Studies of Burial Metamorphism in the Cretaceous Sediments of the Southern Benue Trough and Anambra Basin, Nigeria: ABSTRACT

Abstract

Organic matter reflectance, illite crystallinity and fluid inclusion techniques are applied to the evaluation of burial history of Cretaceous sediments in the southern Benue Trough and Anambra Basin. The successions are invaded by intrusives, volcanic rocks and intra-formational veins especially in the Albian sections of the Abakaliki anticline and sub-bituminous coals in the Lower Maastrichtian sections of the Anambra Basin. Vitrinite reflectance (Rm) data from exposed NW/SE sections from Enugu to Abakaliki are ca: .55% in the Lower Maastrichtian coals and shales, 0.67% in the Coniacian shales, 0.91 in the Turonian shales and 4.31% in the Albian shales. A corresponding decrease in illite crystallinity indices coupled with a decrease in the percentage of smectite from 30% to 0% (%S in I/S) was observed on the NW/SE section. Fluid inclusion temperatures from vein quartz in the Albian shales range from 170 to 250{degrees}C. Our data suggest that sediments in the study area were buried to ranks within and beyond the oil window at their present outcrop levels. Possibilities for Cretaceous targets should be sought in the deeper non emergent sections of the Benue Trough and the Anambra Basin.