STRATIGRAPHY AND SEDIMENTOLOGY OF ENAGI FORMATION, BIDA BASIN, NORTH WESTERN NIGERIA

Abstract

Detailed facies and architectural element analyses of the sediments of Enagi Siltstone and part of the Jima Member of Bida Formation in the northern part of Bida basin reveal eight (8) lithofacies, five (5) architectural elements and three (3) large scale outcrop facies associations (OFA). The lithofacies include: conglomerate (F1); trough cross bedded sandstone (F2); planar cross bedded sandstone (F3); epsilon cross bedded sandstone (F4); tabular bedded sandstone (F5); heterolithic mudstones and siltstones (F6); erosive based siltstone (F7); and mudstone (F8) lithofacies. The identified architectural elements are: downstream macroforms (DA) recording downstream accretion within channels; sandy bedload macroforms (SB) suggesting gradual infilling of channels by normal regime bedflow sedimentation; lateral accretion macroforms (LA) suggesting deposition by high sinuosity channels; overbank element (OF) recording sedimentation outsides the confines of channels; and channel element (CH). The large scale outcrop facies associations (OFA) include: 1) OFA1, sand dominated with sands to mud interval ratio of approximately 70:30; 2) OFA2, 60:40 sand to mud/silt ratio; and 3) OFA3, mudstone/siltstone dominated. This study suggests the elevation of Enagi Siltstone to Enagi Formation status based on the heterogeneous nature of the sediment. Four reference sections were recommended to illustrate the typical features of the Enagi Formation.