Abstract
A new high-resolution stratigraphic framework for the thick and well-exposed Lower Cretaceous rocks of Saudi Arabia has been provided. The studied successions consist mainly of carbonates with minor interbedded siliciclastics, forming the Silayy, Yamamah and Buwaib formations in the study area (north of Ar Riyad city). Based on the integrated sedimentary fades analysis, a relative sea-level curve for the Berriasian-Valanginian interval has been established, including stacking pattern of the different facies cycles. Two transgressive-regressive facies cycles have been identified and documented in the studied sections. The first cycle started during the middle Berriasian (similar to 143 Ma), comprising the Silayy and Yamamah formations. It terminated at the Yamamah-Buwaib formational contact during the early Valanginian (similar to 138 Ma), characterized by a friable brownish ferruginous sandstone bed at the base of the Buwaib Formation. The second transgressive-regressive cycle encompasses the entire lower Valanginian Buwaib Formation. A major unconformity surface formed during the early late Valanginian (similar to 136 Ma), marking the end of the second cycle and characterized by a distinctive hardground condensation. The correlation and dating of the recognized cycles, identified in central Saudi Arabia, shows a contemporaneity to equivalent surfaces globally and thus strongly supports an isochronous formation of Berriasian-Valanginian facies cycles by eustatic sea-level changes.