The Silurian of Saudi Arabia: thermal maturity, burial history and geotectonic environment

Abstract

Chitinozoan reflectivities were measured from five sub-surface Silurian sequences in central and northern Saudi Arabia. These defined steep reflectivity gradients which demonstrate a pre-Permian episode of high heat flow. Consideration of Palaeozoic burial history shows a coincidence of high heat flow with high sedimentation rates indicating a Silurian thermal event. Calculated geothermal gradients are all in excess of 90°C/km. These high geothermal gradients can be kinetically modelled by assuming an Early Silurian thermal event with a 15 Myr duration. The geotectonic environment of this high heat flow is considered to be an extensional rift. The implications for hydrocarbon generation are early oil generation in areas with the highest reflectivity gradients. Some wells still have immature Silurian source rocks which indicates that there may still be areas under deeper Mesozoic burial with a younger history of hydrocarbon generation.