Sentence:  The Middle Voltaian lies unconformably on the Lower Voltaian with a basal <WSD>conglomerate</WSD> that can be correlated with <WSD>conglomerates</WSD> of the Buem Formation. Both sets of <WSD>conglomerates</WSD> have been interpreted as tillites, possibly equivalent to the Infracambrian tillites of the Rokelide–Mauritanide belt west of the craton ... and in the Taoudeni Basinnb.... 
Meaning of the word marked with <WSD> tags:  A rock consisting of gravel or pebbles embedded in a matrix.