A modern analogue for the Lower Ordovician Obolus conglomerate of Estonia

Phosphate-bearing rocks of the lower Ordovician Kallavere Formation, northern Estonia, contain diverse fragments and, more rarely, complete shells of the phosphatic inarticulate brachiopods Schmidtites and Ungula. In places the concentration of brachiopod debris in sandstones is so dense that economically exploitable seams of phosphorite are formed. A directly analogous situation occurs along the coast of Namibia today. In places the extant phosphatic inarticulate brachiopod Discinisca is washed up on the beach in such large numbers that its shells dominate the littoral sediment. The distribution range of this species suggests that it is a product of the Benguela upwelling ecosystem, and the inference is drawn that the Estonian deposits are the products of a similar palaeo-upwelling system.