| Popis: |
An extensive geological field survey was carried out where lithostratigraphic sections of Yolde Formation were measured. Features such as textures interpreted, physical and biogenic sedimentary structures (facies variations and associations were documented). Some selected representative samples of the sedimentary depositional facies were also subjected to grain size analysis and multivariate analysis. The Yolde Formation in the study area were lithologically made up of sandstones with dark grey to purple interbedded mottled clay and shales. The formation is structurally characterized by assymmetrical ripple, tabular and trough crossbedding, convolute bedding as well as hummocky and herringbone cross-stratification with reactivation surfaces, channel fillings sandstone and bioturbation. The granulometric studies typified the sandstone facies to be positively near symmetrical to negatively skewed, leptokurtic to extremely leptokurtic, angular to sub angular with high spherecity, mineralogically immature, moderately to well sorted Arkose. The result of the Linear Discriminate Function (LDF) analysis scatter plot for the sandstone facies of the Yolde Formation indicate a shallow marine depositional environment. Field and textural studies of the formation suggests the sediments to be deposited in relatively high energy environment with tidal and wave influence of transport and deciphered ten (10) lithofacies grouped into four associations that is, FA-1 (subtidal), FA-2 (Intertidal), FA-3 (supratidal) and FA-4 (Shoreface). Analyses of textural, structure and statistic revealed that the sediments in the study area were deposited in shallow marine environment. Sets of the synnsedimentary faults with slickenside down thrown (0.49 – 1.41m) were classified into the NE – SW trending faults in the Gongola Sub-Basin. |
