The stratigraphy and structure of the Madamar-Salakh-Qusaybah range and Natih-Fahud area in the Oman mountains

Abstract EN

Melanges and debris flows with clasts derived from the top of the Natih Formation found in shales in the base of the Aruma Group indicate that a period of Structural growth on the platform took place during Aruma deposition in the Late Cretaceous.

In this respect the platform in the Jebel Salakh area may have undergone a similar period of structural growth in the Late Cretaceous to the Fahud area where a syn-Aruma normal fault down throwing to the South accounts for a difference in the stratigraphic thickness of the Aruma of 1 km.

A younger series of debris flows in the Aruma of the Sufrat al Khays area to the South of Jehel Salakh is dated as Campanian/Maastrichtian.

The clasts in these flows were derived exclusively from the Simsima limestones.

Natih-derived elasts are conspicuously absent.

This is taken to indicate that the Madamar-Salakh Qusaybah range was covered by Aruma sediments at this time and did not form the distinctive positive feature seen at present - i.e.

Madamar-Salakh-Qusaybah range folding though partly Late Cretaceous is mainly Post-Manslrichtian in age.

This Post Maastrichtian event in the Madamar-Salakh-Qusaybah range produced a series of doubly-plunging anticlines in the Cretaceous strata- These folds show a high degree of brittle extension in the form of normal faults and extensional fractures, The faults are delineated by fault gouge with visibly interconnected void space.

In the subsurface, if such fractures were developed in a fold closure similar to those seen at the surface in the Madamar-Salakh-Qusaybah range.

then they could provide preferred conduits for oil flow and the harrier to fluid flow provided by the Aruma shale seal could lead to a hydrocarbon accumulation.