related to the Andean uplift and it still is one of the least understood Brazilian sedimentary basins due in part to difficulties in accessing outcrops. Its geological history is related to several subandean basins including Marañon, Ucayali and Madre de Dios in Peru, and the Solimões Basin in Brazil. These basins have potential for oil and gas which raised interest in the Brazilian oil industry since 1930. During this period, 11 wells were drilled in Acre, one of which is herein studied (2CDST001-AC). Available information from this 2600 m-thick borehole suggested an age spanning from the Albian to the Pliocene. We performed palynological analyses in 29 core-samples spread along the well. Our new data indicated much younger ages, spanning from Eocene to late Miocene together with a middle to late Miocene marine incursion. The palynological assemblage of the Solimões Formation in the Acre basin is similar to that of the adjacent Solimões Basin, but with a much thicker stratigraphic sequence offering a greater potential to unravel the history of western Amazonia during the Cenozoic.