Abstract
Twenty eight sediment samples were obtained from road cuts and stream cuts in Ilu Titun area of Ondo State, Nigeria and were subjected to Grain Size Distribution (GSD) analysis, from which statistical parameters were calculated and used to determine the environment of deposition of the sediments. Six representative samples were selected for petrographic studies to determine the heavy mineral content of the sediments with a view to establishing the sediments source of Ilu Titun and environs which mark the eastern margin of the Dahomey basin. The Graphic Mean (Mz) ranges from 0.700F to 1.667&Phi while the Inclusive Graphic Standard Deviation (&sigma i ) range from 0.960 to 1.319. The Inclusive Graphic Skewness ( SK I ) of the samples ranges from -0.665 to 0.803 while Kurtosis range from 1.652 to 3.309. The bivariate plot of mean size against the Inclusive graphic standard deviation show that the sediments were deposited by river and beach processes. The plot of skewness against the Inclusive graphic standard deviation confirmed that the sediments were deposited by river processes. The results of the petrographic studies show that Slides EK 01 and EK 08 have Kyanite and Staurolite. Slides EK 13 and EK 24 have Staurolite, Tourmaline and Garnet. Slides EK 26 and 28 have Tourmaline and Zircon present in them. Bivariate plots using the statistical parameters show that the sediments were deposited by fluvial processes. The results from the petrographic studies indicate that the sediments were sourced from metamorphic rocks and pegmatites.
Highlights
Provenance questions must be answered in all sedimentary basins
The composition of sedimentary rocks is controlled by a complex system of factor which acts on the rock from the source location and lithology to the time of sedimentary rock formation
The method employed to carry out the statistical analysis depended on results of the statistical parameters calculated from the percentile values derived from the cumulative curve of the grain size distribution of sediments
Summary
In the case of ancient basins which have evolved through several regimes of tectonic upheavals, such provenance questions are answered without the benefit of obvious source regions for the sediments, due to either or both of the disappearance or dislocation of source rocks (through various processes such as tectonic movements, weathering and erosion). The composition of sedimentary rocks is controlled by a complex system of factor which acts on the rock from the source location and lithology to the time of sedimentary rock formation Some of these factors include weathering, erosion, hydrodynamic effects and diagenesis-all of which are affected by other contributing factors such as transport distance, time, energy and climate (Johnsson, 1993)
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