Microfossils or pseudofossils? Cu-Co sulphide microfeatures in the Neoproterozoic Katangan Supergroup, Democratic Republic of Congo

Abstract

In this paper we investigate a group of microfeatures discovered in the mineralised, Neoproterozoic Mines Subgroup of the Katangan Copperbelt, Democratic Republic of Congo (DRC), at the Mashitu South Cu-Co deposit. The features are bacillus-shaped, composed of Cu-Co sulphides and occur within syn-diagenetic apatite veins in a low-grade metasedimentary shale. They exhibit a range of evidence for biogenicity, including indicators of cellular complexity, and were therefore investigated as candidate microfossils of chasmoendolithic prokaryotes. However, our study found that the features are likely to be pseudofossils, formed from abiogenic rutile crystals which have been replaced by sulphides in such a way as to mimic biogenicity indicators. This method of sulphide-replacement adds to the list of possible ‘false-positives’ in the search for early life, and emphasises the importance for micropalaeontological studies to consider such features with a sceptical, holistic approach and rigorous scientific method.