We studied the rarely exposed Oligocene Ma'ahm Beds at Quriyat for their lithostratigraphy, microfacies and depositional environment. In addition, we intend to contribute to the general understanding of coral patch reefs. Our bed-scale logs include thin-section analyses of standard microfacies (SMF) types allowing direct comparisons with those of the Ma'ahm Beds 80 km to the NW in the Al-Khod area, the so far best-described outcrop area of Oligocene age in Oman. The Ma'ahm Beds at Quriyat are ∼50 m thick, which lies within the thickness range of the Ma'ahm Beds at Al-Khod. Coral patch reef complexes occur in both places. The one at Quriyat contains reefs of different symmetries. The SMF types of the massively bedded reefs and the associated bioclastic limestone beds represent facies zone 7 as at Al-Khod, indicating a depositional environment within the photic zone, above fair-weather wave base, in an open lagoon. In both regions, the lagoons were most likely protected by coral barrier reefs with intervening gaps. The patch reefs at Quriyat were abandoned, and new ones formed in oceanward direction to keep up with a dropping eustatic sea-level. At the flanks of the largest patch reef at Quriyat, bioclastic limestones with reef debris display onlap geometries. Only the limestones at Quriyat are associated with silty marl and calcareous, marly sandstone, which accumulated in a foreshore environment, either as longshore drift, or cays or combination/alternation thereof. These siliciclastic deposits are likely more voluminous than the limestones of the Ma'ahm Beds in the eastern part of the Arabian Plate, which should be considered when constructing paleo-facies maps. This abundant fine-grained marly material implies that Oligocene aquiclude horizons exist. We suggest that coral patch reefs should measure at least 5 m in diameter to fulfill typical ecological reef functions.
The Oligocene “Ma’ahm Beds” of NE Oman (eastern Arabia): Microfacies and lithostratigraphy of a mixed carbonate system with coral patch reefs.
Gianluca Frijia
2026
Abstract
We studied the rarely exposed Oligocene Ma'ahm Beds at Quriyat for their lithostratigraphy, microfacies and depositional environment. In addition, we intend to contribute to the general understanding of coral patch reefs. Our bed-scale logs include thin-section analyses of standard microfacies (SMF) types allowing direct comparisons with those of the Ma'ahm Beds 80 km to the NW in the Al-Khod area, the so far best-described outcrop area of Oligocene age in Oman. The Ma'ahm Beds at Quriyat are ∼50 m thick, which lies within the thickness range of the Ma'ahm Beds at Al-Khod. Coral patch reef complexes occur in both places. The one at Quriyat contains reefs of different symmetries. The SMF types of the massively bedded reefs and the associated bioclastic limestone beds represent facies zone 7 as at Al-Khod, indicating a depositional environment within the photic zone, above fair-weather wave base, in an open lagoon. In both regions, the lagoons were most likely protected by coral barrier reefs with intervening gaps. The patch reefs at Quriyat were abandoned, and new ones formed in oceanward direction to keep up with a dropping eustatic sea-level. At the flanks of the largest patch reef at Quriyat, bioclastic limestones with reef debris display onlap geometries. Only the limestones at Quriyat are associated with silty marl and calcareous, marly sandstone, which accumulated in a foreshore environment, either as longshore drift, or cays or combination/alternation thereof. These siliciclastic deposits are likely more voluminous than the limestones of the Ma'ahm Beds in the eastern part of the Arabian Plate, which should be considered when constructing paleo-facies maps. This abundant fine-grained marly material implies that Oligocene aquiclude horizons exist. We suggest that coral patch reefs should measure at least 5 m in diameter to fulfill typical ecological reef functions.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
