Introduction

Holocene sediments extending from the Dukhan sabkha north to Bir Zikrit in Qatar present a modern example of coastal sedimentation in an arid climate that provides an analogue for some ancient, arid carbonates such as the Jurassic Arab C Formation at the Dukhan Field. The Holocene at Dukhan illustrates sedimentation and diagenetic patterns that differ from those documented in ‘classical’ sabkha models which are dominated by examples from Abu Dhabi. In these models facies tracts and diagenetic profiles are characterized by linear facies belts that systematically prograde seaward. Cross-sections of these sabkhas show strata dipping gently seaward, providing a medium for dense fluids to flow from updip to downdip, mixing with marine waters.

At Dukhan, sedimentation processes form a mosaic of sabkha sub-environments, influenced by local circulation and topography. Grain-rich sediments occur on wind-ward facing beaches and as ellipsoidal deposits in the lee of antecedent highs. Because the depositional surface has such low-relief, facies tracts are offset dramatically due to low amplitude (1–4m), high-frequency (2000–4000 year) oscillations in sea level and low accommodation space. Most of the inland, upper sabkha facies are remnants of an older Holocene highstand. As a result, the Dukhan sabkha sediments consist of unconformable cycles, separated by minor hiatuses of variable duration. While filling and general shallowing of the shallow marine system into coastal sabkha can be observed from shallow sediment stacking and map patterns, systematic, linear seaward progradation is not the norm. Irregular, non-Waltherian facies transitions appear to be more dominant.

Coastal areas of the Arabian Gulf have been the subject of study for many years for the purpose of applying the principles of sedimentation and early diagenesis to the understanding and modeling of ancient carbonate systems. This unique setting with its relatively low-angle profile and arid conditions provides one of the few areas in the world where ramp-style carbonates are being deposited adjacent to modern coastal sabkhas (Figure 1). Many authors have contributed to this work including Purser and others (1970), Shinn, (1969), and many works by Kendall and Warner (1985, 1992 for example). Alsharhan and Kendall (2004) cover a number of Holocene analogues along the Abu Dhabi coast and apply them to many important arid carbonate reservoirs. In most of these studies, comparisons are made with ancient petroleum reservoirs where data is limited to widely separate well locations and comparatively poor vertical resolution seismic data. Detailed temporal and spatial sediment distribution patterns along with early diagenetic processes that can be observed today or occur in the recent past (Holocene) provide subsurface geologists and reservoir engineers with viable trends (e.g., variogram) and shape (e.g., objects) distributions. This environment of deposition (EOD) information promotes the construction of more robust and realistic reservoir models.

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