Abstract
Grain size distribution and classes present in sedimentary rocks are responsive to the physical changes of the transporting media and the basin of deposition. Analyzing grain size data is germane in reconstructing the sedimentary processes including identifying the palaeoenvironment of deposition. Twenty-three (23) samples, mainly sandstones, collected within latitude 6 055’-6 059’N and Longitude 005 044’-005 053’E in the Anambra Basin, were subjected to granulometric analysis, where grain size parameters (mean grain size, sorting, skewness, and kurtosis) sensitive to environmental conditions were calculated. These parameters were integrated with bivariate and multivariate analyses. Graphics mean (Mz) in the study area range from 1.1 to 2.27 ɸ with an average value of 1.7 ɸ, suggesting that grains are predominantly fine to medium; sorting range from 0.71 to 1.36 ɸ with an average value of 1.02 ɸ, suggesting sediments are moderately sorted; skewness range from -0.57 to 0.51 ɸ with an average value of 1.28 ɸ suggesting coarsely skewed to fine skewed with a predominating near symmetrical skewness and kurtosis range from 0.57 to 1.51ɸ, with an average of 1.28 ɸ suggesting a very platykurtic to leptokurtic character. Bivariate scatter plots of the grains size parameters predicted the environment of deposition as a shallow marine. Multivariate analysis calculated from established functions suggested environments that range from the beach (backshore) to shallow marine (subtidal). The integration of the granulometric parameters, bivariate and multivariate plots predict an environment that is dominated by high energy indicating that the sediments of the study area were deposited in a shallow marine environment. In addition, the Visher and Passega’s C-M diagrams characterized the transport mechanism of the sediments as predominantly by saltation although traction and suspension modes also play some roles. Keywords: transportation mechanism, granulometric parameters, bivariate analysis, multivariate analysis http://doi.org/10.35180/gse-2019-0002
Highlights
The use of particle size distribution and the assemblages of heavy minerals in sedimentary rocks make it possible to effectively locate and make use of grain size distribution and essential minerals in predicting depositional settings and processes as well as sediment source [1]
The integration of the granulometric parameters, bivariate and multivariate plots predict an environment that is dominated by high energy indicating that the sediments of the study area were deposited in shallow marine environment
The mean grain size, represented by the graphic mean Mean grain size (Mz) in the study area range from 1.1 to 2.27 ɸ with an average value of 1.7 ɸ (Table 2). It could be inferred from the average value of the graphic mean of grains that they are fine to medium sands
Summary
The use of particle size distribution and the assemblages of heavy minerals in sedimentary rocks make it possible to effectively locate and make use of grain size distribution and essential minerals in predicting depositional settings and processes as well as sediment source [1]. The provenance of sediment material as well as the environment of deposition may be obtained from an analysis of the grain sizes present in the sediment studied. The basic property of sediments affecting their transportation and deposition is the grain size. Grain size analysis gives important insights to sediment’s provenance, transport history and depositional conditions [2,3,4]. Grain size distribution and classes in a clastic sedimentary rock is sensitive to the physical changes of the transporting media and the depositional basin. The reconstruction of sedimentary processes, the identification of depositional environment, presentation and analysis of grain size data are all fundamental to understanding the basin formation with a view to unravelling its petroleum potentials
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