Sedimentology, depositional architecture and diagenetic overprints of a carbonate tidal channel system: An example from the Middle Eocene of northern Egypt

Abstract

The carbonate tidal channels are major compartment in the carbonate platform environments. Sedimentology and heterogeneities of the carbonate tidal channels are poorly documented in the rock record as most studies focused on recent analogues. This study introduces a sedimentological model for carbonate tidal channels using a Bartonian outcrop example from northern Egypt, and it contributes to understanding their reservoir controls. Five channel architectures were identified including braided type (tidal inlet), laterally migrating, stacked meandering, single meandering, and small-scale tidal creek channels depending on both the macroscale outcrop and microscale petrograhic investigations. Four sedimentary facies types have been recognized: stratified and cross-stratifed bioclastic foraminiferal grainstone, wavy bedded foraminiferal packstone, laminated to structureless foraminiferal wackestone and structureless lime mudstone. The tidal inlet channel shows the highest reservoir quality and larger reservoir bodies. The stacked and lateral migrating meandering channels are characterized by good reservoir quality. They grade lagoon-ward into single meandering channel and subsequently to tidal creeks, whereas the reservoir quality decreases toward the lagoon. On the mesoscale, the grainestone-rich bodies at the channel lower part exhibit good reservoir quality, while the muddy-rich ponds behave as barriers. On the microscale, the dissolution and microfracturing are the main diagenetic processes enhancing the reservoir quality, while the cementation, compaction, micritization and neomorphism diminishing the reservoir quality.