This study identifies and defines for the first time the Sarab Formation, a new formation in the uppermost part of the Ediacaran - Cambrian Huqf Supergroup of the Suhanate of Oman. The potential importance of this new formation is that it could be the long sought after outcrop- equivalent of the subsurface Ara Group, which is one of the most significant petroleum play systems in Oman. In most of the Huqf area, the Sarab Formation conformably overlies the Buah Fontiation. However, at some localities, on what were probably fauh-bounded palaeo-topographic highs, the Sarab Formation rests unconformably either on the eroded Buah Formation or directly on the even older Shuram Formation. The Sarab Formation is overlain with marked angular unconformity by the siliciclastics of the Haima Supergroup. The formation is here fonnally described and subdivided into three principal members: the lower Ramayli Member, middle Shital Member and upper Aswad Member. A fourth member, the Salutiyyat Member, can be recognized where the Sarab Formation lies on eroded Nafun Group palaeo-topographic highs, and is probably the lateral equivalent, at least in part, of the upper Ramayli Member. The Ramayli and Shital Members contain evaporite units, including halite beds, and cyclical peritidai carbonates, indicating that the Huqf area was a trough or graben during this period. The middle and upper members contain significant microbial build-ups, including thrombolite framestone reefs, and rare crinkly laminites. In order to clarify its age and chronostratigraphy, a high-resolution composite carbon isotope chemostratigraphic curve is erected for the Sarab Formation. Over a thousand surface and subsurface samples were selected and analysed for their carbon and oxygen isotopic variations. Samples were subjected to extensive diagenetic screening involving petrography, elemental concentration and carbon/oxygen covariance analysis. Based on this evidence, Sarab Formation dolomites formed early, are possibly even primary. In many cases the dolomites show good primary fabric preservation, allowing micrite samples and samples lacking major recrystallization to be selected. These preliminary results minimize the influence of diagenesis on chemostratigraphic data reliability. The composite 8'^C curve presented here shows that the upper part of the Buah Formation is dominated by a stable, slightly negative 5'’C signature. The transition into the Sarab Formation is marked by the 8'^C signature changing to a much more erratic style, and from negative to positive values. The carbon isotopic signature of the Ramayli Member is characterised by a small positive excursion before a negative excursion with 8'’’C values around -5%o. This positive to negative

This study identifies and defines for the first time the Sarab Formation, a new formation in the uppermost part of the Ediacaran - Cambrian Huqf Supergroup of the Suhanate of Oman. The potential importance of this new formation is that it could be the long sought after outcrop- equivalent of the sub...