Mixed siliciclastic-carbonate sequence stratigraphy, Miocene Dam Formation, Saudi Arabia

Sequence stratigraphy of the mixed siliciclastic-carbonate successions is considered to be more complex than their counterparts of pure siliciclastic or carbonate systems. This is due to the higher number of controlling factors in the depositional environment. Consequently, the reservoir and source rock characterization within these systems is relatively more difficult in term of the spatial distribution of the lithologic unit and its petrophysical properties heterogeneity.

Following Scharland et al., 2001, the Miocene Dam Formation is regarded as a third-order sequence which consists of both siliciclastic and carbonate sediments, with the dominance of carbonates. Three fourth-order sequences are well exposed in the Lidam area, Eastern Saudi Arabia. Sequence boundaries are delineated using the existing Rhizolith and desiccation cracks in the most upper part of the high stand systems tract, where it is dominated by shallow marine carbonate deposits. The early low stand systems tract is of dolomitic mudstone interbedded with dissolved chicken-wire anhydrite. Fine sandstone of estuarine origin, in addition to intertidal mudstone-sandstone succession, represent the late low stand systems tract. Transgressive surfaces are either sharp erosional surfaces or ravinement surfaces with intraformational lag deposits. Subtidal quartz skeletal wackestone with pieces of evidence of storm events represent the transgressive systems tract. Going toward the end of the vertical succession of the Dam Formation, shallow marine siliciclastics dominate. A set of incised channels filled with intraformational boulders of calcareous sandstone lies over the shallow marine siliciclastics succession, indicating a great drop in the sea level. Finally, a fluvial system of high energy braided stream origin, composed of medium to coarse ferruginous sandstone within a fining upward succession and high abundance of plant remains, represent the Hufouf Formation base and the start of a new third-order sequence. The heterogeneity of the lithofacies is intense, but the sequence stratigraphic framework helps in their rearrangement vertically into packages, which helps in the prediction of their spatial distribution.