SEDIMENTOLOGY OF DUKUL FORMATION IN GUYUK, NORTHEASTERN, NIGERIA.

ABSTRACT The study focuses on the sedimentology of the Dukul formation in Guyuk, Northeastern Nigeria, wityh emphasis on the lithological, textural, and petrographic characteristics of the limestone units. Geological mapping and field observations revealed that the formation is dominated by limestone interbedded with marl and shale, exposed as massive to blocky outcrops. Petrographic analysis under plane and cross polarized light showed that the samples are composed predominantly of calcite occurring as both micritic and sparry varieties, with scattered bioclasts and fossil fragments embedded within a fine-grained matrix. Grain boundaries in many sections are partially obscured due to strong cementation, and the sorting is generally poor to moderate. The textures range from micritic to bioclastic, suggesting variations in depositional energy and post depositional recrystallization. Based on these sedimentological and petrographic observations, the Dukul formation is classified mainly as wacke stone to pack stone, indicating deposition in a low energy shallow marine environment, likely a lagoonal or protected shelf setting, where carbonate mud and fossil debris settled in relatively calm conditions. This study provides insights into the facies development and diagenetic evolution of the Dukul carbonates, contributing to the understanding of the Upper Cretaceous carbonate system within the Yola Arm of the Upper Benue Trough, Northeastern Nigeria.