Lithofacies and microfacies and depositional environment model of the Cenozoic carbonate platform: an example from the Upper Jafnayn Formation of Jafnayn area in north-east Oman

This paper presents a comprehensive lithofacies and microfacies analysis of the exposed Cenozoic (Late Paleocene to Early Eocene) Upper Jafnayn Formation in the Jafnayn area, Northern Oman. The study meticulously documents the color, lithology, grain composition, bed thickness, types, and nature of bed contacts and fossil content of the formation. Over 85 fresh rock samples from various lithofacies were collected for this analysis. The samples were treated with blue epoxy, thin-sectioned, and half-stained with potassium ferricyanide and alizarin red to aid in mineralogical identification. To accurately determine microfacies, quantify components, reconstruct origins, and build a depositional model for the Upper Jafnayn Formation, 300 points were counted per thin section using a point-counting method. This analysis identified five distinct facies and 16 microfacies, with ten containing quartz grains and six lacking quartz sand. The microfacies provide insights into the depositional environments of the Upper Jafnayn Formation: four represent backshoal conditions, seven indicate shoal environments, three correspond to foreshoal settings, and two exhibit characteristics overlapping between backshoal and foreshoal environments. The presence of Alveolinid foraminifera, red algae, and occasional coarse coral debris within the cleaner limestone sections further characterizes the formation. The diverse lithofacies and microfacies of the Upper Jafnayn Formation reveal a dynamic interplay between high-energy and low-energy depositional environments, influenced by sea level fluctuations. This comprehensive understanding of the formation’s depositional history is crucial for research teams aiming to identify potential hydrocarbon traps and reservoirs in the region.