Sedimentology and diagenesis of the middle jurassic Msolwa succession in the Ruvu basin Tanzania

This study presents outcrop-based sedimentology and post-depositional diagenetic processes that characterize the Middle Jurassic Msolwa in the Ruvu basin, eastern Tanzania. Sedimentological analysis reveals 4 genetically-related facies associations comprising 8 facies, which are used to recognize 4 depositional environments: 1) alluvial fan 2) braided river channels 3) overbank environments and 4) intertidal flat environments. The identified lithofacies across the Msolwa succession suggests high energy mass flows influenced by shallow marine water. These mass flows were triggered by tectonic activities mainly the Middle Jurassic reactivation of the Tanga fault caused by the break-up of Gondwana Super continent and associated transgression. Petrographic analysis reveals that the Msolwa sedimentary rocks have undergone multiple diagenetic alteration including cementation, compaction, neomorphism, dissolution and microbial micritization. These postdepositional processes appear to have reduced porosity (and permiability) of the Msolwa sedimentary rock units and thus negatively affecting their reservoir capacity. The results obtained may be of help in predicting reservoir quality and properties of the equivalent sedimentary units deposited in different contexts.