Sedimentology and diagenesis of the middle jurassic lugoba carbonate succession in the Ruvu basin, coastal Tanzania

This study presents the first detailed, outcrop-based sedimentologic investigation, and petrographic analysis of the Middle Jurassic (Bajocian-Bathonian) Lugoba succession of the Ruvu Basin, located in the northern coastal Tanzania. The aim of this investigation is to characterize sedimentary facies, establish depositional environments and determine carbonate diagenesis and their effect on porosity of these successions. Three diagnostic facies associations comprising seven facies were identified and provide the basis for recognition of three key depositional environments: 1) lagoon; 2) reefal; and 3) beach environments. Petrographic analysis of the carbonate facies reveals four main diagenetic processes: 1) cementation; 2) micritization; 3) bioclastic neomorphism; and 4) dolomitization. The diagenetic processes occurred mainly in the eogenesis diagenetic regime. Calcite cementation and neomorphism are the major diagenetic processes that occluded the porosity in some intervals of the Middle Jurassic Lugoba carbonates. The observed porosity is low in reefal and lagoonal deposits, typically less than 6, but relatively higher (moderate reservoir quality) in beach related deposits. This discovery of potential new Jurassic hydrocarbon reservoir in coastal Tanzania basin could be important for future on/offshore oil and gas exploration in East Africa.