Depositional environment and sequence stratigraphy of the Upper Cretaceous Aruma Formation, NE Riyadh, Saudi Arabia

Abstract

The Campanian to Maastrichtian Aruma Formation represents a distinctive depositional system of the carbonate-dominated ramp along the Arabian plate. Sedimentologic characteristics and stratigraphic relations are integrated with carbon and oxygen stable-isotope data to interpret the depositional environments in a sequence stratigraphic framework. One siliciclastic facies association (FA1) and eight carbonate microfacies (MF 1–8) belonging to four facies belts (FB1–4) were identified. Facies characteristics support accumulations on a carbonate ramp environment that extends from offshore/outer ramp to middle and inner ramp settings. Stable-isotope data are correlated to the oscillating global sea-level curve and global excursions’ events in order to refine the sequence stratigraphy of the Aruma Formation. Carbon-isotope chemostratigraphy shows remarkable long-time excursions, which are correlated to the two global negative excursions (Late Campanian event “LCE” and Campanian–Maastrichtian boundary event “CMBE”) as well as the positive δ13 C excursion of Middle Maastrichtian event “MME” and the uppermost negative δ13 C excursion toward the K–Pg boundary. The negative shift in the δ13 C values associated with relatively positive values in the δ18 O herald three marked sea-level falls, which can be coincided with global sequence boundaries. The merged surfaces TS1/SB1 and TS2/SB2 can be correlated to the Campanian events KCa3 (80 Ma) and KCa6 (75.4 Ma), respectively. The coplanar surface TS3/SB3 matches well with the Maastrichtian event KMa3 (69.4 Ma). The positive values of δ13 C and/or negative values of δ18 O coincide with periods of maximum transgressions. The minor pulses are mostly attributed to cyclic fourth-order sequences. The established sequence stratigraphic architecture and depositional model of the outcrop data herein will be useful in regional correlations with analogous subsurface successions along the Arabian plate and enhancement of potential petroleum explorations.