Abstract
The paleoweathering, provenance, and tectonic setting of sediments of the western coast of Ghana were unraveled using the geochemistry of 29 beach sands, which are characterized by coarse-, medium-, and fine-grained sizes. The coarse-grained beach sands contain higher SiO2 content (2.9-96 wt.%) than the medium-grained (4.9-94 wt.%) and fine-grained (16.1-90.7 wt.%) sands, implying that the increase in grain size is related to the increase in SiO2 content. Al2O3 and CaO concentrations are higher in the fine- and medium-grained sands than the coarse-grained sands. The beach sands are compositionally immature based on the index of compositional variable values (1.17-141) and Th/Sc versus Zr/Sc diagram although they have high SiO2/Al2O3 values. The high SiO2/ Al2O3 is not indicative of the weathering conditions of the coastal sediments in the area. The sands are chemically unaltered clastic materials of first cycle regime that still have their labile minerals retained in them very close to the sediment source based on the chemical index of alteration values, plagioclase index of alteration values, and A-CN-K and A-CNK-FM ternary diagrams. The total rare earth elements (ΣREE) content increases with decreasing grain size. However, there are some discrepancies where some coarsegrained samples have high ΣREE content. This suggests that apart from the grain size, the provenance of the sediments has direct control over their geochemical composition. The correlation of the rare earth elements patterns of the beach sands with those of adjacent source rocks points to felsic sources for their derivation. The felsic (granodioritic composition) igneous suites of the Paleoproterozoic Birimian highland rocks adjacent to the beach sediments in the western coast are possibly the source rocks of the beach sands. Rifting in the continents is the tectonic regime probably during the Paleoproterozoic times responsible for deposition of the beach sands in the western coast of Ghana.
Highlights
IntroductionThe geochemistry of siliciclastic sediments has proven to be a suitable tool for deciphering their source (Basu et al, 1975; Cullers, 1994; Armstrong-Altrin, 2009; Gürsu et al, 2017), tectonic setting (Verma and Armstrong-Altrin, 2013, 2016; Khan and Khan, 2015; Etemad-Saeed et al, 2015), and paleoweathering history of the source areas (Rashid and Ganai, 2015; Ma et al, 2017)
10 samples were characterized as medium-grained samples with mean grain sizes ranging from 2.4 to 2.9 φ whereas 9 samples with mean grain sizes ranging from –0.1 to 0.0 φ were characterized as coarse-grained samples (Table 1)
Based on the mean grain sizes of the samples (Mzφ: –0.1 to 4.1; Table 1), they all appear to be predominantly sand-size characterized as fine-grained sands, medium-grained sands, and coarse-grained sands agreeing with the classification of Wentworth (1922)
Summary
The geochemistry of siliciclastic sediments has proven to be a suitable tool for deciphering their source (Basu et al, 1975; Cullers, 1994; Armstrong-Altrin, 2009; Gürsu et al, 2017), tectonic setting (Verma and Armstrong-Altrin, 2013, 2016; Khan and Khan, 2015; Etemad-Saeed et al, 2015), and paleoweathering history of the source areas (Rashid and Ganai, 2015; Ma et al, 2017). ABU and SUNKARI / Turkish J Earth Sci the Mexican coastal areas, beach sand geochemistry has been suitably used to understand their provenance and tectonic setting (e.g., Kasper-Zubillaga et al, 1999; KasperZubillaga and Dickinson, 2001; Armstrong-Altrin, 2015; Hernández-Hinojosa et al, 2018). This has since become a reliable tool for beach sand provenance studies across the globe
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