oa High-Resolution Lithofacies Analyses of Predominantly Organic-Rich Carbonates from the Natih-B Intrashelf Basin, North Oman

Recent research, utilizing high-resolution petrographic and geochemical analyses on samples collected from North Oman, has revealed that the predominantly fine-grained carbonates of the Natih-B Member contain a great deal of previously unrecognized lithofacies variability, developed at cm to sub-mm scales. Most geologists have largely overlooked the significance of this small-scale variability, attributing changes observed to either influence of varying primary production or oxygen concentration in the water column. Detailed analyses of the textures (e.g., relict thin beds, burrow mottles, organo-mineralic aggregates and lenticular laminae) and components (including fossil and mineral assemblages) present at these small scales suggest that this lithofacies variability reflects bed-scale processes. Moreover, it indicates that many of the Natih-B intrashelf-basinal sediments, rather than being deposited directly from suspension settling under predominantly low-energy conditions, were actually deposited, at least partially, by episodic and advective events. These sediments, following compaction, developed thin beds and then were subsequently burrowed by diminutive infauna. Furthermore, analyses of successive samples within laterally-equivalent intervals suggest that there was significant temporal and spatial variability in sediment supply and accommodation availability, in addition to local changes in primary production, sediment accumulation and burial rates that fundamentally controlled organic-matter enrichment in the Natih-B Member.