Abstract A high resolution sequence stratigraphic model has been constructed for the mid-Cretaceous Sarvak Formation (in the High Zagros region of SW Iran) which was deposited close to the eastern margin of the Arabian Plate. The exceptional outcrop quality, displaying the detailed facies patterns in the transition zone from carbonate platform to intra-shelf basin, offers the rare opportunity to distinguish between the relative control of carbonate sediment supply (S) and accommodation (A) on the depositional geometries of third- and fourth-order depositional sequences. Four third-order sequences have been distinguished in the Sarvak Formation, with a duration varying between 1.5 and 3 Ma, and a thickness of 50–150 m. These are in turn composed of fourth- and fifth-order sequences that form the stratigraphic building blocks of this carbonate system. A significant distinction has been made in the third-order sequences between the early transgression (e-TST) when the system was still flat, and corresponds to a ramp setting, and the late transgression (l-TST) when the carbonate platform to intra-shelf basin topography was created. The rate of accommodation creation is identified as the dominant factor controlling the morphology of the depositional profile, and, as such, the driving motor behind the dynamics of this type of carbonate system. The dip angle of the depositional profile has a major influence on: (1) the hydrodynamics of the system; (2) the type of carbonate sediment; and (3) the volume of carbonate sediment produced. A good correlation with the third-order sequences of the Natih Formation in Oman is demonstrated, which supports a dominant control by eustatic sea-level changes and a similar response of the carbonate system to changes in the rate of sea-level rise on the southern part of the Arabian Plate. This outcrop analogue can be considered as a good reference model for the Cenomanian–Turonian carbonate platform margins of the Arabian Plate, but also as a textbook example of the response of carbonate systems to sea-level fluctuations (relative influence of accommodation and sediment supply).

Abstract The Sarvak Formation (Cenomanian–Turonian) forms one of the main reservoir rocks in many oilfields in southern Iran. Extensive lateral and vertical facies variations as well as effects caused mainly by the subaerial exposure associated with the regional Turonian unconformity have resulted in variable porosity and permeability. Dissolution affected the entire upper part of the Sarvak Formation and is the most important process related to subaerial exposure. Brecciation, development of palaeosol and formation of bauxite deposits are also limited to the upper few metres of the top of the Sarvak Formation and indicate warm and humid climatic conditions. Subaerial exposure had varying effects on the diagenesis depending on its duration, palaeotopography and the availability of meteoric water. The δ 18 O and δ 13 C values obtained from calcitic matrix, various generations of calcite cements and calcitic rudist shells in the Upper Sarvak overlap to a large extent, indicating their equilibration with fluids of similar isotopic composition. Negative δ 18 O values (i.e. −6.6‰ to −1.7‰) suggest a significant meteoric component. More 18 O-depleted values (e.g. −12.3‰) obtained from late calcite cements indicate their precipitatation from warm fluids. Positive δ 13 C values (i.e. 0.00‰ to 3.4‰) in the various carbonate phases reflect values of seawater coeval with an Oceanic Anoxic Event and later modified by meteoric waters.