Diagenesis and reservoir-quality evolution of fluvial sandstones during progressive burial and uplift: Evidence from the Upper Jurassic Boipeba Member, Reconcavo basin, northeastern Brazil

The reservoir quality of fluvial sandstones of the Upper Jurassic Boipeba M ember, Reconcavo basin, northeastern Brazil, is highly heterogeneous and co ntrolled by eodiagenesis under semiarid climate, mesodiagenesis during buri al to a depth of 3500 m, and telodiagenesis due to local uplift. Eodiagenes is resulted in mechanical compaction, calcite cementation, clay infiltratio n, and limited grain dissolution, whereas mesodiagenesis resulted in the pr ecipitation of calcite cement and quartz overgrowths, intergranular quartz- grain dissolution, chloritization and illitization of smectite, and albitiz ation of feldspars. Sandstones continuously buried at maximum burial depths of about 1600 m (T = 65 degrees C) since 125 Ma display a relatively great er degree of mesogenetic modifications and, on average, poorer reservoir qu ality than sandstones that were buried deeper (2100 m, T = 75 degrees C) pr ior to uplift, but only since 13 Ma. Uplift, which affected the sequence al ong the western border of the basin, has resulted in telogenetic dissolutio n of framework silicates and formation of kaolinite. Relatively good reserv oir quality in the deeply buried sandstones occurs when (1) the grains are coated with a thin layer of chloritized infiltrated smectite, (2) there is little or no pseudomatrix, and (3) there are widely scattered patches of eo genetic calcite cement that supported the framework of sandstones against c ompaction.