PETROGRAPHIC ANALYSIS AND DIGENETIC CHARACTERIZATION OF YOLDE FORMATION OUTCROPS ALONG PANTAMI STREAM GOMBE STATE NIGERIA

ABSTRACT The Yolde Formation constitutes an important transitional sedimentary unit within the Gongola Sub-basin of the Upper Benue Trough, Nigeria, and has attracted considerable geological interest due to its depositional history and reservoir potential. This study investigated the petrographic characteristics and diagenetic features of the Yolde Formation exposed along Pantami Stream in Gombe State, northeastern Nigeria. The objectives were to determine the mineralogical composition of the sandstone units, document lithological variations through field mapping, and characterize the diagenetic processes that have influenced the formation. Field investigations involved geological mapping and the collection of eleven (11) representative sandstone samples from exposed outcrops. The samples were subjected to petrographic analysis using standard thin-section preparation techniques and examined under a polarizing microscope to identify mineral constituents, textures, and optical properties. The results indicate that the sandstones are predominantly composed of quartz, orthoclase, altered feldspar, and andesine, with accessory minerals including iron oxide and limonite. Quartz is the dominant framework mineral, suggesting derivation from a relatively stable continental source, while the presence of feldspar minerals indicates moderate compositional maturity and limited transport from the source area. Diagenetic features observed include feldspar alteration, iron oxide and limonite cementation, and moderate compaction, which have influenced the mineralogical composition and pore characteristics of the rocks. The study concludes that the Yolde Formation sandstones are subarkosic to arkosic in composition and were deposited in a fluvial to shallow marine transitional environment. Petrographic evidence indicates moderate diagenetic modification under oxidizing conditions. These findings contribute to a better understanding of the provenance, depositional environment, and diagenetic evolution of the Yolde Formation and provide valuable baseline information for future geological investigations, reservoir characterization, groundwater exploration, and hydrocarbon assessment within the Upper Benue Trough.