SEDIMENTOLOGICAL STUDY AND HEAVY MINERAL ANALYSIS OF SEDIMENT SAMPLES FROM WELL-S, NIGER DELTA, NIGERIA

Sedimentological study and petrographic analyses were carried out on thirty ditch cutting samples from well-S, Niger Delta, Nigeria, with the aim of determining the provenance and depositional environment of the sediments.

The samples were subjected to soxhlet extraction for the removal of soluble organic matter from them and particle size analyses using Pipette and Emery sedimentation techniques in order to determine the grain size distribution of the sediments. Separation of heavy of mineral from the samples was done with the aid of bromoform to enable petrographic analyses of the heavy mineral suite, under the polarising microscope.

The data obtained from the grain size analysis were used in preparing histograms, from which some simple statistical parameters were derived. Graphic mean values obtained range between 0.74 and 2.64 Ø, which implies that the sediments are predominantly fine-medium grained. The inclusive standard deviation values ranges from 0.53 to 1.24 Ø, indicating that the sediments are moderately well sorted to moderately sorted. Inclusive graphic skewness values of 0.29 to 0.70 indicate that the sediments ranges from finely skewed to strongly finely skewed and the graphic kurtosis values of 0.61 to 1.54 shows that the sediments are predominately very platykurtic which implies a low energy environment of deposition. The polymodal nature displayed by the histograms indicates that the sediments have been derived from various sources. The observed moderately well sorted to moderately sorted and very platykurtic nature of the sample show that the sediments were transported for a long distance by saltation and suspension and deposited in a fluvio-marine environment.

The heavy mineral assemblages have the opaque minerals as the most abundant, followed by tourmaline, staurolite, rutile, zircon, apatite, kyanite, amphibole, monazite and olivine. This heavy mineral suite indicates that the sediments originate from metamorphic and acid igneous rocks of the Nigeria Basement Complex. The presence of rutile, tourmaline, zircon, kyanite and apatite suggest that the sediments are stable and mineralogically sub-mature to mature.