Depositional Environments and Sequence Stratigraphy of Carbonate Mudrocks Using Sedimentology, Multi-Scale Electrofacies Visualization, and Geochemical Analyses: Tuwaiq Mountain and Hanifa Formations, Saudi Arabia

Abstract

Depositional interpretation and sequence stratigraphic analysis of carbonate mudrocks requires numerical analysis and data integration to achieve quantitative, predictive stratigraphic and geochemical models. To demonstrate proof of concept, a depositional and sequence stratigraphic analysis has been done on a basinal interval of the Tuwaiq Mountain and Hanifa formations, Saudi Arabia. Conventional geologic interpretation, automated electrofacies analysis, and geochemical interpretation are integrated using quantitative means. Cluster analysis of well-logs using self-organizing maps and hierarchical clustering allowed for a multiscale electrofacies analysis. This is useful for identifying major lithological surfaces, which commonly correspond to sequence stratigraphic surfaces. Geochemical data was used for depositional environment interpretation, such as sediment provenance, redox, and paleoproductivity conditions. Factor analysis is used to group element data. Redox and paleoproductivity indices were calculated using electrofacies clustering of different elemental groups. Electrofacies analysis shows good correlation with the lithofacies. Five major lithofacies have been identified in the studied interval. The majority of the interval is interpreted to be deposited as gravity flow deposits in an outer ramp setting. Two major sequences have been identified in the Tuwaiq Mountain Formation. The first is composed of the Atash, Hisyan, and Baladiyah (T1) members. The second corresponds to the Maysiyah (T2), and Daddiyah (T3) members. Two major depositional sequences have been identified in the Hanifa Formation corresponding to the Hawtah and Ulayyah members. The uppermost bioturbated packstones of the Ulayyah Member are interpreted to be a lowstand systems tract with subsequent restriction leading to the deposition of anhydrite. In the studied interval, total organic carbon content (TOC) correlates well with suboxic to anoxic intervals that have high paleoproductivity. Complete anoxia is not a prerequisite for organic matter preservation. High TOC intervals are mainly in transgressive systems tracts.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015