Diagenetic Processes in Sabkha Deposits and Exploration Potential of the Intracratonic Parecis Basin, Western Brazil
The Parecis Basin is a large intracratonic basin in western Brazil, with an area of approximately 500,000 km2 and a sedimentary fill more than 6 km thick. Knowledge on the geology and stratigraphy of the basin is very scarce, and there are no petrologic studies published on its sedimentary rocks. The petrologic study of coastal sabkha deposits from the Paleozoic Pimenta Bueno Formation revealed that the diagenetic processes are largely facies-controlled, with substantial differences among tidal flat, deltaic and hypersaline lagoon deposits. The sequence of diagenetic processes indicates that diagenetic fluids of two main compositions were responsible for the precipitation of the authigenic minerals. Diagenesis was initially controlled by saline-alkaline, oxidizing porewaters that precipitated Fe oxide coatings, quartz and feldspar overgrowths, anhydrite, dolomite, calcite, chalcedony and microquartz cements. Later introduction of meteoric waters led to the precipitation of calcite, kaolinite and megaquartz. Deltaic sandstones from the Pimenta Bueno Formation show relatively good porosity and occurrences of residual bitumen. Such evidence, together with similarities in depositional facies and diagenetic evolution between the Pimenta Bueno Formation and the Carboniferous deposits of the Juruá Formation, important reservoirs of the Solimões Basin, western Amazon Region, suggests a good potential for hydrocarbon exploration in the Parecis Basin.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009