Chris Anani

Sandstone petrology and provenance of the Neoproterozoic Voltaian Group in the southeastern Voltaian Basin, Ghana

Abstract The Neoproterozoic strata in the eastern part of the Voltaian Basin are divided into the Lower, Middle and Upper Voltaian formations. The Kwahu Sandstone and Anyaboni Sandstone members are within the Lower and Middle Voltaian formations, respectively. Modal plots for the Kwahu Sandstone indicate a craton interior provenance. Quartz-type analysis suggests a mostly plutonic origin, and the tourmaline chemistry indicates a major granitic source with associated metasedimentary rocks. The sandstones of the Anyaboni Sandstone plot mostly in the transitional continental and partly in the craton interior provenances on QFL and QmFLt diagrams. Quartz-type analysis suggests a source of medium-grade metamorphic rocks; tourmaline analysis indicates a metasedimentary origin. The sedimentological data and interpretations suggest that the Kwahu Sandstone originated from the Birimian Supergroup located in the west and south of the Voltaian Basin. The Anyaboni Sandstone is thought to have been derived from the same supergroup, but from the southwest of the Voltaian Basin. The differences in sandstone composition between the Kwahu Sandstone and Anyaboni Sandstone seem to be due to tectonic movements, probably intracontinental rifts, and to a possible climatic effect in the source areas and within the sedimentary basin.

Provenance of shales and sandstones from the Devonian Accraian Group, southern Ghana

Petrographic and whole rock geochemical studies were carried out on sandstones and shales of the Devonian Accraian Group of southern Ghana to constrain their provenance and tectonic setting. Modal petrographic analysis on the sandstones show that the framework grains are sub-angular to rounded in shape. Upper continental crust normalized multi-element plots, as well as trace element ratios, suggests that the sandstones and shales were mainly derived from felsic and recycled sources. Modal mineralogy of the sandstones, and major and trace element geochemistry of sandstones and shales further suggest that they are of recycled orogenic provenance. Discriminant function based major-element diagram suggests that the Accraian sandstones and shales were deposited in a Passive margin setting. Weathering indices suggest high degree of source area weathering. It is of the view that the Accraian sandstones and shales, most probably, received sediment input mostly from the Paleoproterozoic Birimian metasedimentary rocks and their associated granitoids and/or the Neoproterozoic sedimentary rocks from the Volta Basin which are both positioned northwest and north, respectively, of the Accraian sedimentary rocks.